WO2022230062A1

WO2022230062A1 - Power conversion device, and method for suppressing inrush current to power conversion device

Info

Publication number: WO2022230062A1
Application number: PCT/JP2021/016830
Authority: WO
Inventors: 直人楠; 俊介久保田; 智一木; 啓介植村
Original assignee: 三菱電機株式会社
Priority date: 2021-04-27
Filing date: 2021-04-27
Publication date: 2022-11-03
Also published as: JP7539563B2; JPWO2022230062A1

Abstract

A power conversion device (1) equipped with a rectifier (4) for converting AC voltage supplied from an AC power source (51) to DC voltage, an inverter (8) for converting the output from the rectifier (4) into an alternating current, and a first smoothing capacitor (6) and a second smoothing capacitor (7) which charge by smoothing the output from the rectifier (4), and are connected in parallel to one another between the rectifier (4) and the inverter (8). The power conversion device (1) is further equipped with: an inrush current prevention circuit (12) which suppresses the inrush current to the rectifier (4) and is configured in a manner such that a first relay (2) and an inrush current prevention element (3) for suppressing the inrush current are connected in parallel to one another on the alternating current input side of the rectifier (4); a second relay (10), which is connected in series to the second smoothing capacitor (7); and a control unit (11) for controlling the first relay (2) and the second relay (10).

Description

POWER CONVERTER AND INRUSH CURRENT SUPPRESSION METHOD IN POWER CONVERTER

The present disclosure relates to a power converter having a function of suppressing inrush current and a method for suppressing inrush current in the power converter.

Conventionally, there has been known a power conversion device that uses an inverter to drive motors used in components such as compressors and fans in electrical equipment such as air conditioners and refrigerators. A power conversion device converts AC power to DC by a diode bridge, boosts the voltage by a converter, and converts it again to AC by an inverter after passing through a smoothing capacitor. Desired AC power can be obtained by using the power converter. AC power obtained by the power converter is supplied to a load such as a motor.

When the power converter is turned on, the smoothing capacitor is not charged. When the power converter is turned on in this state, a large current called rush current flows through the diode bridge, the converter, and the smoothing capacitor, destroying the diode bridge and other elements. I was afraid. For this reason, devices are being developed to suppress the inrush current from flowing through the power conversion device by means of measures such as installing an inrush current prevention element or dispersing the inrush current.

Further, in Patent Document 1, a smoothing capacitor provided in a DC intermediate circuit that connects a DC side of a rectifier and a DC side of an inverter is divided into two, and an inrush current is reduced by dividing charging of the two smoothing capacitors. Suppression is disclosed.

JP-A-5-76135

However, in the technique of Patent Document 1, since a transistor switch element is used to switch charging of the two smoothing capacitors, there is a problem that the size and weight of the circuit are increased.

The present disclosure has been made in view of the above, and aims to obtain a power conversion device capable of suppressing inrush current without increasing the size and weight.

In order to solve the above-described problems and achieve the object, the power converter according to the present disclosure includes a rectifier that converts AC voltage supplied from an AC power supply to DC voltage, and an inverter that converts the output from the rectifier to AC. and a first smoothing capacitor and a second smoothing capacitor connected in parallel between the rectifier and the inverter for smoothing and charging the output of the rectifier. The power converter includes an inrush current prevention circuit configured to suppress inrush current to the rectifier by parallel connection of an inrush current prevention element and a first relay for suppressing inrush current on the AC input side of the rectifier, and a second smoothing capacitor. and a control unit that controls the first relay and the second relay.

The power conversion device according to the present disclosure has the effect of being able to suppress inrush current without increasing the size and weight.

A circuit diagram of the power converter according to the first embodiment 4 is a time chart showing the operation of the power conversion device according to the first embodiment; 4 is a flowchart showing the procedure of operation of the power converter according to the first embodiment; Circuit diagram of the power converter according to the second embodiment Time chart showing the operation of the power converter according to the second embodiment Circuit diagram of the power converter according to the third embodiment Time chart showing the operation of the power converter according to the third embodiment 10 is a flow chart showing the procedure of operation of the power conversion device according to the third embodiment; FIG. 4 is a diagram showing a processor in which the functions of the control unit in

Embodiments

1, 2, and 3 are realized by the processor; FIG. 4 is a diagram showing a processing circuit when at least part of the functions of the control unit according to the first, second, and third embodiments are realized by the processing circuit;

A power conversion device according to an embodiment and a method for suppressing inrush current in the power conversion device will be described in detail below with reference to the drawings.

