JP7599802B2 - Power Conversion Equipment - Google Patents

Description

An embodiment of the present invention relates to a power conversion device.

Some power conversion devices are equipped with a protection circuit that detects abnormalities in the converter and protects it. The protection circuit does not operate during normal operation of the converter. For this reason, the protection circuit is inspected for its soundness when the device is stopped. Inspecting the protection circuit often requires work by an inspector, such as circuit treatment and connection of external devices, which can lead to increased inspection time and costs. For this reason, it is desirable to make it easier to inspect the protection circuit in power conversion devices.

Japanese Patent Application Publication No. 5-3680

Embodiments of the present invention provide a power conversion device that makes it easier to inspect the protection circuit.

According to an embodiment of the present invention, a power supply system includes a main circuit section having a plurality of converters connected in series and converting power by operation of the plurality of converters, a control device for controlling the operation of the main circuit section, and a plurality of protection circuits provided in each of the plurality of converters, detecting abnormalities in the plurality of converters and performing a protection operation in response to the detection of the abnormality, thereby protecting the plurality of converters, each of the plurality of converters having a pair of connection terminals, a plurality of switching elements, and a charge storage element connected in parallel to the plurality of switching elements, and connected in series via the pair of connection terminals, and switching the plurality of switching elements to convert a voltage of the charge storage element into a voltage of the pair of connection terminals. a bypass state in which electrical continuity is established between the pair of connection terminals, and a stopped state in which the plurality of switching elements are in an off state, and the control device can confirm the operation of the protection circuit by performing an abnormality simulation operation of the converter, which operates the converter so that the protection circuit detects an abnormality in the converter , and the control device performs the abnormality simulation operation for a predetermined number of the plurality of converters connected in series during normal operation of the main circuit unit that converts power, and confirms the operation of the protection circuit of each of the plurality of converters by sequentially changing the predetermined number of converters that are subjected to the abnormality simulation operation .

A power conversion device is provided that allows for easier inspection of protection circuits.

1 is a block diagram illustrating a power conversion device according to a first embodiment. FIG. 2 is a block diagram illustrating a converter. FIG. 13 is a block diagram illustrating a modified example of the converter. FIG. 11 is a block diagram illustrating a power conversion device according to a second embodiment. FIG. 1 is an explanatory diagram illustrating an example of an abnormality simulation operation.

Each embodiment will be described below with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as in reality. Even when the same part is shown, the dimensions and ratios of each part may be different depending on the drawing.
In this specification and each drawing, elements similar to those described above with reference to the previous drawings are given the same reference numerals and detailed descriptions thereof will be omitted as appropriate.

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

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

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 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. In this way, the power conversion device 10 performs AC-to-DC conversion from AC to DC, and DC-to-AC conversion.

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

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

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

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

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

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

In the main circuit unit 12, the first leg LG1 is formed by the first arm portion 22a and the second arm portion 22b, the second leg LG2 is formed by the third arm portion 22c and the fourth arm portion 22d, and the third leg LG3 is formed by the fifth arm portion 22e and the sixth arm portion 22f. That is, in this example, the main circuit unit 12 is a three-phase inverter with three legs and six arms. 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 unit 12 has a plurality of arms and a plurality of legs formed by a plurality of switching elements. The main circuit unit 12 may be, for example, a single-phase inverter with two legs and four arms. The number of arms and legs is not limited to the above and may be any number.

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

However, in the following, when referring to the converters UP1, UP2... _UPM1 , UN1, UN2... _UNM2 , VP1, VP2... _VPM3 , VN1, VN2... _VNM4 , WP1, WP2... _WPM5 , and WN1, WN2... _WNM6 collectively, they will be referred to as "converter CEL".

In each of the arm sections 22a to 22f, _M1 , _M2 , _M3 , _M4 , _M5 , and _M6 represent the number of converters CEL connected in series. In each of the arm sections 22a to 22f, the number of converters CEL connected in series is, for example, about 100 to 120. However, the number of converters CEL connected in series is not limited to this and may be any number.

The number of converters CEL provided in each arm section 22a to 22f is substantially the same. For example, when multiple converters CEL are connected, the number of converters CEL provided in each arm section 22a to 22f may differ as long as it does not affect the operation of the main circuit section 12. For example, when 100 converters CEL are connected in series to one arm section, the number of converters CEL provided in another arm section may differ by one or two.

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

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

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 or the like (not shown). The current detector 24a inputs the detected current value of the first arm portion 22a to the control device 14. As a result, the current value of the first arm portion 22a is input to the control device 14.

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

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.

