Title of Invention	METHOD FOR OPERATION OF A CONVERTER CIRCUIT, AS WELL AS AN APPARATUS FOR CARRYING OUT THE METHOD
Abstract	A method for operation of a converter circuit is specified, wherein the converter circuit has a converter unit (1) with a multiplicity of drivable power semiconductor switches and an LCL filter (3) which is connected to each phase connection (2) of the converter unit (1) , in which method the drivable power semiconductor switches are driven by means of a drive signal (S) which is formed from reference voltages (ui, u2, u3) . The reference voltages (ui, u2, u3) are formed by subtraction of damping voltages (udi, ud2, ud3) from reference-phase connection voltages (un, ui2, u*i3) , with the damping voltages (udi, usd2, ud3) being formed from filter capacitance currents (icfi/ icf2r icf3) / weighted with a variable damping factor (Kf) of the LCL filter (3) . An apparatus for carrying out the method is also specified. Fig. 1

Title of Invention

METHOD FOR OPERATION OF A CONVERTER CIRCUIT, AS WELL AS AN APPARATUS FOR CARRYING OUT THE METHOD

Abstract

A method for operation of a converter circuit is specified, wherein the converter circuit has a converter unit (1) with a multiplicity of drivable power semiconductor switches and an LCL filter (3) which is connected to each phase connection (2) of the converter unit (1) , in which method the drivable power semiconductor switches are driven by means of a drive signal (S) which is formed from reference voltages (u*i, u*2, u*3) . The reference voltages (u*i, u*2, u*3) are formed by subtraction of damping voltages (udi, ud2, ud3) from reference-phase connection voltages (u*n, u*i2, u*i3) , with the damping voltages (udi, usd2, ud3) being formed from filter capacitance currents (icfi/ icf2r icf3) / weighted with a variable damping factor (Kf) of the LCL filter (3) . An apparatus for carrying out the method is also specified. Fig. 1