Embodiment 1.
FIG. 1 is a circuit diagram of a power converter 1 according to a first embodiment. The power converter 1 shown in FIG. 1 converts AC power, which is a system power supply, into DC and then into AC, and supplies the converted current to a load 52 to drive the load 52 . The power conversion device 1 includes a first relay 2, an inrush current prevention element 3, a rectifier 4, a converter 5, a first smoothing capacitor 6, a second smoothing capacitor 7, an inverter 8, and a voltage detector 9. , a second relay 10 and a control unit 11 .

The first relay 2 is arranged between an AC power supply 51 that supplies an AC voltage to the power converter 1 and the rectifier 4 to constitute an inrush current prevention circuit 12 . That is, the inrush current prevention circuit 12 is configured by connecting in parallel the inrush current prevention element 3 that suppresses the inrush current on the AC input side of the rectifier 4 and the first relay 2 to suppress the inrush current to the rectifier 4 . The first relay 2 is an a-contact relay. The operation of the first relay 2 is controlled by the controller 11 . The first relay 2 opens and closes based on a control signal transmitted from the control section 11 .

The inrush current prevention element 3 suppresses inrush current, which is a large current flowing through the power converter 1 when an AC voltage is applied from the AC power supply 51 to the rectifier 4 . When the first relay 2 is in an off state, that is, when the first relay 2 is in an open circuit state, the rectifier 4 is connected to the AC power supply 51 via the inrush current prevention element 3 . Therefore, when the first relay 2 is in an open circuit state, the inrush current, which is a large current flowing through the rectifier 4, is suppressed. A PTC thermistor (PTC: Positive Temperature Coefficient), for example, is used as the inrush current prevention element 3 . Also shown in FIG. 1 is an AC power supply 51 .

The rectifier 4 rectifies the input AC voltage from the AC power supply 51 . That is, the rectifier 4 is connected to the AC power supply 51, rectifies the AC voltage supplied from the AC power supply 51, converts it into a DC voltage, and outputs the DC voltage. The rectifier 4 uses, for example, a diode bridge in which four diodes (not shown) are bridge-connected.

The converter 5 is a booster circuit that boosts the DC voltage output from the rectifier 4 . Converter 5 does not operate when first smoothing capacitor 6 and second smoothing capacitor 7 are charged, that is, when a rush current is generated. Various known techniques such as a boost chopper circuit can be used for the converter 5 .

The voltage detector 9 detects the voltage across the first smoothing capacitor 6 or the second smoothing capacitor 7 . The voltage detector 9 outputs the detected voltage value of the voltage across the first smoothing capacitor 6 or the second smoothing capacitor 7 to the control unit 11 . A method of detecting the inter-terminal voltage in the voltage detector 9 is not particularly limited, and various known techniques such as a technique using a microcomputer can be used.

The first smoothing capacitor 6 and the second smoothing capacitor 7 smooth and charge the output from the converter 5, and are connected to a DC intermediate circuit connecting the DC side of the converter 5 and the DC side of the inverter 8. and connected in parallel with each other. The first smoothing capacitor 6 is arranged relative to the inverter 8 . The second smoothing capacitor 7 is arranged relatively on the converter 5 side.

The second relay 10 is connected in series with the second smoothing capacitor 7 . By turning on and off the second relay 10, that is, by switching the second relay 10 between the open circuit state and the closed circuit state, the smoothing capacitor through which the current flows is selected. For example, when the second relay 10 is in an open circuit state, current does not flow through the second smoothing capacitor 7 and current flows through the first smoothing capacitor 6 . Also, when the second relay 10 is in the closed state, current flows through the second smoothing capacitor 7 and the first smoothing capacitor 6 . The second relay 10 is an a-contact relay. The operation of the second relay 10 is controlled by the control section 11 . The second relay 10 opens and closes based on a control signal transmitted from the control section 11 .

The inverter 8 converts the DC voltage output from the converter 5 into an AC voltage of constant voltage and constant frequency for driving the load 52 . The inverter 8 is composed of a plurality of switching elements. The inverter 8 supplies the AC voltage obtained by conversion to the load 52 . A load 52 is also shown in FIG.

