Power Conversion Equipment

Abstract

To provide a power conversion apparatus capable of improving stability and operability.SOLUTION: A power conversion apparatus comprises: a main circuit unit that has a plurality of converters connected in series and converts power by operating the plurality of converters; and a control device that controls the operation of the main circuit unit. Each of the plurality of converters has a pair of connection terminals, a plurality of switching elements, a charge storage element disposed in parallel with the plurality of switching elements, and a drive circuit for switching the on-state and the off-state of the plurality of switching elements. The control device causes the main circuit unit to continue the power conversion when the number of converters set in a bypass state is yet to reach a prescribed number. The drive circuit releases the bypass state of the converters when the switching elements are normal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] FIELD An embodiment of the present invention relates to a power conversion device. [Background technology]

[0002] There is known a power conversion device including a main circuit section that performs at least one of conversion from AC power to DC power and conversion from DC power to AC power, and a control device that controls the operation of the main circuit section. In such a power conversion device, a multi-stage main circuit section in which a plurality of converters are connected in series is used. A power conversion device including a multi-stage main circuit section is used, for example, in a DC power transmission system that converts AC power to DC power and transmits the power.

[0003] Each converter has a plurality of switching elements and a charge storage element connected in parallel to the plurality of switching elements, and each converter has a pair of connection terminals and is connected in series via the pair of connection terminals.

[0004] In a multi-stage main circuit, when an abnormality occurs in any of the converters, the pair of connection terminals of the converter in which the abnormality occurred can be short-circuited to allow the remaining converters to continue operation. Shorting a pair of connection terminals in this way is sometimes called a bypass.

[0005] The bypassed converter continues to be in the bypassed state until the operation of the power conversion device is stopped. However, as the number of bypassed converters increases among multiple converters connected in series, the stability of operation of the main circuit unit decreases. When the number of bypassed converters reaches a predetermined number, the operation of the power conversion device is stopped. In this way, bypassing a converter in which an abnormality has occurred may cause a decrease in the stability of operation of the main circuit unit and a decrease in operability due to the operation stop of the power conversion device. For this reason, improved stability and operability are desired in a power conversion device in which multiple converters are connected in series. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-140738 A Summary of the Invention [Problem to be solved by the invention]

[0007] Advantageous Effects of Invention An embodiment of the present invention provides a power conversion device capable of improving stability and operability. [Means for solving the problem]

[0008] According to an embodiment of the present invention, there is provided a power converter including a main circuit section having a plurality of converters connected in series and converting power by the operation of the plurality of converters, and a control device for controlling the operation of the main circuit section, wherein each of the plurality of converters has a pair of connection terminals, a plurality of switching elements, a charge storage element connected in parallel to the plurality of switching elements, and a drive circuit for switching between an on state and an off state of the plurality of switching elements, and is connected in series via the pair of connection terminals, and has an output state in which a voltage of the charge storage element is output between the pair of connection terminals by switching the plurality of switching elements, and The converter can be switched between a bypass state in which the pair of connection terminals are conductive and a stop state in which the multiple switching elements are in an off state, and the drive circuit switches the converter to the bypass state when the DC voltage of the charge storage element becomes equal to or higher than an upper limit value or equal to or lower than a lower limit value, and the control device allows the main circuit unit to continue power conversion when the number of the converters in the bypass state has not reached a predetermined number, and the drive circuit, after switching to the bypass state, checks the soundness of the multiple switching elements, and releases the bypass state of the converter when it is confirmed that the multiple switching elements are sound. The plurality of switching elements each have a pair of main terminals and a control terminal, and the drive circuit checks whether the voltage of the control terminal is normal to check the soundness of the plurality of switching elements. A power converter is provided. Effect of the Invention

[0009] A power conversion device capable of improving stability and operability is provided. [Brief description of the drawings]

[0010] [Figure 1] 1 is a block diagram illustrating a power conversion device according to a first embodiment. [Diagram 2] FIG. 2 is a block diagram illustrating a converter. [Diagram 3] 10 is a flowchart illustrating an example of an operation of the converter. [Figure 4] 10 is a flow chart that illustrates a schematic modification of the operation of the converter. [Diagram 5] 10 is a flow chart that illustrates a schematic modification of the operation of the converter. [Figure 6] FIG. 11 is a block diagram illustrating a power conversion device according to a second embodiment. [Figure 7] FIG. 13 is a block diagram illustrating a modified example of the converter. [Figure 8] FIG. 13 is a block diagram illustrating a modified example of the converter. [Figure 9] FIG. 13 is a block diagram illustrating a modified example of the converter.

[0011] 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 parts, etc. are not necessarily the same as in reality. Even when the same part is shown, the dimensions and ratios of each part may be different depending on the drawing. In this specification and each drawing, elements similar to those described above with reference to the previous drawings are given the same reference numerals and detailed descriptions thereof will be omitted as appropriate.

[0012] (First embodiment) FIG. 1 is a block diagram illustrating a power conversion device according to a first embodiment. 1, the power conversion device 10 includes a main circuit unit 12 and a control device 14. The power conversion device 10 is used, for example, in a DC power transmission system. The power conversion device 10 is connected to an AC power system 2 and a pair of DC transmission lines 3 and 4 in the DC power transmission system.

[0013] The DC transmission system has, for example, a transformer 6. The main circuit section 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 section 12. The transformer 6 changes the effective value of each phase of the three-phase AC power in accordance with the main circuit section 12. The transformer 6 is a three-phase transformer. The transformer 6 is provided as necessary and can be omitted. The three-phase AC power of the AC power system 2 may be directly supplied to the main circuit section 12.

[0014] The power conversion device 10 converts three-phase AC power supplied from the AC power system 2 into DC power, and supplies the converted DC power to the DC transmission lines 3 and 4. The power conversion device 10 also converts DC power supplied from the DC transmission lines 3 and 4 into three-phase AC power, and supplies the converted three-phase AC power to the AC power system 2. In this manner, the power conversion device 10 performs AC-DC conversion from AC to DC, and DC-DC conversion from DC to AC. In this example, the AC power system 2 is shown as an AC circuit, and the DC transmission lines 3 and 4 are shown as DC circuits. The AC circuit may be, for example, an AC load or an AC power source. The DC circuit may be, for example, a DC load or a DC power source.

[0015] For example, the DC transmission line 3 is a high-voltage side transmission line of DC power, and the DC transmission line 4 is a low-voltage side transmission line of DC power. The power conversion device 10 outputs converted DC power to the DC transmission lines 3 and 4 so that the DC transmission line 3 side is high voltage and the DC transmission line 4 side is low voltage.

[0016] The main circuit unit 12 is provided between the AC power system 2 and each of the DC transmission lines 3 and 4. The main circuit unit 12 converts three-phase AC power to DC power and converts DC power to three-phase AC power. The main circuit unit 12 is, for example, a multilevel power converter having a plurality of converters connected in series. The main circuit unit 12 is, for example, an MMC (Modular Multilevel Converter) type power converter. The MMC type main circuit unit 12 has a plurality of converters connected in series. Each converter has a plurality of switching elements connected in half-bridge connection or full-bridge connection, and a charge storage element connected in parallel to each switching element. The main circuit unit 12 converts power by the operation of the plurality of converters. The main circuit unit 12 converts AC to DC by, for example, switching each switching element of the plurality of converters.

[0017] The control device 14 is connected to the main circuit section 12. The control device 14 controls the on / off of each switching element to control the conversion from three-phase AC power to DC power and the conversion from DC power to three-phase AC power by the main circuit section 12.

