WO2021049016A1

WO2021049016A1 - Power conversion device

Info

Publication number: WO2021049016A1
Application number: PCT/JP2019/036158
Authority: WO
Inventors: 嗣大宅野; 拓志地道
Original assignee: 三菱電機株式会社
Priority date: 2019-09-13
Filing date: 2019-09-13
Publication date: 2021-03-18
Also published as: JP7043607B2; JPWO2021049016A1

Abstract

The present invention obtains a power conversion device in which a ground fault can be detected even when the ground fault occurs on the DC side of the power conversion device. The power conversion device is provided with: an AC/DC conversion unit having a first DC output terminal that is a positive side terminal on the DC output side, a second DC output terminal that is a negative side terminal on the DC output side, and a third DC output terminal that is a neutral terminal on the DC output side and converting three-phase AC power, one phase of which is a grounded phase, to DC power to output the DC power; a first capacitor having one end connected to the first DC output terminal and the other end connected to the third DC output terminal; and a second capacitor having one end connected to the third DC output terminal and the other end connected to the second DC output terminal. The third DC output terminal has the same potential as that of the grounded phase.

Description

Power converter

The present invention relates to a power conversion device that converts three-phase AC power of a system in which one of the three-phase ACs is grounded into DC power.

Conventionally, various power conversion devices that convert AC power into DC power have been proposed. As a conventional power conversion device, there is an example in which a rectifying bridge circuit provided with a rectifying diode, a capacitor connected to a terminal of the rectifying diode, and a pair of output terminals for outputting DC power are provided. Further, there is an example in which a step-down chopper circuit that is connected to the pair of output terminals and steps down DC power is combined. (See, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2011-30329 (paragraphs 4 to 7, FIG. 1)

In the power conversion device described in Patent Document 1, when the circuit on the DC side of the power conversion device has a ground fault, there is a problem that the ground fault cannot be detected because there is no path for the ground fault current to flow on the DC side.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a power conversion device that can easily detect a ground fault even when a ground fault occurs on the DC side of the power conversion device. ..

The power conversion device in the present invention is a first DC output terminal which is a positive terminal on the DC output side, a second DC output terminal which is a negative terminal on the DC output side, and a neutral terminal on the DC output side. An AC / DC converter that has a third DC output terminal and converts three-phase AC power, which is a grounded phase with one phase grounded, into DC power and outputs it, and one end is connected to the first DC output terminal. The other end is connected to the first DC output terminal, one end is connected to the third DC output terminal, and the other end is connected to the second DC output terminal. The third DC output terminal includes two capacitors and has the same potential as the ground phase.

According to the present invention, it is possible to obtain a power conversion device that can easily detect a ground fault even when a ground fault occurs on the DC side of the power conversion device.

It is a circuit diagram of the power conversion apparatus in Embodiment 1 of this invention. It is a schematic diagram which shows the current path at the time of a normal time of the power conversion apparatus in Embodiment 1 of this invention. It is a schematic diagram which shows the current path when the ground fault occurs on the positive side of the DC output of the power conversion apparatus in Embodiment 1 of this invention. It is a schematic diagram which shows the current path when the ground fault occurs on the negative side of the DC output of the power conversion apparatus in Embodiment 1 of this invention. It is a circuit diagram of the power conversion apparatus in Embodiment 2 of this invention. It is a circuit diagram which shows the modification example of the power conversion apparatus in Embodiment 2 of this invention. It is a circuit diagram of the AC / DC conversion part in Embodiment 3 of this invention. It is a circuit diagram which shows the modification example of the AC / DC conversion part in Embodiment 3 of this invention. It is a circuit diagram of the power conversion apparatus in Embodiment 4 of this invention. It is a hardware block diagram of the ground fault determination part of the power conversion apparatus in Embodiment 4 of this invention. It is a circuit diagram of the power conversion apparatus in Embodiment 4 of this invention. It is a circuit diagram of the power conversion apparatus in Embodiment 4 of this invention. It is a circuit diagram of the power conversion apparatus in Embodiment 4 of this invention. It is a circuit diagram of the power conversion apparatus in Embodiment 4 of this invention. It is a circuit diagram of the power conversion apparatus in Embodiment 4 of this invention. It is a circuit diagram of the power conversion apparatus in Embodiment 4 of this invention. It is a circuit diagram of the power conversion apparatus in Embodiment 4 of this invention. This is an example of the voltage waveform of the chopper portion in the fifth embodiment of the present invention. This is an example of the voltage waveform of the chopper portion in the fifth embodiment of the present invention. It is a circuit diagram of the power conversion apparatus in Embodiment 5 of this invention. It is a figure which shows the hardware composition of the control part of the power conversion apparatus in Embodiment 5 of this invention.

Embodiment 1.
FIG. 1 is a circuit diagram of a power conversion device according to a first embodiment of the present invention. The power conversion device 100 according to the first embodiment of the present invention includes an AC / DC conversion unit 1 that converts power between three-phase AC power and DC power, a capacitor 21 (first capacitor), and a capacitor 22 (second capacitor). Capacitor) and.

Further, the power conversion device 100 according to the first embodiment of the present invention is connected to the three-phase AC power supply 90 via a power receiving transformer 91. When the insulation between the windings of the power receiving transformer 91 is lost, the low voltage side and the high voltage side of the transformer winding come into contact with each other, and the low voltage side voltage is applied to the low voltage side terminal. One phase on the side is often grounded.

One phase of the three-phase alternating current connected to the power conversion device 100 according to the first embodiment of the present invention is also grounded. Since the power receiving transformer 91 is a well-known technique, detailed description thereof will be omitted. Further, in the drawings other than FIG. 1, the description of the power receiving transformer 91 is omitted.

The AC / DC conversion unit 1 converts the three-phase AC power from the three-phase AC power supply 90 obtained via the power receiving transformer 91 into DC power and outputs it. One of the three phases connected from the power receiving transformer 91 to the AC / DC converter 1 is grounded (hereinafter referred to as a grounded phase).

