JP7325673B2 - Power converter and air conditioner - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to a power conversion device that converts power from an AC power supply into an arbitrary frequency and an arbitrary voltage and supplies it to a load such as an electric motor, and an air conditioner provided with the same.

A power converter is known that rectifies a commercial AC power source into a DC power source with a rectifier circuit, converts it into an arbitrary frequency and voltage with an inverter circuit, and supplies it to a load such as an electric motor. A smoothing capacitor is arranged between the rectifier circuit and the inverter circuit for the purpose of smoothing voltage pulsation due to the frequency of the AC power supply or absorbing surge voltage due to switching of the inverter.

In general, the DC voltage between the rectifier circuit and the inverter circuit, that is, the voltage across the smoothing capacitor is called a bus voltage or a DC link voltage. In conventional power converters, it is known that an overvoltage protection circuit is provided in preparation for a case where the bus voltage rises due to an increase in the voltage of the AC power supply or the stoppage of the output of the inverter circuit while the motor is rotating. (See Patent Document 1, for example).

The overvoltage protection circuit provided in the power converter disclosed in Patent Document 1 is composed of a regenerative resistor and a semiconductor element connected in series with each other. Also, the overvoltage protection circuit is connected in parallel with the smoothing capacitor. In the power conversion device described in Patent Document 1, when the bus voltage increases, a current is passed through the regenerative resistor of the overvoltage protection circuit to consume power, thereby protecting the elements that make up the inverter circuit from overvoltage. is proposed.

However, in the circuit configuration of the power converter disclosed in Patent Document 1, when the power is turned on, an inrush current that is several times higher than that in a steady state flows through the smoothing capacitor. When an inrush current flows, in some cases, malfunctions such as failure of elements of internal circuits constituting the power conversion device or disconnection of wires occur, thereby reducing the reliability of the power conversion device.

Therefore, as a method of suppressing such inrush current, a method of utilizing an inrush prevention resistor is known (see, for example, Patent Document 2).

In the power conversion device described in Patent Document 2, a high-frequency reactor and a switching element are connected in series between output terminals of a full-wave rectifier circuit, and a diode for a reverse current element is provided at a connection point between the reactor and the switching element. It is connected. These reactors, switching elements, and diodes constitute a boost chopper circuit. Also, the first switch and the low-frequency reactor, which are connected in series, are connected in parallel to the reactor and the diode of the boost chopper circuit. A second switch and a smoothing capacitor are connected in series between the output terminals of the boost chopper circuit. A rush prevention resistor is connected in parallel to the second switch. As described above, Patent Document 2 proposes a configuration in which a relay configured by a first switch and a second switch is connected in series to a smoothing capacitor through which a small amount of current flows, thereby reducing the size of the relay. there is

JP 2020-124104 A Japanese Unexamined Patent Application Publication No. 2009-60705

However, in the circuit configuration of Patent Document 1, when the circuit configuration of Patent Document 1 and the circuit configuration of Patent Document 2 are simply combined in order to suppress the inrush current, the regeneration circuit of Patent Document 1 and the circuit configuration of Patent Document 1 2 circuits for rush prevention are prepared separately. Therefore, there is a problem that the circuit configuration becomes complicated and the cost of the device increases.

The present disclosure has been made to solve such problems, and a power conversion device that can protect each element provided in the power conversion device from both overvoltage and inrush current without increasing the cost of parts, and It aims at obtaining an air conditioner provided with it.

A power converter according to the present disclosure includes a rectifier circuit that rectifies an AC voltage supplied from an AC power supply and converts it to a DC voltage, an inverter circuit that converts the DC voltage to an AC voltage and supplies it to a load, and the rectification a bus voltage control circuit connected to a bus between the output end of the circuit and the input end of the inverter circuit for controlling a bus voltage of the bus; The bus voltage control circuit includes a resistor having one end connected to the positive bus, a first diode having an anode connected to the other end of the resistor, and a first diode having an anode connected to the other end of the resistor. a capacitor connected to the cathode of the first diode and having the other end connected to the negative bus; a relay connected in parallel to the resistor and the first diode; and a semiconductor switch connected in parallel to the inverter circuit, the power conversion device comprising: a current detection unit for detecting a current value flowing from the inverter circuit toward the load and outputting current information; a bus voltage control unit that controls conduction and opening of the relay based on the current information that has been obtained, and the bus voltage control unit controls the inverter circuit based on the current information output from the current detection unit. It is determined whether the inverter circuit is in operation or not, and when the inverter circuit is in operation, the relay is made conductive, and when the inverter circuit is not in operation, the relay is opened.
Further, a power converter according to the present disclosure includes a rectifier circuit that rectifies an AC voltage supplied from an AC power supply and converts it into a DC voltage, an inverter circuit that converts the DC voltage into an AC voltage and supplies it to a load, a bus voltage control circuit connected to a bus between the output terminal of the rectifier circuit and the input terminal of the inverter circuit for controlling a bus voltage of the bus, wherein the bus is connected to a positive bus on a high potential side; , and a negative bus on the low potential side, the bus voltage control circuit comprising: a resistor having one end connected to the positive bus; a first diode having an anode connected to the other end of the resistor; A capacitor having one end connected to the cathode of the first diode and the other end connected to the negative bus, a relay connected in parallel to the resistor and the first diode, the first diode and the a semiconductor switch connected in parallel to the capacitor, disposed between the resistor and the semiconductor switch, and connected in series with the semiconductor switch to assist regeneration when the resistor acts as a regeneration resistor. It has a first auxiliary resistor acting as a resistor.
Further, a power converter according to the present disclosure includes a rectifier circuit that rectifies an AC voltage supplied from an AC power supply and converts it into a DC voltage, an inverter circuit that converts the DC voltage into an AC voltage and supplies it to a load, a bus voltage control circuit connected to a bus between the output terminal of the rectifier circuit and the input terminal of the inverter circuit for controlling a bus voltage of the bus, wherein the bus is connected to a positive bus on a high potential side; , and a negative bus on the low potential side, the bus voltage control circuit comprising: a resistor having one end connected to the positive bus; a first diode having an anode connected to the other end of the resistor; A capacitor having one end connected to the cathode of the first diode and the other end connected to the negative bus, a relay connected in parallel to the resistor and the first diode, the first diode and the a semiconductor switch connected in parallel with a capacitor, connected in series between the first diode and the capacitor, and connected in parallel with the relay, the resistor acting as an inrush prevention resistor. It is provided with a second auxiliary resistor that acts as an inrush prevention auxiliary resistance when the

The air conditioner according to the present disclosure includes the power conversion device, a compressor driven by the electric motor that is the load of the power conversion device, a condenser that condenses refrigerant discharged from the compressor, and a condensed a refrigeration cycle device including an expansion valve that decompresses the refrigerant; an evaporator that evaporates the decompressed refrigerant; and a blower that blows air to at least one of the condenser and the evaporator of the refrigeration cycle device. It is prepared.

