JP4423950B2 - AC / AC direct converter controller - Google Patents

Description

  The present invention relates to a control device for an AC / AC direct converter that converts a polyphase AC voltage to a polyphase AC voltage having an arbitrary magnitude and frequency using a semiconductor switch, and is particularly assumed in a power converter such as a matrix converter. The present invention relates to a control device characterized by PWM pulse generation means for controlling the virtual PWM rectifier and the virtual PWM inverter.

  An AC switch is constituted by at least two unidirectional semiconductor switches capable of controlling a unidirectional current, and this AC switch group is switched to directly obtain a three-phase AC voltage of arbitrary magnitude and frequency from a three-phase AC power source. As an AC / AC direct converter, a matrix converter will be described below as an example.

  FIG. 4 is a prior art block diagram showing the matrix converter 20 and its control device. Here, the matrix converter 20 includes a bidirectional AC switch S1 between each phase input terminal R, S, T connected to a three-phase AC power source and each phase output terminal U, V, W on the load side. To S9 are connected. In addition, as described above, these AC switches S1 to S9 are, for example, two unidirectional semiconductor switches in which two unidirectional semiconductor switches having a bidirectional breakdown voltage are connected in reverse parallel or antiparallel diodes are respectively connected. Are connected in series in the opposite direction.

In the matrix converter 20, the unidirectional switches constituting the AC switches S1 to S9 are PWM-controlled to directly extract a three-phase AC voltage, and a three-phase AC voltage having an arbitrary magnitude and frequency is obtained and supplied to a load. Yes.
Here, as a control method of the input current and output voltage of the matrix converter, a virtual PWM rectifier (hereinafter simply referred to as a virtual rectifier if necessary) and a virtual PWM inverter (also simply referred to as a virtual inverter) are included in the matrix converter. And a virtual AC / DC / AC conversion system that performs PWM control of these is known (see Non-Patent Document 1 described later).
The outline of this virtual AC / DC / AC conversion method will be described below.

  In the prior art of FIG. 4, the input current is controlled by a virtual rectifier. That is, a trapezoidal wave input current command for switching only one phase is generated from the input current command by the trapezoidal wave command generating means 11. Then, the input current command and the carrier generated by the carrier generating means 12 are compared by the comparing means 13 to obtain a PWM pulse pattern on the virtual rectifier side.

  On the other hand, on the virtual inverter side, the on / off ratio of the phase in which the virtual rectifier is switched is extracted by the on / off ratio extraction means 16 based on the PWM pulse pattern output from the comparison means 13, and this on / off ratio is used as the carrier. A symmetrical triangular wave generator 14 generates a deformed triangular wave that has moved the apex position of a certain triangular wave. Then, the symmetrical deformed triangular wave is compared with the output voltage command by the comparison means 15 to obtain a PWM pulse pattern on the virtual inverter side.

  Thereafter, the PWM pulse synthesizing unit 17 synthesizes the PWM pulse pattern of the virtual rectifier and the virtual inverter, obtains the PWM pulse pattern of the matrix converter 20, and switches the AC switches S1 to S9.

Here, FIG. 5 shows a virtual rectifier PWM pulse, a PWM pulse of the upper and lower arms of the virtual inverter, and a PWM pulse of the matrix converter 20 when a symmetrical modified triangular wave is used for the virtual inverter carrier.
As shown in the figure, the Up / Down pattern of the virtual inverter carrier is switched according to the Up / Down of the virtual rectifier carrier (output of the carrier generating means 12). In FIG. 5, the peak value of the virtual inverter carrier is set (preset) at the time of the maximum value and the minimum value (mountain, valley) of the virtual rectifier carrier by the interrupt processing in the symmetric deformation triangular wave generation means 14.

The ratio between Up and Down of the virtual inverter carrier is determined by the on / off ratio (duty ratio) of the virtual rectifier PWM pulse. As a result, as shown in FIG. 5, the virtual inverter carrier becomes a symmetrical triangular wave symmetrical with the peaks and valleys of the virtual rectifier carrier. As a result, the upper arm PWM pulse and the lower arm PWM pulse of the virtual inverter It becomes symmetrical with respect to the valley of the carrier.
In FIG. 5, a to d indicate timings when the virtual rectifier PWM pulse changes.