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

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, for example, a transformer 6.

Each converter CEL is connected to the control device 14, for example, via a signal line 26. The control device 14 controls the operation of the converter CEL by inputting a control signal to the converter CEL via the signal line 26. The converter CEL also 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. The communication method between the control device 14 and each converter CEL is not limited to the above. For example, multiple converters CEL connected in series may be daisy-chained, and the control device 14 may communicate only with the converter CEL at one end of the daisy-chained converter and the converter CEL at the other end. The communication method between the control device 14 and each converter CEL may be any communication method that can appropriately communicate between the control device 14 and each converter CEL.

FIG. 2 is a block diagram that illustrates a schematic representation of a converter.
As shown in FIG. 2, the converter CEL has a plurality of switching elements 41, 42, a plurality of rectifying elements 51, 52, a plurality of driving circuits 61, 62, a pair of connecting terminals 71, 72, a charge 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. Each switching element 41, 42 is, for example, a self-extinguishing element such as an IGBT. The pair of main terminals is, for example, an emitter and a collector, and the control terminal is, for example, a gate.

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

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

A pair of main terminals of the switching element 42 is 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 this example, the converter CEL is a converter in a half-bridge configuration.

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

The multiple converters CEL in the same arm are connected in series via a pair of connection terminals 71, 72. Power is supplied to the converters CEL via each of the 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.

The control circuit 80 is connected to the control device 14 via signal line 26. The control device 14 transmits a control signal for controlling the on/off of each switching element 41, 42 to the control circuit 80 via signal line 26. The control circuit 80 inputs a drive signal for switching the 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 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, 62 switch the switching elements 41, 42 on and off based on the drive signal input from the control circuit 80. This controls the on and off of each switching element 41, 42 in response to a control signal from the control device 14. The control device 14 generates a control signal for each converter CEL and controls the on and off of each switching element 41, 42 of each converter CEL. This allows the control device 14 to control the conversion of power by the main circuit unit 12.

The configuration of the drive circuits 61, 62 and the control circuit 80 is not limited to the above, and may be any configuration that can control the on/off of each switching element 41, 42. For example, a control signal from the control device 14 may be input directly to the drive circuits 61, 62. In this case, the control circuit 80 can be omitted.

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.

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 is substantially zero.

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

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

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

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

The method of supplying power to the drive circuits 61, 62 and the control circuit 80 is not limited to the above. For example, power may be supplied to the drive circuits 61, 62 and the control circuit 80 from a power source separate from the charge storage element 74. The method of supplying power 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.

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.

The converter CEL has a substrate 90 for operating the multiple switching elements 41, 42. For example, the drive circuits 61, 62, the power supply circuit 76, the voltage detection circuit 78, and the control circuit 80 are mounted on the substrate 90. However, the configuration of the substrate 90 is not limited to this. For example, the power supply circuit 76 and the voltage detection circuit 78 do not necessarily have to be mounted on the substrate 90. The substrate 90 may have any configuration capable of operating the multiple switching elements 41, 42.

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 becomes equal to or higher than an upper limit value. The protection circuit 82 switches the converter CEL to a bypass state when the DC voltage of the charge storage element 74 becomes equal to or higher than an upper limit value.

For example, when an abnormality in the control circuit 80 causes the switching elements 41 and 42 to switch at an unexpected timing, the voltage of the charge storage element 74 may rise. Such an increase in the voltage of the charge storage element 74 may cause failures in various parts of the converter CEL, such as the switching elements 41 and 42 and the charge storage element 74.

For this reason, the protection circuit 82 switches the converter CEL to a bypass state when the DC voltage of the charge storage element 74 becomes equal to or higher than the upper limit value based on the voltage detection value from the voltage detection circuit 78. This makes it possible to suppress failure of the converter CEL due to an increase in the voltage of the charge storage element 74, and also makes it possible to continue operation of the power conversion device 10 with the remaining converters CEL in the same arm section while bypassing the converter CEL in which an abnormality has occurred.

The configuration of the protection circuit 82 is not limited to the above. For example, the protection circuit 82 does not necessarily need to be provided within the control circuit 80, and may be provided separately from the control circuit 80. For example, the 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.

As described above, the protection circuit 82 operates only when some abnormality occurs in the converter CEL. In this example, the protection circuit 82 detects an abnormality in the converter CEL and performs a protective operation only when the DC voltage of the charge storage element 74 exceeds the upper limit value.

The control device 14 then intentionally operates the converter CEL to operate the converter CEL so that the protection circuit 82 detects the abnormality of the converter CEL, thereby causing the protection circuit 82 to detect the abnormality of the converter CEL and perform a protection operation. In this way, the control device 14 checks the operation of the protection circuit 82.

