JP2018007516A - Power conversion device and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device and control method therefor having high reliability.SOLUTION: According to an embodiment, there is provided a power conversion device comprising a main circuit unit, voltage detection unit, and control circuit. The main circuit unit is connected to an AC power system having three-phase AC power to perform power conversion on the three-phase AC power. The voltage detection unit includes a first and second detection systems to acquire at least two of voltage values of respective phases of the AC power system. The control circuit controls operation of the main circuit unit on the basis of the respective voltage values acquired by the voltage detection unit. The control circuit, on the basis of respective detection results of the first and second detection systems, detects occurrence of a zero-phase-sequence component; and determines that the detection systems are normal when no zero-phase-sequence component is detected in both of the first and second detection systems, determines that a single line-to-ground fault has occurred when zero-phase-sequence components are detected in both of the first and second detection systems, and determines that a fault has occurred in one of the first and second detection systems when a zero-phase-sequence component is detected in the one detection system.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a power conversion device and a control method thereof.

  There is a power converter that is linked to a three-phase AC power system. The power conversion device converts, for example, three-phase AC power of the power system into another power and supplies it to a load or the like. Alternatively, power supplied from another power supply source is converted into three-phase AC power and supplied to the power system. The power conversion device detects a system voltage of each phase of the power system, and controls power conversion based on the detected system voltage of each phase.

  In such a power converter, it is desired that the operation of the power converter can be continued even when a one-line ground fault occurs. The occurrence of a one-line ground fault can be detected by detecting the occurrence of a zero-phase three-phase AC voltage, for example. However, the zero-phase component of the three-phase AC voltage also occurs when any voltage detector in each phase fails. When the voltage detector fails, it is necessary to stop the power conversion operation to protect the operation of the apparatus. Thus, simply detecting the occurrence of the zero phase cannot distinguish between a one-wire ground fault and a voltage detector failure, and the operation must be stopped.

  For this reason, in a power converter, it is desired to improve reliability by distinguishing between a one-wire ground fault and a voltage detector failure and enabling appropriate measures in each case.

JP2012-223001A

  Embodiments of the present invention provide a highly reliable power conversion device and a control method thereof.

  According to the embodiment of the present invention, a power conversion device including a main circuit unit, a voltage detection unit, and a control circuit is provided. The main circuit unit is connected to an AC power system of three-phase AC power, and performs at least one of conversion from three-phase AC power to another power and conversion from another power to three-phase AC power. The voltage detection unit includes a first detection system and a second detection system, and acquires at least two voltage values of each phase of the AC power system by the first detection system and the second detection system. The control circuit controls the operation of the main circuit unit based on each voltage value acquired by the voltage detection unit. The control circuit detects occurrence of a zero phase of the AC power system based on a detection result of the first detection system, and detects a zero phase component of the AC power system based on a detection result of the second detection system. When the occurrence of zero phase is not detected in both the first detection system and the second detection system, it is determined that the AC power system and the voltage detection unit are normal, When occurrence of a zero phase is detected in both the first detection system and the second detection system, it is determined that a one-line ground fault has occurred in the AC power system, and only in the first detection system When the occurrence of the zero phase is detected, it is determined that the first detection system is faulty. When the occurrence of the zero phase is detected only by the second detection system, the second detection system is faulty. judge.

  A highly reliable power conversion device and a control method thereof are provided.

It is a block diagram showing typically the power converter concerning an embodiment. It is a block diagram showing a converter typically. It is a block diagram showing typically a part of power converter concerning an embodiment. It is a graph which represents typically an example of the detection result of the alternating voltage of each phase of an alternating current power system. It is a flowchart which represents typically an example of operation | movement of the power converter device which concerns on embodiment. FIGS. 6A and 6B are block diagrams schematically showing a modification of the voltage detection unit. It is a block diagram showing typically the modification of a converter. It is a block diagram which represents typically the modification of a main circuit part.

Each embodiment will be described below with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between the parts, and the like are not necessarily the same as actual ones. Further, even when the same part is represented, the dimensions and ratios may be represented differently depending on the drawings.
In the present specification and drawings, the same elements as those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

FIG. 1 is a block diagram schematically illustrating a power conversion device according to the embodiment.
As illustrated in FIG. 1, the power conversion device 10 includes a main circuit unit 12 and a control circuit 14. The power converter 10 is used for a DC power transmission system, for example. The power converter 10 is connected to the AC power system 2 and the pair of DC power transmission lines 3 and 4 in the DC power transmission system.

  The DC power transmission system includes, for example, a transformer 6. The main circuit unit 12 of the power conversion device 10 is connected to the AC power system 2 via the transformer 6. The AC power of the AC power system 2 is three-phase AC power. More specifically, it is symmetrical three-phase AC power. The transformer 6 converts the three-phase AC power of the AC power system 2 into AC power corresponding to the main circuit unit 12. The transformer 6 changes the effective value of each phase of the three-phase AC power in accordance with the main circuit unit 12. The transformer 6 is a three-phase transformer. The transformer 6 is provided as necessary and can be omitted. The main circuit unit 12 may be directly supplied with the three-phase AC power of the AC power system 2.

  The power converter 10 converts the three-phase AC power supplied from the AC power system 2 into DC power, and supplies the converted DC power to the DC power transmission lines 3 and 4. Further, the power conversion device 10 converts the DC power supplied from the DC power transmission lines 3 and 4 into three-phase AC power, and supplies the converted three-phase AC power to the AC power system 2. As described above, the power conversion apparatus 10 performs AC / DC conversion from AC to DC and AC / DC conversion from DC to AC.