Full Text	Method for operation of a converter circuit, as well as an apparatus for carrying out the method DESCRIPTION Technical field The invention relates to the field of power electronics, and is based on a method for operation of a converter circuit, as well as an apparatus for carrying out the method, as claimed in the preamble of the independent claims. Prior art Conventional converter circuits have a converter unit with a multiplicity of drivable power semiconductor switches, which are connected in a known manner in order to switch at least two switching voltage levels. An LCL filter is connected to each phase connection of the converter unit. A capacitive energy store is also connected to the converter unit, and is normally formed by one or more capacitors. An apparatus is provided for operation of the converter circuit, which apparatus has a regulation device for production of reference voltages and is connected via a drive circuit for formation of a drive signal from the reference voltages to the drivable power semiconductor switches. The power semiconductor switches are thus driven by means of the drive signal. The converter circuit mentioned above is subject to the problem but the LCL filters can cause permanent distortion, that is to say undesirable oscillations, in the filter output currents and filter voltages, resulting from resonant oscillations of the LCL filters. In an electrical ac voltage supply system, which is typically connected to the filter outputs, or in an electrical load which, is connected to the filter outputs, such distortion can lead to damage or even destruction, and is therefore very undesirable. Description of the invention One object of the invention is therefore to specify a method for operation of a converter circuit, by means of which it is possible to actively damp distortion, caused by LCL filters connected to the converter circuit, in the filter output currents and filter output voltages. A further object of the invention is to specify an apparatus by means of which the method can be carried out in a particularly simple manner. These objects are achieved by the features of claim 1 and claim 7, respectively. Advantageous developments of the invention are specified in the dependent claims. The converter circuit has a converter,'-, unit with a multiplicity of drivable power semiconductor switches, and an LCL filter which is connected to each phase connection of the converter unit. In the method according to the invention for operation of the converter circuit, the drivable power semiconductor switches are now driven by means of a drive signal which is formed from reference voltages. According to the invention, the reference voltages are formed from the subtraction of damping voltages from reference-phase connection voltages, with the damping voltages being formed from filter capacitance currents (which are weighted with a variable damping factor) of the LCL filters. The damping voltages are thus proportional to the filter capacitance currents and are then subtracted from the reference-phase connection voltages, which is equivalent to connection of a damping resistance to each phase connection of the converter unit. Distortion, that is to say undesirable oscillations, in the filter, output currents and filter output voltages can therefore advantageously be actively damped, so that this type of distortion is greatly reduced and, in the ideal case, is very largely suppressed, A further advantage of the method according to the invention is that there is no need to connect any discrete, highly space-consuming damping resistor, which is complex to provide and is therefore expensive, to each phase connection in order to allow the undesirable distortion to be effectively damped. The apparatus according to the invention for carrying out the method for operation of the converter circuit has a regulation device which is used to produce reference voltages and is connected via a drive circuit for formation of a drive signal to the drivable power semiconductor switches. According to the invention, the regulation device has a first calculating unit for formation of reference voltages from the subtraction of damping voltages from reference-phase connection voltages, with the first calculation unit being supplied with reference-phase connection voltages and, in order to form the damper voltages, filter capacitance currents of the LCL filters. Furthermore, the regulation device has a regulator unit for production of the reference-phase connection voltages. The apparatus according to the invention for carrying out the method for operation of the converter circuit can thus be implemented very easily and cost-effectively, since the circuit complexity can be kept extremely low and, furthermore, only a small number of components are required to construct it. The method according to the invention can thus be carried out particularly easily by means of this apparatus. These and further objects, advantages and features of the invention will become evident from the following detailed description of preferred embodiments of the invention, in conjunction with the drawing. Brief description of the drawings In the figures: Figure 1 shows one embodiment of an apparatus according to the invention for carrying out the method according to the invention for operation of a converter circuit, Figure 2 shows one embodiment of a second calculation unit, Figure 3 shows a waveform of the filter output currents with active damping using the method according to the invention, and Figure 4 shows a waveform of the filter output currents with active damping and additional active reduction of harmonics using the method according to the invention. The reference symbols used in the drawing, and their meanings, are listed in a summarized form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures. The described embodiments represent examples of the subject matter of the invention, and have no restrictive effect. Approaches to implementation off the invention Figure 1 shows one embodiment of an apparatus according to the invention for carrying out the method according to the invention for operation of a converter circuit. As shown in Figure 1, the converter circuit has a converter unit 1 with a multiplicity of drivable power semiconductor switches and an LCL filter 3, which is connected to each phase connection 2 of the converter unit 1, Each LCL filter 3 accordingly has a first filter inductance Lfi, a second filter inductance Lfg as well as a filter capacitance Cf, with the first filter inductance Lfi being connected to the associated phase connection 2 of the converter unit 1, to the second filter inductance Lfg and to the filter capacitance Cf. Furthermore, the filter capacitances Cf of the individual LCL filters 3 are connected to one another. Each LCL filter 3 typically has a virtually negligible filter resistance Rf, which is connected in series with the filter capacitance Cf of the associated LCL filter 3 and represents resistive losses in the LCL filter 3. By way of example, the converter unit 1 shown in Figure 1 is a three-phase unit. It should be mentioned that the converter unit 1 may in general be any form of converter unit 1 for switching of > 2 switching voltage levels (multi-level converter circuit) with respect to the voltage of a capacitive energy store 9 which is connected to the converter unit 1, with the capacitive energy store 9 then being formed by any desired number of capacitances, which are then connected such that they are matched to the appropriately configured converter circuit element. In the method according to the invention for operation of the converter circuit, the drivable power semiconductor switches of the conversion unit 1 are now driven by means of a drive signal S which is formed from reference voltages ui, u2, u3. A look-up table is normally used to form the drive signal, in which appropriate drive signals are permanently associated with reference voltage values, or a modulator which is based on pulse-width modulation. According to the invention, the reference voltages ui, u2, u3 are formed from subtraction of damping voltages udi, ud2, ud3 from reference-phase connection voltages uiif ui2, ui3, with the damping voltages udi, ud2/ ud3 being formed from filter capacitance currents icfi, icf2/ icf3/ which are weighted with a variable damping factor Kf, of the LCL filters 3, as illustrated in particular by the following formula. Ud = Kf iCf * The damping voltages udi, ud2/ ud3 are thus proportional to the filter capacitance currents icfi/ i-ctzr icf3 and are then subtracted from the reference-phase connection voltages u11, ui2, ui3, which corresponds to the connection of a damping resistor to each phase connection 2 of the converter unit 1. This advantageously allows active damping of distortion, that is to say undesirable oscillations, in the filter output currents ifgi, ifg2/ ifg3 and filter output voltages ugi, ug2, ug3, so that this distortion is greatly reduced and, in the ideal case is very largely suppressed. Furthermore, there is no need for connection of discrete, very space-consuming damping resistors, which are complex to implement and are therefore expensive to the respective phase connection in order to allow effective damping of the undesirable distortion. The damping factor Kf is preferably set such that the undesirable oscillations of the filter output voltages ugi, ug2, ug3 or of phase-connection voltages, in particular harmonics, are just not amplified. As shown in Figure 1, the apparatus according to the invention for carrying out the method according to the invention for operation of a converter circuit for this purpose has a regulation device 4, which is used to produce the reference voltages ui, u2, u3 and is connected via a drive circuit 5 for formation of the drive signal S to the drivable power semiconductor switches. By way of example, the drive circuit 5 has a look-up table in which appropriate drive signals are permanently associated with reference-voltage values, or a modulator which is based on pulse-width modulation. According to the invention, the regulation device 4 has a first calculation unit 6 for formation of reference voltages ui, u2/ u3 from the subtraction of damping voltages udi, ud2, ud3 from reference-phase connection voltages uu, ui2, ui3, with the first calculation unit 6 being supplied with reference-phase connection voltages uu, ui2, ui3 and, in order to form the damper voltages udi, ud2, ud3, filter capacitance currents icfi, ict2f icf3 °f the LCL filters 3. As shown in Figure 1, the filter capacitance currents icfi, icf2r icf3 are measured by appropriate measurement devices. Furthermore, the regulation device 4 has a regulation unit 7 for production of the reference-phase connection voltages uii, ui2, ui3. The apparatus according to the invention for carrying out the method for operation of the converter circuit can accordingly be produced very easily and cost-effectively, since the circuit complexity can be kept extremely low and, furthermore, only a small number of components are required to construct it. This apparatus allows the method according to the invention . to be carried out particularly easily. It has been found to be advantageous for the filter capacitance currents icfir icf2/ icf3 to be filtered by means of a high-pass filter. This means that the damping voltages udi, ud2, ud3 are formed only from harmonics of the filter