Title of Invention

A DEVICE FOR SYNCHRONOUS RECTIFICATION OF THE OUTPUT OF AN AUTOMOBILE ALTERNATOR

Abstract

A device for the synchronous rectification of the output ofan automobile alternator comprising a set of comparators for sensing the line voltages of the alternator and detecting the zero crossings in the line voltages ofthe alternator; a digital programmable device (dpd), the output voltages ofthe said set of comparators being the inputs to the said dpd; a set of MOSFEfS connected in three phase bridge fashion and driver circuits for driving the said MOSFETS. the output points ofthe dpd being connected to the said driver circuits, the said dpd being programmed to (i) determine alternator speed from the sensed line voltages (ii) determine the duration over which the MOSFETS are to be turned ON based on the determined speed value and predetermined time durations for different speeds, the said speed and duration of MOSFET turn ON being updated periodically or continuously (iii) to turn the MOSFETS ON when transitions from high to low or low to high occur in the input to the dpd and (iv) turn the MOSFETS OFF after the predetermined time has elapsed fi'om the instant of their turn ON.

Full Text

This invention relates to a device for synchro¬nous rectification of the output of an automobile alternator. By synchronous rectification is meant that the device proposed herein enables MOSFETS to be switched ON and OFF at a frequency equal to that of the generated AC output of the said alternator which is required for supplying power to the automobile electrical load and also for charging the battery. While MOSFETS have been used for AC to DC conver¬sion, there are several means adopted for the purpose and known to the art; however, these means suffer from the following disadvantages: Current transducers are required for identi¬fying the instant of turning ON the MOSFET switch; and the presence of current sensors adds to the system cost (ii) The duration for keeping the MOSFET switches ON in the individual phases could be different in different phases on account of the controller configuration. Such operation will lead to imbalance in the operation of the alternator leading to 3 large current ripple in the DC output cur¬rent . (iii> Presence of analog electronics in the con¬troller is a disadvantage from the standpoint of the system integration for mass production through large scale integrated circuits dedicated for this application- (a) On the other hand, the device proposed herein switches the MOSFETS at the same frequency as that of the generated voltages in the alternator. The use of currents sensors is eliminated. (b) The ON time of all the MOSFETs used for rectification is decided by a single timing de¬vice, to avoid unbalanced operation of the alter¬nator. the rectifier output side is obviated, so that the invention may be used in systems with differ¬ ent battery voltages. (d) The device proposed herein provides means for control with digital implementation suitable for large scale manufacture. (e) The device proposed herein provides improved speeds close to performance of the alternator at low/idling , (f) In the device proposed herein, the duration of turn ON of the MOSFETs is decided on the basis of the speed at which the alternator rotor ro¬ tates, such duration including zero, that is, fully OFF. Various other features of this invention will be apparent from the further description thereof given hereunder. The device, according to this invention, for synchronous rectification of the output of an automobile alternator, comprises a set of compara¬tors for sensing the line voltages of the alterna¬tor and detecting the zero crossings in the line voltages of the alternator; a digital programmable device (dpd>, the output voltages of the said set of comparators being the inputs to the said dpd; a set of MOBFETS connected in three phase bridge fashion and driver circuits for driving the said MOSFETS, the output points of the dpd being con¬nected to the said driver circuits, the said dpd being programmed to turn the Mosfets OFF after the predetermined time has elapsed from the instant of their turn ON. This invention will now be described with refer¬ence to the accompanying drawings which illustrate in Fig.l the wave form of the alternator current using the known diode rectifier Fig.2 the wave form of the alternator current using the device proposed herein, highlighting the absence of the zero interval in the phase current waveform, which is present in the waveform in Fig.l Figs. 3 and 4 the bridge connection and a schemat¬ic of the controller. The sensed inputs to the controller are the line voltages of the alternator. A set of three com¬parators derives the zero crossings of the line voltages from the sensed input voltages. The voltage pulses at the output of the comparators form the inputs to a digital programmable device. The outputs from the digital programmable device are signals that enable/disable the MOSFETs. The process by which the enabling signals to the MOSFETs are derived from the inputs to the digital programmable device is described below. The term digital programmable device includes but is not restricted to a microprocessor. The digital programmable device detects the low to high or high to low transitions in the outputs of the zero crossing detectors (ZCDs). The time interval between two such transitions is used to serve as an indicator of alternator speed. This is monitored periodically by the digital programmable device, say once in every cycle corresponding to the generated current of the alternator. Depending on the determined speed value the digi— tal programmable device selects