  For example, the DC transmission line 3 is a transmission line on the high voltage side of DC power, and the DC transmission line 4 is a transmission line on the low voltage side of DC power. The power conversion device 10 outputs the converted DC power to the DC transmission lines 3 and 4 so that the DC transmission line 3 side is at a high voltage and the DC transmission line 4 side is at a low voltage.

  The main circuit unit 12 is provided between the AC power system 2 and the DC power transmission lines 3 and 4. The main circuit unit 12 performs conversion from three-phase AC power to DC power and conversion from DC power to three-phase AC power. The main circuit unit 12 is, for example, an MMC (Modular Multilevel Converter) type power converter. The MMC type main circuit section 12 has a plurality of converters connected in series. Each converter includes a plurality of switching elements that are half-bridge connected or full-bridge connected, and a charge storage element that is connected in parallel to each switching element. The main circuit unit 12 performs AC / DC conversion by switching of each switching element.

  The control circuit 14 is connected to the main circuit unit 12. The control circuit 14 controls the conversion from the three-phase AC power to the DC power and the conversion from the DC power to the three-phase AC power by the main circuit unit 12 by controlling on / off of each switching element.

  The main circuit section 12 includes a first and second pair of DC terminals 20a and 20b, first to third AC terminals 21a to 21c, and first to sixth arm sections 22a to 22f. Have.

  The first DC terminal 20a is connected to the DC transmission line 3 on the high voltage side. The second DC terminal 20b is connected to the DC transmission line 4 on the low voltage side. Thus, the DC power converted by the main circuit unit 12 is supplied to the DC power transmission lines 3 and 4, and the DC power supplied from the DC power transmission lines 3 and 4 is input to the main circuit unit 12.

  The first arm portion 22a is connected to the first DC terminal 20a. The second arm portion 22b is connected between the first arm portion 22a and the second DC terminal 20b. The first arm portion 22a and the second arm portion 22b are connected in series between the DC terminals 20a and 20b.

  The third arm portion 22c is connected to the first DC terminal 20a. The fourth arm portion 22d is connected between the third arm portion 22c and the second DC terminal 20b. The third arm part 22c and the fourth arm part 22d are connected in parallel to the first arm part 22a and the second arm part 22b.

  The fifth arm portion 22e is connected to the first DC terminal 20a. The sixth arm portion 22f is connected between the fifth arm portion 22e and the second DC terminal 20b. That is, the fifth arm portion 22e and the sixth arm portion 22f are connected in parallel to the first arm portion 22a and the second arm portion 22b, and to the third arm portion 22c and the fourth arm portion 22d. Connected in parallel.

  In the main circuit unit 12, the first leg LG1 is configured by the first arm unit 22a and the second arm unit 22b, the second leg LG2 is configured by the third arm unit 22c and the fourth arm unit 22d, and the fifth arm unit. The third leg LG3 is configured by the 22e and the sixth arm portion 22f. That is, in this example, the main circuit unit 12 is a three-leg, six-arm three-phase inverter. The first arm portion 22a, the third arm portion 22c, and the fifth arm portion 22e are upper arms. The second arm part 22b, the fourth arm part 22d, and the sixth arm part 22f are lower arms.

The first arm unit 22a includes a plurality of converters UP1, UP2,... UPM ₁ connected in series. The second arm portion 22b has a plurality of transducers UN1, UN2 ... UNM ₂ connected in series. The third arm portion 22c has a plurality of converters VP1, VP2,... VPM ₃ connected in series. The fourth arm portion 22d has a plurality of converters VN1, VN2,... VNM ₄ connected in series. The fifth arm portion 22e has a plurality of converters WP1, WP2,... WPM ₅ connected in series. The sixth arm portion 22f includes a plurality of converters WN1, WN2,... WNM ₆ connected in series.

However, in the following, each transducer _{UP1, UP2 ... UPM 1, UN1} , UN2 ... UNM 2, VP1, VP2 ... VPM 3, VN1, VN2 ... VNM 4, WP1, WP2 ... WPM 5, WN1, WN2 ... WNM 6 When collectively referred to, it is referred to as “converter CEL”.

In each of the arm portions _{22a~22f, M 1, M 2,} M 3, M 4, M 5, M 6 represents a series-connected converter CEL in number. In each arm part 22a-22f, the number of the converters CEL connected in series is about 100 to 120, for example. However, the number of converters CEL connected in series is not limited to this and may be any number.

  The number of converters CEL provided in each of the arm portions 22a to 22f is substantially the same. For example, when a large number of converters CEL are connected, the number of converters CEL provided in each of the arm units 22a to 22f may be different within a range that does not affect the operation of the main circuit unit 12. For example, when 100 converters CEL are connected in series to one arm part, the number of converters CEL provided in another arm part may differ by one or two.

  Each of the arm portions 22a to 22f further includes a buffer reactor 23a to 23f and a plurality of current detectors 24a to 24f. The power conversion device 10 further includes a voltage detection unit 25.

  Each buffer reactor 23a-23f is connected in series with each converter CEL in each of arm parts 22a-22f. The buffer reactor 23a of the first arm portion 22a is provided between a connection point between the AC terminal 21a and the first arm portion 22a and the second arm portion 22b and the converter UP1. The buffer reactor 23b of the second arm portion 22b is provided between a connection point between the AC terminal 21a, the first arm portion 22a and the second arm portion 22b, and the converter UN1. The buffer reactor 23c of the third arm portion 22c is provided between a connection point between the AC terminal 21b, the third arm portion 22c and the fourth arm portion 22d, and the converter VP1. The buffer reactor 23d of the fourth arm portion 22d is provided between a connection point between the AC terminal 21b, the third arm portion 22c and the fourth arm portion 22d, and the converter VN1. The buffer reactor 23e of the fifth arm portion 22e is provided between the connection point between the AC terminal 21c and the fifth arm portion 22e and the sixth arm portion 22f and the converter WP1. The buffer reactor 23f of the sixth arm portion 22f is provided between the connection point between the AC terminal 21c, the fifth arm portion 22e, and the sixth arm portion 22f and the converter WN1.

