Title of Invention	MOTOR CONTROL DEVICE
Abstract	Provided is a motor control device for limiting a motor current command value according to a arotating state of a motor, thereby making it possible to appropriately protect the motor from being overheated. The motor control device includes a pwm inverter for driving a brushless motor, a position sensor for detecting a magnetic pole position of a rotor of the motor, a current detector for detecting motor driving currents iu, iv, and iw which are inputted to the motor, a current command value calculating section for generating the motor current command values id and iq of the motor, and a microcontroller for controlling the pwm inverter according to the motor current command values. The microcontroller calculates motro current limit values. The microcontroller calculates motor current limit values that limits the motor current command values on the basis of the rotation speed of the motor which is calcultaed for the magnetic pole position and the motor driving currents.

Title of Invention

MOTOR CONTROL DEVICE

Abstract

Provided is a motor control device for limiting a motor current command value according to a arotating state of a motor, thereby making it possible to appropriately protect the motor from being overheated. The motor control device includes a pwm inverter for driving a brushless motor, a position sensor for detecting a magnetic pole position of a rotor of the motor, a current detector for detecting motor driving currents iu, iv, and iw which are inputted to the motor, a current command value calculating section for generating the motor current command values id and iq of the motor, and a microcontroller for controlling the pwm inverter according to the motor current command values. The microcontroller calculates motro current limit values. The microcontroller calculates motor current limit values that limits the motor current command values on the basis of the rotation speed of the motor which is calcultaed for the magnetic pole position and the motor driving currents.