Operation of the converter CEL such that the protection circuit 82 detects an abnormality in the converter CEL is, in other words, operation that simulates an abnormality in the converter CEL. Hereinafter, operation of the converter CEL such that the protection circuit 82 detects an abnormality in the converter CEL is referred to as abnormality simulation operation.

After starting the abnormality simulation operation, when the protection circuit 82 properly detects an abnormality in the converter CEL and performs a protective operation, the control device 14 determines that the protection circuit 82 is normal. Then, when the protection circuit 82 does not perform a protective operation even after starting the abnormality simulation operation, the control device 14 determines that the protection circuit 82 is abnormal.

The control device 14 judges the protection circuit 82 to be abnormal, for example, if the protection circuit 82 does not perform a protective operation even when a predetermined condition is satisfied after the start of the abnormality simulation operation. The predetermined condition is, for example, the DC voltage of the charge storage element 74. The control device 14 judges the protection circuit 82 to be abnormal, for example, if the protection circuit 82 does not perform a protective operation even when the DC voltage of the charge storage element 74 becomes equal to or exceeds a threshold value set higher than the upper limit value after the start of the abnormality simulation operation.

The predetermined condition may be, for example, the time elapsed from the start of the abnormality simulation operation. For example, the control device 14 may determine that the protection circuit 82 is abnormal if, after the abnormality simulation operation is started, the protection circuit 82 has not performed a protective operation even when a predetermined time has elapsed from the start of the abnormality simulation operation. The predetermined condition is not limited to the above, and may be any condition that can appropriately determine whether the protection circuit 82 is abnormal.

In addition, whether or not the protection circuit 82 has performed a protection operation may be determined based on a signal input from the converter CEL to the control device 14. The signal input from the converter CEL to the control device 14 includes, for example, information representing the voltage of the control terminals of each switching element 41, 42. In other words, the signal input from the converter CEL to the control device 14 includes information representing the on and off states of each switching element 41, 42. The control device 14 determines whether or not the protection circuit 82 has performed a protection operation by determining the state of each switching element 41, 42 based on, for example, the signal input from the converter CEL. However, the method of determining whether or not the protection circuit 82 has performed a protection operation is not limited to this. For example, the signal input from the converter CEL to the control device 14 includes information representing the presence or absence of the operation of the protection circuit 82, and the control device 14 may determine whether or not the protection circuit 82 has performed a protection operation based on the information representing the presence or absence of the operation of the protection circuit 82. The method for determining whether the protection circuit 82 has performed a protection operation may be any method that allows the control device 14 to appropriately determine whether the protection circuit 82 has performed a protection operation based on the signal input from the converter CEL to the control device 14.

The control device 14 performs an abnormality simulation operation, for example, by stopping the converter CEL. When the converter CEL is stopped, as described above, the charge storage element 74 is charged by the arm current, and the voltage of the charge storage element 74 rises. This simulates an abnormality in the converter CEL, and by causing the DC voltage of the charge storage element 74 to exceed an upper limit value, the protection circuit 82 can be made to detect an abnormality in the converter CEL and perform a protection operation.

As mentioned above, in the MMC type main circuit unit 12, even if a certain number of the multiple converters CEL connected in series to each arm unit 22a to 22f are stopped, the main circuit unit 12 can continue normal operation with the remaining converters CEL. Therefore, in the MMC type main circuit unit 12, during normal operation in which power is converted by the operation of the multiple converters CEL, the above-mentioned abnormality simulation operation can be performed for a certain number of the multiple converters CEL.

During normal operation of the main circuit section 12 that converts power, the control device 14 performs an abnormality simulation operation for a predetermined number of converters CEL among the multiple converters CEL connected in series to each arm section 22a to 22f, and checks the operation of the protection circuit 82 of each of the multiple converters CEL by sequentially changing the predetermined number of converters CEL that perform the abnormality simulation operation.

The control device 14 performs, for example, an abnormality simulation operation on the first and second converters CEL of the multiple converters CEL connected in series to each arm section 22a to 22f, and after checking the operation of the protection circuit 82 of the first and second converters CEL, checks the operation of the protection circuit 82 of the third and fourth converters CEL of the multiple converters CEL. The control device 14 then repeats the same process up to the last converter CEL of the multiple converters CEL to check the operation of the protection circuit 82 of each of the multiple converters CEL. Note that the number of the predetermined number of converters CEL is not limited to two, and may be one, or three or more. The number of the predetermined number of converters CEL may be set to any number that allows the remaining converters CEL to continue normal operation of the main circuit section 12 appropriately.