[0018] The main circuit portion 12 has a pair of first and second DC terminals 20a, 20b, three AC terminals (first to third) 21a to 21c, and six arm portions (first to sixth) 22a to 22f.

[0019] The first DC terminal 20a is connected to the high-voltage side DC transmission line 3. The second DC terminal 20b is connected to the low-voltage side DC transmission line 4. As a result, DC power converted by the main circuit unit 12 is supplied to the DC transmission lines 3 and 4, and DC power supplied from the DC transmission lines 3 and 4 is input to the main circuit unit 12.

[0020] 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, 20b.

[0021] 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 portion 22c and the fourth arm portion 22d are connected in parallel to the first arm portion 22a and the second arm portion 22b.

[0022] 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 are connected in parallel to the third arm portion 22c and the fourth arm portion 22d.

[0023] In the main circuit unit 12, the first leg LG1 is formed by the first arm portion 22a and the second arm portion 22b, the second leg LG2 is formed by the third arm portion 22c and the fourth arm portion 22d, and the third leg LG3 is formed by the fifth arm portion 22e and the sixth arm portion 22f. That is, in this example, the main circuit unit 12 is a three-phase inverter with three legs and six arms. In other words, the main circuit unit 12 has a plurality of bridge-connected arm portions 22a to 22f. In this example, the main circuit unit 12 has six three-phase bridge-connected arm portions 22a to 22f.

[0024] The first arm portion 22a, the third arm portion 22c, and the fifth arm portion 22e are upper arms. The second arm portion 22b, the fourth arm portion 22d, and the sixth arm portion 22f are lower arms. In this manner, the main circuit portion 12 has a plurality of arms and a plurality of legs each formed by a plurality of switching elements. The main circuit portion 12 may be, for example, a two-leg or four-arm single-phase inverter. The number of arms and legs is not limited to the above and may be any number.

[0025] The first arm section 22a has a plurality of converters UP1, UP2...UPM1 connected in series. The second arm section 22b has a plurality of converters UN1, UN2...UNM2 connected in series. The third arm section 22c has a plurality of converters VP1, VP2...VPM3 connected in series. The fourth arm section 22d has a plurality of converters VN1, VN2...VNM4 connected in series. The fifth arm section 22e has a plurality of converters WP1, WP2...WPM5 connected in series. The sixth arm section 22f has a plurality of converters WN1, WN2...WNM6 connected in series.

[0026] However, in the following, when the converters UP1, UP2...UPM1, UN1, UN2...UNM2, VP1, VP2...VPM3, VN1, VN2...VNM4, WP1, WP2...WPM5, WN1, WN2...WNM6 are referred to collectively as the "converter CEL."

[0027] In each of the arm sections 22a to 22f, M1, M2, M3, M4, M5, and M6 represent the number of converters CEL connected in series. In each of the arm sections 22a to 22f, the number of converters CEL connected in series is, for example, about 100 to 120. However, the number of converters CEL connected in series is not limited to this and may be any number.

[0028] The number of converters CEL provided in each of the arm sections 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 sections 22a to 22f may differ within a range that does not affect the operation of the main circuit section 12. For example, when 100 converters CEL are connected in series to one arm section, the number of converters CEL provided in another arm section may differ by one or two.

[0029] The arm sections 22a to 22f further include buffer reactors 23a to 23f and a plurality of current detectors 24a to 24f, respectively. The power conversion device 10 further includes a voltage detection section 25.

[0030] The buffer reactors 23a to 23f are connected in series to the converters CEL in the arm sections 22a to 22f, respectively. The buffer reactor 23a of the first arm section 22a is provided between the converter UP1 and a connection point between the AC terminal 21a and the first arm section 22a and the second arm section 22b. The buffer reactor 23b of the second arm section 22b is provided between the converter UN1 and a connection point between the AC terminal 21a and the first arm section 22a and the second arm section 22b. The buffer reactor 23c of the third arm section 22c is provided between the converter VP1 and a connection point between the AC terminal 21b and the third arm section 22c and the fourth arm section 22d. The buffer reactor 23d of the fourth arm section 22d is provided between the converter VN1 and a connection point between the AC terminal 21b and the third arm section 22c and the fourth arm section 22d. The buffer reactor 23e of the fifth arm portion 22e is provided between the converter WP1 and a connection point between the AC terminal 21c and the fifth arm portion 22e and the sixth arm portion 22f. The buffer reactor 23f of the sixth arm portion 22f is provided between the converter WN1 and a connection point between the AC terminal 21c and the fifth arm portion 22e and the sixth arm portion 22f.

[0031] The current detector 24a is provided in the first arm portion 22a and detects a current flowing through the first arm portion 22a. That is, the current detector 24a detects an arm current of the first arm portion 22a. The current detector 24a is connected to the control device 14 via wiring or the like (not shown). The current detector 24a inputs the detected current value of the first arm portion 22a to the control device 14. As a result, the current value of the first arm portion 22a is input to the control device 14.

[0032] Similarly, current detector 24b detects the current flowing through the second arm portion 22b and inputs the detected current value to the control device 14. Current detector 24c detects the current flowing through the third arm portion 22c and inputs the detected current value to the control device 14. Current detector 24d detects the current flowing through the fourth arm portion 22d and inputs the detected current value to the control device 14. Current detector 24e detects the current flowing through the fifth arm portion 22e and inputs the detected current value to the control device 14. Current detector 24f detects the current flowing through the sixth arm portion 22f and inputs the detected current value to the control device 14.

[0033] The voltage detection unit 25 detects the AC voltage (phase voltage) of each phase of the AC power system 2, and inputs the detected value to the control device 14. The voltage detection unit 25 may be connected to the primary side or the secondary side of the transformer 6.

[0034] In the main circuit section 12, the connection point between the first arm section 22a and the second arm section 22b, the connection point between the third arm section 22c and the fourth arm section 22d, and the connection point between the fifth arm section 22e and the sixth arm section 22f are each an AC output point.

[0035] 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 of the AC terminals 21a to 21c is connected to a transformer 6, for example.

[0036] Each converter CEL is connected to the control device 14, for example, via a signal line 26. The control device 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 the control and operational protection of the converter CEL to the control device 14 via another signal line (not shown).

[0037] The communication method between the control device 14 and each converter CEL is not limited to the above. For example, a plurality of converters CEL connected in series may be connected in a daisy chain, and the control device 14 may communicate only with the converter CEL at one end of the daisy chain and the converter CEL at the other end. The communication method between the control device 14 and each converter CEL may be any communication method that can appropriately communicate between the control device 14 and each converter CEL.

[0038] FIG. 2 is a block diagram that illustrates a schematic representation of a converter. As shown in FIG. 2, the converter CEL has a plurality of switching elements 41, 42, a plurality of rectifying elements 51, 52, a charge storage element 60, a pair of connection terminals 61, 62, a drive circuit 64, a main circuit power supply circuit 66, and a transmission circuit 68.

[0039] Each of the switching elements 41, 42 has a pair of main terminals and a control terminal. The control terminal controls a current flowing between the pair of main terminals. A self-extinguishing element such as an IGBT is used for each of the switching elements 41, 42. The pair of main terminals is, for example, an emitter and a collector, and the control terminal is, for example, a gate.

