JP5229880B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device including a DC capacitor in a DC side circuit, and more particularly to a power conversion device having a protection function that suppresses an overvoltage caused by charging of a DC capacitor with external energy.

A power converter provided with a DC capacitor in a DC side circuit is widely used as a voltage-type power converter. In such a power converter, during normal operation, the voltage applied to the DC capacitor is supplied, for example, according to the operation of the converter circuit for supplying DC voltage, and is not overcharged. However, the voltage applied to the DC capacitor may greatly exceed the rated voltage due to a failure of a switching element in the power conversion device or a failure of a peripheral circuit. As a protection circuit for this purpose, a series circuit of a resistor and a turn-off thyristor is provided in parallel with the DC capacitor. Proposals have been made to suppress overvoltage (for example, see Patent Document 1).
JP-A-7-250430 (page 2-4, FIG. 1)

  The conventional DC overvoltage suppression circuit disclosed in Patent Document 1 consumes the energy stored in the DC capacitor using a resistor, and thus becomes a large resistor. Accordingly, the device is also increased in size, cost, and low. There was a problem of being efficient.

  The present invention has been made to solve the above-described problems, and provides a power converter that can suppress overcharge of a DC capacitor without attaching an auxiliary circuit such as a DC overvoltage suppression circuit. With the goal.

  In order to achieve the above object, a power conversion device according to a first aspect of the present invention includes a three-level DC power source, positive and negative DC capacitors fed from the DC power source, and the DC capacitor. A three-level inverter that converts an applied three-level DC voltage into an AC voltage to drive an AC motor, and inverter control means that supplies gate pulses to the three-phase outer and inner switching elements constituting the three-level inverter And a first element breakdown detecting means for detecting that any one of the switching elements, flywheel diodes and clamp diodes constituting the three-level inverter has a short circuit failure, and the inverter control means comprises the first When the element destruction detecting means 1 detects a short circuit failure, a gate extinguishing signal is output to the outer switching element. And it is characterized in that so as to output the gate firing signals to said inner switching elements.

  The power conversion device according to the second aspect of the present invention includes a three-level DC power source, positive and negative DC capacitors fed from the DC power source, and a three-level DC power applied to the DC capacitor. A three-level inverter that converts the DC voltage into an AC voltage to drive the AC motor, inverter control means that supplies a gate pulse to the switching element that constitutes the three-level inverter, and substantially three-phase input to the AC motor Short-circuiting means for short-circuiting, and first element breakdown detection means for detecting that any of the switching elements, flywheel diodes and clamp diodes constituting the three-level inverter has a short-circuit failure, and the inverter control means When the first element breakdown detecting means detects a short circuit failure, the switching element has a gate arc extinguishing Outputs No. is characterized in that so as to short-circuit three phases of an input of the AC motor by the short-circuiting means.

  According to the present invention, it is possible to provide a power converter that can suppress overcharging of a DC capacitor without attaching an attached circuit such as a DC overvoltage suppressing circuit.

  Embodiments of the present invention will be described below with reference to the drawings.

  Hereinafter, the power converter concerning Example 1 of the present invention is explained with reference to Drawing 1 thru / or Drawing 5. FIG.

  FIG. 1 is a circuit configuration diagram of a power conversion apparatus according to Embodiment 1 of the present invention. In FIG. 1, an AC voltage is supplied to a three-level converter circuit 13 from a power system (not shown) via a circuit breaker 11 and a transformer 12. Here, the circuit breaker 11 is a circuit breaker for disconnecting the energy supply from the power system in the event of an accident. A three-level converter circuit 13 converts the AC voltage into a three-level DC voltage and supplies it to the three-level inverter circuit 14. The three-level inverter circuit 14 outputs a three-phase AC voltage and drives the AC motor 15. Here, although the capacitors for smoothing the DC voltage are distributed in the three-level converter circuit 13 and the three-level inverter circuit 14, they may be concentrated in the DC link portion.