  The current detector 24a is provided in the first arm part 22a and detects a current flowing through the first arm part 22a. That is, the current detector 24a detects the arm current of the first arm portion 22a. The current detector 24a is connected to the control circuit 14 via a wiring not shown. The current detector 24 a inputs the detected current value of the first arm portion 22 a to the control circuit 14. As a result, the current value of the first arm portion 22 a is input to the control circuit 14.

  Similarly, the current detector 24 b detects the current flowing through the second arm portion 22 b and inputs the detected current value to the control circuit 14. The current detector 24 c detects the current flowing through the third arm portion 22 c and inputs the detected current value to the control circuit 14. The current detector 24 d detects the current flowing through the fourth arm portion 22 d and inputs the detected current value to the control circuit 14. The current detector 24 e detects the current flowing through the fifth arm portion 22 e and inputs the detected current value to the control circuit 14. The current detector 24 f detects the current flowing through the sixth arm portion 22 f and inputs the detected current value to the control circuit 14.

  The voltage detection unit 25 detects an AC voltage (phase voltage) of each phase of the AC power system 2 and inputs a detection value to the control circuit 14. The voltage detection unit 25 may be connected to the primary side of the transformer 6 or may be connected to the secondary side.

  In the main circuit part 12, the connection point between the first arm part 22a and the second arm part 22b, the connection point between the third arm part 22c and the fourth arm part 22d, and the fifth arm part 22e and the sixth arm part. Each of the connection points with 22f becomes an AC output point.

  The first AC terminal 21a is connected to a connection point between the first arm portion 22a and the second arm portion 22b. The second AC terminal 21b is connected to a connection point between the third arm portion 22c and the fourth arm portion 22d. The third AC terminal 21c is connected to a connection point between the fifth arm portion 22e and the sixth arm portion 22f. Each AC terminal 21a-21c is connected to the transformer 6, for example.

  Each converter CEL is connected to the control circuit 14 via a signal line 26. The control circuit 14 controls the operation of the converter CEL by inputting a control signal to the converter CEL via the signal line 26. In addition, the converter CEL inputs, for example, a control signal and a protection signal related to control and operation protection of the converter CEL to the control circuit 14 via another signal line (not shown).

FIG. 2 is a block diagram schematically showing the converter.
As illustrated in FIG. 2, the converter CEL includes the first connection terminal 40 a, the second connection terminal 40 b, the first switching element 41, the second switching element 42, the charge storage element 45, and the driver circuit 46. And having.

  Each of the switching elements 41 and 42 includes a pair of main terminals and a control terminal. The control terminal controls a current flowing between the pair of main terminals. For each switching element 41, 42, for example, a self-extinguishing element such as an IGBT is used. The pair of main terminals is, for example, an emitter and a collector, and the control terminal is, for example, a gate. For each switching element 41, 42, for example, a normally-off type semiconductor element is used.

  The pair of main terminals of the second switching element 42 are connected in series to the pair of main terminals of the first switching element 41. The charge storage element 45 is connected in parallel to the first switching element 41 and the second switching element 42. The charge storage element 45 is a capacitor, for example. The first connection terminal 40 a is connected between the first switching element 41 and the second switching element 42. The second connection terminal 40 b is connected to the main terminal on the opposite side of the main terminal connected to the second switching element 42 of the first switching element 41.

  The first switching element 41 is connected to a rectifying element 41d in antiparallel with the pair of main terminals. The forward direction of the rectifying element 41 d is opposite to the direction of the current flowing between the pair of main terminals of the first switching element 41. Similarly, the rectifying element 42d is connected to the second switching element 42 in antiparallel with the pair of main terminals. The rectifying elements 41d and 42d are so-called reflux diodes.

  Power is supplied to the converter CEL through the connection terminals 40a and 40b. In the converter CEL, the switching elements 41 and 42 are half-bridge connected. In other words, the converter CEL is a bidirectional chopper. The first switching element 41 is a so-called low-side switch, and the second switching element 42 is a so-called high-side switch.

  The control terminals of the switching elements 41 and 42 are input to the driver circuit 46. The driver circuit 46 is connected to the control circuit 14 via the signal line 26. The control circuit 14 transmits a control signal for controlling on / off of each switching element 41, 42 to the driver circuit 46 via the signal line 26. The driver circuit 46 switches the switching elements 41 and 42 on and off based on the input control signal. Thereby, on / off of each switching element 41 and 42 is controlled according to the control signal from the control circuit 14. The control circuit 14 generates a control signal for each converter CEL and controls on / off of each switching element 41, 42 of each converter CEL. Thereby, the control circuit 14 controls the conversion of power by the main circuit unit 12.

FIG. 3 is a block diagram schematically illustrating a part of the power conversion apparatus according to the embodiment.
As shown in FIG. 3, the voltage detection unit 25 includes a first detection system 25a and a second detection system 25b. The first detection system 25a includes a main voltage detector 61, an auxiliary voltage detector 62, and A / D converters 63 to 65.

  The primary side of the main voltage detector 61 is connected to the AC power system 2. The primary side of the auxiliary voltage detector 62 is connected to the secondary side of the main voltage detector 61. Although not shown in FIG. 3, three main voltage detectors 61 and three auxiliary voltage detectors 62 are actually provided corresponding to each phase of the AC power system 2. One auxiliary voltage detector 62 is connected to the secondary side of one main voltage detector 61. The main voltage detector 61 and the auxiliary voltage detector 62 detect the AC voltage (phase voltage) of each phase of the AC power system 2.