Full Text	FORM 2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE SPECIFICATION (See Section 10; rule 13) TITLE MOTOR CONTROL DEVICE APPLICANT MITSUBISHI DENKIKABUSHIKIKAISHA 2-3, Marunouchi 2-chome Chiyoda-ku Tokyo 100-8310 Japan Nationality : a Japanese company The following specification particularly describes the nature of this invention and the manner in which it is to be performed MOTOR CONTROL DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device for limiting a motor current command value such as a brushless motor. 2. Description of the Related Art A conventional motor control device includes a driver circuit for driving a polyphase motor, and a microcontroller for controlling the driver circuit. The microcontroller limits a motor current according to an integrated value of a given function of a phase current (for example, refer to JP 2002-238293 A). In the conventional motor control device, because a rotating state of a motor is not taken into consideration, in a case where an electric power is supplied to the motor in a state where the motor stops, a current of a specific motor phase increases. As a result, there has been a problem in that the specific motor phase is overheated as compared with other motor phases. In addition, in a case where the electric power is supplied to the motor in a state where the motor rotates, there has been a problem in that a microcontroller limits a motor current and the motor current is excessively limited even in a state where the heat is averagely applied to each phase. 1 SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and therefore an object of the present invention is to provide a motor control device for limiting a motor current command value according to a rotating state of a motor, thereby making it possible to appropriately protect the motor from being overheated. According to the present invention, there is provided a motor control device, including: an inverter unit for driving a polyphase motor; position detecting means for detecting a magnetic pole position of a rotor of the polyphase motor; driving current detecting means for detecting a motor driving current inputted to the polyphase motor from the inverter unit; current command value calculating means for generating a motor current command value of the polyphase motor; and motor control means for controlling the inverter unit according to the motor current command value, in which the motor control means calculates a motor current limit value that limits the motor current command value on the basis of the rotation speed of the polyphase motor calculated from the magnetic pole position and the motor driving current. According to the motor control device of the present invention, since the motor current command value can be limited according to the rotating state of the motor, the motor can be appropriately protected from being overheated. 2 BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: FIG. 1 is a block diagram showing a motor control device according to a first embodiment of the present invention, together with peripheral devices; FIG. 2 is a flowchart showing the operation of a program of software that is installed in the microcontroller shown in FIG. 1; FIG. 3 is an explanatory diagram showing a motor current limit value of the motor control device according to the first embodiment of the present invention; FIG. 4 is a diagram showing characteristics of a synthetic driving current to a motor current limit value change speed at the time of rotating the motor and at the time of stopping the motor in the motor control device according to the first embodiment of the present invention; FIG. 5 is an explanatory diagram showing a d-axis current limit value and a q-axis current limit value at the time of rotating the motor and at the time of stopping the motor in the motor control device according to the first embodiment of the present invention; FIG- 6 is a block diagram showing another motor control device according to the first embodiment of the present invention, together with peripheral devices; FIG. 7 is an explanatory diagram showing a method of obtaining 3 a motor current limit value change speed by using a rotating speed of the motor in the motor control device according to the first embodiment of the present invention; FIG- 8 is an explanatory diagram showing another method of obtaining a motor current limit value change speed by using a rotating speed of the motor in the motor control device according to the first embodiment of the present invention; FIG. 9 is a block diagram showing a motor control device according to a second embodiment of the present invention, together with peripheral devices; and FIG. 10 is a block diagram showing a motor control device according to a third embodiment of the present invention, together with peripheral devices* DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a description will be given in more detail of the respective preferred embodiments of the present invention with reference to the accompanying drawings. In the respective drawings, identical or corresponding members and portions are denoted by the same reference symbols. First Embodiment FIG, 1 is a block diagram showing a motor control device according to a first embodiment of the present invention, together with peripheral devices, 4 Referring to FIG- 1, the motor control device is connected to a three-phase brushless motor 1 (hereinafter referred to as “motor 1”) which is a polyphase motor. The motor control device includes a position sensor (position detecting means) 2 which detects a magnetic pole position of a rotor of the motor 1, a PWM inverter (inverter unit) 3 which drives the motor 1, and a current detector (driving current detecting means) 4 which detects three-phase motor driving currents lu, Iv, and Iw which are inputted to the motor 1 from the PWM inverter 3. The motor control device also includes a current command value calculating section 5 that generates a d-axis (magnetic flux axis) command current Id* and a q-axis (torque axis) command current Iq* which are the motor current command values of the motor 1 on the basis of a torque command value T* and a magnetic flax command value F* which are given from the external, and a microcontroller 6 (motor control means) which controls the PWM inverter 3 by using tine motor current command values (Id, Iq). The microcontroller 6 includes an overheat protecting section 7 that limits the motor current command values (Id, Iq) to prevent overheat, A/D converters 8u and 8v {hereinafter referred to as A/D converter 8”) which convert the outputs of the current detector 4 into digital values, and a three-phase to dq coordinates converting section 9 that converts the output of the A/D converter 8 from three-phase AC coordinates into dq coordinates composed of a d-axis 5 and a q-axis orthogonal to the d-axis. The microcontroller 6 also includes subtracters 18d and 18q (hereinafter referred to as “subtracter 18”) which output a difference between an output of a motor current limiting section 14 which will be described later and an output of the three-phase to dq coordinate converting section 9, and current control sections l0d and l0q (hereinafter referred to as “current control section 10”) which conduct feedback control on the dq coordinates on the basis of the output of the substracter 18. The microcontroller 6 further includes a dq to three-phase coordinates converting section 11 that converts an output of the current control section 10 from the dq coordinates into three-phase AC coordinates, and a motor rotation speed calculating section 12 that calculates a rotation speed Rl of the motor 1 from the magnetic pole position of the rotor. The overheat protecting section 7 includes a motor current limit value calculating section 13 that calculates motor current limit values that limit the motor current command values (Id, Iq) on the basis of the motor rotation speed Rl that is outputted from the motor rotation speed calculating section 12 and the motor driving current that is outputted from the three-phase to dq coordinates converting section 9. The overheat protecting section 7 also includes motor current limiting sections 14d and I4q (hereinafter referred to as “motor current limiting section 14”) which limit the motor current command values (Id, Iq) on the basis of the 6 motor current limit values which are outputted from the motor current limit value calculating section 13. In this example, the three-phase to dq coordinates converting “section 9, the current control section 10/ the dq to three-phase coordinates converting section 11, the motor rotation speed calculating section 12, the motor current limit value calculating section 13, and the motor current limiting section 14 are incorporated into the microcontroller 6 as software - FIG. 2 is a flowchart showing the operation of a program of software that is installed in the microcontroller 6 shown in FIG. 1- the program is cyclically repeatedly called up. Hereinafter, a description will be given of the operation of the motor control device with the above structure with reference to FIG. 2. First, the position sensor 2 detects the magnetic pole position of the rotor of the motor 1 for every given period, the motor rotation speed calculating section 12 calculates a difference between the detected magnetic pole position and the magnetic pole position that has been previously detected, and calculates and outputs the motor rotation speed Rl (Step S21). Also, the current detector 4 detects the u-phase driving current Iu and the v-phase driving current Iv among the three-phase motor driving currents which are inputted to the motor 1 from the PWM inverter 3. Then, the current detector 4 calculates the w-phase 7 driving current: Iw by the following expression (1), and outputs the three-phase motor driving currents Iu, Iv, and Iw (Step S22) . Iw = -Iu - Iv ... (1) The A/D converter 8 converts the three-phase motor driving currents lu, Iv, and Iv; into digital signals/ and thereafter the three-phase to &q coordinates converting section 9 converts the digital signals into the dq coordinates and then outputs the dq coordinates as the d-axis driving current (d-axis component current) Id and the q-axis driving current (q-axis component current) Iq which are shown in FIG. 3 (Step 323). The motor current limit value calculating section 13 synthesizes the d-axis driving current Id and the q-axis driving current Iq in vector by the following expression (2) to obtain a synthetic driving current (synthetic current) Is (Step S24) , Is=~jd2 +lq2 . (2) In this example, with the synthetic driving current Is kept constant, a circle with a constant radius which is indicated by a broken line in FIG. 3 can be expressed as a motor current limit value- This fact means that a resultant value from synthesizing the three-phase motor driving currents Iu, Iv, and Iw is a constant current value. Also, the ayntheticdriving current Is is not affected by the magnetic pole position of the rotor of the motor 1, that is, a phase angle 91 (hereinafter referred to as “current phase angle 81”) that is defined by the q-axis and the synthetic driving 8 current Is, and can be represented by a current value that is fed to the motor 1. Likewise, the motor current limit value calculating section 13 obtains the motor current limit value that limits the motor current command value (Id, Iq) from the synthetic driving current Is and the motor rotation speed Rl, and outputs a d-axis current limit value Idr and a q-axis current limit value Iqr of the motor current limit value (Step S25). The motor current limit section 14 limits the d-axis command current Id* and the q-axis command current Iq* to the d-axis current limit value Idr or less and the q-axis current limit value Iqr or less, respectively, and then outputs those currents as a d-axis limited current Idr* and a q-axis limited current Iqr* (Steps S26 and S27) . The subtracter 18 outputs a difference between the d-axis limited current Idr* and the d-axis driving current id, and a difference between the q-axis limited current Iqr* and the q-axis driving current Iq, and the current control section 10 conducts feedback control on the basis of an output of the subtracter 18 (Steps S28 arid S29) . The dq to three-phase coordinates converting section 11 converts the output of the current control section 10 from the dq coordinates into the three-phase AC coordinates and outputs the converted output to the PWM inverter 3 (Step S30) , The motor 1 is 9 driven according to the output of the PWM inverter 3. Subsequently, a description will be given in more detail of the operation of the motor control device in Step S25, The motor current limit value calculating section 13 calculates a motor current limit value change speed Vm that gradually decreases or gradually increases the maximum current which is permitted by the motor 1 on the basis of the characteristics (given function) shown in FIG. 4 with the use of the motor rotation speed Rl and the synthetic driving current Is, Then, the motor current limit value calculating section 13 integrates the motor current limit value change speeds Vm, and calculates the motor current limit values (Idr, Iqr) . The motor current limit values (Idr, Iqr) limit the motor current command values (Id, Iq) on the dq coordinates. In this example, the motor current limit value calculating section 13 determines that the motor 1 is rotating when the motor rotation speed Rl is equal to or higher than a given rotation speed I wnich is arbitrarily set, and calculates the motor current limit values tldr, Iqr) by using the motor current limit value change speed Vrr\ (refer to FIG. 4) indicated by a broken line. Alternatively, the motor current limit value calculating section 13 determines that the motor 1 is stopped when the motor rotation speed Rl is equal to or lower than a given rotation speed {which is arbitrarily set, and calculates the motor current limit values (Idr, Iqr) by using the motor current limit value change speed Vm (refer to FIG. 4) indicated by a solid line. Accordingly, since a slope of the gradual decrease of the maximum current that is permitted by the motor 1 can be switched over according to the motor rotation speed Rl, the slope of the gradual decrease at the time of rotating the motor 1 can be made smaller than that at the time of stopping the motor 1. In the case of gradually increasing the motor current limit values (Idr, iqr), the motor carrent limit values (Idr, Iqr) are determined according to the heat radiation characteristics of the microcontroller 6 or the motor 1 regardless of the rotating time or stopping time of the motor 1, with the result that the rotating time and the stopping time of the motor 1 are set as the identical parameter. The motor current limit valaes (Idr, Iqr) are broken down into the d-axis current limit value Idr and the q-axis current limit value Iqr so that the current phase angle 91 (refer to FIG. 3) is kept constant, and then outputted to the motor current limit section 14. The d-axis current limit value Idr and the q-axis current limit value Iqr at the time of rotating the motor and at the time of stopping the motor are shown, for example, in FIG, 5. In the motor control device according to the first embodiment of the present invention, since the motor current limit values (Idr, Iqr) can toe calculated according to the motor rotation speed Rl, the motor 1 can be appropriately protected from being overheated. 