JP2002354832A - Power inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power inverter which can protect a power inverting circuit from an overcurrent, when a switching means of low response speed is used as a switching means in a breaking circuit for preventing an overcurrent from flowing in an input side which is caused by phase difference between an input voltage and an output voltage. SOLUTION: A switching means whose response speed is low as compared with a semiconductor switching element is used in a breaking circuit 2. An overcurrent detecting circuit 3 detects whether an input current is an overcurrent. While the overcurrent detecting circuit 3 detects an overcurrent, a command input obstructing circuit 4 prevents an instantaneous current control signal and an instantaneous voltage control signal from inputting in a drive signal generating circuit 5. When an overcurrent flows for a long term, the breaking circuit 2 operates and a breaking state is set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for temporarily converting AC power into DC power, and further converting DC power back into AC power.

[0002]

2. Description of the Related Art Conventionally, a so-called three-arm type power converter has been known. The power conversion circuit used in this conventional power conversion device includes a plurality of switching elements each including a switching element including a transistor capable of controlling conduction in one direction and a switching circuit including a diode connected in anti-parallel to the switching element. A first switch group connected in series, second and third switch groups configured similarly to the first switch group, and a capacitor are connected in parallel. Since this power conversion circuit is composed of three switch groups, each switch group is called a three-arm system when viewed as one arm. In this power conversion circuit, AC power is full-wave rectified by a first switch group and a second switch group to charge a capacitor, and appears at both ends of the capacitor by a second switch group and a third switch group. The DC voltage is converted to an AC voltage, and the DC power is converted back to the AC power.

[0003]

In the conventional three-arm power converter, the second switch group is used for both power conversion and re-conversion, so that the phase between the input voltage and the output voltage is reduced. If there is a deviation, a large current flows on the input side. Therefore, conventionally, a method was used in which a frequency or phase abnormality was detected at high speed, and when an abnormality was detected, a thyristor switch connected in anti-parallel to the input side was used to shut off the power conversion circuit from the system side. . However, the cutoff circuit using a thyristor switch is expensive and requires a drive circuit that outputs a higher voltage than a logic circuit.
It was difficult to reduce the price of the power converter.

An object of the present invention is to provide a power conversion device using a so-called three-arm power conversion circuit, in which an overcurrent flows into an input side when a phase shift occurs between an input voltage and an output voltage. It is an object of the present invention to provide a power conversion device that can use a switching means having a low response speed as a shut-off circuit for preventing the switching.

Another object of the present invention is to provide a power conversion device capable of protecting a power conversion circuit from overcurrent even when switching means having a low response speed is used as a cutoff circuit.

Another object of the present invention is to provide an inexpensive power converter.

[0007]

According to the present invention, a plurality of switching circuits each including a switching element capable of controlling conduction in one direction and a diode connected in anti-parallel to the switching element are connected in series. A first switch group, a second and third switch group configured in the same manner as the first switch group, a power conversion circuit in which a capacitor is connected in parallel, and an intermediate between the first switch group. A reactor (first reactor) disposed between the point and one of two input terminals of the AC power supply, an instantaneous current control system that outputs an instantaneous current control signal based on a DC voltage command value, and an output voltage command An instantaneous voltage control system that outputs an instantaneous voltage control signal based on a value, and a plurality of first to third switch groups of a power conversion circuit that receive the instantaneous current control signal and the instantaneous voltage control signal as inputs. A drive signal generating circuit configured to supply a drive signal to a switching element at a predetermined timing to cause a power converter to perform a converter operation and an inverter operation, and one of two input terminals of an AC power supply and a first Connected between the AC power supply and the AC power supply circuit and the AC voltage converted by the power conversion circuit. And an interruption circuit for preventing application of an AC voltage from an AC power supply.

More specifically, a first connection circuit for electrically connecting an intermediate point of the second switch group to the other end of the two input terminals and one end of the two AC output terminals of the AC power supply; A second connection circuit for connecting an intermediate point of the third switch group to the other ends of the two AC output terminals via the second reactor.