  For example, the main voltage detector 61 converts a high voltage (for example, 275 kV) of the AC power system 2 into a medium voltage (for example, 110 V). For example, the auxiliary voltage detector 62 converts the voltage output from the main voltage detector 61 into an electronic circuit level voltage (for example, 7 V). In other words, the main voltage detector 61 and the auxiliary voltage detector 62 are measurement transformers. The number of auxiliary voltage detectors 62 is not limited to one and may be two or more. If the AC voltage of the AC power system 2 is relatively low, the auxiliary voltage detector 62 may be omitted.

  Each A / D converter 63 to 65 is connected to the secondary side of the auxiliary voltage detector 62. Each A / D converter 63 to 65 is connected to the secondary side of each of the three auxiliary voltage detectors 62. Each A / D converter 63-65 converts the analog detection signal output from each auxiliary voltage detector 62 into a digital signal. Thereby, the voltage value of the AC voltage of each phase of the AC power system 2 is detected by the main voltage detector 61, the auxiliary voltage detector 62, and the A / D converters 63 to 65.

Here, the three phases of the AC power system 2 are referred to as a U phase, a V phase, and a W phase, respectively. The voltage value of the U-phase AC voltage is Vs_U, the voltage value of the V-phase AC voltage is Vs_V, and the voltage value of the W-phase AC voltage is Vs_W. The A / D converter 63 detects the U-phase voltage value Vs_U ₁ . The A / D converter 64 detects the V-phase voltage value Vs_V ₁ . The A / D converter 65 detects the W-phase voltage value Vs_W ₁ .

The second detection system 25b includes a main voltage detector 71, an auxiliary voltage detector 72, and A / D converters 73 to 75. For example, the second detection system 25b is connected in parallel to the first detection system 25a. Since the configuration of the second detection system 25b is substantially the same as the configuration of the first detection system 25a, detailed description thereof is omitted. A / D converter 73 detects the voltage value Vs_U ₂ of U-phase. A / D converter 74 detects the voltage value Vs_V ₂ of V-phase. A / D converter 75 detects the voltage value Vs_W ₂ of W-phase.

  As described above, the voltage detection unit 25 acquires two voltage values Vs_U, Vs_V, and Vs_W of the AC voltage of each phase of the AC power system 2 by the first detection system 25a and the second detection system 25b. The number of detection systems provided in the voltage detection unit 25 may be three or more. The voltage detection unit 25 may acquire three or more voltage values Vs_U, Vs_V, and Vs_W of the AC voltage of each phase of the AC power system 2. That is, the voltage detection unit 25 may acquire at least two voltage values Vs_U, Vs_V, and Vs_W of the AC voltage of each phase of the AC power system 2.

The control circuit 14 includes a control signal generation unit 80 and a zero phase detection unit 82. The voltage values Vs_U ₁ , Vs_V ₁ , Vs_W ₁ detected by the first detection system 25 a of the voltage detection unit 25 and the voltage values Vs_U ₂ , Vs_V ₂ , Vs_W ₂ detected by the second detection system 25 b are controlled. The signal is input to each of the signal generator 80 and the zero-phase detector 82.

The zero phase detection unit 82 includes a first detection unit 82a and a second detection unit 82b. The first detection unit 82 a includes an adder 83, an absolute value detection circuit 84, and a level detection circuit 85. Each voltage value Vs_U ₁ , Vs_V ₁ , Vs_W ₁ acquired by the first detection system 25 a of the voltage detector 25 is input to the adder 83.

The adder 83 adds the input voltage values Vs_U ₁ , Vs_V ₁ , and Vs_W ₁ . Thereby, the adder 83 calculates the voltage value Vs_ 0 ₁ for the zero phase of the AC power system 2 from the input voltage values Vs_U ₁ , Vs_V ₁ , Vs_W ₁ . The adder 83 inputs the calculated zero-phase voltage value Vs — 0 ₁ to the absolute value detection circuit 84.

The absolute value detection circuit 84 detects the absolute value of the input zero-phase voltage value Vs — 0 ₁ and inputs the detected absolute value to the level detection circuit 85. The level detection circuit 85 is connected to the control signal generation unit 80. For example, when the absolute value of the input zero-phase voltage value Vs — 0 ₁ is less than a predetermined value, the level detection circuit 85 outputs “0” to the control signal generation unit 80 and is greater than or equal to the predetermined value. In addition, “1” is output to the control signal generator 80.

FIG. 4 is a graph schematically showing an example of the detection result of the AC voltage of each phase of the AC power system.
FIG. 4 schematically illustrates a state in which the U phase of the AC power system 2 has caused a one-line ground fault at time T1.
As shown in FIG. 4, when the AC power system 2 is normal, the sum of the voltage values Vs_U, Vs_V, and Vs_W is substantially 0 (time T0 to time T1 in FIG. 4). That is, when the AC power system 2 is normal, the zero-phase voltage value Vs_0 is substantially zero. When the AC power system 2 causes a one-line ground fault, the total voltage of the remaining two phases appears as the voltage value Vs_0 for the zero phase (time T1 to time T2 in FIG. 4). Therefore, when the absolute value of the zero-phase voltage value Vs_0 is equal to or greater than a predetermined value, it can be considered that a one-line ground fault has occurred in the AC power system 2.

  The waveform shown in FIG. 4 also occurs when a failure occurs in the U-phase detection system at time T1. That is, the waveform shown in FIG. 4 also occurs when a failure occurs in any of the U-phase main voltage detector 61, the U-phase auxiliary voltage detector 62, and the A / D converter 63.