11 Also, since the motor current limit values (Idr, Iqr) are calculated according to the synthetic driving current Is, the motor control device can cope with the concentration of heat into a specific motor phase at the time of stopping the motor 1, and also can cope with a status in which the heat generation at the time of rotating the motor 1 is averaged. Also, the motor current limit values (Idr, Iqr} that are calculated by the motor current limit value calculating section 13 limit the motor current command values (Id, Iq) on the dq coordinates. Because the motor current limit values (Idr, Iqr) limit the motor current command values (Id, Iq) before being converted into the three-phase AC coordinates, the current can be gradually decreased while the current balance of the respective motor phase is kept according to the rotating status of the motor 1. Also, because the motor current limit values (Idr, Iqr) are calculated by using the synthetic driving current Is, it is unnecessary to calculate the motor current limit values (Idr, Iqr) in each of the phase currents. As a result, because the calculating process can be simplified, a processing load of tne motor current limit value calculating section 13 can be reduced. Also, since the motor current limit values (Idr, Iqr) are calculated so as to maintain the current phase angle 81, the motor current command values (Id, Iq) can be limited while the motor rotation speed Rl and the torque are gradually decreased with a 12 proper balance. In the above first embodiment, the motor current limit value calculating section 13 calculates the motor current limit values (Idr, Iqr) by using the synthetic driving current Is. Alternatively, the motor current limit values (Icir, Iqr) may be calculated by using a power function (given function) of the synthetic driving current Is. A loss of the motor 1 or the PWM inverter 3 is substantially in proportion to the first to second powers of the motor driving current, thereby making it possible to more properly protect the motor from being overheated. In this example, the power functions are expressed by, for example, the following expressions (3) to (5). fl(i) = i3//2 .,.(3) f2(i) =I2 .,,(4) f3(i) = i3//2 + a ...(5) In the above expressions, fl, f2, and f3 are power functions, is a motor current, and a is an arbitrary constant. In this situation, in the case where the power function of the synthetic driving current Is is represented by the expression (2), the expression (41) can be represented by the following expression (6) . f2 (Is) = Id2 + Iq2 ...(6) The use of the expression (6) makes it possible to simplify the arithmetic expression, and also makes it possible to reduce 13 the processing load of the motor current limit value calculating section 13- Also, the above power function is subjected to polynomial approximation or polygonal-line approximation, thereby making it possible to further reduce the amount of calculation. As a result, the processing load of the motor current limit value calculating section 13 can be reduced* Also, at is possible that a part or all of the above calculations are tabled, and the amount of calculations can also be reduced with reference to the table. Also, in the above first embodiment/ the synthetic driving current Is is obtained from the d-axis driving current Id and the q-axis driving current Iq. It is needless to say that the present invention is not limited to this embodiment- In general, in the control of the motor 1, the d-axis driving current Id that is a magnetic flux axis is normally used as a weaker magnetic flux control/ which is, in many cases, smaller than the q-axis driving current Iq which is the torque axis. Under the circumstances, in the case where the d-axis driving current Id is sufficiently smaller than the q-axis driving current Iq, the synthetic driving current Is is simplified as indicated by the following expression (7) , thereby making it possible to further reduce the amount of calculation. As a result, the processing load of the motor current limit value calculating section 13 can be reduced. Is = Id + Iq ...(7) 14 Also, in the case of effectively controlling the motor 1, the d-axis driving current Id is normally controlled to 0. In this case, because the d-axis driving current Id is 0, the synthetic driving current Is may he regarded as the q-axis driving current Iq. Also, under the motor control where the q-axis driving current Iq hardly flows, the synthetic driving current Is may be regarded as the d-axis driving current Id. Also, the maximum values of the d-axis driving current Id and the q-axis driving current Iq are selected as the synthetic driving current Is, In the above case, the amount of calculation can also be further reduced, and the processing load of the motor current limit value calculating section 13 can be reduced. Also, in the above first embodiment, the motor current limit values (Icir, Iqrj are obtained by using the synthetic driving current Is. Alternatively, the motor current limit values (Idr, Iqr) may be obtained by using the d-axis driving current Id and the q-axis driving current Iq, respectively. Also, in the above first embodiment, the synthetic driving current Is is obtained dy using the d-axis driving current Id and the q-axis driving current Iq. Alternatively, in order to smooth the absolute values of the d-axis driving current Id and the q-axis driving current Iq in time, after the d-axis driving current Id and the q-axis driving current Iqare added in arbitrary predetermined 15 cycles for an arbitrary predetermined period of time, respectively, the synthetic driving current Is may be obtained. Also, in the above first embodiment, the motor current limit value {Idr, Iqr) is calculated by using the d-axis driving current Id and the q-axis driving current Iq. Alternatively, as shown in FIG- 6, the motor current limit value (Idr, Iqr) may be calculated by using the d-axis command current (d-axis component current) Id* and the q-axis command current (q-axis component current) Iq. In this case, the present invention can be applied to the motor control device having no detector circuit of the respective phase currents such as an open loop control. Also, in the above first embodiment, the three-phase brushless motor 1 is used as the polyphase motor. It is needless to say that the present invention is not limited to this embodiment, but the same effects can be obtained as long as the motor is a polyphase motor such as an induction motor. Also, in the above first embodiment, the motor current limit values are broken down into the d-axis current limit value Idr and the q-axis current limit value Iqr so that the current phase angle ©1 is Jcept constant. Alternatively, the current phase angle 81 may be changed. In this case, there are proposed a method of allowing the d-axis current to flow preferentially and a method of allowing the q-axis current to flow preferentially while the synthetic command current 16 of the d-axis command current Id and the q-axis command current Iq* is restricted to a given value or less. As shown in the above first embodiment, in the case of controlling the three-phase brashless motor 2, a weaker magnetic field effect is obtained when the d-axis driving current Id is caused to flow in a negative direction. Accordingly, when the d-axis driving current is caused to flow preferentially, the motor 1 can be driven with the preference of the rotation speed. Also, when the magnetic field is kept constant, since the q-axis driving current Iq is in proportion to the output torque, the motor 1 can be driven with the preference of the torque when the q-axis driving current Iq is caused to flow preferentially. Also, the above method can be applied to a case in which the magnetic flux is controlled by an excitation current as with the induction motor. The above first embodiment shows a method in which the three-phase brushless motor 1 is controlled on the dq coordinates . However, in the case where the induction motor is controlled on the \b coordinates, the y-axis rotor inter linkage magnetic flux density and the 6-axis stator current may be uniformly gradually decreased. Also, in the above first embodiment, the presence or absence of rotations of the motor 1 is determined with the given rotation speed 5 of the motor 1 which is arbitrarily set as a threshold value, and the parameter of the motor current limit value change speed 17 Vm is switched over. It is needless to say that the present invention is not limited to this structure. For example, the motor current limit value calculating section 13 may be structured as shown in FIG. 7 - In FIG. 7, the motor current limit value calculating section 13 includes a rotation coefficient table 13a for output a rotation coefficient Kr which is equal to or less than 1 according to the motor rotation speed Rl, a motor current limit value change speed table 13b for outputting a motor current limit value change speed Vm’ according to the synthetic driving current Is, and a multiplier 13c for multiplying the rotation coefficient Kr and the motor current limit value change speed Vm’ - The rotation coefficient Kr that is outputted from the rotation coefficient table 13a and the motor current limit value change speed Vm’ that is outputted from the motor current limit value change speed table 13b are multiplied by the multiplier 13c and then outputted as the motor current limit value change speed Vm. As a result, it is possible to more finely obtain the motor current limit values (Idr, Iqr) according to the motor rotation speed Rl. Also, as shown in FIG. 8, a value resulting from multiplying the rotation coefficient Kr that is outputted from the rotation coefficient table 13a by the synthetic driving current Is may be inputted to the motor current limit value change speed table 13b. Likewise, the same effects as described above can be obtained in 18 this case. Second Embodiment In the above first embodiment, the current control section 10 subjects the limited current to the feedback control on the dq coordinates, but may subject the limited current to the feedback control on the three-phase AC coordinates. Also, in order to obtain the motor rotation speed, the motor rotation speed is calculated by using the magnetic pole position of the rotor which is detected by the position sensor 2- Alternatively, the motor rotation speed may be estimated according to the motor terminal voltage and the motor driving current. FIG. 9 is a block diagram showing a motor control device according to a second embodiment of the present invention, together with peripheral devices. Referring to FIG, 9, the motor control device includes a dq to three-phase coordinates converting section 15 for converting the motor current command values (Id, Iq) from the dq coordinates into the three-phase AC coordinates, and a terminal voltage detecting section (terminal voltage detecting means) 16 for detecting the motor terminal voltage that is applied to the motor 1 from the PWM inverter 3. Also, the motor rotation speed calculating section 12 shown in FIG. 1 is omitted from FIG. 9, and the motor control device shown in FIG. 9 includes a mot or rotation speed estimate calculating section 19 17 for estimating the motor rotation speed on the basis of the motor terminal voltage and the motor driving current. Also, the dq to three-phase coordinates converting section 11 shown in FIG, 1 is omitted, and an adder 19 is connected to the Output portion of the current control means 10, Other structures are the same at those in the first embodiment, and therefore their description will be omitted- Also, a program that is installed in a microcontroller 6B is the same as that in the first embodiment, and their description will be omitted. Hereinafter, the operation of the motor control device with the above structure will be described. The description on the same operation as that in the first embodiment will be omitted. First, the three-phase motor driving currents Iu, Iv, and Iw which are outputted from the current detector 4 are converted into the digital signals by the A/D converter 8, and thereafter inputted to the motor rotation speed estimate calculating section 17. Also, the three-phase motor terminal voltages Vu, Vv, and Vw that are detected by the terminal voltage detecting section 16 are inputted to the motor rotation speed estimate calculating section 17. In this example, the model of the three-phase permanent magnet synchronous motor can be generally represented by the following expression {8} . 20 In this expression, u is a motor rotation speed, 62 is a motor angle based on the u phase, R is an armature resistance, L is a self inductance of the armature coil, M is a mutual inductance of the armature coil, $ is a maximum value of the interlinkage magnetic flux, and p is a differential operator (d/dt), In this example, when the motor 1 is driven, there exists a motor angle that satisfies Iv = -Iw, At this time, the u-phase terminal voltage can be represented by the following expression (9). Vu = -cosin (62) ...