According to the power conversion device and the air conditioner according to the present disclosure, one resistor can play two roles of regenerative resistance and inrush prevention resistance by the operation of the relay and the semiconductor switch. As a result, each element provided in the power converter can be protected from both overvoltage and inrush current without increasing the cost of parts.

1 is a circuit block diagram showing an example of a configuration of a power conversion device 100 according to Embodiment 1; FIG. 4 is a flow chart showing a bus voltage control loop executed by a bus voltage control unit 7 of the power converter 100 according to Embodiment 1. FIG. FIG. 4 is a circuit block diagram showing an example of a configuration of a power conversion device 100A according to Embodiment 2; FIG. 11 is a circuit block diagram showing an example of a configuration of a power conversion device 100B according to Embodiment 3; FIG. 11 is a circuit block diagram showing an example of a configuration of a power conversion device 100C according to Embodiment 4; FIG. 11 is a configuration diagram showing an example of the configuration of an air conditioner 400 according to Embodiment 5;

Hereinafter, embodiments of a power conversion device and an air conditioner according to the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present disclosure. In addition, the present disclosure includes all combinations of configurations that can be combined among configurations shown in the following embodiments and modifications thereof. Also, in each figure, the same reference numerals denote the same or corresponding parts, which are common throughout the specification. In each drawing, the relative dimensional relationship, shape, etc. of each component may differ from the actual one.

Embodiment 1.
The power conversion apparatus according to Embodiment 1 converts the power of an AC power supply into an arbitrary frequency and an arbitrary voltage and supplies the electric power to a load such as an electric motor to drive the load. The power converter according to Embodiment 1 has a function of preventing rush current and a function of protecting against regenerative voltage.

[Configuration of power converter 100]
FIG. 1 is a circuit block diagram showing an example of the configuration of a power converter 100 according to Embodiment 1. As shown in FIG. As shown in FIG. 1, an AC power supply 1 as a power source and an electric motor 2 as a load are connected to a power conversion device 100 . For example, the AC power supply 1 is a three-phase commercial power supply having, for example, U phase, V phase, and W phase. The electric motor 2 is, for example, a three-phase permanent magnet synchronous motor having U-phase, V-phase, and W-phase.

The power converter 100 includes a rectifier circuit 3, a bus voltage control circuit 4, an inverter circuit 5, and a current detector 6, as shown in FIG. The power converter 100 also includes a bus voltage controller 7 and an inverter circuit controller 8 . These constituent elements are described below.

The rectifier circuit 3 is connected to the AC power supply 1 . The rectifier circuit 3 rectifies the AC voltage supplied from the AC power supply 1 and converts it into a DC voltage. The DC voltage rectified by the rectifier circuit 3 contains low-order harmonic components due to the voltage frequency of the AC power supply 1 . The low-order harmonic component is also called a pulsation component. The low-order harmonic component pulsates at a frequency six times the voltage frequency of the AC power supply 1, for example. The rectifier circuit 3 is composed of, for example, a full bridge circuit including six rectifying diodes 30 . Specifically, two rectifying diodes 30 are connected in series to form a series body. By preparing three series bodies and connecting the three series bodies in parallel, a full bridge circuit is formed. A switching element such as a transistor may be used in the rectifier circuit 3 instead of the rectifier diode 30 . The output terminal of the rectifier circuit 3 is connected to the bus of the power converter 100 (see symbols 11 and 12). The bus of the power conversion device 100 includes a positive bus 11 and a negative bus 12 . The positive bus line 11 is the bus line on the high potential side, and the negative bus line 12 is the bus line on the low potential side. Hereinafter, the positive bus 11 and the negative bus 12 may be collectively referred to as the bus 11 and 12 .

The bus voltage control circuit 4 is connected to the bus between the output end of the rectifier circuit 3 and the input end of the inverter circuit 5 . That is, the bus voltage control circuit 4 is arranged between the output terminal of the rectifier circuit 3 and the input terminal of the inverter circuit 5 and is connected to the positive bus line 11 and the negative bus line 12 . A bus voltage control circuit 4 controls bus voltages of the buses 11 and 12 . The bus voltage is the potential difference between the positive bus 11 on the high potential side and the negative bus 12 on the low potential side. The bus voltage control circuit 4 includes a resistor 41 , a first diode 42 , a capacitor 43 , a relay 44 and a semiconductor switch 45 .

As shown in FIG. 1, a resistor 41, a first diode 42 whose anode is on the high potential side, and a capacitor 43 are connected in series in this order from the high potential side to the low potential side. That is, one end of the resistor 41 is connected to the positive bus 11 and the other end of the resistor 41 is connected to the anode of the first diode 42. The cathode of the first diode 42 is connected to the positive electrode of the capacitor 43. It is A negative electrode of the capacitor 43 is connected to the negative bus 12 . Hereinafter, the connection point between the resistor 41 and the positive bus line 11 is called a connection point C1, and the connection point between the negative electrode of the capacitor 43 and the negative bus line 12 is called a connection point C2.

The capacitor 43 is composed of, for example, an electrolytic capacitor having a large electrostatic capacity and having an effect of smoothing the waveform of the low-order harmonic component of the DC voltage rectified by the rectifier circuit 3 . However, the capacitor 43 is not limited to this case, and may be one that does not have a smoothing effect. That is, the capacitor 43 may be composed of a capacitor that has a small capacitance and does not smooth the waveform of the low-order harmonic component of the DC voltage rectified by the rectifier circuit 3 . As the non-smoothing small-capacity capacitor, for example, a film capacitor or a ceramic capacitor is used. If the capacitor 43 is made of a film capacitor or a ceramic capacitor, the fluctuation of the voltage that can be absorbed by the capacitor 43 is reduced, so the need for the bus voltage control section 7 of the first embodiment is increased, and the effect of the control section 7 is increased. growing.