For example, the drive signal generation circuit controls the power conversion circuit to perform a converter operation for charging a capacitor by controlling conduction of a plurality of switching elements constituting the first and second switch groups. By controlling the conduction of a plurality of switching elements constituting the third switch group, the power conversion circuit performs an inverter operation of converting a DC voltage appearing at both ends of the capacitor into an AC voltage, so that an intermediate operation of the second switch group is performed. It can be configured to output the AC voltage converted from the point and the intermediate point of the third switch group. Further, the capacitor may be charged only by the first switch group.

In the present invention, a switching means having a slow response speed as compared with a semiconductor switching element is used as the cutoff circuit. Further, in the present invention, a current detector for measuring an alternating current flowing into an intermediate point of the first switch group and an overcurrent detection circuit for detecting that an overcurrent has flowed based on an output of the current detector are used. . Further, a command input blocking circuit for preventing the instantaneous current control signal and the instantaneous voltage control signal from being input to the drive signal generation circuit while the overcurrent detection circuit detects that the overcurrent is flowing is provided. I have.

[0011] When the phase difference between the input AC voltage and the output AC voltage of the power conversion circuit increases, an overcurrent flows. The current to this power conversion circuit is detected by a current detector,
When the overcurrent detection circuit detects that the input current detected by the current detector is a current (overcurrent) larger than a predetermined value, the command input prevention circuit sends an instantaneous current control signal and an instantaneous voltage control to the drive signal generation circuit. Blocks incoming signals. As a result, the switching elements constituting the first to third switch groups of the power conversion circuit are turned off, and it is possible to prevent an overcurrent from flowing through the switching elements and to prevent the switching elements from being destroyed. When the command input blocking circuit blocks the input of the instantaneous current control signal and the instantaneous voltage control signal to the drive signal generation circuit, the switching element of the power conversion circuit becomes non-conductive, and the overcurrent sharply decreases. Therefore, the overcurrent detection circuit does not detect the overcurrent, and the command input blocking circuit allows the drive signal generation circuit to input the instantaneous current control signal and the instantaneous voltage control signal. As a result, the power conversion circuit starts the conversion operation again. At that time, if the phase difference between the input AC voltage and the output AC voltage is still large, an overcurrent flows again, and this overcurrent is detected by the overcurrent detection circuit. In the same manner as described above, the command input blocking circuit operates and the power conversion circuit enters a non-operating state.
Thereafter, this operation is repeated unless the phase difference between the input AC voltage and the output AC voltage decreases. If the state where the overcurrent still flows continues, the low-speed cutoff circuit enters the cutoff state, and the overcurrent is completely cut off. As described above, according to the present invention, since the overcurrent is intermittently prevented by the blocking operation of the command input blocking circuit until the blocking circuit enters the cutoff state, The switching elements used in the power conversion circuit can be prevented from being destroyed.

In order to protect the switching elements by disabling the power conversion circuit, an output blocking circuit for preventing a signal output from the drive signal generation circuit from being input to each switching element of the power conversion circuit. May be provided. In that case, a current detector that measures an AC current flowing into the intermediate point of the first switch group, an overcurrent detection circuit that detects that an overcurrent flows based on an output of the current detector, It is sufficient to provide an output blocking circuit for preventing the drive signal from being output from the drive signal generation circuit while the detection circuit is detecting that an overcurrent is flowing.

