WO2020105169A1

WO2020105169A1 - Electric power conversion device

Info

Publication number: WO2020105169A1
Application number: PCT/JP2018/043167
Authority: WO
Inventors: 竹内　勇人; 研一福野; 時男中島; 拓志地道
Original assignee: 三菱電機株式会社
Priority date: 2018-11-22
Filing date: 2018-11-22
Publication date: 2020-05-28
Also published as: JP6636219B1; JPWO2020105169A1

Abstract

An electric power conversion device (3) comprises: an AC-DC converter unit (31) having semiconductor switching elements (311); an AC filter unit (32) that has a filter capacitor part (321) made up of three capacitors connected in a star connection and that is connected to AC terminals of the AC-DC converter unit (31); a DC filter unit (33) that has a capacitor part (331) made up of two capacitors connected in series and that is connected to DC terminals of the AC-DC converter unit (31); and a controller (34) that controls an on-off state of the semiconductor switching elements (311). The neutral point of the three capacitors connected in the star connection and the node of the two capacitors connected in series are connected together without being connected to ground potential.

Description

Power converter

The present application relates to a power conversion device that converts an AC voltage into a DC voltage.

A converter that converts AC voltage into DC voltage, an inverter that converts DC voltage into AC voltage, and a capacitor connected between the converter and the inverter convert AC voltage into DC voltage, and further convert DC voltage into AC voltage. Thus, a device that drives a motor is disclosed. Then, in order to suppress the noise generated by the converter, connect a common mode reactor (common mode choke coil), and connect a neutral point of the star-connected capacitor to the ground via another capacitor. There was a technique used (for example, Patent Document 1).

JP, 2005-204438, A

Conventionally, when a converter and a filter circuit for noise suppression are used as a power conversion device for power reception of a DC distribution system, the DC bus voltage oscillates with respect to the ground potential. Therefore, there is a problem that a load device connected to the DC bus may malfunction and a ground fault detection device may malfunction.

The present application discloses a technique for solving the above problems, and prevents a malfunction of a DC load by preventing a zero-phase voltage generated by an AC / DC converter from flowing out. At the same time, the purpose is to prevent the DC bus voltage from vibrating with respect to the ground potential.

The power conversion device disclosed in the present application is a power conversion device that converts a three-phase input AC voltage into a DC voltage, and the power conversion device is star-connected to an AC / DC conversion unit having a semiconductor switching element. An AC / DC conversion unit having a filter capacitor unit having at least three capacitors, the AC filter unit being connected to each AC terminal of the AC / DC conversion unit, and the capacitor unit having at least one capacitor. A DC filter unit connected to a DC terminal of the unit, and a controller for controlling ON / OFF of the semiconductor switching element,
One end of the at least three capacitors of the filter capacitor unit is connected to a neutral point in the star connection, and the other end of the at least three capacitors is connected to each AC terminal of the AC / DC converter, One end of the at least one capacitor of the capacitor unit is connected to the positive electrode side or the negative electrode side of the DC terminal of the AC / DC converting unit, and the other end of the at least one capacitor is not grounded to the ground potential. It is connected to the neutral point.

According to the power conversion device disclosed in the present application, it is possible to prevent the zero-phase voltage generated by the AC / DC conversion unit from flowing out, and the ground voltage of the DC bus line does not vibrate. It is possible to prevent malfunction of the fault detection device.

FIG. 3 is a block configuration diagram showing a system using the power conversion device according to the first embodiment. FIG. 3 is a block diagram showing a configuration of a controller of the power conversion device according to the first embodiment. FIG. 3 is a block diagram showing a configuration of a comparison unit according to the first embodiment. 5 is a waveform diagram for explaining the operation of the controller according to the first embodiment. FIG. FIG. 3 is a zero-phase equivalent circuit diagram of the entire system when the power conversion device according to the first embodiment is used. FIG. 6 is a block configuration diagram showing a system using a power conversion device according to a second embodiment. 5 is a block diagram showing a configuration of a controller of the power conversion device according to the second embodiment. FIG. FIG. 7 is a waveform diagram for explaining the operation of the controller according to the second embodiment. FIG. 9 is a zero-phase equivalent circuit diagram of the entire system when the power conversion device according to the second embodiment is used. FIG. 9 is a circuit diagram showing a common mode reactor part in a power conversion device according to a third embodiment. FIG. 9 is a circuit diagram showing a common mode reactor part in a power conversion device according to a third embodiment. FIG. 11 is a configuration diagram showing an outline of a structure of a filter reactor portion in a power conversion device according to a third embodiment.

