TWI505625B - Power conversion system and its control method - Google Patents

Description

Power conversion system and control method thereof

The present invention relates to a power conversion system and a control method thereof, and more particularly to a power conversion system and a motor power device that are combined with a power converter and a motor device including a plurality of semiconductor switching elements, and can continue to operate when a semiconductor switching element fails. Its control method.

A power converter such as an inverter or a converter is configured by a semiconductor switching element such as a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor) or a GTO (Gate Turn Off Thyristor). Such a power converter can convert electric power such as AC/DC conversion into a desired mode by controlling ON/OFF of these semiconductor switching elements.

Thereby, various uses for converting the power type, for example, a 50 Hz/60 Hz frequency conversion of an AC power transmission system of the power system or an AC/DC conversion connection between an AC power transmission network and a DC power transmission network, or a natural condition The variable power generation power is integrated into the power system frequency to transmit power to the wind power generation system or the solar power generation system.

In the power converter used in the power system, since the failure of the power converter is a cause of power failure, it is sought to continue the power conversion operation even when a part of the components constituting the power converter fails. Further, in a wind power generation system or a solar power generation system, the power generation stoppage due to a failure may impair the power generation benefit of the power generation company. Therefore, it is important to minimize the power generation stop period and increase the equipment operation rate. In places where the maintenance of equipment such as the ocean or the mountainous area is difficult, it is particularly important that the power generation system continues to operate when the power converter fails.

As a method of detecting a failure of a self-turn-off type semiconductor switching element constituting a power converter, for example, Patent Document 1 discloses that a main body of a self-extinguishing semiconductor switching element is detected by comparison. The detection signal applied between the electrodes and the driving signal of the self-extinguishing semiconductor switching element are turned on/off (ON/OFF) to detect a short-circuit fault, an open fault, or an abnormality of the driving circuit of the self-extinguishing semiconductor switching element. s method.

Further, as a technique that can continue to operate even when the power converter fails, for example, Patent Document 2 discloses a power conversion of a phase module including at least two or more power conversion modules in which a plurality of single phases are connected in series. When the single-phase power conversion module constituting the phase module fails, the voltage of the output of the single-phase power conversion module corresponding to the other sound phase module is controlled to be 0. Continue the technology of power conversion.

Further, Patent Document 3 discloses a rectifying diode element connected by a self-extinguishing semiconductor switching element and a reverse parallel connection therewith The switch module formed by the device is connected to the pressure-contact type switching element in parallel, and when the self-extinguishing type semiconductor switching element fails, the voltage-switching type switching element becomes a short-circuit state, and the power conversion technique is continued.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2008-11608

[Patent Document 2] Japanese Special Table 2009-509483

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2001-238460

The technique described in the above-mentioned Patent Document 1 is based on the premise that the failure of the self-extinguishing semiconductor switching element is detected, and in order to continue the operation of the power converter by the technique described in Patent Document 2 or Patent Document 3, it is necessary to constitute a phase. It is premised that the modules are connected in series to form a power converter. This is because when one or two of the modules connected in series are faulty, it is necessary to share the voltage of the faulty mode component at the time of sounding with the module that is not faulty.

However, the voltage shared by a healthy module increases as the number of failed modules increases. The maximum voltage (withstand voltage) that can be tolerated by the self-extinguishing semiconductor switching element or the diode element used in the module is fixed, and even for the failure of the entire module constituting the phase There is a limit to the number of modules that can continue to operate. Exceeding this upper limit In the event of a failure, a sound module will fail in a chain due to insufficient pressure, and the power converter will not continue to operate.

In addition, wind power generation systems or solar power generation systems are often used under high voltage (more than 600V and below 7kV) or low voltage (below 600V). Considering the operation in a healthy state, most of the modules are not connected in series. In order to implement the continuation of the operation of the module, the techniques of Patent Documents 1 to 3 are applied, and it is necessary to connect the majority of the high-voltage components required for the voltages to be shared by the modules at the time of sounding. The composition will increase the conduction loss or the number of parts.