According to the present invention, even when the price of the power converter is reduced by using a low-speed switch as a shut-off circuit for preventing the inflow of overcurrent on the input side due to a phase shift between the input voltage and the output voltage, the power is reduced. The conversion circuit can be protected from overcurrent.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of an embodiment of a power converter according to the present invention will be described in detail with reference to the drawings. FIG.
1 is a circuit diagram showing a configuration of a power conversion device according to an embodiment of the present invention. In FIG. 1, a power conversion circuit 1 of a power conversion device includes a first switch group SW1, a second switch group SW
2, a third switch group SW3 and a capacitor C2 are connected in parallel. First switch group SW1
Is a switching circuit composed of a switching element T1 composed of a transistor capable of controlling conduction in one direction and a diode D1 connected antiparallel to the switching element T1, and a switching element T2 composed of a transistor and antiparallel connected to the switching element T2. And a switching circuit including the diode D2 connected in series. Similarly to the first switch group SW1, the second switch group SW2 and the third switch group SW3 also include switching elements T3 to T6 and diodes D3 to D6. Between the midpoint CP1 of the first switch group SW1 and one input terminal a of the AC power supply, the cutoff circuit 2 and the first reactor L1 are connected in series. A current detection unit of a current detector CT including a current transformer is mounted on a power supply line between the cutoff circuit 2 and the first reactor L1. A capacitor C1 is connected between a connection point between the cutoff circuit 2 and the first reactor L1 and the other input terminal b of the AC power supply. The cutoff circuit 2 operates when the AC input current becomes equal to or greater than a predetermined value, and operates in an emergency such as other circuit operation abnormality or input abnormality. As shown in FIG. 5, the cutoff circuit used in this embodiment is an inexpensive switching means such as an electromagnetic relay 2A having a slower response speed than an expensive cutoff circuit configured by connecting thyristors in reverse parallel. And a drive circuit 2B for driving the switching means. This shutoff circuit 2
Is controlled by the output of the overcurrent detection circuit 3 which determines that the input current is an overcurrent when the input current detected by the current detector CT is equal to or greater than a predetermined current reference value.
As shown in FIG. 5, the drive circuit 2B of the cutoff circuit 2
For example, the configuration is such that the output of the overcurrent detection circuit 3 is integrated, and the exciting current continues to flow through the electromagnetic coil while the integration value continues to increase. Therefore, when the overcurrent detection circuit 3 detects the overcurrent continuously or intermittently for a certain period, the switching means (for example, the contact point of the electromagnetic relay 2A) in the cutoff circuit 2 is in the cutoff state (open state). Status)
As a result, the supply of power from the AC power supply to the power conversion circuit 1 is stopped. The output of the overcurrent detection circuit 3 is output to a command input blocking circuit 4 described later. The command input blocking circuit 4 outputs a command signal while the overcurrent detection circuit 3 detects an overcurrent. 5 is prevented from being input. Also, an intermediate point CP of the second switch group SW2
2 and the other input terminal b of the AC power supply are connected to a first connection circuit CL.
1 are connected. And the third switch group S
Intermediate point CP3 of W3 and one output c of two AC output terminals
Is connected to the second reactor L2. The circuit including the second reactor L2 is a second connection circuit CL2
It is. The other ends d of the two AC output terminals are connected to the input terminal b of the AC power supply via a first connection circuit CL1, and a capacitor C3 is connected between the AC output terminal c and the other end d of the AC output terminal. Is connected.

A series circuit of a diode D7 and a battery BA is connected in parallel to both ends of the capacitor C2 of the power conversion circuit 1, and functions as an uninterruptible power supply when the AC power supply is cut or cut off. ing. This uses the DC power of the battery instead of charging the capacitor C2 in the converter operation. In this case, it is necessary to separately prepare a battery charging device and always charge the battery. The DC voltage appearing at both ends of the capacitor C2 is converted into AC power by the second and third switch groups SW2 and SW3, and functions as an uninterruptible power supply.