When the control device 14 detects an abnormality in the protection circuit 82 through the abnormality simulation operation, it notifies, for example, the protection circuit 82 (converter CEL) that has detected the abnormality. This makes it possible to notify, for example, the administrator of the power conversion device 10 of the abnormality in the protection circuit 82. For example, it is possible to prompt the administrator of the power conversion device 10 to replace the protection circuit 82.

The control device 14, for example, has a display unit (not shown), and notifies the protection circuit 82 that has detected an abnormality by displaying information about the protection circuit 82 that has detected an abnormality on the display unit. For example, the protection circuit 82 that has detected an abnormality may be notified by transmitting information about the protection circuit 82 that has detected an abnormality to a mobile terminal of an administrator or the like, and displaying the information on the display unit of the mobile terminal. In this way, the protection circuit 82 that has detected an abnormality may be notified by outputting information to an external terminal or the like. The mode of notifying the protection circuit 82 that has detected an abnormality may be any mode that can appropriately notify the administrator of the power conversion device 10 of the abnormality in the protection circuit 82.

As described above, in the power conversion device 10 according to this embodiment, the control device 14 checks the operation of the protection circuit 82 by performing an abnormality simulation operation. As a result, in the power conversion device 10 according to this embodiment, for example, an inspector can save the trouble of inspecting the protection circuit 82 by performing treatment on the protection circuit 82 or connecting an external device to the protection circuit 82 when the power conversion device 10 is stopped. Therefore, in the power conversion device 10 according to this embodiment, the protection circuit 82 can be inspected more easily. For example, an increase in the time required to inspect the protection circuit 82 and an increase in costs associated with the inspection can be suppressed.

In addition, in the power conversion device 10 according to this embodiment, during normal operation of the main circuit section 12 that converts power, the control device 14 performs an abnormality simulation operation for a predetermined number of the multiple converters CEL connected in series to each arm section 22a to 22f. This makes it possible to perform an abnormality simulation operation more efficiently for the multiple converters CEL, and further reduce the effort required for inspecting the protection circuit 82.

However, in an MMC-type main circuit unit 12, the abnormality simulation operation does not necessarily have to be performed during normal operation of the main circuit unit 12. The abnormality simulation operation may be performed simultaneously for multiple converters CEL, for example, when normal operation of the main circuit unit 12 is stopped.

FIG. 3 is a block diagram showing a schematic diagram of a modified example of the converter.
3, the converter CELa of this example includes switching elements 41 and 42, and further includes switching elements 43 and 44. For the switching elements 43 and 44, substantially the same elements as the switching elements 41 and 42 are used.

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

The converter CELa further includes rectifying elements 53 and 54, and drive circuits 63 and 64. The rectifying element 53 is connected in anti-parallel to the switching element 43. The rectifying element 54 is connected in anti-parallel to the switching element 44. In the converter CELa, the control circuit 80 inputs drive signals to the drive circuits 61 to 64 for switching the switching elements 41 to 44 on and off based on a control signal input from the control device 14. The drive circuit 63 switches the switching element 43 between the on state and the off state based on the drive signal input from the control circuit 80. The drive circuit 64 switches the switching element 44 between the on state and the off state based on the drive signal input from the control circuit 80. The drive circuits 63 and 64 are mounted on, for example, a substrate 90.

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

In converter CELa, when the voltage of charge storage element 74 is set to Vc, switching elements 41 and 44 are turned on and switching elements 42 and 43 are turned off, causing a voltage of -Vc to appear between connection terminals 71 and 72.

In addition, by turning on switching element 42 and switching element 43 and turning off switching element 41 and switching element 44, a voltage of +Vc appears between each connection terminal 71, 72.

Furthermore, the low-side switching elements 41 and 43 are turned on, and the high-side switching elements 42 and 44 are turned off. Alternatively, the high-side switching elements 42 and 44 are turned on, and the low-side switching elements 41 and 43 are turned off. This provides electrical continuity between the connection terminals 71 and 72, and substantially 0 V appears between the connection terminals 71 and 72.

In this way, the converter CELa can output three voltage levels, +Vc, 0, and -Vc, between the connection terminals 71 and 72. By switching the multiple switching elements 41 to 44, the converter CELa can switch between a first output state in which a voltage of +Vc is output between the connection terminals 71 and 72, a second output state in which a voltage of -Vc is output between the connection terminals 71 and 72, a bypass state in which the connection terminals 71 and 72 are conductive, and a stop state in which the switching elements 41 to 44 are turned off.