Next, FIG. 6 shows a circuit for one phase of the output of the matrix converter 20. In the matrix converter 20, a switch that switches according to the maximum / intermediate / minimum of the power supply voltage value is selected to control the output voltage.
6 is an AC switch connected between the maximum phase, the intermediate phase, the minimum phase and the U phase on the output side according to the magnitude of the R-phase, S-phase, and T-phase voltages on the power source side in FIG. 21, 22, and 23 are shown. For example, when the R phase is the maximum phase, the S phase is the intermediate phase, and the T phase is the minimum phase, the AC switches 21, 22, and 23 in FIG. 6 correspond to the AC switches S1, S4, and S7 in FIG.

In FIG. 6, the switches 21a and 23a with the reference symbol a added to the polarity of the applied voltage due to the connection relationship with the maximum phase, the intermediate phase, and the minimum phase are the switches that operate in the IGBT mode and the reference symbol b. Switches 21b and 23b are switches that operate in a freewheeling diode mode, respectively.
Here, the IGBT mode refers to an operation mode in which a forward voltage is applied between the collector and the emitter (the collector voltage is higher than the emitter voltage), and is an operation mode in which a current flows at the same time as the gate is turned on. The freewheeling diode mode is an operation mode in which a reverse voltage is applied between the collector and the emitter (the collector voltage is lower than the emitter voltage). In this case, the forward voltage is applied and the gate is not turned on. Since the current does not flow and the operation is almost the same as that of the freewheeling diode in the inverter, it is called the freewheeling diode mode.
The switches 22a / b and 22b / a of the AC switch 22 connected to the intermediate phase are switched between the maximum phase and the intermediate phase (when the AC switch 22 operates as a lower arm), and the intermediate phase. In addition, when switching between the minimum phases (when the AC switch 22 operates as an upper arm), both switches that are in the IGBT mode and the freewheeling diode mode are switched. For this reason, 2a / b and 2b / a are added to the reference symbols.

  For example, in the case of switching with the AC switches 21 and 22 between the maximum phase and the intermediate phase in FIG. 6, the switches 22a / b are in the IGBT mode and 22b / a is in the freewheeling diode mode, and between the intermediate phase and the minimum phase. When switching is performed using the AC switches 22 and 23, the switch 22a / b is in the freewheeling diode mode and 22b / a is in the IGBT mode.

In the virtual AC / DC / AC conversion method described above, there are “upper arm switching” and “lower arm switching” as basic concepts regarding the switching mode.
“Upper arm switching” is a mode in which the upper arm PWM pulse of the virtual inverter is distributed and switched by the PWM pulses of the maximum-phase and intermediate-phase AC switches, and “lower arm switching” is the lower arm of the virtual inverter. In this mode, the PWM pulse is distributed and switched by the PWM pulse of the AC switch of the intermediate phase and the minimum phase.
Here, “distribute” means that, for example, at the time of “upper arm switching”, the upper arm PWM pulse of the virtual inverter becomes the logical sum of the PWM pulses of the maximum-phase and intermediate-phase AC switches.

“Upper arm switching” or “Lower arm switching” depends on the polarity of the intermediate phase voltage (hereinafter referred to as “intermediate voltage”). When the intermediate voltage is positive, “upper arm switching”, the intermediate voltage is When negative, “lower arm switch” is selected.
For example, when the intermediate voltage is positive (upper arm switching), the PWM pulse of the U-phase upper arm of the virtual inverter is distributed by the PWM pulses of the AC switches 21 and 22 in FIG. 6, and the intermediate voltage is negative (lower arm switching). In this case, the PWM pulse of the U-phase lower arm of the virtual inverter is distributed by the PWM pulses of the AC switches 22 and 23 in FIG.

With respect to this operation, referring to FIG. 5 described above, in the “upper arm switching” when the intermediate voltage is positive, a total of six PWM pulses of the matrix converter are performed during one switching period (virtual rectifier carrier period). Switching is performed.
In addition, in the “lower arm switching” when the intermediate voltage is negative, a total of four switching operations are performed during one switching cycle.

Junichi Ito and two others, “Improvement of input / output waveform of matrix converter by virtual AC / DC / AC conversion method”, Institute of Electrical Engineers of Japan (Semiconductor power conversion / industrial power / electricity application joint study group), SPC-02 -77-96, IEA-02-18-37, November 14, 2002, p. 75-80

The switching method of the matrix converter based on the virtual AC / DC / AC conversion method described above has the following problems.
(1) Since the number of times of switching when switching the upper arm is large, switching loss and generated noise increase. As a result, the volume of the radiating fins and the volume of the noise filter are increased, and the entire apparatus is increased in size.
(2) Since the number of times of switching differs between upper arm switching and lower arm switching, the output voltage error due to commutation that occurs during switching differs between upper arm switching and lower arm switching. For this reason, the control accuracy of the output voltage is deteriorated, the waveform distortion is increased, and torque ripple and noise are caused when the load is an electric motor.

