JP6131197B2 - Power converter and failure detection method for power converter - Google Patents

Description

  The present invention relates to a power conversion device that converts AC power into DC power or vice versa, and a failure detection method for the power conversion device.

In recent years, power converters that convert alternating current to direct current or direct current to alternating current have been used. These power conversion devices often use switching elements that can be controlled on and off, such as IGBTs (Insulated Gate Bipolar Transistors). Further, in order to handle a high voltage, an MMC (modular multilevel converter) circuit system including an arm in which one or a plurality of unit converters are connected in series is often employed.
In the MMC circuit type power converter, in order to continue the operation even when any unit converter fails, it must be possible to energize the failed unit converter without any trouble. That is, the unit converter needs to maintain a short circuit state between the terminals in the failure state. The invention described in Patent Document 1 is a unit converter using a module type IGBT, and realizes a short circuit between terminals in a failure state.

  The problem of Patent Document 1 is described as “allowing reliable bridging of a failed submodule at the same time as low cost”, and the solution means “power semiconductor circuit (T1, T2, D1, D2) and a series circuit of submodules (7) having an energy storage (8) in a parallel circuit of power semiconductor circuits (T1, T2, D1, D2), and each submodule (7) has a submodule. It relates to the device (1) to which the short-circuit device for short-circuit of (7) is attached.According to the present invention, the short-circuit device is the vacuum switch tube (100). "

JP 2010-524426 A

However, the technique described in Patent Document 1 requires a short-circuit device for short-circuiting the unit converter that is a submodule.
On the other hand, in a power thyristor or the like, a technology has been established that allows the operation to be continued without using a short-circuit device by using a semiconductor device having a press-contact structure that is short-circuited when a failure occurs.

Even in the MMC circuit type power converter, it is conceivable to employ a pressure contact IGBT for the unit converter. As a result, like the power thyristor, the IGBT having the pressure contact structure is short-circuited when the semiconductor device fails, and thus the terminals of the unit converter are short-circuited. Since power is supplied if the terminals of the failed unit converter are short-circuited, the power converter can continue to operate.
However, each unit converter of the MMC circuit system is also connected with an energy storage such as a capacitor in parallel with the power semiconductor circuit. For this reason, there is a problem that in the case of a short circuit failure of the unit converter, it cannot be determined from the outside whether the failure part is a semiconductor device or an energy storage.
When the energy store has a short circuit failure, a large current flows through the failed energy store. Therefore, current must be bypassed immediately to prevent the current from flowing through the energy accumulator, or the entire power converter must be stopped.

  Therefore, the present invention uses a semiconductor element that is in a short-circuit state at the time of a failure, and determines and treats a device short-circuit and a short-circuit of the energy storage without providing a short-circuit device in the unit converter. It is an object of the present invention to provide a device failure detection method.

  The power conversion device of the present invention includes a series circuit in which a plurality of switching elements that are short-circuited in the event of a failure are connected in series, and a plurality of energy accumulators that are connected in parallel to the series circuit. And a plurality of unit converters that output a voltage depending on the voltage of the energy accumulator or a zero voltage, and a plurality of arms in which the unit converters are connected in series. Furthermore, a current sensor that detects a current flowing between the switching element and the energy storage, a voltage sensor that detects a voltage of the energy storage, a current detection value by the current sensor, and a voltage detection by the voltage sensor A failure determination treatment unit that determines and treats the failure point of the unit converter from the value as to which of the switching element and the energy storage unit.

The failure detection method of the present invention is executed by the failure determination processing unit of the power converter. The failure determination treatment unit detects a current detection value by a current sensor that detects a current flowing between the switching element and the energy storage, and voltage detection by a voltage sensor that detects a voltage across the energy storage. A step of detecting a value, and a step of determining, based on a current detection value of the current sensor and a voltage detection value of the voltage sensor, whether the fault location of the unit converter is the switching element or the energy storage And execute.
Other means will be described in the embodiment for carrying out the invention.

  According to the present invention, a power conversion device and a power conversion which use a semiconductor element that is in a short-circuit state at the time of failure and determine and treat a device short-circuit and a short-circuit of an energy storage without providing a short-circuit device in a unit converter. An apparatus failure detection method can be provided.