  Hereinafter, the internal configuration of the three-level converter circuit 13 and the three-level inverter circuit 14 will be described.

  The three-level converter circuit 13 is composed of a parallel circuit of switching legs that constitutes three phases of R phase, S phase, and T phase. Since the configuration of each switching leg is the same, the configuration of the R-phase switching leg will be described below.

  The basic circuit of the R-phase switching leg is a series circuit composed of switching elements 1R1, 1R2, 1R3, and 1R4. Flywheel diodes 2R1, 2R2, 2R3, and 2R4 are connected in antiparallel to each switching element 1R1, 1R2, 1R3, and 1R4, respectively. Switching elements 1R1, 1R2 constitute a positive arm, and switching elements 1R3, 1R4 constitute a negative arm. The R-phase secondary output of the transformer 12 is connected to an intermediate point between the two arms, that is, a connection point between the switching elements 1R2 and 1R3. Further, the two switching elements 1R1, 1R4 constituting both ends of the series circuit are referred to as outer switching elements, and the two switching elements 1R2, 1R3 constituting the inner side are referred to as inner switching elements.

  The positive electrode of the switching element 1R1 is connected to the positive electrode of the DC capacitor 5R1 through the fuse 4R1. The negative electrode of the switching element 1R4 is connected to the negative electrode of the DC capacitor 5R2 via the fuse 4R2. The direct current capacitor 5R1 and the direct current capacitor 5R2 are connected in series, and the connection point between them forms a neutral point. The positive clamp diode 3R1 is connected from the neutral point to the midpoint of the positive arm, that is, the connection point of the switching elements 1R1 and 1R2. Similarly, a negative clamp diode 3R2 is connected from the midpoint of the negative arm, that is, from the connection point of the switching elements 1R3 and 1R4 to the neutral point.

  Next, the main circuit configuration of the three-level inverter circuit 14 will be described. The three-level inverter circuit 14 is also composed of a parallel circuit of switching legs, each of which constitutes a U-phase, a V-phase, and a W-phase. Since the configuration of each switching leg is the same, the configuration of the U-phase switching leg will be described below.

  The basic circuit of the U-phase switching leg is a series circuit composed of switching elements 1U1, 1U2, 1U3 and 1U4. Flywheel diodes 2U1, 2U2, 2U3, and 2U4 are connected in antiparallel to the switching elements 1U1, 1U2, 1U3, and 1U4, respectively. The switching elements 1U1, 1U2 constitute a positive arm, and the switching elements 1U3, 1U4 constitute a negative arm. A U-phase AC output is obtained from an intermediate point between the two arms, that is, a connection point between the switching elements 1U2 and 1U3, and is connected to the U-phase terminal of the AC motor 15. Again, the two switching elements 1U1 and 1U4 constituting both ends of the series circuit are referred to as outer switching elements, and the two switching elements 1U2 and 1U3 constituting the inner side are referred to as inner switching elements.

  The positive electrode of the switching element 1U1 is connected to the positive electrode of the DC capacitor 5U1 through the fuse 4U1. The negative electrode of the switching element 1U4 is connected to the negative electrode of the DC capacitor 5U2 via the fuse 4U2. The direct current capacitor 5U1 and the direct current capacitor 5U2 are connected in series, and the connection point between them forms a neutral point. The DC capacitor 5U1 is supplied with a positive DC output from the three-level converter circuit 13, and the DC capacitor 5U2 is supplied with a negative DC output from the three-level converter circuit 13. A positive clamp diode 3U1 is connected from the neutral point to the midpoint of the positive arm, that is, the connection point of the switching elements 1U1 and 1U2. Similarly, a negative clamp diode 3U2 is connected from the midpoint of the negative arm, that is, from the connection point of the switching elements 1U3 and 1U4 to the neutral point.