The control unit 11 uses the voltage value detected by the voltage detector 9 to control opening and closing of the first relay 2 or the second relay 10 . Specifically, control unit 11 uses the voltage value detected by voltage detector 9 to generate a control signal for operating first relay 2 or second relay 10 . Control unit 11 outputs the generated control signal to first relay 2 or second relay 10 .

Note that the control unit 11 includes an inverter drive circuit (not shown) that drives the inverter 8 and an inverter circuit drive control unit (not shown) that controls the inverter drive circuit. Therefore, detailed description is omitted.

Next, the operation of the power converter 1 will be described. FIG. 2 is a time chart showing the operation of the power converter 1 according to the first embodiment. FIG. 3 is a flow chart showing the operation procedure of the power converter 1 according to the first embodiment. The time chart shown in FIG. 2 shows which of the open circuit state and the closed circuit state the first relay 2 and the second relay 10 are in. For the first smoothing capacitor 6 and the second smoothing capacitor 7, the state of charge, that is, the voltage is shown.

First, in step S110, the control unit 11 performs control to turn off the first relay 2 and the second relay 10, that is, control to open the first relay 2 and the second relay 10. The first relay 2 and the second relay 10 are opened according to the control of the controller 11 .

In step S120, an AC voltage is applied from the AC power supply 51 to the rectifier 4. The rectifier 4 rectifies the AC voltage supplied from the AC power supply 51, converts it into a DC voltage, and outputs the DC voltage.

In step S130, the output from the converter 5 charges the first smoothing capacitor 6. At this time, since the second relay 10 is open, no current flows through the second smoothing capacitor 7 and the second smoothing capacitor 7 is not charged.

In step S140, the control unit 11 determines whether or not the potential of the first smoothing capacitor 6 has reached a predetermined threshold value A. Specifically, the voltage detector 9 detects the voltage across the first smoothing capacitor 6 and outputs the detected voltage value to the controller 11 . Based on the voltage value of the voltage across the first smoothing capacitor 6 obtained from the voltage detector 9, the control unit 11 determines whether or not the potential of the first smoothing capacitor 6 has reached a predetermined threshold value A. . The threshold A is a threshold for the control unit 11 to determine whether or not charging of the first smoothing capacitor 6 has temporarily ended. The threshold A is a value lower than the value of the target voltage V1, which is the target voltage for charging the first smoothing capacitor 6 and the second smoothing capacitor 7 . The threshold A is determined in advance and stored in the controller 11 .

If it is determined that the potential of the first smoothing capacitor 6 has not reached the predetermined threshold value A, the result is No in step S140, and the control unit 11 determines that the charging of the first smoothing capacitor 6 has not temporarily ended. It determines and repeats step S140. If it is determined that the potential of the first smoothing capacitor 6 has reached the predetermined threshold value A, the determination in step S140 is Yes, and the control unit 11 determines that the charging of the first smoothing capacitor 6 has been provisionally terminated. , the process proceeds to step S150. That is, when the potential of the first smoothing capacitor 6 reaches a predetermined threshold value A, the control unit 11 detects temporary termination of charging of the first smoothing capacitor 6 .

In step S150, the control unit 11 determines whether or not a predetermined charging completion period t1 has elapsed. In the charge completion period t1, the first smoothing capacitor 6 is completely charged to the target voltage V1 from the time when the potential of the first smoothing capacitor 6 reaches a predetermined threshold value A, and charging of the first smoothing capacitor 6 is completed. This is a waiting period until the voltage and charge of the first smoothing capacitor 6 are stabilized, and is determined in advance and stored in the control unit 11 . The charging completion period t1 can be rephrased as a first smoothing capacitor voltage stabilization period, which is a period until the voltage of the first smoothing capacitor 6 is stabilized.

When it is determined that the charging completion period t1 has not elapsed, the determination in step S150 is No, and the control unit 11 repeats step S150. If it is determined that the charging completion period t1 has elapsed, the determination in step S150 is Yes, and the process proceeds to step S160.

In step S160, the control unit 11 performs control to turn on the second relay 10, that is, control to close the second relay 10. The second relay 10 is closed under the control of the controller 11 .

In step S170, the second smoothing capacitor 7 is charged by the output from the converter 5 as the second relay 10 is closed.