(9) In this case, 92 is a given value because the motor angle is a given angle, and R, L, and $ are determined according to the characteristic of the motor 1 to detect Vu and Iu. Accordingly, when Iv = -Iw, the motor rotation speed CJ can be calculated. Also, in the case of Iu = -Iw as well as Iu = -Iv, the rotation speed u can be obtained in the same manner. The motor current limit value calculating section 13 obtains the motor current limit values (Idr, Iqr) in the same method as that described in the first embodiment by using the d-axis driving 21 current Id, the q-axis driving current Iq, and the motor rotation speed CJ that is calculated in the motor rotation speed estimate calculating section 17, Also, the dq to three-phase coordinates converting section 15 converts the d-axis command current Id, the q-axis command current Iq* into the u-phase command current Iu* and the v-phase command current Iv* on the three-phase AC coordinates. The motor current limit values (Idr,Iqr that are calculated by the motor current limit value calculating section 13 limit the peak values of the three-phase AC current. Therefore, the motor current limit section 14 limits the peak values of the u-phase command current Iu* and the v-phase- command current Iv* to be equal to or less than a motor current limit value, and outputs those currents as a u-phase controlled current Iur* and a v-phase controlled current Ivr. The subtracter 18 outputs a difference between the u-phase controlled current lur and the u-phase driving current Iu, and a difference between the v-phase controlled current Ivr* and the v-phase driving current Iv, and the current control section 10 conducts the feedback control on the basis of the output of the subtracter 18. The output of the current control section 10 is inputted to the PWM inverter 3 in response to a demand of the w-phase current from the adder 19- The motor 1 is driven by the output of the PWM inverter 3. 22 In the motor control device according to the second embodiment of the present invention, since the motor current command values (la, Iv) can be limited on the three-phase AC coordinates according to the motor rotation speed CJ, the motor 1 can be appropriately protected from being overheated. In the above second embodiment, the motor rotation speed o is estimated from the motor terminal voltages Vu, Vv, Vw, and the motor driving currents Iu, Iv, Iw on the three-phase AC coordinates. Alternatively, the motor rotation speed may be estimated from the motor terminal voltages Vd, Vq, and the motor driving currents Iu, Iv, Iw on the dq coordinates. In the case where the motor terminal voltages Vu, Vv, Vw, and themotor driving currents la, Iv, Iwonthethree-phaseAC coordinates are converted into dq coordinates on the orthogonal coordinate system, the model of the three-phase permanent magnet synchronous motor can be generally described as indicated in the following expression (10) . = In the above expression, Of is an interlinkage magnetic flux on the dq coordinates. In this example, when Id = 0, the q-axis terminal voltage can be represented by the following expression (11), Vq = (R + pL)Iq + WƠf ..-(11) 23 In this case, R, L, and of are determined according to the motor characteristics, and Vq and Iq can be calculated according to the dq coordinate conversion. Accordingly, the motor rotation speed u can be obtained. Also, in the case where the motor control device according to the above second embodiment is used in an electric power steering device, the motor rotation speed may be estimated by a sensor that detects a handle angle or a steering angle sensor for detecting a steering angle of a steering wheel, instead. Third Embodiment In the above first and second embodiments, the motor current lirmiti values (Idr, Iqr) are calculated according to the d-axis driving current Id and the q-axis driving current Iq- Alternatively, the motor current limit values (Idr, Iqr) may be calculated on the basis of deviations between threshold values for overheat protection determination, and the d-axis driving current Id and the q-axis driving current Iq, respectively, FIG, 10 is a block diagram showing a motor control device according to a third embodiment of the present invention, together with peripheral devices. Referring to FIG- 10, a microcontroller 6C is given a threshold value for the overheat projection determination which is arbitrarily set. Also, the microcontroller 6C has subtracters 20d and 20q (hereinafter, collectively referred to as substracter 20”) which 24 output differences between the d-axis driving current Id and the q-axis driving current Iq, and the threshold values for the overheat protection determinations, respectively. Other structures are the same as those in the first embodiment, and their description will be omitted. Also, a program that is installed in the microcontroller 6C is identical with that shown in the first embodiment, and its description will be omitted. Hereinafter, the operation of the motor control device with the above structure will be described. The same operation as that in the first embodiment will be omitted. The subtracter 20 compares the d--axis driving current Id and the q-axis driving current Iq which are outputted from the dq to three-phase coordinates converting section 15 with the overheat protection determination threshold values, respectively, to obtain the deviations. The maximum values of the respective deviations are outputted as the motor current limit value change speeds, for examplef according to the same characteristics as those in FIG. 4- In this situation, in the axis of abscissa shown in FIG- 4, the synthetic driving current is replaced with the deviation. Subsequently, the motor current limit value change speeds are integrated to calculate the motor current limit values (Idr, Iqr) . In the motor control device according to the third embodiment of the present invention, the motor current limit values (Idr, Iqr) are calculated on the basis of the deviations between the overheat 25 protection determination threshold values, and the d-axis driving current Id and the q-axis driving current Iq. As a result, the motor current command values (Id, Iq} can be restricted early when the motor driving current is large and lately when the motor driving current is small, thereby making it possible to execute the more practicable overheat protection. When, for example, the current value (hereinafter referred to as “continuous rated current”) which is capable of continuously driving the motor 1 is set as the above overheat protection determination threshold value, a large current is supplied according to a short time rating of the motor 1 or the PWM inverter 3 for a short period of time, and the motor current can be smoothly converged into the continuous rated current according to the running status. Also, in the above third embodiment, the maximum currents are gradually decreased or gradually increased on the basis of the deviations between the coordinate converted current, that is, the synthetic driving current Is and the given overheat protection determination threshold value. Alternatively, the maximum current may be gradually decreased or gradually increased on the basis of the integrated value of the deviations between the power functions of the coordinated converted current and the given overheat protection determination threshold value. Because the loss of the motor 1 or the PWM inverter 3 is substantially in proportion to the first to second power of the 26 motor driving current, the above method is capable of conducting the overheat protection more appropriately. Also, the same effects can be obtained even in the case where the maximum current is gradually decreased or gradually increased on the basis of the power function of the deviation between the synthetic driving current Is and the given overheat protection determination threshold value as described in the above first embodiment 27, WHAT IS CLAIMED IS: 1. A motor control device, comprising: an inverter unit for driving a polyphase motor; position detecting means for detecting a magnetic pole posit ion of a rotor of the polyphase motors- driving current detecting means for detecting a motor driving current inputted to the polyphase motor from the inverter unit; current command value calculating means for generating a motor current command value of the polyphase motor; and motor control means for controlling the inverter unit according to the motor current command value, wherein the motor control means calculates a motor current limit value that limits the motor current command value on the basis of the rotation speed of the polyphase motor calculated from the magnetic pole position and the motor driving current. 2. A motor control device, comprising: an inverter unit for driving a polyphase motor; terminal voltage detecting means for detecting a terminal voltage applied to the polyphase motor from the inverter unit; driving current detecting means for detecting a motor driving current inputted to the polyphase motor from the inverter unit; current command vaiue calculating means for generating a motor current command value of the polyphase motor; and 28 motor control means for controlling the inverter unit according to the motor current command value, wherein the motor control means calculates a motor current limit value that limits the motor current command value on the basis of the rotation speed of the polyphase motor calculated from the terminal voltage and the motor driving current, and the motor driving current. 3. A motor control device, comprising: an inverter unit for driving a polyphase motor; position detecting means for detecting a magnetic pole position of a rotor of the polyphase motor; current command value calculating means for generating a motor current command value of the polyphase motor; and motor control means for controlling the inverter unit according to the motor current command value, wherein the motor control means calculates a motor current limit value that limits the motor current command value on the basis of the rotation speed of the polyphase motor calculated from the magnetic pole position and the motor current command value. 4. A motor control device, comprising: an inverter unit for driving a polyphase motor; terminal voltage detecting means for detecting a terminal 29 voltage applied to the polyphase motor from the inverter unit; driving current detecting means for detecting a motor driving current inputted to the polyphase motor from the inverter unit; current command value calculating means for generating a motor current command value of the polyphase motor; and motor control means for controlling the inverter unit according to the motor current command value, wherein the motor control means calculates a :motor current limit value that limits the motor current command value on the basis of the rotation speed of the polyphase motor calculated from the terminal voltage and the motor driving current, and the motor current command value. 5- A motor control device according to any one of claims 1 to 4, wherein the motor control means calculates the motor current limit value according to an integrated value of a given function of one of the motor driving current and the motor current command value. 6, A motor control device according to any one of claims 1 to 4, wherein the motor control means determines the presence or absence of the rotations of the polyphase motor from the rotation speed to calculate the motor current limit value, 30 7. A motor control device according to claim 5, wherein the motor control means obtains the integrated value after a coefficient equal to or less than 1 according to the rotation speed is multiplied by a value obtained by the given function. 8. A motor control device according to claim 5, wherein the given function is a power function. 9. A motor control device according to any one of claims 1 to 4, wherein the motor control means converts one of the motor driving current and the motor current command value into a d-axis (magnetic flax axis) component current and a q-axis (torque axis) component current orthogonal to the d-axis component current to calculate the motor current limit value. 10. A motor control device according to claim 9/ wherein the motor control means calculates the motor current limit value according to any one of the d-axis component current and the q-axis component current - 11. A motor control device according to claim 9, wherein the motor control means calculates the motor current limit value according to a synthetic current obtained by synthesizing the d-axis component current and the q-axis component current. 31 12. A motor control device according to claim 9, wherein the motor control means calculates the motor current limit value according to a current larger in supply amount of the d-axis component current and the q-axis component current. 13. A motor control device according to claim 9, wherein the motor control means calculates the motor current limit value according to a deviation among a threshold value for the overheat protection determination, and the d-axis component current and the q-axis component current. 14. A motor control device according to any one of claims 1 to 4, wherein the motor control means converts the motor current command value into a d-axis command current and a q-axis command current orthogonal to the d-axis command current, and limits at ] east one of the d-axis command current and the q-axis command current on the basis of the motor current limit value. 15. A motor control device according to claim 14, wherein the motor control means maintains an angle defined by the q-axis command current, and a synthetic command current resulting from synthesizing the d-axis command current and the q-axis command current. 32 16. A motor control device according to any one of claims 1 to 4, wherein the motor control means converts the motor current command value into a d-axis command current and a q-axis command current orthogonal to the d-axis command current, and limits a synthetic command current resulting from synthesizing the d-axis command current and the q-axis command current on the basis of the motor current limit value, 17. A motor control device according to claim 16, wherein the motor control means controls the synthetic command current on the basis of the motor current limit value so that any one of the d-axis command current and the q-axis command current is given priority. 18. A motor control device according to any one of claims 1 to 4, wherein the motor control means limits a peak value of the phase current of the motor current command value on the basis of the motor current limit value. 33