The AC / DC converter 1 includes a DC output terminal 11 (first DC output terminal) which is a positive terminal of a DC output to which DC power is output, and a DC output terminal 12 (second DC output terminal) which is a negative terminal of the DC output. (DC output terminal) and a neutral terminal 13 (third DC output terminal) drawn from the DC neutral point.

The DC neutral point, that is, the neutral terminal 13 is provided so as to have the same potential as the ground phase of the inputs of the three-phase AC power. That is, the neutral terminal 13 is connected to the ground phase.

In the power conversion device 100 according to the first embodiment of the present invention, the side where the three-phase AC power is input is defined as the first stage, and the side where the three-phase AC power is converted into power and the DC power is output is defined as the second stage.

At this time, the capacitor 21 and the capacitor 22 are provided after the AC / DC conversion unit 1. One end of the capacitor 21 is connected to the DC output terminal 11, and the other end is connected to the neutral terminal 13. One end of the capacitor 22 is connected to the DC output terminal 12, and the other end is connected to the neutral terminal 13. That is, the capacitor 21 and the capacitor 22 are symmetrically connected to the neutral terminal 13 on the positive side of the DC output and the negative side of the DC output.

By connecting in this way, it is possible to respond to power fluctuations without sudden voltage rise or fall. Therefore, it has the effect of stabilizing the DC voltage.

In the case of such a circuit, the operation of the AC / DC converter 1 is usually controlled so that the voltage of the capacitor 21 on the positive side of the DC output and the capacitor 22 on the negative side of the DC output are equal.

FIG. 2 is a schematic diagram showing a current path during normal operation of the power conversion device 100 according to the first embodiment of the present invention. The solid line and the dotted line in FIG. 2 show the current flow. As described above, the operation of the AC / DC converter 1 is controlled so that the voltages of the capacitor 21 and the capacitor 22 become equal. Normally, the load 10 between the positive side of the DC output and the negative side of the DC output is balanced. That is, the voltages on the positive side and the negative side are equal, and the same amount of current is supplied to the loads on the positive side and the negative side. Here, it is assumed that the load 10 is integrally connected between the positive side of the DC output and the negative side of the DC output.

The dotted line in FIG. 2 shows the current supplied to the load 10 from the positive side of the DC output and the current supplied to the load 10 from the negative side of the DC output. At this time, the line connecting the neutral point of the load 10 and the neutral terminal 13 (hereinafter referred to as a DC neutral line) is a load that flows from the positive side of the DC output to the positive side of the load 10 to the DC neutral line. The current and the load current flowing from the DC neutral line to the negative side of the DC output flow. As described above, the load currents at this time are equal.

As a result, in the DC neutral wire, the load current flowing from the positive side of the DC output through the positive side of the load 10 to the DC neutral wire and the load current flowing from the DC neutral wire to the negative side of the DC output cancel each other out. , Almost no current flows. That is, as shown by the solid line in FIG. 2, the load current flows from the positive side of the DC output through the load 10 and through the path returning to the negative side of the DC output.

FIG. 3 is a schematic diagram showing a current path when a ground fault occurs on the positive side of the DC output in the subsequent stage of the AC / DC conversion unit 1 of the power conversion device 100 according to the first embodiment of the invention. FIG. 4 is a schematic diagram showing a current path when a ground fault occurs on the negative side of the DC output in the subsequent stage of the AC / DC conversion unit 1 of the power conversion device 100 according to the first embodiment of the present invention.

For example, a case where a ground fault occurs on the positive side of the DC output in the subsequent stage of the AC / DC converter 1 will be described with reference to FIG. The solid line and the alternate long and short dash line in FIG. 3 indicate the current flow.

The solid line in FIG. 3 shows the path of the ground fault current passing through the ground fault point P and the ground phase of the three-phase AC from the positive side of the DC output when a ground fault occurs on the positive side of the DC output and passing through the neutral DC point. Is. That is, a current returns from the ground fault point P to the neutral terminal 13 having the same potential as the ground phase via the ground.

The alternate long and short dash line in FIG. 3 is a load current path that passes from the neutral DC point to the negative side of the load 10 and passes through the negative side of the DC output when a ground fault occurs on the positive side of the DC output.

In this way, when a ground fault occurs on the positive side of the DC output, a load current flowing through the path passing through the load 10 and a ground fault current flowing through the path passing through the DC neutral point are generated.

Next, a case where a ground fault occurs on the negative side of the DC output in the subsequent stage from the AC / DC converter 1 will be described with reference to FIG. The solid line and the alternate long and short dash line in FIG. 4 show the current flow.

The solid line in FIG. 4 is the path of the ground fault current from the neutral DC point to the ground phase of the three-phase AC and from the ground fault point P to the negative side of the DC output. The alternate long and short dash line in FIG. 4 is a load current path that passes from the positive side of the DC output to the positive side of the load 10 and passes through the DC neutral point.

In this way, even when a ground fault occurs on the negative side of the DC output, a load current flowing through the path passing through the load 10 and a ground fault current flowing through the path passing through the DC neutral point are generated.

Therefore, by configuring the ground phase and the neutral terminal 13 to have the same potential, the ground phase and the neutral terminal can be connected to each other regardless of whether a ground fault occurs on the positive side or the negative side of the DC output. The current that passes through flows. Further, the current flowing through the DC neutral wire is not canceled, and the current corresponding to the magnitude of the load 10 flows.

In either case, a larger current will flow than during normal operation. A ground fault can be detected by measuring each of these currents using, for example,

current detection units

66, 67, 68 and the like. The

current detection units

66, 67, and 68 measure the current flowing through the wiring drawn out from the

output terminals

11, 12, and 13 of the DC output of the AC / DC conversion unit 1. As a result, the

current detection units

66, 67, 68 can detect the current at the time of a ground fault. The detection positions of the

current detection units

66, 67, and 68 are examples, and may be provided so as to be able to detect the current in each current path at the time of the ground fault described above. The ground fault can be determined according to the detected current value.

That is, the ground fault can be easily detected by detecting the current flowing at the time of the ground fault on at least one of the AC side and the DC side of the power conversion device 100. The above description is based on the case where the neutral point of the load 10 and the neutral terminal 13 are explicitly connected, but when the neutral point of the load 10 is grounded and is not connected to the neutral terminal 13. This is the same because the neutral point of the load 10 and the neutral terminal 13 have the same potential.

