WO2014073247A1

WO2014073247A1 - Power conversion device

Info

Publication number: WO2014073247A1
Application number: PCT/JP2013/070873
Authority: WO
Inventors: 東　聖
Original assignee: 三菱電機株式会社
Priority date: 2012-11-07
Filing date: 2013-08-01
Publication date: 2014-05-15
Also published as: JPWO2014073247A1; JP5819010B2

Abstract

A three-phase inverter (10) is provided with a switching unit (1) in which three legs are connected in a three-phase bridge, and an auxiliary circuit (23) composed of a single leg. A pseudo-impedance (21, 22) is connected to the auxiliary circuit (23). A first control unit (1) changes a switching pattern which has been temporarily set so that a zero-vector interval (t1), in which all upper arms of the switching unit (1) are on in a single cycle, and a zero-vector interval (t7), in which all lower arms are on, are the same length so as to offset the switching pattern of a first phase having the longest on-interval or a second phase having the shortest on-interval to eliminate the zero-vector interval and control the switching operation of the switching unit (1). The second control unit (24) controls the switching operation of the auxiliary circuit (23) so as to be the reverse of the third-phase switching operation of the switching unit (1).

Description

Power converter

The present invention relates to a power conversion device, and more particularly to a power conversion device capable of reducing a leakage current generated by switching accompanying power conversion.

In an inverter as a conventional power converter, a series circuit in which first and second switches are connected in series is connected in a three-phase bridge, and the switching operation of the first and second switches of each phase is performed by a space vector method. There is a two-level inverter that converts a DC voltage into a three-phase AC voltage by controlling. A leakage current flows between the neutral point of the AC motor and the inverter through the floating capacity of the AC motor and the inverter due to the switching, and generates common mode noise.

In order to reduce such leakage current, for example, a method of reducing leakage current by changing the switching pattern of the inverter in a certain cycle has been proposed. Specifically, for example, the leakage current is canceled by shifting the switching operation of the U phase that is the phase with the longest on-time in a certain cycle to reverse the switching operation of the W phase that is the phase with the shortest on-time. (For example, refer nonpatent literature 1).

The conventional inverter is configured as described above, and even if the switching operations of the U phase and the W phase are reversed, a leakage current is generated due to the switching operation of the remaining phase, so that the leakage current cannot be sufficiently reduced. was there. This is a problem that is required to be further solved by the increase in the switching frequency of the inverter accompanying the recent improvement in performance of the switching element.

The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a power conversion device capable of reducing leakage current generated by switching associated with power conversion.

The power converter according to the present invention includes a switching circuit, a control device that controls the switching circuit, and an auxiliary device. In the switching circuit, three legs each having an upper arm and a lower arm are connected in a three-phase bridge, and the AC side is connected to an AC side device via a connection line. The control device switches each phase so that a first zero vector period in which all the upper arms are turned on and a second zero vector period in which all the lower arms are turned on have the same length in one cycle. Temporarily setting a pattern and shifting the first phase switching pattern of the first phase having the longest on period or the switching pattern of the second phase having the shortest on period in the temporarily set switching pattern of each phase. The switching pattern is changed so as to eliminate the zero vector period, and the switching operation of the switching circuit is controlled. The auxiliary device has an auxiliary circuit, a simulated impedance, and an auxiliary control device. The auxiliary circuit includes a first switch and a second switch connected in series, and both ends thereof are connected in parallel to the leg. The simulated impedance is obtained by simulating the impedance between the connection line and the AC-side device, and is inserted between the connection between the first switch and the second switch and the ground. The auxiliary control device controls the switching operation of the auxiliary circuit so as to be opposite to the switching operation of the remaining third phase excluding the first phase and the second phase of the switching circuit.

Since the power conversion device according to the present invention is configured as described above, it is possible to reduce the leakage current generated by switching associated with power conversion.

