Power conversion device

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

Technical Field

[0001] Embodiments of the present invention relate to a power conversion device.

Background Art

[0002] There is a power conversion device 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.

[0003] In such a power conversion device, when a short-circuit fault occurs in each switching element so as to short-circuit the charge storage element, the charge of the charge storage element is discharged in a short time, and a large current may flow through each switching element. When a large current flows through each switching element, each switching element may be damaged and scattered around, damaging surrounding sound supplies and inducing a secondary fault.

[0004] For example, by designing the main circuit conductor so as to increase the inductance of the current loop at the time of short circuit of each switching element, the current peak can be reduced, and even when a short-circuit fault occurs in each switching element, damage to each switching element can be suppressed. However, in this method, due to the increased inductance, the surge voltage increases, and it is necessary to increase the gate resistance to suppress this. There is a concern that this may increase the switching loss.

[0005] Therefore, in a power conversion device in which a plurality of converters are connected in series, it is desired to suppress an increase in switching loss and suppress damage to each switching element at the time of a short-circuit fault.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] An embodiment of the present invention provides a power conversion device that can suppress an increase in switching loss of a plurality of serially connected converters and suppress damage to each switching element during a short-circuit fault.

MEANS FOR SOLVING THE PROBLEMS

[0008] According to an embodiment of the present invention, there is provided a main circuit section having a plurality of serially connected converters that perform power conversion by the operation of the plurality of converters, and a control device that controls the operation of the main circuit section. 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 loop-shaped conductor. The pair of connection terminals are serially connected via the pair of connection terminals, and the voltage of the charge storage element is output between the pair of connection terminals by switching of the plurality of switching elements, a bypass state in which the pair of connection terminals are made conductive, and a stop state in which the plurality of switching elements are turned off. The loop-shaped conductor is magnetically coupled to a loop-shaped main circuit conductor section formed by the plurality of switching elements, the charge storage element, and wiring members connecting the plurality of switching elements and the charge storage element. When a short-circuit fault occurs in the plurality of switching elements and the charge storage element is short-circuited, an induced current flows in response to the magnetic flux generated by the short-circuit current of the charge storage element flowing through the main circuit conductor section, thereby reducing the short-circuit current flowing through the main circuit conductor section. A power conversion device is provided.

EFFECTS OF THE INVENTION

[0009] A power conversion device is provided that can suppress an increase in switching loss of a plurality of serially connected converters and suppress damage to each switching element during a short-circuit fault.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0011] Hereinafter, each embodiment will be described 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 ratio of the sizes between parts, etc. are not necessarily the same as those in reality. Also, even when representing the same part, there are cases where the dimensions and ratios are represented differently in the drawings. 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 previously shown figures, and the detailed description is omitted as appropriate.

[0012] FIG. 1 is a block diagram schematically showing a power conversion device according to an embodiment. As shown in FIG. 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 power transmission lines 3 and 4 in the DC power transmission system.

[0013] The DC power 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 symmetric 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. The transformer 6 is a three-phase transformer. The transformer 6 is provided as needed 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 the three-phase AC power supplied from the AC power system 2 into DC power and supplies the converted DC power to the DC power transmission lines 3 and 4. Also, the power conversion device 10 converts the DC power supplied from the DC power transmission lines 3 and 4 into three-phase AC power and supplies the converted three-phase AC power to the AC power system 2. Thus, the power conversion device 10 performs AC-DC conversion from AC to DC and AC-DC conversion from DC to AC.

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

[0016] The main circuit section 12 is provided between the AC power system 2 and each of the DC transmission lines 3 and 4. The main circuit section 12 performs conversion from three-phase AC power to DC power and conversion from 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 performs power conversion 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.

[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 section 12 has a pair of first and second DC terminals 20a and 20b, three AC terminals 21a to 21c from the first to the third, and six arm sections 22a to 22f from the first to the sixth.

[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. Thereby, 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.

[0020] The first arm section 22a is connected to the first DC terminal 20a. The second arm section 22b is connected between the first arm section 22a and the second DC terminal 20b. The first arm section 22a and the second arm section 22b are connected in series between the respective DC terminals 20a and 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 with respect 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 with respect to the first arm portion 22a and the second arm portion 22b and are also connected in parallel with respect to the third arm portion 22c and the fourth arm portion 22d.