It is a circuit diagram which shows the power converter device in 1st Embodiment. It is a circuit diagram which shows each unit converter in 1st Embodiment. It is explanatory drawing of the switching element short circuit detection operation | movement of each unit converter in 1st Embodiment. It is explanatory drawing of the capacitor | condenser short circuit detection operation | movement of each unit converter in 1st Embodiment. It is a flowchart which shows the short circuit determination treatment process in 1st Embodiment. It is a circuit diagram which shows each unit converter in 2nd Embodiment. It is a flowchart which shows the short circuit determination treatment process in 2nd Embodiment. It is a circuit diagram which shows each unit converter in 3rd Embodiment. It is a flowchart which shows the short circuit determination treatment process in 3rd Embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
(First embodiment)
In the first embodiment, when a unit converter having a bidirectional chopper circuit fails, it is determined whether the cause of the failure is a capacitor or a semiconductor element. Hereinafter, the configuration of the power conversion device according to the first embodiment will be described with reference to FIGS. 1 and 2. Operation | movement of the power converter device of 1st Embodiment is demonstrated using FIGS. 3-5.

FIG. 1 is a circuit diagram illustrating a power conversion device 103a according to the first embodiment.
As shown in FIG. 1, the power conversion device 103 a is connected to the three-phase power system 101 a via the transformer 102 a to exchange AC power.
The power conversion device 103b is connected between the DC terminals P and N of the power conversion device 103a. The power converters 103a and 103b exchange DC power flowing through the DC terminals P and N.
The power converter 103b is connected to the three-phase power system 101b via the transformer 102b to exchange AC power. The AC frequency of the three-phase power system 101b of the first embodiment is different from the AC frequency of the three-phase power system 101a. The power conversion devices 103a and 103b exchange power between, for example, two power systems having different AC frequencies. The power converters 103a and 103b are not limited to this, and may exchange power between two power systems having the same AC frequency, and are not limited.
The power conversion device 103b and the transformer 102b have the same configuration and function as the power conversion device 103a and the transformer 102a. Therefore, hereinafter, the configuration and function of the power conversion device 103a will be described, and the description of the configuration and function of the power conversion device 103b will be omitted.

The three-phase power system 101a is connected to the R-phase, S-phase, and T-phase on the primary side of the transformer 102a and applies phase voltages VR, VS, and VT, respectively.
The U-phase, V-phase, and W-phase on the secondary side of the transformer 102a are connected to the U-point, V-point, and W-point, which are AC phases of the power converter 103a. For example, the neutral point of the secondary side of the transformer 102a is grounded. However, the connection form of the transformer 102a is not limited to this.
A phase current IU flows from the U phase on the secondary side of the transformer 102a toward the U point of the power converter 103a. A phase current IV flows from the V phase on the secondary side of the transformer 102a toward the V point of the power converter 103a. A phase current IW flows from the W phase on the secondary side of the transformer 102a toward the W phase of the power converter 103a.

The power conversion device 103a is an MMC circuit system and includes an arm 104 in which one or a plurality of unit converters 105 are connected in series. The arm 104 of the first embodiment includes N unit converters 105.
One end of the arms 104UH, 104VH, and 104WH of the first embodiment is connected to the DC terminal P. One end of each of the arms 104UL, 104VL, and 104WL is connected to the DC terminal N.
The other end of the arm 104UH is connected to a U point (AC U phase) via a current sensor 109 and a reactor 106. The other end of the arm 104UL is connected to a U point (AC U phase) via a current sensor 109 and a reactor 106.
The other end of arm 104VH is connected to point V (alternating current V phase) via current sensor 109 and reactor 106. The other end of arm 104VL is connected to point V (alternating current V phase) via current sensor 109 and reactor 106.

The other end of the arm 104WH is connected to a W point (AC W phase) via a current sensor 109 and a reactor 106. The other end of the arm 104WL is connected to a W point (AC W phase) via a current sensor 109 and a reactor 106. Thereby, the serial connection of each arm 104 and the reactor 106 is connected to each phase of the secondary side of the transformer 102a. Each current sensor 109 is, for example, a current transformer. The output side of each current sensor 109 is connected to a central controller 107 described later. As a result, the central controller 107 can detect the phase current flowing through each arm 104.
The present invention is not limited to the arm 104 in the first embodiment. For example, the reactor 106 may not be connected and is not limited.