As described above, the level detection circuit 85 outputs “0” when the absolute value of the zero-phase voltage value Vs — 0 ₁ is less than the predetermined value, and outputs “1” when the absolute value is equal to or greater than the predetermined value. Output. That is, the level detection circuit 85 outputs “0” when the AC power system 2 and the voltage detection unit 25 are normal, and outputs to at least one of the AC power system 2 and the first detection system 25 a of the voltage detection unit 25. When an abnormality occurs, “1” is output.

The second detection unit 82 b includes an adder 86, an absolute value detection circuit 87, and a level detection circuit 88. The configuration of the second detection unit 82b is substantially the same as the configuration of the first detection unit 82a. Each voltage value Vs_U ₂ , Vs_V ₂ , Vs_W ₂ acquired by the second detection system 25 b of the voltage detection unit 25 is input to the adder 86. The adder 86, the voltage value Vs_U _2, Vs_V _2, calculates a voltage value Vs_0 ₂ of the zero-phase alternating-current power system 2 from Vs_W _2. Absolute value detecting circuit 87 detects the absolute value of the voltage value Vs_0 ₂ zero phase. Level detecting circuit 88, for example, when the voltage value Vs_0 ₂ of the absolute value of the zero-phase-sequence input is less than a predetermined value, outputs "0" to the control signal generating unit 80, when a predetermined value or more In addition, “1” is output to the control signal generator 80.

  The control signal generation unit 80 determines the states of the AC power system 2 and the voltage detection unit 25 based on the outputs of the level detection circuits 85 and 88.

  The control signal generation unit 80 determines that the AC power system 2 and the voltage detection unit 25 are normal when the outputs of the level detection circuits 85 and 88 are both “0”. That is, the control signal generation unit 80 determines that the AC power system 2 and the voltage detection unit 25 are normal when the generation of the zero phase is not detected in both the first detection system 25a and the second detection system 25b. judge.

  The control signal generation unit 80 determines that a one-line ground fault has occurred in the AC power system 2 when the outputs of the level detection circuits 85 and 88 are both “1”. That is, the control signal generation unit 80 determines that a one-line ground fault has occurred when occurrence of a zero-phase component is detected in both the first detection system 25a and the second detection system 25b.

  When the output of the level detection circuit 85 is “1” and the output of the level detection circuit 88 is “0”, the control signal generation unit 80 determines that the first detection system 25a has failed. That is, the control signal generation unit 80 determines that the first detection system 25a is out of order when only the first detection system 25a detects the occurrence of the zero phase.

  Then, when the output of the level detection circuit 85 is “0” and the output of the level detection circuit 88 is “1”, the control signal generation unit 80 determines that the second detection system 25b has failed. The control signal generation unit 80 determines that the second detection system 25b has failed when occurrence of the zero phase is detected only by the second detection system 25b.

  When the control signal generation unit 80 determines that the AC power system 2 and the voltage detection unit 25 are normal, the control signal generation unit 80 determines each converter CEL based on the detection results of the current detectors 24a to 24f and the voltage detection unit 25. By generating a control signal and inputting the control signal to each converter CEL, power conversion by the main circuit unit 12 is controlled.

  The control signal generation unit 80, for example, based on the detection results of the current detectors 24 a to 24 f and the voltage detection unit 25, the detected value of the DC current flowing in each DC power transmission line 3, 4, and the AC power system 2 The detection value of the alternating current of each phase is acquired.

  In addition, the control signal generation unit 80 receives a DC current command value of a DC current flowing through each DC power transmission line 3, 4 and an AC current command value of an AC current of each phase of the AC power system 2. The direct current command value and the alternating current command value are input to the control signal generation unit 80 from, for example, a host controller of the direct current power transmission system.

  The control signal generator 80, for example, each of the converters CEL so that the acquired detected value of the direct current and the detected value of the alternating current of each phase match the direct current command value and the alternating current command value. The timing for turning on / off the switching elements 41, 42 is determined, and on / off of the switching elements 41, 42 is controlled at the determined timing. As described above, the control circuit 14 is configured so that the main circuit unit has a current value corresponding to the direct current command value and the alternating current command value based on the detection values of the current detectors 24a to 24f and the voltage detection unit 25. 12 operations are controlled.

At this time, the control signal generation unit 80 also detects the voltage values Vs_U ₁ , Vs_V ₁ , Vs_W ₁ detected by the first detection system 25a of the voltage detection unit 25, and the voltages detected by the second detection system 25b. value Vs_U _2, Vs_V _2, based on Vs_W _2, determines the voltage value of each phase of the AC power system 2. The control signal generation unit 80 controls the operation of the main circuit unit 12 as described above based on the determined voltage value of each phase.

For example, the control signal generation unit 80 determines the minimum value of the detection value of the first detection system 25a and the detection value of the second detection system 25b for each phase. Specifically, the smaller the absolute value of the voltage value Vs_U ₁ and the voltage value Vs_U _2, is determined as a voltage value of U-phase.

  The method for determining the voltage value of each phase is not limited to the above. For example, contrary to the above, the maximum value of the detection value of the first detection system 25a and the detection value of the second detection system 25b may be selected. Moreover, you may select the detection value of the predetermined one among the 1st detection system 25a and the 2nd detection system 25b. Or you may determine the average value of the detection value of the 1st detection system 25a and the detection value of the 2nd detection system 25b as a voltage value of each phase. For example, when the voltage detection unit 25 has three or more detection systems, an intermediate value of detection values of each detection system may be determined as a voltage value of each phase.