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

[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. Thus, the main circuit portion 12 has a plurality of arm portions and a plurality of legs constituted by a plurality of switching elements. The main circuit portion 12 may be, for example, a two-leg, four-arm single-phase inverter or the like. The number of arm portions and legs is not limited to the above and may be any number.

[0025] 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 converters 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 converters WP1, WP2, …, WPM5 connected in series. The sixth arm portion 22f has a plurality of converters WN1, WN2, …, WNM6 connected in series.

[0026] However, hereinafter, when collectively referring to each of the converters UP1, UP2, …, UPM1, UN1, UN2, …, UNM2, VP1, VP2, …, VPM3, VN1, VN2, …, VNM4, WP1, WP2, …, WPM5, and WN1, WN2, …, WNM6, they are referred to as "converter CEL".

[0027] In each of the arm portions 22a to 22f, M1, M2, M3, M4, M5, and M6 represent the number of converters CEL connected in series. In each of the arm portions 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 portions 22a to 22f is substantially the same. For example, when a large number of each converter CEL is connected, the number of converters CEL provided in each of the arm portions 22a to 22f may be different within a range that does not affect the operation of the main circuit portion 12. For example, when 100 converters CEL are connected in series to one arm portion, the number of converters CEL provided in another arm portion may differ by 1 to 2.

[0029] Each of the arm portions 22a to 22f further has buffer reactors 23a to 23f and a plurality of current detectors 24a to 24f. The power conversion device 10 further has a voltage detection unit 25.

[0030] Each buffer reactor 23a to 23f is connected in series to each converter CEL in each of the arm portions 22a to 22f. The buffer reactor 23a of the first arm portion 22a is provided between the AC terminal 21a and the connection point of 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 AC terminal 21a and the connection point of 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 AC terminal 21b and the connection point of 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 AC terminal 21b and the connection point of 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 AC terminal 21c and the connection point of 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 AC terminal 21c and the connection point of the fifth arm portion 22e and the sixth arm portion 22f and the converter WN1.

[0031] The current detector 24a is provided in 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). The current detector 24a inputs the detected current value of the first arm portion 22a to the control device 14. Thereby, the current value of the first arm portion 22a is input to the control device 14.

[0032] 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.

[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 unit 12, each of the connection points between the first arm portion 22a and the second arm portion 22b, the connection point between the third arm portion 22c and the fourth arm portion 22d, and the connection point between the fifth arm portion 22e and the sixth arm portion 22f becomes an AC output point.

[0035] The first AC terminal 21a is connected to the connection point between the first arm portion 22a and the second arm portion 22b. The second AC terminal 21b is connected to the connection point between the third arm portion 22c and the fourth arm portion 22d. The third AC terminal 21c is connected to the 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 the transformer 6, for example.

[0036] Each converter CEL is connected to the control device 14 via, for example, the 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. Further, the converter CEL inputs, for example, control signals and protection signals related to the 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 serially connected converters CEL may be daisy-chain connected, and the control device 14 may communicate only with the converter CEL at one end and the converter 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 can appropriately communicate between the control device 14 and each converter CEL.

[0037] FIG. 2 is a block diagram schematically showing a 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, a charge storage element 74, a power supply circuit 76, a voltage detection circuit 78, and a control circuit 80.

[0038] Each of the switching elements 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 example, a self-extinguishing element such as an IGBT is used for each of the switching elements 41, 42. The pair of main terminals are, for example, an emitter and a collector, and the control terminal is, for example, a gate. Each of the switching elements 41, 42 is, for example, a pressure-contact type switching element.

[0039] Each of the switching elements 41 and 42 switches between an on state in which current can flow between a pair of main terminals and an off state in which the current flowing between the pair of main terminals is interrupted. The off state is not limited to a state in which no current flows completely 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 made sufficiently small.

[0040] For example, normally-off semiconductor elements are used for each of the switching elements 41 and 42. Each of the switching elements 41 and 42 becomes an on state when the voltage of the control terminal is high and becomes an off state when the voltage of the control terminal is low. Each of the switching elements 41 and 42 becomes an off state when the voltage of the control terminal is lower than the on state. For example, each of the switching elements 41 and 42 becomes an on state when a positive voltage is applied to the control terminal, and becomes an off state when the voltage of the control terminal is set to 0V or a negative voltage is applied to the control terminal.