It is a figure which shows the structure of the three-phase inverter by Embodiment 1 of this invention. It is a figure which shows the switching pattern of the three-phase inverter by Embodiment 1 of this invention. It is a figure which shows the switching pattern and leakage current of the three-phase inverter by a 1st comparative example. It is a wave form diagram of each phase voltage and common mode voltage in the 1st comparative example. It is a figure which shows the locus | trajectory of the flux linkage number vector given to an alternating current motor in a 1st comparative example. It is a figure which shows the voltage vector and flux linkage number vector in a three-phase inverter. It is a figure which shows the switching pattern and leakage current of the three-phase inverter by a 2nd comparative example. It is a wave form diagram of each phase voltage and common mode voltage by the 2nd comparative example. It is a figure which shows the locus | trajectory of the flux linkage number vector given to an alternating current motor in Embodiment 1 of this invention. It is a figure which shows the modification of the switching pattern of the three-phase inverter by Embodiment 1 of this invention. It is a figure which shows the switching pattern and leakage current of the three-phase inverter by a 3rd comparative example. It is a wave form diagram of each phase voltage and common mode voltage in the 3rd comparative example. It is a figure which shows the locus | trajectory of the flux linkage number vector given to an alternating current motor in the modification of Embodiment 1 of this invention. It is a figure which shows the structure of the three-phase inverter by Embodiment 2 of this invention. FIGS. 15A and 15B are diagrams showing a one-phase portion of a switching unit according to Embodiment 2 of the present invention, FIG. 15A is a diagram of a case where a positive current flows, and FIG. 15B is a diagram of a case where a negative current flows. is there. It is a figure for demonstrating the dead time period in the switching pattern of the three-phase inverter by Embodiment 2 of this invention. It is a figure which shows the switching pattern of the three-phase inverter by Embodiment 2 of this invention. It is a figure which shows the switching pattern of the three-phase inverter by Embodiment 2 of this invention, and the switching pattern of each arm of an auxiliary circuit.

Embodiment 1 FIG.
FIGS. 1 to 13 are diagrams for explaining the first embodiment for carrying out the present invention. FIG. 1 is a configuration diagram showing a configuration of a three-phase inverter, and FIG. 2 is a diagram showing a switching pattern of the three-phase inverter. It is. 3 to 5 are diagrams showing a first comparative example, FIG. 3 is a diagram showing a switching pattern and a leakage current of a conventional three-phase inverter as a first comparative example, and FIG. 4 is a three-phase diagram of FIG. FIG. 5 is a diagram showing a waveform diagram of each phase voltage and common mode voltage of the inverter, and FIG. 5 is a diagram showing a locus of flux linkage vector in the three-phase inverter of FIG. FIG. 6 is a diagram showing a voltage vector and a flux linkage vector in a three-phase inverter.
7 and 8 are diagrams showing a second comparative example, FIG. 7 is a diagram showing a switching pattern and a leakage current of the three-phase inverter according to the second comparative example, and FIG. 8 is a diagram of the three-phase inverter of FIG. It is a figure which shows the wave form diagram of each phase voltage and a common mode voltage. FIG. 9 is a diagram showing the trajectory of the flux linkage number vector in the three-phase inverter according to Embodiment 1 of the present invention, and is also a diagram showing the trajectory of the flux linkage number vector according to the second comparative example.
FIG. 10 is a diagram showing a switching pattern of a three-phase inverter which is a modification of the first embodiment. 11 and 12 are diagrams showing a third comparative example, FIG. 11 is a diagram showing a switching pattern and a leakage current of a three-phase inverter according to the third comparative example, and FIG. 12 is a diagram showing each of the three-phase inverters of FIG. It is a figure which shows the wave form diagram of a phase voltage and a common mode voltage. FIG. 13 is a diagram showing the trajectory of the flux linkage number vector in the three-phase inverter according to the modification of the first embodiment of the present invention, and is also a diagram showing the trajectory of the flux linkage number vector according to the third comparative example.

In FIG. 1, a three-phase inverter 10 as a power conversion device includes a switching unit 1 as a switching circuit, a first control unit 7 as a control device that controls the switching unit 1, and an auxiliary device 20.
The switching unit 1 has a DC side connected to the smoothing capacitor 2 and an AC side connected to an AC motor 6 as an AC side device via a wiring 5. A DC voltage is supplied to the switching unit 1 from a converter (not shown) via a smoothing capacitor 2. The wiring 5 is expressed by the impedance between the inductor and the resistor. Radiating fins 3 are provided on the upper arm and lower arms 1a to 1f (details will be described later) of the switching unit 1. A stray capacitance 4 exists between the radiation fin 3 and the upper and lower arms 1a to 1f.