  When it is determined that a one-line ground fault has occurred, the control signal generation unit 80 continues the operation of the main circuit unit 12 under the operating conditions at the time of the system fault. The operating condition at the time of a system fault is, for example, an operating condition in which the output is reduced as compared with the normal time. When supplying DC power from the AC power system 2 to the DC power transmission lines 3 and 4, the operating conditions at the time of a system fault are, for example, operating conditions in which the DC power supplied to the DC power transmission lines 3 and 4 is lower than normal. It is. When three-phase AC power is supplied from the DC power transmission lines 3 and 4 to the AC power system 2, the operating conditions at the time of a system fault are, for example, three-phase AC power (active power) supplied to the AC power system 2 more than normal. This is an operating condition in which At this time, the method for determining the voltage value of each phase of the AC power system 2 may be the same as in the normal state.

  For example, the control signal generation unit 80 counts a predetermined time from the occurrence of the one-line ground fault, and stops the operation of the main circuit unit 12 when the one-line ground fault is continued for a predetermined time. . For example, the control signal generation unit 80 stops the operation of the main circuit unit 12 when the one-line ground fault has continued for 1 second or longer.

  The control circuit 14 may perform a notification operation when detecting the occurrence of a one-line ground fault. The notification may be notification to a person such as an administrator or notification (signal transmission) to a host controller or the like. When notifying a person, for example, the power converter 10 is provided with a notification unit. For example, the control circuit 14 performs notification by operating a notification unit in response to detection of a one-line ground fault. The notification unit may be of any configuration capable of notifying the occurrence of a one-line ground fault, such as a speaker that outputs sound and a display that displays characters and symbols.

When determining that the first detection system 25a has failed, the control signal generator 80 operates the main circuit unit 12 based on the voltage values Vs_U ₂ , Vs_V ₂ , and Vs_W ₂ detected by the second detection system 25b. Let it continue. Similarly, when the control signal generation unit 80 determines that the second detection system 25b has failed, the control signal generation unit 80 determines the main circuit unit 12 based on the voltage values Vs_U ₁ , Vs_V ₁ , and Vs_W ₁ detected by the first detection system 25a. Continue driving. In addition, the control signal generation unit 80 detects a failure of the first detection system 25a when the second detection system 25b detects the occurrence of the zero phase and detects a failure of the second detection system 25b. In the state, when the first detection system 25a detects the occurrence of the zero phase, the operation of the main circuit unit 12 is stopped.

  For example, the control signal generation unit 80 stops the operation of the main circuit unit 12 in response to the failure determination when the failure of the first detection system 25a is determined and when the failure of the second detection system 25b is determined. May be. Further, the control circuit 14 may perform a notification operation when detecting a failure in the first detection system 25a or a failure in the second detection system 25b. The notification operation at the time of failure detection may be the same as in the case of a one-line ground fault.

FIG. 5 is a flowchart schematically illustrating an example of the operation of the power conversion device according to the embodiment.
As illustrated in FIG. 5, when the power conversion device 10 starts operation, the power conversion device 10 detects the current values of the arm portions 22 a to 22 f by the current detectors 24 a to 24 f and the voltages of the phases of the AC power system 2. The value is detected by each of the first detection system 25a and the second detection system 25b of the voltage detection unit 25 (step S1 in FIG. 5).

The control circuit 14 of the power conversion device 10 detects the zero phase of the AC power system 2 in the zero phase detection unit 82. The zero phase detection unit 82 detects the occurrence of the zero phase of the AC power system 2 from each voltage value Vs_U ₁ , Vs_V ₁ , Vs_W ₁ detected by the first detection system 25a and also detects by the second detection system 25b. Generation of the zero phase of the AC power system 2 is detected from each of the voltage values Vs_U ₂ , Vs_V ₂ , Vs_W ₂ . The zero phase detection unit 82 inputs the detection result for the zero phase of the AC power system 2 to the control signal generation unit 80.

  Based on the detection result of the zero-phase detection unit 82, the control signal generation unit 80 is normal in the AC power system 2 and the voltage detection unit 25, the occurrence of a one-wire ground fault, the failure in the first detection system 25a, and the second One of the failures in the detection system 25b is determined.

  When the control signal generation unit 80 determines that the AC power system 2 and the voltage detection unit 25 are normal (“Y” in step S2 of FIG. 5), each detection of the first detection system 25a and the second detection system 25b. Based on the result, the voltage value of each phase of the AC power system 2 is determined (step S3 in FIG. 5).

  The control signal generation unit 80 generates a control signal for each converter CEL based on the determined voltage value of each phase of the AC power system 2 and each detection result of each of the current detectors 24a to 24f. By inputting to each converter CEL, power conversion by the main circuit unit 12 is controlled (step S4 in FIG. 5). As a result, power is supplied from the AC power system 2 to the DC power transmission lines 3 and 4. Alternatively, power is supplied from the DC power transmission lines 3 and 4 to the AC power system 2. Thereafter, the control circuit 14 returns to the operation of step S1.

  When it is determined that a one-line ground fault has occurred ("Y" in step S5 in FIG. 5), the control signal generator 80 generates an alternating current based on the detection results of the first detection system 25a and the second detection system 25b. The voltage value of each phase of the electric power grid | system 2 is determined (step S6 of FIG. 5).

  Thereafter, the control signal generation unit 80 generates a control signal for each converter CEL based on the operating condition at the time of the system fault, and inputs the control signal to each converter CEL, thereby operating the operating condition at the time of the system fault. The operation of the main circuit unit 12 is continued (step S7 in FIG. 5). Thereafter, the control circuit 14 returns to the operation of step S1. At this time, the control circuit 14 measures the time and stops the operation of the main circuit unit 12 when the one-line ground fault is continued for a predetermined time.