  Each arm 104 has a plurality of unit converters 105 connected in series. Therefore, when IGBT which comprises the unit converter 105 fails by a short circuit, the power converter device 103a can continue an operation | movement with the remaining unit converters 105. FIG. The element in which the failure mode of the IGBT is short-circuited is, for example, a pressure contact type IGBT. The power converter 103a according to the first embodiment connects more unit converters 105 than necessary so that the operation can be continued when only one unit converter 105 including the press-contact type IGBT is short-circuited. doing.

  Each unit converter 105 includes a bidirectional chopper circuit 2 (see FIG. 2) including capacitors C1 and C2 (see FIG. 2) which are energy storages. Each unit converter 105 is connected to the outside through at least two terminals, and the voltage between these two terminals can be controlled to either the voltage across the capacitors C1 and C2 or the zero voltage.

The central controller 107 controls the entire power conversion device 103a.
The central controller 107 is connected to the chassis, for example, and is connected to the output side of the AC voltage sensor 108 and the output side of each current sensor 109. The central controller 107 further includes two optical transceivers 110 and is connected to each unit converter 105 in a daisy chain via an optical fiber cable 111. The central controller 107 communicates with each unit converter 105 via the optical fiber cable 111 by the optical transceiver 110 and controls the current flowing through each arm 104. However, the connection of the central controller 107 is not limited to the configuration of FIG.

  The AC voltage sensor 108 has an input side connected to each phase of the three-phase power system 101 a and an output side connected to the central controller 107. The AC voltage sensor 108 detects the phase voltages VR, VS, VT of each phase of the three-phase power system 101 a and transmits the instantaneous value signal to the central controller 107.

  Each current sensor 109 detects each arm current IUH, IVH, IWH, IUL, IVL, IWL, and transmits the instantaneous value signal to the central controller 107. The central controller 107 receives the instantaneous value signals of the arm currents IUH, IVH, IWH, IUL, IVL, IWL, controls the unit converter 105 of each arm 104, and flows the arm currents IUH, IVH, IWH, IUL. , IVL, IWL are controlled. Thereby, the power converter device 103a can transfer AC power to and from the three-phase power system 101a.

FIG. 2 is a circuit diagram showing each unit converter 105 in the first embodiment.
As shown in FIG. 2, the unit converter 105 is a voltage dividing circuit in which a cell controller 4 that is a failure determination processing unit, gate drivers 31H and 31L, a bidirectional chopper circuit 2, and resistors R1 and R2 are connected in series. And a voltage sensor 5 connected in parallel with the resistor R2. This unit converter 105 operates with power supplied from the external power supply Vd.

  The bidirectional chopper circuit 2 includes a series circuit in which switching elements 21H and 21L that are short-circuited at the time of failure are connected in series, and a plurality of capacitors C1 and C2 that are connected in parallel to the series circuit (an example of an energy storage device). And a current sensor CT. The bidirectional chopper circuit 2 is connected to the outside by output terminals PBUS and NBUS. The bidirectional chopper circuit 2 outputs either the voltage across the capacitors C1 and C2 or the zero voltage to the output terminals PBUS and NBUS depending on on / off of the switching elements 21H and 21L.

  The output terminal PBUS is connected to a connection node between the emitter of the switching element 21H and the collector of the switching element 21L. The output terminal NBUS is connected to the emitter of the switching element 21L on the low side. Capacitors C1 and C2 are connected in parallel between the collector of the switching element 21H and the emitter of the switching element 21L.

The switching element 21H includes an IGBT element 211H and a diode D1H connected in parallel in the opposite direction to the IGBT element 211H.
The switching element 21L includes an IGBT element 211L and a diode D1L connected in parallel to the IGBT element 211L in the reverse direction.
In the first embodiment, the emitter of the IGBT element 211L of the switching element 21L and the capacitors C1 and C2 are connected via the current sensor CT. The current sensor CT is, for example, a current transformer, detects a current Is0 that flows between the switching elements 21H and 21L and the capacitors C1 and C2, and transmits the current Is0 to the cell controller 4.
The current sensor CT is not limited to this, and may be connected between the collector of the IGBT element 211H of the switching element 21H and the capacitors C1 and C2.