Next, the configuration of the control system of the power conversion circuit 1 will be described. This control system mainly includes an instantaneous current control system 6, an instantaneous voltage control system 7, a DC voltage control system 8, and an effective value voltage control system 9. An input current command based on a command from the DC voltage control system 8 is input to the instantaneous current control system 6. The DC voltage control system 8 receives a difference voltage between a DC voltage command value given from a control command device of the power supply device and a charging voltage of the capacitor C2 of the power conversion circuit 1, that is, a rectified DC voltage. This difference voltage is applied to the power conversion circuit 1
Is a command value for causing the rectified voltage obtained in step (1) to match the DC voltage command value. The DC voltage control system 8 converts this difference voltage into an AC voltage signal. The AC voltage signal of the difference voltage is converted so that it can be multiplied by the AC voltage of the AC power source input from before the shutoff circuit 2, and then multiplied by the AC voltage to be converted into an AC input current command. This input current command is subtracted from the output of the current detector CT (the difference between the command and the actual input current value) and input to the instantaneous current control system 6. The difference signal input to the instantaneous current control system 6 is input to the inverting input terminal of the comparator 62 through the current control circuit 61 in the instantaneous current control system 6. A sawtooth signal is input to the non-inverting input terminal of the comparator 62 as a modulation signal.
The comparator 62 includes a sawtooth signal and a current control circuit 61.
And outputs an instantaneous current control signal having a PWM waveform (this signal is also referred to as a gate signal of the first arm). The instantaneous current control signal is input to the command input blocking circuit 4 as it is, is inverted by the inverter IV1, is input to the command input blocking circuit 4, and is input to the drive signal generating circuit 5 via the command input blocking circuit 4. The drive signal generation circuit 5 controls the conduction of the switching elements T1 and T2 of the first switch group SW1 based on the input instantaneous current control signal and the inversion command to charge the capacitor C2 (the AC operation). To generate DC power. Note that the switching element T
The conduction between T3 and T4 may be controlled.

The instantaneous voltage control system 7 includes an effective value voltage control system 9
The instantaneous voltage control signal is output using the difference between the output voltage command output from the controller and the actual AC output voltage as an input. The output voltage command is a difference between the output voltage command value of the DC value given from the control command device of the power supply device and the AC output voltage from the power conversion circuit 1 converted to the effective value by the effective value calculation circuit 11. It is input to the control system 9 and converted into an AC value,
This value is obtained by multiplying the output of the PLL circuit 10 that outputs a sine wave synchronized with the input voltage. Instantaneous voltage control system 7
Then, the input is passed through the voltage control circuit 71 and then divided into two parts. One is supplied to the comparator 72 and the other is supplied to the phase inversion circuit 73.
Through the comparator 74. Comparator 7
In steps 2 and 74, the signals are compared with a sawtooth signal as a modulation signal (these comparison values are also referred to as gate signals of a second arm and a third arm), and the compared PWM waveform signals are inverted through inverters IV2 and IV3, respectively. The result is input to the command input blocking circuit 4 as an instantaneous voltage control signal. These four instantaneous voltage control signals are input to the drive signal generation circuit 5, and the drive signal generation circuit 5
Generates a drive signal for controlling the conduction of the semiconductor switching elements T3 to T6 of the second and third switch groups SW2 and SW3 to perform an inverter operation for converting a DC voltage appearing across the capacitor C2 into an AC voltage. .
As described above, it goes without saying that the second switch group SW2 may be used for the converter operation.

FIG. 2 is a diagram showing the command input blocking circuit 4 of the present invention and its peripheral circuits. The command input blocking circuit 4
And an AND circuit. The output of the instantaneous current control system 6 becomes the gate signal of the first arm, and the output of the instantaneous voltage control system 7 becomes the gate signal of the second arm and the gate signal of the third arm. It is input to one input terminal of the six AND circuits of the circuit 4. Then, the current value detected by the current detector CT is input to the overcurrent detection circuit 3, and if this current value is larger than the current reference value, it is determined that an overcurrent has occurred and LOW.
Six ANs constituting a command input blocking circuit 4 for level signals
Output to D circuit. As a result, the command input blocking circuit 4
Block one gate signal. When the output of the current detector CT falls below the current reference value, the overcurrent detection
The H-level signal is output, and the command input blocking circuit 4 enters a state where the gate signal is allowed to pass.

