JP2023037869A - Power conversion device - Google Patents

Abstract

Kind Code: A1 A power converter is provided that can suppress an unstable short-circuit state of a switching element having a short-circuit failure when a short-circuit failure of a switching element occurs in a plurality of converters connected in series. The main circuit unit converts electric power by operating a plurality of converters connected in series, and a control device controls the operation of the main circuit unit. a pair of connection terminals, a plurality of switching elements, and a charge storage element connected in parallel to the plurality of switching elements; When a short-circuit fault is detected in any of the multiple switching elements in any of the multiple converters, the main circuit section for the converter in which the short-circuit fault has occurred in any of the multiple switching elements A power converter is provided that controls the operation of a plurality of converters to provide a circulating circulating current. [Selection drawing] Fig. 3

Description

TECHNICAL FIELD Embodiments of the present invention relate to power converters.

There is a power converter in which a plurality of converters are connected in series. Each converter has a pair of connection terminals, a plurality of switching elements, and a charge storage element connected in parallel to the plurality of switching elements. Each converter is connected in series via a pair of connection terminals.

In such a power conversion device, even when a predetermined number of converters out of a plurality of converters fails, operation is resumed with the remaining converters by short-circuiting the pair of connection terminals of the failed converter. can continue. Such short-circuiting between a pair of connection terminals is sometimes called bypass. For example, an abnormality or failure of a converter is detected, and the converter in which the abnormality or failure is detected is placed in a bypass state so that the remaining converters continue to operate.

Moreover, in such a power converter, the switching element of each converter may cause a short-circuit failure. When a short-circuit failure occurs in one of a plurality of switching elements in a converter, the short-circuited switching element causes a short circuit between a pair of connection terminals, and the converter enters a bypass state. , operation can continue with the remaining converters.

However, when a switching element causes a short-circuit failure, the short-circuit state of the switching element differs depending on the mode of failure. In some cases, a short circuit may occur with a high resistance value, resulting in large heat generation or voltage generation between the pair of connection terminals.

For this reason, in a power conversion device in which a plurality of converters are connected in series, it is desirable to be able to suppress an unstable short-circuit state of a switching element that has a short-circuit failure when a short-circuit failure occurs in the switching element.

JP 2020-54223 A

An embodiment of the present invention provides a power converter that can suppress an unstable short-circuit state of a switching element having a short-circuit failure when a short-circuit failure of a switching element occurs in a plurality of converters connected in series.

According to an embodiment of the present invention, a main circuit unit includes a plurality of converters connected in series, and the operation of the plurality of converters converts power, and the operation of the main circuit unit is controlled. a control device, wherein each of the plurality of converters has a pair of connection terminals, a plurality of switching elements, and a charge storage element connected in parallel to the plurality of switching elements; an output state in which the charge storage element is connected in series via the pair of connection terminals and outputs the voltage of the charge storage element between the pair of connection terminals by switching of the plurality of switching elements; and a stop state in which the plurality of switching elements are turned off, and the control device detects short-circuit failures of the plurality of switching elements of the plurality of converters. and when any one of the plurality of converters detects a short-circuit failure of one of the plurality of switching elements, the main A power converter is provided that controls the operation of a plurality of said converters to provide a circulating current that circulates in a circuit section.

Provided is a power converter capable of suppressing an unstable short-circuit state of a switching element having a short-circuit failure when a short-circuit failure of a switching element occurs in a plurality of converters connected in series.

1 is a block diagram schematically showing a power converter according to a first embodiment; FIG. 1 is a block diagram schematically representing a converter; FIG. It is explanatory drawing which represents typically an example of operation|movement of a power converter device. FIG. 11 is a block diagram schematically showing a modified example of the converter;

Each embodiment will be described below with reference to the drawings.
Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each portion, the size ratio between portions, and the like are not necessarily the same as the actual ones. Also, even when the same parts are shown, the dimensions and ratios may be different depending on the drawing.
In addition, in the present specification and each figure, the same reference numerals are given to the same elements as those described above with respect to the already-appearing figures, and detailed description thereof will be omitted as appropriate.

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

The DC power transmission system has a transformer 6, for example. A main circuit unit 12 of the power converter 10 is connected to the AC power system 2 via a 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 according to the main circuit section 12 . Transformer 6 is a three-phase transformer. The transformer 6 is provided as required and can be omitted. The three-phase AC power of the AC power system 2 may be directly supplied to the main circuit unit 12 .