The gate drivers 31H and 31L are connected to the cell controller 4 on the input side. The output side of the gate driver 31H is connected to the gate of the switching element 21H. The output side of the gate driver 31L is connected to the gate of the switching element 21L. The gate drivers 31H and 31L convert the voltage level of the pulse command for driving the switching elements 21H and 21L, and output the gate voltage to the IGBT elements 211H and 211L.
The voltage dividing circuit in which the resistors R1 and R2 are connected in series is a circuit that divides the voltage across the capacitors C1 and C2. The voltage sensor 5 detects a capacitor voltage Vc 0 corresponding to the voltage across the capacitors C 1 and C 2 and transmits it to the cell controller 4.

The cell controller 4 is communicably connected to the central controller 107 (see FIG. 1) via the optical fiber cable 111 and another unit converter 105. An external power supply Vd is connected to the power supply line of the cell controller 4. The cell controller 4 receives output signals from the current sensor CT and the voltage sensor 5. The cell controller 4 outputs a pulse command for driving the IGBT elements 211H and 211L to the gate drivers 31H and 31L. The gate driver 31H outputs a gate voltage to the IGBT element 211H. The gate driver 31L outputs a gate voltage to the IGBT element 211L.
The bidirectional chopper circuit 2 transfers power between the capacitors C1 and C2 that are energy storages and the output terminals PBUS and NBUS through a series circuit in which switching elements 21H and 21L are connected in series.

As the failure of the bi-directional chopper circuit 2, there are considered a case where both the switching elements 21H and 21L are short-circuited and a case where a short circuit occurs inside or in the capacitors C1 and C2. If only one of the switching elements 21H and 21L is short-circuited, a large current flows when the other switching element is turned on, and the other also short-circuits. Therefore, here, the switching elements 21H and 21L will be described as being short-circuited.
Hereinafter, a current path flowing from the capacitors C1 and C2 when each part fails will be described with reference to FIGS.
FIG. 3 is an explanatory diagram of a short circuit detection operation of the switching elements 21H and 21L of each unit converter 105 in the first embodiment.
When one or both of the switching elements 21H and 21L are short-circuited, an unintended short-circuit current Is1 flows from both ends of the capacitors C1 and C2 via the switching elements 21H and 21L. As a result, the current Is0 detected by the current sensor CT increases.
As the short-circuit current Is1 flows, the charges stored in the capacitors C1 and C2 are discharged. As a result, the capacitor voltage Vc0 detected by the voltage sensor 5 decreases.

FIG. 4 is an explanatory diagram of the short-circuit detection operation of the capacitors C1 and C2 of each unit converter 105 in the first embodiment.
As shown in FIG. 4, when the capacitor C2 is short-circuited, an unintended short-circuit current Is2 flows through the short-circuited capacitor C2. However, the short circuit current Is2 does not flow through the current sensor CT.
As the short-circuit current Is2 flows, the charge stored in the capacitor C1 is discharged. As a result, the capacitor voltage Vc0 detected by the voltage sensor 5 decreases.
Similarly, when the capacitor C1 is short-circuited or when both the capacitors C1 and C2 are short-circuited at the same time, the capacitor voltage Vc0 detected by the voltage sensor 5 decreases.

FIG. 5 is a flowchart illustrating a short circuit detection process according to the first embodiment. As shown in FIG. 5, the cell controller 4 confirms the abnormality of the unit converter 105 from the increase in the current Is0 and the decrease in the capacitor voltage Vc0.
When the unit converter 105 is activated and starts operating, the cell controller 4 starts short circuit detection processing.

In step S10, the cell controller 4 measures the current Is0 by the current sensor CT.
In step S11, the cell controller 4 determines whether or not the measured current Is0 is 200% or more with respect to the rated value, for example. If the current Is0 is 200% or more with respect to the rated value (Yes), the cell controller 4 performs the process of Step S12. If the current Is0 is less than 200% with respect to the rated value (No), the process of Step S17 is performed. I do. The cell controller 4 determines that the failure location is the switching elements 21H and 21L based on the current Is0.
In step S <b> 12, the cell controller 4 measures the capacitor voltage Vc <b> 0 by the voltage sensor 5.