At this time, when the second relay 10 is closed, a short-circuit current flows from the first smoothing capacitor 6 to the second smoothing capacitor 7, and the potential of the first smoothing capacitor 6 drops. That is, a short-circuit current flows through the first smoothing capacitor 6 to the second relay 10 and the second smoothing capacitor 7, thereby causing the potential of the first smoothing capacitor 6 to drop. After that, the first smoothing capacitor 6 and the second smoothing capacitor 7 are charged by the output from the converter 5 . After that, the charging of the first smoothing capacitor 6 is completed again when the electric charge corresponding to the decrease due to the flow of the short-circuit current is accumulated.

In step S180, the control unit 11 determines whether or not a predetermined second smoothing capacitor voltage stabilization period t2 has elapsed. In the second smoothing capacitor voltage stabilization period t2, the second smoothing capacitor 7 is completely charged to the target voltage V1 from the time the potential of the first smoothing capacitor 6 reaches a predetermined threshold value A, and the second smoothing capacitor 7 is completed and the voltage and charge of the second smoothing capacitor 7 are stabilized.

If it is determined that the second smoothing capacitor voltage stabilization period t2 has not elapsed, the determination in step S180 is No, and the control unit 11 repeats step S180. When it is determined that the second smoothing capacitor voltage stabilization period t2 has elapsed, the determination in step S180 is Yes, and the process proceeds to step S190.

In step S190, the control unit 11 performs control to turn on the first relay 2, that is, control to close the first relay 2. The first relay 2 is closed under the control of the controller 11 .

By performing the above operations, charging of the first smoothing capacitor 6 and the second smoothing capacitor 7 is completed.

Here, the charge completion period t1 and the second smoothing capacitor voltage stabilization period t2 are calculated in advance through experiments and simulations so that the first smoothing capacitor 6 and the second smoothing capacitor 7 can be stably charged. It is the set time. There are two reasons for setting the charging completion period t1.

First, the first reason for setting the charging completion period t1 will be described. Considering variations in accuracy of parts such as the first smoothing capacitor 6 and the voltage detector 9, and short-circuit current flowing from the first smoothing capacitor 6 to the second smoothing capacitor 7 when the second relay 10 is closed, To prevent erroneous ON and OFF operations of the second relay 10, the threshold A is set to a value slightly lower than the target voltage V1. In this case, if the charging completion period t1 is not set, the second relay 10 is closed while the first smoothing capacitor 6 is not completely charged, and the current flowing from the converter 5 is reduced to the first smoothing capacitor 6. , and the second smoothing capacitor 7 .

Although the potential of the first smoothing capacitor 6 has reached a voltage very close to the target bus voltage Vdc, it may not reach the target bus voltage Vdc due to variations in accuracy of the components of the first smoothing capacitor 6. In this case, charging of the first smoothing capacitor 6 is actually completed, but the second relay 10 does not proceed to the next operation, that is, the closing operation.

Therefore, the charging completion period t1 is set to prevent the second relay 10 from not moving to the next operation, that is, to prevent malfunction of the second relay 10 as described above.

At this time, if the threshold A is set to the target bus voltage Vdc, that is, if the threshold A=the target bus voltage Vdc, charging of the first smoothing capacitor 6 is actually completed. However, the second relay 10 does not move to the next operation, that is, the closing operation.

Therefore, in order to prevent the second relay 10 from not moving to the next operation as described above, that is, to prevent malfunction of the second relay 10, the threshold value A is set to a value slightly lower than the target bus voltage Vdc. be. Then, the charging completion period t1 starts when the potential of the first smoothing capacitor 6 reaches the threshold value A, the first smoothing capacitor 6 is completely charged, the charging of the first smoothing capacitor 6 is completed, and the first smoothing capacitor It is set to a period until the potential and charge of 6 are stabilized.

Also, when the first smoothing capacitor 6 is charged, erroneous turn-on or erroneous turn-off of the second relay 10 may occur due to fluctuations in the potential of the first smoothing capacitor 6 caused by noise or the like. The charging completion period t1 is set to prevent such erroneous turning-on of the second relay 10 or erroneous turning-off of the second relay 10 . By changing the ON/OFF control method of the second relay 10 from the current control based on the potential of the first smoothing capacitor 6 to time control based on the charging completion period t1, the above-mentioned erroneous ON of the second relay 10 can be prevented. Alternatively, erroneous turning off of the second relay 10 can be prevented.