A relay 44 is connected in parallel with the resistor 41 and the first diode 42 . That is, the resistor 41 and the first diode 42 are connected in series to form a series body, and the relay 44 is connected in parallel with the series body. Relay 44 is, for example, a mechanical relay. The relay 44 conducts and opens in accordance with a protection switch signal output by the bus voltage controller 7, which will be described later. When the relay 44 is conducting, current flows through the relay 44 and current does not flow through the resistor 41 and the first diode 42 . On the other hand, when the relay 44 is open, current does not flow through the relay 44 and current flows through the resistor 41 and the first diode 42 .

A semiconductor switch 45 is connected in parallel with the first diode 42 and the capacitor 43 . That is, the first diode 42 and the capacitor 43 are connected in series to form a series body, and the semiconductor switch 45 is connected in parallel to the series body. The semiconductor switch 45 is, for example, a switching element such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). The semiconductor switch 45 performs an ON operation and an OFF operation according to a protection switch signal output by the bus voltage controller 7, which will be described later. When the semiconductor switch 45 is on, current flows through the semiconductor switch 45 and current does not flow through the first diode 42 and the capacitor 43 . On the other hand, when the semiconductor switch 45 is turned off, current does not flow through the semiconductor switch 45 and current flows toward the capacitor 43 via the relay 44 or via the resistor 41 and the first diode 42 .

The resistor 41 acts as a regenerative resistor that consumes regenerated electric power regenerated from the electric motor 2 when the relay 44 is open and the semiconductor switch 45 is on. Also, the resistor 41 acts as an inrush prevention resistor that consumes an inrush current generated when the AC power supply 1 is turned on when the relay 44 is open and the semiconductor switch 45 is off. The resistance value of the resistor 41 is appropriately determined according to the values of the regenerated electric power and the rush current.

The inverter circuit 5 is connected to the positive bus line 11 and the negative bus line 12, which are the output terminals of the bus voltage control circuit 4, as shown in FIG. The inverter circuit 5 converts the DC voltage rectified by the rectifier circuit 3 into an AC voltage and outputs the AC voltage to the electric motor 2 . Although the electric motor 2 is described here as an example of the load of the power conversion device 100, the load of the power conversion device 100 may be another device. The inverter circuit 5 is composed of, for example, a full bridge circuit with six IGBTs. Specifically, two IGBTs 50 are connected in series to form a series body. A full bridge circuit is formed by preparing three series bodies and connecting the three series bodies in parallel. In the series body, the IGBTs 50 connected to the positive bus 11 are hereinafter referred to as upper IGBTs 50 , and the IGBTs 50 connected to the negative bus 12 are referred to as lower IGBTs 50 . A freewheeling diode 51 is connected in anti-parallel to each IBGT 50 . Each IGBT 50 performs ON/OFF operations independently of each other according to a drive switch signal output by an inverter circuit control section 8, which will be described later. The on/off operation converts a DC voltage into an AC voltage. Note that the inverter circuit 5 may use other switching elements such as MOSFETs instead of the IGBTs 50 .

The current detection unit 6 is provided in wiring that connects the inverter circuit 5 and the electric motor 2 . The current detection unit 6 detects the current value of the current flowing from the inverter circuit 5 to the electric motor 2 and outputs current information. If the electric motor 2 is a three-phase motor, the current information includes values of phase currents of the three phases of U-phase, V-phase, and W-phase. The current detection unit 6 is, for example, a current sensor using a current transformer for instrument called a CT (Current Transformer). Note that the current detection unit 6 may be composed of another current sensor. Specifically, the current detection unit 6 may be configured by a one-shunt current detection type current sensor using a shunt resistor provided on the negative bus line 12 on the low potential side of the power converter 100 . Alternatively, the current detection unit 6 may be composed of a three-shunt current detection type current sensor using a shunt resistor connected in series to the IGBT 50 on the lower side of the inverter circuit 5 .

An inverter circuit operation mode output from an inverter circuit control unit 8 (to be described later) is input to the bus voltage control unit 7 . The inverter circuit operation mode is a signal indicating whether the inverter circuit 5 is in operation. For example, when the inverter circuit 5 is in operation, the value of the inverter circuit operation mode is "1", and when the inverter circuit 5 is not in operation, the value of the inverter circuit operation mode is "0". Bus voltage control unit 7 detects the bus voltage and outputs protection switch signals for operating relay 44 and semiconductor switch 45 based on the detected bus voltage and the inverter circuit operation mode. The operation of the bus voltage control unit 7 will be described later using the flowchart of FIG. Also, the bus voltage controller 7 outputs the detected bus voltage to the inverter circuit controller 8 . As is generally known, bus voltage can be detected by observing a value obtained by dividing the bus voltage by resistors.

Operation commands such as a speed command and a torque command are input to the inverter circuit control unit 8 from the outside. The inverter circuit control unit 8 outputs a drive switch signal to the inverter circuit 5 based on the operation command. As one method of controlling the speed and torque of the electric motor 2, for example, vector control is known, which feedback-controls the current flowing through the electric motor 2 using a dq coordinate system. In the case of vector control, the inverter circuit control unit 8 performs vector control using a drive command, current information obtained from the current detection unit 6, and bus voltage information obtained from the bus voltage control unit 7. The inverter circuit control unit 8 is not limited to vector control, and other methods may be used. That is, the inverter circuit control unit 8 may use V/f constant control that outputs a voltage proportional to the operating frequency of the electric motor 2 or direct torque control that controls the magnetic flux and torque of the electric motor 2 .

Further, the inverter circuit control unit 8 generates an inverter circuit operation mode indicating whether the inverter circuit 5 is operating or not, based on the current information from the current detection unit 6 . The inverter circuit operation mode is a signal indicating whether or not the inverter circuit 5 operates the drive switch to drive the electric motor 2 . The inverter circuit control unit 8 outputs the generated inverter circuit operation mode to the bus voltage control unit 7 .

Here, hardware configurations of the bus voltage controller 7 and the inverter circuit controller 8 will be described. Both the bus voltage control unit 7 and the inverter circuit control unit 8 are configured by processing circuits. The processing circuitry consists of dedicated hardware or a processor. Dedicated hardware is, for example, ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array). The processor executes programs stored in memory. The bus voltage controller 7 and the inverter circuit controller 8 each have a memory. Memory is non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), or disk such as magnetic disk, flexible disk, or optical disk. be.

[Operation of power converter 100]
Next, the overall operation of the power converter 100 will be briefly described.