In this way, in order to achieve continuous operation when the power converter fails with a small number of parts, it is necessary to apply the voltage of each sound module at the time of the fault, always in the self-extinguishing semiconductor switch constituting the module. The component is equal to or less than the upper limit of the withstand voltage.

The present invention has been made in view of the above-described viewpoints, and an object of the invention is to provide a method for reducing a voltage applied to a power converter even when a module of a self-extinguishing semiconductor switching element or the like constituting a power converter fails. Power conversion system and its control method.

In order to achieve the above object, the power conversion system of the present invention is characterized in that it has a switching module composed of a self-extinguishing semiconductor switching element and a rectifying element connected in reverse parallel to the self-extinguishing semiconductor switching element, and detecting The fault detecting means of the fault of the switch module, and the foregoing switch module for detecting the fault by the fault detecting means A power converter configured by connecting a plurality of circuits including short-circuiting devices for electrical short-circuiting in series, and a DC-port voltage means for detecting a DC voltage of the power converter, and an AC for reducing a voltage of an AC portion of the power converter a portion voltage lowering mechanism that lowers a voltage command value of a DC voltage of the power converter by lowering a voltage command value of a DC voltage of the power converter when the fault detecting means detects a failure of the switch module, and further reduces the DC voltage The voltage lowering mechanism outputs a control device for the action signal.

Further, in order to achieve the above object, the control method of the power conversion system of the present invention is characterized in that a self-turn-off type semiconductor switching element is connected and connected in reverse parallel to the self-extinguishing type semiconductor switching element. a plurality of circuits including a switching module formed by the rectifying element, a fault detector for detecting a fault of the switch module, and a short circuit device for electrically shorting the switch module that detects the fault by the fault detector are connected in series The DC voltage of the power converter connected to the power converter is detected by the DC voltage detecting means, and when the fault detector detects the failure of the switching module, the voltage of the DC voltage of the power converter is controlled by the control device. The command value is lowered to lower the DC voltage than during the sound period, and the operation signal is outputted to the AC voltage drop means.

According to the present invention, even in the case where the module of the self-extinguishing semiconductor switching element or the like constituting the power converter fails, the voltage applied to the power converter can be reduced without being applied to the sound module. The voltage is higher than the withstand voltage and the chain is faulty, so that continuous operation can be achieved.

1‧‧‧Power Converter

2‧‧‧Self-turn-off type semiconductor switching elements

3‧‧‧Diode components

4‧‧‧Semiconductor switch module

5‧‧‧Short device

6‧‧‧Fault detector

7‧‧‧Smoothing capacitor

8‧‧‧Capacitor voltage detector

9‧‧‧ Current Detector

10‧‧‧Voltage detector

11‧‧‧Control device

12‧‧‧ Transformer with load tap changer

13‧‧‧Contact points

14‧‧‧DC voltage controller

15‧‧‧AC current controller

16‧‧‧pulse calculator

17‧‧‧Capacitor voltage command value calculator

18‧‧‧Rolling Synchronous Machine

19‧‧‧Rolling type 2 times of excitation rotary machine

20‧‧‧Rotor winding of the rotating machine

21‧‧‧Rotor winding of the rotating machine

22‧‧‧Rotation number control mechanism

23‧‧‧1st rotating machine

24‧‧‧2nd rotating machine

25‧‧‧Rotary number detector

26‧‧‧Power System

27‧‧‧Amplitude Phase Calculator

28‧‧‧dq component calculator

S1‧‧‧ Capacitor voltage detection value

S1*‧‧‧ capacitor voltage command value

S2‧‧‧ current detection value

S2*‧‧‧ current command value

S3‧‧‧ voltage detection value

S3*‧‧‧ voltage command value

Status signal of S4‧‧‧ semiconductor switch module

S5‧‧‧Semiconductor switching element drive signal

S6‧‧‧External signal

Fig. 1 is a view showing a schematic configuration of an embodiment of a power conversion system according to the first embodiment of the present invention, which is an example of a tap changeover transformer when a load is used as an AC voltage reduction mechanism.