  Appropriate gate pulses are supplied to the switching elements of the three-level converter circuit 13 and the three-level inverter circuit 14 described above from the converter control circuit 30 and the inverter control circuit 40, respectively. In the normal operation mode, the three-level converter circuit 13 The three-level inverter circuit 14 is controlled to drive the AC motor 15 with the desired three-level three-phase AC output.

  The converter control circuit 30 and the inverter control circuit 40 are supplied with element breakdown detection signals obtained from respective parts of the three-level converter circuit 13 and the three-level inverter circuit 14 (not shown). For example, in the case of the three-level inverter circuit 14, the element breakdown detection signal can use auxiliary contact signals of the fuses 4U1, 4U2, 4V1, 4V2, 4W1, and 4W2. Although the circuit configuration is complicated, a monitoring circuit that detects a short circuit failure of each element by detecting an element voltage based on gate timing may be provided to obtain the element breakdown detection signal.

  Whether the three-level inverter circuit 14 and the three-level converter circuit 13 are the first element breakdown detection signal obtained from the three-level inverter circuit 14 when the element breakdown detection signal is given. Alternatively, different operations are performed depending on whether the second element breakdown detection signal is obtained from the three-level converter circuit 13. When the element breakdown detection signal is the first element breakdown detection signal obtained from the three-level inverter circuit 14, the inverter control circuit 40 switches the switching element 1U1 outside the three-level inverter circuit 14 as shown in FIG. 1V1, 1W1, 1U4, 1V4 and 1W4 are given a gate extinguishing signal (off signal), and inner switching elements 2U1, 2V1, 2W1, 3U4, 3V4 and 3W4 are given a gate firing signal (on signal). . Converter control circuit 30 also provides a gate extinguishing signal to all switching elements.

  On the other hand, when the element breakdown detection signal is the second element breakdown detection signal obtained from the three-level converter circuit 13, the converter control circuit 30 is connected to the outside of the three-level converter circuit 13 as shown in FIG. The switching elements 1R1, 1S1, 1T1, 1R4, 1S4 and 1T4 are given a gate extinction signal, and the inner switching elements 2R1, 2S1, 2T1, 3R4, 3S4 and 3T4 are given a gate firing signal. The inverter control circuit 40 gives a gate extinguishing signal to all the switching elements.

  With reference to FIGS. 3 to 8, the following description will be made on the function and effect of preventing the DC capacitor from being overcharged by the protection operation shown in FIGS.

  FIG. 3 is an explanatory diagram of an overcharge route when the inner switching element of the three-level inverter circuit 14 is damaged. As shown in FIG. 3, a case is considered in which, for example, the U-phase switching element 1U2 is short-circuited while the AC motor 15 is in operation, and a protective gate extinguishing signal is given to all the switching elements. At this time, as shown by the broken line in FIG. 3, the charging current passing through the damaged switching element 1U2 flows to the positive DC capacitors 5R1, 5S1, 5T1, 5U1, 5V1 and 5W1, and the DC capacitors 5R1, 5S1, 5T1, 5U1. 5V1 and 5W1 are charged to the peak value of the line voltage Vm of the AC motor 15.

  As apparent from FIG. 3, the same phenomenon occurs even when the flywheel diode 2U2 is short-circuited. Further, when the inner switching element that has caused the short-circuit failure is the negative arm, the circuit configuration of the three-level inverter circuit 14 is symmetrical, so that the negative DC capacitors 5R2, 5S2, 5T2, 5U2, 5V2 and 5W2 will be charged.

  FIG. 4 is an explanatory diagram of an overcharge route when the clamp diode of the three-level inverter circuit 14 is damaged. As shown in FIG. 4, consider a case where the positive side clamp diode 3U1 is short-circuited while the AC motor 15 is in operation and a gate extinguishing signal is given to all the switching elements. At this time, the charging current passing through the damaged clamp diode 3U1 flows to the negative DC capacitors 5R2, 5S2, 5T2, 5U2, 5V2 and 5W2 as shown by the broken lines in the figure, and the DC capacitors 5R2, 5S2, 5T2, 5U2, 5V2 and 5W2 are charged with the peak value of the line voltage Vm of the AC motor 15. On the other hand, when the negative clamp diode is short-circuited, the positive DC capacitor is charged because the circuit is symmetrical.

