JP2023166163A - Electric power conversion device - Google Patents

Abstract

To provide an electric power conversion device capable of suppressing breakdown of respective switching elements in a short-circuit failure while suppressing an increase in switching loss of a plurality of converters which are connected in series.SOLUTION: There is provided an electric power conversion device that comprises: a main circuit part which has a plurality of converters connected in series and converts electric power through the operation of the plurality of converters; and a control device which controls the operation of the main circuit part. The plurality of converters each has a pair of connection terminals, a plurality of switching elements, a charge storage element connected to the plurality of switching elements in parallel, and a looped conductor. The looped conductor is magnetically coupled to a looped main circuit conductor part consisting of the plurality of switching elements, the charge storage element, and a wiring member connecting the plurality of switching elements and the charge storage element together.SELECTED DRAWING: Figure 3

Description

Embodiments of the present invention relate to a power conversion device.

There is a power conversion device in which multiple 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, when a short-circuit failure occurs in each switching element, such as short-circuiting a charge storage element, the charge in the charge storage element is discharged in a short period of time, causing a large current to flow through each switching element. It may flow. When a large current flows through each switching element, each switching element is damaged and scattered around, potentially damaging surrounding healthy items and inducing secondary failure.

For example, by designing the main circuit conductor to increase the inductance of the current loop when each switching element is short-circuited, the current peak can be reduced, and even when a short-circuit failure occurs in each switching element, the main circuit conductor can be designed to increase the inductance of the current loop when each switching element is shorted. It is possible to suppress damage. However, with this method, the surge voltage increases due to the increased inductance, and in order to suppress this, it becomes necessary to increase the gate resistance. There is a concern that this will increase switching loss.

Therefore, in a power conversion device in which a plurality of converters are connected in series, it is desirable to be able to suppress damage to each switching element in the event of a short-circuit failure while suppressing an increase in switching loss.

JP2020-54223A

Embodiments of the present invention provide a power converter device that can suppress damage to each switching element in the event of a short-circuit failure while suppressing an increase in switching loss of a plurality of converters connected in series.

According to an embodiment of the present invention, the main circuit unit includes a plurality of converters connected in series, and controls the operation of the main circuit unit that converts power and the operation of the main circuit unit by the operation of the plurality of converters. A control device, each of the plurality of converters includes 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 loop-shaped conductor. and an output state in which the charge storage element is connected in series through the pair of connection terminals, and the voltage of the charge storage element is output between the pair of connection terminals by switching the plurality of switching elements; It is possible to switch between a bypass state in which conduction occurs between the pair of connection terminals and a stop state in which the plurality of switching elements are turned off, and the loop-shaped conductor connects the plurality of switching elements and the charge storage. element and a loop-shaped main circuit conductor portion formed by a wiring member connecting the plurality of switching elements and the charge storage element, and a short circuit failure occurs in the plurality of switching elements, and the When the charge storage element is short-circuited, the short-circuit current flowing in the main circuit conductor part is reduced by flowing an induced current according to the magnetic flux generated by the short-circuit current of the charge storage element flowing in the main circuit conductor part. A power conversion device is provided.

A power conversion device is provided that can suppress damage to each switching element in the event of a short-circuit failure while suppressing an increase in switching loss of a plurality of converters connected in series.

FIG. 1 is a block diagram schematically representing a power conversion device according to an embodiment. FIG. 2 is a block diagram schematically representing a converter. It is an explanatory view showing a part of a converter typically. FIGS. 4(a) and 4(b) are graphs schematically representing an example of the operation of the converter. FIGS. 5A and 5B are graphs schematically representing an example of the characteristics of a conductor.

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 part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be shown differently depending on the drawing.
In the present specification and each figure, the same elements as those described above with respect to the existing figures are denoted by the same reference numerals, and detailed explanations are omitted as appropriate.

FIG. 1 is a block diagram schematically representing a power conversion device according to an embodiment.
As shown in FIG. 1, the power conversion device 10 includes a main circuit section 12 and a control device 14. The power converter 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 power transmission lines 3 and 4 in a DC power transmission system.

The DC power transmission system includes, for example, a transformer 6. Main circuit section 12 of power conversion device 10 is connected to AC power system 2 via 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 compatible with 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 . Transformer 6 is a three-phase transformer. The transformer 6 is provided as needed and can be omitted. The main circuit section 12 may be directly supplied with three-phase AC power from the AC power system 2 .