Embodiment 1.
FIG. 1 is a block configuration diagram showing a system using the power conversion device according to the first embodiment. The input side of the power conversion device 3 is connected to the commercial power supply 1 via the transformer 2. The output side of the power converter 3 is connected to a DC load 5 via a DC bus 4.
The commercial power supply 1 generates an alternating voltage. The frequency of this AC voltage is 50 Hz or 60 Hz. Hereinafter, this AC voltage is referred to as an input AC voltage.

Transformer 2 is grounded to ground potential 6. As a method of grounding, for example, as shown in FIG. 1, there is a method in which a contact prevention plate 21 installed between the primary winding and the secondary winding is grounded to the ground potential 6. As another method, the secondary winding may be star-connected and the neutral point thereof may be grounded to the ground potential 6. In this embodiment, the method of grounding the transformer 2 is not limited, and it is assumed that the anti-contact plate 21, the frame (not shown), and one or more locations of the winding are grounded to the ground potential 6. .. That is, the three-phase input AC voltage is supplied through the transformer 2 in which at least one place is grounded to the ground potential.

The DC load 5 has a portion that consumes electric power (indicated by a simulated load 51 in FIG. 1), and is grounded to the ground potential 6 via the capacitor 52. Like the transformer 2, a frame (not shown) may be grounded with respect to the ground potential 6.
In the present embodiment, the transformer 2 and the DC load 5 are grounded for reasons such as ensuring safety. The purpose of the present invention is to prevent the zero-phase voltage (common mode voltage) generated by the power conversion device 3 from adversely affecting the DC load 5 when there is a path through which a current flows via the ground line.
The power converter 3 includes an AC / DC converter 31, an AC filter 32, a DC filter 33, and a controller 34.

The AC / DC converter 31 is composed of six semiconductor switching elements 311 and six freewheeling diodes 312 connected in antiparallel to each semiconductor switching element 311. The AC / DC converter 31 is configured by a so-called three-phase bridge circuit. A pair of circuits in which the semiconductor switching element 311 and the freewheeling diode 312 are connected in parallel are connected in series to each other to form a leg, and the connecting portions in the two sets of circuits are AC terminals, and both ends of the leg are DC. It becomes a terminal. The DC terminals of the legs for the three phases are connected to the DC capacitor 313 and to the DC bus 4.

As the semiconductor switching element 311, a semiconductor such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is used. Further, as the DC capacitor 313, an electrolytic capacitor or a film capacitor is used.

The AC filter unit 32 is connected to the AC terminal of the AC / DC converting unit 31, and has a filter capacitor unit 321 and a filter reactor 322. In FIG. 1, in the filter capacitor unit 321, three capacitors (first capacitors) are provided for each phase and are connected by star connection. As the filter reactor 322, a three-phase reactor in which each phase is magnetically coupled to each other may be used, or three single-phase reactors may be used.
In FIG. 1, the DC filter unit 33 is connected to the DC terminal of the AC / DC converting unit 31 and is composed of a capacitor unit 331. In the capacitor section 331, two capacitors (second capacitors) are connected in series, and both ends thereof are connected to the positive electrode side and the negative electrode side of the DC terminal, respectively. That is, the capacitor section 331 has a series connection body in which two capacitors (second capacitors) are connected in series, and the series connection body is connected to the positive electrode side and the negative electrode side of the DC terminal.
A feature of this embodiment is that the neutral point of the star connection of the filter capacitor unit 321 and the connection point of the two capacitors of the capacitor unit 331 connected in series are connected to each other without being grounded to the ground potential 6. Is to be done.