[0040] Each of the switching elements 41, 42 switches between an on state that allows current to flow between a pair of main terminals and an off state that blocks the current flowing between the pair of main terminals. The off state is not limited to a state in which no current flows between the pair of main terminals, but may be, for example, a state in which a weak current that does not affect the operation of the converter CEL flows between the pair of main terminals. In other words, the off state is a state in which the current flowing between the pair of main terminals is sufficiently small.

[0041] Each of the switching elements 41, 42 is, for example, a normally-off type semiconductor element. Each of the switching elements 41, 42 is in an on state when the voltage of the control terminal is high, and in an off state when the voltage of the control terminal is low. Each of the switching elements 41, 42 is in an off state when the voltage of the control terminal is lower than the on state. Each of the switching elements 41, 42 is in an on state when a positive voltage is applied to the control terminal, and in an off state when the voltage of the control terminal is set to 0 V or a negative voltage is applied to the control terminal.

[0042] A pair of main terminals of the switching element 42 are connected in series to a pair of main terminals of the switching element 41. In this example, the converter CEL has two switching elements 41, 42 connected in series. In other words, the converter CEL has two switching elements 41, 42 connected in half-bridge configuration. In this example, the converter CEL is a converter with a half-bridge configuration.

[0043] The rectifier element 51 is connected in anti-parallel to a pair of main terminals of the switching element 41. The forward direction of the rectifier element 51 is opposite to the direction of the current flowing between the pair of main terminals of the switching element 41. Similarly, the rectifier element 52 is connected in anti-parallel to the pair of main terminals of the switching element 42. The rectifier elements 51 and 52 are so-called freewheel diodes.

[0044] The connection terminal 61 is connected between the switching element 41 and the switching element 42. The connection terminal 62 is connected to a main terminal of the switching element 41 opposite to the main terminal connected to the switching element 42.

[0045] The multiple converters CEL in the same arm portion are connected in series via a pair of connection terminals 61, 62. Power is supplied to the converters CEL via each of the connection terminals 61, 62. The switching element 41 is a so-called low-side switch, and the switching element 42 is a so-called high-side switch.

[0046] The transmission circuit 68 communicates with the control device 14, for example, via a signal line 26. The control device 14 transmits control signals for controlling the on / off of each of the switching elements 41, 42 to the transmission circuit 68 via the signal line 26. The transmission circuit 68 inputs the input control signals to the drive circuit 64.

[0047] The drive circuit 64 is connected to the control terminals of each of the switching elements 41, 42. The drive circuit 64 switches between the on and off states of each of the switching elements 41, 42 based on a control signal input from the transmission circuit 68. This controls the on / off of each of the switching elements 41, 42 in response to a control signal from the control device 14. The control device 14 generates a control signal for each converter CEL and controls the on / off of each of the switching elements 41, 42 of each converter CEL. In this way, the control device 14 controls the power conversion by the main circuit unit 12.

[0048] The configurations of the drive circuit 64 and the transmission circuit 68 are not limited to those described above, and any configuration capable of controlling the on / off of each of the switching elements 41, 42 may be used.

[0049] The charge storage element 60 is connected in parallel to the switching element 41 and the switching element 42. The charge storage element 60 is, for example, a capacitor.

[0050] When the switching element 41 is in the off state and the switching element 42 is in the on state, the voltage of the charge storage element 60 appears between the connection terminals 61, 62. When the switching element 41 is in the on state and the switching element 42 is in the off state, the connection terminals 61, 62 are conductive, and the voltage between the connection terminals 61, 62 becomes substantially zero.

[0051] In this way, the converter CEL switches between an output state in which the voltage of the charge storage element 60 is output between the connection terminals 61, 62, a bypass state in which the connection terminals 61, 62 are conductive, and a stop state in which the switching elements 41, 42 are turned off, by switching the switching elements 41, 42 based on control signals from the control device 14. The converter CEL is brought into the bypass state by turning on the lower switching element 41 of the two half-bridge connected switching elements 41, 42.

[0052] In each of the arm sections 22a to 22f, the total voltage of the converters CEL in the output state becomes the voltage of the arm section 22a to 22f. The main circuit section 12 and the control device 14 perform multi-level power conversion by controlling the number of converters CEL in the output state.

[0053] When both switching elements 41, 42 are in the off state (when converter CEL is in the stopped state), the voltage between each connection terminal 61, 62 is determined by the direction of the arm current. For example, when the arm current flows from connection terminal 62 to connection terminal 61, rectifier element 51 turns on, and the voltage between each connection terminal 61, 62 becomes substantially zero. Conversely, when the arm current flows from connection terminal 61 to connection terminal 62, rectifier element 52 turns on, charge storage element 60 is charged, and the voltage of charge storage element 60 appears between each connection terminal 61, 62.

[0054] The main circuit power supply circuit 66 is connected in parallel to the charge storage element 60. The main circuit power supply circuit 66 generates drive power for the drive circuit 64 and the transmission circuit 68 based on the charge stored in the charge storage element 60, and supplies the generated drive power to the drive circuit 64 and the transmission circuit 68. The drive circuit 64 and the transmission circuit 68 operate in response to the supply of drive power from the main circuit power supply circuit 66.

[0055] The method of supplying power to the drive circuit 64 and the transmission circuit 68 is not limited to the above. For example, power may be supplied to the drive circuit 64 and the transmission circuit 68 from a power source separate from the charge storage element 60. The method of supplying power to the drive circuit 64 and the transmission circuit 68 may be any method that can appropriately supply power to the drive circuit 64 and the transmission circuit 68.

[0056] The drive circuit 64 detects the DC voltage of the charge storage element 60, and performs a protective operation when the DC voltage of the charge storage element 60 becomes equal to or greater than an upper limit value or equal to or less than a lower limit value. When the DC voltage of the charge storage element 60 becomes equal to or greater than an upper limit value or equal to or less than a lower limit value, the drive circuit 64 switches the converter CEL to a bypass state.

[0057] For example, the voltage of the charge storage element 60 may rise or fall when the switching of the switching elements 41, 42 is not performed at the intended timing due to an abnormality in the drive circuit 64 or an abnormality in communication with the control device 14. Such an increase in the voltage of the charge storage element 60 may cause failures in various parts of the converter CEL, such as the switching elements 41, 42 and the charge storage element 60. A decrease in the voltage of the charge storage element 60 may cause malfunctions in various parts of the converter CEL.

[0058] Therefore, when the DC voltage of the charge storage element 60 becomes equal to or higher than the upper limit value or equal to or lower than the lower limit value, the drive circuit 64 switches the converter CEL to the bypass state. This makes it possible to suppress the failure of the converter CEL due to an increase in the voltage of the charge storage element 60 and the malfunction of the converter CEL due to a decrease in the voltage of the charge storage element 60.

[0059] The determination of whether the DC voltage of the charge storage element 60 is equal to or greater than the upper limit and equal to or less than the lower limit may be performed by the drive circuit 64 by directly inputting the DC voltage of the charge storage element 60 to the drive circuit 64, or may be performed by a separate voltage detection circuit that detects the DC voltage of the charge storage element 60. For example, the DC voltage of the charge storage element 60 may be detected by a separate voltage detection circuit, and when the DC voltage of the charge storage element 60 is equal to or greater than the upper limit or equal to or less than the lower limit, a detection signal may be input from the voltage detection circuit to the drive circuit 64, so that the drive circuit 64 can detect that the DC voltage of the charge storage element 60 is equal to or greater than the upper limit or equal to or less than the lower limit.