The protection circuit 82 switches the converter CELa to a bypass state, for example, when the DC voltage of the charge storage element 74 exceeds an upper limit value.

In converter CELa of the full-bridge circuit, when all switching elements 41 to 44 are in the off state (converter CELa is in the stopped state), the charge storage element 74 is charged by the arm current. For example, when the arm current flows from connection terminal 71 to connection terminal 72, rectifier elements 52 and 53 are turned on and charge storage element 74 is charged. Conversely, when the arm current flows from connection terminal 72 to connection terminal 71, rectifier elements 51 and 54 are turned on and charge storage element 74 is charged.

As a result, in the case of the converter CELa of the full-bridge circuit, as in the above embodiment, it is possible to perform an abnormality simulation operation by stopping the converter CELa. In this way, in the MMC type main circuit unit 12, the converter may be configured as a half-bridge circuit or a full-bridge circuit.

In the above embodiment, an MMC type power converter is used for the main circuit unit 12. The main circuit unit 12 is not limited to the MMC type, and may be, for example, another type of power converter in which multiple converters CEL (converters CELa) are connected in series.

The power conversion device 10 is not limited to DC transmission systems, but may also 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 unit 12 is not limited to both AC to DC and DC to AC, but may be only AC to DC or DC to AC. The main circuit unit 12 may also be, for example, an AC-AC direct conversion circuit.

The main circuit unit 12 may be configured, for example, with multiple arm units in a star connection, delta connection, or matrix connection. The main circuit unit 12 may be, for example, a modular matrix converter. The main circuit unit 12 does not necessarily have to have multiple legs. The main circuit unit only needs to have at least multiple arm units. The main circuit unit may be configured in any manner that allows power conversion. The power conversion device may be, for example, a frequency conversion device, a DC transmission device, a reactive power compensation device, or a power flow control device. In these power conversion devices, the operation of the protection circuits provided in each converter can also be confirmed by performing an abnormality simulation operation as described above.

In the above embodiment, in the main circuit section 12 in which multiple converters are connected in series, the protection circuit 82 detects an overvoltage of the DC voltage of the charge storage element 74 as a converter abnormality. The control device 14 then performs an operation to increase the voltage of the charge storage element 74 as an abnormality simulation operation. However, in the main circuit section 12 in which multiple converters are connected in series, the converter abnormality detected by the protection circuit 82 is not limited to an overvoltage of the charge storage element 74.

The protection circuit 82 may detect, for example, a drop in the voltage of the charge storage element 74 as an abnormality in the converter. In this case, the control device 14 can perform an abnormality simulation operation by, for example, putting the converter into a bypass state and discharging the charge storage element 74.

The protection circuit 82 may detect, for example, an overcurrent flowing through each arm 22a to 22f as an abnormality. In other words, the protection circuit 82 may detect, for example, an overcurrent flowing through a plurality of converters CEL connected in series as an abnormality. The protection circuit 82 detects an overcurrent of a current flowing through each arm 22a to 22f based on the detection results of the current detectors 24a to 24f, and performs a protective operation in response to the detection of the overcurrent. The protection circuit 82 performs, for example, stopping the operation of the converter CEL (gate blocking) as a protective operation. In this case, the control device 14 checks the operation of the protection circuit 82 by, for example, changing the control command value and performing an operation in which an overcurrent is simulated to flow through each arm 22a to 22f as an abnormality simulation operation. The simulated overcurrent is, for example, a current that the protection circuit 82 detects an overcurrent and does not exceed the rated current of the switching element. It is preferable that the simulated overcurrent is, for example, a current that circulates through each arm section 22a to 22f and does not affect the AC power system 2 or the DC transmission lines 3 and 4. In this case, it is preferable that the abnormality simulation operation is performed collectively for multiple converters CEL for each arm section 22a to 22f, for example, at the timing when the normal operation of the main circuit section 12 is stopped.

In this way, when an overcurrent flowing through each of the arm sections 22a to 22f is detected as an abnormality, the protection circuit may be configured to be provided in the control device 14. The protection circuit provided in the control device 14 may be configured to detect an overcurrent in the current flowing through each of the arm sections 22a to 22f, and perform a protection operation by stopping the operation of the converter CEL in response to the detection of the overcurrent.

The protection circuit 82 may detect, for example, an abnormality in the substrate 90 of the converter. In other words, the protection circuit 82 may detect, for example, an abnormality in peripheral devices such as the drive circuits 61 and 62, the power supply circuit 76, the voltage detection circuit 78, and the control circuit 80. In this case, the control device 14 checks the operation of the protection circuit 82 by, for example, performing an abnormality simulation operation in which a signal that causes the protection circuit 82 to detect an abnormality in the substrate 90 is intentionally input to the protection circuit 82 from the control circuit 80 or another circuit.