The controller 34 generates a gate signal 345 and controls ON / OFF of the semiconductor switching element 311. FIG. 2 is a block diagram showing the configuration of the controller. In FIG. 2, the controller 34 generates a gate signal 345 for controlling on / off of the semiconductor switching element 311 so that the voltage of the DC bus 4 has a desired value. In the controller 34, the DC bus voltage control unit 341 first generates an input current command so that the voltage of the DC bus 4 becomes a desired value. The input current is a current flowing into the AC terminal of the AC / DC converter 31. Next, the input current control unit 342 generates a voltage command so that the input current matches the input current command. The voltage mentioned here is the voltage of the AC terminal of the AC / DC converter 31. After that, the comparison unit 343 generates the gate signal 345.

FIG. 3 is a block diagram showing the configuration of the comparison unit. The comparison unit 343 determines an ON / OFF signal of the semiconductor switching element 311 based on the voltage command. Generally, a method called PWM (Pulse Width Modulation) is used. The comparison unit 343, based on the U-phase, V-phase, and W-phase voltage commands, causes the voltage command and the output voltage (voltage at the AC terminal of the AC / DC conversion unit 31) to match in one cycle of switching. The comparator 3431 compares each phase voltage command with the carrier signal to generate the gate signal 345. Since a triangular wave signal is used as the carrier signal and each semiconductor switching element 311 is turned on / off once in one cycle of the triangular wave, the frequency of the carrier signal matches the switching frequency.

When the voltage command is larger than the carrier signal, the comparator 3431 turns on the gate signal corresponding to the positive side semiconductor switching element 311 of the corresponding phase and turns on the gate signal corresponding to the negative side semiconductor switching element 311. Is turned off by the NOT circuit 3432 (inversion circuit) in the subsequent stage. A short circuit prevention time (dead time) may be superimposed on the gate signal. Since the method of providing the short-circuit prevention time is a known technique, detailed description thereof will be omitted.

Next, the voltage command generated by the input current control unit 342 will be described as an example. The U-phase, V-phase, and W-phase voltage commands Vu *, Vv *, and Vw * can be assumed as shown in equations (1), (2), and (3) below.
Vu * = V × sinωt ・・・・・・・・・・ (1)
Vv * = V × sin (ωt-2π / 3) ... (2)
Vw * = V × sin (ωt + 2π / 3) ... (3)
Here, V is the peak voltage of each phase voltage command, ω is the angular frequency, and t is time. In this case, the average of the sum of the voltage commands for each phase, that is, the zero-phase voltage is as shown in equation (4), and the voltage command does not include the zero-phase voltage.
Vz * = (Vu * + Vv * + Vw *) / 3 = 0 ... (4)

FIG. 4 is a waveform diagram for explaining the operation of the controller 34. In FIG. 4, the voltage command and carrier signal of each phase, the positive and negative gate signals of each phase, and the AC terminal side of each phase are shown. To the AC terminal side and the zero-phase voltage (common mode voltage) actually output to the AC terminal side are shown. In FIG. 4, FIG. 4A is a waveform diagram showing the relationship between each phase voltage command and the carrier signal. In FIG. 4A, a is a carrier signal, b is a U phase voltage command, c is a V phase voltage command, and d is W. The respective waveforms of the phase voltage command are shown.
FIG. 4B shows the waveform of the U-phase positive side gate signal. FIG. 4C shows the waveform of the U-phase negative side gate signal. FIG. 4D shows the waveform of the V-phase positive side gate signal. FIG. 4E shows the waveform of the V-phase negative side gate signal.
FIG. 4F shows the waveform of the W-phase positive side gate signal. FIG. 4G shows the waveform of the W-phase negative side gate signal. FIG. 4H shows the waveform of the U-phase output voltage. FIG. 4I shows the waveform of the V-phase output voltage. FIG. 4J shows the waveform of the W-phase output voltage. FIG. 4K shows the waveform of the common mode voltage.