[0041] 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 and 42 connected in series. In other words, the converter CEL has two switching elements 41 and 42 connected in a half-bridge configuration. In this example, the converter CEL is a converter with a half-bridge configuration.

[0042] The rectifying element 51 is connected in anti-parallel to a 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 a pair of main terminals of the switching element 42. The rectifying elements 51 and 52 are so-called freewheeling diodes.

[0043] 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 on the side opposite to the main terminal connected to the switching element 42.

[0044] A plurality of converters CEL within the same arm portion are connected in series via a pair of connection terminals 71 and 72. Power is supplied to the converter CEL via each of the connection terminals 71 and 72. The switching element 41 is a so-called low-side switch, and the switching element 42 is a so-called high-side switch.

[0045] The control circuit 80 is connected to the control device 14 via the signal line 26. The control device 14 transmits a control signal for controlling the on / off of each of the switching elements 41 and 42 to the control circuit 80 via the signal line 26. The control circuit 80 inputs a drive signal for switching the on / off of each of the switching elements 41 and 42 to the drive circuits 61 and 62 based on the input control signal.

[0046] 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 the on / off of each of the switching elements 41 and 42 based on the drive signal input from the control circuit 80. Thereby, the on / off of each of the switching elements 41 and 42 is controlled according to the 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 and 42 of each converter CEL. Thereby, the control device 14 controls the power conversion by the main circuit section 12.

[0047] Note that the configurations of the drive circuits 61 and 62 and the control circuit 80 are not limited to the above, and any configuration capable of controlling the on / off of each of the switching elements 41 and 42 may be used. For example, the control signal from the control device 14 may be directly input to the drive circuits 61 and 62. In this case, the control circuit 80 may be omitted.

[0048] The charge storage element 74 is connected in parallel to the switching element 41 and the switching element 42. The charge storage element 74 is, for example, a capacitor.

[0049] 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 conductive, and the voltage between the connection terminals 71 and 72 becomes substantially zero.

[0050] In this way, the converter CEL switches between an output state in which the voltage of the charge storage element 74 is output between the connection terminals 71 and 72 by switching of the switching elements 41 and 42 based on a control signal from the control device 14, a bypass state in which the connection terminals 71 and 72 are made conductive, and a stop state in which the switching elements 41 and 42 are in the off state.

[0051] In each of the arm portions 22a to 22f, the total voltage of the converters CEL in the output state becomes the voltage of each of the arm portions 22a to 22f. The main circuit portion 12 and the control device 14 perform multi-level power conversion by controlling the number of converters CEL in the output state.

[0052] When both of the switching elements 41 and 42 are in the off state (when the converter CEL is in the stop 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 is flowing from the connection terminal 72 toward 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 is flowing from the connection terminal 71 toward the connection terminal 72, the rectifying element 52 is turned on, the charge storage element 74 is charged, and the voltage of the charge storage element 74 appears between the connection terminals 71 and 72.

[0053] The power supply circuit 76 is connected in parallel to the charge storage element 74. Based on the charge stored in the charge storage element 74, the power supply circuit 76 generates a driving power supply for the driving circuits 61, 62, and the control circuit 80, and supplies the generated driving power supply to the driving circuits 61, 62, and the control circuit 80. The driving circuits 61, 62, and the control circuit 80 operate in response to the supply of the driving power supply from the power supply circuit 76.

[0054] Note that the power supply method for the driving circuits 61, 62, and the control circuit 80 is not limited to the above. For example, power may be supplied to the driving circuits 61, 62, and the control circuit 80 from a power source different from the charge storage element 74. The power supply method for the driving circuits 61, 62, and the control circuit 80 may be any method that can appropriately supply power to the driving circuits 61, 62, and the control circuit 80.

[0055] The voltage detection circuit 78 is connected in parallel to the charge storage element 74. The voltage detection circuit 78 is connected to 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.

[0056] Figure 3 is an explanatory diagram schematically showing a part of the converter. As shown in Figure 3, each converter CEL further has loop-shaped conductors 91, 92. The conductors 91, 92 are arranged near the loop-shaped main circuit conductor part constituted by the switching elements 41, 42, the charge storage element 74, and the wiring members connecting the switching elements 41, 42 and the charge storage element 74, and are magnetically coupled to the main circuit conductor part.