  Therefore, the present invention provides an AC / AC direct converter that is PWM-controlled by a virtual AC / DC / AC conversion method. It is an object of the present invention to provide a small and high-performance AC / AC direct converter control device that reduces noise and improves output voltage control accuracy.

In order to solve the above-mentioned problem, the invention described in claim 1 comprises an AC switch group by providing a plurality of bidirectional AC switches composed of at least two unidirectional semiconductor switches capable of controlling a unidirectional current. A control device for an AC / AC direct converter for directly converting a polyphase AC voltage to a polyphase AC voltage having an arbitrary magnitude and frequency by the AC switch group connected to each phase of a polyphase AC power source, PWM pulse synthesizing means for synthesizing each PWM pulse for the virtual rectifier and virtual inverter assumed in the direct converter and giving the PWM to the direct converter, and a carrier generated according to the on / off ratio of the PWM pulse of the virtual rectifier as a virtual inverter carrier In a control device for an AC / AC direct converter provided with a virtual inverter carrier generating means generated as
The virtual inverter carrier generating means is
The up / down signal of the virtual inverter carrier as the second Up / Down signal generated from the Up / Down signal of the virtual rectifier carrier as the first Up / Down signal and the virtual rectifier PWM pulse is supplied to each phase power supply. Means for reversing the voltage according to the voltage polarity of the intermediate voltage phase,
Means for generating a virtual inverter carrier by setting a zero or predetermined peak value at the peak of the virtual rectifier carrier according to the second Up / Down signal and performing a counting operation.

According to a second aspect of the present invention, there is provided the control apparatus for the AC / AC direct converter according to the first aspect, wherein the second Up / Down signal is obtained by combining the first Up / Down signal and the virtual rectifier PWM pulse . It is generated by exclusive OR .

According to a third aspect of the present invention, in the control device for the AC / AC direct conversion device according to the first or second aspect, the predetermined peak value is a value corresponding to a pulse width of the virtual rectifier PWM pulse. .

According to a fourth aspect of the present invention, in the control apparatus for an AC / AC direct converter according to any one of the first to third aspects, the direct conversion is performed even when the voltage polarity of the intermediate voltage phase is positive or negative. The number of times of switching in one cycle of the device is the same number (for example, 4 times) .

The invention described in claim 5 is a matrix converter in which the AC / AC direct converter performs three-phase to three-phase direct conversion in the AC / AC direct converter control device according to any one of claims 1 to 4. characterized in that there.

According to the present invention, in an AC / AC direct converter such as a matrix converter, by switching the carrier of the virtual inverter in accordance with the polarity of the intermediate voltage, the number of switching times during both upper arm switching and lower arm switching over the entire power cycle. The switching loss and noise can be reduced. As a result, it is possible to prevent the volume of the heat dissipating fins and the noise filter from increasing, and to reduce the size of the entire apparatus.
In addition, by switching the number of times of switching between the upper arm and the lower arm, it is possible to eliminate distortion of the output voltage waveform without causing a deterioration in output voltage control accuracy due to an output voltage error, as well as torque ripple and noise. It is possible to realize a high-performance AC / AC direct converter that suppresses the generation of the above.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of this embodiment. The same components as those in FIG. 4 are denoted by the same reference numerals and description thereof will be omitted. Hereinafter, portions different from FIG. 4 will be mainly described.

  In FIG. 1, reference numeral 18 denotes a symmetric deformation triangular wave generating means for reducing the number of switchings as a virtual inverter carrier generating means. An intermediate phase voltage (intermediate voltage) among R, S, and T phases is input. The deformed triangular wave generating means 18 creates a symmetrical deformed triangular wave based on these inputs and outputs it as a carrier on the virtual inverter side.

As described above, the upper arm switching and the lower arm switching occur depending on the polarity of the intermediate voltage, and the number of times of switching changes. Therefore, in this embodiment, the intermediate voltage detected from the power supply voltage of each phase is reduced symmetrically for the number of times of switching. The triangular wave generating means 18 is input, and the generating means 18 generates carriers depending on the intermediate voltage to obtain the PWM pulse of the virtual inverter.
Hereinafter, the principle of generating PWM pulses and the principle of reducing the number of switching operations according to the present embodiment will be described.