Fig. 2 is a block diagram for explaining a method of controlling the voltage of the smoothing capacitor incorporated in the power conversion system of Fig. 1 to a specific voltage.

Fig. 3 is a view showing a schematic configuration of an example of a power conversion system according to the second embodiment of the present invention, in which a tap changeover transformer, a permanent magnet type rotary machine, or a winding type synchronous machine are used as a communication unit voltage reduction mechanism.

Fig. 4 is a view showing a schematic configuration of an example of a power conversion system according to the second embodiment of the present invention, in which a load switching transformer and a winding type secondary electromagnetic rotating machine are used as an alternating current voltage reducing mechanism.

Fig. 5 is a characteristic diagram showing the relationship between the number of revolutions and the induced voltage in the case of the permanent magnet type rotating machine or the winding type synchronous machine shown in Fig. 3.

Fig. 6 is a characteristic diagram showing the relationship between the number of revolutions and the induced voltage in the case of the winding type secondary electromagnetic rotating machine shown in Fig. 4.

Fig. 7 is a view showing a schematic configuration of an example in which the first rotating machine and the second rotating machine are used as the alternating current unit voltage reducing mechanism in the third embodiment of the power conversion system according to the present invention.

Fig. 8 is a graph showing the relationship between the number of revolutions and the induced voltage in the case where the first and second rotating machines shown in Fig. 7 are wound-type secondary electromagnetic rotating machines. Figure.

FIG. 9 is a characteristic diagram showing the relationship between the number of revolutions and the induced voltage when the first rotating machine shown in FIG. 7 is a permanent magnet type rotating machine or a winding type synchronous machine, and the second rotating machine is a winding type secondary exciting rotating machine. .

Hereinafter, a power conversion system and a control method therefor according to the present invention will be described based on the illustrated embodiments. In the respective drawings, the same reference numerals are given to the same portions, and the overlapping description will be omitted.

[Example 1]

Fig. 1 shows Embodiment 1 of the power conversion system of the present invention. As shown in the figure, the power converter 1 is a semiconductor switch module 4 including a self-extinguishing semiconductor switching element 2 and a diode element 3 of a rectifying element connected in anti-parallel thereto, and detecting the semiconductor switching module 4 The fault detector 6 of the failure of the semiconductor switch module 4 is connected in parallel to the semiconductor switch module 4, and the circuit formed by the short circuit device 5 for electrically detecting the faulty semiconductor switch module 4 by the fault detector 6 is A plurality of circuits are connected in series to form a phase circuit. Further, the short-circuiting device 5 may be operated by the short-circuiting device alone or by the detected value of the failure detector 6.

Further, the DC portion of the power converter 1 is mounted with a smoothing capacitor 7, and the voltage across the smoothing capacitor 7 is monitored by the capacitor voltage detector 8, whereby the smoothing capacitor 7 and the smoothing capacitor voltage detector 8 form a DC voltage detection. means.

On the other hand, the alternating current unit of the power converter 1 is connected to a transformer (communication unit voltage reducing means) 12 of a tap-change switch with a load that can perform tap switching when an external signal is energized by a load current, and flows. The current of the circuit of the transformer 12 connecting the power converter 1 and the load tap changer is monitored by the current detector 9, and the voltage at the point of contact 13 between the power converter 1 and the power system 26 is controlled by a voltage detector. 10 to monitor.

Further, when the failure detector 6 detects a failure of the semiconductor switch module 4, the DC voltage is lowered more than the sound voltage by lowering the voltage command value of the DC voltage of the power converter 1, and the load is applied. The transformer 12 of the tap changer outputs a control device 11 for the action signal.