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 transmission lines 3 and 4 . The power conversion device 10 also converts the 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 . Thus, the power converter 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 converted DC power to the DC transmission lines 3 and 4 so that the DC transmission line 3 side has a high voltage and the DC transmission line 4 side has a low voltage.

The main circuit unit 12 is provided between the AC power system 2 and 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 section 12 is, for example, a multi-level 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 section 12 has a plurality of converters connected in series. Each converter has a plurality of half-bridge-connected or full-bridge-connected switching elements and a charge storage element connected in parallel to each switching element. The main circuit unit 12 converts electric power by operating a plurality of converters. The main circuit unit 12 performs AC/DC conversion by, for example, switching each switching element of a plurality of converters.

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

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

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. As a result, the DC power converted by the main circuit section 12 is supplied to the DC transmission lines 3 and 4 , and the DC power supplied from the DC transmission lines 3 and 4 is input to the main circuit section 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 portion 22c and the fourth arm portion 22d are connected in parallel to the first arm portion 22a and the second arm portion 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 the third arm portion 22c and the fourth arm portion 22d. connected in parallel.

In the main circuit section 12, the first leg LG1 is configured by the first arm section 22a and the second arm section 22b, the second leg LG2 is configured by the third arm section 22c and the fourth arm section 22d, and the fifth arm section. 3rd leg LG3 is comprised by 22e and the 6th arm part 22f. That is, in this example, the main circuit section 12 is a 3-leg, 6-arm three-phase inverter. In other words, the main circuit section 12 has a plurality of bridge-connected arm sections 22a to 22f. In this example, the main circuit section 12 has six arm sections 22a to 22f that are three-phase bridge-connected.

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 way, the main circuit section 12 has a plurality of arm sections and a plurality of legs that are configured by a plurality of switching elements. The main circuit unit 12 may be, for example, a 2-leg, 4-arm single-phase inverter. The number of arms and legs is not limited to the above, and may be any number.

The first arm portion 22a has a plurality of converters UP1, UP2 . . . _UPM1 connected in series. The second arm portion 22b has a plurality of transducers UN1, UN2 . . . _UNM2 connected in series. The third arm portion 22c has a plurality of converters VP1, VP2 . . . _VPM3 connected in series. The fourth arm portion 22d has a plurality of converters VN1, VN2 . . . _VNM4 connected in series. The fifth arm portion 22e has a plurality of transducers WP1, WP2 . . . WPM ₅ connected in series. The sixth arm portion 22f has a plurality of transducers WN1, WN2 . . . WNM ₆ connected in series.

However, hereinafter, each converter UP1, UP2... _UPM1 , UN1, UN2...UNM2, VP1, VP2... _VPM3 , _VN1 , VN2... _VNM4 , WP1, WP2... _WPM5 , WN1, WN2... _WNM6 When collectively referred to, they are referred to as "converter CEL".

In each arm 22a-22f, M ₁ , M ₂ , M ₃ , M ₄ , M ₅ , M ₆ represent the number of converters CEL connected in series. In each of the arms 22a-22f, the number of converters CEL connected in series is, for example, about 100-120. However, the number of converters CEL connected in series is not limited to this, and may be any number.

The number of transducers CEL provided in each arm portion 22a-22f is substantially the same. For example, when a large number of converters CEL are connected, the number of converters CEL provided in each arm section 22a to 22f may be different as long as the operation of the main circuit section 12 is not affected. For example, when 100 transducers CEL are connected in series to one arm, the number of transducers CEL provided to another arm may differ by one or two.

Each arm portion 22a-22f further has a buffer reactor 23a-23f and a plurality of current detectors 24a-24f. Moreover, the power conversion device 10 further has a voltage detection unit 25 .

Each buffer reactor 23a-23f is connected in series with each converter CEL in each arm portion 22a-22f. The buffer reactor 23a of the first arm portion 22a is provided between the connection point between the AC terminal 21a, 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 the 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 the 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 the 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, 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 on the first arm portion 22a and detects the current flowing through the first arm portion 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 device 14 via wiring (not shown) or the like. The current detector 24 a inputs the detected current value of the first arm portion 22 a to the control device 14 . Thereby, the current value of the first arm portion 22 a is input to the control device 14 .