As described above, in the first embodiment of the present invention, the DC neutral point has the same potential as the ground phase of the three-phase AC, so that when a ground fault occurs on the DC output side, the AC side of the power conversion device 100 Alternatively, a power conversion device that can easily detect a ground fault on the DC side can be obtained.

Embodiment 2.
Conventionally, there is an example in which a rectifier for rectifying an AC voltage and a DC power conversion circuit are provided, the device has a plurality of output terminals, and a voltage suitable for the required voltage is supplied (for example, Japanese Patent Application Laid-Open No. 2012-95450 (FIG. 2). )). However, even in such an example, when the circuit on the DC side has a ground fault, there is a problem that the ground fault cannot be detected because there is no path through which the ground fault current flows. There was also the issue of increasing the number of elements. A mode for solving these problems will be described in the second embodiment of the present invention.

FIG. 5 is a circuit diagram of the power conversion device according to the second embodiment of the present invention, and FIG. 6 is a circuit diagram showing a modified example of the power conversion device according to the second embodiment of the present invention. Those having the same reference numerals as those in FIG. 1 indicate the same or corresponding configurations, and the description thereof will be omitted. The configuration on the rear stage side of the AC / DC conversion unit 1 is different from that of the first embodiment. Only the parts having different configurations and operations from those of the first embodiment will be described.

In the power conversion device 101 of the second embodiment, the chopper circuit 3, the DC filter reactor 41 (first DC filter reactor) and the DC filter reactor 42 (second DC filter reactor) are located behind the capacitor 21 and the capacitor 22. , A DC filter capacitor 51 (first DC filter capacitor) and a DC filter capacitor 52 (second DC filter capacitor) are provided.

The chopper circuit 3 has a first DC input terminal connected to the DC output terminal 11, a second DC input terminal connected to the DC output terminal 12, and a third connected to the neutral terminal 13 on the DC input side. Has a DC input terminal. Further, the chopper circuit 3 has a positive output terminal (fourth DC output terminal), a negative output terminal (fifth DC output terminal), and an output neutral terminal (fifth DC output terminal) that output DC power to the DC output side. It has a sixth DC output terminal). The chopper circuit 3 converts the DC power input from each input terminal into power and outputs it from each output terminal.

The chopper circuit 3 is a half bridge 301 (first half bridge) and a half bridge 302 that are symmetrically connected to the first DC input terminal side and the second DC input terminal side with respect to the third DC input terminal. Consists of (second half bridge).

The half bridge 301 is composed of a semiconductor switch 303 and a semiconductor switch 304 connected in series, and an output terminal of the half bridge 301 is pulled out from a connection point between the semiconductor switch 303 and the semiconductor switch 304. This output terminal is the output terminal on the positive side of the chopper circuit 3.

The half bridge 302 is composed of a semiconductor switch 305 and a semiconductor switch 306 connected in series like the half bridge 301. Then, the output terminal of the half bridge 302 is pulled out from the connection point between the semiconductor switch 305 and the semiconductor switch 306. This output terminal is an output terminal on the negative side of the chopper circuit 3.

The output terminal is pulled out from the connection point between the half bridge 301 and the half bridge 302. This output terminal is an output neutral terminal of the chopper circuit 3. This output neutral terminal is connected to the neutral terminal 13. That is, they are connected so as to have the same potential as the ground phase of three-phase alternating current.

One end of the DC filter reactor 41 is connected to an output terminal drawn from the half bridge 301. Further, one end of the DC filter reactor 42 is connected to an output terminal drawn from the half bridge 302.

One end of the DC filter capacitor 51 is connected to the rear stage of the DC filter reactor 41, and the other end is connected to the output neutral terminal. One end of the DC filter capacitor 52 is connected to the rear stage of the DC filter reactor 42, and the other end is connected to the output neutral terminal.

Each output terminal of the power conversion device 101 drawn out after the DC filter capacitor 51 and the DC filter capacitor 52 is connected to, for example, a load (not shown) as in the first embodiment. Of the output terminals, the output neutral terminal is connected to the neutral point of the load.

In such a configuration, in the chopper circuit 3, each semiconductor switch is controlled so that the DC output voltage on the positive side of the DC output and the DC output voltage on the negative side of the DC output are equal. This has the effect of being able to output a desired DC voltage regardless of the voltage on the AC side.

Next, a modified example of the power conversion device 101 according to the second embodiment of the present invention will be described with reference to FIG. Those having the same reference numerals as those in FIGS. 1 to 5 indicate the same or corresponding configurations, and the description thereof will be omitted.

An example of modification of the power conversion device 101 shown in FIG. 6 further includes a chopper circuit 31, a DC filter reactor 43 and a DC filter reactor 44, a DC filter capacitor 53, and a DC filter capacitor 54.

The chopper circuit 31 has the same configuration as the chopper circuit 3 described above. That is, it is composed of a half bridge 311 and a half bridge 312 having the same configuration as the half bridge 301 and the half bridge 302. Each DC input terminal of the chopper circuit 3 and the chopper circuit 31 is connected in parallel.

The output terminal is pulled out from the connection point of each semiconductor switch constituting the half bridge 311. This output terminal is the output terminal on the positive side of the chopper circuit 31. Similarly, the output terminal is pulled out from the connection point of each semiconductor switch constituting the half bridge 312. This output terminal is an output terminal on the negative side of the chopper circuit 31.

The output terminal is pulled out from the connection point between the half bridge 311 and the half bridge 312. This output terminal is an output neutral terminal of the chopper circuit 31. This output neutral terminal is connected to the output neutral terminal of the chopper circuit 3. That is, they are connected so as to have the same potential as the ground phase of three-phase alternating current.

The DC filter reactor 43, the DC filter reactor 44, the DC filter capacitor 53, and the DC filter capacitor 54 are connected to the subsequent stage of the chopper circuit 31. These are connected to the chopper circuit 31 in the same arrangement as those in which the DC filter reactor 41 and the DC filter reactor 42, the DC filter capacitor 51 and the DC filter capacitor 52 are connected to the subsequent stage of the chopper circuit 3.