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 power transmission lines 3 and 4. The power converter 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 way, the power conversion device 10 performs AC/DC conversion from AC to DC, and AC/DC conversion from DC to AC.

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

The main circuit section 12 is provided between the AC power system 2 and each DC power transmission line 3, 4. The main circuit section 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 multilevel power converter having a plurality of converters connected in series. The main circuit section 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 switching elements connected in a half-bridge connection or a full-bridge connection, and a charge storage element connected in parallel to each switching element. The main circuit section 12 converts power by operating a plurality of converters. The main circuit section 12 performs AC/DC conversion, for example, by 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 three-phase AC power to DC power and the conversion of DC power to three-phase AC power by the main circuit section 12 by controlling on/off of each switching element.

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

The first DC terminal 20a is connected to the high voltage side DC power transmission line 3. The second DC terminal 20b is connected to the low voltage side DC power transmission line 4. Thereby, the DC power converted by the main circuit section 12 is supplied to the DC power transmission lines 3 and 4, and the DC power supplied from the DC power transmission lines 3 and 4 is input to the main circuit 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 each DC terminal 20a, 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 section 22c and the fourth arm section 22d are connected in parallel to the first arm section 22a and the second arm section 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 section 22e and the sixth arm section 22f are connected in parallel to the first arm section 22a and the second arm section 22b, and are connected in parallel to the third arm section 22c and the fourth arm section 22d. connected in parallel.

In the main circuit section 12, the first arm section 22a and the second arm section 22b constitute a first leg LG1, the third arm section 22c and the fourth arm section 22d constitute a second leg LG2, and the fifth arm section 22e and the sixth arm portion 22f constitute a third leg LG3. That is, in this example, the main circuit section 12 is a three-phase inverter with three legs and six arms. 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 connected in a three-phase bridge.

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 configured by a plurality of switching elements. The main circuit section 12 may be, for example, a two-leg, four-arm single-phase inverter. The number of arm portions and legs is not limited to the above, and may be any number.

The first arm portion 22a includes a plurality of converters UP1, UP2... _UPM1 connected in series. The second arm portion 22b includes a plurality of converters UN1, UN2... _UNM2 connected in series. The third arm portion 22c includes a plurality of converters VP1, VP2... _VPM3 connected in series. The fourth arm portion 22d includes a plurality of converters VN1, VN2... _VNM4 connected in series. The fifth arm portion 22e includes a plurality of converters WP1, WP2... _WPM5 connected in series. The sixth arm portion 22f has a plurality of converters WN1, WN2... _WNM6 connected in series.

However, in the following, each converter UP1, UP2...UPM ₁ , UN1, UN2...UNM ₂ , VP1, VP2...VPM ₃ , VN1, VN2...VNM ₄ , WP1, WP2...WPM ₅ , WN1, WN2...WNM ₆ When collectively called, they are called "converter CEL".

In each arm portion 22a to 22f, M ₁ , M ₂ , M ₃ , M ₄ , M ₅ , and M ₆ 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.

The number of converters CEL provided in each arm portion 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 arm part 22a to 22f may be different within a range that does not affect the operation of the main circuit part 12. For example, when 100 converters CEL are connected in series to one arm, the number of converters CEL provided in another arm may differ by 1 to 2 units.

Each of the arm portions 22a to 22f further includes buffer reactors 23a to 23f and a plurality of current detectors 24a to 24f. Moreover, the power conversion device 10 further includes a voltage detection section 25.

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

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 24c detects the current flowing through the third arm portion 22c, and inputs the detected current value to the control device 14. The current detector 24d detects the current flowing through the fourth arm portion 22d, and inputs the detected current value to the control device 14. The current detector 24e detects the current flowing through the fifth arm portion 22e, and inputs the detected current value to the control device 14. The current detector 24f detects the current flowing through the sixth arm portion 22f, 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 detection unit 25 may be connected to the primary side of the transformer 6 or may be connected to the secondary side.

In the main circuit section 12, there are 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. Each connection point with 22f becomes an AC output point.

The first AC terminal 21a is connected to a connection point between the first arm section 22a and the second arm section 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 section 22e and the sixth arm section 22f. Each AC terminal 21a to 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 a control signal to the converter CEL via a signal line 26 . Further, the converter CEL inputs, for example, a control signal and a protection signal related to control and operation protection of the converter CEL to the control device 14 via another signal line (not shown). Note that 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 connection 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 allows appropriate communication between the control device 14 and each converter CEL.