  By the way, the relationship between the line voltage Vm and the DC voltage (positive side or negative side) E can be expressed as E = √2 × Vm / (√3 × k), where k is the degree of modulation in PWM modulation. Therefore, the voltage design of the DC capacitors on the positive side and the negative side is performed with this value of E. On the other hand, E = √2 × Vm when the inner element of FIG. 3 is broken or when the clamp diode of FIG. 4 is broken, so that a voltage (√3 × k) times the DC voltage at the time of design is applied. . In this case, the DC capacitor may be destroyed by overvoltage. Moreover, in order to prevent overvoltage breakdown, it is necessary to consider a voltage margin of (√3 × k) times, so there is a concern about an increase in the size of the DC capacitor.

  In the above situation, if a short circuit failure of the element is detected by some method as shown in FIG. 1 and the inner switching element of the three-level inverter circuit 14 is ignited, the AC motor 15 as shown by the broken line in FIG. A short-circuit current that shorts the three-phase terminals flows, and the DC capacitor is not overcharged. It should be noted that short-circuit tolerance is required for the inner switching element and the clamp diode of the three-level inverter circuit 14 only for the time during which the short-circuit current of the AC motor 15 flows (for example, several seconds until the induced voltage of the AC motor 15 disappears).

  Also, as shown in FIG. 5, when a DC short circuit occurs due to element breakage, for example, the switching elements 1U1, 1U2 and 1U3 are broken, and the capacitor energy of the positive side DC capacitors 5R1, 5S1, 5T1, 5U1, 5V1 and 5W1 Flows into the damaged phase U phase, and even if the fuse 4U1 is activated (blown) and disconnects the failed phase, the positive DC capacitor 5R1, through the damaged switching element 2U1 and the clamp diode 3U1, as in FIG. 5S1, 5T1, 5U1, 5V1, and 5W1 are overcharged to the peak value of the line voltage Vm. In this case, since the negative inner switching element 1U3 is also short-circuited, as shown in FIG. 6, the negative DC capacitor 5R2 is passed through the damaged switching element 1U3 and the clamp diode 3U2 as in FIG. 5S2, 5T2, 5U2, 5V2, and 5W2 are also overcharged to the peak value of the line voltage Vm.

  Even in the overcharge mode shown in FIGS. 5 and 6, as shown in FIG. 1, the inverter control circuit 40 has the switching elements 1U1, 1V1, 1W1, 1U4, 1V4, and 1W4 outside the three-level inverter circuit 14. If the gate extinguishing signal is given to the inner switching elements 2U1, 2V1, 2W1, 3U4, 3V4 and 3W4, the three-phase terminal of the AC motor 15 is substantially set as described above. Since it is in a short-circuited state, overcharging does not occur.

  FIG. 7 is an explanatory diagram of an overcharge route when the inner switching element of the three-level converter circuit 13 is damaged. As shown in FIG. 7, a case is considered in which the switching element 1R2 is short-circuited during operation of the three-level converter circuit 13 and a protective gate extinguishing signal is given to all the switching elements. At this time, as shown by the broken line in the figure, the charging current passing through the damaged switching element 1R2 flows to the positive DC capacitors 5R1, 5S1, 5T1, 5U1, 5V1 and 5W1, and the DC capacitors 5R1, 5S1, 5T1, 5U1, 5V1 and 5W1 are charged with the peak value of the output line voltage Vtr of the transformer 12.