The control device 11 that controls the power converter 1 is incorporated into a control means for controlling the voltage of the smoothing capacitor 7 to a specific voltage, and uses the above-described respective detection values, that is, the capacitor voltage detection value obtained by the capacitor voltage detector 8. The current detection value S2 obtained by the current detector 9, and the voltage detection value S3 obtained by the voltage detector 10 are subjected to feedback control. The control method in this case is shown in Figure 2.

As shown in FIG. 2, the control device 11 takes as input the capacitor voltage detection value S1, the current detection value S2, and the voltage detection value S3 detected by the capacitor voltage detector 8 and the state signal S4 of the semiconductor switch module 4. The capacitor voltage command value calculator 17 calculates and outputs a semiconductor switching element drive signal S5 for controlling the capacitor voltage to a specific capacitor voltage command value S1*.

In order to calculate the semiconductor switching element drive signal S5, the amplitude phase calculator 27 detects the voltage amplitude and phase of the power system 26 from the voltage detection value S3, and the phase detected by the amplitude phase calculator 27 is used as a reference by the dq component calculation. The device 28 decomposes the current detection value S2 into an in-phase component (effective current component) and a 90 phase phase component (invalid current component), and the capacitor voltage command value S1* and the capacitor voltage detection value S1 are controlled by the DC voltage controller 14. The difference is used as an input to calculate the effective current command value S2* _d . The current command value S2* calculated by the DC voltage controller 14 and the current detection value S2 are input, and the voltage command value S3* is calculated by the AC current controller 15, and the voltage command value S3* calculated by the AC current controller 15 is used. The semiconductor switching element driving signal S5 is calculated by the pulse calculator 16.

Further, although the configuration of the two-level power converter is shown in FIG. 1, the pulse calculator 16 is configured in accordance with the configuration of an arbitrary power converter and the state of the semiconductor switch module 4 constituting the same. Calculate the appropriate pulse.

Further, the control method of the capacitor voltage is described with reference to Fig. 2. However, some of the detected values may be estimated values calculated using other detected values, and are not limited to feedback control. Further, although the invalid current command value S2* _q is 0 in FIG. 2, it may be any value other than 0 in the case of the control target caused by the force rate condition or the like, or other invalid current, regardless of the effect of the present invention. .

In addition, the capacitor voltage command value S1*, the state signal S4 of the semiconductor switch module 4 outputted by the fault detector 6 detects whether the semiconductor switch module 4 constituting the phase has a fault, and the total number of the semiconductor switch module 4 corresponds to the fault mode. The number of groups, the calculation of the capacitor voltage command value S1*, and the output of the external signal S6 to the mechanism for reducing the voltage of the connected machine. For example, a capacitor voltage command value S1 * S1 * the initial value _INI, full switch module of each phase is N _all, the maximum number of modules in each phase of the fault is N, constituting the semiconductor switch modules 4 In the semiconductor element (self-extinguishing semiconductor switching element 2 and diode element 3), the value of the withstand voltage is small [v[V], and when the boundary of the withstand voltage is α, the capacitor voltage command value S1* is S1*=MIN(S1* _ini (N _all -N)/N _all , α(N _all -N)v). Where α is a number below 1 and MIN is a function that selects (in parentheses) the value of the small argument.

In addition, the transformer 12 with the tap changer at the load causes the peak value of the voltage between the AC lines to not exceed (N _all -N)v/ by the signal of the external signal S6. 2 tap changer.

According to the present embodiment, when the semiconductor switch module 4 constituting the power converter 1 fails, the voltage applied to the sound semiconductor switch module 4 can be made less than the withstand voltage, and the interlocking failure can be prevented. A power converter system that continues to operate is realized.