Control signal generating unit 80, when determining the failure of the first detection system 25a ( "Y" in step S8 in FIG. 5), the voltage values detected by the second detection system _{25b Vs_U 2, Vs_V 2, Vs_W} 2 Based on the detection results of the current detectors 24a to 24f, a control signal for each converter CEL is generated, and the control signal is input to each converter CEL, so that the operation of the main circuit unit 12 is continued. (Step S9 in FIG. 5). Thereafter, the control circuit 14 returns to the operation of step S1.

When the control signal generation unit 80 determines that the second detection system 25b has failed ("N" in step S8 in FIG. 5), the voltage values Vs_U ₁ , Vs_V ₁ detected by the first detection system 25a, Based on each detection result of Vs_W ₁ and each of the current detectors 24a to 24f, a control signal for each converter CEL is generated, and the control signal is input to each converter CEL, thereby operating the main circuit unit 12. Continue (step S10 in FIG. 5). Thereafter, the control circuit 14 returns to the operation of step S1, and thereafter repeats the same processing.

  Thus, in the power converter device 10 according to the present embodiment, it is possible to distinguish between a one-wire ground fault of the AC power system 2 and a failure of the voltage detection unit 25 and perform appropriate measures in each case. Thereby, in the power converter device 10, reliability can be improved compared with the case where operation | movement is stopped according to the detection of the zero phase component.

  FIGS. 6A and 6B are block diagrams schematically showing a modification of the voltage detection unit. As shown in FIG. 6A, in this example, the main voltage detector 71 is omitted in the second detection system 25b of the voltage detection unit 25. In this example, the auxiliary voltage detector 72 of the second detection system 25b is connected to the secondary side of the main voltage detector 61 of the first detection system 25a.

  In the example shown in FIG. 6B, the main voltage detector 71 and the auxiliary voltage detector 72 are omitted in the second detection system 25b. In the example of FIG. 6B, the A / D converters 73 to 75 of the second detection system 25b are connected to the secondary side of the auxiliary voltage detector 62 of the first detection system 25a.

  As described above, the redundant portion in the voltage detection unit 25 may be a subsequent stage from the main voltage detectors 61 and 71, may be a subsequent stage from the auxiliary voltage detectors 62 and 72, or may be A / D converters 63 to 65, Only 73-75 may be sufficient. What is necessary is just to select arbitrarily the part made redundant in the voltage detection part 25 according to the specification of a system. The voltage detection unit 25 includes a first detection system 25a and a second detection system 25b, and may have an arbitrary configuration that can acquire at least two voltage values of the AC voltage of each phase of the AC power system 2.

FIG. 7 is a block diagram schematically showing a modification of the converter.
As illustrated in FIG. 7, in this example, the converter CEL further includes a third switching element 43 and a fourth switching element 44. The third switching element 43 and the fourth switching element 44 are substantially the same elements as the first switching element 41 and the second switching element 42.

  The pair of main terminals of the fourth switching element 44 are connected in series to the pair of main terminals of the third switching element 43. The third switching element 43 and the fourth switching element 44 are connected in parallel to the first switching element 41 and the second switching element 42. The charge storage element 45 is connected in parallel to the first switching element 41 and the second switching element 42 and is connected in parallel to the third switching element 43 and the fourth switching element 44.

  The third switching element 43 is connected with a rectifying element 43d in antiparallel with the pair of main terminals. A rectifying element 44d is connected to the fourth switching element 44 in antiparallel with the pair of main terminals.

  The first connection terminal 40 a of the converter CEL is connected between the first switching element 41 and the second switching element 42. The second connection terminal 40 b is connected between the third switching element 43 and the fourth switching element 44. In this example, the second connection terminal 40 b is connected to the main terminal opposite to the main terminal connected to the second switching element 42 of the first switching element 41 via the third switching element 43. That is, in this example, the switching elements 41 to 44 are connected by a full bridge. In this example, the converter CEL is a full bridge circuit. The driver circuit 46 switches on / off of each of the switching elements 41 to 44 based on the input control signal.

  Thus, the converter CEL used in the MMC type main circuit unit 12 may be a half-bridge circuit or a full-bridge circuit.

FIG. 8 is a block diagram schematically illustrating a modification of the main circuit unit.
As shown in FIG. 8, in the main circuit unit 12a of this example, the transformer 6 and the buffer reactors 23a to 23f shown in FIG. 1 are omitted, and three-winding transformers 111 to 113 are provided instead. It has been.

  The three-winding transformer 111 is provided between the first arm portion 22a and the second arm portion 22b. The three-winding transformer 111 includes a primary winding 111a, a secondary winding 111b, and a tertiary winding 111c. A primary winding 111 a of the three-winding transformer 111 is connected to the AC power system 2. The secondary winding 111b is connected to the negative terminal of the first arm portion 22a that is the upper arm. The tertiary winding 111c is connected to the positive terminal of the second arm portion 22b that is the lower arm.

  The 3-winding transformer 112 is provided between the third arm portion 22c and the fourth arm portion 22d. The 3-winding transformer 112 has a primary winding 112a, a secondary winding 112b, and a tertiary winding 112c. The primary winding 112 a of the three-winding transformer 112 is connected to the AC power system 2. The secondary winding 112b is connected to the negative terminal of the third arm portion 22c that is the upper arm. The tertiary winding 112c is connected to the positive terminal of the fourth arm portion 22d that is the lower arm.

  The 3-winding transformer 113 is provided between the fifth arm portion 22e and the sixth arm portion 22f. The 3-winding transformer 113 includes a primary winding 113a, a secondary winding 113b, and a tertiary winding 113c. A primary winding 113 a of the three-winding transformer 113 is connected to the AC power system 2. The secondary winding 113b is connected to the negative terminal of the fifth arm portion 22e that is the upper arm. The tertiary winding 113c is connected to the positive terminal of the sixth arm portion 22f that is the lower arm.