  As is apparent from FIG. 7, the same phenomenon occurs even when the flywheel diode 2R2 is short-circuited. When the inner switching element that has caused the short-circuit failure is a negative arm, the circuit configuration of the three-level converter circuit 13 is symmetric with respect to the positive and negative DC capacitors 5R2, 5S2, 5T2, 5U2, 5V2 and 5W2 will be charged.

  FIG. 8 is an explanatory diagram of an overcharge route when the clamp diode of the three-level converter circuit 13 is damaged. As shown in FIG. 8, a case is considered where the clamp diode 3R1 on the positive side is short-circuited during operation of the three-level converter circuit 13 and gate extinguishing signals are given to all the switching elements. At this time, as shown by the broken line in the figure, the charging current passing through the damaged clamp diode 3R1 flows to the negative DC capacitors 5R2, 5S2, 5T2, 5U2, 5V2, and 5W2, and the DC capacitors 5R2, 5S2, 5T2, 5U2, 5V2 and 5W2 are charged with the peak value of the output line voltage Vm of the transformer 12. On the other hand, when the negative clamp diode is short-circuited, the positive DC capacitor is charged because the circuit is symmetrical.

  7 and FIG. 8, if a short circuit failure of the element is detected by some method as shown in FIG. 2 and the inner switching element of the three-level converter circuit 13 is ignited, the broken line in FIG. Thus, a short-circuit current that short-circuits the secondary output terminal of the transformer 12 flows, and the DC capacitor is not overcharged. It should be noted that the inner switching element and the clamp diode of the three-level converter circuit 13 need to have a short-circuit tolerance only during the time when the secondary short-circuit current of the transformer 12 flows (for example, for several cycles until the input switch 11 is shut off).

  In the three-level converter circuit 13, the operation when a plurality of elements are short-circuited due to a DC short circuit is the same as the operation of the three-level inverter circuit 14, and thus description thereof is omitted. Further, the relationship between the secondary voltage Vtr of the transformer 12 and the DC voltage E is the same as the relationship between the line voltage Vm of the AC motor 15 and the DC voltage E, and the description thereof is omitted.

  As described above, when a short-circuit fault occurs in the switching element, flywheel diode, and clamp diode, the switching element inside the three-level converter circuit or the three-level inverter circuit in which the short-circuit fault has occurred is substantially fired. If a short-circuit loop is formed, it is possible to prevent overcharging of the DC capacitor. When the power supply to the DC capacitor is performed by a diode rectifier without using the three-level converter circuit, it is obvious that the protection operation should be performed only by the three-level inverter circuit.

  FIG. 9 is a circuit configuration diagram of the power conversion device according to the second embodiment of the present invention. In the second embodiment, the same parts as those in the circuit configuration diagram of the power conversion apparatus according to the first embodiment of the present invention shown in FIG. The second embodiment is different from the first embodiment in that a short circuit 16 capable of short-circuiting the three-phase terminals of the AC motor 15 by a thyristor 16T is provided via a diode bridge, and the three-level inverter circuit 14 When the main circuit element is destroyed, the inverter control circuit 40 is configured to provide a gate extinguishing signal to all the switching elements of the three-level inverter circuit 14 and a signal for starting the thyristor 16T.

  In the second embodiment, when a short circuit failure occurs in the elements in the three-level inverter circuit 14, the thyristor 16T of the short circuit 16 is ignited and the three-phase terminals of the AC motor 15 are substantially short-circuited. It is possible to prevent overcharging of the capacitor.

FIG. 10 is a circuit configuration diagram of the power conversion device according to the third embodiment of the present invention. In the third embodiment, the same parts as those in the circuit configuration diagram of the power conversion apparatus according to the first embodiment of the present invention shown in FIG. The third embodiment is different from the first embodiment in that a short circuit 17 capable of short-circuiting the three-phase output terminals of the transformer 12 by a thyristor 17T via a diode bridge is provided, and a three-level converter circuit 13 When the main circuit element is destroyed, the converter control circuit 30 provides a gate extinguishing signal to all the switching elements of the three-level converter circuit 13 and a signal for starting the thyristor 17T.