capacitance currents icfir icf2r iCf3, in particular higher-frequency harmonics of the filter capacitance currents icfir ict2/ icf3f and the variable damping factor Kf, so that the active damping according to the invention advantageously acts only on the harmonics in the filter output currents ifgi, ifg2r ifg3 and filter output voltages ugi, ug2, ug3. High-pass filtering of the filter capacitance currents icfir icf2, icf3 is carried out by a high-pass filter which is connected between the measurement devices for measurement of the filter capacitance currents icfir icf2/ icf3 and the first calculation unit 6, with the high-pass filter not being shown in Figure 1, for clarity reasons. The reference-phase connection voltages un, ui2, ui3 are formed from a d-component of the Park-Clarke transformation (produced by regulation of the dc voltage udc of a capacitive energy store 9 which is connected to the converter unit 1 at a dc voltage reference value udc of reference-phase connection currents ifid and from a predeterminable q-component of the Park-Clarke transformation of the reference-phase connection currents ifiq. The regulation is preferably carried out using a proportional-integral characteristic. As shown in figure 1, the regulator unit 7 for regulation of the dc voltage udc of the capacitive energy store 9 at the dc voltage reference value udc has a first proportional-integral regulator 8, to whose input the difference between the dc voltage (udc) of the capacitive energy store 9 and the dc voltage reference value udc is supplied, and at whose output the d-component of the Park-Clarke transformation of the reference-phase connection currents ifid is produced. The Park-Clarke transformation is in general defined as: x = (xd + jxq)ejcc)t using the variables illustrated in Figure 1: where x is a complex variable, xd is the d-component of the Park-Clarke transformation of the variable x and xq is the q-component of the Park-Clarke transformation of the variable x All of the Park-Clarke transformations of variables which have already been mentioned and those which will be mentioned in the following text are produced using the formula quoted above. The Park-Clarke transformation advantageously transforms not only the fundamental of the complex variable x , but also all of the harmonics that occur of the complex variable x . The regulation device 4 shown in Figure 1 has a third calculation unit 16 for formation of the d-component of the Park-Clarke transformation of the filter output voltages ugd, of the q-component of the Park-Clarke transformation of the filter output voltages ugq and of the fundamental angle cot of the filter output voltages ugi, ug2, ug3, with the input side of the third calculation unit 16 being supplied with the filter output voltages ugi, ug2, ug3 of the LCL filters 3. The third calculation unit 16 is preferably a phase locked loop, in which case the Park-Clarke transformations of the individual variables are carried out using the definitions given above. Furthermore, the d-component of the Park-Clarke transformation of the reference-filter output voltages ugd is produced by regulation of the d-component of the Park-Clarke transformation of the phase connection current ifid at the sum of the d-component of the Park-Clarke transformation of the reference-phase connection currents ifid and a d-component of the Park-Clarke transformation of at least one harmonic of filter output currents ifghd with respect to the fundamental of the filter output currents ifgi, ifg2r ifg3- The regulation is preferably carried out using a proportional-integral characteristic. Furthermore, the q-component of the Park-Clarke transformation of the. reference filter output voltages ugq is produced by-regulation of the q-component of the Park-Clarke transformation of the phase connection currents ifiq at ■ the sum of the q-component of the Park-Clarke transformation of the reference-phase connection currents ifiq and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents if9hq with respect to the fundamental of the filter output currents ifgi, ifg2 ifg3* The regulation is preferably carried out using a proportional-integral characteristic. The index h of the d-component and the q-component of the Park-Clarke transformation of a harmonic of the filter output currents ifghd, ifghq represents the h-th harmonic of these variables, where h = 1, 2, 3, ... The additional . variables introduced in the following text with the index h likewise use the index h for the h-th harmonic of the associated variable, h = 1, 2, 3, ... As shown in Figure 1, the regulator unit 7 for regulation of the d-component of the Park-Clarke transformation of the phase connection currents if±d at the sum of the d-component of the Park-Clarke transformation of the reference phase connection currents ifid and a d-component of the Park-Clarke transformation of at least one harmonic of the filter output currents ifghd with respect to the fundamental of the filter output currents ifgi, ifg2f ifg3 has a second proportional- . integral regulator 10 to whose input side the difference between the sum of the d-component of the Park-Clarke transformation of the reference-phase -connection currents ifid and a d-component of the Park-Clarke transformation of at least one harmonic of the filter output currents ifghd with respect to the fundamental of the filter output currents ifgi, Xfg2r ifg3 and the d-component of the Park-Clarke transformation of the phase connection currents ifid are supplied, and on whose output side the d-component s of the Park-Clarke transformation of the reference-filter output voltages ugd is produced. Furthermore, for regulation of the q-component of the Park-Clark transformation of the phase connection currents ifiq at the sum of the q-component of the Park-Clarke transformation of the • reference phase connection currents ifiq and the q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents ifghq with respect to the fundamental of the filter output currents ifgi, ifg2 ifg3, the regulator unit 7 has a third proportional-integral regulator 11 to whose input side the difference between the sum of the q-component of the Park-Clarke transformation of the reference phase connection currents ifiq and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents ifghq with respect to the fundamental of the filter output currents ifgi, ifg2/ ifg3 • and the q-components of the Park-Clarke transformation of the phase connection currents ifiq are supplied, and on whose output side the q-component of the Park-Clarke transformation of the reference-filter output voltages ugq is produced. Furthermore, the d-component of the Park-Clarke transformation of the reference-phase connection voltages uid is produced by the sum of the d-component of the Park-Clarke transformation of the reference filter output voltages ugd and the d-component of the filter output voltages ugd and a d-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages ughd. In addition the q-component of the Park-Clarke transformation of the reference-phase connection voltages uiq is produced by the sum of the q-component of the Park-Clarke transformation of the reference-filter output voltages ugq and the q-component of the Park-Clarke transformation of the filter-output voltages ugq and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages ughq. In.order to produce the d-component of the Park-Clarke transformation of the reference-phase connection voltages uid, the regulator unit 7 has a first adder 12, to which the d-component of the Park-Clarke transformation of the reference filter output voltages ugd, the d-component of the filter output voltages ugd and the d-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages ughd are supplied. In addition, in order the produce the q-component of the Park-Clarke transformation of the reference phase connection voltages uiq/ the regulator unit 7 has, as shown in Figure 1, a second adder 13, to which the q-component of the Park-Clarke transformation of the reference-filter output voltages ugq, the q-component of the Park-Clarke transformation of the filter output voltages ugq and the q-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages ughq are supplied. In order to form the d-component of the Park-Clarke transformation, as has already been mentioned above, of at least one harmonic of the filter output currents ifghd with respect to the fundamental of the filter output currents ifgi, ifg2/ ifg3r the q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents ifghq with respect to the fundamental of the filter output currents ifgi, ifg2, ifg3f the d-component of the Park-Clarke transformation of the at least one harmonic of the reference filter . output voltages ughd anc the q-component of the Park-Clarke transformation of the at least one harmonic of the reference-filter output voltages ughq the regulation unit .4 has a second calculation unit 15, as shown in Figure 1. As shown in Figure 1, the input side of the second calculation unit 15 is supplied with the d-component with the filter output voltages ugd, the q-component of th.e filter output voltages ugq, the phase connection currents im, im, if±3f the filter capacitance currents iCfi, icf2f icf3 and the fundamental angle ot of the filter output voltages ugi, ug2, ug3. In order to illustrate the formation of the individual variables in the calculation unit 15, Figure 2 shows one embodiment of the second calculation unit 15, in which the input variables shown in Figure 2 are obtained using the following formula: ifghd + jifghq - ifihd + jifihq ~ (icfhd + j icfhq) with the d-components of the Park-Clarke transformation and the q-components of the Park-Clarke transformation being obtained by applications of the Park-Clarke transformation to the measured phase connection currents if a, ifi2, ifi3 including the associated harmonics, and filter capacitance currents ictif i-cf2, .iCf3 including the associated harmonics. This Park-Clarke" transformation is carried out in particular in the second calculation unit 15, although this is not illustrated in the second calculation unit 15 shown in Figure 2, for clarity reasons. Finally, the reference-phase connection voltages uii, ui2, ui3 are produced by an inverse Park-Clarke transformation of the d-component of the Park-Clarke transformation of the reference-phase connection voltages uid. and the q-component of the Park-Clarke transformation of the reference-phase connection voltages uiq. As shown in Figure 1, the regulator unit 7 for this purpose has a calculation unit 14 for formation of the reference-phase connection voltages uii, ui2, ui3 by inverse Park-Clarke transformation, to whose input side the d-component of the Park-Clarke transformation of the reference-phase connection voltages uid and the q-component of the Park-Clarke transformation of the reference-phase connection voltages uiq are supplied. In order to illustrate the method of operation of the active damping based on the method according to the invention as explained above, Figure 3 shows a waveform of the filter output currents ifgi, ifg2/ ifg3 in which undesirable oscillations in the filter output currents ifgi/ ifg2/ ifg3 are actively damped, so that this distortion is greatly reduced. A further improvement in the reduction of harmonics is shown in a waveform of the filter output currents ifgi, if92/ ifg3 in figure 4 with active damping, and additional active reduction