[Embodiment 2]

3 and 4 show Embodiment 2 of the power conversion system of the present invention. 3 is a case where the rotating machine to which the stator winding 20 of the rotating machine is connected to the power converter 1 is a permanent magnet type or a winding type synchronous machine 18, and the exciting device for the winding type synchronous machine 18 is omitted. Figure 4 The rotary machine to which the rotor winding 21 of the rotating machine is connected to the power converter 1 is a winding type secondary exciting rotary machine 19.

In the first embodiment shown in FIG. 1, the AC terminal of the power converter 1 is connected to the transformer 12 of the tap changer with load. In contrast, in the present embodiment, one side of the AC terminal of the power converter 1 is connected. In the case of the permanent magnet type or the winding type synchronous machine 18 or the winding type secondary electromagnetic rotating machine 19, the following description will be given on the portion related to the permanent magnet type or the winding type synchronous machine 18 and the winding type secondary electromagnetic rotating machine 19. .

In general, the induced voltage characteristics of the number of revolutions vary depending on the type of the rotating machine. That is, in the case of the permanent magnet type or winding type synchronous machine 18 shown in Fig. 3, the time change rate of the magnetic flux locked to the stator winding 20 of the rotating machine is determined in accordance with the number of rotations, so as shown in Fig. 5, the number of rotations is as shown in Fig. 5. The relationship with the induced voltage is approximately linear.

On the other hand, in the case of the winding type secondary electromagnetic rotating machine 19 shown in Fig. 4, the stator winding 20 of the rotating machine is excited by the commercial frequency power supply of the electric power system 26, the number of poles of the rotating machine is p, and the commercial frequency is f. In the case of [Hz], the difference between the number of synchronous rotations obtained by the equation (1) and the number of rotations (generally referred to as sliding) determines the magnitude of the induced voltage, and the relationship shown in FIG. 6 is obtained.

Synchronous rotation number [rpm]=120f/p (1)

That is, the rotation number control unit 22 receives the external signal S6 outputted from the control device 11 of the power converter 1 and the permanent magnet type or winding type synchronous machine 18 or the winding type detected by the rotation number detector 25 twice. The number of rotations of the exciting rotary machine 19 limits the range of the number of revolutions based on the induced voltage characteristics shown in FIGS. 5 and 6. In the case of the permanent magnet type or the winding type synchronous machine 18, in order to lower the induced voltage to a specific voltage or lower, the number of rotations is limited to the low speed region. On the other hand, in the case of the winding type secondary electromagnetic rotating machine 19, in order to reduce the induced voltage to a specific voltage or lower, the number of rotations is limited to a region in the vicinity of the number of synchronous rotations.

Further, the above-described number-of-rotation control means 22 controls the number of revolutions of the rotary machine by controlling the angle of attack of the blades that control the number of revolutions of the wind turbine with respect to the wind speed, for example, in the wind power generation system. Further, in the case of the hydroelectric power system, the waterwheel controller controls the number of revolutions of the rotary machine by controlling the guide vanes or the waterwheel blades that control the flow of the water to control the number of rotations of the waterwheel.

Even in the configuration of the present embodiment, the same effects as those of the first embodiment can be obtained.

[Example 3]

Fig. 7 is a view showing Embodiment 3 of the power conversion system of the present invention. In the present embodiment, the second rotating machine 24 is provided instead of the transformer 12 with the load tap changer of the second embodiment, and the permanent magnet type or the winding type synchronous machine 18 or the winding type secondary electromagnetic rotating machine 19 is used as the first rotation. Machine 23. In the third embodiment shown in FIG. 7, the first rotating machine 23 and the second rotating machine 24 are both a winding type rotating machine, and the first rotating machine 23 and the second rotating machine 24 are rotated coaxially.

Further, when the rotation axes are different, the first rotating machine 23 and the second rotating machine 24 are provided with the rotation number control means 22 and the rotation number check. The detector 25 is also possible. Further, the synchronous machine may be a rotating field magnetic type as shown in FIG. 3 or a fixed field magnetic type.