Full Text

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
COMPLETE
SPECIFICATION
(See Section 10; rule 13)
TITLE
MOTOR CONTROL DEVICE
APPLICANT
MITSUBISHI DENKIKABUSHIKIKAISHA
2-3, Marunouchi 2-chome
Chiyoda-ku
Tokyo 100-8310
Japan
Nationality : a Japanese company
The following specification particularly describes
the nature of this invention and the manner
in which it is to be performed

MOTOR CONTROL DEVICE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor control device for limiting a motor current command value such as a brushless motor.
2. Description of the Related Art
A conventional motor control device includes a driver circuit for driving a polyphase motor, and a microcontroller for controlling the driver circuit. The microcontroller limits a motor current according to an integrated value of a given function of a phase current (for example, refer to JP 2002-238293 A).
In the conventional motor control device, because a rotating state of a motor is not taken into consideration, in a case where an electric power is supplied to the motor in a state where the motor stops, a current of a specific motor phase increases. As a result, there has been a problem in that the specific motor phase is overheated as compared with other motor phases.
In addition, in a case where the electric power is supplied to the motor in a state where the motor rotates, there has been a problem in that a microcontroller limits a motor current and the motor current is excessively limited even in a state where the heat is averagely applied to each phase.
1

SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems, and therefore an object of the present invention is to provide a motor control device for limiting a motor current command value according to a rotating state of a motor, thereby making it possible to appropriately protect the motor from being overheated.
According to the present invention, there is provided a motor control device, including: an inverter unit for driving a polyphase motor; position detecting means for detecting a magnetic pole position of a rotor of the polyphase motor; driving current detecting means for detecting a motor driving current inputted to the polyphase motor from the inverter unit; current command value calculating means for generating a motor current command value of the polyphase motor; and motor control means for controlling the inverter unit according to the motor current command value, in which the motor control means calculates a motor current limit value that limits the motor current command value on the basis of the rotation speed of the polyphase motor calculated from the magnetic pole position and the motor driving current.
According to the motor control device of the present invention, since the motor current command value can be limited according to the rotating state of the motor, the motor can be appropriately protected from being overheated.
2

BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a block diagram showing a motor control device according to a first embodiment of the present invention, together with peripheral devices;
FIG. 2 is a flowchart showing the operation of a program of software that is installed in the microcontroller shown in FIG.
1;
FIG. 3 is an explanatory diagram showing a motor current limit value of the motor control device according to the first embodiment of the present invention;
FIG. 4 is a diagram showing characteristics of a synthetic driving current to a motor current limit value change speed at the time of rotating the motor and at the time of stopping the motor in the motor control device according to the first embodiment of the present invention;
FIG. 5 is an explanatory diagram showing a d-axis current limit value and a q-axis current limit value at the time of rotating the motor and at the time of stopping the motor in the motor control device according to the first embodiment of the present invention;
FIG- 6 is a block diagram showing another motor control device according to the first embodiment of the present invention, together with peripheral devices;
FIG. 7 is an explanatory diagram showing a method of obtaining
3

a motor current limit value change speed by using a rotating speed of the motor in the motor control device according to the first embodiment of the present invention;
FIG- 8 is an explanatory diagram showing another method of obtaining a motor current limit value change speed by using a rotating speed of the motor in the motor control device according to the first embodiment of the present invention;
FIG. 9 is a block diagram showing a motor control device according to a second embodiment of the present invention, together with peripheral devices; and
FIG. 10 is a block diagram showing a motor control device according to a third embodiment of the present invention, together with peripheral devices*
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a description will be given in more detail of the respective preferred embodiments of the present invention with reference to the accompanying drawings. In the respective drawings, identical or corresponding members and portions are denoted by the same reference symbols. First Embodiment
FIG, 1 is a block diagram showing a motor control device
according to a first embodiment of the present invention, together with peripheral devices,
4

Referring to FIG- 1, the motor control device is connected to a three-phase brushless motor 1 (hereinafter referred to as “motor 1”) which is a polyphase motor.
The motor control device includes a position sensor (position detecting means) 2 which detects a magnetic pole position of a rotor of the motor 1, a PWM inverter (inverter unit) 3 which drives the motor 1, and a current detector (driving current detecting means) 4 which detects three-phase motor driving currents lu, Iv, and Iw which are inputted to the motor 1 from the PWM inverter 3. The motor control device also includes a current command value calculating section 5 that generates a d-axis (magnetic flux axis) command current Id* and a q-axis (torque axis) command current Iq* which are the motor current command values of the motor 1 on the basis of a torque command value T* and a magnetic flax command value F* which are given from the external, and a microcontroller 6 (motor control means) which controls the PWM inverter 3 by using tine motor current command values (Id*, Iq*).
The microcontroller 6 includes an overheat protecting section 7 that limits the motor current command values (Id*, Iq*) to prevent overheat, A/D converters 8u and 8v {hereinafter referred to as A/D converter 8”) which convert the outputs of the current detector 4 into digital values, and a three-phase to dq coordinates converting section 9 that converts the output of the A/D converter 8 from three-phase AC coordinates into dq coordinates composed of a d-axis
5

and a q-axis orthogonal to the d-axis. The microcontroller 6 also includes subtracters 18d and 18q (hereinafter referred to as “subtracter 18”) which output a difference between an output of a motor current limiting section 14 which will be described later and an output of the three-phase to dq coordinate converting section 9, and current control sections l0d and l0q (hereinafter referred to as “current control section 10”) which conduct feedback control on the dq coordinates on the basis of the output of the substracter 18. The microcontroller 6 further includes a dq to three-phase coordinates converting section 11 that converts an output of the current control section 10 from the dq coordinates into three-phase AC coordinates, and a motor rotation speed calculating section 12 that calculates a rotation speed Rl of the motor 1 from the magnetic pole position of the rotor.
The overheat protecting section 7 includes a motor current limit value calculating section 13 that calculates motor current limit values that limit the motor current command values (Id*, Iq*) on the basis of the motor rotation speed Rl that is outputted from the motor rotation speed calculating section 12 and the motor driving current that is outputted from the three-phase to dq coordinates converting section 9. The overheat protecting section 7 also includes motor current limiting sections 14d and I4q (hereinafter referred to as “motor current limiting section 14”) which limit the motor current command values (Id*, Iq*) on the basis of the
6

motor current limit values which are outputted from the motor current limit value calculating section 13.
In this example, the three-phase to dq coordinates converting “section 9, the current control section 10/ the dq to three-phase coordinates converting section 11, the motor rotation speed calculating section 12, the motor current limit value calculating section 13, and the motor current limiting section 14 are incorporated into the microcontroller 6 as software -
FIG. 2 is a flowchart showing the operation of a program of software that is installed in the microcontroller 6 shown in FIG. 1- the program is cyclically repeatedly called up.
Hereinafter, a description will be given of the operation of the motor control device with the above structure with reference to FIG. 2.
First, the position sensor 2 detects the magnetic pole position of the rotor of the motor 1 for every given period, the motor rotation speed calculating section 12 calculates a difference between the detected magnetic pole position and the magnetic pole position that has been previously detected, and calculates and outputs the motor rotation speed Rl (Step S21).
Also, the current detector 4 detects the u-phase driving current Iu and the v-phase driving current Iv among the three-phase motor driving currents which are inputted to the motor 1 from the PWM inverter 3. Then, the current detector 4 calculates the w-phase
7

driving current: Iw by the following expression (1), and outputs the three-phase motor driving currents Iu, Iv, and Iw (Step S22) .
Iw = -Iu - Iv ... (1)
The A/D converter 8 converts the three-phase motor driving currents lu, Iv, and Iv; into digital signals/ and thereafter the three-phase to &q coordinates converting section 9 converts the digital signals into the dq coordinates and then outputs the dq coordinates as the d-axis driving current (d-axis component current) Id and the q-axis driving current (q-axis component current) Iq which are shown in FIG. 3 (Step 323).
The motor current limit value calculating section 13 synthesizes the d-axis driving current Id and the q-axis driving current Iq in vector by the following expression (2) to obtain a synthetic driving current (synthetic current) Is (Step S24) ,
Is=~jd2 +lq2 . (2)
In this example, with the synthetic driving current Is kept
constant, a circle with a constant radius which is indicated by a broken line in FIG. 3 can be expressed as a motor current limit value- This fact means that a resultant value from synthesizing the three-phase motor driving currents Iu, Iv, and Iw is a constant current value. Also, the ayntheticdriving current Is is not affected by the magnetic pole position of the rotor of the motor 1, that is, a phase angle 91 (hereinafter referred to as “current phase angle 81”) that is defined by the q-axis and the synthetic driving
8