<Normal operation>
The operation of the power converter 100 shown in FIG. 1 during normal operation will be described. During normal operation, in the bus voltage control circuit 4, the relay 44 is conductive and the semiconductor switch 45 is off. In the power conversion device 100, the rectifier circuit 3 rectifies an AC voltage input from the AC power supply 1 and converts it into a DC voltage. During normal operation, the bus voltage is below a preset reference value. That is, when some kind of abnormality occurs in the power conversion device 100, the bus voltage becomes equal to or higher than the reference value. The reference value is determined in advance in consideration of the withstand voltage of each element of the power converter 100 and the operation speed of the relay 44 and the semiconductor switch 45, and is stored in the memory of the bus voltage controller 7.

The bus voltage controller 7 detects a bus voltage and determines whether or not the bus voltage is lower than a reference value. The bus voltage control unit 7 also determines whether the inverter circuit 5 is in operation based on the inverter circuit operation mode input from the inverter circuit control unit 8 . As a result of these determinations, if the bus voltage is lower than the reference value and the inverter circuit 5 is operating, the bus voltage control unit 7 keeps the relay 44 conducting and the semiconductor switch 45 off. . As a result, the path between the positive bus line 11 and the negative bus line 12 is formed by only the relay 44 and the capacitor 43 . That is, no current flows through the resistor 41 and the first diode 42 .

The inverter circuit control unit 8 outputs a drive switch signal to the inverter circuit 5 based on the operation command input from the outside and the current information output from the current detection unit 6 . The inverter circuit 5 turns the IGBTs 50 on and off according to the drive switch signal output by the inverter circuit control unit 8, thereby converting the DC voltage rectified by the rectifier circuit 3 into a desired frequency and a desired voltage according to the operation command. It is converted into AC voltage and output to the electric motor 2 .

Thus, during normal operation of the power conversion device 100 , the path between the positive bus 11 and the negative bus 12 is only the relay 44 and the capacitor 43 . Therefore, since no current flows through the resistor 41 , power can be supplied to the electric motor 2 without causing loss in the resistor 41 .

<When power is turned on (inrush current prevention operation)>
The operation of the power converter 100 shown in FIG. 1 when the power is turned on will be described. Before the power converter 100 operates, that is, when no voltage is input from the AC power supply 1 to the power converter 100, the bus voltage control unit 7 detects the bus voltage, and the bus voltage is smaller than the reference value. Determine whether or not At this time, since no voltage is input from the AC power supply 1 to the power converter 100, the bus voltage is smaller than the reference value.

The bus voltage control unit 7 also determines whether the inverter circuit 5 is in operation based on the inverter circuit operation mode input from the inverter circuit control unit 8 . At this time, the inverter circuit 5 is not in operation.

The bus voltage controller 7 determines that the bus voltage is lower than the reference value and that the inverter circuit 5 is not in operation, and outputs a protection switch signal to open the relay 44 and turn off the semiconductor switch 45 . As a result, a path of the resistor 41 , the first diode 42 and the capacitor 43 is formed between the positive bus 11 and the negative bus 12 . In this state, when the voltage from the AC power supply 1 is input to the power conversion device 100, an inrush current several times higher than that in the steady state flows toward the capacitor 43. FIG. However, at this time, the inrush current flows through the resistor 41 toward the capacitor 43, so the inrush current is consumed by the resistor 41, and the inrush current to the capacitor 43 can be prevented. At this time, the resistor 41 acts as an inrush prevention resistor for preventing an inrush current when the power is turned on.

<When an error occurs (Protective operation from regenerative voltage)>
An operation when an abnormality occurs in the power converter 100 shown in FIG. 1 will be described. During the operation of the power conversion device 100, for some reason, for example, the inverter circuit control unit 8 detects an abnormality and turns off all the drive switch signals, and a large amount of power is supplied from the electric motor 2 to the power conversion device 100. is assumed to be regenerated. In this case, the bus voltage suddenly rises above the reference value.

The bus voltage control unit 7 detects the bus voltage, and outputs a protection switch signal to open the relay 44 and turn on the semiconductor switch 45 when determining that the bus voltage is equal to or higher than the reference value. As a result, the path between the positive bus line 11 and the negative bus line 12 is formed only by the resistor 41 and the semiconductor switch 45 . Therefore, the regenerated electric power from the electric motor 2 is consumed by the resistor 41, and the bus voltage can be lowered to the level of the AC power supply 1 voltage. At this time, the resistor 41 acts as a regenerative resistor that protects each element of the power conversion device 100 from regenerative power.

Thus, in Embodiment 1, the resistor 41 has two functions, ie, a function as an inrush prevention resistor and a function as a regenerative resistor.

[Operation of Bus Voltage Control Unit 7]
Next, operation of the bus voltage controller 7 will be described. FIG. 2 is a flow chart showing a bus voltage control loop executed by the bus voltage control unit 7 of the power converter 100 according to the first embodiment. The bus voltage control loop is repeatedly executed at a predetermined cycle.

As shown in FIG. 2, in the bus voltage control loop, the bus voltage controller 7 first determines whether or not the bus voltage is lower than a reference value in step S1. If the bus voltage is lower than the reference value (Yes), go to step S2. On the other hand, when the bus voltage is equal to or higher than the reference value (No), the process proceeds to step S7.

In step S<b>2 , the bus voltage controller 7 determines whether the inverter circuit 5 is operating based on the current information from the current detector 6 . When the inverter circuit 5 is in operation (Yes), the process proceeds to step S3. On the other hand, when the inverter circuit 5 is not in operation (No), the process proceeds to step S5.

In step S3, the bus voltage controller 7 outputs a protection switch signal to turn on the relay 44, and proceeds to step S4. In step S4, the bus voltage controller 7 outputs a protection switch signal to turn off the semiconductor switch 45. FIG.

On the other hand, in step S5, the bus voltage controller 7 outputs a protection switch signal to open the relay 44, and proceeds to step S6. In step S6, the bus voltage controller 7 outputs a protection switch signal to turn off the semiconductor switch 45. FIG.

Further, in step S7, the bus voltage control unit 7 outputs a protection switch signal to open the relay 44, and proceeds to step S8. In step S8, the bus voltage controller 7 outputs a protection switch signal to turn on the semiconductor switch 45. FIG.

[Effects of Bus Voltage Control Circuit 4 and Bus Voltage Control Unit 7]
Here, effects of the bus voltage control circuit 4 and the bus voltage control section 7 will be described. When the power conversion device 100 is in normal operation, steps S1, S2, S3, and S4 in the flow chart of FIG. 2 are performed. Therefore, the path between the positive bus 11 and the negative bus 12 is only the relay 44 and the capacitor 43 . Therefore, since the resistor 41 is skipped, the power conversion device 100 can supply electric power to the electric motor 2 without generating loss in the resistor 41 .