of harmonics using the method according to the invention as described above. It should be mentioned that all of the steps of the method according to the invention may by implemented in the form of software, which can then be loaded and then run for example on a computer system, in particular with a digital signal processor. The digital delay times which occur in systems such as this, in particular for the calculations, may be in general be taken into account, for example, by addition of an additional term to the fundamental angle cot in the Park-Clarke transformation. Furthermore, the apparatus according to the invention, as described in detail above, can also be implemented in a computer system, in particular in the digital signal processor. Overall, it has been possible to show that the apparatus according to the'invention, in particular as shown in Figure 1, for carrying out the method according to the invention for operation of the converter circuit can be implemented very easily and cost-effectively, since the circuit complexity is extremely low and, furthermore, only a small number of components are required to construct it. This apparatus therefore makes it possible to carry out the method according to the invention particularly easily. List of reference symbols 1 Converter unit 2 Phase connection of the converter unit 3 LCL filter 4 Regulation device 5 Drive circuit 6 First calculation unit of the regulation device 7 Regulator unit 8 First proportional-integral regulator 9 Capacitive energy store 10 Second proportional-integral regulator 11 Third proportional-integral regulator 12 First adder 13 Second,adder 14 Calculation unit for the regulator unit 15 Second calculation unit of the regulation device 16 third calculation unit of the regulation device PATENT CLAIMS 1. A method for operation of a converter circuit, in which the converter circuit has a converter unit (1) with a multiplicity of drivable power semiconductor switches and an LCL filter (3) which is connected to each phase connection (2) of the converter unit (1), in which the drivable power semiconductor switches are driven by means of a drive signal (S) which is formed from reference voltages (ui, u2, u3) , characterized in that the reference voltages (ui, u2/ u3) are formed by subtraction of damping voltages (ud1, ud2, ud3) from reference-phase connection voltages (un, ui2, ui3) , with the damping voltages (udi, ud2, ud3) being formed from filter capacitance currents (icfif icf2r icf3) / weighted with a variable damping factor (Kf) of the LCL filter (3) and in that the filter capacitance currents (icfif icf2/ icf3) sre. filtered by means of a high-pass filter. 2. The method as claimed in claim 1, characterized in that the reference-phase connection voltages (un, ui2, ui3) are formed from a d-component of the Park-Clarke transformation (produced by regulation of a dc voltage (udc) of a capacitive energy store (9) which is connected to the converter unit (1) at a dc voltage reference value (udc) of reference-phase connection currents (ifid) and from a predeterminable q-component of the Park-Clarke transformation of the reference-phase connection currents (ifiq) . 3. The method as claimed in claim 2, characterized in that the d-component of the Park-Clarke transformation of reference-filter output voltages (ugd) is produced by regulation of the d-component of the Park Clarke transformation of the phase connection currents (if id) AMENDED SHEET at the sum of the d-component of the Park-Clarke transformation of the reference-phase connection currents (ifid) and a d-component of the Park-Clarke transformation of at least one harmonic of filter output currents (ifghd) with respect to the fundamental of the filter output currents (ifgi, if92, ifg3) t and in that the q-component of the Park-Clarke transformation of the reference-filter output voltages (ugq) is produced by regulation of the q-component of the Park-Clarke transformation of the phase connection currents (ifiq) at the sum of the q-component of the Park-Clarke transformation of the reference-phase connection currents (ifiq) and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents (itghq) with respect to the fundamental of the filter output currents (ifgi, ifg2/- ifg3) - 4. The method as claimed in claim 3, characterized in that the d-component of the Park-Clarke transformation of the reference-phase connection voltages (uid) is produced by the sum of the d-component of the Park-Clarke transformation of the reference-filter output voltages (ugd) and the d-component of filter output voltages (ugd) and a d-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages (ughd) and in that the q-component of the Park-Clarke transformation of the reference-phase connection voltages (uiq) is produced by the sum of the q-component of the Park-Clarke transformation of the reference-filter output voltages (ugq) and the q-component of the Park-Clarke transformation of the filter output voltages (ugq) and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages (ughq) • 5. The method as claimed in claim 4, characterized in that the reference-phase connection voltages (uii, u±2/ ui3) are produced by inverse Park-Clarke transformation of the d-component of the Park-Clarke transformation of the reference-phase connection voltages (uid) and the q-component of the Park-Clarke transformation of the reference-phase connection voltages (uiq) - 6. An apparatus for carrying out a method for operation of a converter circuit, in which the converter circuit has a converter unit (1) with a multiplicity of drivable power semiconductor switches and an LCL filter (3) which is connected to each phase connection (2) of the converter unit (1), having a regulation device (4) which is used for production of reference voltages (ui, u2, u3) and is connected via a drive circuit (5) for formation of a drive signal (S) to the drivable power semiconductor switches, characterized in that the regulation device (4) has a first calculating unit (6) for formation of reference ' voltages (ui, u2r u3) from the subtraction of damping voltages (udi, ud2, ud3) from reference-phase connection voltages (uii, ui2, ui3) , with the first calculation unit (6) being supplied with reference-phase connection voltages (un, ui2, ui3) and, in order to form the damper voltages (udi, ud2/ ud3) , filter capacitance currents (icfi, ictir icf3) °f the LCL filters (3), and a regulator unit (7) , with the filter capacitance currents (icfi, icf2r icf3) being filtered by means of a high-pass filter. 7. The apparatus as claimed in claim 6, characterized ' in that the regulator unit (7) has a first proportional-integral regulator (8) to whose input side ZXMF.KfDF.D SHEET the difference between the dc voltage (udc) of a capacitive energy store (9) , which is connected to the converter unit (1) and a dc voltage reference value (udc) are supplied, and on whose output side the d-component of the Park-Clarke transformation of reference-phase connection currents (ifid) is produced. 8. The apparatus as claimed in claim 7, characterized in that the regulator unit (7) has a second proportional-integral regulator (10), to whose input side the difference between the sum of the d-component of the Park-Clarke transformation of the reference-phase connection currents (ifid) and a d-component of the Park-Clarke transformation of at least one harmonic of the filter output currents (ifghd) with respect to the fundamental of the filter output currents (ifgi, ifg2r ifg3) and the d-component of the Park-Clarke transformation of the phase connection currents (ifid) are supplied, and on whose output side the d-component of the Park-Clarke transformation of the reference-filter output voltages (ugd) is produced, and in that the regulator unit (7) has a third proportional-integral regulator (11), to whose input side the difference between the sum of the q-component of the Park-Clarke transformation of the reference-phase connection currents (ifiq) and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents (ifghq) with respect to the fundamental of the filter output currents (ifgi/ ifg2/ ifg3) and the q-component s of the Park-Clarke transformation of the phase connection currents (ifiq) are supplied, and on whose output side the q-component of the Park-Clarke transformation of the reference-filter output voltages (ugq) is produced. 9. The apparatus as claimed in claim 8, characterized in that the regulator unit (7) has a first adder (12) for production of the d-component of the Park-Clarke transformation of the reference-phase connection voltages (uid) , to which the d-component of the Park- Clarke transformation of the reference-filter output voltages (ugd) , the d-component of the filter output voltages (ugd) and a d-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages (ughd) are supplied, and in that the regulator (7) has a second adder (13) for production of the q-component of the Park-Clarke transformation of the reference-phase connection voltages (uiq) , to which the q-component of the Park-Clarke transformation of the reference-filter output voltages (ugq) , the q-component of the Park-Clarke transformation of the filter output voltages (ugq) and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages (ughq) are supplied, 10. The apparatus as claimed in claim 9, characterized in that the regulator unit (7) has a calculation unit (14) for formation of the reference-phase connection voltages . (u^, u±2, ui3) by inverse Park-Clarke transformation, to whose input side the d-component of the Park-Clarke transformation of the reference-phase connection voltages (uid) and the q-component of the Park-Clarke transformation of the reference-phase connection voltages (uiq) are supplied. 11. The apparatus as claimed in one of claims 7 to 10, characterized in that the regulation device (4) has a second calculation unit (15) for the formation of a d-component of the Park-Clarke transformation of at least one harmonic of the filter output currents (ifghd) with respect to the fundamental of the filter output currents (ifgi, ifg2, ifg3) / of a q~component of the Park-Clarke transformation of at least one harmonic of the filter output currents (ifghq) with respect to the fundamental of the filter output currents (ifgi, ifg2/ ifg3) t of the d-component of the Park-Clarke transformation of the at least one harmonic of the reference-filter output voltages (ughd) and of the q-component of the Park-Clarke transformation of the at least one harmonic of the reference-filter output voltages (u*ghq) , with the input side of the second calculation unit (15) being supplied with the d-component of the filter output voltages (ugd) , with the q-component of the filter output voltages (ugq) , the phase connection currents (if±i, ifi2/ if±3) / the filter capacitance currents (icfi/ ict2r icf3) and the fundamental angle (cot) of the filter output voltages (Ugl, Ug2, Ug3) - 12. The apparatus as claimed in claim 11, characterized in that the regulation device (4) has a third calculation unit (16) for formation of the d-component of the Park-Clarke transformation of the filter output voltages (ugd) , of the q-component of the Park-Clarke transformation of the filter output voltages (ugq) and of the fundamental angle (cot) of the filter output voltages (ugi, ug2, ug3) , with the input side of the third calculation unit (16) being supplied with filter output voltages (ugi, ug2, ug3) of the LCL filters (3).