In step S13, the cell controller 4 determines whether or not the measured capacitor voltage Vc0 is, for example, 20% or less with respect to the rated value. If the capacitor voltage Vc0 is 20% or less with respect to the rated value (Yes), the cell controller 4 performs the process of step S14, and if the capacitor voltage Vc0 exceeds 20% with respect to the rated value (No), The process returns to step S10.
In step S14, the cell controller 4 determines that the switching elements 21H and 21L have failed. That is, the cell controller 4 detects a failure of the unit converter 105.
In step S15, the switching element of the unit converter 105 is short-circuited due to a failure.
In step S16, in the unit converter 105, the output terminal PBUS and the output terminal NBUS are short-circuited. Thereby, the unit converter 105 which failed is energized without trouble, and the operation of the power converter 103a can be continued.

In step S <b> 17, the cell controller 4 measures the capacitor voltage Vc <b> 0 by the voltage sensor 5.
In step S18, the cell controller 4 determines whether or not the measured capacitor voltage Vc0 is 20% or less with respect to the rated value, for example. If the capacitor voltage Vc0 is 20% or less with respect to the rated value (Yes), the cell controller 4 performs the process of step S19. If the capacitor voltage Vc0 exceeds 20% with respect to the rated value (No), The process returns to step S10.

In step S19, the cell controller 4 determines that the capacitors C1 and C2 have failed. That is, the cell controller 4 detects a failure of the unit converter 105.
In step S <b> 20, the cell controller 4 treats the switching element 21 </ b> L to turn on and short-circuit. Thereby, the malfunction by the short circuit of capacitor | condenser C1, C2 can be avoided. When the process of step S20 ends, the unit converter 105 transitions to step S16.
Thus, the cell controller 4 can determine the cause of the failure and take action.

  According to the present embodiment, the unit converter 105 using a switching element that is in a short-circuit state at the time of a failure as a semiconductor device determines whether it is a failure of the switching element or a failure of the capacitors C1 and C2 at the time of its own failure. It becomes possible. As a result of this determination, when the capacitors C1 and C2 (energy accumulators) fail, the output terminals of the unit converter 105 can be short-circuited by a procedure to turn on the switching element 21L.

(Second Embodiment)
FIG. 6 is a circuit diagram showing each unit converter 105A in the second embodiment. The same elements as those of the unit converter 105 of the first embodiment shown in FIG.
As shown in FIG. 6, the unit converter 105A of the second embodiment includes a full bridge circuit 2A different from the bidirectional chopper circuit 2 of the first embodiment, and further includes gate drivers 32H and 32L. . This unit converter 105A operates by being supplied with an external power supply Vd.
The full bridge circuit 2A includes a first series circuit in which switching elements 21H and 21L that are short-circuited at the time of failure are connected in series, and a second series circuit in which switching elements 22H and 22L that are short-circuited at the time of failure are connected in series. I have. The full bridge circuit 2 </ b> A further includes capacitors C <b> 1 and C <b> 2 (an example of an energy storage) connected in parallel to the first series circuit and the second series circuit, and a current sensor CT. The full bridge circuit 2A is connected to the outside by output terminals PBUS and NBUS. The full bridge circuit 2A outputs either positive voltage, negative voltage, or zero voltage at both ends of the capacitors C1, C2 to the output terminals PBUS, NBUS depending on on / off of the switching elements 21H, 21L, 22H, 22L. Is output. The full bridge circuit 2A can output a negative voltage across the capacitors C1 and C2, and thus can be controlled more precisely than the bidirectional chopper circuit 2.

  The output terminal PBUS is connected to a connection node between the emitter of the switching element 21H and the collector of the switching element 21L. The output terminal NBUS is connected to a connection node between the emitter of the switching element 22H and the collector of the switching element 22L. Capacitors C1 and C2 are connected in parallel between the collector of the switching element 21H and the emitter of the switching element 21L, and between the collector of the switching element 22H and the emitter of the switching element 22L.