The switching unit 1 is composed of three-phase legs of U, V, and W phases. The U phase is composed of a leg in which an upper arm 1a and a lower arm 1b are connected in series, the V phase is composed of a leg in which an upper arm 1c and a lower arm 1d are connected in series, and the W phase is an upper phase. The arm 1e and the lower arm 1f are configured by legs connected in series, and a three-phase AC motor 6 is connected to a connection point of each arm via a wiring 5. Each arm 1a to 1f has a transistor such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET as a switching element and a diode connected in reverse parallel thereto, and changes the voltage applied to the AC motor 6 by the switching operation of the transistor. Let The first control unit 7 includes a microprocessor (not shown), and the control of the switching unit 1 by the first control unit 7 is performed on a program incorporated in the microprocessor.

The auxiliary device 20 includes a first impedance 21, a second impedance 22, an auxiliary circuit 23, and a second control unit 24 as an auxiliary control device. The auxiliary circuit 23 includes a leg in which an upper arm 23 a as a first switch and a lower arm 23 b as a second switch are connected in series, and is connected in parallel with each leg of the switching unit 1. Each

arm

23a, 23b has a transistor such as an IGBT or a MOSFET and a diode connected in antiparallel thereto. A series connection body of the first impedance 21 and the second impedance 22 is inserted as a simulated impedance between a connection point between the upper arm 23a and the lower arm 23b and the ground.
The first impedance 21 is an impedance that simulates one phase of the wiring 5, and the second impedance 22 is an impedance that simulates one phase of the AC motor 6.
The second control unit 24 has a microprocessor (not shown). The control of the auxiliary circuit 23 by the second control unit 24 is performed on a program incorporated in the microprocessor.

Next, the operation of the three-phase inverter 10 will be described. FIG. 2 shows the switching pattern of each phase in a certain cycle T, that is, the U, V, W phase of the switching unit 1 and the X phase which is the leg of the auxiliary circuit 23.
Prior to the description of the operation by the switching pattern of FIG. 2, the operation when a conventional general three-phase inverter without the auxiliary circuit 23 is connected to an AC motor will be described as a first comparative example. For example, in one cycle T, the voltage of each phase of U, V, and W is controlled with a switching pattern as shown in FIG. In FIG. 3, periods t1 and t7 are called zero vector periods, and no voltage is generated between the lines of the AC motor. First, as the first zero vector period, the zero vector period t1 in which all lower arms are turned on is set at two places, the beginning and end of one cycle T, and the center part of the one cycle T (the previous T / 2 period As the second zero vector period at the end and the beginning of the subsequent T / 2 period, two zero vector periods t7 in which all the upper arms are turned on are set. Here, the zero vector period t1 and the zero vector period t7 have the same length.

FIG. 4 shows the voltages of the U, V, and W phases and the potential at the neutral point of the AC motor, that is, the common mode voltage. Note that the voltage of the DC power supply is 1.0. With the switching operation of the three-phase inverter, the common mode voltage changes between 0 and 1.0 as shown in FIG. The trajectory of the flux linkage vector given to the AC motor is as shown in FIG. 5 in the one cycle, and the zero vector φ0 is given at the start point St of one cycle, and thereafter φ1, φ2, φ7, φ2 , Φ1, φ0 (where φ0 and φ7 are zero vectors) in this order, and the start point St and the end point End are on one circular locus Cr. In FIG. 5, zero vectors φ0 and φ7 are represented by black circles.
FIG. 6 shows the voltage vector Vn and the flux linkage number vector φn in the three-phase inverter. The transistors constituting the arm of each phase perform switching operation six times in one cycle, and during the switching operation, the leakage current as shown in FIG. 3 is caused by the AC motor and the three-phase inverter through the ground floating capacity of the AC motor. Flows between the neutral point and the three-phase inverter, generating common mode noise.