Full Text

Method for operation of a converter circuit, as well as an apparatus for carrying out the method
DESCRIPTION
Technical field
The invention relates to the field of power electronics, and is based on a method for operation of a converter circuit, as well as an apparatus for carrying out the method, as claimed in the preamble of the independent claims.
Prior art
Conventional converter circuits have a converter unit with a multiplicity of drivable power semiconductor switches, which are connected in a known manner in order to switch at least two switching voltage levels. An LCL filter is connected to each phase connection of the converter unit. A capacitive energy store is also connected to the converter unit, and is normally formed by one or more capacitors. An apparatus is provided for operation of the converter circuit, which apparatus has a regulation device for production of reference voltages and is connected via a drive circuit for formation of a drive signal from the reference voltages to the drivable power semiconductor switches. The power semiconductor switches are thus driven by means of the drive signal.
The converter circuit mentioned above is subject to the problem but the LCL filters can cause permanent distortion, that is to say undesirable oscillations, in the filter output currents and filter voltages, resulting from resonant oscillations of the LCL filters. In an electrical ac voltage supply system, which is typically connected to the filter outputs, or

in an electrical load which, is connected to the filter outputs, such distortion can lead to damage or even destruction, and is therefore very undesirable.
Description of the invention
One object of the invention is therefore to specify a method for operation of a converter circuit, by means of which it is possible to actively damp distortion, caused by LCL filters connected to the converter circuit, in the filter output currents and filter output voltages. A further object of the invention is to specify an apparatus by means of which the method can be carried out in a particularly simple manner. These objects are achieved by the features of claim 1 and claim 7, respectively. Advantageous developments of the invention are specified in the dependent claims.
The converter circuit has a converter,'-, unit with a multiplicity of drivable power semiconductor switches, and an LCL filter which is connected to each phase connection of the converter unit. In the method according to the invention for operation of the converter circuit, the drivable power semiconductor switches are now driven by means of a drive signal which is formed from reference voltages. According to the invention, the reference voltages are formed from the subtraction of damping voltages from reference-phase connection voltages, with the damping voltages being formed from filter capacitance currents (which are weighted with a variable damping factor) of the LCL filters. The damping voltages are thus proportional to the filter capacitance currents and are then subtracted from the reference-phase connection voltages, which is equivalent to connection of a damping resistance to each phase connection of the converter unit. Distortion, that is to say undesirable oscillations, in the filter, output currents and filter output voltages

can therefore advantageously be actively damped, so that this type of distortion is greatly reduced and, in the ideal case, is very largely suppressed, A further advantage of the method according to the invention is that there is no need to connect any discrete, highly space-consuming damping resistor, which is complex to provide and is therefore expensive, to each phase connection in order to allow the undesirable distortion to be effectively damped.
The apparatus according to the invention for carrying out the method for operation of the converter circuit has a regulation device which is used to produce reference voltages and is connected via a drive circuit for formation of a drive signal to the drivable power semiconductor switches. According to the invention, the regulation device has a first calculating unit for formation of reference voltages from the subtraction of damping voltages from reference-phase connection voltages, with the first calculation unit being supplied with reference-phase connection voltages and, in order to form the damper voltages, filter capacitance currents of the LCL filters. Furthermore, the regulation device has a regulator unit for production of the reference-phase connection voltages. The apparatus according to the invention for carrying out the method for operation of the converter circuit can thus be implemented very easily and cost-effectively, since the circuit complexity can be kept extremely low and, furthermore, only a small number of components are required to construct it. The method according to the invention can thus be carried out particularly easily by means of this apparatus.
These and further objects, advantages and features of the invention will become evident from the following detailed description of preferred embodiments of the invention, in conjunction with the drawing.

Brief description of the drawings
In the figures:
Figure 1 shows one embodiment of an apparatus according to the invention for carrying out the method according to the invention for operation of a converter circuit,
Figure 2 shows one embodiment of a second calculation unit,
Figure 3 shows a waveform of the filter output currents with active damping using the method according to the invention, and
Figure 4 shows a waveform of the filter output currents with active damping and additional active reduction of harmonics using the method according to the invention.
The reference symbols used in the drawing, and their meanings, are listed in a summarized form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures. The described embodiments represent examples of the subject matter of the invention, and have no restrictive effect.
Approaches to implementation off the invention
Figure 1 shows one embodiment of an apparatus according to the invention for carrying out the method according to the invention for operation of a converter circuit. As shown in Figure 1, the converter circuit has a converter unit 1 with a multiplicity of drivable power semiconductor switches and an LCL filter 3, which is

connected to each phase connection 2 of the converter unit 1, Each LCL filter 3 accordingly has a first filter inductance Lfi, a second filter inductance Lfg as well as a filter capacitance Cf, with the first filter inductance Lfi being connected to the associated phase connection 2 of the converter unit 1, to the second filter inductance Lfg and to the filter capacitance Cf. Furthermore, the filter capacitances Cf of the individual LCL filters 3 are connected to one another. Each LCL filter 3 typically has a virtually negligible filter resistance Rf, which is connected in series with the filter capacitance Cf of the associated LCL filter 3 and represents resistive losses in the LCL filter 3. By way of example, the converter unit 1 shown in Figure 1 is a three-phase unit. It should be mentioned that the converter unit 1 may in general be any form of converter unit 1 for switching of > 2 switching voltage levels (multi-level converter circuit) with respect to the voltage of a capacitive energy store 9 which is connected to the converter unit 1, with the capacitive energy store 9 then being formed by any desired number of capacitances, which are then connected such that they are matched to the appropriately configured converter circuit element.
In the method according to the invention for operation of the converter circuit, the drivable power semiconductor switches of the conversion unit 1 are now driven by means of a drive signal S which is formed from reference voltages u*i, u*2, u*3. A look-up table is normally used to form the drive signal, in which appropriate drive signals are permanently associated with reference voltage values, or a modulator which is based on pulse-width modulation. According to the invention, the reference voltages u*i, u*2, u*3 are formed from subtraction of damping voltages udi, ud2, ud3 from reference-phase connection voltages u*iif u*i2, u*i3, with the damping voltages udi, ud2/ ud3 being

formed from filter capacitance currents icfi, icf2/ icf3/ which are weighted with a variable damping factor Kf, of the LCL filters 3, as illustrated in particular by the following formula.
Ud = Kf * iCf *
The damping voltages udi, ud2/ ud3 are thus proportional to the filter capacitance currents icfi/ i-ctzr icf3 and are then subtracted from the reference-phase connection voltages u*11, u*i2, u*i3, which corresponds to the connection of a damping resistor to each phase connection 2 of the converter unit 1. This advantageously allows active damping of distortion, that is to say undesirable oscillations, in the filter output currents ifgi, ifg2/ ifg3 and filter output voltages ugi, ug2, ug3, so that this distortion is greatly reduced and, in the ideal case is very largely suppressed. Furthermore, there is no need for connection of discrete, very space-consuming damping resistors, which are complex to implement and are therefore expensive to the respective phase connection in order to allow effective damping of the undesirable distortion.
The damping factor Kf is preferably set such that the undesirable oscillations of the filter output voltages ugi, ug2, ug3 or of phase-connection voltages, in particular harmonics, are just not amplified.
As shown in Figure 1, the apparatus according to the invention for carrying out the method according to the invention for operation of a converter circuit for this purpose has a regulation device 4, which is used to produce the reference voltages u*i, u*2, u*3 and is connected via a drive circuit 5 for formation of the drive signal S to the drivable power semiconductor switches. By way of example, the drive circuit 5 has a