  In the third embodiment, when a short circuit failure occurs in the element in the three-level converter circuit 13, the thyristor 17T of the short circuit 17 is fired to substantially short the three-phase output terminal of the transformer 12. It is possible to prevent overcharging of the series capacitor. Further, in the operation of the short circuit 17, a short circuit current determined by the impedance of the transformer 12 flows. However, the short circuit current 11 is allowed to pass through the zero point in the primary circuit breaker 11 to reliably open the circuit breaker 11. It becomes important. This also applies to the case of the first embodiment shown in FIG.

  In the configuration of the first embodiment, when a so-called voltage-driven element such as IGBT is used as a switching element instead of a so-called current-driven element such as GCT, an inner switching element is used to prevent overcharging. If the three-phase terminal of the AC motor 15 or the three-phase output terminal of the transformer 12 is substantially short-circuited after firing, the short-circuit withstand capability of the switching element may be insufficient, resulting in element damage. On the other hand, as shown in the second or third embodiment, if a so-called current-driven element having a sufficient short-circuit resistance is used as the short-circuit thyristor 16T or 17T, it is possible to prevent element damage.

FIG. 1 is a circuit configuration diagram (1) of a power conversion device according to a first embodiment of the present invention. The circuit block diagram (2) of the power converter device which concerns on Example 1 of this invention. Explanatory drawing of the overcharge route when the inner side switching element of a 3 level inverter circuit is damaged. Explanatory drawing of the overcharge route when the clamp diode of a 3 level inverter circuit is damaged. Explanatory drawing (1) of the overcharge route when the direct current short circuit accompanying the element breakage of a 3 level inverter circuit generate | occur | produces. Explanatory drawing (2) of the overcharge route when the direct current short circuit accompanying the element failure of a 3 level inverter circuit generate | occur | produces. Explanatory drawing of an overcharge route when the inner side switching element of a 3 level converter circuit is damaged. Explanatory drawing of an overcharge route when the clamp diode of a three-level converter circuit is damaged. The circuit block diagram of the power converter device which concerns on Example 2 of this invention. The circuit block diagram of the power converter device which concerns on Example 3 of this invention.

Explanation of symbols

11 circuit breaker 12 transformer 13 three-level converter circuit 1R1, 1R2, 1R3, 1R4, 1S1, 1S2, 1S3, 1S4, 1T1, 1T2, 1T3, 1T4 switching elements 2R1, 2R2, 2R3, 2R4, 2S1, 2S2, 2S3, 2S4, 2T1, 2T2, 2T3, 2T4 Flywheel diodes 3R1, 3R2, 3S1, 3S2, 3T1, 3T2 Clamp diodes 4R1, 4R2, 4S1, 4S2, 4T1, 4T2 Fuses 5R1, 5R2, 5S1, 5S2, 5T1, 5T2 DC capacitors 14 3-level inverter circuit 1U1, 1U2, 1U3, 1U4, 1V1, 1V2, 1V3, 1V4, 1W1, 1W2, 1W3, 1W4 Switching elements 2U1, 2U2, 2U3, 2U4, 2V1, 2V2, 2V3, 2V4, 2W1, 2W2, 2W3, 2W4 Flywheel diode 3U1, 3U2, 3V1, 3V2, 3W1, 3W2 Clamp diode 4U1, 4U2, 4V1, 4V2, 4W1, 4W2 Fuse 5U1, 5U2, 5V1, 5V2, 5W1, 5W2 DC capacitor 15 AC motor 16 , 17 Short circuit 16T, 17T Thyristor 30 Converter control circuit 40 Inverter control circuit

Claims (9)