[0060] When the DC voltage of the charge storage element 60 becomes equal to or higher than the upper limit value or equal to or lower than the lower limit value and the converter CEL is switched to the bypass state, the drive circuit 64 transmits a bypass signal indicating the bypass state to the control device 14.

[0061] When the control device 14 receives a bypass signal and detects an abnormality in communication with any of the multiple converters CEL, the control device 14 judges whether the number of converters CEL in the bypass state in the same arm unit has reached a predetermined number. For example, when there is no signal input from a converter CEL even at a timing when a signal should be input from the converter CEL under normal circumstances, the control device 14 detects an abnormality in communication with the converter CEL.

[0062] When the control device 14 determines that the predetermined number has not been reached, the remaining converters CEL in the same arm continue the power conversion by the main circuit unit 12. On the other hand, when the control device 14 determines that the predetermined number has been reached, the control device 14 stops the power conversion by the main circuit unit 12.

[0063] In this way, even if an abnormality occurs in any of the multiple converters CEL connected in series, the power conversion device 10 can continue operation by putting the converter CEL in a bypass state where the abnormality has occurred until the number of converters CEL in a bypass state in the same arm section reaches a predetermined number, thereby improving operability.

[0064] In the bypass state where the connection terminals 61, 62 are electrically connected, the DC voltage of the charge storage element 60 gradually decreases. For example, when the DC voltage of the charge storage element 60 becomes equal to or higher than the upper limit and the converter CEL is switched to the bypass state, the drive circuit 64 checks the soundness of the switching elements 41, 42 when the DC voltage of the charge storage element 60 becomes equal to or lower than a predetermined value. The predetermined value is, for example, the same as the upper limit (threshold value of overvoltage). The predetermined value may be a dedicated threshold value different from the upper limit. The predetermined value is set to, for example, a value lower than the upper limit. This makes it possible to prevent, for example, the DC voltage of the charge storage element 60 from being determined to be equal to or lower than the predetermined value and then being determined to be equal to or higher than the upper limit again. However, the predetermined value may be set to a value higher than the upper limit. The predetermined value may be any value set for the DC voltage of the charge storage element 60.

[0065] In addition, the drive circuit 64 checks the soundness of the multiple switching elements 41, 42, for example, when the DC voltage of the charge storage element 60 becomes equal to or lower than a lower limit and the converter CEL is switched to a bypass state, and then the DC voltage of the charge storage element 60 becomes equal to or higher than a predetermined value. The predetermined value is, for example, the same as the lower limit (low voltage threshold). The predetermined value may be a dedicated threshold different from the lower limit. The predetermined value is set to, for example, a value higher than the lower limit. This makes it possible to prevent, for example, the DC voltage of the charge storage element 60 from being determined to be equal to or higher than the predetermined value and then being determined to be equal to or lower than the lower limit again. However, the predetermined value may be set to a value lower than the lower limit. The predetermined value may be any value set for the DC voltage of the charge storage element 60.

[0066] In addition, when the DC voltage of the charge storage element 60 falls below a lower limit value and the drive circuit 64 switches the converter CEL to a bypass state, the drive circuit 64 may perform an operation to charge the charge storage element 60, such as temporarily switching the converter CEL to an output state.

[0067] The drive circuit 64 has a confirmation circuit 70 for confirming the soundness of the multiple switching elements 41, 42. The confirmation circuit 70 confirms the soundness of the switching elements 41, 42 based on the voltages at the control terminals of the switching elements 41, 42. More specifically, the confirmation circuit 70 confirms the soundness of the switching elements 41, 42 based on the voltages between the control terminals of the switching elements 41, 42 and the main terminals on the low potential side. For example, if the switching elements 41, 42 are IGBTs, the confirmation circuit 70 confirms the soundness of the switching elements 41, 42 based on the gate-emitter voltage.

[0068] The drive circuit 64 switches the converter CEL from the bypass state to the stopped state when, for example, the DC voltage of the charge storage element 60 becomes equal to or greater than an upper limit value, the converter CEL is switched to the bypass state, and then the DC voltage of the charge storage element 60 becomes equal to or less than a predetermined value. Similarly, the drive circuit 64 switches the converter CEL from the bypass state to the stopped state when, for example, the DC voltage of the charge storage element 60 becomes equal to or greater than a lower limit value, the converter CEL is switched to the bypass state, and then the DC voltage of the charge storage element 60 becomes equal to or greater than a predetermined value.

[0069] For example, when a negative bias (negative voltage) is applied to the control terminals to turn off the switching elements 41, 42, if the switching elements 41, 42 are healthy, a negative bias appears at the control terminals of the switching elements 41, 42. On the other hand, if the switching elements 41, 42 have a short-circuit failure, the voltages of the control terminals of the switching elements 41, 42 are substantially 0 V even if a negative bias is applied to the control terminals. In other words, if the switching elements 41, 42 have a short-circuit failure, the absolute value of the voltages of the control terminals of the switching elements 41, 42 will be smaller than the absolute value of the negative bias voltage, even if a negative bias is applied to the control terminals.

[0070] The confirmation circuit 70 judges the switching elements 41, 42 to be healthy when the voltage of the control terminal becomes negative bias after the drive circuit 64 applies a negative bias to the control terminals of the switching elements 41, 42 and switches the converter CEL from the bypass state to the stopped state. The confirmation circuit 70 judges the switching elements 41, 42 to be abnormal when the voltage of the control terminal is substantially 0V (when the absolute value of the voltage of the control terminal is smaller than the absolute value of the negative bias voltage) after the drive circuit 64 applies a negative bias to the control terminals of the switching elements 41, 42 and switches the converter CEL from the bypass state to the stopped state. This allows the drive circuit 64 to check the health of the switching elements 41, 42. In this way, the drive circuit 64 checks the health of the multiple switching elements 41, 42, for example, by checking whether the voltage of the control terminals of the multiple switching elements 41, 42 is normal or not.

[0071] FIG. 3 is a flowchart illustrating an example of the operation of the converter. 3, the drive circuit 64 of the converter CEL determines whether the DC voltage of the charge storage element 60 is equal to or greater than an upper limit value or equal to or less than a lower limit value (step S101 in FIG. 3). When the DC voltage of the charge storage element 60 is within a range greater than the lower limit value and less than the upper limit value, the drive circuit 64 controls the on / off of the switching elements 41, 42 in response to a control signal from the control device 14 to convert power.

[0072] When the DC voltage of the charge storage element 60 becomes equal to or higher than the upper limit value or equal to or lower than the lower limit value, the drive circuit 64 switches the converter CEL to the bypass state (step S102 in FIG. 3). This makes it possible to suppress failures of the charge storage element 60 and the switching elements 41 and 42, or malfunctions of the converter CEL.

[0073] When the drive circuit 64 switches to the bypass state, the drive circuit 64 transmits a bypass signal indicating that the drive circuit 64 is in the bypass state to the control device 14 via the transmission circuit 68 or the like (step S103 in FIG. 3).

[0074] When the control device 14 receives the bypass signal, it judges whether or not the number of converters CEL in the bypass state in the same arm reaches a predetermined number. When the number of converters CEL in the bypass state reaches a predetermined number, the control device 14 stops the power conversion by the main circuit unit 12. When the number of converters CEL in the bypass state does not reach a predetermined number, the control device 14 removes the converter CEL in the bypass state from the control target, and the remaining converters CEL in the same arm continue the power conversion by the main circuit unit 12. In this case, the control device 14, for example, stops sending a control signal to the converter CEL in the bypass state. In addition, in this case, the control device 14 may change the manner of control of the remaining converters CEL compared to a case where there is no converter CEL in the bypass state so as to suppress the influence of the converter CEL in the bypass state.