Also, during the charging completion period t1, the potential of the first smoothing capacitor 6 decreases when a short-circuit current flows from the first smoothing capacitor 6 to the second smoothing capacitor 7 when the second relay 10 is closed. This is set to prevent the second relay 10 from being erroneously turned off. By changing the ON/OFF control method of the second relay 10 from the current control based on the potential of the first smoothing capacitor 6 to time control based on the charging completion period t1, the above-mentioned erroneous ON of the second relay 10 can be prevented. Alternatively, erroneous turning off of the second relay 10 can be prevented.

Next, the second reason for setting the charging completion period t1 will be described. In the actual charging of the first smoothing capacitor 6 in the power conversion device 1, an overshoot occurs once, after which the voltage of the first smoothing capacitor 6 becomes a constant voltage. Therefore, if the second relay 10 is closed immediately after it is detected that the potential of the first smoothing capacitor 6 has reached the threshold value A, the energy at the time of overshoot will be the first It may occur as a short-circuit current flowing from the smoothing capacitor 6 to the second smoothing capacitor 7 . In this case, the second relay 10 may be damaged, and the selection of parts for the second relay 10 becomes difficult. The charging completion period t1 is also set to solve such a problem.

Next, the reason for setting the second smoothing capacitor voltage stabilization period t2, that is, the reason why the control method of the first relay 2 is time control will be described. When the second smoothing capacitor 7 is charged, the voltage across the first smoothing capacitor 6 and the voltage across the second smoothing capacitor 7 become the same. Although it is the voltage between the terminals, the voltage across the first smoothing capacitor 6 exceeds the threshold value A when the first smoothing capacitor 6 is charged, so the second smoothing capacitor voltage stabilization period t2 is set.

When the second smoothing capacitor 7 is charged, the voltage across the terminals of the first smoothing capacitor 6 equals the voltage across the terminals of the second smoothing capacitor 7, and the voltage across the first smoothing capacitor 6 becomes the threshold when the first smoothing capacitor 6 is charged. exceeds A. Therefore, when the first relay 2 is turned on based on the voltage across the terminals of the second smoothing capacitor 7 , that is, when the control method of the first relay 2 is voltage control, the second smoothing capacitor 7 Immediately after the charging of the first relay 2 is started, the first relay 2 is turned on, and malfunction of the first relay 2 occurs. The second smoothing capacitor voltage stabilization period t2 is set in order to prevent malfunction of the first relay 2 by using time control to turn on the first relay 2 .

In addition, the second smoothing capacitor voltage stabilization period t2 starts when the potential of the second smoothing capacitor 7 reaches a predetermined threshold, in the same manner as the charging completion period t1. It is also possible to set a waiting period until the second smoothing capacitor 7 is completely charged to the voltage V1, charging of the second smoothing capacitor 7 is completed, and the voltage and charge of the second smoothing capacitor 7 are stabilized. The threshold in this case is a value lower than the target voltage V1, and is the same value as the threshold A, for example.

In the power converter 1 described above, when the first smoothing capacitor 6 is charged in step S130, the second relay 10 is opened so that the charging path is changed to the AC power supply 51, the inrush current prevention element 3, the rectifier 4, the converter 5, The route is taken in order of the first smoothing capacitor 6 . When the second smoothing capacitor 7 is charged in step S170, the second relay 10 is closed and charging of the first smoothing capacitor 6 is completed. 5, the second relay 10, and the second smoothing capacitor 7 in that order.

As a result, compared to the case where the first smoothing capacitor 6 and the second smoothing capacitor 7 are charged simultaneously without providing the second relay 10, the circuit of the charging path when charging the first smoothing capacitor 6 in step S130, that is, The impedance of the circuit of the AC power supply 51, the inrush current prevention element 3, the rectifier 4, the converter 5, and the first smoothing capacitor 6 is increased, and the excessive inrush current flowing through the rectifier 4, the converter 5, and the first smoothing capacitor 6 is suppressed. can do. In addition, compared to the case where the first smoothing capacitor 6 and the second smoothing capacitor 7 are charged simultaneously without providing the second relay 10, the circuit of the charging path when charging the second smoothing capacitor 7 in step S170, that is, the AC The impedance of the circuit of the power supply 51, the inrush current prevention element 3, the rectifier 4, the converter 5, the second relay 10, and the second smoothing capacitor 7 is increased, and the rectifier 4, the converter 5, the second relay 10, and the second smoothing capacitor 7 It is possible to suppress the flow of an excessive rush current.