current Is, and can be represented by a current value that is fed to the motor 1.
Likewise, the motor current limit value calculating section 13 obtains the motor current limit value that limits the motor current command value (Id*, Iq*) from the synthetic driving current Is and the motor rotation speed Rl, and outputs a d-axis current limit value Idr and a q-axis current limit value Iqr of the motor current limit value (Step S25).
The motor current limit section 14 limits the d-axis command current Id* and the q-axis command current Iq* to the d-axis current limit value Idr or less and the q-axis current limit value Iqr or less, respectively, and then outputs those currents as a d-axis limited current Idr* and a q-axis limited current Iqr* (Steps S26 and S27) .
The subtracter 18 outputs a difference between the d-axis limited current Idr* and the d-axis driving current id, and a difference between the q-axis limited current Iqr* and the q-axis driving current Iq, and the current control section 10 conducts feedback control on the basis of an output of the subtracter 18 (Steps S28 arid S29) .
The dq to three-phase coordinates converting section 11 converts the output of the current control section 10 from the dq coordinates into the three-phase AC coordinates and outputs the converted output to the PWM inverter 3 (Step S30) , The motor 1 is
9

driven according to the output of the PWM inverter 3.
Subsequently, a description will be given in more detail of the operation of the motor control device in Step S25,
The motor current limit value calculating section 13 calculates a motor current limit value change speed Vm that gradually decreases or gradually increases the maximum current which is permitted by the motor 1 on the basis of the characteristics (given function) shown in FIG. 4 with the use of the motor rotation speed Rl and the synthetic driving current Is, Then, the motor current limit value calculating section 13 integrates the motor current limit value change speeds Vm, and calculates the motor current limit values (Idr, Iqr) . The motor current limit values (Idr, Iqr) limit the motor current command values (Id*, Iq*) on the dq coordinates.
In this example, the motor current limit value calculating section 13 determines that the motor 1 is rotating when the motor rotation speed Rl is equal to or higher than a given rotation speed I wnich is arbitrarily set, and calculates the motor current limit values tldr, Iqr) by using the motor current limit value change speed Vrr\ (refer to FIG. 4) indicated by a broken line.
Alternatively, the motor current limit value calculating section 13 determines that the motor 1 is stopped when the motor rotation speed Rl is equal to or lower than a given rotation speed {which is arbitrarily set, and calculates the motor current limit values (Idr, Iqr) by using the motor current limit value change

speed Vm (refer to FIG. 4) indicated by a solid line.
Accordingly, since a slope of the gradual decrease of the maximum current that is permitted by the motor 1 can be switched over according to the motor rotation speed Rl, the slope of the gradual decrease at the time of rotating the motor 1 can be made smaller than that at the time of stopping the motor 1.
In the case of gradually increasing the motor current limit values (Idr, iqr), the motor carrent limit values (Idr, Iqr) are determined according to the heat radiation characteristics of the microcontroller 6 or the motor 1 regardless of the rotating time or stopping time of the motor 1, with the result that the rotating time and the stopping time of the motor 1 are set as the identical parameter.
The motor current limit valaes (Idr, Iqr) are broken down into the d-axis current limit value Idr and the q-axis current limit value Iqr so that the current phase angle 91 (refer to FIG. 3) is kept constant, and then outputted to the motor current limit section 14. The d-axis current limit value Idr and the q-axis current limit value Iqr at the time of rotating the motor and at the time of stopping the motor are shown, for example, in FIG, 5.
In the motor control device according to the first embodiment of the present invention, since the motor current limit values (Idr, Iqr) can toe calculated according to the motor rotation speed Rl, the motor 1 can be appropriately protected from being overheated.
11

Also, since the motor current limit values (Idr, Iqr) are calculated according to the synthetic driving current Is, the motor control device can cope with the concentration of heat into a specific motor phase at the time of stopping the motor 1, and also can cope with a status in which the heat generation at the time of rotating the motor 1 is averaged.
Also, the motor current limit values (Idr, Iqr} that are calculated by the motor current limit value calculating section 13 limit the motor current command values (Id*, Iq*) on the dq coordinates. Because the motor current limit values (Idr, Iqr) limit the motor current command values (Id*, Iq*) before being converted into the three-phase AC coordinates, the current can be gradually decreased while the current balance of the respective motor phase is kept according to the rotating status of the motor 1.
Also, because the motor current limit values (Idr, Iqr) are calculated by using the synthetic driving current Is, it is unnecessary to calculate the motor current limit values (Idr, Iqr) in each of the phase currents. As a result, because the calculating process can be simplified, a processing load of tne motor current limit value calculating section 13 can be reduced.
Also, since the motor current limit values (Idr, Iqr) are calculated so as to maintain the current phase angle 81, the motor current command values (Id*, Iq*) can be limited while the motor rotation speed Rl and the torque are gradually decreased with a
12

proper balance.
In the above first embodiment, the motor current limit value calculating section 13 calculates the motor current limit values (Idr, Iqr) by using the synthetic driving current Is. Alternatively, the motor current limit values (Icir, Iqr) may be calculated by using a power function (given function) of the synthetic driving current Is. A loss of the motor 1 or the PWM inverter 3 is substantially in proportion to the first to second powers of the motor driving current, thereby making it possible to more properly protect the motor from being overheated.
In this example, the power functions are expressed by, for example, the following expressions (3) to (5).
fl(i) = i3//2 .,.(3)
f2(i) =I2 .,,(4)
f3(i) = i3//2 + a ...(5)
In the above expressions, fl, f2, and f3 are power functions, is a motor current, and a is an arbitrary constant.
In this situation, in the case where the power function of the synthetic driving current Is is represented by the expression (2), the expression (41) can be represented by the following expression (6) .
f2 (Is) = Id2 + Iq2 ...(6)
The use of the expression (6) makes it possible to simplify the arithmetic expression, and also makes it possible to reduce
13

the processing load of the motor current limit value calculating section 13-
Also, the above power function is subjected to polynomial approximation or polygonal-line approximation, thereby making it possible to further reduce the amount of calculation. As a result, the processing load of the motor current limit value calculating section 13 can be reduced* Also, at is possible that a part or all of the above calculations are tabled, and the amount of calculations can also be reduced with reference to the table.
Also, in the above first embodiment/ the synthetic driving current Is is obtained from the d-axis driving current Id and the q-axis driving current
Iq. It is needless to say that the present invention is not limited to this embodiment- In general, in the control of the motor 1, the d-axis driving current Id that is a magnetic flux axis is normally used as a weaker magnetic flux control/ which is, in many cases, smaller than the q-axis driving current Iq which is the torque axis. Under the circumstances, in the case where the d-axis driving current Id is sufficiently smaller than the q-axis driving current Iq, the synthetic driving current Is is simplified as indicated by the following expression (7) , thereby making it possible to further reduce the amount of calculation. As a result, the processing load of the motor current limit value calculating section 13 can be reduced.
Is = Id + Iq ...(7)
14

Also, in the case of effectively controlling the motor 1, the d-axis driving current Id is normally controlled to 0. In this case, because the d-axis driving current Id is 0, the synthetic driving current Is may he regarded as the q-axis driving current Iq.
Also, under the motor control where the q-axis driving current Iq hardly flows, the synthetic driving current Is may be regarded as the d-axis driving current Id.
Also, the maximum values of the d-axis driving current Id and the q-axis driving current Iq are selected as the synthetic driving current Is,
In the above case, the amount of calculation can also be further reduced, and the processing load of the motor current limit value calculating section 13 can be reduced.
Also, in the above first embodiment, the motor current limit values (Icir, Iqrj are obtained by using the synthetic driving current Is. Alternatively, the motor current limit values (Idr, Iqr) may be obtained by using the d-axis driving current Id and the q-axis driving current Iq, respectively.
Also, in the above first embodiment, the synthetic driving current Is is obtained dy using the d-axis driving current Id and the q-axis driving current Iq. Alternatively, in order to smooth the absolute values of the d-axis driving current Id and the q-axis driving current Iq in time, after the d-axis driving current Id and the q-axis driving current Iqare added in arbitrary predetermined
15

cycles for an arbitrary predetermined period of time, respectively, the synthetic driving current Is may be obtained.
Also, in the above first embodiment, the motor current limit value {Idr, Iqr) is calculated by using the d-axis driving current Id and the q-axis driving current Iq. Alternatively, as shown in FIG- 6, the motor current limit value (Idr, Iqr) may be calculated by using the d-axis command current (d-axis component current) Id* and the q-axis command current (q-axis component current) Iq*. In this case, the present invention can be applied to the motor control device having no detector circuit of the respective phase currents such as an open loop control.
Also, in the above first embodiment, the three-phase brushless motor 1 is used as the polyphase motor. It is needless to say that the present invention is not limited to this embodiment, but the same effects can be obtained as long as the motor is a polyphase motor such as an induction motor.
Also, in the above first embodiment, the motor current limit values are broken down into the d-axis current limit value Idr and the q-axis current limit value Iqr so that the current phase angle ©1 is Jcept constant. Alternatively, the current phase angle 81 may be changed.
In this case, there are proposed a method of allowing the d-axis current to flow preferentially and a method of allowing the q-axis current to flow preferentially while the synthetic command current
16