In the present embodiment, when the phase difference between the input AC voltage and the output AC voltage of the power conversion circuit 1 increases, an overcurrent flows to the power conversion circuit 1. Power conversion circuit 1
The current flowing to is detected by the current detector CT. When the overcurrent detection circuit 3 detects that the input current detected by the current detector CT is a current value (overcurrent) larger than a predetermined current value, the command input prevention circuit 4 instantaneously informs the drive signal generation circuit 5 Blocking the input of the current control signal and the instantaneous voltage control signal. Then, since the switching elements T1 to T6 constituting the first to third switch groups SW1 to SW3 of the power conversion circuit 1 are turned off, an overcurrent flows through these switching elements T1 to T6, and the switching elements are destroyed. Can be prevented.

When the command input blocking circuit 4 blocks the input of the instantaneous current control signal and the instantaneous voltage control signal to the drive signal generation circuit 5, the switching element T1 of the power conversion circuit 1
Then, T6 becomes non-conductive, and the overcurrent sharply decreases. Therefore, the overcurrent detection circuit 3 does not detect the overcurrent, and the command input prevention circuit 4 allows the drive signal generation circuit 5 to input the instantaneous current control signal and the instantaneous voltage control signal. As a result, the power conversion circuit 1 starts the conversion operation again, and if the phase difference between the input AC voltage and the output AC voltage is still large at that time, an overcurrent flows again,
This overcurrent is detected by the overcurrent detection circuit 3, and the command input blocking circuit 4 operates as described above, so that the power conversion circuit 1 becomes inactive. Thereafter, this operation is repeated until the phase difference between the input AC voltage and the output AC voltage decreases. When the state in which the overcurrent flows continues, the low-speed cutoff circuit 2 enters the cutoff state, and completely shuts off the overcurrent. Until the shutoff circuit 2 enters the cutoff state, the overcurrent is intermittently prevented by the blocking operation of the command input blocking circuit 4, so that the power conversion circuit 1 is used until the cutoff circuit 2 enters the cutoff state. It is possible to prevent the switching elements T1 to T6 from being destroyed.

FIG. 3A shows the operation waveform of the embodiment of FIG. 1, in which the frequency of the input AC voltage is 60H.
It is a simulation waveform of input / output current and input / output voltage when changing from z to 70 Hz. In FIG. 3A, the upper diagram shows the waveforms of the input current, the input voltage, and the DC voltage appearing across the capacitor C2, and the lower diagram shows the waveforms of the output current and the output voltage. The frequency of the input voltage was changed from 60 Hz at 0 to 100 ms in the above figure to 100
In 200 ms, the frequency is changed to 70 Hz. At this time, shortly after the input current was switched to 70 Hz, the current 1
The 0A peak gradually increases, but when it reaches the 20A peak, it is determined that an overcurrent has occurred, and the current is suppressed while oscillating to 20A. In the meantime, the DC voltage, which had been around 175 V before, increased, and the scale is over in this figure, but thereafter, the cutoff circuit 2 worked to recover by 200 ms. The output during this period is as shown in the lower diagram of FIG. 3 (A), and there is no significant change except for the influence of the oscillation observed in the input current on the output voltage waveform.

FIG. 3B shows a waveform when the command input blocking circuit 4 is not inserted. Similarly, the upper diagram is the diagram on the input side, and the input current is shortly after 100 ms when it is switched to 70 Hz, and the 10 A peak up to that time gradually increases. In the example, the overcurrent of the scale over continues intermittently until the sixth cycle.

The overcurrent of the input current due to the phase shift between the input and the output degrades the performance of the switching elements T1 to T6 of the switch groups SW1 to SW3, and in some cases, burns the switching elements.

FIG. 4 is a circuit diagram showing a configuration of another embodiment of the power converter of the present invention. In the embodiment shown in FIG. 1, the command input blocking circuit 4 is provided on the input side of the drive signal generation circuit 5, but in this embodiment, the overcurrent detection circuit 3 is provided on the output side of the drive signal generation circuit 5. 1 is different from the embodiment of FIG. 1 in that an output blocking circuit 14 for preventing the drive signal from being output from the drive signal generating circuit 5 is provided during the detection of the flow of the current. Other points are the same as those of the embodiment of FIG. Output blocking circuit 1 used in this embodiment
4 can also be realized by the same configuration as the command input blocking circuit 4 composed of the AND circuit shown in FIG.