In order to reduce such leakage current, for example, as described in the background art, a method of reducing leakage current by changing the switching pattern of the inverter has been proposed. Specifically, for example, as in the second comparative example shown in FIG. 7, the switching operation of the U phase (first phase), which is the phase with the longest on time in a certain cycle T, is shifted to the phase with the shortest on time. By reversing the switching operation of a certain W phase (second phase), the leakage current is canceled out. The switching pattern shown in FIG. 7 is determined as follows. The second comparative example is the same as the U, V, W phase switching pattern (see FIG. 2) of the switching unit 1 of the three-phase inverter 10 according to the first embodiment.

First, a switching pattern similar to that shown in FIG. 3 is temporarily set. Next, the U-phase pulse generation period is shifted as shown in FIG. 2 so that the zero vector periods t1 and t7 are eliminated, so that the U-phase off period is opposite to the W-phase on period. That is, the switching-off timing in the U phase that is the phase with the longest on period and the switching on timing in the W phase that is the phase with the shortest on period are combined, and the switching on timing in the U phase and the W phase And the switching-off timing at. In this way, switching of the switching unit 1 is controlled by changing the switching pattern.
Here, the output voltage of the three-phase inverter does not change as an average value.

Thus, by shifting the switching pattern of one phase, the switching (timing) of the U phase and the W phase is synchronized and switched in opposite directions. For this reason, potential fluctuations associated with the switching of the U phase and the W phase are offset, and the leakage current is also canceled. As shown in FIG. 7, the leakage current is only generated during the V-phase switching operation, and is reduced to 1/3 compared to the first comparative example.

FIG. 8 shows the voltages of the U, V, and W phases and the common mode voltage according to the second comparative example. In FIG. 8, when the voltage of the DC power supply is 1.0, the common mode voltage changes between about 0.66 and about 0.33 by the V-phase switching operation, and the voltage fluctuation is the same as that of the first comparative example. In comparison, it is reduced to 1/3.
7 is the same as that of the three-phase inverter 10 according to the first embodiment of the present invention, and the locus of the flux linkage number vector given to the AC motor when switching is performed with the switching pattern according to the second comparative example shown in FIG. 9 shows.
In FIG. 9, the flux linkage vector φ1, φ2, φ4, φ2, φ1 changes in order from the start point St of one cycle, and at the end point End, the end point in the three-phase inverter of the first comparative example shown in FIG. Same as End.

In the second comparative example, leakage current due to V-phase switching still remains. In this embodiment, the auxiliary device 20 including the auxiliary circuit 23 is provided, and the second control unit 24 performs switching control of the leg (X phase) of the auxiliary circuit 23.
As shown in FIG. 2, the U, V, and W phases of the switching unit 1 of the three-phase inverter 10 are controlled by the first control unit 7 with the same switching pattern as in the second comparative example described above, and the auxiliary circuit 23 The X phase is controlled by the second control unit 24 as follows. That is, the upper arm 23a and the lower arm 23b of the auxiliary circuit 23 are switched in a pattern opposite to the V-phase switching pattern in synchronization with the V-phase switching that is the third phase. Thereby, the leakage current due to the V-phase switching and the leakage current due to the X-phase switching cancel each other, and the leakage current flowing through the AC motor 6 is almost completely canceled out.

As a modification, the switching pattern may be as shown in FIG. That is, in FIG. 10, the switching operation of the W phase (second phase) that is the phase with the shortest on time in one cycle T is shifted to switch the U phase (first phase) that is the phase with the longest on time. The operation is reversed. Further, the X phase by the auxiliary circuit 23 is similarly switched in a switching pattern opposite to the V phase in synchronization with the V phase switching.
Also in this case, the leakage current due to the W-phase switching and the leakage current due to the U-phase switching cancel each other, and further, the leakage current due to the V-phase switching and the leakage current due to the X-phase switching cancel each other. Almost no leakage current flows through.

FIG. 11 shows a third comparative example which is a comparative example for the modification shown in FIG. The third comparative example does not have the X phase of the switching pattern of FIG. 10 and is a switching pattern of only the U, V, and W phases. In this case, the common mode voltage between the AC motor and the ground is as shown in FIG. 12, the voltage fluctuation is reduced to 1/3 as compared with the first comparative example, and the leakage current shown in FIG. Although it is reduced to 1/3 as compared with one comparative example, it remains.
The trajectory of the flux linkage vector at this time is the same in the modified example shown in FIG. 10 and the third comparative example shown in FIG. 11, as shown in FIG. 13, and the start point St and end point End of one cycle Are at the same position on the same circular locus Cr as shown in FIG.