of the d-axis command current Id* and the q-axis command current Iq* is restricted to a given value or less. As shown in the above first embodiment, in the case of controlling the three-phase brashless motor 2, a weaker magnetic field effect is obtained when the d-axis driving current Id is caused to flow in a negative direction. Accordingly, when the d-axis driving current is caused to flow preferentially, the motor 1 can be driven with the preference of the rotation speed.
Also, when the magnetic field is kept constant, since the q-axis driving current Iq is in proportion to the output torque, the motor 1 can be driven with the preference of the torque when the q-axis driving current Iq is caused to flow preferentially.
Also, the above method can be applied to a case in which the magnetic flux is controlled by an excitation current as with the induction motor. The above first embodiment shows a method in which the three-phase brushless motor 1 is controlled on the dq coordinates . However, in the case where the induction motor is controlled on the \b coordinates, the y-axis rotor inter linkage magnetic flux density and the 6-axis stator current may be uniformly gradually decreased.
Also, in the above first embodiment, the presence or absence of rotations of the motor 1 is determined with the given rotation speed 5 of the motor 1 which is arbitrarily set as a threshold value, and the parameter of the motor current limit value change speed
17

Vm is switched over. It is needless to say that the present invention is not limited to this structure.
For example, the motor current limit value calculating section 13 may be structured as shown in FIG. 7 - In FIG. 7, the motor current limit value calculating section 13 includes a rotation coefficient table 13a for output a rotation coefficient Kr which is equal to or less than 1 according to the motor rotation speed Rl, a motor current limit value change speed table 13b for outputting a motor current limit value change speed Vm’ according to the synthetic driving current Is, and a multiplier 13c for multiplying the rotation coefficient Kr and the motor current limit value change speed Vm’ -
The rotation coefficient Kr that is outputted from the rotation coefficient table 13a and the motor current limit value change speed Vm’ that is outputted from the motor current limit value change speed table 13b are multiplied by the multiplier 13c and then outputted as the motor current limit value change speed Vm.
As a result, it is possible to more finely obtain the motor current limit values (Idr, Iqr) according to the motor rotation speed Rl.
Also, as shown in FIG. 8, a value resulting from multiplying the rotation coefficient Kr that is outputted from the rotation coefficient table 13a by the synthetic driving current Is may be inputted to the motor current limit value change speed table 13b. Likewise, the same effects as described above can be obtained in
18

this case.
Second Embodiment
In the above first embodiment, the current control section 10 subjects the limited current to the feedback control on the dq coordinates, but may subject the limited current to the feedback control on the three-phase AC coordinates. Also, in order to obtain the motor rotation speed, the motor rotation speed is calculated by using the magnetic pole position of the rotor which is detected by the position sensor 2- Alternatively, the motor rotation speed may be estimated according to the motor terminal voltage and the motor driving current.
FIG. 9 is a block diagram showing a motor control device according to a second embodiment of the present invention, together with peripheral devices.
Referring to FIG, 9, the motor control device includes a dq to three-phase coordinates converting section 15 for converting the motor current command values (Id*, Iq*) from the dq coordinates into the three-phase AC coordinates, and a terminal voltage detecting section (terminal voltage detecting means) 16 for detecting the motor terminal voltage that is applied to the motor 1 from the PWM inverter 3.
Also, the motor rotation speed calculating section 12 shown in FIG. 1 is omitted from FIG. 9, and the motor control device shown in FIG. 9 includes a mot or rotation speed estimate calculating section
19

17 for estimating the motor rotation speed on the basis of the motor terminal voltage and the motor driving current. Also, the dq to three-phase coordinates converting section 11 shown in FIG, 1 is omitted, and an adder 19 is connected to the Output portion of the current control means 10,
Other structures are the same at those in the first embodiment, and therefore their description will be omitted- Also, a program that is installed in a microcontroller 6B is the same as that in the first embodiment, and their description will be omitted.
Hereinafter, the operation of the motor control device with the above structure will be described. The description on the same operation as that in the first embodiment will be omitted.
First, the three-phase motor driving currents Iu, Iv, and Iw which are outputted from the current detector 4 are converted into the digital signals by the A/D converter 8, and thereafter inputted to the motor rotation speed estimate calculating section 17.
Also, the three-phase motor terminal voltages Vu, Vv, and Vw that are detected by the terminal voltage detecting section 16 are inputted to the motor rotation speed estimate calculating section 17.
In this example, the model of the three-phase permanent magnet synchronous motor can be generally represented by the following expression {8} .
20

In this expression, u is a motor rotation speed, 62 is a motor angle based on the u phase, R is an armature resistance, L is a self inductance of the armature coil, M is a mutual inductance of the armature coil, $ is a maximum value of the interlinkage magnetic flux, and p is a differential operator (d/dt),
In this example, when the motor 1 is driven, there exists a motor angle that satisfies Iv = -Iw, At this time, the u-phase terminal voltage can be represented by the following expression (9).
Vu = -co*sin (62) ...(9)
In this case, 92 is a given value because the motor angle is a given angle, and R, L, and $ are determined according to the characteristic of the motor 1 to detect Vu and Iu.
Accordingly, when Iv = -Iw, the motor rotation speed CJ can be calculated.
Also, in the case of Iu = -Iw as well as Iu = -Iv, the rotation speed u can be obtained in the same manner.
The motor current limit value calculating section 13 obtains the motor current limit values (Idr, Iqr) in the same method as that described in the first embodiment by using the d-axis driving
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current Id, the q-axis driving current Iq, and the motor rotation speed CJ that is calculated in the motor rotation speed estimate calculating section 17,
Also, the dq to three-phase coordinates converting section 15 converts the d-axis command current Id*, the q-axis command current Iq* into the u-phase command current Iu* and the v-phase command current Iv* on the three-phase AC coordinates.
The motor current limit values (Idr,Iqr that are calculated by the motor current limit value calculating section 13 limit the peak values of the three-phase AC current. Therefore, the motor current limit section 14 limits the peak values of the u-phase command current Iu* and the v-phase- command current Iv* to be equal to or less than a motor current limit value, and outputs those currents as a u-phase controlled current Iur* and a v-phase controlled current Ivr*.
The subtracter 18 outputs a difference between the u-phase controlled current lur* and the u-phase driving current Iu, and a difference between the v-phase controlled current Ivr* and the v-phase driving current Iv, and the current control section 10 conducts the feedback control on the basis of the output of the subtracter 18. The output of the current control section 10 is inputted to the PWM inverter 3 in response to a demand of the w-phase current from the adder 19- The motor 1 is driven by the output of the PWM inverter 3.
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In the motor control device according to the second embodiment of the present invention, since the motor current command values (la*, Iv*) can be limited on the three-phase AC coordinates according to the motor rotation speed CJ, the motor 1 can be appropriately protected from being overheated.
In the above second embodiment, the motor rotation speed o is estimated from the motor terminal voltages Vu, Vv, Vw, and the motor driving currents Iu, Iv, Iw on the three-phase AC coordinates. Alternatively, the motor rotation speed may be estimated from the motor terminal voltages Vd, Vq, and the motor driving currents Iu, Iv, Iw on the dq coordinates.
In the case where the motor terminal voltages Vu, Vv, Vw, and themotor driving currents la, Iv, Iwonthethree-phaseAC coordinates are converted into dq coordinates on the orthogonal coordinate system, the model of the three-phase permanent magnet synchronous motor can be generally described as indicated in the following expression (10) .
=