[0057] As shown in Figure 3, when a short circuit fault occurs in each of the switching elements 41, 42 and the charge storage element 74 is short-circuited, the conductors 91, 92 cause an induced current I dc to flow according to the magnetic flux generated by the short-circuit current I angle of the charge storage element 74 flowing through the main circuit conductor part, and generate losses due to the resistance component, thereby reducing the short-circuit current I dc flowing through the main circuit conductor part.

[0058] Figures 4(a) and 4(b) are graphs schematically showing an example of the operation of the converter. Figure 4(a) schematically shows an example of the short-circuit current I flowing through the main circuit conductor portion. dc Figure 4(b) schematically shows an example of the induced current I flowing through the conductors 91 and 92. angle Also, in Figure 4(a), an example of the short-circuit current I when the conductors 91 and 92 are provided is represented by a solid line, and an example of the short-circuit current I when the conductors 91 and 92 are not provided is represented by a dashed line. dc dc

[0059] As shown in Figure 4(a), the short-circuit current I flowing through the main circuit conductor portion is a current that oscillates at a high frequency. As shown in Figure 4(b), the conductors 91 and 92 flow an induced current I that oscillates in the opposite direction to the short-circuit current I, thereby attenuating the short-circuit current I. This can suppress a large current instantaneously flowing through each of the switching elements 41 and 42 due to a short circuit of the charge storage element 74, and prevent each of the switching elements 41 and 42 from being damaged, or fragments flying off due to the damage and damaging surrounding sound articles. dc dc angle dc

[0060] The conductors 91 and 92 are, for example, substantially rectangular frame-shaped. 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 frame-shaped or annular, and may be, for example, a coil-shaped wound multiple times in a spiral. The shape of the conductors 91 and 92 may be any shape that can be magnetically coupled to the main circuit conductor portion and flow an induced current according to the magnetic flux generated in the main circuit conductor portion. In this specification, the loop shape means a shape such as a frame shape, an annular shape, or a coil shape that allows current to circulate in the conductor.

[0061] The conductors 91 and 92 are, for example, as shown in Figure 3, the short-circuit current I of the charge storage element 74 flowing through the main circuit conductor portion.dc The magnetic flux generated by dc is arranged to pass through the space inside the conductors 91 and 92. Thereby, for example, the magnetic coupling between the conductors 91 and 92 and the main circuit conductor portion is strengthened, and the short-circuit current I flowing through the main circuit conductor portion dc can be easily reduced.

[0062] In FIG. 3, each converter CEL has two conductors 91 and 92 arranged so as 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 is the short-circuit current I flowing through the main circuit conductor portion at the time of a short-circuit failure of each switching element 41 and 42 dc may be any number that can appropriately reduce it.

[0063] FIGS. 5(a) and 5(b) are graphs schematically showing an example of the characteristics of the conductors. FIG. 5(a) schematically shows 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 flowing through the main circuit conductor portion dc . FIG. 5(b) schematically shows an example of the relationship between the frequency of the induced current I flowing through the conductors 91 and 92 and the resistance values of the conductors 91 and 92. angle

[0064] As shown in FIG. 5(a), the resistance values of the conductors 91 and 92 include the short-circuit current I flowing through the main circuit conductor portion at the time of a short-circuit failure dcThere exists an optimal resistance value (impedance matching condition) at which the current squared time product is minimized. The resistance values of conductors 91 and 92 are designed to be the above-mentioned optimal resistance value. The resistance values of conductors 91 and 92 are set to be the above-mentioned optimal resistance value. More specifically, the resistance values of conductors 91 and 92 are resistance values obtained from the cross-sectional areas of conductors 91 and 92, the lengths (perimeter lengths) of conductors 91 and 92, and the resistivity of conductors 91 and 92. The optimal resistance value can be derived, for example, using simulation and mathematical optimization. Mathematical optimization is a technique and discipline that systematically organizes the trial and error performed by human hands to automatically search for better characteristics based on simulation results by a certain algorithm.

[0065] Also, as shown in Fig. 5(b), the resistance values of conductors 91 and 92 have frequency characteristics due to the skin effect. Therefore, the shapes of conductors 91 and 92 are designed so that the above-mentioned optimal resistance value is obtained at the resonance frequency during a short circuit. In other words, the shapes of conductors 91 and 92 are set to be the above-mentioned optimal resistance value at the frequency of the induced current I angle flowing during a short circuit failure of each switching element 41, 42.