In this way, in the main circuit section 12 in which multiple converters are connected in series, the converter abnormality detected by the protection circuit 82 is not limited to an overvoltage of the charge storage element 74, but may be any converter abnormality. The abnormality simulation operation performed by the control device 14 may be any operation that can intentionally cause the protection circuit 82 to detect an abnormality. The abnormality simulation operation may be set appropriately according to the configuration of the protection circuit 82.

Second Embodiment
FIG. 4 is a block diagram illustrating a power conversion device according to the second embodiment.
As shown in FIG. 4, the power conversion device 100 includes a main circuit unit 102 and a control device 104. In the power conversion device 100, the main circuit unit 102 includes one converter CELb. The converter CELb includes six switching elements 111 to 116 connected in a three-phase bridge configuration, six rectifier elements 121 to 126 connected in anti-parallel to each of the six switching elements 111 to 116, a charge storage element 130 connected in parallel to each of the six switching elements 111 to 116, and drive circuits 131 to 136 that switch the switching elements 111 to 116 on and off. The converter CELb also includes a substrate 138 for operating the multiple switching elements 111 to 116. For example, the drive circuits 131 to 136 are mounted on the substrate 138. However, the configuration of the substrate 138 is not limited to this, and any configuration capable of operating the multiple switching elements 111 to 116 may be used.

In converter CELb, both ends of each switching element 111 to 116 form a pair of DC terminals 106a, 106b, and the connection point between switching element 111 and switching element 112, the connection point between switching element 113 and switching element 114, and the connection point between switching element 115 and switching element 116 form three AC terminals 108a to 108c, respectively. Converter CELb is a so-called three-phase two-level inverter.

The converter CELb is connected to the AC power system via the AC terminals 108a to 108c. The AC terminals 108a to 108c are connected to the AC power system via, for example, a circuit breaker or a transformer (not shown). The converter CELb is also connected to a DC power source or a DC load via a pair of DC terminals 106a, 106b. As a result, the main circuit unit 102 converts power by the operation of the converter CELb. The main circuit unit 102 converts DC to AC and/or AC to DC by, for example, switching the switching elements 111 to 116 of the converter CELb.

The control device 104 is connected to the main circuit section 102. The control device 104 transmits control signals to, for example, the drive circuits 131-136. The drive circuits 131-136 switch the switching elements 111-116 on and off based on the control signals input from the control device 104. The control device 104 transmits control signals to the drive circuits 131-136 and controls the on and off of the switching elements 111-116, thereby controlling the power conversion by the main circuit section 102.

The main circuit unit 102 further includes, for example, current detectors 141-143. The current detectors 141-143 detect the current flowing through the AC terminals 108a-108c of the converter CELb. The current detectors 141-143 are electrically connected to the control device 104. The current detectors 141-143 input the detection results of the current flowing through the AC terminals 108a-108c to the control device 104.

The power conversion device 100 further includes a protection circuit 150. The protection circuit 150 is provided in, for example, the control device 104. The protection circuit 150 performs a protection operation when the current flowing through the converter CELb reaches or exceeds an upper limit based on the detection results of the current detectors 141-143. For example, when the current flowing through the converter CELb reaches or exceeds an upper limit, the protection circuit 150 stops the operation of the converter CELb by turning off each of the switching elements 111-116. In this way, the protection circuit 150 detects an overcurrent in the converter CELb as an abnormality in the converter CELb and performs a protection operation.

The configuration of the protection circuit 150 is not limited to the above. The protection circuit 150 does not necessarily need to be provided within the control device 104, and may be provided separately from the control device 104. The protection circuit 150 may be provided in the converter CELb, for example. For example, multiple protection circuits 150 may be provided corresponding to the multiple switching elements 111 to 116, respectively.

The control device 104 intentionally performs an abnormality simulation operation of the converter CELb such that the protection circuit 150 detects an abnormality in the converter CELb, thereby causing the protection circuit 150 to detect an abnormality in the converter CELb and perform a protection operation. In this way, the control device 104 checks the operation of the protection circuit 150.

FIG. 5 is an explanatory diagram illustrating an example of an abnormality simulation operation.
5, the control device 104 performs an abnormality simulation operation, for example, with the circuit breaker open and the converter CELb disconnected from the AC power system. The control device 104 performs an abnormality simulation operation, for example, at the timing when the power conversion device 100 stops operating and the circuit breaker is opened. In other words, the control device 104 performs an abnormality simulation operation when the normal operation of the main circuit unit 102 that converts power is stopped and the circuit breaker is opened.