[0075] After switching the converter CEL to the bypass state, the drive circuit 64 judges whether the DC voltage of the charge storage element 60 is appropriate or not (step S104 in FIG. 3). That is, when the DC voltage of the charge storage element 60 is equal to or higher than the upper limit and the drive circuit 64 switches the converter CEL to the bypass state, the drive circuit 64 judges whether the DC voltage of the charge storage element 60 is equal to or lower than a predetermined value or not, and when the DC voltage of the charge storage element 60 is equal to or lower than a lower limit and the drive circuit 64 switches the converter CEL to the bypass state, the drive circuit 64 judges whether the DC voltage of the charge storage element 60 is equal to or higher than a predetermined value or not.

[0076] When the DC voltage of the charge storage element 60 is not appropriate, the drive circuit 64 continues the bypass state of the converter CEL. On the other hand, when the DC voltage of the charge storage element 60 is appropriate, the drive circuit 64 switches the converter CEL from the bypass state to the stopped state (step S105 in FIG. 3). That is, the drive circuit 64 switches the converter CEL from the bypass state to the stopped state when the DC voltage of the charge storage element 60 becomes equal to or lower than a predetermined value after switching the converter CEL to the bypass state because the DC voltage of the charge storage element 60 is equal to or higher than an upper limit value, or when the DC voltage of the charge storage element 60 becomes equal to or higher than a predetermined value after switching the converter CEL to the bypass state because the DC voltage of the charge storage element 60 is equal to or lower than a lower limit value.

[0077] After the converter CEL is switched to the stopped state, the confirmation circuit 70 of the drive circuit 64 confirms whether the voltages of the control terminals of the switching elements 41, 42 are negatively biased or substantially 0 V (step S106 in FIG. 3).

[0078] When the voltage at the control terminals of the switching elements 41, 42 is substantially 0V, the drive circuit 64 determines that the switching elements 41, 42 have a short-circuit fault or the like, and switches the converter CEL from the stopped state back to the bypass state (step S107 in FIG. 3).

[0079] When the voltages of the control terminals of the switching elements 41, 42 are negatively biased, the drive circuit 64 determines that the switching elements 41, 42 are healthy and releases the bypass state (step S108 in FIG. 3). When the drive circuit 64 determines that the switching elements 41, 42 are healthy, it transmits, for example, a bypass release request to the control device 14 via the transmission circuit 68 or the like to request the control device 14 to release the bypass state.

[0080] When the control device 14 receives the bypass release request, it restores the corresponding converter CEL to the control targets. For example, after restoring the corresponding converter CEL to the control targets, the control device 14 resumes sending a control signal to the corresponding converter CEL. For example, the drive circuit 64 releases the bypass state in response to the input of a control signal from the control device 14, and resumes controlling the on / off of each switching element 41, 42 based on the control signal.

[0081] The bypass state may be released not only by the control device 14 but also by the drive circuit 64 or the confirmation circuit 70 of the converter CEL. For example, even after the converter CEL is in the bypass state, the control device 14 continues to transmit a control signal to the converter CEL. In this case, when it is confirmed that the switching elements 41 and 42 are healthy, the drive circuit 64 or the confirmation circuit 70 of the converter CEL releases the bypass state of the converter CEL, and the control of the switching elements 41 and 42 can be resumed based on the control signal input from the control device 14. In this case, for example, a bypass release signal indicating that the bypass state has been released is transmitted to the control device 14 to notify the control device 14 of the release of the bypass state. In this way, when the control device 14 receives a bypass signal, it is not necessary to remove the converter CEL in the bypass state from the control target. For example, even when the control device 14 receives a bypass signal, the control device 14 may generate a control signal for each converter CEL in the same way as when the bypass signal is not received, and transmit the generated control signal to each converter CEL. In this case, even when a control signal is input on the side of the converter CEL in the bypass state, the bypass state may be continued.

[0082] In this way, in the power conversion device 10 according to the present embodiment, after the converter CEL is switched to the bypass state, when the DC voltage of the charge storage element 60 returns to an appropriate value, the drive circuit 64 checks the soundness of the multiple switching elements 41, 42. Then, when it is confirmed that the multiple switching elements 41, 42 are sound, the drive circuit 64 releases the bypass state of the converter CEL.

[0083] This makes it possible to suppress a decrease in the stability of the operation of the main circuit unit 12 caused by an increase in the number of bypassed converters CEL among the multiple converters CEL connected in series, and a decrease in the operability of the power conversion device 10 due to the stop of operation of the power conversion device 10. Therefore, it is possible to provide a power conversion device 10 with improved stability and operability.

[0084] FIG. 4 is a flow chart that illustrates a schematic modification of the operation of the converter. Steps S201 to S207 in FIG. 4 are similar to steps S101 to S107 described with reference to FIG. 3, and therefore a detailed description thereof will be omitted.

[0085] As shown in FIG. 4, in this example, the drive circuit 64 checks the operation of the multiple switching elements 41, 42 after confirming that the voltages of the control terminals of the switching elements 41, 42 are negative bias (step S208 in FIG. 4).

[0086] The drive circuit 64, for example, switches the switching element 41 between the on state and the off state, and checks whether the switching element 41 operates normally based on the voltage of the control terminal of the switching element 41. The drive circuit 64 determines that the switching element 41 operates normally, for example, when the voltage of the control terminal switches from a negative bias to substantially 0 V in response to switching of the switching element 41 from the off state to the on state, and when the voltage of the control terminal switches from substantially 0 V to a negative bias in response to switching of the switching element 41 from the on state to the off state. The drive circuit 64 determines that the switching element 41 does not operate normally, for example, when the voltage of the control terminal does not change appropriately even when switching of the switching element 41 between the on state and the off state.

[0087] Similarly, the drive circuit 64 switches the switching element 42 between the on and off states, and checks whether the switching element 42 operates normally based on the voltage at the control terminal of the switching element 42. When the switching element 42, which is the upper element, is switched to the on state, the voltage of the charge storage element 60 rises. Therefore, the switching element 42 is switched to the on state only for a short period of time so that the charge storage element 60 does not become overvoltage.

[0088] When the drive circuit 64 determines that either the switching element 41 or 42 is not operating normally, it switches the converter CEL from the stopped state back to the bypass state.

[0089] On the other hand, when the drive circuit 64 confirms that the switching elements 41, 42 are operating normally, it determines that the switching elements 41, 42 are sound, and releases the bypass state (step S209 in FIG. 4). For example, the drive circuit 64 transmits a bypass release request to the control device 14 via the transmission circuit 68 or the like to request the control device 14 to release the bypass state, and releases the bypass state in response to the input of a control signal from the control device 14.

[0090] In this way, the drive circuit 64 may check whether the voltage of the control terminal when the converter CEL is switched to the stopped state is normal or not, and then check the operation of the switching elements 41, 42 to check the soundness of the multiple switching elements 41, 42. This makes it possible to more appropriately check the soundness of the multiple switching elements 41, 42.

[0091] FIG. 5 is a flow chart that illustrates a modified example of the operation of the converter. Steps S301 to S303 in FIG. 5 are similar to steps S101 to S103 described with reference to FIG. 3, and therefore a detailed description thereof will be omitted.