In the above description, the configuration of the control system of the power conversion circuit 1 has been described using an analog circuit. However, it is possible to realize the technical idea of the present invention by using a digital circuit. Including the configuration of. It is well known that the multiplication circuit, the subtraction circuit, the comparator, the phase inversion circuit, the effective value calculation circuit, and the like described above can be realized by a digital circuit.

Although a sawtooth signal is used as a modulation signal and a gate signal having a PWM waveform has been described above as an example, the present invention is not limited to this.

According to each of the above embodiments, an overcurrent of an input current due to a phase shift between an input and an output in a three-arm power converter is detected by an overcurrent detection circuit 3 and a drive signal generation circuit 5. The switching circuit, which has a slower response speed than a semiconductor switching element, is used for the shutoff circuit 2 for blocking with the command input blocking circuit 4 or the output blocking circuit 14 inserted at the preceding stage or the subsequent stage and for blocking the AC power supply. Therefore, there is an advantage that a compact power converter can be provided.

[0028]

According to the present invention, in a power conversion device using a so-called three-arm type power conversion circuit, as a cut-off circuit for preventing an overcurrent from flowing into the input side due to a phase shift between an input voltage and an output voltage. Even when the price of the power conversion device is reduced by using a switching unit having a low response speed, the power conversion circuit can be protected from overcurrent.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an example of an embodiment of a power conversion device of the present invention.

FIG. 2 is a circuit diagram showing an example of a configuration of a command input blocking circuit.

FIG. 3A is a waveform of current and voltage of input and output in the present invention, and FIG. 3B is a waveform when a command input blocking circuit is not inserted.

FIG. 4 is a circuit diagram showing a configuration of another embodiment of the power converter of the present invention.

FIG. 5 is a circuit diagram showing an example of a cutoff circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power conversion circuit 2 Interruption circuit 3 Overcurrent detection circuit 4 Command input prevention circuit 5 Drive signal generation circuit 6 Instantaneous current control system 7 Instantaneous voltage control system 8 DC voltage control system 9 RMS voltage control system 10 PLL circuit 11 Effective value calculation Circuit 14 Output blocking circuit a, b AC power input terminals BA batteries c, d Output terminals C1 to C3 Capacitor CL1 First connection circuit CL2 Second connection circuit CT Current detector D1 to D7 Diode L1, L2 Reactor SW1 to SW3 Switch group T1 to T6 Switching element

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroshi Sakaba F-term (reference) 5H006 CA01 CB01 CC01 CC02 CC08 DB01 DC02 DC05 FA02 5H007 CA01 CB02 1-15-1, Kita-Otsuka, Toshima-ku, Tokyo CB05 CC01 CC03 CC12 DA06 DB01 DC02 DC05 EA04 FA03 FA12 FA17 FA19

Claims (7)