As can be seen from the zero-phase voltage (common mode voltage) of FIG. 4K, the zero-phase voltage of each phase command is zero as described above, but the zero-phase voltage of the output voltage based on switching is the carrier signal a. The frequency, that is, the zero-phase voltage having a frequency component substantially the same as the switching frequency is included.
When the structure according to the present embodiment is not used, the zero-phase voltage causes a zero-phase current to flow through the ground wire of the transformer 2 and the DC load 5, causing a malfunction of the DC load 5 and a ground fault detection device (not shown). there is a possibility. Further, the zero-phase voltage may vibrate the ground potential of the voltage of the DC bus 4 and induce a malfunction of the DC load 5.

FIG. 5 is a diagram showing a zero-phase equivalent circuit of the entire system when the power conversion device 3 according to the first embodiment is used. The zero-phase equivalent circuit includes a stray capacitance 2E of the transformer 2, a zero-phase impedance 321E of the filter capacitor unit 321 in the AC filter unit 32, a zero-phase impedance 322E of the filter reactor 322, a zero-phase voltage source 31E, and a capacitor in the DC filter unit 33. It is represented by the zero-phase impedance 331E of the portion 331 and the ground capacitance 52E of the DC load 5. Here, the zero-phase voltage source 31E is equivalent to the zero-phase voltage (common mode voltage) shown in FIG. 4 (FIG. 4K).

In the filter configuration according to the present embodiment, a closed loop is configured by the zero-phase voltage source 31E, the zero-phase impedance 322E of the filter reactor 322, the zero-phase impedance 321E of the filter capacitor unit 321 and the zero-phase impedance 331E of the capacitor unit 331. Therefore, the zero-phase current generated by the zero-phase voltage source 31E does not flow out. Furthermore, since the filter capacitor section 321 and the capacitor section 331 are not grounded with respect to the ground potential, the ground potential of the DC bus bar 4 does not vibrate.

Further, the resonance frequency of the zero-phase impedance of the filter circuit configured by the DC filter unit 33 and the AC filter unit 32 can be made lower than the switching frequency when turning on / off the semiconductor switching element 311.
The frequency of the zero-phase voltage source 31E is the same as the switching frequency. Therefore, if the resonance frequency obtained by the inductance value and the capacitance value in the filter reactor 322, the filter capacitor unit 321, and the capacitor unit 331 is set to be smaller than the switching frequency, a large damping effect can be obtained. Since it is necessary to attenuate the same component as the switching frequency, a large damping effect can be obtained by setting the resonance frequency below this frequency component. That is, the relationship between the resonance frequency and the attenuation in the filter including LC is based on the principle of a general electric circuit.

Although FIG. 1 shows the case where two capacitors are used as the capacitor section 331, as can be seen from the equivalent circuit of FIG. 5, the filter capacitor section 321 and the capacitor section 331 are connected in series with respect to the current flow path. Therefore, only one capacitor may be connected between the positive electrode side or the negative electrode side of the DC bus bar 4 and the neutral point of the filter capacitor section 321. However, in these cases, since it is necessary to use a capacitor having good high frequency characteristics as the DC capacitor 313, it is more effective to use the configuration of FIG. 1 as much as possible.

As described above, the power converter according to the first embodiment has the filter capacitors in the AC filter unit 32 and the DC filter unit 33, respectively, and the neutral point or the connection point of the filter capacitors is not grounded with respect to the ground potential. It is connected to the. Therefore, it is possible to prevent the zero-phase voltage generated by the AC / DC converting unit 31 from flowing out, and to suppress the malfunction of the DC load 5.

The configurations of the AC filter unit 32 and the DC filter unit 33 illustrated in FIG. 1 are merely examples, and other configurations may be used. In the filter capacitor section 321 of the AC filter section 32 shown in FIG. 1, one capacitor is provided for each phase, but the AC filter section 32 includes at least three star-connected capacitors. Instead, one capacitor for each phase may be replaced with a plurality of capacitors connected in series. Also, as for each capacitor that constitutes the capacitor section 331 of the DC filter section 33, a plurality of capacitors connected in series may be used instead of one capacitor.
Further, in the capacitor unit 331 of FIG. 1, a series connection body composed of two capacitors is connected to the positive electrode side and the negative electrode side of the DC terminal of the AC / DC conversion unit 31, but the capacitor unit 331 is a single capacitor. And one end of this capacitor is connected to either the positive electrode side or the negative electrode side of the DC terminal and the other end is grounded to the ground potential, and the neutral point of the star-connected capacitor of the AC filter unit 32 is connected. May be connected to. Instead of one capacitor of the capacitor section 331, a plurality of capacitors connected in series may be applied.
Note that connection means electrical connection and does not necessarily mean a state of direct connection. The type of connection between the capacitor section 331 and the DC terminal includes not only the capacitor section 331 directly connected to the DC terminal but also the connection to the DC terminal via the bus bar. Similarly, as the type of connection between the filter capacitor unit 321 and the AC terminal, not only the form in which the filter capacitor unit 321 is directly connected to the AC terminal but also the form in which the filter capacitor unit 321 is connected to an electric wire or the like connected to the AC terminal included.