In the case where the first rotating machine 23 and the second rotating machine 24 of the present embodiment are winding type rotating machines, the relationship between the induced voltage applied to the power converter 1 and the number of revolutions is shown in FIG.

In the case of the winding type exciter described in the second embodiment, the details are the same, and as shown in FIG. 8, when it is limited to a specific voltage or lower, it is necessary to limit the difference between the first rotating machine 23 and the second rotating machine 24, respectively. The induced voltage simultaneously becomes a rotation number region of a specific voltage or lower. When the first rotating machine 23 and the second rotating machine 24 are both a permanent magnet type rotating machine and a winding type rotating machine, they may be limited to the number of rotations shown in FIG.

Even in the configuration of the present embodiment, the same effects as those of the first embodiment can be obtained.

[Example 4]

Although not specifically illustrated, for example, a system for controlling a DC voltage of a solar power generation system or the like is replaced with a voltage of a smoothing capacitor 7 of the first embodiment, and is controlled to a specific voltage or less by voltage control of a system for controlling a DC voltage. The voltage applied to the power converter 1 is controlled to be lower than a specific voltage in response to the fault state of the power converter 1, and the semiconductor switch module 4 does not interlock when the semiconductor switch module 4 fails. The present invention can also be applied to the case where the semiconductor switch module 4 is broken and the operation is continued.

Further, the present invention is not limited to the foregoing embodiment, and includes the species. A variant of this kind. For example, the above-described embodiments have been described in detail in order to facilitate the understanding of the present invention, but are not limited to having all of the configurations described above. Further, it is also possible to replace a part of the configuration of a certain embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of another embodiment. Further, it is possible to add, delete, or replace other components for a part of the configuration of each embodiment.

1‧‧‧Power Converter

2‧‧‧Self-turn-off type semiconductor switching elements

3‧‧‧Diode components

4‧‧‧Semiconductor switch module

5‧‧‧Short device

6‧‧‧Fault detector

7‧‧‧Smoothing capacitor

8‧‧‧Capacitor voltage detector

9‧‧‧ Current Detector

10‧‧‧Voltage detector

11‧‧‧Control device

12‧‧‧ Transformer with load tap changer

13‧‧‧Contact points

26‧‧‧Power System

S1‧‧‧ Capacitor voltage detection value

S2‧‧‧ current detection value

S3‧‧‧ voltage detection value

Status signal of S4‧‧‧ semiconductor switch module

S5‧‧‧Semiconductor switching element drive signal

S6‧‧‧External signal

Claims (13)