[Claims] A first switch group configured by serially connecting a plurality of switching circuits each including a switching element capable of controlling conduction in one direction and a diode connected in antiparallel to the switching element; A second and third switch group configured in the same manner as the first switch group, a power conversion circuit in which a capacitor is connected in parallel, and an intermediate point of the first switch group and an AC power supply. An instantaneous current control system that outputs an instantaneous current control signal based on a DC voltage command value, and an instantaneous voltage control signal that outputs an instantaneous voltage control signal based on the output voltage command value A voltage control system, and a plurality of the switching elements constituting the first to third switch groups of the power conversion circuit by using the instantaneous current control signal and the instantaneous voltage control signal as inputs. A drive signal generation circuit that provides a drive signal at a predetermined timing to cause the power conversion circuit to perform a converter operation and an inverter operation, and is connected between one end of the two input terminals of the AC power supply and the reactor. A shut-off circuit that shuts off when an overcurrent flows from the AC power supply and blocks the application of the AC voltage from the AC power supply, wherein the shut-off circuit has a slower response speed than a semiconductor switching element. A power detector configured to measure an alternating current flowing into an intermediate point of the first switch group, wherein the overcurrent flows based on an output of the current detector. An overcurrent detection circuit for detecting that the overcurrent is flowing. Power converter, wherein the instantaneous current control signal and the instantaneous voltage control signal further comprises a command input blocking circuit to prevent the input to the circuit. 2. The drive signal generation circuit receives the instantaneous current control signal and the instantaneous voltage control signal as input and supplies a predetermined signal to a plurality of switching elements constituting the first to third switch groups of the power conversion circuit. Giving a drive signal at the timing of, causing the power conversion circuit to perform a converter operation for charging the capacitor by controlling conduction of the plurality of switching elements constituting the first switch group, Controlling the conduction of a plurality of the switching elements constituting a third switch group to cause the power conversion circuit to perform an inverter operation of converting a DC voltage appearing at both ends of the capacitor into an AC voltage; The AC voltage converted from the intermediate point of the switch group and the intermediate point of the third switch group is output. The power conversion device according to claim 1, wherein 3. The drive signal generation circuit receives the instantaneous current control signal and the instantaneous voltage control signal as input and supplies a predetermined signal to a plurality of switching elements constituting the first to third switch groups of the power conversion circuit. Giving a drive signal at the timing of, causing the power conversion circuit to perform a converter operation of charging the capacitor by controlling conduction of the plurality of switching elements constituting the first and second switch groups, Controlling the conduction of the plurality of switching elements constituting the second and third switch groups to cause the power conversion circuit to perform an inverter operation of converting a DC voltage appearing at both ends of the capacitor into an AC voltage, The AC voltage converted from the intermediate point of the second switch group and the intermediate point of the third switch group is output. The power converter according to claim 1, wherein the power converter is configured as follows. 4. A first switch group comprising two switching circuits connected in series, each including a switching element capable of controlling conduction in one direction and a diode connected in anti-parallel to the switching element; A second and a third switch group configured similarly to the first switch group;
A power conversion circuit in which a capacitor is connected in parallel; a first reactor disposed between an intermediate point of the first switch group and one end of two input terminals of an AC power supply; A first connection circuit that electrically connects an intermediate point of the switch group to the other end of the two input terminals and one end of the two AC output terminals of the AC power supply; and an intermediate point of the third switch group. A second connection circuit connected to the other ends of the two AC output terminals via the second reactor, an instantaneous current control system for outputting an instantaneous current control signal based on the DC voltage command value, and an output voltage command value An instantaneous voltage control system that outputs an instantaneous voltage control signal, and the plurality of switching elements that form the first to third switch groups of the power conversion circuit by using the instantaneous current control signal and the instantaneous voltage control signal as inputs. Predetermined time Providing a drive signal to control the conduction of the plurality of switching elements constituting the first and second switch groups, thereby causing the power conversion circuit to perform a converter operation of charging the capacitor, 2nd and 3rd