Embodiment 2.
FIG. 6 is a block configuration diagram showing a system using the power conversion device according to the second embodiment. Similar to the first embodiment, the input side of the power conversion device 3 is connected to the commercial power supply 1 via the transformer 2. The output side of the power converter 3 is connected to a DC load 5 via a DC bus 4. The difference between the second embodiment and the first embodiment is the filter configuration of the power conversion device 3, which can further strengthen the effect of suppressing the zero-phase voltage as compared with the first embodiment, and can be further downsized. Is.

The AC filter unit 32 of the power conversion device 3 illustrated in FIG. 6 includes a filter capacitor unit 321, a filter reactor unit 323, a filter capacitor unit 324, and a filter reactor unit 325. The filter reactor unit 323 is a common mode reactor (first common mode reactor), and the filter reactor unit 325 is a normal mode reactor.
The DC filter unit 33 of the power conversion device 3 is connected to the filter reactor unit 332 in addition to the capacitor unit 331 described in the first embodiment. The filter reactor unit 332 is a common mode reactor (second common mode reactor). In the capacitor section 331, two capacitors are connected in series, and both ends thereof are connected to the positive electrode side and the negative electrode side of the DC terminal, respectively.

The feature of this embodiment is that the neutral point of the star connection of the filter capacitor section 321 and the connection point of the capacitor section 331 in which two capacitors are connected in series are not grounded with respect to the ground potential 6. It is the point where they are connected to each other.
The normal-mode reactor is a normal-mode current component (the sum of the positive-phase current component and the negative-phase current component), that is, a component that sums the three-phase currents to zero Is magnetically coupled, and has a feature that it can be made smaller than using three single-phase reactors. On the other hand, the normal mode reactor has almost no inductance with respect to the common mode current component (zero-phase current component), that is, the component that does not become zero by summing the three-phase currents. In the AC filter unit 32, the common mode reactor (filter reactor unit 323) and the normal mode reactor (filter reactor unit 325) are separately configured, so that the overall size of the device can be reduced.

The common-mode reactor is a three-phase magnetic coupling that increases the inductance with respect to the common-mode current component (zero-phase current component), and can be made smaller than using three single-phase reactors. There is. On the other hand, the common mode reactor has almost no inductance with respect to the normal mode current component (the total of the positive phase current component and the negative phase current component).

As shown in this embodiment, by separating the normal mode reactor and the common mode reactor, the inductance for the zero-phase current component can be increased without increasing the size and weight. Further, since the DC filter unit 33 also includes the filter reactor unit 332, the inductance for the zero-phase current component can be further increased. Therefore, even when the zero-phase voltage generated by the AC / DC converter 31 is large, a high damping effect can be exhibited.

FIG. 7 is a block diagram showing the configuration of the controller according to the second embodiment. The controller 34 is provided with a zero-phase voltage superposition unit 344 next to the DC bus voltage control unit 341 and the input current control unit 342, and further, the comparison unit 343 generates the gate signal 345.
The difference from the first embodiment is that the zero-phase voltage superimposing unit 344 is provided. The zero-phase voltage superimposing unit 344 superimposes the zero-phase voltage command Vz * on the U-phase, V-phase, and W-phase voltage commands Vu *, Vv *, and Vw * generated by the input current control unit 342. .. Then, as shown in equations (5), (6), and (7) below, the voltage commands Vu **, Vv **, and Vw ** of each phase are newly calculated and sent to the comparison unit 343.
Vu ** = V × sinωt + Vz * ・・・・・・・・・・ (5)
Vv ** = V × sin (ωt-2π / 3) + Vz * ... (6)
Vw ** = V × sin (ωt + 2π / 3) + Vz * ... (7)