Similarly, the current detector 24b detects the current flowing through the second arm portion 22b and inputs the detected current value to the control device 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 controller 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 controller 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 controller 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 device 14 .

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 detector 25 may be connected to the primary side of the transformer 6 or may be connected to the secondary side.

In the main circuit section 12, a connection point between the first arm section 22a and the second arm section 22b, a connection point between the third arm section 22c and the fourth arm section 22d, and a connection point between the fifth arm section 22e and the sixth arm section 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 a transformer 6, for example.

Each converter CEL is connected to the control device 14 via a signal line 26, for example. The control device 14 controls the operation of the converter CEL by inputting control signals to the converter CEL via the signal line 26 . Further, the converter CEL inputs, for example, a control signal and a protection signal relating to the control and operation protection of the converter CEL to the control device 14 via another signal line (not shown). The communication method between the control device 14 and each converter CEL is not limited to the above. For example, a plurality of serially connected converters CEL may be daisy-chained, and the controller 14 may communicate only with the converters CEL at one end and the converters CEL at the other end of the daisy-chain connection. The communication method between the control device 14 and each converter CEL may be any communication method that allows proper communication between the control device 14 and each converter CEL.

FIG. 2 is a block diagram schematically representing a converter.
As shown in FIG. 2, the converter CEL includes a plurality of switching elements 41 and 42, a plurality of rectifying elements 51 and 52, a plurality of drive circuits 61 and 62, a pair of connection terminals 71 and 72, a charge It has a storage element 74 , a power supply circuit 76 , a voltage detection circuit 78 and a control circuit 80 .

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

Each of the switching elements 41 and 42 switches between an ON state that allows current to flow between the pair of main terminals and an OFF state that cuts off 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. For example, a weak current that does not affect the operation of the converter CEL may flow 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 reduced.

A normally-off semiconductor element, for example, is used for each of the switching elements 41 and 42 . Each of the switching elements 41 and 42 is turned on when the voltage of the control terminal is high, and turned off when the voltage of the control terminal is low. Each of the switching elements 41 and 42 is turned off when the voltage of the control terminal is lower than that of the on state. Each of the switching elements 41 and 42 is, for example, turned on when a positive voltage is applied to the control terminal, and turned off when the voltage of the control terminal is set to 0V or when a negative voltage is applied to the control terminal.

A pair of main terminals of the switching element 42 are connected in series with 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 a half-bridge. In this example, the converter CEL is a half-bridge configured converter.

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

The connection terminal 71 is connected between the switching element 41 and the switching element 42 . The connection terminal 72 is connected to the main terminal of the switching element 41 opposite to the main terminal connected to the switching element 42 .

A plurality of transducers CEL within the same arm are connected in series via a pair of connection terminals 71 and 72 . Power is supplied to the converter CEL via respective connection terminals 71 , 72 . The switching element 41 is a so-called low-side switch, and the switching element 42 is a so-called high-side switch.

Control circuit 80 is connected to control device 14 via signal line 26 . The control device 14 transmits a control signal for controlling ON/OFF of the switching elements 41 and 42 to the control circuit 80 via the signal line 26 . The control circuit 80 inputs driving signals for switching on/off of the switching elements 41 and 42 to the driving circuits 61 and 62 based on the input control signals.

The drive circuit 61 is connected to the control terminal of the switching element 41 . The drive circuit 62 is connected to the control terminal of the switching element 42 . The drive circuits 61 and 62 switch ON/OFF of the respective switching elements 41 and 42 based on the drive signal input from the control circuit 80 . Thus, the switching elements 41 and 42 are controlled to be on/off according to the control signal from the control device 14 . The control device 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 device 14 controls power conversion by the main circuit section 12 .

The configurations of the drive circuits 61 and 62 and the control circuit 80 are not limited to those described above, and may be any configuration capable of controlling the on/off of the switching elements 41 and 42 . For example, control signals from the control device 14 may be directly input to the drive circuits 61 and 62 . In this case, the control circuit 80 can be omitted.

The charge storage element 74 is connected in parallel with the switching element 41 and the switching element 42 . Charge storage element 74 is, for example, a capacitor.

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 74 appears between the connection terminals 71 and 72 . When the switching element 41 is in the ON state and the switching element 42 is in the OFF state, the connection terminals 71 and 72 are electrically connected and the voltage between the connection terminals 71 and 72 becomes substantially zero.