the time duration for which the MOSFETs shall be turned ON. These durations are predetermined and stored in the digital programmable device. If the duration so determined is zero, the MOSFETs are not turned ON. A low to high or high to low transition in the voltage pulses indicates that the MOSFET in the corresponding phase is to be turned ON. For exam¬ple, a high to low transition in ZCD corresponding to line voltage RY (out of R—Y—B), indicates that the MOSFET MOSl in the bridge connection of Fig.l is to be turned ON. When there is a low to high transition in the ZCD corresponding to line voltage RY, the MOSFET M0S4 in the bridge connect¬ing to Fig.l is to be turned ON. Once a MOSFET is turned ON, further transitions in the correspond¬ing ZCD are ignored until after the MOSFET has been turned OFF. The MOSFETS are turned OFF after the predetermined time for the particular speed has elapsed from the time of their turn ON. The outputs of the digital programmable device;are C connected to circuitry/capable of driving the MOSFETs. In another embodiment of the present invention,the digital programmable device monitors the speed of the alternator by considering the time duration between every successive transition. This speed information is used to update the duration for which the MOSFETs are to (at turned ON. In yet another embodiment of the present inven¬tion ,whenever there is a change in the time dura¬tion for which the MOSFETs are to turned ON, the said change is carried out in a gradual manner to avoid rapid transients in the generated output from the alternator. The terms and expressions in this specification are of description and not of limitation, there being no intention of excluding any equivalents of the features illustrated and described, but it is understood that various other embodiments of the device proposed herein are possible without de¬parting from the scope and ambit of this inven¬tion . We Claim: 1. A device for synchronous rectification of the output of an automobile alternator comprising a set of comparators for sensing the line voltages of the alternator and detecting the zero crossings in the line voltages of the alternator; a digital programmable device (dpd), the output voltages of the said set of comparators being the inputs to the said dpd; a set of MOSFETS connected in three phase bridge fashion and driver circuits for driving the said MOSFETS, the output points of the dpd being connected to the said driver circuits, the said dpd being programmed to (i) determine alternator speed from the sensed line voltages (ii) determine the duration over which the MOSFETS are to be turned ON based on the determined speed value and predetermined time durations for differ¬ent speeds, the said speed and duration of MOSFET turn ON being updated periodically or continuous¬ly (iii> to turn the MOSFETS ON when transitions from high to low or low to high occur in the inputs to the dpd and (iv) turn the Mosfets OFF after the predetermined time has elapsed from the instant of their turn ON. 2. A device for synchronous rectification of the output of an automobile alternator substantially as herein described with reference to, and as illustrated in. Fig. 2 to 4- of the accompanying drawings. This invention relates to a device for synchro¬nous rectification of the output of an automobile alternator. By synchronous rectification is meant that the device proposed herein enables MOSFETS to be switched ON and OFF at a frequency equal to that of the generated AC output of the said alternator which is required for supplying power to the automobile electrical load and also for charging the battery. While MOSFETS have been used for AC to DC conver¬sion, there are several means adopted for the purpose and known to the art; however, these means suffer from the following disadvantages: Current transducers are required for identi¬fying the instant of turning ON the MOSFET switch; and the presence of current sensors adds to the system cost (ii) The duration for keeping the MOSFET switches ON in the individual phases could be different in different phases on account of the controller configuration. Such operation will lead to imbalance in the operation of the alternator leading to 3 large current ripple in the DC output cur¬rent . (iii> Presence of analog electronics in the con¬troller is a disadvantage from the standpoint of the system integration for mass production through large scale integrated circuits dedicated for this application- (a) On the other hand, the device proposed herein switches the MOSFETS at the same frequency as that of the generated voltages in the alternator. The use of currents sensors is eliminated. (b) The ON time of all the MOSFETs used for rectification is decided by a single timing de¬vice, to avoid unbalanced operation of the alter¬nator. the rectifier output side is obviated, so that the invention may be used in systems with differ¬ ent battery voltages. (d) The device proposed herein provides means for control with digital implementation suitable for large scale manufacture. (e) The device proposed herein provides improved speeds close to performance of the alternator at low/idling , (f) In the device proposed herein, the duration of turn ON of the MOSFETs is decided on the basis of the speed at which the alternator rotor ro¬ tates, such duration including zero, that is, fully OFF. Various other features of this invention will be apparent from the further description thereof given hereunder. The device, according to this invention, for synchronous rectification of the output of an automobile alternator, comprises a set of compara¬tors for sensing the line voltages of the alterna¬tor