Before the power conversion device 100 operates, ie, when no voltage is input from the AC power supply 1, steps S1, S2, S5, and S6 in the flow chart of FIG. 2 are performed. Therefore, a path of the resistor 41 , the first diode 42 and the capacitor 43 is formed between the positive bus 11 and the negative bus 12 . Therefore, when a voltage is input from the AC power supply 1 in this state, a current flows through the resistor 41, so that a rush current can be prevented from being input to the capacitor 43. FIG. At this time, the resistor 41 acts as a rush prevention resistor.

Also, if for some reason a large amount of regenerative power is input from the electric motor 2 during operation of the power converter 100 and the bus voltage rises, steps S1, S7, and S8 in the flow chart of FIG. 2 are passed. Therefore, a path of the resistor 41 and the semiconductor switch 45 is formed between the positive bus 11 and the negative bus 12 . Therefore, the regenerated power is consumed by the resistor 41 and the bus voltage can be lowered to the level of the voltage of the AC power supply 1 . At this time, the resistor 41 acts as a regenerative resistor.

As described above, in Embodiment 1, by providing the bus voltage control circuit 4 and the bus voltage control unit 7, one resistor 41 can be used as both an inrush prevention resistor and a regenerative resistor. Therefore, each element of the power conversion device 100 can be protected from both overvoltage due to regenerative power and rush current when the power is turned on without increasing the component cost of the power conversion device 100 .

Embodiment 2.
The power conversion device 100A according to the second embodiment makes it possible to change the resistance value of the rush prevention resistor and the resistance value of the regenerative resistor. FIG. 3 is a circuit block diagram showing an example of the configuration of the power converter 100A according to the second embodiment. The power converter 100A according to the second embodiment differs from the configuration of the first embodiment shown in FIG. 1 in that a bus voltage control circuit 4A is provided instead of the bus voltage control circuit 4 shown in FIG. be. In the bus voltage control circuit 4A, as shown in FIG. 3, a first auxiliary resistor 46 arranged between the resistor 41 and the semiconductor switch 45 and connected in series with the semiconductor switch 45 is added. Since other configurations are the same as those of the first embodiment, they are denoted by the same reference numerals, and descriptions thereof are omitted here.

A detailed description will be given below. In the bus voltage control circuit 4A of the power converter 100A shown in FIG. 3, the connection point between the resistor 41 and the first diode 42 is assumed to be a connection point C3. A first auxiliary resistor 46 is connected in series between the connection point C3 and the semiconductor switch 45 . The first auxiliary resistor 46 acts as a regenerative auxiliary resistor when the resistor 41 acts as a regenerative resistor.

[Operation of Bus Voltage Control Circuit 4A and Bus Voltage Control Unit 7]
The operation of the bus voltage control unit 7 is basically the same as the flowchart of FIG. 2 described above. Therefore, here, description will be made with reference to FIG.

When the power conversion device 100 is in normal operation, steps S1, S2, S3, and S4 in the flow chart of FIG. 2 are performed. Therefore, the path between the positive bus 11 and the negative bus 12 is only the relay 44 and the capacitor 43 . Therefore, since the resistor 41 is skipped, the power conversion device 100 can supply electric power to the electric motor 2 without generating loss in the resistor 41 .

Before the power conversion device 100 operates, ie, when no voltage is input from the AC power supply 1, steps S1, S2, S5, and S6 in the flow chart of FIG. 2 are performed. Therefore, a path of the resistor 41 , the first diode 42 and the capacitor 43 is formed between the positive bus 11 and the negative bus 12 . Therefore, when a voltage is input from the AC power supply 1 in this state, it passes through the resistor 41, so an inrush current can be prevented. At this time, the resistor 41 acts as a rush prevention resistor.

Also, if for some reason a large amount of regenerative power is input from the electric motor 2 during operation of the power converter 100 and the bus voltage rises, steps S1, S7, and S8 in the flow chart of FIG. 2 are passed. Therefore, a path of the resistor 41 , the first auxiliary resistor 46 and the semiconductor switch 45 is formed between the positive bus 11 and the negative bus 12 . At this time, it differs from the first embodiment in that the path includes the first auxiliary resistor 46 . In the second embodiment, the resistor 41 and the first auxiliary resistor 46 consume the regenerated electric power and lower the bus voltage to the voltage level of the AC power supply 1 . At this time, the resistor 41 and the first auxiliary resistor 46 act as regenerative resistors.

If the bus voltage control circuit 4A is configured as shown in FIG. 3, the rush prevention resistor is only the resistor 41, but the regenerative resistors are the resistor 41 and the first auxiliary resistor . Therefore, the resistance value of the regenerative resistor can be made larger than the resistance value of the rush prevention resistor by the resistance value of the first auxiliary resistor 46 . Also in the second embodiment, as in the first embodiment, the resistor 41 is used both as an inrush prevention resistor and as a regenerative resistor. Therefore, most of the regenerated power can be consumed by resistor 41 . Since the first auxiliary resistor 46 is arranged to assist the resistor 41, an inexpensive resistor with a low resistance value can be used. Therefore, the cost can be reduced more in the second embodiment than in the case of combining the patent documents 1 and 2, in which two separate circuits for rush prevention and regeneration are prepared. can.

If the resistance value of the rush prevention resistor is designed to be greater than the resistance value of the regenerative resistor, a second auxiliary resistor 49 for rush prevention may be added as indicated by the dashed line in FIG. Assuming that the connection point between the cathode of the first diode 42 and the relay 44 is a connection point C4, the second auxiliary resistor 49 is connected between the cathode of the first diode 42 and the connection point C4. That is, the second auxiliary resistor 49 is connected in series between the first diode 42 and the capacitor 43 and connected in parallel with the relay 44 . The second auxiliary resistor 49 acts as a rush prevention auxiliary resistor when the resistor 41 acts as a rush prevention resistor.

In this way, when the second auxiliary resistor 49 for rush prevention is arranged between the first diode 42 and the capacitor 43, the resistance value of the second auxiliary resistor 49 is greater than the resistance value of the regenerative resistor. The resistance value of the rush prevention resistor can be increased. Also in the second embodiment, as in the first embodiment, the resistor 41 is used both as an inrush prevention resistor and as a regenerative resistor. Therefore, most of the inrush current can be consumed by resistor 41 . Since the second auxiliary resistor 49 is arranged to assist the resistor 41, an inexpensive resistor with a low resistance value can be used. Therefore, the cost can be reduced more in the second embodiment than in the case of combining the patent documents 1 and 2, in which two separate circuits for rush prevention and regeneration are prepared. can.