In this way, the converter CEL has an output state in which the voltage of the charge storage element 74 is output between the connection terminals 71 and 72 by switching the switching elements 41 and 42 based on the control signal from the control device 14, and each It switches between a bypass state in which the connection terminals 71 and 72 are electrically connected and a stopped state in which the switching elements 41 and 42 are turned off.

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

When both the switching elements 41 and 42 are in the OFF state (when the converter CEL is in the stopped state), the voltage between the connection terminals 71 and 72 is determined by the direction of the arm current. For example, when the arm current flows from the connection terminal 72 to the connection terminal 71, the rectifying element 51 is turned on and the voltage between the connection terminals 71 and 72 becomes substantially zero. Conversely, when the arm current flows in the direction from the connection terminal 71 to the connection terminal 72, the rectifying element 52 is turned on, the charge storage element 74 is charged, and the charge storage element 74 voltage appears.

The power supply circuit 76 is connected in parallel with the charge storage element 74 . The power supply circuit 76 generates drive power for the drive circuits 61 and 62 and the control circuit 80 based on the charge accumulated in the charge storage element 74, and supplies the generated drive power to the drive circuits 61 and 62 and the control circuit 80. do. The drive circuits 61 and 62 and the control circuit 80 operate according to the supply of drive power from the power supply circuit 76 .

The method of supplying power to the drive circuits 61 and 62 and the control circuit 80 is not limited to the above. For example, power may be supplied to the drive circuits 61 and 62 and the control circuit 80 from a power supply other than the charge storage element 74 . A method of supplying power to the drive circuits 61 and 62 and the control circuit 80 may be any method that can appropriately supply power to the drive circuits 61 and 62 and the control circuit 80 .

A voltage detection circuit 78 is connected in parallel with the charge storage element 74 . The voltage detection circuit 78 is connected with the control circuit 80 . The voltage detection circuit 78 detects the DC voltage of the charge storage element 74 and inputs the voltage detection value of the DC voltage of the charge storage element 74 to the control circuit 80 .

The control circuit 80 has a protection circuit 82 . The protection circuit 82 performs a protection operation when the DC voltage of the charge storage element 74 detected by the voltage detection circuit 78 exceeds the upper limit value. The protection circuit 82 switches the converter CEL to the bypass state when the DC voltage of the charge storage element 74 exceeds the upper limit value.

For example, when the switching elements 41 and 42 are not switched at the intended timing due to an abnormality in the control circuit 80, the voltage of the charge storage element 74 may rise. Such an increase in the voltage of the charge accumulating element 74 causes failure of each part of the converter CEL such as the switching elements 41 and 42 and the charge accumulating element 74 .

Therefore, based on the voltage detection value from the voltage detection circuit 78, the protection circuit 82 switches the converter CEL to the bypass state when the DC voltage of the charge storage element 74 exceeds the upper limit value. As a result, it is possible to suppress the failure of the converter CEL due to an increase in the voltage of the charge storage element 74, and to bypass the converter CEL in which the abnormality has occurred, and the remaining converters CEL in the same arm section can be used as the power conversion device. 10 runs can be continued.

Note that the configuration of the protection circuit 82 is not limited to the above. For example, the protection circuit 82 does not necessarily have to be provided within the control circuit 80 and may be provided separately from the control circuit 80 . For example, a protection circuit 82 provided separately from the control circuit 80 may be connected in parallel to the charge storage element 74 so that the protection circuit 82 detects the DC voltage of the charge storage element 74 . In this case, the voltage detection circuit 78 can be omitted.

The control device 14 detects short-circuit failures of the plurality of switching elements 41 and 42 for each of the plurality of converters CEL.

In the converter CEL, a short-circuit failure of each switching element 41, 42 is caused, for example, by simultaneously turning on each switching element 41, 42 and short-circuiting both ends of the charge storage element 74 via each switching element 41, 42. It can occur in the event of a so-called DC short circuit. For each of the switching elements 41 and 42, for example, pressure contact type switching elements are used. In pressure contact type switching elements, the failure mode when a DC short circuit occurs is a short circuit failure. However, the switching elements 41 and 42 are not limited to pressure contact type switching elements. Each switching element 41, 42 may be any switching element having a failure mode of, for example, a short circuit failure.