The switching element 22H includes an IGBT element 221H and a diode D2H connected in parallel in the opposite direction to the IGBT element 221H.
The switching element 22L includes an IGBT element 221L and a diode D2L connected in parallel to the IGBT element 221L in the reverse direction.
In the second embodiment, the emitter of the IGBT element 221L of the switching element 22L and the capacitors C1 and C2 are connected via the current sensor CT. The current sensor CT is, for example, a current transformer, and detects a current Is0 flowing between the switching elements 21H, 21L, 22H, and 22L and the capacitors C1 and C2, and transmits the current Is0 to the cell controller 4.
The current sensor CT is not limited to this, and may be connected between the collector of the IGBT element 221H of the switching element 22H and the capacitors C1 and C2.

The gate drivers 32H and 32L are connected to the cell controller 4 on the input side. The output side of the gate driver 32H is connected to the gate of the switching element 22H. The output side of the gate driver 32L is connected to the gate of the switching element 22L. Similarly to the gate drivers 31H and 31L, the gate drivers 32H and 32L convert voltage levels of pulse commands for driving the switching elements 22H and 22L, and output gate voltages to the IGBT elements 221H and 221L.
The voltage dividing circuit in which the resistors R1 and R2 are connected in series is a circuit that divides the voltage across the capacitors C1 and C2. The voltage sensor 5 detects a capacitor voltage Vc 0 corresponding to the voltage across the capacitors C 1 and C 2 and transmits it to the cell controller 4.

The cell controller 4 of the second embodiment is the same as that of the first embodiment shown in FIG.
The full bridge circuit 2A transmits and receives electric power between the capacitors C1 and C2 that are energy storages and the output terminals PBUS and NBUS via the switching elements 21H, 21L, 22H, and 22L.
The failure of the full bridge circuit 2A includes a case where the switching elements 21H, 21L, 22H and 22L fail and a case where a short circuit occurs inside or in the capacitors C1 and C2. If only one of the switching elements 21H and 21L is short-circuited, a large current flows when the other switching element is turned on, and the other also short-circuits. Similarly, if only one of the switching elements 22H and 22L is short-circuited, a large current flows when the other switching element is turned on, and the other also short-circuits. Therefore, here, it is assumed that both switching elements 21H and 21L or both switching elements 22H and 22L are short-circuited. In the following, referring to FIG. 7, a description will be given of processing related to determination and treatment at the time of the short circuit.

FIG. 7 is a flowchart showing a short-circuit detection process in the second embodiment. The same elements as those in the short-circuit detection process of the first embodiment shown in FIG.
After starting the processing, the processing in steps S10 to S19 is the same as the processing in steps S10 to S19 of the first embodiment. Thereby, it is possible to distinguish between the short-circuit failure of the switching elements 21H and 21L and the short-circuit failure of the capacitors C1 and C2 without providing the unit converter 105 with a short-circuit device. If the cell controller 4 determines that the failure location is the capacitors C1 and C2, the cell controller 4 performs the process of step S20A.
In step S20A of the second embodiment, the cell controller 4 commands to turn on, for example, two of the low-side switching elements 21L and 22L. Thereby, the cell controller 4 short-circuits between the output terminals PBUS and NBUS. Note that the cell controller 4 may instruct to turn on the two high-side switching elements 21H and 22H, or instruct to turn on all the switching elements 21L, 22L, 21H and 22H. Good. The full bridge circuit 2A of the second embodiment can reliably short-circuit the output terminals PBUS and NBUS by short-circuiting a plurality of paths.
In this way, the cell controller 4 also performs a measure of short-circuiting between the output terminals PBUS and NBUS of the unit converter 105A even in the full bridge circuit 2A. Thereby, the unit converter 105A which failed is energized without trouble, and the operation of the power conversion device 103a can be continued.

(Third embodiment)
In the self-powered power supply system in which the control power of the unit converter is supplied from the capacitors C1 and C2 (energy storage), the energy supply source of the unit converter is lost due to the failure of the capacitors C1 and C2. For this reason, the self-supplied power source unit converter cannot maintain the short-circuited state of the switching element when the capacitors C1 and C2 fail. For this reason, when the failure of the capacitors C1 and C2 is detected, the entire power conversion device 103a is stopped.