The purpose of superimposing the zero-phase voltage command Vz * is to reduce the peak value of each phase voltage command.
For example, as the zero-phase voltage command Vz *, in order to reduce the peak value of each phase voltage command, a zero-phase voltage command having a frequency that is three times the frequency of the input AC voltage is superimposed as shown in equation (8). To do.
Vz * = V / 6 × sin3ωt ... (8)
Although various methods can be considered for giving the zero-phase voltage command Vz *, it is characterized by having a frequency three times the frequency of the input AC voltage.

FIG. 8 is a waveform diagram for explaining the operation of the controller 34. FIG. 8A is a waveform diagram showing each phase voltage command by the input current control unit 342. In FIG. 8A, Vu * indicates the waveform of the U-phase voltage command. Vv * indicates the waveform of the V-phase voltage command. Vw * indicates the waveform of the W-phase voltage command. FIG. 8B shows the waveform of the zero-phase voltage command Vz *. FIG. 8C is a waveform diagram of each phase voltage command superimposed by the zero-phase voltage superimposing unit 344. In FIG. 8C, Vu ** indicates the waveform of the U-phase voltage command. Vv ** indicates the waveform of the V-phase voltage command. Vw ** indicates the waveform of the W-phase voltage command.
In FIG. 8, the peak voltage V of each phase voltage command is illustrated as 0.8 pu. The base of the unit pu corresponds to the case where the voltage across the DC bus 4 is ± 1 pu (width 2 pu).

As shown in FIG. 8, while the peak voltage of each phase voltage command Vu *, Vv *, Vw * by the input current control unit 342 is 0.8 pu, each phase voltage command Vu superposed by the zero phase voltage superposition unit 344. The peak voltage of **, Vv **, and Vw ** is 0.7 pu. This peak voltage is related to the DC voltage of the AC / DC converter 31. In other words, it can be reduced to 0.7 / 0.8 = 0.87 times.
By reducing the DC voltage, it is possible to reduce the loss associated with the switching operation of the semiconductor switching element 311, that is, the switching loss.
The purpose is to give a zero-phase voltage so as to reduce the peak voltage of each phase, and in the case of three phases, a zero-phase voltage command that cancels the peak voltage three times in one cycle is required as shown in FIG. Become. Therefore, as described above, the zero-phase voltage command having a frequency three times the frequency of the input AC voltage is superimposed.
It is a feature of the present embodiment that the voltage is reduced by superimposing the zero-phase voltage command, and a measure is taken against the noise increase.

However, since the zero-phase voltage having a frequency component three times as high as the input AC voltage is superimposed as the voltage command, the AC / DC converter 31 adds the zero-phase voltage of the switching frequency component described in the first embodiment. Thus, it also has a zero-phase voltage having a frequency component three times as high as the input AC voltage.
In the second embodiment, as described above, since the common mode reactors (filter reactors 323 and 332) are used for the AC filter unit 32 and the DC filter unit 33, the zero-phase voltage damping effect is large, so that the zero-phase voltage is reduced. The effect is exhibited even when the voltage has a low frequency and the amplitude becomes large. That is, the equation of (noise current) = (voltage serving as noise source) ÷ (ωL) holds, so that the noise current increases when the zero-phase voltage has a low frequency (ωL is small) and the amplitude is large. Even in such a case, since the common mode reactors (filter reactors 323 and 332) are used for the AC filter unit 32 and the DC filter unit 33, the zero-phase voltage attenuation effect becomes more remarkable.