FIG. 3 is an explanatory diagram schematically showing an example of the operation of the power converter.
When the control device 14 detects a short-circuit fault in one of the switching elements 41 and 42 in one of the plurality of converters CEL, as shown in FIG. , and supply a circulating current circulating in the main circuit unit 12 to the converter CEL in which a short-circuit fault has occurred in one of the switching elements 41 and 42. It controls the operation of a plurality of converters CEL so as to do so. When the control device 14 detects a short circuit failure of one of the switching elements 41 and 42 in one of the plurality of converters CEL, the control device 14 supplies power to the load side such as the AC power system 2 and the DC transmission lines 3 and 4. , the operation of the plurality of converters CEL is controlled so as to supply a circulating current to the converter CEL in which one of the switching elements 41 and 42 has a short-circuit failure.

FIG. 3 illustrates a case where a short circuit failure occurs in the switching elements 41 and 42 of the converter WP1 of the fifth arm portion 22e. In this case, for example, as shown in FIG. 3, the control device 14 moves from the fifth arm portion 22e through the sixth arm portion 22f, the fourth arm portion 22d, and the third arm portion 22c to the fifth arm again. A circulating current is supplied to the path returning to the portion 22e. Thus, the circulating current is, for example, a current that circulates through the plurality of bridge-connected arm portions 22a to 22f in the main circuit portion 12. FIG. The controller 14 supplies a circulating current to circulate through the bridge-connected arms 22a-22f. However, the path for supplying the circulating current is not limited to this, and may be any path including the converter CEL in which one of the switching elements 41 and 42 has a short-circuit failure. In the example of FIG. 3, any path that can supply circulating current to at least the fifth arm portion 22e may be used.

When the control device 14 detects a short-circuit fault in one of the switching elements 41 and 42 in one of the plurality of converters CEL, for example, it controls the command value of the arm current flowing through each of the arm portions 22a to 22f. Thereby, the operations of the plurality of converters CEL are controlled so as to supply a circulating current circulating in the main circuit section 12 to the converter CEL in which one of the switching elements 41 and 42 has a short-circuit failure. can be done.

The short-circuit state of the switching elements 41 and 42 when the switching elements 41 and 42 have a short-circuit failure differs depending on the mode of failure. In some cases, short-circuiting may occur with a high resistance value, resulting in large heat generation or voltage generation between the pair of connection terminals 71 and 72 .

On the other hand, in the power conversion device 10 according to the present embodiment, the control device 14 detects a short-circuit failure in the switching elements 41 and 42 of the plurality of converters CEL, and the switching element in one of the plurality of converters CEL. A circulating current circulating in the main circuit unit 12 is supplied to the converter CEL in which a short circuit fault has occurred in one of the switching elements 41 and 42 when a short circuit fault in one of the switching elements 41 and 42 is detected. , controls the operation of a plurality of converters CEL.

By superimposing the circulating current on the arm current in this way, the arm current supplied to the converter CEL in which one of the switching elements 41 and 42 has a short-circuit failure is temporarily increased. By applying a large current to the switching element 41 that has a small contact surface and a high resistance value, the contact surface can be stabilized by its own heat generation, and the resistance value can be reduced. As a result, for example, during the normal operation of the power conversion device 10 that supplies power to the AC power system 2 and the DC transmission lines 3 and 4 (the operation of converting DC to AC or vice versa), the switching element 41, In the converter CEL in which one of the short-circuit failures of 42 has occurred, generation of large heat and generation of voltage between the pair of connection terminals 71 and 72 can be suppressed.

The circulating current only needs to flow until the resistance value is stabilized, so a short time is sufficient. Therefore, when a short-circuit fault is detected in one of the switching elements 41 and 42, the short-circuit state of the switching element 41 is stabilized by controlling the flow of a circulating current to the arm portion where the converter CEL exists for a short period of time. It is possible to improve the continuity of operation. Moreover, since the circulating current is a current that circulates in the main circuit section 12, it does not contribute to the AC power system 2 side or the DC transmission lines 3, 4 side.

Also, in this case, the control device 14 supplies a circulating current in a direction from one of the pair of connection terminals 71 and 72 to the other or in a direction from the other of the pair of connection terminals 71 and 72 to one. When the converter CEL has a half-bridge configuration, the direction in which the circulating current is supplied to the switching elements 41 and 42 may be any direction that can increase the arm current.