The impedance Z1 during charging of the first smoothing capacitor 6 is expressed by the following formula (1).

　Z1=1/jwC1...(1)

The impedance Z2 during charging of the second smoothing capacitor 7 is expressed by the following equation (2).

　Z2=1/jw(C1+C2)...(2)

In addition, in the circuit shown in FIG. 1 with the second relay 10 removed, the impedance Z3 when the first smoothing capacitor 6 and the second smoothing capacitor 7 are simultaneously charged is expressed by the following equation (3). be.

　Z3=1/jw(C1+C2)...(3)

1/wC1 is the reactance of the first smoothing capacitor 6; 1/wC2 is the reactance of the second smoothing capacitor 7; j is the imaginary unit.

From the above formula, the impedance Z1 when the first smoothing capacitor 6 is charged becomes larger than the impedance Z3 when the first smoothing capacitor 6 and the second smoothing capacitor 7 are charged simultaneously.

Also, the impedance Z2 when the second smoothing capacitor 7 is charged has the same formula as the impedance Z3 when the first smoothing capacitor 6 and the second smoothing capacitor 7 are charged simultaneously. However, when the second smoothing capacitor 7 is charged, electric charge is accumulated in the first smoothing capacitor 6. Considering the impedance formula: Z=V/I, I becomes small. Z is the impedance of the target circuit, V is the voltage of the target circuit, and I is the current flowing through the target circuit. Since Z increases as I decreases, the apparent impedance increases. As a result, the apparent impedance Z2 when the second smoothing capacitor 7 is charged becomes larger than the impedance Z3 when the first smoothing capacitor 6 and the second smoothing capacitor 7 are charged simultaneously.

When a PTC thermistor is used as the inrush current prevention element 3, the resistance value of the PTC thermistor rises due to the current flowing through the PTC thermistor when the first smoothing capacitor 6 is charged due to the characteristics of the PTC thermistor when the second smoothing capacitor 7 is charged. is doing. Therefore, the resistance value of the rush current prevention element 3 when charging the second smoothing capacitor 7 is greater than the resistance value of the PTC thermistor when charging the first smoothing capacitor. As a result, when the second smoothing capacitor 7 is charged, the rush current flowing from the AC power supply 51 to the rectifier 4 can be suppressed more than when the first smoothing capacitor 6 is charged.

By suppressing the inrush current flowing from the AC power supply 51 to the rectifier 4, the specifications of the inrush current prevention element 3, the rectifier 4, and the converter 5 can be suppressed, and the inrush current prevention element 3, the rectifier 4, and the converter 5 are low in cost. It is possible to reduce the size, size, and weight of the product. As a result, it is possible to reduce the cost, size, and weight of the power conversion device 1 . In addition, by suppressing the rush current flowing from the AC power supply 51 to the rectifier 4, the life of the first smoothing capacitor 6 and the second smoothing capacitor 7 can be extended. Thereby, the life of the power conversion device 1 can be extended.

In addition, since the power conversion device 1 according to the first embodiment does not use a transistor switch element for switching charging of the two smoothing capacitors, the cost of the circuit that controls the transistor switch element increases and the control becomes complicated. This eliminates problems such as miniaturization, enlargement of the circuit of the power converter 1, occurrence of switching loss in the transistor switch element, and occurrence of conduction loss due to the transistor switch element.

In addition, since the power conversion device 1 according to the first embodiment does not require a configuration such as a plurality of inrush current prevention circuits for suppressing inrush current, it is possible to increase the capacity of the power conversion device and the size of the circuit of the power conversion device. There are no problems such as simplification and cost increase.

Therefore, the power converter 1 according to the first embodiment has the effect of being able to suppress the inrush current without increasing the size and weight.

Embodiment 2.
In the second embodiment, when the second relay 10 is turned on, that is, when the second relay 10 is closed, the current flows through the first smoothing capacitor 6 to the second relay 10 and the second smoothing capacitor 7 . A case of suppressing short-circuit current will be described.