FIG. 2 is a block diagram schematically representing the converter.
As shown in FIG. 2, the converter CEL includes a plurality of switching elements 41, 42, a plurality of rectifying elements 51, 52, a plurality of drive circuits 61, 62, a pair of connection terminals 71, 72, and a charger. 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 the current flowing between the pair of main terminals. For each of the switching elements 41 and 42, a self-extinguishing element such as an IGBT is used, for example. The pair of main terminals is, for example, an emitter and a collector, and the control terminal is, for example, a gate. Each of the switching elements 41 and 42 is, for example, a pressure contact type switching element.

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 that flows between the pair of main terminals. The OFF state is not limited to a state in which no current flows completely between the pair of main terminals, and 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.

For each of the switching elements 41 and 42, a normally-off semiconductor element is used, for example. Each of the switching elements 41 and 42 is turned on when the voltage at the control terminal is high, and turned off when the voltage at the control terminal is low. Each of the switching elements 41 and 42 is in the off state when the voltage at the control terminal is lower than in the on state. Each of the switching elements 41 and 42 is turned on, for example, when a positive voltage is applied to the control terminal, and turned off when the voltage at 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 to a pair of main terminals of the switching element 41. In this example, 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 manner. In this example, converter CEL is a converter in half-bridge configuration.

The rectifying element 51 is connected in antiparallel 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 antiparallel to the pair of main terminals of the switching element 42. The rectifying elements 51 and 52 are so-called free wheel diodes.

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

A plurality of converters CEL in the same arm section are connected in series via a pair of connection terminals 71 and 72. Power is supplied to the converter CEL via each connection terminal 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 each switching element 41 and 42 to the control circuit 80 via the signal line 26. The control circuit 80 inputs a drive signal for switching on/off of each switching element 41, 42 to the drive circuits 61, 62 based on the input control signal.

The drive circuit 61 is connected to a control terminal of the switching element 41. The drive circuit 62 is connected to a control terminal of the switching element 42. The drive circuits 61 and 62 turn on and off each switching element 41 and 42 based on a drive signal input from the control circuit 80. Thereby, depending on the control signal from the control device 14, the on/off of each switching element 41, 42 is controlled. 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 the power conversion by the main circuit section 12.

Note that 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 that can control on/off of each switching element 41 and 42. For example, the control signal from the control device 14 may be input directly to the drive circuits 61 and 62. In this case, the control circuit 80 can be omitted.

Charge storage element 74 is connected in parallel to switching element 41 and 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 respective 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 each connection terminal 71 and 72 by switching each switching element 41 and 42 based on a control signal from the control device 14, and an output state in which the voltage of the charge storage element 74 is output between each connection terminal 71 and 72. 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 are switched.

In each arm portion 22a to 22f, the total voltage of the converter CEL in the output state becomes the voltage of each arm portion 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 to be in an output state.

When both switching elements 41 and 42 are in the off state (converter CEL is in a stopped state), the voltage between each connection terminal 71 and 72 is determined by the direction of the arm current. For example, when the arm current is flowing in the direction 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. On the contrary, when the arm current is flowing in the direction from the connection terminal 71 to the connection terminal 72, the rectifying element 52 is turned on and the charge storage element 74 is charged, and there is no charge storage element between the connection terminals 71 and 72. 74 voltages appear.

The power supply circuit 76 is connected in parallel to 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 charges 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 in response to supply of drive power from the power supply circuit 76.

Note that the method of feeding 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 source different from that of the charge storage element 74. The power supply method to the drive circuits 61, 62 and the control circuit 80 may be any method that can appropriately supply power to the drive circuits 61, 62 and the control circuit 80.

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

FIG. 3 is an explanatory diagram schematically showing a part of the converter.
As represented in FIG. 3, each converter CEL further includes loop-shaped conductors 91, 92. The conductors 91 and 92 are located in the vicinity of a loop-shaped main circuit conductor section formed by each of the switching elements 41 and 42, the charge storage element 74, and a wiring member connecting each of the switching elements 41 and 42 and the charge storage element 74. and is magnetically coupled to the main circuit conductor.

As shown in FIG. 3, the conductors 91 and 92 are connected to the short-circuit current of the charge storage element 74 that flows to the main circuit conductor when a short-circuit failure occurs in each of the switching elements 41 and 42 and the charge storage element 74 is short-circuited. The short circuit current I _dc flowing through the main circuit conductor is reduced by causing an induced current I _angle to flow in accordance with the magnetic flux generated by I _dc and generating loss due to the resistance component.