The control device 14 detects a short-circuit fault in one of the switching elements 41 and 42 in one of the plurality of converters CEL, and circulates to the converter CEL in which the short-circuit fault has occurred in one of the switching elements 41 and 42. After starting the control of the supply of the current, for example, the control of the supply of the circulating current is stopped when a predetermined time has elapsed from the start of the supply of the circulating current.

The circulating current is set within a range that does not affect the operation of other converters CEL due to the circulating current being superimposed on the arm current. The circulating current may be any magnitude of current that is equal to or less than the rated current of the switching elements 41 and 42 and is capable of stabilizing the contact surface of the short-circuited switching element 41 . Moreover, the predetermined time for which the circulating current is supplied may be any time during which the circulating current can stabilize the contact surface of the short-circuited switching element 41 .

As described above, in the power conversion device 10 according to the present embodiment, when a short-circuit failure occurs in the switching elements 41 and 42, an unstable short-circuit state of the switching element 41 that has the short-circuit failure can be suppressed. .

FIG. 4 is a block diagram schematically showing a modification of the converter.
As represented in FIG. 4 , the converter CELa in this example has switching elements 41 and 42 and further has switching elements 43 and 44 . Substantially the same elements as the switching elements 41 and 42 are used for the switching elements 43 and 44 .

The switching elements 43 and 44 are connected in series. The series connection body of the switching elements 43 and 44 is connected in parallel to the series connection body of the switching elements 41 and 42 . That is, in this example, the converter CELa has four switching elements 41-44 connected in a full bridge. In this example, the converter CELa is a full-bridge converter.

The converter CELa further comprises rectifying elements 53,54 and drive circuits 63,64. The rectifying element 53 is connected in anti-parallel with the switching element 43 . The rectifying element 54 is connected in anti-parallel with the switching element 44 . In the converter CELa, the control circuit 80 inputs drive signals for switching on/off of the switching elements 41 to 44 to the drive circuits 61 to 64 based on the control signals input from the control device 14 . The drive circuit 63 switches the switching element 43 between an ON state and an OFF state based on the drive signal input from the control circuit 80 . The drive circuit 64 switches the switching element 44 between an ON state and an OFF state based on the drive signal input from the control circuit 80 .

In converter CELa, connection terminal 71 is connected between switching element 41 and switching element 42 . The connection terminal 72 is connected between the switching element 43 and the switching element 44 . In this example, the connection terminal 72 is connected via the switching element 43 to the main terminal of the switching element 41 opposite to the main terminal connected to the switching element 42 .

In the converter CELa, when the voltage of the charge storage element 74 is Vc, the switching elements 41 and 44 are turned on, and the switching elements 42 and 43 are turned off. , 72 appears a voltage of -Vc.

By turning on the switching elements 42 and 43 and turning off the switching elements 41 and 44 , a voltage of +Vc appears between the connection terminals 71 and 72 .

Furthermore, the switching elements 41 and 43 on the low side are turned on, and the switching elements 42 and 44 on the high side are turned off. Alternatively, the switching elements 42 and 44 on the high side are turned on, and the switching elements 41 and 43 on the low side are turned off. As a result, the connection terminals 71 and 72 are electrically connected, and substantially 0 V appears between the connection terminals 71 and 72 .

In this manner, the converter CELa can output voltages of three levels of +Vc, 0, and -Vc between the connection terminals 71 and 72, respectively. The converter CELa outputs a voltage of +Vc between the connection terminals 71 and 72 and a voltage of −Vc between the connection terminals 71 and 72 by switching the switching elements 41 to 44. a second output state, in which the connection terminals 71 and 72 are electrically connected, and a stop state in which the switching elements 41 to 44 are turned off.

The protection circuit 82 switches the converter CELa to the bypass state, for example, when the DC voltage of the charge storage element 74 becomes equal to or higher than the upper limit value.

Also in the converter CELa, for example, a short-circuit failure of the switching elements 41-44 may occur when a DC short-circuit occurs. The control device 14 detects short-circuit failures of the switching elements 41 to 44 of the plurality of converters CELa, and when detecting a short-circuit failure of any of the switching elements 41 to 44 in any of the plurality of converters CELa, The operation of the plurality of converters CELa is controlled so as to supply a circulating current circulating in the main circuit section 12 to the converter CELa in which one of the switching elements 41 to 44 has a short-circuit failure. As a result, even in the converter CELa of the full-bridge circuit, as in the above-described embodiment, it is possible to suppress an unstable short-circuit state of the switching elements 41 to 44 having a short-circuit failure.