When the circuit breaker is opened and converter CELb is disconnected from the AC power system, the load on the AC side of converter CELb can generally be considered to be an inductive load. After opening the circuit breaker and disconnecting converter CELb from the AC power system, the control device 104 performs an abnormality simulation operation by switching the switching elements 111 to 116 between the on and off states so as to pass a load current to the load on the AC side, as shown in FIG. 5, for example.

More specifically, the control device 104 turns on one of the high-side switching elements 111, 113, and 115 and turns off the remaining, and turns on one of the low-side switching elements 112, 114, and 116 and turns off the remaining. In addition, the control device 104 sets the high-side switching element and the low-side switching element to be turned on to different phases so as not to cause a DC short circuit. This allows the control device 104 to pass a load current to the AC load as shown in FIG. 5. Note that in FIG. 5, only a part of the converter CELb is simplified for ease of illustration. In addition, in FIG. 5, the switching elements 111 to 116 are illustrated with different symbols from those in FIG. 4 to make the on and off states of the switching elements 111 to 116 easier to understand.

As described above, when a load current is passed through the load on the AC side, the load current increases according to the voltage of the charge storage element 130 and the inductance of the inductive load on the AC side. This allows an abnormality in the converter CELb to be simulated, and the current flowing through the converter CELb to exceed the upper limit, causing the protection circuit 150 to detect an abnormality in the converter CELb and perform a protection operation. At this time, by performing the abnormality simulation operation with the circuit breaker open and the converter CELb disconnected from the AC power system, it is possible to prevent the abnormality simulation operation from affecting the AC power system even when a load current that would cause the protection circuit 150 to detect an abnormality is passed.

The control device 104 judges the protection circuit 150 to be abnormal, for example, if the protection circuit 150 does not perform a protective operation even when a predetermined condition is satisfied after the start of the abnormality simulation operation. The predetermined condition is, for example, the current flowing through the converter CELb. The control device 104 judges the protection circuit 150 to be abnormal, for example, if the protection circuit 150 does not perform a protective operation even when the current flowing through the converter CELb becomes equal to or exceeds a threshold value set higher than the upper limit value after the start of the abnormality simulation operation. However, the predetermined condition is not limited to the above, and may be any condition that can appropriately determine an abnormality in the protection circuit 150.

For example, if the control device 104 detects an abnormality in the protection circuit 150 through an abnormality simulation operation, it notifies the user of the protection circuit 150 that has detected the abnormality, as in the first embodiment described above.

In this way, even in the power conversion device 100 according to this embodiment, the control device 104 can check the operation of the protection circuit 150 by performing an abnormality simulation operation. This makes it easier to inspect the protection circuit 150 in the power conversion device 100 as in the first embodiment.

In this way, the configuration of the main circuit unit 102 is not limited to a configuration in which multiple converters CEL are connected in series, but may be a three-phase two-level inverter, etc. Even with the main circuit unit 102 configured in this way, the operation of the protection circuit 150 can be confirmed by performing an abnormality simulation operation as described above.

The configuration of the main circuit unit 102 is not limited to a three-phase two-level inverter, but may be a single-phase two-level inverter, a single-phase three-level inverter, a three-phase three-level inverter, etc. In these configurations, similar to the above, an abnormality simulation operation can be performed by opening the circuit breaker and disconnecting the converter CELb from the AC power system, and then switching the on and off states of multiple switching elements so that a load current flows through the load on the AC side.

The configuration of the main circuit section is not limited to the configurations shown in the above embodiments, but may be any configuration that has a converter and converts power by the operation of the converter.

In the example shown in FIG. 4, the protection circuit 150 detects an overcurrent in the converter CELb as an abnormality in the converter CELb and performs a protection operation. The protection circuit 150 is not limited to this, and may be configured to detect, for example, an overvoltage in the converter CELb as an abnormality in the converter CELb and perform a protection operation.

In the example shown in FIG. 4, an abnormality in the converter CELb is detected by one protection circuit 150. This is not limited to the above, and for example, by providing multiple protection circuits corresponding to each of the multiple switching elements 111 to 116, the overcurrent or overvoltage of each of the multiple switching elements 111 to 116 may be detected as an abnormality in the converter CEL.