Also, each

chopper circuit

3 and 31 is controlled so as to have a different output voltage. This makes it possible to output different voltages by adding a chopper circuit. That is, it is possible to obtain DC outputs of a plurality of voltages at the same time.

Further, the output neutral terminals drawn out after the DC filter capacitor 53 and the DC filter capacitor 54 are connected so as to have the same potential as the ground phase of the three-phase AC. In this case, the reference potentials of the plurality of output voltages are DC neutral points.

Therefore, in the case of a ground fault on the DC output side as in the first embodiment, there is an effect that a power conversion device capable of easily detecting the ground fault on the AC side or the DC side of the AC / DC conversion unit 1 can be obtained. Play. Further, it has the effect of being able to obtain a plurality of desired DC voltages having a uniform reference potential.

In the second embodiment of the present invention, two sets of chopper circuits are connected, but there may be three or more sets of chopper circuits. Further, although the semiconductor switch is represented by the MOSFET symbol, the semiconductor element is not limited to the MOSFET, and may be another type of element such as a bipolar transistor, an IGBT, or a JFET. Even in this case, the above-mentioned effects are obtained.

Embodiment 3.
FIG. 7 is a circuit diagram of the AC / DC converter 1 according to the third embodiment of the present invention. FIG. 8 is a circuit diagram showing a modified example of the AC / DC converter 1 according to the third embodiment of the present invention. Only the parts having different configurations and operations from those of the first embodiment and the second embodiment will be described.

As shown in FIG. 7, the AC / DC converter 1 according to the third embodiment of the present invention is composed of a half bridge (third half bridge) composed of

semiconductor switches

1001 and 1002, and

semiconductor switches

1003 and 1004. It is composed of a full bridge using a half bridge (fourth half bridge). Further, an AC filter matching the harmonic regulation value on the system side is connected to the AC side of the full bridge. Regarding the configuration of the AC filter, the one composed of the

capacitors

501 and 502 and the

reactors

401 and 402 is shown in the figure, but since it is a well-known technique, detailed description thereof will be omitted.

The full bridge according to the third embodiment of the present invention is configured by connecting each half bridge in which one end is connected to the DC output terminal 11 and the other end is connected to the DC output terminal 12 in parallel.

The DC terminal on the positive side of the full bridge corresponds to the positive side of the DC output of the AC / DC converter 1. Further, the DC terminal on the negative side of the full bridge corresponds to the negative side of the DC output of the AC / DC conversion unit 1. Then, the DC neutral point is connected so as to have the same potential as the ground phase of the three-phase AC.

The connection points of the

semiconductor switches

1001 and 1002 are connected to one phase other than the ground phase of three-phase alternating current. Further, the connection points of the

semiconductor switches

1003 and 1004 are connected to a ground phase of three-phase alternating current and a phase other than the one phase.

As described above, the AC / DC conversion unit 1 is an AC / DC conversion circuit composed of a full bridge using each semiconductor switch. As a result, even if the voltage on the AC side fluctuates, it is possible to control the DC link voltage so as to keep it constant. Further, by switching at a frequency sufficiently higher than the power supply frequency, the effect of suppressing low-order harmonics on the AC side is obtained.

FIG. 8 shows each of the above-mentioned full-bridge semiconductor switches configured by using each

diode

1005, 1006, 1007, 1008. An AC-DC conversion circuit in which a full bridge is configured by using each diode is cheaper than a circuit composed of each semiconductor switch and does not require a control system, so that it has an advantageous effect in terms of cost.

That is, when it is desired to suppress harmonics, the AC-DC conversion circuit shown in FIG. 7 is selected, and when harmonics are acceptable, the AC-DC conversion circuit shown in FIG. 8 is selected. As a result, in addition to the effects of the first and second embodiments of the present invention, the effects of the AC / DC conversion circuits described above in the third embodiment of the present invention are exhibited.

Further, in the case of a ground fault on the DC output side as in the first and second embodiments, a power conversion device capable of easily detecting the ground fault on the AC side or the DC side of the AC / DC conversion unit 1 is obtained. It has an effect that can be achieved. In addition, it has the effect of obtaining a desired DC voltage.

Further, as shown in the second embodiment of the present invention, when the chopper circuit 3 is connected to the rear stage side of the DC output of the AC / DC conversion unit 1, the AC input voltage fluctuation becomes the DC output by the control of the chopper circuit 3. It has the effect of suppressing the effect.

The AC filter shown in FIGS. 7 and 8 is an example, and other types of filters may be used. Further, any AC / DC conversion circuit connected so that the grounded phase of the three-phase AC and the DC neutral point have the same potential can be applied, and other circuit types may be used.

Although the semiconductor switch is represented by the MOSFET symbol, the semiconductor element is not limited to the MOSFET, and may be another type of element such as a bipolar transistor, an IGBT, or a JFET. Even in these cases, the above-mentioned effects are obtained.

Embodiment 4.
As shown in the first to third embodiments of the present invention, in each power conversion device according to the embodiment of the present invention, when a ground fault occurs on the DC output side, the AC side or DC of the AC / DC conversion unit 1 It becomes easy to detect the ground fault on the side.

Since the ground fault current is a current of a magnitude that is not expected in normal operation, it may damage the power converter and the wiring of the path through which the ground fault current flows. Therefore, it is necessary to determine the presence or absence of a ground fault. Furthermore, after detecting the ground fault, it is necessary to appropriately cut off the ground fault current.

In the fourth embodiment of the present invention, a power conversion device capable of detecting a ground fault will be described. FIG. 9 is a circuit diagram of the power conversion device according to the fourth embodiment of the present invention. Those having the same reference numerals as those in FIGS. 1 to 8 indicate the same or corresponding configurations, and the description thereof will be omitted.

An example of detecting a ground fault current will be described with reference to FIG. 9 to 16 have a ground fault determining means 60 for detecting at least one current on the AC side or the DC side of the AC / DC conversion unit 1 according to the embodiment of the present invention.