[0092] 5, in this example, after switching the converter CEL to the bypass state, the drive circuit 64 determines whether a predetermined time has elapsed from the timing of switching to the bypass state (step S304 in FIG. 5). The predetermined time is set to, for example, a time when the DC voltage of the charge storage element 60 is considered to return to an appropriate range after it becomes equal to or higher than the upper limit value or equal to or lower than the lower limit value.

[0093] If the predetermined time has not elapsed, the drive circuit 64 continues the bypass state of the converter CEL. On the other hand, if the predetermined time has elapsed, the drive circuit 64 switches the converter CEL from the bypass state to the stopped state (step S305 in FIG. 5). Since steps S306 to S308 in FIG. 5 are the same as steps S106 to S108 described with reference to FIG. 3, detailed description thereof will be omitted.

[0094] In this way, after the converter CEL is switched to the bypass state, the health of the multiple switching elements 41, 42 may be checked not only when the DC voltage of the charge storage element 60 returns to an appropriate value, but also when a predetermined time has elapsed since the timing of switching to the bypass state.

[0095] The timing when the drive circuit 64 checks the soundness of the multiple switching elements 41, 42 is not limited to the above, and may be any timing after the converter CEL is switched to the bypass state. However, as described above, by checking the soundness of the multiple switching elements 41, 42 when the DC voltage of the charge storage element 60 returns to an appropriate value or when a predetermined time has elapsed since the timing of switching to the bypass state, the bypass state of the converter CEL can be released at an appropriate timing. For example, it is possible to prevent the converter CEL from returning to the bypass state immediately after the bypass state is released.

[0096] Second Embodiment FIG. 6 is a block diagram illustrating a power conversion device according to the second embodiment. 6, the power conversion device 10a includes two control devices 14, a first control device 14a and a second control device 14b. Note that components that are substantially the same in function and configuration as those in the first embodiment are given the same reference numerals and detailed description thereof will be omitted.

[0097] The first control device 14a and the second control device 14b are connected to the main circuit unit 12. The first control device 14a and the second control device 14b control the on / off of each switching element to control the conversion from AC power to DC power and the conversion from DC power to AC power by the main circuit unit 12.

[0098] Each converter CEL is connected to the first control device 14a via a signal line 26. Also, each converter CEL is connected to the second control device 14b via a signal line 27. The first control device 14a controls the operation of each converter CEL by inputting a control signal to each converter CEL via the signal line 26. The second control device 14b controls the operation of each converter CEL by inputting a control signal to each converter CEL via the signal line 27.

[0099] In this manner, the power conversion device 10a controls the operation of the main circuit unit 12 by either the first control device 14a or the second control device 14b. That is, the power conversion device 10a has a redundant configuration of the first control device 14a and the second control device 14b.

[0100] In the power conversion device 10a, one of the first control device 14a and the second control device 14b is a control device of the operating system, and the other is a control device of the standby system. The control device of the operating system is a control device that actually controls the operation of the main circuit unit 12. The control device of the standby system is a spare control device that controls the operation of the main circuit unit 12 instead of the control device of the operating system when the control device of the operating system breaks down or is under maintenance. The power conversion device 10a switches between the operating system and the standby system of the first control device 14a and the second control device 14b in response to a breakdown, maintenance, or the like. That is, when the first control device 14a is the operating system, the second control device 14b becomes the standby system, and when the second control device 14b is the operating system, the first control device 14a becomes the standby system. As a result, even if one of the first control device 14a and the second control device 14b breaks down, the other can be used to continue the operation of the main circuit unit 12, thereby improving the reliability and operability of the power conversion device 10a.

[0101] In addition, in the power conversion device 10a, for example, even while the control device of the operating system is operating normally, the control device of the standby system is operated in synchronization with the control device of the operating system. The first control device 14a and the second control device 14b each input a control signal to the main circuit unit 12. The main circuit unit 12 operates based on the control signal of the control device of the operating system, either the first control device 14a or the second control device 14b. That is, in the first control device 14a and the second control device 14b, the control device of the standby system operates in a so-called hot standby mode. This makes it possible to immediately switch to the control device of the standby system when a failure or the like occurs in the control device of the operating system. When switching from the control device of the operating system to the control device of the standby system, the operation of the main circuit unit 12 is prevented from stopping, and more stable operation can be obtained in the power conversion device 10a.

[0102] The first control device 14a and the second control device 14b communicate with a higher-level controller via a network or the like, and control the operation of the main circuit unit 12 based on command values ​​input from the higher-level controller. The first control device 14a and the second control device 14b also communicate with each other, for example, to synchronize the operation of the standby control device with the operation of the operating control device, and to check each other's operating status. The communication between the first control device 14a and the second control device 14b may be wired or wireless.

[0103] When the DC voltage of the charge storage element 60 becomes above an upper limit value or below a lower limit value and the converter CEL is switched to a bypass state, each converter CEL sends a bypass signal indicating that it is in the bypass state to each of the first control device 14a and the second control device 14b.

[0104] At this time, each converter CEL includes in the bypass signal cause information indicating whether the cause of the bypass state is a communication-related bypass due to a communication abnormality with the control device of the operation system, or a non-communication-related bypass due to a cause other than the communication abnormality with the control device of the operation system.

[0105] When the first control device 14a and the second control device 14b receive a bypass signal and detect an abnormality in communication with any of the multiple converters CEL, they determine whether the number of converters CEL in the bypass state within the same arm section has reached a predetermined number.

[0106] When the number of converters CEL in the bypass state has not reached a predetermined number, the control device of the operation system, for example, removes the converter CEL in the bypass state from the control targets, and the remaining converters CEL in the same arm section continue power conversion by the main circuit unit 12. Note that, as described in relation to the first embodiment, the control device of the operation system does not necessarily have to remove the converter CEL in the bypass state from the control targets.

[0107] On the other hand, when the number of converters CEL in the bypass state reaches a predetermined number, the control device of the operation system, for example, communicates with the control device of the standby system to check whether the number of converters CEL in the bypass state by the non-communication-related bypass in the control device of the standby system has reached a predetermined number. In other words, the control device of the operation system checks whether the control device of the standby system recognizes the converters CEL in the bypass state by the communication-related bypass.

[0108] When the control device of the operation system confirms that the number of converters CEL that have been put into a bypass state by the non-communication-related bypass in the control device of the standby system has reached a predetermined number, it stops the power conversion by the main circuit unit 12.

[0109] On the other hand, when the control device of the operating system confirms that the number of converters CEL that have been put into a bypass state by the non-communication-related bypass in the control device of the standby system has not reached a predetermined number, it performs system switching between the control device of the operating system and the control device of the standby system.

[0110] In this way, when the number of converters CEL in the bypass state reaches a predetermined number, the operation system control device switches between the operation system control device and the standby system control device if operation can be continued on the standby system control device.

[0111] After the standby system control device is switched over to the operating system control device, it continues the power conversion by the main circuit unit 12 in the remaining converter CEL in the same arm section, and communicates with the converter CEL that has been placed in a bypass state by the communication-related bypass, thereby allowing the converter CEL that has been placed in a bypass state by the communication-related bypass to check the health of the multiple switching elements 41, 42.

[0112] At this time, if the standby control device is unable to communicate with all of the converters CEL that have been bypassed by the corresponding communication-related bypass, the control device stops the power conversion by the main circuit unit 12. If the control device is unable to communicate with some of the converters CEL that have been bypassed by the communication-related bypass, the control device continues the bypass state of the converters CEL with which communication could not be performed, and determines whether the number of converters CEL that are in the bypass state in the same arm unit has reached a predetermined number. If the control device determines that the predetermined number has been reached, it stops the power conversion by the main circuit unit 12. Then, if the control device determines that the predetermined number has not been reached, it causes the communicable converter CEL that has been bypassed by the communication-related bypass to check the soundness of the multiple switching elements 41, 42.