FIG. 2 is a diagram illustrating a virtual rectifier carrier, a virtual rectifier PWM pulse, a virtual inverter carrier, a virtual inverter upper arm PWM pulse, a PWM pulse of a matrix converter at the time of upper arm switching, and the like.
The reason why the number of times of switching increases at the time of switching the upper arm is that a pulse change accompanying a PWM pulse change of the virtual rectifier appears in the PWM pulse of the matrix converter 20 as is apparent from the above-described ad of FIG.
On the other hand, in the lower arm switching, the PWM pulse change of the virtual rectifier appears when the PWM pulse of the AC switch connected to the minimum phase of the matrix converter (lower arm of the virtual inverter) is off, and the PWM of the virtual rectifier The pulse change accompanying the pulse change does not appear in the PWM pulse of the matrix converter.

That is, if the virtual rectifier is switched when the virtual inverter PWM pulse of the same arm as the switching arm (for example, the upper arm when the upper arm is switched or the lower arm when the lower arm is switched) is OFF, the PWM pulse change of the virtual rectifier is changed. It does not appear in the PWM pulse of the matrix converter, and the switching frequency can be reduced.
Therefore, as shown in FIG. 2, for example, when the upper arm is switched when the intermediate voltage is positive, zero is set in the Up / Down counter (to be described later) as the value of the virtual inverter carrier by the interrupt process at the timing of the peak and valley of the virtual rectifier carrier. At the same time, the Up / Down timing of the virtual inverter carrier is inverted with respect to the prior art of FIG. 5 (the virtual inverter carrier is inverted 180 °). It should be noted that the inversion of the Up / Down timing is performed by switching the Up / Down count of the Up / Down counter.

As a result, as shown in FIG. 2, the turning point (top point) of the peak of the virtual inverter carrier and the PWM pulse change time of the virtual rectifier are synchronized.
As a result, the PWM pulse change of the virtual rectifier occurs only when the upper arm AC switch connected to the maximum phase is off, and the pulse change of the virtual PWM rectifier appears in the PWM pulse of the matrix converter. Absent.
Therefore, the number of times of switching of the matrix converter 20 when the upper arm is switched can be set to four as shown in FIG.

  Even if the phase of the virtual inverter carrier is reversed, if the carrier waveform is a straight line, the carrier comparison method uses an on / off ratio according to the output voltage command during one switching cycle (one cycle of the virtual rectifier carrier or virtual inverter carrier). Therefore, an output voltage corresponding to the output voltage command can be obtained.

  Although not shown in the figure, when switching the lower arm where the intermediate voltage is negative, the virtual inverter carrier value is set according to the pulse width of the virtual rectifier PWM pulse as a value of the virtual inverter carrier by interrupt processing of the peak and valley timing of the virtual rectifier carrier The peak value may be set in the Up / Down counter and the virtual inverter carrier may be inverted by 180 ° with respect to FIG.

Next, FIG. 3 is a block diagram showing a hardware configuration of the symmetric deformation triangular wave generating means 18 for reducing the number of switching times in FIG.
In FIG. 3, reference numeral 181 denotes an intermediate voltage positive / negative discrimination circuit to which an intermediate voltage is inputted, 182 denotes an XOR (exclusive OR) circuit to which an up / down signal of the virtual rectifier carrier and a virtual rectifier PWM pulse are inputted, and 183 denotes an XOR circuit. A NOT circuit to which the output of 182 is added, 184 is a selector that switches between the output of the XOR circuit 182 and the output of the NOT circuit 183 in accordance with the polarity of the intermediate voltage, and outputs either of them as a virtual inverter carrier Up / Down signal, Reference numeral 185 denotes an Up / Down counter which counts Up / Down according to the virtual inverter carrier Up / Down signal from the selector 184 and receives the peak value of the virtual rectifier carrier and zero, and the output of the counter 185 is Input to the comparison means 15 as a virtual inverter carrier That.
Reference numerals 186 and 187 denote voltage command registers that hold the output voltage command of the virtual inverter. Reference numeral 188 denotes a selector that selects the registers 186 and 187 in accordance with the virtual rectifier PWM pulse and outputs a predetermined voltage command to the comparison means 15. It is.