FIG. 9 is a diagram showing an example of detecting a ground fault on the AC side of the power conversion device 102. The ground fault determining means 60 in FIG. 9 has a current detecting unit 61 and a ground fault determining unit 70.

The current detection unit 61 is provided on the AC side of the AC / DC conversion unit 1. Specifically, it is provided between the place where the grounding phase is grounded and the AC / DC conversion unit 1. Then, the three-phase current during this period is measured collectively.

The ground fault determination unit 70 determines the presence or absence of a ground fault based on the detected current value detected by the current detection unit 61.

The AC side of the AC / DC converter 1 is in a three-phase equilibrium state or a state close to three-phase equilibrium during normal operation. At this time, the sum of the three-phase currents on the AC side is 0 or a very small value. On the other hand, at the time of a ground fault, an imbalance occurs in the current of each phase. The occurrence of a ground fault can be detected by measuring the current imbalance of each phase. Therefore, the current detection unit 61 measures the current imbalance of each phase by measuring the zero-phase component of the three-phase alternating current.

Then, the ground fault determination unit 70 determines that a ground fault has occurred when the zero-phase component detected by the current detection unit 61 exceeds a predetermined size. Therefore, it is possible to detect a ground fault on the AC side of the AC / DC conversion unit 1.

FIG. 10 is a hardware configuration diagram of the ground fault determination unit 70 of FIG. In FIG. 10, the ground fault determination unit 70 includes a processor 33 and a storage unit 34. The processor 33 performs the above-mentioned processing of the ground fault determination unit 70 by executing the program stored in the storage unit 34. Here, the storage unit 34 is composed of a memory in which parameters necessary for determination, a program describing the above processing, and the like are stored. The processor 33 is composed of a processor logically configured in a hardware circuit such as a microcomputer (microcomputer), a DSP (Digital Signal Processor), or an FPGA (Field Programmable Gate Array). Further, the plurality of processors 33 and the plurality of storage units 34 may cooperate to execute the above function. The same applies to the ground fault determination unit 70 described below.

Next, an example of detecting a ground fault on the AC side of the power conversion device 102 shown in FIG. 11 will be described. The ground fault determining means 60 in FIG. 11 includes current detecting

units

62, 63, 64 and a ground fault determining unit 70.

Each

current detection unit

62, 63, 64 is provided between a place where the ground phase is grounded and the AC / DC conversion unit 1. Each

current detection unit

62, 63, 64 detects currents of different phases.

The zero-phase component, that is, the zero-phase current can be obtained by taking the sum of the measured values individually measured by each

current detection unit

62, 63, 64.

Then, the ground fault determination unit 70 states that a ground fault has occurred when the zero-phase current calculated from the current detection values detected by the

current detection units

62, 63, 64 exceeds a predetermined magnitude. judge. Therefore, it is possible to detect a ground fault on the AC side of the AC / DC conversion unit 1.

Next, an example of detecting a ground fault on the AC side of the power conversion device 102 shown in FIG. 12 will be described.
The ground fault determining means 60 in FIG. 12 includes a current detecting unit 63 and a ground fault determining unit 70. This is the configuration in which the

current detection units

62 and 64 are omitted from the configuration shown in FIG.

The current detection unit 63 is provided in the ground phase between the place where the ground phase is grounded and the AC / DC conversion unit 1. No current flows through the ground phase during normal operation, but when a ground fault occurs, a ground fault current flows. By measuring the current of the ground phase with the current detection unit 63, it is possible to detect the ground fault current.

Then, the ground fault determination unit 70 determines that a ground fault has occurred when the current detection value detected by the current detection unit 63 exceeds a predetermined magnitude. Therefore, it is possible to detect a ground fault on the AC side of the AC / DC conversion unit 1.

Next, an example of detecting a ground fault on the AC side of the power conversion device 102 shown in FIG. 13 will be described. The ground fault determining means 60 in FIG. 13 includes a current detecting unit 65 for detecting the current of the line grounding the grounding phase of the three-phase alternating current and a ground fault determining unit 70.

A line that is grounded to the grounding phase of three-phase AC does not allow current to flow during normal operation, but when a ground fault occurs, a ground fault current flows. The current detection unit 65 measures the ground fault current flowing through the line that grounds the ground phase of the three-phase alternating current.

Then, the ground fault determination unit 70 determines that a ground fault has occurred when the current detection value detected by the current detection unit 65 is larger than a predetermined value. This makes it possible to detect a ground fault on the AC side of the AC / DC conversion unit 1.

Next, an example of detecting a ground fault on the DC side of the power conversion device 102 shown in FIG. 14 will be described. The ground fault determining means 60 in FIG. 14 includes current detecting

units

66 and 67 and a ground fault determining unit 70.

Specifically, the current detection unit 66 is provided after the capacitor 21, and detects the current flowing through the line on the positive side of the DC output of the AC / DC conversion unit 1. The current detection unit 67 is provided after the capacitor 22, and detects the current flowing through the line on the negative side of the DC output of the AC / DC conversion unit 1.

Further, the current detection unit 66 is provided after each DC filter reactor and each DC filter capacitor when each DC filter reactor and each DC capacitor are provided on the DC output side. The current detection unit 67 is provided after each DC filter reactor and each DC filter capacitor when each DC filter reactor and each DC capacitor are provided on the DC output side.

The current value flowing through the line on the positive side of the DC output of the AC / DC converter 1 and the current value flowing through the line on the negative side of the DC output are the same during normal operation. That is, the current flowing through the DC neutral wire is 0 or a very small value. On the other hand, when a ground fault occurs, the current values flowing in the lines on the positive side of the DC output and the lines on the negative side of the DC output are different, and the ground fault current flows in the neutral DC line.

Therefore, the ground fault determination unit 70 utilizes the fact that the current values on the positive side and the negative side of the DC output are different when a ground fault occurs, and obtains each current detection value measured by the current detection unit 66 and the current detection unit 67. Can be used to determine ground faults.