[0113] The converter CEL, which has entered the bypass state due to the communication-related bypass, checks the soundness of the multiple switching elements 41, 42 in response to an instruction from the control device. The method for checking the soundness of the multiple switching elements 41, 42 may be the method shown in Fig. 3, or the method shown in Fig. 4 or 5. When the converter CEL confirms that the multiple switching elements 41, 42 are operating normally, it releases the bypass state. When the converter CEL confirms that the multiple switching elements 41, 42 are operating normally, it transmits, for example, a bypass release request to the control device of the current operating system.

[0114] When the control device of the operation system receives the bypass release request, for example, it returns the corresponding converter CEL to the object of control.

[0115] In this way, in the power conversion device 10a of this embodiment, by providing two control devices 14, the first control device 14a and the second control device 14b, even if the converter CEL goes into a bypass state due to a communication abnormality, it is possible to continue operation by switching to the standby control device.

[0116] This makes it possible to more reliably prevent the number of bypassed converters CEL from increasing among the multiple converters CEL connected in series, which would result in a decrease in the stability of the operation of the main circuit unit 12, and a decrease in the operability of the power conversion device 10a due to the operation stop of the power conversion device 10a. Therefore, it is possible to provide a power conversion device 10a with improved stability and operability.

[0117] In the above example, when the control device of the operating system confirms that the number of converters CEL in the bypass state due to the non-communication-related bypass in the control device of the standby system has not reached a predetermined number, system switching between the control device of the operating system and the control device of the standby system is performed. Without being limited to this, for example, when the number of converters CEL in the bypass state reaches a predetermined number, the control device of the operating system may communicate with the control device of the standby system to confirm whether or not the control device of the standby system has received a bypass release request, and if the request to release the bypass has been received, system switching may be performed.

[0118] For example, in the case where a converter CEL is in a bypass state due to a communication-related bypass, when the number of converters CEL in a bypass state in the control device of the operating system reaches a predetermined number, the control device of the standby system may have already received a bypass release request from the corresponding converter CEL. In such a case, as described above, it may be confirmed whether or not the control device of the standby system has received a bypass release request, and if the bypass release request has been received, system switching may be performed.

[0119] In this way, when the number of converters CEL in the bypass state reaches a predetermined number, the method of checking whether operation can be continued in the standby control device is not limited to the above, and any method that can appropriately check whether operation can be continued in the standby control device may be used.

[0120] FIG. 7 is a block diagram showing a schematic diagram of a modified example of the converter. 7, the converter CELa further includes another switching element 72. The converter CELa can be used in place of the converter CEL in either the first or second embodiment.

[0121] The switching element 72 is provided between the pair of connection terminals 61, 62. In the converter CELa, the converter CELa can be put into a bypass state by turning on the switching element 72. The switching element 72 is a so-called bypass switch.

[0122] The on and off states of the switching element 72 are switched by the drive circuit 64. The drive circuit 64 keeps the switching element 72 in the on state, thereby putting the converter CELa into a bypass state. The switching element 72 is, for example, a thyristor element. The switching element 72 brings the pair of connection terminals 61, 62 into conduction in the direction from the connection terminal 61 to the connection terminal 62, for example. However, the switching element 72 is not limited to a thyristor element, and may be any switching element that can bring the pair of connection terminals 61, 62 into conduction.

[0123] In this way, the converter CELa may be configured to be switched to the bypass state by a switching element 72 separate from the switching elements 41, 42 that switch between the output state and the stop state. The converter CELa may be configured in any way that can switch, by switching a plurality of switching elements, between an output state in which the voltage of the charge storage element 60 is output between a pair of connection terminals 61, 62, a stop state in which the output of the voltage of the charge storage element 60 to the pair of connection terminals 61, 62 is stopped, and a bypass state in which conduction is established between the pair of connection terminals 61, 62.

[0124] FIG. 8 is a block diagram showing a schematic diagram of a modified example of the converter. 8, the converter CELb further includes switching elements 43 and 44 and rectifying elements 53 and 54. The switching elements 43 and 44 are substantially the same as the switching elements 41 and 42. The converter CELb can be used in place of the converter CEL in both the first and second embodiments.

[0125] A pair of main terminals of the switching element 44 are connected in series to a pair of main terminals of the switching element 43. Moreover, the switching elements 43 and 44 are connected in parallel to the switching elements 41 and 42. The charge storage element 60 is connected in parallel to the switching elements 41 and 42, and is also connected in parallel to the switching elements 43 and 44.

[0126] The rectifying element 53 is connected in anti-parallel to a pair of main terminals of the switching element 43. The rectifying element 54 is connected in anti-parallel to a pair of main terminals of the switching element 44.

[0127] A connection terminal 61 of the converter CELb is connected between the switching element 41 and the switching element 42. A connection terminal 62 is connected between the switching element 43 and the switching element 44. In this example, the connection terminal 62 is connected via the switching element 43 to a main terminal of the switching element 41 opposite to the main terminal connected to the switching element 42. That is, in this example, the switching elements 41 to 44 are full-bridge connected. The converter CELb is a full-bridge circuit. The converter CELb of the full-bridge circuit can be used in place of the converter CEL in both the first and second embodiments.

[0128] The drive circuit 64 switches the switching elements 41 to 44 on and off based on a control signal input from the control device 14, or the first control device 14a and the second control device 14b.

[0129] In this manner, the converter used in the MMC type main circuit section 12 may be a half-bridge circuit or a full-bridge circuit.

[0130] In the converter CELb of the full-bridge circuit, +Vc is output between each of the connection terminals 61, 62 when the switching element 42 and the switching element 43 are turned on and the switching element 41 and the switching element 44 are turned off.

[0131] When the switching elements 41 and 44 are turned on and the switching elements 42 and 43 are turned off, −Vc is output between the connection terminals 61 and 62 .

[0132] When switching elements 41 and 43 are turned on and switching elements 42 and 44 are turned off, or when switching elements 42 and 44 are turned on and switching elements 41 and 43 are turned off, substantially 0 V is output between each connection terminal 61, 62.

[0133] In this way, the converter CELb of the full-bridge circuit can output three levels of power, +Vc, 0, and -Vc, by combining the switching elements 41 to 44 that are turned on and off.

[0134] In this converter CELb, for example, a state in which +Vc is output is a first output state, a state in which -Vc is output is a second output state, a state in which 0V is output is a bypass state, and a state in which each of the switching elements 41 to 44 is in an off state is a stopped state. The converter CELb is in a bypass state by turning on the upper two switching elements 42, 44 or the lower two switching elements 41, 43 of the four full-bridge-connected switching elements 41 to 44. The switching of each state of the converter CELb can be realized, for example, by making the control signal a ternary signal corresponding to three levels.

[0135] In the full-bridge circuit converter CELb, as in the half-bridge circuit converter, after the converter CELb is switched to a bypass state, when the DC voltage of the charge storage element 60 falls below a predetermined value, the health of the multiple switching elements 41-44 is checked, and if it is confirmed that the multiple switching elements 41-44 are healthy, the corresponding converter CELb is returned to the control target, thereby improving the stability and operability of the power conversion device.