Thus, in a three-phase inverter, there is an effect that leakage current can be reduced by a simple method of shifting a certain one-phase switching pattern. Further, as shown in FIGS. 5, 9, and 12, the output voltage of the three-phase inverter, that is, the start point St and the end point End of the flux linkage number vector do not change, so that a desired voltage is given to the AC motor 6. There is an effect that can be. Further, since only the switching pattern is shifted, there is an effect that the restriction on the output voltage is small. Further, the operation of the auxiliary circuit 23 can reduce the leakage current flowing through the AC motor 6 almost completely, that is, to a sufficient level.

In this embodiment, the auxiliary circuit 23 is connected to a simulated impedance by the first impedance 21 and the second impedance 22. In particular, the second impedance 22 expresses the floating impedance of the AC motor 6 as a load, and is generally a high impedance. Therefore, the current output from the auxiliary circuit 23 is sufficiently smaller than the current output from the switching unit 1. For this reason, the upper arm 23a and the lower arm 23b constituting the auxiliary circuit 23 can be configured by elements having a small current capacity, and a small and inexpensive auxiliary circuit 23 can be realized.

Note that the switching pattern shown in FIG. 2 may be a switching pattern in which all the U phases are turned on and all the W phases are turned off. In this case as well, the same effect can be obtained by performing the X-phase switching in a pattern opposite to the V-phase switching pattern in synchronization with the V-phase switching.

Embodiment 2. FIG.
14 to 18 show the second embodiment. FIG. 14 is a block diagram showing the configuration of the three-phase inverter 30 according to the second embodiment. FIG. 15 shows one phase of the switching unit 1. FIG. In particular, FIG. 15A shows a case where a positive current indicated by an arrow flows, and FIG. 15B shows a case where a negative current flows. FIG. 16 is a diagram for explaining a dead time period in the switching pattern of the three-phase inverter, and FIG. 17 is a diagram showing a switching pattern of the three-phase inverter 30 according to the second embodiment.
As shown in FIG. 14, the three-phase inverter 30 is provided with a third control unit 37 as a control device that controls the switching unit 1. Since other configurations are the same as those of the first embodiment shown in FIG. 1, the corresponding components are denoted by the same reference numerals and description thereof is omitted.

Generally, in inverter switching, a dead time period Td is set in order to prevent occurrence of a short-circuit current due to simultaneous conduction of the upper arm 1a and the lower arm 1b shown in FIG. Here, each phase voltage in the dead time period Td depends on the direction of the current. As shown in FIG. 15A, when the current polarity is positive, the diode on the lower arm 1b side conducts during the dead time period Td, and the low potential side voltage is output. On the other hand, as shown in FIG. 15B, when the current polarity is negative, the diode on the upper arm 1a side conducts during the dead time period Td, and the high potential side voltage is output.

The actual output voltage when the dead time period Td is set in the switching pattern according to the first embodiment will be described with reference to FIG. In the figure, the U phase and the W phase are the case of FIG. 15A, and the current polarity is positive. At this time, since there is a dead time period Td when the ON state is switched from the

lower arms

1b and 1f to the

upper arms

1a and 1e, the voltage pulse pattern is missing in the shaded areas A1 and A3 in the figure, The voltage waveform is not rectangular according to the switching pattern. When switching from the

upper arms

1a, 1e to the

lower arms

1b, 1f, the diodes on the

lower arms

1b, 1f are automatically turned on as soon as the dead time period Td is entered, so that the pulse pattern is not lost.

On the other hand, the V phase is the case of FIG. 15B, and the current polarity is negative. At this time, there is a dead time period Td when the ON state is switched from the upper arm 1c to the lower arm 1d. Therefore, an extra voltage pulse pattern is generated in the voltage region of the shaded portion A2 in the figure, and the switching pattern It does not become a rectangular voltage waveform. When switching from the lower arm 1d to the upper arm 1c, the diode on the upper arm 1c side is automatically turned on as soon as the dead time period Td is entered, so that the pulse pattern is not excessively generated.