As a method of determining a ground fault, for example, there is a method of using the difference between each current detection value. The difference between each current detection value can be obtained, and a ground fault can be detected when this difference becomes large. Specifically, a reference value for the difference when a ground fault occurs is set in advance, and this reference value is compared with the detected difference value, and when the difference value becomes larger than the reference value, the ground value is set. Try to determine that it is entangled. Alternatively, the difference value of each current detection value in the normal time may be used as a reference value, the difference value between this and each current detection value may be compared, and the determination may be made based on the increase from the reference value in the normal time.

Another determination method is to use the sum of the current detection values. In this case, it is utilized that the added value becomes almost 0 at the time of normal operation and becomes a larger value than that at the time of a ground fault. That is, when the sum of the current detection values becomes larger than the predetermined reference value, it is determined that the ground fault has occurred. As described above, the ground fault can be detected by comparing the value using each current detection value with a predetermined reference value.

Next, an example of detecting a ground fault on the DC side of the power conversion device 102 shown in FIG. 15 will be described. The ground fault determining means 60 in FIG. 15 includes a current detecting unit 68 and a ground fault determining unit 70. The current detection unit 68 is provided on the DC neutral wire and detects the current of the DC neutral wire.

As described in the first embodiment of the present invention, almost no current flows through the DC neutral wire during normal operation.

On the other hand, at the time of a ground fault, a ground fault current flows through the DC neutral wire. That is, it is possible to detect a ground fault by using the current detection value of the DC neutral wire detected by the current detection unit 68.

Therefore, the ground fault can be detected by comparing the current detection value of the current detection unit 68 with a predetermined reference value. Further, the ground fault can be detected by increasing the current detection value of the current detection unit 68.

Next, an example of detecting a ground fault on the DC side of the power conversion device 102 shown in FIG. 16 will be described. The ground fault determining means 60 in FIG. 16 has a current detecting unit 69 and a ground fault determining unit 70. The current detection unit 69 measures the positive side of the DC output and the negative side of the DC output of the AC / DC conversion unit 1 collectively, and is installed so as not to measure the current of the DC neutral wire.

During normal operation, if the direct current is detected all at once, the current flowing on the positive side and the current flowing on the negative side cancel each other out, and almost no current is detected. On the other hand, when a ground fault occurs, the current on the positive side of the DC output and the current on the negative side of the DC output are not canceled, so that a large current flows as compared with the normal operation. By using this, it becomes possible to detect a ground fault.

That is, it can be determined that a ground fault has occurred by comparing the current detection value of the current detection unit 69 with a predetermined reference value.

Therefore, when a ground fault occurs on the DC side of each power conversion device, the effect is that the ground fault can be detected on the AC side or the DC side of the AC / DC conversion unit 1.

Note that, in FIGS. 9 to 16, the ground fault determination unit 70 may perform control to stop the operation of the power conversion device 102 so as to cut off the ground fault current when the ground fault is determined.

For example, when a ground fault is detected in each power conversion device having a chopper circuit 3 or a chopper circuit 31, the ground fault current is cut off by stopping the switching of the semiconductor switch of each

chopper circuit

3 or 31. It becomes possible. This has the effect of preventing damage to each power conversion device and route wiring due to ground fault current.

Further, although the power conversion device 102 having the ground fault determination means 60 has been described with reference to FIGS. 9 to 16, the power conversion device 102 may have a circuit breaker 80 as shown in FIG. As the circuit breaker 80, for example, an MCCB (Molded Case Circuit Breaker), an earth leakage breaker, or the like is used. In this case, the ground fault is determined by each of the above-mentioned methods according to the current value detected by each current detection unit, and after detecting the ground fault, the ground fault current is cut off by turning off the circuit breaker 80. be able to.

That is, by combining with the circuit breaker 80, the detection current value of the ground fault determining means 60 is used, and the effect of making it possible to cut off the ground fault current is achieved.

For example, CT (Current Transformer) is used for each of the above-mentioned current detection units. For example, when an MCCB or an earth leakage breaker is used as the circuit breaker 80, each current detection unit and the ground fault determination unit 70 are used as the circuit breaker 80. It may be built-in. In this case, the ground fault determination unit 70 outside the circuit breaker 80 may detect the ground fault by detecting the operation of the circuit breaker 80 with an auxiliary contact or the like.

Therefore, according to the present embodiment, in the case of a ground fault on the DC side, the effect of facilitating the detection of the ground fault on the AC side or the DC side of the AC / DC conversion unit 1 is obtained. Further, by using the current measurement value of each current detection unit and the ground fault determination unit 70 or the circuit breaker 80, the effect of being able to cut off the ground fault current after detecting the ground fault is obtained. Further, it has an effect of preventing damage to each power conversion device and path wiring due to ground fault current.

Although each example in which each current detection unit is provided is shown in the fourth embodiment, it is sufficient that any of the current detection units of FIGS. 9 to 16 is provided on either the AC side or the DC side. The current detection units shown in FIGS. 9 to 16 may be used in combination. Even in this case, the above-mentioned effect is obtained.

Further, as long as it can cut off the ground fault current based on the current detection value of the current detection unit, it can be applied to other than the above-mentioned circuit breaker 80.

Embodiment 5.
In the second embodiment of the present invention, the power conversion device 101 provided with the chopper circuit 3 has been described with reference to FIGS. 5 and 6. In the fifth embodiment of the present invention, the control of the switching timing of each half bridge of the chopper circuit 3 will be described.

FIG. 18 shows a voltage waveform when the switch timings of the half bridges of the chopper circuit according to the fifth embodiment of the present invention are the same. FIG. 19 shows the voltage waveforms when the switch timings of the half bridges of the chopper circuit according to the fifth embodiment of the present invention are the same and different.

In a switching type converter, it is generally known that a common mode voltage is generated with the switching of a semiconductor switch. This common mode voltage becomes a common mode current when it is applied to a stray capacitance between the converter and the reference potential. The common mode current causes common mode noise, which is a noise component, and an increase in loss with respect to the current during normal operation. Therefore, it is desirable to suppress the generation of common mode voltage.

In the circuit of the chopper circuit 3 according to the embodiment of the present invention, the half bridges 301 and 302 are symmetrically connected to the DC neutral wire on the positive side and the negative side of the DC output. In such a circuit type, the generation of the common mode voltage can be suppressed by aligning the switching timing of the half bridge 301 on the positive side of the DC output and the switching timing of the half bridge 302 on the negative side of the DC output. ..