[0136] FIG. 9 is a block diagram showing a schematic diagram of a modified example of the converter. 9, the converter CELc further includes another switching element 74. The converter CELc can be used in place of the converter CEL in either the first embodiment or the second embodiment.

[0137] The switching element 74 is provided between the pair of connection terminals 61, 62. In the converter CELc, the converter CELc can be put into a bypass state by turning on the switching element 74. The switching element 74 is a so-called bypass switch.

[0138] The on and off states of the switching element 74 are switched by the drive circuit 64. The drive circuit 64 keeps the switching element 74 in the on state, thereby putting the converter CELc into a bypass state.

[0139] In this manner, by providing the switching element 74 in the converter CELc of the full-bridge circuit, a configuration in which the switching element 74 switches to the bypass state may be adopted.

[0140] The switching element 74 is, for example, a bidirectional thyristor element. The switching element 74 provides electrical continuity between the pair of connection terminals 61, 62 in both directions, for example, from the connection terminal 61 toward the connection terminal 62 and from the connection terminal 62 toward the connection terminal 61. However, the switching element 74 is not limited to a bidirectional thyristor element, and may be any switching element that can provide electrical continuity between the pair of connection terminals 61, 62 in both directions, that is, from the connection terminal 61 toward the connection terminal 62 and from the connection terminal 62 toward the connection terminal 61.

[0141] In each of the above embodiments, an MMC type power converter is used for the main circuit unit 12. The main circuit unit 12 is not limited to the MMC type, and may be, for example, a power converter of another type in which a plurality of converters CEL are connected in series, such as an MV (Medium Voltage) type power converter.

[0142] The power conversion device is not limited to a DC transmission system, but may be applied to any other system that requires conversion from AC to DC and from DC to AC. The AC / DC conversion by the power conversion device is not limited to both AC to DC and DC to AC, but may be only AC to DC or DC to AC.

[0143] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0144] 2...AC power system, 3, 4...DC transmission line, 6...transformer, 10, 10a...power conversion device, 12...main circuit section, 14...control device, 14a...first control device, 14b...second control device, 20a, 20b...DC terminal, 21a-21c...first to third AC terminals, 22a-22f...first to sixth arm sections, 23a-23f...buffer reactor, 24a-24f...current detector, 25...voltage detector, 26, 27...signal line, 41-44...switching element, 51-54...rectifier element, 60...charge storage element, 61, 62...connection terminal, 64...drive circuit, 66...main circuit power supply circuit, 68...transmission circuit, 70...confirmation circuit, 72, 74...switching element, CEL, CELa~CELc... Converter

Claims

1. A main circuit unit includes a plurality of converters connected in series, and converts power by the operation of the plurality of converters; A control device for controlling the operation of the main circuit unit; Equipped with Each of the plurality of converters comprises: A pair of connection terminals; A plurality of switching elements; a charge storage element connected in parallel to the plurality of switching elements; a drive circuit for switching the on and off states of the plurality of switching elements; and the charge storage element is connected in series via the pair of connection terminals, and is capable of switching between an output state in which a voltage of the charge storage element is output between the pair of connection terminals, a bypass state in which the pair of connection terminals are electrically connected, and a stop state in which the plurality of switching elements are in an off state by switching the plurality of switching elements; the drive circuit switches the converter to the bypass state when the DC voltage of the charge storage element becomes equal to or greater than an upper limit value or equal to or less than a lower limit value; When the number of the converters in the bypass state has not reached a predetermined number, the control device continues the power conversion by the main circuit unit, After switching to the bypass state, the drive circuit checks the health of the plurality of switching elements, and when it is confirmed that the plurality of switching elements are healthy, releases the bypass state of the converter; The plurality of switching elements each have a pair of main terminals and a control terminal, The drive circuit confirms whether the voltage at the control terminal is normal, thereby confirming the soundness of the multiple switching elements.

2. A main circuit section having a plurality of converters connected in series and converting power by the operation of the plurality of converters; A control device for controlling the operation of the main circuit unit; Equipped with Each of the plurality of converters comprises: A pair of connection terminals; A plurality of switching elements; a charge storage element connected in parallel to the plurality of switching elements; a drive circuit for switching the on and off states of the plurality of switching elements; and the charge storage element is connected in series via the pair of connection terminals, and is capable of switching between an output state in which a voltage of the charge storage element is output between the pair of connection terminals, a bypass state in which the pair of connection terminals are electrically connected, and a stop state in which the plurality of switching elements are in an off state by switching the plurality of switching elements; the drive circuit switches the converter to the bypass state when the DC voltage of the charge storage element becomes equal to or greater than an upper limit value or equal to or less than a lower limit value; When the number of the converters in the bypass state has not reached a predetermined number, the control device continues the power conversion by the main circuit unit, After switching to the bypass state, the drive circuit checks the health of the plurality of switching elements, and when it is confirmed that the plurality of switching elements are healthy, releases the bypass state of the converter; The drive circuit is a power conversion device that checks the health of the multiple switching elements when the DC voltage of the charge storage element becomes equal to or lower than the lower limit value, switches the converter to the bypass state, and then checks the health of the multiple switching elements when the DC voltage of the charge storage element becomes equal to or higher than a predetermined value.

3. 3. The power conversion device according to claim 1, wherein the drive circuit checks the health of the plurality of switching elements when the DC voltage of the charge storage element becomes equal to or higher than the upper limit value and the converter is switched to the bypass state, and then when the DC voltage of the charge storage element becomes equal to or lower than a predetermined value.

4. 2. The power conversion device according to claim 1, wherein the drive circuit checks the health of the plurality of switching elements when a predetermined time has elapsed since the converter was switched to the bypass state after the DC voltage of the charge storage element becomes equal to or greater than the upper limit value or equal to or less than the lower limit value and the converter was switched to the bypass state.

5. The power conversion device according to any one of claims 1 to 4, wherein, when the number of the converters in the bypass state has not reached a predetermined number, the control device removes the converters in the bypass state from the control targets and allows the remaining converters to continue converting power using the main circuit unit.

6. 2. The power conversion device according to claim 1, wherein the drive circuit checks whether the voltage at the control terminal is normal or not, and then checks the operation of the plurality of switching elements to check the soundness of the plurality of switching elements.

7. The system includes two control devices, a first control device and a second control device, One of the first control device and the second control device is a control device of an operating system, and the other is a control device of a standby system, and the operation of the main circuit unit is controlled by one of the control devices that is the control device of the operating system, The power conversion device according to any one of claims 1 to 6, wherein when the number of the converters in the bypass state reaches the predetermined number, the control device of the operation system switches between the control device of the operation system and the control device of the standby system if operation can be continued in the control device of the standby system.

8. The converter has two of the switching elements connected in a half-bridge configuration, and the converter is placed in the bypass state by turning on a lower switching element of the two half-bridge connected switching elements. The power conversion device according to any one of claims 1 to 7.

9. The converter has two of the switching elements connected in a half-bridge configuration and another switching element provided between the pair of connection terminals, and the converter is set to the bypass state by turning on the other switching element. The power conversion device according to any one of claims 1 to 7.

10. The converter has four switching elements in a full bridge connection, and the converter is set to the bypass state by turning on two upper switching elements or two lower switching elements of the four full bridge connected switching elements. The power conversion device according to any one of claims 1 to 7.

11. The power conversion device according to any one of claims 1 to 7, wherein the converter has four of the switching elements connected in a full bridge configuration and another switching element provided between the pair of connection terminals, and the converter is set to the bypass state by turning on the other switching element.

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