As described above, the power conversion device 100 according to Embodiment 2 basically has the same configuration as that of Embodiment 1, so that the same effects as those of Embodiment 1 can be obtained. Furthermore, in the second embodiment, since the first auxiliary resistor 46 for regeneration is connected in series between the resistor 41 and the semiconductor switch 45, the resistance value of the regeneration resistor is higher than the resistance value of the rush prevention resistor. You can make it bigger. Further, when the second auxiliary resistor 49 for rush prevention is arranged between the first diode 42 and the capacitor 43, the resistance value of the rush prevention resistor can be made larger than the resistance value of the regenerative resistor. Thus, by adding the first auxiliary resistor 46 or the second auxiliary resistor 49 according to the purpose, the resistance value of the rush prevention resistor and the resistance value of the regenerative resistor can be changed.

Embodiment 3.
In the third embodiment, the semiconductor switch 45 shares the switching element provided in the inverter circuit 5A. In this case, the inverter circuit 5A is composed of an intelligent power module (hereinafter referred to as IPM (Intelligent Power Module)). An IPM is a high-performance module in which a dedicated drive circuit is installed in order to bring out the performance of the IGBT, and a self-protection function against short circuit, power supply voltage drop, overheating, etc. is made into a dedicated IC.

FIG. 4 is a circuit block diagram showing an example of the configuration of the power converter 100B according to the third embodiment. A power converter 100B according to the third embodiment differs from the second embodiment in that a bus voltage control circuit 4B and an inverter circuit 5A are provided instead of the bus voltage control circuit 4A and the inverter circuit 5 of FIG. This is the point.

An inverter circuit 5A shown in FIG. 4 is an IPM provided with a regeneration module. In general, an IPM provided with a regenerative module is provided with a protection circuit 52 as a part of the regenerative module on the input terminal side. The protection circuit 52 has a second diode 53 whose cathode is connected to the positive bus line 11 and a switching element 54 whose one end is connected to the anode of the second diode 53 . The other end of the switching element 54 is connected to the negative bus 12 . That is, in the protection circuit 52, from the high potential side to the low potential side, the second diode 53 whose cathode is the high potential side and the semiconductor switch 45 connected to the anode of the second diode 53 are arranged in this order. connected in series. In the third embodiment, by connecting the connection point C3 between the resistor 41 and the first diode 42 and the connection point C5 between the second diode 53 and the switching element 54, the switching element 54 of the IPM is connected to the bus voltage. It is shared as the semiconductor switch 45 of the control circuit 4B.

The switching element 54 of the IPM, like the semiconductor switch 45 of the bus voltage control circuit 4, is composed of a switching element such as IGBT or MOSFET, for example. The switching element 54 performs ON operation and OFF operation according to the protection switch signal output by the bus voltage control unit 7 . When the switching element 54 is on, current flows through the switching element 54 and current does not flow through the first diode 42 and the capacitor 43 . On the other hand, when the switching element 54 is turned off, no current flows through the switching element 54 .

3 and 4, the semiconductor switch 45 of the bus voltage control circuit 4A shown in FIG. 3 is not provided in the bus voltage control circuit 4B shown in FIG. If the bus voltage control circuit 4B is configured as shown in FIG. 4 and the switching element 54 is used as the semiconductor switch 45, the rush prevention circuit and the regenerative protection circuit can be provided without adding a new semiconductor switch. be able to.

In addition, in the bus voltage control circuit 4B of FIG. 4, one end of the first auxiliary resistor 46 on the low potential side is connected to the connection point C5. However, the first auxiliary resistor 46 does not necessarily have to be provided as long as the connection point C3 and the connection point C5 are connected.

Since other configurations are the same as those of the second embodiment, they are denoted by the same reference numerals, and descriptions thereof are omitted here.

[Operation of Bus Voltage Control Circuit 4B and Bus Voltage Control Unit 7]
The operation of the bus voltage control unit 7 is basically the same as the flowchart of FIG. 2 described above. Therefore, here, description will be made with reference to FIG. However, the "semiconductor switch" in FIG. 2 is read as "switching element".

When the power conversion device 100 is in normal operation, steps S1, S2, S3, and S4 in the flow chart of FIG. 2 are performed. Therefore, the path between the positive bus 11 and the negative bus 12 is only the relay 44 and the capacitor 43 . Therefore, since the resistor 41 is skipped, the power conversion device 100 can supply electric power to the electric motor 2 without generating loss in the resistor 41 .

Before the power conversion device 100 operates, ie, when no voltage is input from the AC power supply 1, steps S1, S2, S5, and S6 in the flow chart of FIG. 2 are performed. Therefore, a path of the resistor 41 , the first diode 42 and the capacitor 43 is formed between the positive bus 11 and the negative bus 12 . Therefore, when a voltage is input from the AC power supply 1 in this state, it passes through the resistor 41, so an inrush current can be prevented. At this time, the resistor 41 acts as a resistor for preventing rush current.

Also, if for some reason a large amount of regenerative power is input from the electric motor 2 during operation of the power converter 100 and the bus voltage rises, steps S1, S7, and S8 in the flow chart of FIG. 2 are passed. Therefore, a path of the resistor 41 , the first auxiliary resistor 46 and the switching element 54 is formed between the positive bus 11 and the negative bus 12 . Therefore, the regenerated power is consumed by the resistor 41 and the first auxiliary resistor 46, and the bus voltage can be lowered to the voltage of the AC power supply 1. At this time, the resistor 41 and the first auxiliary resistor 46 act as regenerative resistors.

As described above, the power conversion device 100B according to Embodiment 3 basically has the same configuration as those of Embodiments 1 and 2, so that effects similar to those of Embodiments 1 and 2 can be obtained. can be done. Furthermore, in the third embodiment, the switching element 54 of the inverter circuit 5A configured by the IPM is shared as the semiconductor switch 45 of the bus voltage control circuit 4B. As a result, a circuit for rush prevention and a circuit for regeneration protection can be prepared without newly providing a semiconductor switch in the bus voltage control circuit 4B.

Embodiment 4.
A power conversion device 100C according to Embodiment 4 includes a discharge resistor 48 . FIG. 5 is a circuit block diagram showing an example of the configuration of a power converter 100C according to the fourth embodiment. A power converter 100C according to Embodiment 4 differs from Embodiment 3 in that a bus voltage control circuit 4C is provided instead of the bus voltage control circuit 4B of FIG. As shown in FIG. 5, a discharge resistor 48 is connected in parallel with the capacitor 43 in the bus voltage control circuit 4C. Since other configurations are the same as those of the third embodiment, they are denoted by the same reference numerals, and descriptions thereof are omitted here.