  In each of the three-winding transformers 111 to 113, the neutral point between the secondary winding 111b and the tertiary winding 111c, the neutral point between the secondary winding 112b and the tertiary winding 112c, and the secondary winding 113b. And the neutral point of the tertiary winding 113c are connected to each other.

  The main circuit unit 12a shown in FIG. 8 can also perform AC / DC conversion by the same operation as the main circuit unit 12 shown in FIG. A one-line ground fault of the AC power system 2 and a failure of the voltage detection unit 25 can be distinguished, and appropriate measures can be taken in each case, and reliability can be improved. Further, in the main circuit unit 12a of this example, the buffer reactors 23a to 23f and the like can be omitted as compared with the main circuit unit 12, and the number of parts can be reduced. For example, an increase in size and cost of the power conversion device 10 can be suppressed.

  In each of the above embodiments, an MMC type power converter is used for the main circuit units 12 and 12a. The main circuit units 12 and 12a are not limited to the MMC type, and may be other types of power converters in which a plurality of converters CEL are connected in series. Further, the main circuit unit is not limited to a system in which a plurality of converters CEL are connected in series, and may be, for example, a two-level inverter or a three-level inverter. The configuration of the main circuit unit may be any configuration that can convert the three-phase AC power into another power.

  The power conversion device 10 is not limited to a DC power transmission system, and may be applied to other arbitrary systems that require conversion from AC to DC and conversion from DC to AC. The AC / DC conversion by the power conversion device 10 is not limited to both AC to DC and DC to AC, and may be only one of AC to DC or DC to AC. Moreover, the power converter device 10 may be, for example, a power converter device that converts three-phase AC power into another AC power having a different frequency or amplitude. The power converter 10 may be an arbitrary power converter connected to the AC power system 2 of three-phase AC power.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  2 ... AC power system, 3, 4 ... DC transmission line, 6 ... Transformer, 10 ... Power converter, 12, 12a ... Main circuit part, 14 ... Control circuit, 20a, 20b ... DC terminal, 21a-21c ... No. 1st-3rd AC terminal, 22a-22f ... 1st-6th arm part, 23a-23f ... Buffer reactor, 24a-24f ... Current detector, 25 ... Voltage detection part, 25a ... 1st detection system, 25b ... 1st 2 detection systems, 26 ... signal lines, 40a, 40b ... first and second connection terminals, 41-44 ... first to fourth switching elements, 45 ... charge storage elements, 46 ... driver circuit, 61, 71 ... main voltage Detector 62, 72 ... Auxiliary voltage detector 63-65, 73-75 ... A / D converter, 80 ... Control signal generator, 82 ... Zero phase detector, 82a ... First detector, 82b ... first 2 detection 83, 86 ... adder, 84, 87 ... absolute value detection circuit, 85, 88 ... level detection circuit, 111-113 ... 3-winding transformer, 111a, 112a, 113a ... primary winding, 111b, 112b, 113b ... Secondary winding, 111c, 112c, 113c ... Tertiary winding, CEL ... Converter

Claims (4)

A main circuit unit connected to the AC power system of the three-phase AC power and performing at least one of conversion from the three-phase AC power to another power and conversion from another power to the three-phase AC power;
A voltage detection unit having a first detection system and a second detection system, and acquiring at least two voltage values of each phase of the AC power system by the first detection system and the second detection system;
Based on each voltage value acquired by the voltage detection unit, a control circuit for controlling the operation of the main circuit unit,
With
The control circuit detects occurrence of a zero phase of the AC power system based on a detection result of the first detection system, and detects a zero phase component of the AC power system based on a detection result of the second detection system. When the occurrence of zero phase is not detected in both the first detection system and the second detection system, it is determined that the AC power system and the voltage detection unit are normal, When occurrence of a zero phase is detected in both the first detection system and the second detection system, it is determined that a one-line ground fault has occurred in the AC power system, and only in the first detection system When the occurrence of the zero phase is detected, it is determined that the first detection system is faulty. When the occurrence of the zero phase is detected only by the second detection system, the second detection system is faulty. A power conversion device for determination.   The power conversion device according to claim 1, wherein the control circuit continues the operation of the main circuit unit under an operation condition at the time of a grid fault when it is determined that the one-wire ground fault has occurred.   When the control circuit determines a failure of the first detection system, the control circuit controls the operation of the main circuit unit based on each voltage value detected by the second detection system. When the operation is continued and the failure of the second detection system is determined, the operation of the main circuit unit is controlled by controlling the operation of the main circuit unit based on each voltage value detected by the first detection system. The power converter according to claim 1 or 2, wherein the operation is continued. A main circuit unit connected to the AC power system of the three-phase AC power and performing at least one of conversion from the three-phase AC power to another power and conversion from another power to the three-phase AC power;
A voltage detection unit having a first detection system and a second detection system, and acquiring at least two voltage values of each phase of the AC power system by the first detection system and the second detection system;
Based on each voltage value acquired by the voltage detection unit, a control circuit for controlling the operation of the main circuit unit,
A method for controlling a power conversion device comprising:
The generation of the zero phase of the AC power system is detected based on the detection result of the first detection system, and the generation of the zero phase of the AC power system is detected based on the detection result of the second detection system. ,
When the occurrence of the zero phase is not detected in both the first detection system and the second detection system, it is determined that the AC power system and the voltage detection unit are normal,
When occurrence of a zero phase is detected in both the first detection system and the second detection system, it is determined that a one-line ground fault has occurred in the AC power system,
When occurrence of the zero phase is detected only in the first detection system, it is determined that the first detection system is faulty,
A method for controlling a power conversion device, which determines that a failure of the second detection system is detected when occurrence of a zero-phase component is detected only in the second detection system.

Images