FIGS. 4(a) and 4(b) are graphs schematically representing an example of the operation of the converter.
FIG. 4A schematically represents an example of the short circuit current I _dc flowing through the main circuit conductor.
FIG. 4(b) schematically represents an example of the induced current I _angle flowing through the conductors 91 and 92.
In addition, in FIG. 4(a), the solid line represents an example of the short circuit current I _dc when the conductors 91 and 92 are provided, and the broken line represents an example of the short circuit current I _dc when the conductors 91 and 92 are not provided. ing.

As shown in FIG. 4(a), the short circuit current I _dc flowing through the main circuit conductor is a current that oscillates at a high frequency. As shown in FIG. 4B, the conductors 91 and 92 attenuate the short circuit current I _dc by causing an induced current I _angle that oscillates in the opposite direction to the short circuit current I _dc to flow. As a result, a large current instantaneously flows through each switching element 41, 42 due to a short circuit in the charge storage element 74, and each switching element 41, 42 may be damaged or fragments may be scattered as a result of the damage. This can prevent you from injuring yourself.

The conductors 91 and 92 have, for example, a substantially rectangular frame shape. In other words, the conductors 91 and 92 are substantially rectangular conductor frames. However, the shape of the conductors 91 and 92 is not limited to the above, and may be, for example, annular. The shape of the conductors 91 and 92 is not limited to a frame shape or an annular shape, and may be, for example, a coil shape wound spirally a plurality of times. The shapes of the conductors 91 and 92 may be any shape capable of magnetically coupling with the main circuit conductor and allowing an induced current to flow in accordance with the magnetic flux generated in the main circuit conductor. In this specification, a loop shape refers to a shape that allows current to circulate within a conductor, such as a frame shape, annular shape, or coil shape.

The conductors 91 and 92 are arranged so that, for example, as shown in FIG. 3, the magnetic flux generated by the short circuit current I _dc of the charge storage element 74 flowing through the main circuit conductor passes through the space inside the conductors 91 and 92. be done. Thereby, for example, the magnetic coupling between the conductors 91 and 92 and the main circuit conductor section can be strengthened, and the short circuit current I _dc flowing through the main circuit conductor section can be easily reduced.

In FIG. 3, each converter CEL has two conductors 91 and 92 arranged to sandwich the main circuit conductor portion. However, the number of conductors provided in each converter CEL is not limited to two, and may be one or three or more. The number of conductors provided in each converter CEL may be any number that can appropriately reduce the short circuit current I _dc flowing through the main circuit conductor portion in the event of a short circuit failure of each switching element 41, 42.

FIGS. 5A and 5B are graphs schematically representing an example of the characteristics of a conductor.
FIG. 5A schematically represents an example of the relationship between the resistance values of the conductors 91 and 92 and the current square time product of the short circuit current I _dc flowing through the main circuit conductor portion.
FIG. 5B schematically represents an example of the relationship between the frequency of the induced current I _angle flowing through the conductors 91 and 92 and the resistance value of the conductors 91 and 92.

As shown in FIG. 5(a), the resistance values of the conductors 91 and ₉₂ have an optimum resistance value (impedance matching condition) exists. The resistance values of the conductors 91 and 92 are designed to have the above-mentioned optimum resistance value. The resistance values of the conductors 91 and 92 are set to the above-mentioned optimum resistance values. More specifically, the resistance value of the conductors 91 and 92 is determined by the cross-sectional area of the conductors 91 and 92, the length (circumferential length) of the conductors 91 and 92, and the resistivity of the conductors 91 and 92. It is a value. The optimal resistance value can be derived using simulation and mathematical optimization, for example. Mathematical optimization is a method of automatically searching for better characteristics based on simulation results using a certain algorithm, and is a technology and study that systematizes trial and error performed by humans.

Furthermore, as shown in FIG. 5(b), the resistance values of the conductors 91 and 92 have frequency characteristics due to the skin effect. For this reason, the shapes of the conductors 91 and 92 are designed so that the above-mentioned optimum resistance value is achieved at the resonant frequency at the time of short circuit. In other words, the shapes of the conductors 91 and 92 are set so as to have the above-mentioned optimum resistance value at the frequency of the induced current I _angle that flows when each switching element 41 and 42 has a short-circuit failure.