If the bus voltage control circuit 4C is configured in this way, the discharge resistor 48 Thus, the charge stored in the capacitor 43 can be discharged. Therefore, circuit maintenance of the power conversion device 100C can be safely performed, and serviceability is improved.

Here, the case where the discharge resistor 48 is provided in the configuration of the third embodiment has been described as an example, but the configuration is not limited to that case, and the discharge resistor 48 is provided in the configuration of the first or second embodiment. may be provided. Even in this case, the electric charge accumulated in the capacitor 43 can be discharged by the discharge resistor 48, so that the circuit maintenance of the power conversion device 100C can be safely performed, and serviceability is improved.

As described above, the power conversion device 100C according to Embodiment 4 basically has the same configuration as those of Embodiments 1 to 3, so that effects similar to those of Embodiments 1 to 3 can be obtained. can be done. Furthermore, in Embodiment 4, a discharge resistor 48 is connected in parallel with the capacitor 43 . Therefore, the electric charge stored in the capacitor 43 can be discharged by the discharge resistor 48 when the power conversion device 100C is not operating. As a result, circuit maintenance of the power converter 100C can be safely performed, and serviceability is improved.

Embodiment 5.
Embodiment 5 describes a case where power converter 100 according to Embodiment 1 is applied to air conditioner 400 .

FIG. 6 is a configuration diagram showing an example configuration of an air conditioner 400 according to Embodiment 5. As shown in FIG. As shown in FIG. 6 , air conditioner 400 includes refrigeration cycle device 300 and blower 401 . A refrigeration cycle device 300 includes a refrigerant compression device 200 , a condenser 301 , an expansion valve 302 and an evaporator 303 . Refrigerant compression device 200 includes compressor 201 and power conversion device 100 .

As shown in FIG. 6, the compressor 201 and the condenser 301 are connected by a refrigerant pipe 304 . Similarly, the refrigerant pipes 304 are connected between the condenser 301 and the expansion valve 302, between the expansion valve 302 and the evaporator 303, and between the evaporator 303 and the compressor 201, respectively. Thus, the compressor 201, the condenser 301, the expansion valve 302, and the evaporator 303 constitute a refrigerant circuit in which refrigerant circulates.

Compressor 201 sucks the refrigerant from the suction port. The compressor 201 compresses the sucked refrigerant into a high-temperature and high-pressure gas refrigerant and discharges it from the discharge port. The compressor 201 has an electric motor 2 whose speed is controlled by the power converter 100 . Compressor 201 is, for example, an inverter compressor. The compressor 201 can arbitrarily change the operating frequency by the inverter circuit 5 of the power converter 100 . Therefore, it is possible to change the refrigerant delivery capacity of the compressor 201 per unit time. Refrigerant discharged from the compressor 201 flows into the condenser 301 .

The condenser 301 exchanges heat between the refrigerant flowing inside and the air. The condenser 301 condenses the high-temperature, high-pressure refrigerant flowing from the compressor 201 into a high-pressure liquid refrigerant (single-phase). The condenser 301 is, for example, a fin-and-tube heat exchanger.

The expansion valve 302 is a decompression device that decompresses and expands the liquid refrigerant discharged from the condenser 301 . The expansion valve 302 is, for example, an electronic expansion valve. When the expansion valve 302 is an electronic expansion valve, the opening degree is adjusted based on instructions from a control device (not shown). Expansion valve 302 is provided between condenser 301 and evaporator 303 . The expansion valve 302 reduces the pressure of the liquid refrigerant flowing out of the condenser 301 to convert it into a two-phase refrigerant of low-pressure gas refrigerant and liquid refrigerant.

The evaporator 303 exchanges heat between the refrigerant flowing inside and the air. The evaporator 303 evaporates the liquid refrigerant portion of the gas-liquid two-phase refrigerant flowing from the expansion valve 302 into a low-pressure gas refrigerant (single-phase). The evaporator 303 is, for example, a fin-and-tube heat exchanger.

Also, the blower 401 blows air to at least one of the condenser 301 and the evaporator 303 .

In the refrigeration cycle device 300, the processes of refrigerant evaporation, compression, condensation, and expansion are repeatedly performed. The refrigerant changes from liquid to gas, and further changes from gas to liquid, whereby heat is exchanged between the refrigerant and outside air. Therefore, the air conditioner 400 can be configured by combining the refrigeration cycle device 300 and the blower 401 that circulates the outside air.

In recent years, the demand for air conditioners has been increasing in emerging countries, so it is significant to provide the air conditioner 400 that controls the speed of the electric motor 2 using the power conversion device 100 at a low price. In the above description, an example in which the power conversion device 100 according to Embodiment 1 is applied to the air conditioner 400 has been described. , 100B, and 100C may be applied to the air conditioner 400. FIG. Thus, by using the power converters 100, 100A, 100B, or 100C of Embodiments 1 to 4, one resistor 41 can be used as both an inrush prevention resistor and a regenerative resistor. Therefore, the parts cost of the power conversion device 100, 100A, 100B, or 100C can be suppressed. As a result, the cost of the components of the air conditioner 400 can be reduced, so that an inexpensive air conditioner can be provided.

By the way, in the above description, the air conditioner 400 was described as an application example of the power converters 100, 100A, 100B, or 100C, but the power converters 100, 100A, 100B, or 100C can also be used in other machines. It goes without saying that we can. For example, the power converters 100, 100A, 100B, or 100C according to the first to fifth embodiments may be applied to mechanical devices such as fans or pumps.

1 AC power supply 2 Electric motor 3 Rectifier circuit 4 Bus voltage control circuit 4A Bus voltage control circuit 4B Bus voltage control circuit 4C Bus voltage control circuit 5 Inverter circuit 5A Inverter circuit 6 Current detector 7 Bus Voltage control unit 8 Inverter circuit control unit 11 Positive bus 12 Negative bus 30 Rectifying diode 41 Resistor 42 First diode 43 Capacitor 44 Relay 45 Semiconductor switch 46 First auxiliary resistor , 48 discharge resistor, 49 second auxiliary resistor, 51 freewheeling diode, 52 protection circuit, 53 second diode, 54 switching element, 100 power conversion device, 100A power conversion device, 100B power conversion device, 100C power conversion device , 200 refrigerant compression device, 201 compressor, 300 refrigeration cycle device, 301 condenser, 302 expansion valve, 303 evaporator, 304 refrigerant pipe, 400 air conditioner, 401 blower.