This will be described in detail with reference to FIG. Each horizontal axis in the upper part of FIG. 18 indicates the time t. The positive half-bridge output voltage shown in the upper part of FIG. 18 indicates the voltage applied to both ends of the DC filter capacitor 51 shown in FIG. 5 based on the DC neutral point potential. The negative half-bridge output voltage shown in the upper part of FIG. 18 indicates the voltage applied to both ends of the DC filter capacitor 52 shown in FIG. 5 based on the DC neutral point potential.

The common mode voltage is the sum of the positive half bridge output voltage and the negative half bridge output voltage. That is, it is the sum of the voltage applied across the DC filter capacitor 51 and the voltage applied across the DC filter capacitor 52.

The upper part of FIG. 18 shows each voltage when an LC filter composed of each

DC filter capacitor

51, 52 and each

DC filter reactor

41, 42 is provided.

On the other hand, in the lower part of FIG. 18, in order to make the circuit operation easier to understand, the positive half bridge output voltage when the LC filter composed of the

DC filter reactors

41 and 42 and the

DC filter capacitors

51 and 52 is not connected is not connected. , Negative half bridge output voltage and common mode voltage are shown.

The horizontal axis in the lower part of FIG. 18 indicates the time t. The positive half-bridge output voltage and the negative half-bridge output voltage shown in the lower part of FIG. 18 are the respective voltages between the connection portion between the semiconductor switches constituting the half bridges 301 and 302 and the DC neutral line. The common mode voltage in this case is also the sum of the positive half bridge output voltage and the negative half bridge output voltage.

As described above, the power converter is controlled so that the positive output voltage of the DC output and the negative output voltage of the DC output are equal. Further, the voltage applied to the capacitor 21 on the positive side and the voltage applied to the capacitor 22 on the negative side are also controlled to be equal to each other.

Therefore, the magnitudes of the positive half-bridge output voltage and the negative half-bridge output voltage when the half bridges 301 and 302 are switched during normal operation are equal. Further, the positive side half bridge output voltage becomes a positive voltage with respect to the DC neutral point potential, and the negative side half bridge output voltage becomes a negative voltage with respect to the DC neutral point potential. Therefore, if the timing of switching between the positive half bridge and the negative half bridge is the same, the common mode voltage represented by the sum of the positive half bridge output voltage and the negative half bridge output voltage becomes 0.

As shown in the upper part of FIG. 18, even when an LC filter is connected, by using a DC filter reactor having the same inductance on the positive side and the negative side and a DC filter capacitor having the same capacitance, the DC output voltage on the positive side can be increased. The ripple voltage and the ripple voltage of the negative DC output voltage have opposite polarities and are equal in magnitude. Therefore, the common mode voltage becomes 0.

In order to align the switching timing of the positive half bridge and the negative half bridge, for example, a carrier signal having the same frequency and phase and reversed polarity is used, and the positive half bridge output voltage and the negative half bridge output voltage are used. A method of generating a gate signal of a semiconductor switch by comparing carriers using each command value can be considered. Further, for one carrier signal, a method of generating a gate signal of each semiconductor switch by comparing carriers using the positive half bridge output voltage command value and the negative half bridge output voltage command value whose polarity is inverted, etc. Can be considered.

By controlling each of the

half bridges

301 and 302 as described above, the common mode voltage can be suppressed, which has the effect of suppressing noise reduction and loss increase.

On the other hand, from the viewpoint of the ripple voltage, the ripple voltage of the DC output voltage when the switching timing is not aligned is suppressed compared to the ripple voltage of the DC output voltage when the switching timing is aligned.

This will be described in detail with reference to FIG. Each horizontal axis in FIG. 19 indicates the time t. From the top of FIG. 19, the positive side half bridge output voltage, the negative side half bridge output voltage, and the output voltage which is the difference voltage between the positive side DC output voltage and the negative side DC output voltage are shown, respectively.

The solid line in FIG. 19 shows the output voltage values when the switch timings of the positive half bridge and the negative half bridge are the same. On the other hand, the dotted line in FIG. 19 shows the output voltage values when the switch timings of the positive half bridge and the negative half bridge are different.

The DC voltage supplied to the load is the difference voltage between the DC output voltage on the positive side and the DC output voltage on the negative side. Therefore, it can be seen that the ripple of the DC voltage is maximized when the switching timings of the

half bridges

301 and 302 are aligned and the timings at which the respective voltages reach their peaks are aligned. When the ripple voltage becomes large, the capacity of the DC filter capacitor required to suppress the voltage fluctuation of the DC output voltage to a desired value increases, which causes an increase in cost and size.

On the other hand, it can be seen from FIG. 19 that when the switching timings are not aligned, the timing at which the DC output voltage on the positive side reaches the peak and the timing at which the DC output voltage on the negative side reaches the peak are different. As a result, the ripple voltage peak value of the DC output voltage is suppressed.

The switch timing can be shifted by shifting the phase of the carrier signal given to the positive half bridge and the phase of the carrier signal given to the negative half bridge. As described above, by controlling the switch timings to be different, the ripple voltage peak value of the DC output voltage can be suppressed.

The above-mentioned control is realized by, for example, a control unit 32 as shown in FIG. FIG. 21 is a hardware configuration diagram of the control unit of FIG. 20. In FIG. 21, the control unit 32 includes a processor 33 and a storage unit 34. The processor 33 performs the processing of the control unit 32 described above by executing the program stored in the storage unit 34. Here, the storage unit 34 is composed of a memory in which parameters necessary for control, a program describing the above processing, and the like are stored. The processor 33 is composed of a microcomputer (microcomputer), a DSP (Digital Signal Processor), an FPGA, and the like. Further, the plurality of processors 33 and the plurality of storage units 34 may cooperate to execute the above function.

As described above, in the case of a ground fault on the DC output side as in the first to fourth embodiments, a power conversion device capable of easily detecting the ground fault on the AC side or the DC side of the AC / DC conversion unit 1 is provided. It has an effect that can be obtained and detected. Further, by controlling the switching timing of the half bridge in the chopper circuit, it is possible to reduce noise and ripple.