A power conversion system characterized by having a switching module formed by a self-turn-off type semiconductor switching element and a rectifying element connected in reverse parallel to the self-extinguishing semiconductor switching element, a power converter configured by connecting a plurality of faulty detectors for detecting a failure of the switch module and a short circuit device for electrically short-circuiting the switch module detected by the fault detector; and configuring the plurality of circuits in series; a DC unit voltage detecting means for detecting a DC voltage of the power converter, an AC voltage lowering means for reducing a voltage of an AC portion of the power converter, and detecting the switch module by the fault detector In the event of a failure, the voltage command value of the DC link voltage of the power converter is lowered to lower the DC voltage than during the sound period, and the control device for outputting the operation signal to the AC voltage drop means is output. A power conversion system according to claim 1, wherein the DC portion voltage detecting means is constituted by a smoothing capacitor and a capacitor voltage detector for detecting a voltage between the electrodes of the smoothing capacitor. The power conversion system according to claim 1 or 2, wherein the alternating current unit voltage reducing means is a load tap changing transformer capable of performing tap switching when an external signal is energized by a load current. The power conversion system according to claim 1 or 2, wherein the alternating current unit voltage reducing means is connected to one of the alternating current terminals of the power conversion system and can be energized by a load signal by an external signal. In the state where the tap changer is switched, the tap changer transformer is configured, and the other AC terminal is connected to the permanent magnet type rotary machine, and the number of revolutions of the permanent magnet type rotary machine is controlled based on an external signal from the control device. Rotation number control mechanism. The power conversion system according to claim 1 or 2, wherein the AC voltage lowering means is connected to an AC terminal of one of the power conversion systems, and can be tapped by an external signal while the load current is energized. The switched-time tap changer transformer is configured to be connected to the winding-type synchronous machine to the other AC terminal, and includes a rotation number control mechanism that controls the number of revolutions of the winding-type synchronous machine based on an external signal from the control device. The power conversion system according to claim 1 or 2, wherein the AC voltage lowering means is connected to an AC terminal of one of the power conversion systems, and can be tapped by an external signal while the load current is energized. The switched load tap changer transformer is configured to be connected to the winding type secondary electromagnetic rotating machine, and the rotation of the number of rotations of the winding type secondary exciting rotary machine is controlled based on an external signal from the control device. Number control mechanism. The power conversion system according to claim 1 or 2, wherein the alternating current unit voltage reducing means is connected to the power conversion system by a first rotating machine connected to one of the alternating current terminals of the power conversion system The second rotating machine of the other alternating current terminal includes a rotation number control mechanism that controls the number of rotations of the first rotating machine and the second rotating machine based on an external signal from the control device. The power conversion system according to claim 7, wherein the first rotating machine and the second rotating machine are winding type rotating machines. The power conversion system according to claim 7, wherein the first rotating machine is a permanent magnet type rotating machine, and the second rotating machine is a winding type rotating machine. A power conversion system according to claim 3, further comprising: a current detector that detects a current flowing in a circuit that connects the power converter and the load when the tap changes the transformer or the rotating machine, and detects the power conversion A voltage detector of the voltage at the point of contact between the device and the power system. A control method for a power conversion system, characterized by a switch module comprising a self-turn-off type semiconductor switching element and a rectifying element connected in reverse parallel to the self-extinguishing semiconductor switching element And a power converter configured by connecting a plurality of circuits including a fault detector for detecting a failure of the switch module and a short circuit device for electrically short-circuiting the switch module detected by the fault detector to be connected in series The DC voltage is detected by the DC voltage detecting means, and when the fault detector detects the fault of the switch module, the control device lowers the voltage command value of the DC voltage of the power converter to make the DC voltage ratio The sound is further reduced, and the operation signal is outputted to the AC voltage reduction means. The control method of the power conversion system according to claim 11, wherein the DC voltage detecting means is provided by a smoothing capacitor and is inspected The capacitor voltage detector for measuring the inter-electrode voltage of the smoothing capacitor is configured, and the alternating current portion voltage lowering means switches the transformer or rotates by a load tap that can be switched by the external signal while the load current is energized. And a current detector that detects a current flowing in a circuit that connects the power converter and the load tap changer transformer or the rotating machine, and detects a tap changeover transformer when the power converter transmits the load Or a voltage detector of a voltage at a contact point of the rotating machine and the power system; the control device, detecting a capacitor voltage detected by the capacitor detector, detecting a current detected by the current detector, and detecting the voltage The voltage detection value detected by the device and the state signal of the switch module are used as inputs, and the drive signal of the previous switch module for controlling the specific capacitor voltage command value is output. The control method of the power conversion system of claim 12, wherein in order to output the driving signal of the switch module, the voltage amplitude and phase of the power system are detected by the amplitude phase calculator from the voltage detection value, and the amplitude phase is The phase detected by the calculator is used as a reference by the dq component calculator, so that the current detection value is decomposed into the same phase component and the 90° phase component, and the capacitor voltage command value and the capacitor voltage detection are detected by the DC voltage controller. The difference between the values is used as an input to calculate the effective current command value, and the calculated current command value and the current detected value are used as inputs, and the AC current controller calculates the voltage command value, and the voltage command value calculated by the AC current controller is used. Pulse calculator for calculating the aforementioned switch module Drive signal.