In the above expression, Of is an interlinkage magnetic flux on the dq coordinates.
In this example, when Id = 0, the q-axis terminal voltage can be represented by the following expression (11),
Vq = (R + pL)Iq + WƠf ..-(11)
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In this case, R, L, and of are determined according to the motor characteristics, and Vq and Iq can be calculated according to the dq coordinate conversion. Accordingly, the motor rotation speed u can be obtained.
Also, in the case where the motor control device according to the above second embodiment is used in an electric power steering device, the motor rotation speed may be estimated by a sensor that detects a handle angle or a steering angle sensor for detecting a steering angle of a steering wheel, instead.
Third Embodiment
In the above first and second embodiments, the motor current lirmiti values (Idr, Iqr) are calculated according to the d-axis driving current Id and the q-axis driving current Iq- Alternatively, the motor current limit values (Idr, Iqr) may be calculated on the basis of deviations between threshold values for overheat protection determination, and the d-axis driving current Id and the q-axis driving current Iq, respectively,
FIG, 10 is a block diagram showing a motor control device according to a third embodiment of the present invention, together with peripheral devices.
Referring to FIG- 10, a microcontroller 6C is given a threshold value for the overheat projection determination which is arbitrarily set. Also, the microcontroller 6C has subtracters 20d and 20q (hereinafter, collectively referred to as substracter 20”) which
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output differences between the d-axis driving current Id and the q-axis driving current Iq, and the threshold values for the overheat protection determinations, respectively.
Other structures are the same as those in the first embodiment, and their description will be omitted. Also, a program that is installed in the microcontroller 6C is identical with that shown in the first embodiment, and its description will be omitted.
Hereinafter, the operation of the motor control device with the above structure will be described. The same operation as that in the first embodiment will be omitted.
The subtracter 20 compares the d--axis driving current Id and the q-axis driving current Iq which are outputted from the dq to three-phase coordinates converting section 15 with the overheat protection determination threshold values, respectively, to obtain the deviations. The maximum values of the respective deviations are outputted as the motor current limit value change speeds, for examplef according to the same characteristics as those in FIG. 4- In this situation, in the axis of abscissa shown in FIG- 4, the synthetic driving current is replaced with the deviation. Subsequently, the motor current limit value change speeds are integrated to calculate the motor current limit values (Idr, Iqr) .
In the motor control device according to the third embodiment of the present invention, the motor current limit values (Idr, Iqr) are calculated on the basis of the deviations between the overheat
25

protection determination threshold values, and the d-axis driving current Id and the q-axis driving current Iq. As a result, the motor current command values (Id*, Iq*} can be restricted early when the motor driving current is large and lately when the motor driving current is small, thereby making it possible to execute the more practicable overheat protection.
When, for example, the current value (hereinafter referred to as “continuous rated current”) which is capable of continuously driving the motor 1 is set as the above overheat protection determination threshold value, a large current is supplied according to a short time rating of the motor 1 or the PWM inverter 3 for a short period of time, and the motor current can be smoothly converged into the continuous rated current according to the running status.
Also, in the above third embodiment, the maximum currents are gradually decreased or gradually increased on the basis of the deviations between the coordinate converted current, that is, the synthetic driving current Is and the given overheat protection determination threshold value. Alternatively, the maximum current may be gradually decreased or gradually increased on the basis of the integrated value of the deviations between the power functions of the coordinated converted current and the given overheat protection determination threshold value.
Because the loss of the motor 1 or the PWM inverter 3 is substantially in proportion to the first to second power of the
26

motor driving current, the above method is capable of conducting the overheat protection more appropriately.
Also, the same effects can be obtained even in the case where the maximum current is gradually decreased or gradually increased on the basis of the power function of the deviation between the synthetic driving current Is and the given overheat protection determination threshold value as described in the above first embodiment
27,

WHAT IS CLAIMED IS:
1. A motor control device, comprising:
an inverter unit for driving a polyphase motor;
position detecting means for detecting a magnetic pole posit ion of a rotor of the polyphase motors-
driving current detecting means for detecting a motor driving current inputted to the polyphase motor from the inverter unit;
current command value calculating means for generating a motor current command value of the polyphase motor; and
motor control means for controlling the inverter unit according to the motor current command value,
wherein the motor control means calculates a motor current
limit value that limits the motor current command value on the basis of the rotation speed of the polyphase motor calculated from the magnetic pole position and the motor driving current.
2. A motor control device, comprising:
an inverter unit for driving a polyphase motor;
terminal voltage detecting means for detecting a terminal voltage applied to the polyphase motor from the inverter unit;
driving current detecting means for detecting a motor driving current inputted to the polyphase motor from the inverter unit;
current command vaiue calculating means for generating a motor current command value of the polyphase motor; and
28

motor control means for controlling the inverter unit according to the motor current command value,
wherein the motor control means calculates a motor current limit value that limits the motor current command value on the basis of the rotation speed of the polyphase motor calculated from the terminal voltage and the motor driving current, and the motor driving current.
3. A motor control device, comprising:
an inverter unit for driving a polyphase motor;
position detecting means for detecting a magnetic pole position of a rotor of the polyphase motor;
current command value calculating means for generating a motor current command value of the polyphase motor; and
motor control means for controlling the inverter unit according to the motor current command value,
wherein the motor control means calculates a motor current limit value that limits the motor current command value on the basis of the rotation speed of the polyphase motor calculated from the magnetic pole position and the motor current command value.
4. A motor control device, comprising:
an inverter unit for driving a polyphase motor;
terminal voltage detecting means for detecting a terminal
29

voltage applied to the polyphase motor from the inverter unit;
driving current detecting means for detecting a motor driving current inputted to the polyphase motor from the inverter unit;
current command value calculating means for generating a motor current command value of the polyphase motor; and
motor control means for controlling the inverter unit according to the motor current command value,
wherein the motor control means calculates a :motor current limit value that limits the motor current command value on the basis of the rotation speed of the polyphase motor calculated from the terminal voltage and the motor driving current, and the motor current command value.
5- A motor control device according to any one of claims 1 to 4, wherein the motor control means calculates the motor current limit value according to an integrated value of a given function of one of the motor driving current and the motor current command value.
6, A motor control device according to any one of claims 1 to 4, wherein the motor control means determines the presence or absence of the rotations of the polyphase motor from the rotation speed to calculate the motor current limit value,
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7. A motor control device according to claim 5, wherein the motor control means obtains the integrated value after a coefficient equal to or less than 1 according to the rotation speed is multiplied by a value obtained by the given function.
8. A motor control device according to claim 5, wherein the given function is a power function.
9. A motor control device according to any one of claims 1 to 4, wherein the motor control means converts one of the motor driving current and the motor current command value into a d-axis (magnetic flax axis) component current and a q-axis (torque axis) component current orthogonal to the d-axis component current to calculate the motor current limit value.
10. A motor control device according to claim 9/ wherein the motor control means calculates the motor current limit value according to any one of the d-axis component current and the q-axis component current -
11. A motor control device according to claim 9, wherein the motor control means calculates the motor current limit value according to a synthetic current obtained by synthesizing the d-axis component current and the q-axis component current.
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12. A motor control device according to claim 9, wherein the motor control means calculates the motor current limit value according to a current larger in supply amount of the d-axis component current and the q-axis component current.
13. A motor control device according to claim 9, wherein the motor control means calculates the motor current limit value according to a deviation among a threshold value for the overheat protection determination, and the d-axis component current and the q-axis component current.
14. A motor control device according to any one of claims 1 to 4, wherein the motor control means converts the motor current command value into a d-axis command current and a q-axis command current orthogonal to the d-axis command current, and limits at ] east one of the d-axis command current and the q-axis command current on the basis of the motor current limit value.
15. A motor control device according to claim 14, wherein the motor control means maintains an angle defined by the q-axis command current, and a synthetic command current resulting from synthesizing the d-axis command current and the q-axis command current.
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16. A motor control device according to any one of claims 1 to 4, wherein the motor control means converts the motor current command value into a d-axis command current and a q-axis command current orthogonal to the d-axis command current, and limits a synthetic command current resulting from synthesizing the d-axis command current and the q-axis command current on the basis of the motor current limit value,
17. A motor control device according to claim 16, wherein the motor control means controls the synthetic command current on the basis of the motor current limit value so that any one of the d-axis command current and the q-axis command current is given priority.
18. A motor control device according to any one of claims 1 to 4, wherein the motor control means limits a peak value of the phase current of the motor current command value on the basis of the motor current limit value.

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Documents:

0437-che-2006 abstract duplicate.pdf

0437-che-2006 claims duplicate.pdf

0437-che-2006 description (complete) duplicate.pdf

0437-che-2006 drawings duplicate.pdf

437-CHE-2006 CORRESPONDENCE OTHERS.pdf

437-CHE-2006 CORRESPONDENCE PO.pdf

437-CHE-2006 FORM 18.pdf

437-che-2006-correspondnece-others.pdf

437-che-2006-description(complete).pdf

437-che-2006-drawings.pdf

437-che-2006-form 1.pdf

437-che-2006-form 26.pdf

437-che-2006-form 3.pdf

437-che-2006-form 5.pdf

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Patent Number

230461

Indian Patent Application Number

437/CHE/2006

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

26-Feb-2009

Date of Filing

10-Mar-2006

Name of Patentee

MITSUBISHI DENKI KABUSHIKI KAISHA

Applicant Address

2-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310,

Inventors:

#	Inventor's Name	Inventor's Address
1	FUJIMOTO, CHIAKI	C/O MITSUBISHI DENKI KABUSHIKI KAISAI, 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310,

PCT International Classification Number

H02P 5/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2005-069044	2005-03-11	Japan