Details will be explained below using an equivalent circuit. FIG. 9 is a zero-phase equivalent circuit of the entire system when the power conversion device 3 according to the second embodiment is used. The zero-phase equivalent circuit includes the stray capacitance 2E of the transformer 2, the zero-phase impedance 321E of the filter capacitor unit 321 in the AC filter unit 32, the zero-phase impedance 323E of the filter reactor unit 323, the zero-phase impedance 324E of the filter capacitor unit 324, and the filter. Zero-phase impedance 325E of reactor section 325, zero-phase voltage source 31E of switching frequency component, zero-phase voltage source 31E3 of frequency component three times the input AC voltage, zero-phase impedance 332E of filter reactor section 332 in DC filter section 33, It is expressed by the zero-phase impedance 331E of the capacitor section 331 and the ground capacitance 52E of the DC load 5.

Here, since the neutral point of the filter capacitor section 324 is grounded anywhere, it does not affect the zero-phase circuit. Further, since the filter reactor section 325 is a normal mode reactor, the zero phase impedance 325E is almost zero.
In the zero-phase equivalent circuit shown in FIG. 9, the zero-phase voltage sources 31E and 31E3, the

filter reactor parts

323 and 332, the filter capacitor part 321 and the capacitor part 331 form a closed loop, which has a great damping effect.

The first common mode reactor (filter reactor unit 323) is connected between the filter capacitor unit 321 and the AC / DC conversion unit 31. By thus connecting the first common mode reactor inside the filter capacitor section 321, the damping effect can be increased. That is, in forming the LC filter, the L value (inductance value) of the LC filter is not increased unless L (inductance element) is inside (the voltage source side that is a noise source). Also connect the first common mode reactor inside.

Further, the second common mode reactor (filter reactor 332) is connected between the capacitor 331 and the AC / DC converter 31. In this way, the damping effect is increased by connecting the common mode reactor inside the capacitor section 331. That is, in constructing the LC filter, the L value (inductance value) of the LC filter is not increased unless L (inductance element) is inside (the voltage source side that is a noise source), so that it is better than the capacitor section 331. Connect the common mode reactor inside.

Since the zero-phase voltage source 31E3 has a frequency three times as high as the input AC voltage, it has a low frequency component of 150 Hz in the 50 Hz system and 180 Hz in the 60 Hz system. This can be said to be a low frequency in comparison with the frequency of the carrier signal, that is, a zero-phase voltage having a frequency component substantially the same as the switching frequency. If the resonance frequency is set by the common mode reactor (filter reactor parts 323, 332), the filter capacitor part 321, and the capacitor part 331 so as to be lower than the frequency three times the input AC voltage, a large damping effect can be obtained. it can. Since it is necessary to attenuate the frequency component that is three times as high as the input AC voltage, if the resonance frequency is set to this frequency component or less, a large attenuation effect can be obtained. That is, the relationship between the resonance frequency and the attenuation in the filter including the LC is based on the principle of a general electric circuit.
In the present embodiment, both filter

reactor parts

323 and 332 which are common mode reactors are connected, but as is apparent from FIG. 9, since they are connected to the same current path, only one of them is connected. Good.

As described above, in the power converter according to the second embodiment, the controller 34 includes the zero-phase voltage superimposing unit 344 for superimposing the zero-phase voltage having a frequency three times the input AC voltage. The voltage can be reduced and the switching loss can be reduced. Further, for the zero-phase voltage source 31E3 by the zero-phase voltage superimposing unit 344, a closed loop is formed by the common mode reactor in the AC filter unit 32, the common mode reactor in the DC filter unit 33, and the filter capacitor unit 321. The malfunction of the DC load 5 and the ground fault detection device can be suppressed.

Embodiment 3.
10A and 10B are circuit diagrams showing a common mode reactor unit in the power conversion device according to the third embodiment. The third embodiment relates to a modification of the common mode reactor in the second embodiment. In the power converter 3 shown in FIG. 6, the filter reactor unit 323 is provided with the auxiliary winding 81 and the resistor 82 as shown in FIG. 10A. Further, in the power conversion device 3 shown in FIG. 6, an auxiliary winding 81 and a resistor 82 are added to the filter reactor section 332 as shown in FIG. 10B. FIG. 11 is a configuration diagram showing an outline of the structure of the filter reactor portion 332. In FIG. 11, a DC wire 84 is wound around the magnetic core 83. As a result, an alternating current component, which is a noise component flowing through the direct current line 84, generates an alternating current in the auxiliary winding 81 by electromagnetic induction and is consumed by the resistor 82. The filter reactor portion 323 also has a similar configuration, and the filter reactor portion 323 has three alternating current lines.