3 level DC power supply,
Positive and negative DC capacitors fed from this DC power supply,
A three-level inverter that converts the three-level DC voltage applied to the DC capacitor into an AC voltage to drive the AC motor;
Inverter control means for supplying gate pulses to the three-phase outer and inner switching elements constituting the three-level inverter;
A first element breakdown detecting means for detecting that any one of the switching element, flywheel diode and clamp diode constituting the three-level inverter has a short circuit failure;
The inverter control means includes
When the first element breakdown detecting means detects a short circuit failure, a gate extinguishing signal is output to the outer switching element, and a gate firing signal is output to the inner switching element. A power conversion device. The three-level DC power supply is a three-level converter that receives a commercial power supply via a transformer,
Converter control means for supplying gate pulses to the three-phase outer and inner switching elements constituting the three-level converter;
A second element breakdown detecting means for detecting that any one of the switching element, flywheel diode and clamp diode constituting the three-level converter has a short circuit failure;
The inverter control means includes
When the second element breakdown detecting means detects a short-circuit fault, a gate extinguishing signal is output to the switching element of the three-level inverter ,
The converter control means includes
When the first element breakdown detecting means detects a short circuit failure, a gate extinguishing signal is output to the switching element of the three-level converter;
When the second element breakdown detecting means detects a short-circuit fault, a gate arc extinguishing signal is output to the outer switching element of the three-level converter, and a gate point is applied to the inner switching element of the three-level converter. The power converter according to claim 1, wherein an arc signal is output. 3 level DC power supply,
Positive and negative DC capacitors fed from this DC power supply,
A three-level inverter that converts the three-level DC voltage applied to the DC capacitor into an AC voltage to drive the AC motor;
Inverter control means for supplying a gate pulse to the switching elements constituting the three-level inverter;
Short-circuit means for substantially short-circuiting the input of the AC motor by three phases;
A first element breakdown detecting means for detecting that any one of the switching element, flywheel diode and clamp diode constituting the three-level inverter has a short circuit failure;
The inverter control means includes
When the first element breakdown detecting means detects a short-circuit failure, a gate arc extinguishing signal is output to the switching element, and the input of the AC motor is short-circuited by the short-circuit means. Power converter. The three-level DC power supply is a three-level converter that receives a commercial power supply via a transformer,
Converter control means for supplying gate pulses to the three-phase switching elements constituting the three-level converter;
Short-circuit means for substantially three-phase short-circuiting the output of the transformer;
A second element breakdown detecting means for detecting that any one of the switching element, flywheel diode and clamp diode constituting the three-level converter has a short circuit failure;
The inverter control means includes
When the second element breakdown detecting means detects a short-circuit fault, a gate extinguishing signal is output to the switching element of the three-level inverter ,
The converter control means includes
When the first element breakdown detecting means detects a short circuit failure, a gate extinguishing signal is output to the switching element of the three-level converter;
When the second element breakdown detecting means detects a short-circuit fault, a gate extinguishing signal is output to the switching element of the three-level converter, and the input of the AC motor is short-circuited by the short-circuit means. The power conversion device according to claim 3. Providing a breaker on the primary side of the transformer;
When the second element breakdown detecting means detects a short-circuit failure and a substantial short-circuit current flows through the circuit breaker, the short-circuit current is passed through a zero point to reliably cut off. The power conversion device according to claim 2 or 4.   The power conversion device according to claim 3 or 4, wherein the short-circuit means includes a diode rectifier bridge and a current-driven switching element connected to an output thereof.   The power conversion device according to claim 1, wherein the switching element is a current-driven switching element. A fuse is provided in each of the positive and negative arms constituting the three-level converter,
5. The power conversion device according to claim 2, wherein the second element breakdown detection unit detects that any one of the fuses is activated. 6. A fuse is provided in each of the positive and negative arms constituting the three-level inverter,
9. The power conversion device according to claim 1, wherein the first element breakdown detection unit detects that any one of the fuses has been activated. 10.

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