[0066] In this way, by designing the shapes of conductors 91 and 92, it is possible to attenuate the current that vibrates at high frequency at the time of a short circuit failure with conductors 91 and 92. And since the main circuit current is low frequency during normal operation, the influence of the skin effect generated in conductors 91 and 92 is suppressed, conductors 91 and 92 become low resistance, and the influence of conductors 91 and 92 on the main circuit conductor part can be mitigated by deviating from the impedance matching condition. Furthermore, by magnetically coupling with conductors 91 and 92, the inductance of the main circuit conductor part can be reduced, so that the surge voltage can be suppressed. For this reason, the resistance value (for example, gate resistance) of the control terminal of each switching element 41, 42 can be lowered, and an increase in the switching loss of each switching element 41, 42 can be suppressed.

[0067] As described above, in the power conversion device 10 according to the present embodiment, it is possible to suppress an increase in the switching loss of a plurality of converters CEL connected in series and suppress damage to each switching element 41, 42 during a short-circuit fault.

[0068] 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, it is desirable to arrange a loop-shaped conductor so as to be magnetically coupled to the main circuit conductor section even when a short-circuit fault occurs in each switching element that short-circuits the charge storage element 74 in any combination of the four switching elements.

[0069] In the above embodiment, an MMC-type power converter is used for the main circuit section 12. The main circuit section 12 is not limited to the MMC type, and for example, a power converter of another method in which a plurality of converters CEL are connected in series may be used.

[0070] 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 conversion from DC to AC, etc. The AC-DC conversion by the main circuit section 12 is not limited to both AC to DC and DC to AC, and may be only one of AC to DC or DC to AC. Further, the main circuit section 12 may be, for example, an AC-AC direct conversion circuit or the like.

[0071] 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 or the like. 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 power conversion. The power conversion device may be, for example, a frequency conversion device, a DC power transmission device, a reactive power compensation device, or a power flow control device.

[0072] Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0073] 2... AC power system, 3, 4... DC transmission lines, 6... transformer, 10... power conversion device, 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 section, 22b... second arm section, 22c... third arm section, 22d... fourth arm section, 22e... fifth arm section, 22f... sixth arm section, 23a to 23f... buffer reactors, 24a to 24f... current detectors, 25... voltage detection section, 26... signal line, 41, 42... switching elements, 51, 52... rectifying elements, 61, 62... drive circuits, 71, 72... connection terminals, 74... charge storage element, 76... power supply circuit, 78... voltage detection circuit, 80... control circuit, 91, 92... conductors, CEL... converter, LG1... first leg, LG2... second leg, LG3... third leg

Claims

1. A main circuit section having a plurality of converters connected in series, and performing power conversion by the operation of the plurality of converters; A control device for controlling the operation of the main circuit section; and comprising: 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 loop-shaped conductor, and is connected in series via the pair of connection terminals, and can switch between 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, a bypass state in which the pair of connection terminals are made conductive, and a stop state in which the plurality of switching elements are turned off; The loop-shaped conductor is magnetically coupled to a loop-shaped main circuit conductor section formed by the plurality of switching elements, the charge storage element, and wiring members connecting the plurality of switching elements and the charge storage element, and when a short-circuit fault occurs in the plurality of switching elements and the charge storage element is short-circuited, an induced current flows in response to the magnetic flux generated by the short-circuit current of the charge storage element flowing through the main circuit conductor section, thereby reducing the short-circuit current flowing through the main circuit conductor section. A power conversion device.

2. The power conversion device according to claim 1, wherein the resistance value of the loop-shaped conductor is set to an optimum resistance value at which the current square time product of the short-circuit current flowing through the main circuit conductor section is minimized.

3. The power conversion device according to claim 2, wherein the shape of the loop-shaped conductor is set to the optimum resistance value at the frequency of the induced current flowing during a short-circuit fault of the plurality of switching elements.

4. The power conversion device according to any one of claims 1 to 3, wherein the loop-shaped conductor is arranged such that the magnetic flux generated by the short-circuit current flowing through the main circuit conductor portion passes through the space inside the loop-shaped conductor.

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