Here, conventionally, the virtual inverter carrier Up / Down is determined using the virtual rectifier PWM pulse and the virtual rectifier carrier Up / Down signal.
However, in the present embodiment, in order to reduce the number of times of switching, Up / Down of the inverter carrier is inverted according to the polarity of the intermediate voltage, and the Up / Down counter 185 is interrupted for each interrupt synchronized with the peak of the virtual rectifier carrier. Then, the inverter carrier peak value is set to a peak value or zero according to the PWM pulse width of the virtual rectifier.
However, Up / Down is always switched at the peak time of the carrier so that the carrier does not jump when the virtual inverter carrier is inverted.

In the lower part of FIG. 2, the virtual rectifier carrier Up / Down signal, the output of the XOR circuit 182 and the output of the NOT circuit 183 in FIG. 3 are shown together. The output of the illustrated XOR circuit 182 and the output of the NOT circuit 183 are selected by the selector 184 according to the polarity of the intermediate voltage, and the selected signal is used as the Up / Down signal of the virtual inverter carrier to generate the illustrated virtual inverter carrier. Is done. Here, the example of FIG. 2 is an example in which the selector 184 selects the output of the NOT circuit 183 and uses this output as the Up / Down signal of the virtual inverter carrier.
Although not shown, in the example of FIG. 2, the number of times of switching in one switching cycle is 4 even when the lower arm is switched.

It is a block diagram which shows embodiment of this invention. It is explanatory drawing, such as each carrier at the time of upper arm switching in the embodiment of this invention, and a PWM pulse. It is a block diagram of the switching frequency reduction symmetrical deformation | transformation triangular wave generation means in FIG. It is a block diagram which shows a prior art. It is explanatory drawing of the virtual rectifier pulse, virtual inverter pulse, etc. in a prior art. It is a circuit diagram for the output one phase of a matrix converter.

Explanation of symbols

11: Trapezoidal wave command generating means 12: Carrier generating means 13, 15: Comparison means 16: On / off ratio extracting means 17: PWM pulse synthesizing means 18: Switching frequency reduction symmetrical deformation triangular wave generating means 20: Matrix converter 181: Intermediate voltage positive / negative discrimination Circuit 182: XOR circuit 183: NOT circuit 184, 188: Selector 185: Up / Down counter 186, 187: Voltage command register S1 to S9: AC switch

Claims (5)

A plurality of bidirectional AC switches composed of at least two unidirectional semiconductor switches capable of controlling a unidirectional current are provided to form an AC switch group, and the AC switch group connected to each phase of the multiphase AC power A control apparatus for an AC / AC direct converter for directly converting a polyphase AC voltage into a polyphase AC voltage having an arbitrary magnitude and frequency, each PWM pulse for a virtual rectifier and a virtual inverter assumed in the direct converter PWM pulse synthesizing means for synthesizing and supplying to the direct converter, and virtual inverter carrier generating means for generating a carrier generated according to the on / off ratio of the PWM pulse of the virtual rectifier as a virtual inverter carrier. In the control device of the converter,
The virtual inverter carrier generating means is
The up / down signal of the virtual inverter carrier as the second Up / Down signal generated from the Up / Down signal of the virtual rectifier carrier as the first Up / Down signal and the virtual rectifier PWM pulse is supplied to each phase power supply. Means for reversing the voltage according to the voltage polarity of the intermediate voltage phase,
Means for generating a virtual inverter carrier by performing a counting operation by setting zero or a predetermined peak value at a peak of the virtual rectifier carrier according to the second Up / Down signal;
An AC / AC direct converter control device comprising: In the control apparatus for an AC / AC direct converter according to claim 1 ,
Said second Up / Down signal, the first Up / Down signal and the virtual rectifier AC AC direct conversion device of the control device, characterized that you generated by exclusive OR of the PWM pulse. In the control apparatus for an AC / AC direct converter according to claim 1 or 2,
The control device for an AC / AC direct converter, wherein the predetermined peak value is a value corresponding to a pulse width of a virtual rectifier PWM pulse . In the control apparatus of the alternating current direct current converter as described in any one of Claims 1-3,
The control apparatus for an AC / AC direct converter , wherein the number of times of switching in one switching cycle of the direct converter is the same regardless of whether the voltage polarity of the intermediate voltage phase is positive or negative . In the control apparatus of the alternating current alternating current direct converter as described in any one of Claims 1-4,
A control apparatus for an AC / AC direct converter, wherein the AC / AC direct converter is a matrix converter that performs three-phase to three-phase direct conversion .

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