The filter reactor part 323 and the filter reactor part 332 are common mode reactors, and a common mode current flows through the auxiliary winding 81 by magnetic coupling. Therefore, by connecting the resistor 82 to the auxiliary winding 81, the impedance with respect to the common mode current can be increased.
By increasing the impedance in this way, it is possible to further suppress the zero-phase current generated by the AC / DC converter 31 described in the first and second embodiments.

In addition, the number, size, material and the like of the above-described constituent parts can be changed as appropriate.
Further, although the present application describes various exemplary embodiments and examples, various features, aspects, and functions described in one or more of the embodiments are not described in particular embodiments. The present invention is not limited to the application, and can be applied to the embodiments alone or in various combinations.
Therefore, innumerable variations not illustrated are envisioned within the scope of the technology disclosed herein. For example, it is assumed that at least one component is modified, added or omitted, and at least one component is extracted and combined with the components of other embodiments.

2 transformers, 3 power converters, 31 AC / DC converters, 32 AC filter units, 33 DC filter units, 34 controllers, 311 semiconductor switching elements, 321, filter capacitor units, 331 capacitor units.

Claims

A power conversion device for converting a three-phase input AC voltage to a DC voltage,
The power converter includes an AC / DC converter having a semiconductor switching element,
An AC filter unit having a filter capacitor unit having at least three star-connected capacitors and connected to each AC terminal of the AC / DC converter unit;
A direct current filter part having a capacitor part having at least one capacitor and connected to a direct current terminal of the alternating current / direct current converter part;
A controller for controlling ON / OFF of the semiconductor switching element,
One ends of the at least three capacitors of the filter capacitor unit are connected to a neutral point in the star connection, and the other ends of the at least three capacitors are connected to respective AC terminals of the AC / DC conversion unit,
One end of the at least one capacitor of the capacitor unit is connected to the positive electrode side or the negative electrode side of the DC terminal of the AC / DC converting unit, the other end of the at least one capacitor is not grounded to ground potential, A power conversion device connected to the neutral point.
The capacitor unit has a series connection body in which at least two capacitors are connected in series,
The series connection body is connected to a positive electrode side and a negative electrode side of a DC terminal of the AC / DC converter,
The power conversion device according to claim 1, wherein a connection point of the at least two capacitors connected in series of the series connection body is connected to the neutral point without being connected to a ground potential.
The power conversion device according to claim 1, wherein the three-phase input AC voltage is supplied via a transformer whose at least one location is grounded to the ground potential.
The said AC filter part is a power converter device as described in any one of Claim 1 to 3 which has a 1st common mode reactor.
The power conversion device according to claim 4, wherein the first common mode reactor is connected between the filter capacitor section and the AC / DC conversion section.
The power converter according to any one of claims 1 to 5, wherein the DC filter unit includes a second common mode reactor.
The power conversion device according to claim 6, wherein the second common mode reactor is connected between the capacitor unit and the AC / DC conversion unit.
The power conversion device according to any one of claims 4 to 7, wherein the AC filter unit includes a normal mode reactor.
The said controller has a zero-phase voltage superposition part which superimposes the zero-phase voltage command which has a frequency component of 3 times the frequency of the said input alternating voltage voltage on the said three-phase voltage command, It has any one of Claim 1 to Claim 8. The power converter according to item 1.
The resonance frequency of the zero-phase impedance of the filter circuit configured by the DC filter unit and the AC filter unit is smaller than the switching frequency when turning on / off the semiconductor switching element. The power converter according to item 1.
The power conversion device according to claim 9, wherein the resonance frequency of the zero-phase impedance of the filter circuit configured by the DC filter unit and the AC filter unit is smaller than three times the frequency of the input AC voltage.
The power conversion device according to claim 4, wherein the first common mode reactor has an auxiliary winding and a resistor.
The power converter according to claim 6, wherein the second common mode reactor has an auxiliary winding and a resistor.