FIG. 8 is a circuit diagram showing each unit converter 105B in the third embodiment. The same elements as those of the unit converter 105 of the first embodiment shown in FIG.
As shown in FIG. 8, the unit converter 105B of the third embodiment includes a self-power supply 6 that is different from that of the first embodiment, and is otherwise configured in the same manner as the first embodiment. .
The self-supplied power source 6 supplies power to the unit converter 105 itself with the energy stored in the capacitors C1 and C2. The input side of the self-supplied power source 6 is connected to the positive side of the capacitors C1 and C2. The output side of the self-supplied power supply 6 is the unit converter 105B itself, and is connected to, for example, the cell controller 4 and the gate drivers 31H and 31L. This self-supplied power source 6 includes an energy storage element inside, and can supply power for a while even when the capacitors C1 and C2 are out of order.
Since unit converter 105B is operated by being supplied with electric power from self-supplied power supply 6, when capacitors C1 and C2 are short-circuited, the ON command for switching element 21L cannot be continued. Therefore, it operates to stop the power converter 103a.

FIG. 9 is a flowchart showing the short-circuit determination processing in the third embodiment. The same elements as those in the short-circuit determination treatment process of the first embodiment shown in FIG.
After starting the processing, the processing in steps S10 to S19 is the same as the processing in steps S10 to S19 of the first embodiment. Thereby, it is possible to distinguish between the short-circuit failure of the switching elements 21H and 21L and the short-circuit failure of the capacitors C1 and C2 without providing the unit converter 105 with a short-circuit device. If the cell controller 4 determines that the failure location is the capacitors C1 and C2, the cell controller 4 performs the process of step S20B.
In step S20B, the cell controller 4 operates to stop the power converter 103a. That is, the cell controller 4 notifies the central controller 107 that one of the capacitors C1 and C2 is short-circuited via the optical fiber cable 111. The central controller 107 immediately stops the power converter 103a.
Even when the capacitors C1 and C2 of the unit converter 105B are short-circuited and the self-supplied power supply 6 stops supplying power, the entire power conversion device 103a is stopped, so that it is possible to prevent the occurrence of chain failures.

(Modification)
The present invention is not limited to the embodiments described above, and includes various modifications. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. A part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

A part or all of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware such as an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by a processor interpreting and executing a program that realizes each function.
In each embodiment, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.
Examples of modifications of the present invention include the following (a) to (j).

(A) The power converters 103a of the first and second embodiments are applied to a three-phase MMC circuit format linked to the three-phase power system 101a. However, the present invention is not limited to this, and the power conversion device of the present invention is a single-phase MMC linked to a single-phase system, an MMC that drives a motor that is a kind of multiphase load, or a zero-phase cancellation type MMC that uses a staggered transformer. You may apply to (ZC-MMC) etc.
(B) The number of phases of the power converter is not limited to three phases.
(C) A current transformer is used for the current sensor CT of the first and second embodiments. However, the present invention is not limited to this, and the current sensor CT may be a shunt resistor or a hall sensor, and is not limited.
(D) The current sensor CT of the first and second embodiments is connected between the switching element on the low side and the negative side of the capacitors C1 and C2. However, the present invention is not limited to this, and the current sensor CT may be connected between the switching element on the high side and the positive side of the capacitors C1 and C2.

(E) Each arm 104 of the power conversion device 103a may include both the bidirectional chopper circuit 2 of the first embodiment and the full bridge circuit 2A of the second embodiment. Thereby, the freedom degree of design of the power converter device 103a can be raised.
(F) The power conversion device may be configured to supply AC power by connecting to a multiphase load or a multiphase power supply instead of connecting to the three-phase power system 101a.
(G) Two or more capacitors provided in the unit converter 105 may be connected in parallel. For example, three or more capacitors may be connected in parallel.
(H) The energy storage is not limited to a capacitor as long as it stores electrical energy such as a secondary battery.
(I) The central controller 107 of the first and second embodiments is connected to each unit converter 105 in a daisy chain via the optical fiber cable 111. However, the present invention is not limited to this, and the central controller 107 of the present invention may be connected to each unit converter 105 in a star shape via the optical fiber cable 111, for example, and the connection topology is not limited.
(J) Each unit converter 105 of the first and second embodiments includes a cell controller 4 that is a failure determination treatment unit. However, the present invention is not limited to this, and the cell controller 4 may be installed, for example, in the vicinity of each unit converter 105 to control the unit converter 105 in the vicinity.