By designing the shapes of the conductors 91 and 92 in this way, the conductors 91 and 92 can attenuate the current that oscillates at high frequency in the event of a short-circuit failure. Since the main circuit current is at a low frequency during normal operation, the influence of the skin effect that occurs in the conductors 91 and 92 is suppressed, and the conductors 91 and 92 have low resistance, which deviates from the impedance matching condition and causes the main circuit conductor to The influence of the conductors 91 and 92 on the conductors 91 and 92 can be alleviated. Furthermore, by magnetically coupling with the conductors 91 and 92, the inductance of the main circuit conductor portion can be reduced, so that surge voltage can be suppressed. Therefore, the resistance value (for example, gate resistance) of the control terminal of each switching element 41, 42 can be lowered, and an increase in switching loss of each switching element 41, 42 can be suppressed.

As described above, in the power conversion device 10 according to the present embodiment, damage to each switching element 41, 42 in the event of a short-circuit failure is achieved while suppressing an increase in switching loss of a plurality of converters CEL connected in series. can be suppressed.

Note that in the MMC type main circuit section 12, the configuration of the converter CEL may be a half-bridge circuit or a full-bridge circuit. In the case of a full-bridge circuit, even if a short-circuit failure occurs in each switching element that short-circuits the charge storage element 74 in any combination of four switching elements, the loop is magnetically coupled to the main circuit conductor. It is desirable to arrange conductors in the form of

In the embodiment described above, the main circuit section 12 uses an MMC type power converter. The main circuit section 12 is not limited to the MMC type, and may be a power converter of another type in which a plurality of converters CEL are connected in series, for example.

The power conversion device 10 is not limited to a DC power transmission system, and 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 main circuit section 12 is not limited to both alternating current to direct current and direct current to alternating current, and may be only one of alternating current to direct current or direct current to alternating current. Further, the main circuit section 12 may be, for example, an 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 only needs to have at least a plurality of arm sections. The configuration of the main circuit section may be any configuration capable of converting power. The power conversion device may be, for example, a frequency conversion device, a DC power transmission device, a reactive power compensation device, a power flow control device, or the like.

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

2... AC power system, 3, 4... DC power transmission line, 6... Transformer, 10... Power converter, 12... Main circuit section, 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 part, 22b...Second arm part, 22c...Third arm part, 22d...Fourth arm part, 22e ...Fifth arm section, 22f...Sixth arm section, 23a to 23f...Buffer reactor, 24a to 24f...Current detector, 25...Voltage detection section, 26...Signal line, 41, 42...Switching element, 51, 52... Rectifying element, 61, 62... Drive circuit, 71, 72... Connection terminal, 74... Charge storage element, 76... Power supply circuit, 78... Voltage detection circuit, 80... Control circuit, 91, 92... Conductor, CEL... Converter, LG1...1st leg, LG2...2nd leg, LG3...3rd leg

Claims (4)

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 that controls the operation of the main circuit section;
Equipped with
Each of the plurality of converters includes:
a pair of connection terminals,
multiple switching elements;
a charge storage element connected in parallel to the plurality of switching elements;
A loop-shaped conductor,
are connected in series via the pair of connection terminals, and output a voltage of the charge storage element between the pair of connection terminals by switching the plurality of switching elements; It is possible to switch between a bypass state in which conduction is established between the connection terminals of and a stop state in which the plurality of switching elements are in an OFF state,
The loop-shaped conductor is magnetically connected to a loop-shaped main circuit conductor portion constituted by the plurality of switching elements, the charge storage element, and a wiring member connecting the plurality of switching elements and the charge storage element. When a short-circuit failure occurs in the plurality of switching elements and the charge storage element is short-circuited, an induced current is caused to flow in accordance with a magnetic flux generated by a short-circuit current of the charge storage element flowing to the main circuit conductor part. A power conversion device that reduces the short circuit current flowing through the main circuit conductor. 2. The power conversion device according to claim 1, wherein the resistance value of the loop-shaped conductor is set to be an optimum resistance value that minimizes the current squared time product of the short circuit current flowing through the main circuit conductor portion. 3. The power conversion device according to claim 2, wherein the shape of the loop-shaped conductor is set to have the optimum resistance value at a frequency of the induced current that flows when a short-circuit failure occurs in the plurality of switching elements. 4. The loop-shaped conductor is arranged so that a magnetic flux generated by the short-circuit current flowing through the main circuit conductor passes through a space inside the loop-shaped conductor. The power conversion device described.

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