Claims (13)

a rectifier circuit that rectifies an AC voltage supplied from an AC power supply and converts it into a DC voltage;
an inverter circuit that converts the DC voltage into an AC voltage and supplies it to a load;
a bus voltage control circuit connected to a bus between the output end of the rectifier circuit and the input end of the inverter circuit, and controlling the bus voltage of the bus;
The busbars include a positive busbar on the high potential side and a negative busbar on the low potential side,
The bus voltage control circuit is
a resistor having one end connected to the positive bus;
a first diode having an anode connected to the other end of the resistor;
a capacitor having one end connected to the cathode of the first diode and the other end connected to the negative bus;
a relay connected in parallel with the resistor and the first diode;
a semiconductor switch connected in parallel with the first diode and the capacitor ,
a current detection unit that detects a current value flowing from the inverter circuit toward the load and outputs current information;
a bus voltage control unit that controls conduction and opening of the relay based on the current information output by the current detection unit;
with
The bus voltage control unit,
Determining whether the inverter circuit is in operation based on the current information output by the current detection unit;
Conducting the relay when the inverter circuit is in operation;
opening the relay when the inverter circuit is not in operation;
Power converter. The resistor is
Acts as a regenerative resistor that consumes regenerative power regenerated from the load when the relay is open and the semiconductor switch is on,
When the relay is open and the semiconductor switch is off, it acts as an inrush prevention resistor that consumes inrush current when the AC power supply is turned on.
The power converter according to claim 1. The bus voltage control unit is
for controlling the on/off operation of the semiconductor switch,
detecting the bus voltage;
Determining whether the detected bus voltage is smaller than a reference value,
turning off the semiconductor switch when the bus voltage is less than the reference value;
when the bus voltage is equal to or higher than the reference value, opening the relay and turning on the semiconductor switch;
The power converter according to claim 1 or 2. a rectifier circuit that rectifies an AC voltage supplied from an AC power supply and converts it into a DC voltage;
an inverter circuit that converts the DC voltage into an AC voltage and supplies it to a load;
a bus voltage control circuit connected to a bus between the output end of the rectifier circuit and the input end of the inverter circuit, the bus voltage control circuit controlling the bus voltage of the bus;
with
The busbars include a positive busbar on the high potential side and a negative busbar on the low potential side,
The bus voltage control circuit,
a resistor having one end connected to the positive bus;
a first diode having an anode connected to the other end of the resistor;
a capacitor having one end connected to the cathode of the first diode and the other end connected to the negative bus;
a relay connected in parallel with the resistor and the first diode;
a semiconductor switch connected in parallel with the first diode and the capacitor;
has
a first auxiliary resistor disposed between the resistor and the semiconductor switch, connected in series with the semiconductor switch, and acting as an auxiliary regeneration resistance when the resistor acts as a regeneration resistance;
Power converter. The resistor is
When the relay is open and the semiconductor switch is on, it acts as the regenerative resistor that consumes the regenerated power regenerated from the load,
When the relay is open and the semiconductor switch is off, it acts as an inrush prevention resistor that consumes an inrush current when the AC power supply is turned on.
The power converter according to claim 4. A bus voltage control unit for controlling the on/off operation of the semiconductor switch,
The bus voltage control unit,
detecting the bus voltage;
Determining whether the detected bus voltage is smaller than a reference value,
turning off the semiconductor switch when the bus voltage is less than the reference value;
when the bus voltage is equal to or higher than the reference value, opening the relay and turning on the semiconductor switch;
The power converter according to claim 4 or 5 . a rectifier circuit that rectifies an AC voltage supplied from an AC power supply and converts it into a DC voltage;
an inverter circuit that converts the DC voltage into an AC voltage and supplies it to a load;
a bus voltage control circuit connected to a bus between the output end of the rectifier circuit and the input end of the inverter circuit, the bus voltage control circuit controlling the bus voltage of the bus;
with
The busbars include a positive busbar on the high potential side and a negative busbar on the low potential side,
The bus voltage control circuit,
a resistor having one end connected to the positive bus;
a first diode having an anode connected to the other end of the resistor;
a capacitor having one end connected to the cathode of the first diode and the other end connected to the negative bus;
a relay connected in parallel with the resistor and the first diode;
a semiconductor switch connected in parallel with the first diode and the capacitor;
has
A second auxiliary resistor connected in series between the first diode and the capacitor and connected in parallel to the relay to act as an auxiliary anti-rush resistor when the resistor acts as an anti-rush resistor. with
Power converter. The resistor is
Acts as a regenerative resistor that consumes regenerative power regenerated from the load when the relay is open and the semiconductor switch is on,
When the relay is open and the semiconductor switch is off, it acts as the inrush prevention resistor that consumes the inrush current when the AC power supply is turned on.
The power converter according to claim 7. A bus voltage control unit for controlling the on/off operation of the semiconductor switch,
The bus voltage control unit is
detecting the bus voltage;
Determining whether the detected bus voltage is smaller than a reference value,
turning off the semiconductor switch when the bus voltage is less than the reference value;
when the bus voltage is equal to or higher than the reference value, opening the relay and turning on the semiconductor switch;
The power converter according to claim 7 or 8. The inverter circuit is an intelligent power module having a protection circuit on the input end side,
The protection circuit is
a second diode having a cathode connected to the positive bus;
a switching element having one end connected to the anode of the second diode and the other end connected to the negative bus,
By connecting a connection point between the resistor and the first diode and a connection point between the second diode and the switching element, the switching element is shared as the semiconductor switch of the bus voltage control circuit. ,
The power converter according to any one of claims 1 to 9 . comprising a discharge resistor connected in parallel with the capacitor;
The power converter according to any one of claims 1 to 10 . The capacity of the capacitor is a capacity that does not smooth the pulsating component due to the voltage frequency of the AC power supply contained in the DC voltage rectified by the rectifier circuit.
The power converter according to any one of claims 1 to 11 . A power conversion device according to any one of claims 1 to 12 , a compressor driven by an electric motor that is the load of the power conversion device, and a condenser that condenses the refrigerant discharged from the compressor. a refrigeration cycle device including an expansion valve that decompresses the condensed refrigerant; and an evaporator that evaporates the decompressed refrigerant;
and an air blower that blows air to at least one of the condenser and the evaporator of the refrigeration cycle device.

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