101a, 101b Three-phase power systems 102a, 102b Transformers 103a, 103b Power converter 104 Arm 105, 105A, 105B Unit converter 106 Reactor 107 Central controller 108 AC voltage sensor 109 Current sensor 110 Optical transceiver 111 Optical fiber cable 2 Bidirectional Chopper circuit 2A Full bridge circuit 21H, 21L, 22H, 22L Switching element 211H, 211L, 221H, 221L IGBT element D1H, D1L, D2H, D2L Diode C1, C2 capacitor (energy storage)
CT Current sensor 31H, 31L, 32H, 32L Gate driver 4 Cell controller (Failure judgment treatment part)
5 Voltage sensor 6 Self-powered power supply R1, R2 Resistor

Claims (11)

A series circuit in which a plurality of switching elements that are short-circuited at the time of failure are connected in series, and a plurality of energy accumulators connected in parallel to the series circuit, the energy accumulator depending on on / off of the switching elements A unit converter that outputs a voltage depending on the voltage of or a zero voltage;
Further comprising a plurality of arms in which a plurality of the unit converters are connected in series;
A current sensor for detecting a current flowing between the switching element and the energy storage;
A voltage sensor for detecting a voltage of the energy storage;
A failure determination treatment unit that determines and treats a failure point of the unit converter from the current detection value by the current sensor and the voltage detection value by the voltage sensor between the switching element and the energy accumulator;
A power conversion device comprising: The unit converter operates with an external power supply,
If it is determined that the failure location of the unit converter is the energy storage unit, the failure determination treatment unit controls the switching element to treat the output terminals of the unit converter so as to be short-circuited.
The power conversion apparatus according to claim 1. The unit converter includes a self-powered power source that supplies power to the failure determination treatment unit by energy accumulated in the energy accumulator,
If the failure determination treatment unit determines that the failure location of the unit converter is the energy accumulator, the failure determination treatment unit takes action to stop the operation of the entire power conversion device.
The power conversion apparatus according to claim 1. The unit converter is a bidirectional chopper circuit provided with a capacitor as the energy storage.
The power conversion apparatus according to claim 1. The unit converter operates with an external power source,
If the failure determination processing unit determines that the failure location of the unit converter is the energy storage, the low potential side of the two switching elements constituting the series circuit is turned on. To treat,
The power conversion device according to claim 4, wherein: The unit converter is a full bridge circuit including a capacitor as the energy storage.
The power conversion apparatus according to claim 1. The arm includes a bidirectional chopper circuit including a capacitor as the energy storage and a full bridge circuit including a capacitor as the energy storage.
The power conversion apparatus according to claim 1. Each AC phase of the power converter is connected to a multiphase power source or a multiphase load.
The power conversion apparatus according to claim 1. The multi-phase power source to which each AC phase of the power converter is connected is a power system.
The power conversion device according to claim 8. A series circuit in which a plurality of switching elements that are short-circuited at the time of failure are connected in series, and a plurality of energy accumulators connected in parallel to the series circuit, the energy accumulator depending on on / off of the switching elements A unit converter that outputs a voltage depending on the voltage of or a zero voltage;
A failure determination treatment unit for determining and treating a failure of the unit converter;
An arm in which a plurality of the unit converters are connected in series;
A failure detection method for a power conversion device comprising a plurality of the arms,
The failure determination treatment section
Detecting a current detection value by a current sensor that detects a current flowing between the switching element and the energy storage;
Detecting a voltage detection value by a voltage sensor that detects a voltage across the energy storage; and
Determining, based on a current detection value of the current sensor and a voltage detection value of the voltage sensor, whether the failure portion of the unit converter is the switching element or the energy storage;
The fault detection method of the power converter device characterized by performing this. The failure determination treatment unit
If it is determined that the failure location of the unit converter is the energy storage, the step of controlling the switching element to short-circuit between the output terminals of the unit converter,
The failure detection method for the power conversion device according to claim 10, wherein:

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