The protection circuit 150 may also be configured to detect overvoltage of the charge storage element 130, for example, in a two-level inverter or a three-level inverter. In this case, the protection circuit 150 performs, for example, switching all of the multiple switching elements to the off state as a protection operation. In other words, the protection circuit 150 performs, for example, switching the converter CELb to a stopped state as a protection operation. In addition, when detecting overvoltage of the charge storage element 130, the protection operation may be, for example, an operation of turning on a brake circuit that inserts a resistor in the DC section to discharge the charge storage element 130.

In this case, the control device 104 changes the control command values of the switching elements 111 to 116, for example, so that the voltage of the charge storage element 130 increases. In this way, the control device 104 checks the operation of the protection circuit 150, for example, by operating the converter CELb, which increases the voltage of the charge storage element 130, as an abnormality simulation operation.

The protection circuit 150 may detect, for example, an abnormality in the board 138 of the converter CELb. In other words, the protection circuit 150 may detect, for example, an abnormality in a peripheral device such as the drive circuits 131 to 136. In this case, the control device 104 checks the operation of the protection circuit 150 by, for example, intentionally inputting a signal to the protection circuit 150 to detect an abnormality in the board 138 as an abnormality simulation operation.

In this way, the configuration of the protection circuit is not limited to the above, but may be any configuration that can protect the converter by detecting an abnormality in the converter and performing a protective operation according to the detected abnormality.

The abnormality simulation operation by the control device is not limited to the above, and may be any operation that can intentionally cause the protection circuit to detect an abnormality in the converter. The abnormality simulation operation may be set appropriately depending on the configuration of the converter and the configuration of the protection circuit, etc.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications 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 included in the scope of the invention and its equivalents described in the claims.

2...AC power system, 3, 4...DC transmission line, 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 reactor, 24a to 24f...Current detector, 25...Voltage detection section, 26...Signal line, 41 to 44...Switching elements, 51 to 54...Rectifier elements, 61 to 64...Drive circuit, 71, 72...Connection terminals, 74...Charge storage element, 76...Power supply circuit, 78...Voltage detection circuit, 80...Control circuit, 82...Protection circuit, 90...Substrate, 100...Power conversion device, 102...Main circuit section, 104...Control device, 111-116...Switching elements, 121-126...Rectifier elements, 130...Charge storage element, 131-136...Drive circuit, 138...Substrate, 141-143...Current detector, 150...Protection circuit, CEL, CELa, CELb...Converter, LG1...First leg, LG2...Second leg, LG3...Third leg

Claims (4)

A main circuit unit includes a plurality of converters connected in series , and converts power by the operation of the plurality of converters;
A control device for controlling the operation of the main circuit unit;
a plurality of protection circuits provided in the plurality of converters, respectively, for detecting an abnormality in the plurality of converters and for performing a protection operation in response to the detection of the abnormality, thereby protecting the plurality of converters;
Equipped with
Each of the plurality of converters comprises:
A pair of connection terminals;
A plurality of switching elements;
a charge storage element connected in parallel to the plurality of switching elements;
and the charge storage element is connected in series via the pair of connection terminals, and is capable of switching between an output state in which a voltage of the charge storage element is output between the pair of connection terminals, a bypass state in which the pair of connection terminals are electrically connected, and a stop state in which the plurality of switching elements are in an off state by switching the plurality of switching elements;
The control device can confirm the operation of the protection circuit by performing an abnormality simulation operation of the converter, which operates the converter so that the protection circuit detects the abnormality of the converter,
The control device is a power conversion device that performs the abnormality simulation operation for a predetermined number of the converters among the plurality of converters connected in series during normal operation of the main circuit unit that converts power, and checks the operation of the protection circuit of each of the plurality of converters by sequentially changing the predetermined number of the converters for which the abnormality simulation operation is performed . the protection circuit performs the protection operation by switching the converter to the bypass state when the DC voltage of the charge storage element becomes equal to or higher than an upper limit value;
The power conversion device according to claim 1 , wherein the control device checks the operation of the protection circuit by performing an operation of the converter in which the voltage of the charge storage element increases as the abnormality simulation operation. The protection circuit detects an overcurrent flowing through the plurality of converters connected in series as an abnormality,
2. The power conversion device according to claim 1 , wherein the control device checks the operation of the protection circuit by performing, as the abnormality simulation operation, an operation in which an overcurrent is simulatively caused to flow through a plurality of the converters connected in series. Each of the plurality of converters has a substrate for operating the plurality of switching elements;
The protection circuit detects an abnormality in the board,
The power conversion device according to claim 1 , wherein the control device checks the operation of the protection circuit by performing the abnormality simulation operation in which a signal for detecting an abnormality in the board is intentionally input to the protection circuit.

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