look-up table in which appropriate drive signals are permanently associated with reference-voltage values, or a modulator which is based on pulse-width modulation. According to the invention, the regulation device 4 has a first calculation unit 6 for formation of reference voltages u*i, u*2/ u*3 from the subtraction of damping voltages udi, ud2, ud3 from reference-phase connection voltages u*u, u*i2, u*i3, with the first calculation unit 6 being supplied with reference-phase connection voltages u*u, u*i2, u*i3 and, in order to form the damper voltages udi, ud2, ud3, filter capacitance currents icfi, ict2f icf3 °f the LCL filters 3. As shown in Figure 1, the filter capacitance currents icfi, icf2r icf3 are measured by appropriate measurement devices. Furthermore, the regulation device 4 has a regulation unit 7 for production of the reference-phase connection voltages u*ii, u*i2, u*i3. The apparatus according to the invention for carrying out the method for operation of the converter circuit can accordingly be produced very easily and cost-effectively, since the circuit complexity can be kept extremely low and, furthermore, only a small number of components are required to construct it. This apparatus allows the method according to the invention . to be carried out particularly easily.
It has been found to be advantageous for the filter capacitance currents icfir icf2/ icf3 to be filtered by means of a high-pass filter. This means that the damping voltages udi, ud2, ud3 are formed only from harmonics of the filter capacitance currents icfir icf2r iCf3, in particular higher-frequency harmonics of the filter capacitance currents icfir ict2/ icf3f and the variable damping factor Kf, so that the active damping according to the invention advantageously acts only on the harmonics in the filter output currents ifgi, ifg2r ifg3 and filter output voltages ugi, ug2, ug3. High-pass filtering of the filter capacitance currents icfir icf2,

icf3 is carried out by a high-pass filter which is connected between the measurement devices for measurement of the filter capacitance currents icfir icf2/ icf3 and the first calculation unit 6, with the high-pass filter not being shown in Figure 1, for clarity reasons.
The reference-phase connection voltages u*n, u*i2, u*i3 are formed from a d-component of the Park-Clarke transformation (produced by regulation of the dc voltage udc of a capacitive energy store 9 which is connected to the converter unit 1 at a dc voltage reference value u*dc of reference-phase connection currents i*fid and from a predeterminable q-component of the Park-Clarke transformation of the reference-phase connection currents i*fiq. The regulation is preferably carried out using a proportional-integral characteristic. As shown in figure 1, the regulator unit 7 for regulation of the dc voltage udc of the capacitive energy store 9 at the dc voltage reference value u*dc has a first proportional-integral regulator 8, to whose input the difference between the dc voltage (udc) of the capacitive energy store 9 and the dc voltage reference value u*dc is supplied, and at whose output the d-component of the Park-Clarke transformation of the reference-phase connection currents i*fid is produced.
The Park-Clarke transformation is in general defined as:
x = (xd + jxq)ejcc)t
using the variables illustrated in Figure 1:

where x is a complex variable, xd is the d-component of the Park-Clarke transformation of the variable x and xq is the q-component of the Park-Clarke transformation of the variable x All of the Park-Clarke transformations of variables which have already been mentioned and those which will be mentioned in the following text are produced using the formula quoted above. The Park-Clarke transformation advantageously transforms not only the fundamental of the complex variable x , but also all of the harmonics that occur of the complex variable x .
The regulation device 4 shown in Figure 1 has a third calculation unit 16 for formation of the d-component of the Park-Clarke transformation of the filter output voltages ugd, of the q-component of the Park-Clarke transformation of the filter output voltages ugq and of the fundamental angle cot of the filter output voltages ugi, ug2, ug3, with the input side of the third calculation unit 16 being supplied with the filter output voltages ugi, ug2, ug3 of the LCL filters 3. The third calculation unit 16 is preferably a phase locked loop, in which case the Park-Clarke transformations of the individual variables are carried out using the definitions given above.
Furthermore, the d-component of the Park-Clarke transformation of the reference-filter output voltages u*gd is produced by regulation of the d-component of the Park-Clarke transformation of the phase connection

current ifid at the sum of the d-component of the Park-Clarke transformation of the reference-phase connection currents i*fid and a d-component of the Park-Clarke transformation of at least one harmonic of filter output currents i*fghd with respect to the fundamental of the filter output currents ifgi, ifg2r ifg3- The regulation is preferably carried out using a proportional-integral characteristic. Furthermore, the q-component of the Park-Clarke transformation of the. reference filter output voltages u*gq is produced by-regulation of the q-component of the Park-Clarke transformation of the phase connection currents ifiq at ■ the sum of the q-component of the Park-Clarke transformation of the reference-phase connection currents i*fiq and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents i*f9hq with respect to the fundamental of the filter output currents ifgi, ifg2* ifg3* The regulation is preferably carried out using a proportional-integral characteristic. The index h of the d-component and the q-component of the Park-Clarke transformation of a harmonic of the filter output currents i*fghd, i*fghq represents the h-th harmonic of these variables, where h = 1, 2, 3, ... The additional . variables introduced in the following text with the index h likewise use the index h for the h-th harmonic of the associated variable, h = 1, 2, 3, ... As shown in Figure 1, the regulator unit 7 for regulation of the d-component of the Park-Clarke transformation of the phase connection currents if±d at the sum of the d-component of the Park-Clarke transformation of the reference phase connection currents i*fid and a d-component of the Park-Clarke transformation of at least one harmonic of the filter output currents i*fghd with respect to the fundamental of the filter output currents ifgi, ifg2f ifg3 has a second proportional- . integral regulator 10 to whose input side the difference between the sum of the d-component of the

Park-Clarke transformation of the reference-phase -connection currents i*fid and a d-component of the Park-Clarke transformation of at least one harmonic of the filter output currents i*fghd with respect to the fundamental of the filter output currents ifgi, Xfg2r ifg3 and the d-component of the Park-Clarke transformation of the phase connection currents ifid are supplied, and on whose output side the d-component s of the Park-Clarke transformation of the reference-filter output voltages u*gd is produced. Furthermore, for regulation of the q-component of the Park-Clark transformation of the phase connection currents ifiq at the sum of the q-component of the Park-Clarke transformation of the • reference phase connection currents i*fiq and the q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents i*fghq with respect to the fundamental of the filter output currents ifgi, ifg2 ifg3, the regulator unit 7 has a third proportional-integral regulator 11 to whose input side the difference between the sum of the q-component of the Park-Clarke transformation of the reference phase connection currents i*fiq and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents i*fghq with respect to the fundamental of the filter output currents ifgi, ifg2/ ifg3 • and the q-components of the Park-Clarke transformation of the phase connection currents ifiq are supplied, and on whose output side the q-component of the Park-Clarke transformation of the reference-filter output voltages u*gq is produced.
Furthermore, the d-component of the Park-Clarke transformation of the reference-phase connection voltages u*id is produced by the sum of the d-component of the Park-Clarke transformation of the reference filter output voltages u*gd and the d-component of the filter output voltages ugd and a d-component of the Park-Clarke transformation of at least one harmonic of