As described above, since the actual output voltage due to the pulse pattern is shifted due to the presence of the dead time period Td, the leakage current cannot be completely canceled. Therefore, in the second embodiment, the third control unit 37 corrects the pulse pattern according to the direction of the current as shown in FIG. 17 in order to eliminate the influence of the dead time period Td. For the U phase and the W phase, the ON time is increased by the width corresponding to the dead time period Td indicated by the hatched portions B1 and B3. That is, the ON timing is advanced by the dead time period Td. For the V phase, the ON time is shortened by a width corresponding to the dead time period Td indicated by the hatched portion B2. That is, the OFF timing is advanced by the dead time period Td. The widths of the hatched portions B1, B2, and B3 and the widths of the hatched portions A1, A2, and A3 are all the same and correspond to the dead time period Td.
As described above, the dead time period Td is set so that the upper arm and the lower arm are not simultaneously turned on. Based on the dead time period Td, the dead time period Td is set according to the direction of the current flowing in the upper arm and the lower arm. Is corrected as shown in FIG.

This makes it possible to further reduce the leakage current because the timing at which the output voltage actually changes matches between the U, V, W, and X phases.

The auxiliary circuit 23 is connected to a simulated impedance by the first impedance 21 and the second impedance 22. In particular, the second impedance 22 expresses the floating impedance of the AC motor 6 as a load, and is generally a high impedance. Therefore, the current output from the auxiliary circuit 23 is sufficiently smaller than the current output from the switching unit 1. In the auxiliary circuit 23, a current with high-frequency vibration flows only at the switching timing, and no current flows thereafter.
For this reason, in the case of the auxiliary circuit 23, unlike the switching unit 1, it is not necessary to determine the switching pattern in consideration of the output voltage in the dead time period Td according to the current polarity. That is, by switching the upper arm 23a and the lower arm 23b of the auxiliary circuit 23 as shown in FIG. 18, a desired output voltage can be obtained for the X phase.

In the present embodiment, the IGBT is illustrated and described using the switching elements constituting the arms 1a to 1f as transistors, but other semiconductor switching elements such as MOSFETs may be used.

In each of the above embodiments, the case where the power conversion device is an inverter has been shown. However, even if it is a converter, the power source and the load are switched, and the power transmission direction is changed, and the same effect can be obtained.

In the present invention, within the scope of the invention, the above-described embodiments can be freely combined, or each embodiment can be appropriately changed or omitted.

Claims

A power conversion device having a switching circuit, a control device for controlling the switching circuit, and an auxiliary device,
In the switching circuit, three legs each having an upper arm and a lower arm are connected in a three-phase bridge, and the AC side is connected to an AC side device via a connection line.
The control device switches each phase so that a first zero vector period in which all the upper arms are turned on and a second zero vector period in which all the lower arms are turned on have the same length in one cycle. Temporarily setting a pattern and shifting the first phase switching pattern of the first phase having the longest on period or the switching pattern of the second phase having the shortest on period in the temporarily set switching pattern of each phase. The switching pattern is changed so as to eliminate the zero vector period, and the switching operation of the switching circuit is controlled.
The auxiliary device has an auxiliary circuit, a simulated impedance, and an auxiliary control device,
The auxiliary circuit is composed of a first switch and a second switch connected in series, and both ends thereof are connected in parallel to the leg,
The simulated impedance is a simulation of the impedance of the connection line and the AC side device, and is inserted between the connection between the first switch and the second switch and the ground,
The auxiliary control device controls the switching operation of the auxiliary circuit so as to be opposite to the switching operation of the remaining third phase excluding the first phase and the second phase of the switching circuit. apparatus.
The control device combines the switching-off timing in the first phase with the switching-on timing in the second phase, and the switching-on timing in the first phase and the switching-off timing in the second phase. The power conversion device according to claim 1, wherein
The control device sets a dead time period so that the upper arm and the lower arm are not simultaneously turned on, and the control device sets the dead time period according to the direction of the current flowing in the upper arm and the lower arm based on the dead time period. The power converter according to claim 1 or 2, which corrects the changed switching pattern.
4. The auxiliary control device according to claim 3, wherein a dead time period is provided immediately before the timing of changing the output voltage of the auxiliary circuit so that the first switch and the second switch are not turned on simultaneously. The power converter described.