Controlling the conduction of a plurality of the switching elements constituting the switch group, causing the power conversion circuit to perform an inverter operation of converting a DC voltage appearing at both ends of the capacitor into an AC voltage, and the second switch group A drive signal generating circuit for outputting the AC voltage converted from the intermediate point of the third switch group and the intermediate point of the third switch group, between one end of the two input terminals of the AC power supply and the first reactor When an overcurrent occurs due to a phase difference generated between the AC voltage from the AC power supply and the AC voltage converted by the power conversion circuit, the AC power is cut off and the AC A shutoff circuit for preventing application of the AC voltage from a power supply, wherein the shutoff circuit uses a switching unit having a slow response speed as compared with a semiconductor switching element. A current detector for measuring an alternating current flowing into an intermediate point of the first switch group, and detecting that an overcurrent has flowed based on an output of the current detector. An overcurrent detection circuit, and preventing the instantaneous current control signal and the instantaneous voltage control signal from being input to the drive signal generation circuit while the overcurrent detection circuit is detecting that the overcurrent is flowing. And a command input blocking circuit. 5. A first switch group comprising a plurality of switching circuits connected in series, each including a switching element capable of controlling conduction in one direction and a diode connected in anti-parallel to the switching element; A second and third switch group configured in the same manner as the first switch group, a power conversion circuit in which a capacitor is connected in parallel, and an intermediate point of the first switch group and an AC power supply. An instantaneous current control system that outputs an instantaneous current control signal based on a DC voltage command value, and an instantaneous voltage control signal that outputs an instantaneous voltage control signal based on an output voltage command value A voltage control system, and a plurality of the switching elements constituting the first to third switch groups of the power conversion circuit by using the instantaneous current control signal and the instantaneous voltage control signal as inputs. A drive signal generation circuit that provides a drive signal at a predetermined timing to cause the power conversion circuit to perform a converter operation and an inverter operation, and is connected between one end of the two input terminals of the AC power supply and the reactor. A shut-off circuit that shuts off when an overcurrent flows from the AC power supply and blocks the application of the AC voltage from the AC power supply, wherein the shut-off circuit has a slower response speed than a semiconductor switching element. A power detector configured to measure an alternating current flowing into an intermediate point of the first switch group, wherein the overcurrent flows based on an output of the current detector. An overcurrent detection circuit for detecting that the overcurrent is flowing. Power conversion apparatus characterized by further comprising an output blocking circuit for blocking the circuit of the drive signal is output. 6. A first switch group comprising two switching circuits each including a switching element capable of controlling conduction in one direction and a diode connected in anti-parallel to the switching element and connected in series; A second and a third switch group configured similarly to the first switch group;
A power conversion circuit in which a capacitor is connected in parallel; a first reactor disposed between an intermediate point of the first switch group and one end of two input terminals of an AC power supply; A first connection circuit that electrically connects an intermediate point of the switch group to the other end of the two input terminals and one end of the two AC output terminals of the AC power supply; and an intermediate point of the third switch group. A second connection circuit connected to the other ends of the two AC output terminals via a second reactor, an instantaneous current control system that outputs an instantaneous current control signal based on a DC voltage command value, and an output voltage command value. An instantaneous voltage control system that outputs an instantaneous voltage control signal based on the instantaneous current control signal and the instantaneous voltage control signal, and a plurality of the switching units that constitute the first to third switch groups of the power conversion circuit. The specified element Providing a drive signal in the timing to control the conduction of a plurality of the switching elements constituting the first and second switch groups, thereby causing the power conversion circuit to perform a converter operation of charging the capacitor, 2nd and 3rd
Controlling the conduction of a plurality of the switching elements constituting the switch group, causing the power conversion circuit to perform an inverter operation of converting a DC voltage appearing at both ends of the capacitor into an AC voltage, and the second switch group A drive signal generating circuit for outputting the AC voltage converted from the intermediate point of the third switch group and the intermediate point of the third switch group, between one end of the two input terminals of the AC power supply and the first reactor When an overcurrent occurs due to a phase difference generated between the AC voltage from the AC power supply and the AC voltage converted by the power conversion circuit, the AC power is cut off and the AC A shutoff circuit for preventing application of the AC voltage from a power supply, wherein the shutoff circuit uses a switching unit having a slow response speed as compared with a semiconductor switching element. A current detector for measuring an alternating current flowing into an intermediate point of the first switch group, and detecting that an overcurrent has flowed based on an output of the current detector. An overcurrent detection circuit; and an output blocking circuit that prevents the drive signal from being output from the drive signal generation circuit while the overcurrent detection circuit detects that the overcurrent is flowing. A power converter, comprising: 7. The power converter according to claim 1, wherein said switching means of said cutoff circuit is an electromagnetic relay.