the filter output voltages u*ghd. In addition the q-component of the Park-Clarke transformation of the reference-phase connection voltages u*iq is produced by the sum of the q-component of the Park-Clarke transformation of the reference-filter output voltages u*gq and the q-component of the Park-Clarke transformation of the filter-output voltages ugq and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages u*ghq. In.order to produce the d-component of the Park-Clarke transformation of the reference-phase connection voltages u*id, the regulator unit 7 has a first adder 12, to which the d-component of the Park-Clarke transformation of the reference filter output voltages u*gd, the d-component of the filter output voltages ugd and the d-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages u*ghd are supplied. In addition, in order the produce the q-component of the Park-Clarke transformation of the reference phase connection voltages u*iq/ the regulator unit 7 has, as shown in Figure 1, a second adder 13, to which the q-component of the Park-Clarke transformation of the reference-filter output voltages u*gq, the q-component of the Park-Clarke transformation of the filter output voltages ugq and the q-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages u*ghq are supplied.
In order to form the d-component of the Park-Clarke transformation, as has already been mentioned above, of at least one harmonic of the filter output currents i*fghd with respect to the fundamental of the filter output currents ifgi, ifg2/ ifg3r the q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents i*fghq with respect to the fundamental of the filter output currents ifgi, ifg2, ifg3f the d-component of the Park-Clarke transformation of the at least one harmonic of the reference filter .

output voltages u*ghd anc* the q-component of the Park-Clarke transformation of the at least one harmonic of the reference-filter output voltages u*ghq the regulation unit .4 has a second calculation unit 15, as shown in Figure 1. As shown in Figure 1, the input side of the second calculation unit 15 is supplied with the d-component with the filter output voltages ugd, the q-component of th.e filter output voltages ugq, the phase connection currents im, im, if±3f the filter capacitance currents iCfi, icf2f icf3 and the fundamental angle ot of the filter output voltages ugi, ug2, ug3. In order to illustrate the formation of the individual variables in the calculation unit 15, Figure 2 shows one embodiment of the second calculation unit 15, in which the input variables shown in Figure 2 are obtained using the following formula:
ifghd + jifghq - ifihd + jifihq ~ (icfhd + j icfhq)
with the d-components of the Park-Clarke transformation and the q-components of the Park-Clarke transformation being obtained by applications of the Park-Clarke transformation to the measured phase connection currents if a, ifi2, ifi3 including the associated harmonics, and filter capacitance currents ictif i-cf2, .iCf3 including the associated harmonics. This Park-Clarke" transformation is carried out in particular in the second calculation unit 15, although this is not illustrated in the second calculation unit 15 shown in Figure 2, for clarity reasons.
Finally, the reference-phase connection voltages u*ii, u*i2, u*i3 are produced by an inverse Park-Clarke transformation of the d-component of the Park-Clarke transformation of the reference-phase connection voltages u*id. and the q-component of the Park-Clarke transformation of the reference-phase connection voltages u*iq. As shown in Figure 1, the regulator unit

7 for this purpose has a calculation unit 14 for formation of the reference-phase connection voltages u*ii, u*i2, u*i3 by inverse Park-Clarke transformation, to whose input side the d-component of the Park-Clarke transformation of the reference-phase connection voltages u*id and the q-component of the Park-Clarke transformation of the reference-phase connection voltages u*iq are supplied.
In order to illustrate the method of operation of the active damping based on the method according to the invention as explained above, Figure 3 shows a waveform of the filter output currents ifgi, ifg2/ ifg3 in which undesirable oscillations in the filter output currents ifgi/ ifg2/ ifg3 are actively damped, so that this distortion is greatly reduced. A further improvement in the reduction of harmonics is shown in a waveform of the filter output currents ifgi, if92/ ifg3 in figure 4 with active damping, and additional active reduction of harmonics using the method according to the invention as described above.
It should be mentioned that all of the steps of the method according to the invention may by implemented in the form of software, which can then be loaded and then run for example on a computer system, in particular with a digital signal processor. The digital delay times which occur in systems such as this, in particular for the calculations, may be in general be taken into account, for example, by addition of an additional term to the fundamental angle cot in the Park-Clarke transformation. Furthermore, the apparatus according to the invention, as described in detail above, can also be implemented in a computer system, in particular in the digital signal processor.
Overall, it has been possible to show that the apparatus according to the'invention, in particular as

shown in Figure 1, for carrying out the method according to the invention for operation of the converter circuit can be implemented very easily and cost-effectively, since the circuit complexity is extremely low and, furthermore, only a small number of components are required to construct it. This apparatus therefore makes it possible to carry out the method according to the invention particularly easily.

List of reference symbols
1 Converter unit
2 Phase connection of the converter unit
3 LCL filter
4 Regulation device
5 Drive circuit
6 First calculation unit of the regulation device
7 Regulator unit
8 First proportional-integral regulator
9 Capacitive energy store
10 Second proportional-integral regulator
11 Third proportional-integral regulator
12 First adder
13 Second,adder
14 Calculation unit for the regulator unit
15 Second calculation unit of the regulation device
16 third calculation unit of the regulation device

PATENT CLAIMS
1. A method for operation of a converter circuit, in
which the converter circuit has a converter unit (1)
with a multiplicity of drivable power semiconductor
switches and an LCL filter (3) which is connected to
each phase connection (2) of the converter unit (1),
in which the drivable power semiconductor switches are driven by means of a drive signal (S) which is formed from reference voltages (u*i, u*2, u*3) , characterized
in that the reference voltages (u*i, u*2/ u*3) are formed by subtraction of damping voltages (ud1, ud2, ud3) from reference-phase connection voltages (u*n, u*i2, u*i3) , with the damping voltages (udi, ud2, ud3) being formed from filter capacitance currents (icfif icf2r icf3) / weighted with a variable damping factor (Kf) of the LCL filter (3) and in that the filter capacitance currents (icfif icf2/ icf3) sre. filtered by means of a high-pass filter.
2. The method as claimed in claim 1, characterized in that the reference-phase connection voltages (u*n, u*i2, u*i3) are formed from a d-component of the Park-Clarke transformation (produced by regulation of a dc voltage (udc) of a capacitive energy store (9) which is connected to the converter unit (1) at a dc voltage reference value (u*dc) of reference-phase connection currents (i*fid) and from a predeterminable q-component of the Park-Clarke transformation of the reference-phase connection currents (i*fiq) .
3. The method as claimed in claim 2, characterized in that the d-component of the Park-Clarke transformation of reference-filter output voltages (u*gd) is produced by regulation of the d-component of the Park Clarke transformation of the phase connection currents (if id)
AMENDED SHEET

at the sum of the d-component of the Park-Clarke transformation of the reference-phase connection currents (i*fid) and a d-component of the Park-Clarke transformation of at least one harmonic of filter output currents (i*fghd) with respect to the fundamental of the filter output currents (ifgi, if92, ifg3) t and in that the q-component of the Park-Clarke transformation of the reference-filter output voltages (u*gq) is produced by regulation of the q-component of the Park-Clarke transformation of the phase connection currents (ifiq) at the sum of the q-component of the Park-Clarke transformation of the reference-phase connection currents (i*fiq) and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents (i*tghq) with respect to the fundamental of the filter output currents (ifgi, ifg2/-
ifg3) -
4. The method as claimed in claim 3, characterized in that the d-component of the Park-Clarke transformation of the reference-phase connection voltages (u*id) is produced by the sum of the d-component of the Park-Clarke transformation of the reference-filter output voltages (u*gd) and the d-component of filter output voltages (ugd) and a d-component of the Park-Clarke transformation of at least one harmonic of the filter
output voltages (u*ghd) * and
in that the q-component of the Park-Clarke transformation of the reference-phase connection voltages (u*iq) is produced by the sum of the q-component of the Park-Clarke transformation of the reference-filter output voltages (u*gq) and the q-component of the Park-Clarke transformation of the filter output voltages (ugq) and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages (u*ghq) •