and detecting the zero crossings in the line voltages of the alternator; a digital programmable device (dpd>, the output voltages of the said set of comparators being the inputs to the said dpd; a set of MOBFETS connected in three phase bridge fashion and driver circuits for driving the said MOSFETS, the output points of the dpd being con¬nected to the said driver circuits, the said dpd being programmed to turn the Mosfets OFF after the predetermined time has elapsed from the instant of their turn ON. This invention will now be described with refer¬ence to the accompanying drawings which illustrate in Fig.l the wave form of the alternator current using the known diode rectifier Fig.2 the wave form of the alternator current using the device proposed herein, highlighting the absence of the zero interval in the phase current waveform, which is present in the waveform in Fig.l Figs. 3 and 4 the bridge connection and a schemat¬ic of the controller. The sensed inputs to the controller are the line voltages of the alternator. A set of three com¬parators derives the zero crossings of the line voltages from the sensed input voltages. The voltage pulses at the output of the comparators form the inputs to a digital programmable device. The outputs from the digital programmable device are signals that enable/disable the MOSFETs. The process by which the enabling signals to the MOSFETs are derived from the inputs to the digital programmable device is described below. The term digital programmable device includes but is not restricted to a microprocessor. The digital programmable device detects the low to high or high to low transitions in the outputs of the zero crossing detectors (ZCDs). The time interval between two such transitions is used to serve as an indicator of alternator speed. This is monitored periodically by the digital programmable device, say once in every cycle corresponding to the generated current of the alternator. Depending on the determined speed value the digi— tal programmable device selects the time duration for which the MOSFETs shall be turned ON. These durations are predetermined and stored in the digital programmable device. If the duration so determined is zero, the MOSFETs are not turned ON. A low to high or high to low transition in the voltage pulses indicates that the MOSFET in the corresponding phase is to be turned ON. For exam¬ple, a high to low transition in ZCD corresponding to line voltage RY (out of R—Y—B), indicates that the MOSFET MOSl in the bridge connection of Fig.l is to be turned ON. When there is a low to high transition in the ZCD corresponding to line voltage RY, the MOSFET M0S4 in the bridge connect¬ing to Fig.l is to be turned ON. Once a MOSFET is turned ON, further transitions in the correspond¬ing ZCD are ignored until after the MOSFET has been turned OFF. The MOSFETS are turned OFF after the predetermined time for the particular speed has elapsed from the time of their turn ON. The outputs of the digital programmable device;are C connected to circuitry/capable of driving the MOSFETs. In another embodiment of the present invention,the digital programmable device monitors the speed of the alternator by considering the time duration between every successive transition. This speed information is used to update the duration for which the MOSFETs are to (at turned ON. In yet another embodiment of the present inven¬tion ,whenever there is a change in the time dura¬tion for which the MOSFETs are to turned ON, the said change is carried out in a gradual manner to avoid rapid transients in the generated output from the alternator. The terms and expressions in this specification are of description and not of limitation, there being no intention of excluding any equivalents of the features illustrated and described, but it is understood that various other embodiments of the device proposed herein are possible without de¬parting from the scope and ambit of this inven¬tion . We Claim: 1. A device for synchronous rectification of the output of an automobile alternator comprising a set of comparators for sensing the line voltages of the alternator and detecting the zero crossings in the line voltages of the alternator; a digital programmable device (dpd), the output voltages of the said set of comparators being the inputs to the said dpd; a set of MOSFETS connected in three phase bridge fashion and driver circuits for driving the said MOSFETS, the output points of the dpd being connected to the said driver circuits, the said dpd being programmed to (i) determine alternator speed from the sensed line voltages (ii) determine the duration over which the MOSFETS are to be turned ON based on the determined speed value and predetermined time durations for differ¬ent speeds, the said speed and duration of MOSFET turn ON being updated periodically or continuous¬ly (iii> to turn the MOSFETS ON when transitions from high to low or low to high occur in the inputs to the dpd and (iv) turn the Mosfets OFF after the predetermined time has elapsed from the instant of their turn ON. 2. A device for synchronous rectification of the output of an automobile alternator substantially as herein described with reference to, and as illustrated in. Fig. 2 to 4- of the accompanying drawings.

Documents:

1030-mas-1999 abstract.pdf

1030-mas-1999 claims-duplicate.pdf

1030-mas-1999 claims.pdf

1030-mas-1999 correspondences-others.pdf

1030-mas-1999 correspondences-po.pdf

1030-mas-1999 drawings-duplicate.pdf

1030-mas-1999 drawings.pdf

1030-mas-1999 form-1.pdf

1030-mas-1999 form-19.pdf

1030-mas-1999 form-26.pdf

1030-mas-1999 description (complete)-duplicate.pdf

1030-mas-1999 description (complete).pdf