In the case of the converter CELa of the full-bridge circuit, the control device 14 supplies circulating current in both directions from the connection terminal 71 to the connection terminal 72 and from the connection terminal 72 to the connection terminal 71, for example. The controller 14 supplies, for example, an alternating circulating current. As a result, the contact surfaces of the switching elements 41 and 43 on the low side or the contact surfaces of the switching elements 42 and 44 on the high side can be stabilized appropriately.

Thus, in the MMC main circuit section 12, the configuration of the converter may be a half-bridge circuit or a full-bridge circuit.

In the above embodiment, an MMC type power converter is used for the main circuit section 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 (converters CELa) are connected in series.

The power conversion device 10 is not limited to a DC power transmission system, and may be applied to any other system that requires AC-to-DC conversion and DC-to-AC conversion. The AC/DC conversion by the main circuit unit 12 is not limited to both AC to DC and DC to AC, but may be AC to DC or DC to AC. Also, the main circuit section 12 may be, for example, an AC/AC direct conversion circuit.

The configuration of the main circuit section 12 may be, for example, a configuration in which a plurality of arm sections are star-connected, delta-connected, or matrix-connected. The main circuit section 12 may be, for example, a modular matrix converter. The main circuit section 12 does not necessarily have to have a plurality of legs. The main circuit section should have at least a plurality of arm sections. The configuration of the main circuit section may be any configuration that can convert power. The power conversion device may be, for example, a frequency conversion device, a DC power transmission device, a reactive power compensator, or a power flow control device.

While several embodiments of the invention have been described, these embodiments have been 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 modifications 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 scope of the invention described in the claims and equivalents thereof.

2 AC power system 3, 4 DC transmission line 6 Transformer 10 Power conversion device 12 Main circuit unit 14 Control device 20a First DC terminal 20b Second DC terminal 21a first AC terminal 21b second AC terminal 21c third AC terminal 22a first arm 22b second arm 22c third arm 22d fourth arm 22e 5th arm 22f 6th arm 23a to 23f buffer reactor 24a to 24f current detector 25 voltage detector 26 signal line 41 to 44 switching element 51 to 54 Rectifying element 61 to 64 Drive circuit 71, 72 Connection terminal 74 Charge storage element 76 Power supply circuit 78 Voltage detection circuit 80 Control circuit 82 Protection circuit CEL, CELa Converter , LG1...1st leg, LG2...2nd leg, LG3...3rd leg

Claims (5)

a main circuit unit having a plurality of converters connected in series and performing power conversion by the operation of the plurality of converters;
a control device that controls the operation of the main circuit unit;
with
each of the plurality of transducers,
a pair of connection terminals;
a plurality of switching elements;
a charge storage element connected in parallel to the plurality of switching elements;
are connected in series via the pair of connection terminals, and an output state in which the voltage of the charge storage element is output between the pair of connection terminals by switching of the plurality of switching elements; can be switched between a bypass state in which the connection terminals of the are electrically connected and a stopped state in which the plurality of switching elements are turned off;
The control device detects a short-circuit failure in a plurality of switching elements of the plurality of converters, and detects a short-circuit failure in any one of the plurality of switching elements in any one of the plurality of converters. A power converter that controls operations of a plurality of converters so as to supply a circulating current circulating in the main circuit unit to the converter in which a short-circuit fault has occurred in any one of the plurality of switching elements. 2. The power converter according to claim 1, wherein said control device stops controlling the supply of said circulating current after a predetermined period of time has elapsed since the start of supplying said circulating current after starting the control of supplying said circulating current. The main circuit section has a plurality of bridge-connected arm sections,
each of the plurality of arm portions has a plurality of the transducers connected in series;
The power converter according to claim 1 or 2, wherein the control device supplies the circulating current so as to circulate through the plurality of bridge-connected arm portions. The plurality of converters have two switching elements connected in half bridges,
4. The control device according to any one of claims 1 to 3, wherein the control device supplies the circulating current in a direction from one of the pair of connection terminals to the other or in a direction from the other of the pair of connection terminals to one. Power converter. The plurality of converters has four switching elements connected in a full bridge,
4. The control device according to any one of claims 1 to 3, wherein the control device supplies the circulating current in a direction from one of the pair of connection terminals to the other or in a direction from the other of the pair of connection terminals to one. Power converter.

Images