5. The method as claimed in claim 4, characterized in that the reference-phase connection voltages (u*ii, u*±2/ u*i3) are produced by inverse Park-Clarke transformation of the d-component of the Park-Clarke transformation of the reference-phase connection voltages (u*id) and the q-component of the Park-Clarke transformation of the reference-phase connection voltages (u*iq) -
6. An apparatus for carrying out a method for operation of a converter circuit, in which the converter circuit has a converter unit (1) with a multiplicity of drivable power semiconductor switches and an LCL filter (3) which is connected to each phase connection (2) of the converter unit (1),
having a regulation device (4) which is used for
production of reference voltages (u*i, u*2, u*3) and is
connected via a drive circuit (5) for formation of a
drive signal (S) to the drivable power semiconductor
switches,
characterized
in that the regulation device (4) has
a first calculating unit (6) for formation of reference '
voltages (u*i, u*2r u*3) from the subtraction of damping
voltages (udi, ud2, ud3) from reference-phase connection
voltages (u*ii, u*i2, u*i3) , with the first calculation
unit (6) being supplied with reference-phase connection
voltages (u*n, u*i2, u*i3) and, in order to form the
damper voltages (udi, ud2/ ud3) , filter capacitance
currents (icfi, ictir icf3) °f the LCL filters (3), and
a regulator unit (7) , with the filter capacitance
currents (icfi, icf2r icf3) being filtered by means of a
high-pass filter.
7. The apparatus as claimed in claim 6, characterized '
in that the regulator unit (7) has a first
proportional-integral regulator (8) to whose input side
ZXMF.KfDF.D SHEET

the difference between the dc voltage (udc) of a capacitive energy store (9) , which is connected to the converter unit (1) and a dc voltage reference value (u*dc) are supplied, and on whose output side the d-component of the Park-Clarke transformation of reference-phase connection currents (i*fid) is produced.
8. The apparatus as claimed in claim 7, characterized in that the regulator unit (7) has a second proportional-integral regulator (10), to whose input side the difference between the sum of the d-component of the Park-Clarke transformation of the reference-phase connection currents (i*fid) and a d-component of the Park-Clarke transformation of at least one harmonic of the filter output currents (i*fghd) with respect to the fundamental of the filter output currents (ifgi, ifg2r ifg3) and the d-component of the Park-Clarke transformation of the phase connection currents (ifid) are supplied, and on whose output side the d-component of the Park-Clarke transformation of the reference-filter output voltages (u*gd) is produced, and
in that the regulator unit (7) has a third proportional-integral regulator (11), to whose input side the difference between the sum of the q-component of the Park-Clarke transformation of the reference-phase connection currents (i*fiq) and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output currents (i*fghq) with respect to the fundamental of the filter output currents (ifgi/ ifg2/ ifg3) and the q-component s of the Park-Clarke transformation of the phase connection currents (ifiq) are supplied, and on whose output side the q-component of the Park-Clarke transformation of the reference-filter output voltages (u*gq) is produced.

9. The apparatus as claimed in claim 8, characterized
in that the regulator unit (7) has a first adder (12)
for production of the d-component of the Park-Clarke
transformation of the reference-phase connection
voltages (u*id) , to which the d-component of the Park-
Clarke transformation of the reference-filter output
voltages (u*gd) , the d-component of the filter output
voltages (ugd) and a d-component of the Park-Clarke
transformation of at least one harmonic of the filter
output voltages (u*ghd) are supplied, and
in that the regulator (7) has a second adder (13) for production of the q-component of the Park-Clarke transformation of the reference-phase connection voltages (u*iq) , to which the q-component of the Park-Clarke transformation of the reference-filter output voltages (u*gq) , the q-component of the Park-Clarke transformation of the filter output voltages (ugq) and a q-component of the Park-Clarke transformation of at least one harmonic of the filter output voltages (u*ghq) are supplied,
10. The apparatus as claimed in claim 9, characterized
in that the regulator unit (7) has a calculation unit
(14) for formation of the reference-phase connection
voltages . (u*^, u*±2, u*i3) by inverse Park-Clarke transformation, to whose input side the d-component of the Park-Clarke transformation of the reference-phase connection voltages (u*id) and the q-component of the Park-Clarke transformation of the reference-phase connection voltages (u*iq) are supplied.
11. The apparatus as claimed in one of claims 7 to 10,
characterized in that the regulation device (4) has a
second calculation unit (15) for the formation of a
d-component of the Park-Clarke transformation of at
least one harmonic of the filter output currents
(i*fghd) with respect to the fundamental of the filter

output currents (ifgi, ifg2, ifg3) / of a q~component of the Park-Clarke transformation of at least one harmonic of the filter output currents (i*fghq) with respect to the fundamental of the filter output currents (ifgi, ifg2/ ifg3) t of the d-component of the Park-Clarke transformation of the at least one harmonic of the reference-filter output voltages (u*ghd) and of the q-component of the Park-Clarke transformation of the at least one harmonic of the reference-filter output voltages (u*ghq) , with the input side of the second calculation unit (15) being supplied with the d-component of the filter output voltages (ugd) , with the q-component of the filter output voltages (ugq) , the phase connection currents (if±i, ifi2/ if±3) / the filter capacitance currents (icfi/ ict2r icf3) and the fundamental angle (cot) of the filter output voltages
(Ugl, Ug2, Ug3) -
12. The apparatus as claimed in claim 11, characterized in that the regulation device (4) has a third calculation unit (16) for formation of the d-component of the Park-Clarke transformation of the filter output voltages (ugd) , of the q-component of the Park-Clarke transformation of the filter output voltages (ugq) and of the fundamental angle (cot) of the filter output voltages (ugi, ug2, ug3) , with the input side of the third calculation unit (16) being supplied with filter output voltages (ugi, ug2, ug3) of the LCL filters (3).

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Patent Number

271539

Indian Patent Application Number

2812/CHENP/2007

PG Journal Number

09/2016

Publication Date

26-Feb-2016

Grant Date

24-Feb-2016

Date of Filing

25-Jun-2007

Name of Patentee

ABB SCHWEIZ AG

Applicant Address

BROWN BOVERI STRASSE 6, CH-5400 BADEN, SWITZERLAND

Inventors:

#	Inventor's Name	Inventor's Address
1	PONNALURI, SRINIVAS	NIEDERWIESSTRASSE 12, CH-5417 UNTERSIGGENTHAL, SWITZERLAND
2	STEINKE, JURGEN	STEIGACKER 14, D079774 ALBBRUCK, GERMANY

PCT International Classification Number

H02M 1/12

PCT International Application Number

PCT/CH05/00293

PCT International Filing date

2005-05-24

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/646,544	2005-01-25	U.S.A.