1 AC / DC converter, 21, 22 capacitors, 3, 31 chopper circuit, 32 control unit, 33 processor, 34 storage unit, 301, 302, 311, 312 half bridge, 303, 304, 305, 306, 1001, 1002, 1003, 1004 semiconductor switch, 10 load, 11, 12 DC output terminal, 13 neutral terminal, 41, 42, 43, 44 DC filter reactor, 401, 402 reactor, 51, 52, 53, 54 DC filter capacitor, 501, 502 capacitor, 60 ground fault determination means, 61, 62, 63, 64, 65, 66, 67, 68, 69 current detector, 70 ground fault determination unit, 80 breaker, 90 three-phase AC power supply, 91 power receiving transformer Vessel, 1005, 1006, 1007, 1008 diode

Claims

It has a first DC output terminal that is a positive terminal on the DC output side, a second DC output terminal that is a negative terminal on the DC output side, and a third DC output terminal that is a neutral terminal on the DC output side. Then, the AC / DC converter that converts the three-phase AC power, which is the grounded phase in which one phase is grounded, into DC power and outputs it,
A first capacitor whose one end is connected to the first DC output terminal and the other end is connected to the third DC output terminal.
A second capacitor whose one end is connected to the third DC output terminal and the other end is connected to the second DC output terminal.
With
The third DC output terminal is a power conversion device having the same potential as the ground phase.
A first DC input terminal connected to the first DC output terminal, a second DC input terminal connected to the second DC output terminal, and a third connected to the third DC output terminal. It has a fourth DC output terminal which is a positive side terminal, a fifth DC output terminal which is a negative side terminal, and a sixth DC output terminal which is a neutral terminal. A chopper circuit that converts the DC power input from the first to third DC input terminals and outputs it.
A first DC filter reactor whose one end is connected to the fourth DC output terminal,
A second DC filter reactor whose one end is connected to the fifth DC output terminal,
A first DC filter capacitor with one end connected to the other end of the first DC filter reactor and the other end connected to the sixth DC output terminal.
A second DC filter capacitor, one end of which is connected to the sixth DC output terminal and the other end of which is connected to the other end of the second DC filter reactor.
With
The power conversion device according to claim 1, wherein the sixth DC output terminal has the same potential as the ground phase.
The chopper circuit
A first half bridge having a plurality of semiconductor switches, one end of which is connected to the first DC input terminal and the other end of which is connected to the third DC input terminal.
A second half bridge composed of a plurality of semiconductor switches, one end of which is connected to the third DC input terminal and the other end of which is connected to the second DC input terminal.
Have,
The fourth DC output terminal is drawn out from the connection points of the plurality of semiconductor switches constituting the first half bridge.
The power conversion device according to claim 2, wherein the fifth DC output terminal is drawn from a connection point of the plurality of semiconductor switches constituting the second half bridge.
It has a control unit that controls the chopper circuit, and has a control unit.
The power conversion device according to claim 3, wherein the control unit controls so that the switch timings of the first half bridge and the second half bridge are aligned.
It has a control unit that controls the chopper circuit, and has a control unit.
The power conversion device according to claim 3, wherein the control unit controls the first half bridge and the second half bridge by shifting the switch timing.
It has a control unit that controls the chopper circuit, and has a control unit.
The power conversion device according to any one of claims 3 to 5, wherein the control unit controls to stop switching of the chopper circuit when a ground fault occurs.
The chopper circuit, the first and second DC filter reactors, and the first and second DC filter capacitors are each provided, and the DC input terminals of the plurality of chopper circuits are connected in parallel. ,
The power conversion device according to any one of claims 2 to 6, wherein the sixth DC output terminals of the plurality of chopper circuits are connected to each other.
It has a ground fault determining means for detecting a ground fault on the DC side of the AC / DC conversion unit.
The ground fault determining means includes a current detecting unit that detects a current on at least one of the DC side and the AC side of the AC / DC conversion unit.
A ground fault determination unit that determines a ground fault based on the detected current value detected by the current detection unit, and a ground fault determination unit.
The power conversion device according to any one of claims 1 to 7.
The current detecting unit detects at least one of the current flowing through the grounding phase and the current of the line grounding the grounding phase, and the ground fault determining unit uses the detected current value detected by the current detecting unit. The power conversion device according to claim 8, wherein the ground fault is determined when the value exceeds a predetermined value.
The current detection unit detects the current on the AC side of the AC / DC conversion unit, and the ground fault determination unit determines in advance the zero-phase component of the AC current obtained from the detected current value detected by the current detection unit. The power conversion device according to claim 8, wherein the ground fault is determined when the value exceeds the value.
The current detection unit detects the current on the DC side of the AC / DC conversion unit, and the ground fault determination unit compares the detected current value detected by the current detection unit with a predetermined value and causes a ground fault. The power conversion device according to claim 8, wherein the power conversion device is determined to have been used.
The power conversion device according to any one of claims 8 to 11, wherein a circuit breaker is provided on the AC side of the AC / DC conversion unit to shut off the circuit breaker when a ground fault occurs.
The AC / DC converter
The third DC output terminal is connected to the ground phase,
A third half bridge composed of semiconductor elements in which two semiconductor elements are connected in series, and
It has a fourth half bridge composed of semiconductor elements in which two semiconductor elements are connected in series.
The positive terminal of the third half bridge and the positive terminal of the fourth half bridge are connected to the first DC output terminal.
The negative terminal of the third half bridge and the negative terminal of the fourth half bridge are connected to the second DC output terminal.
The connection point of each semiconductor element constituting the third half bridge is connected to one phase other than the ground phase.
The power conversion device according to any one of claims 1 to 12, wherein the connection point of each semiconductor element constituting the fourth half bridge is connected to the ground phase and a phase different from the one phase.
The power conversion device according to claim 13, wherein the third half bridge and the fourth half bridge are each connected in series with two semiconductor switches.
The power conversion device according to claim 13, wherein the third half bridge and the fourth half bridge are each connected in series with two diodes.