FIG. 4 is a circuit diagram of the power converter 1a according to the second embodiment. FIG. 5 is a time chart showing the operation of the power converter 1a according to the second embodiment. The time chart shown in FIG. 5 shows which of the open circuit state and the closed circuit state the first relay 2 and the second relay 10 are in. For the first smoothing capacitor 6 and the second smoothing capacitor 7, the state of charge, that is, the voltage is shown.

A power conversion device 1a according to the second embodiment has a backflow prevention diode 21 added to the configuration of the power conversion device 1 according to the first embodiment described above. Backflow prevention diode 21 is connected to one end of first smoothing capacitor 6 and one end of second relay 10 in a DC intermediate circuit that connects the DC side of converter 5 and the DC side of inverter 8. It is That is, the backflow prevention diode 21 is arranged between one end side of the first smoothing capacitor 6 and one end side of the second smoothing capacitor 7 in the DC intermediate circuit. Also, the backflow prevention diode 21 is a backflow prevention diode arranged between the first smoothing capacitor 6 and the second smoothing capacitor 7 with the first smoothing capacitor 6 side as the cathode side.

Next, the operation of the power converter 1a will be described. The operation of the power converter 1a is the same as the operation of the power converter 1 according to the first embodiment described above. That is, in the power converter 1a, the first smoothing capacitor 6 and the second smoothing capacitor 7 are charged by performing the operation described along FIG.

Here, in the power converter 1a according to the second embodiment, since the backflow prevention diode 21 is provided, when the second relay 10 is turned on in step S160, that is, the second relay 10 is closed. At times, the short-circuit current flowing through the first smoothing capacitor 6 to the second relay 10 and the second smoothing capacitor 7 can be suppressed. For this reason, in the time chart shown in FIG. 5, the first smoothing capacitor 7 is caused by the short-circuit current flowing through the first smoothing capacitor 6 to the second relay 10 and the second smoothing capacitor 7 shown in the time chart shown in FIG. 6 does not drop in potential.

By suppressing the short-circuit current flowing through the second relay 10 and the second smoothing capacitor 7 through the first smoothing capacitor 6, the specifications of the second relay 10 can be suppressed, the cost of the second relay 10 can be reduced, and the second relay 10 and the weight of the second relay 10 can be reduced. This makes it possible to reduce the cost, size, and weight of the power converter 1a.

Also, by suppressing the short-circuit current flowing through the first smoothing capacitor 6 to the second relay 10 and the second smoothing capacitor 7, the life of the second smoothing capacitor 7 can be extended. Thereby, the life of the power converter 1a can be extended.

Embodiment 3.
In the second embodiment described above, the case of suppressing the short-circuit current by the anti-backflow diode 21 in addition to suppressing the inrush current has been described. explain.

FIG. 6 is a circuit diagram of the power converter 1b according to the third embodiment. A power conversion device 1b according to the third embodiment has a configuration in which a third relay 22 is added to the configuration of the power conversion device 1 according to the first embodiment. The third relay 22 is a b-contact relay. The third relay 22 is connected to one end of the first smoothing capacitor 6 and one end of the second relay 10 in a DC intermediate circuit that connects the DC side of the converter 5 and the DC side of the inverter 8. It is That is, the power converter 1b according to the third embodiment has a configuration in which the backflow prevention diode 21 in the power converter 1a according to the second embodiment is replaced with the third relay 22. FIG.

Next, the operation of the power converter 1b will be described. FIG. 7 is a time chart showing the operation of the power converter 1b according to the third embodiment. FIG. 8 is a flow chart showing the operation procedure of the power converter 1b according to the third embodiment. In the time chart shown in FIG. 7, the first relay 2, the second relay 10, and the third relay 22 are shown in which open state or closed state. For the first smoothing capacitor 6 and the second smoothing capacitor 7, the state of charge, that is, the voltage is shown.

First, in step S310, the control unit 11 performs control to open the first relay 2 and the second relay 10. The first relay 2 and the second relay 10 are opened according to the control of the controller 11 . Further, the control unit 11 performs control to close the third relay 22 . The third relay 22 is closed under the control of the control section 11 .

Next, step S320 is performed in the same manner as step S120.

Next, step S330 is performed in the same manner as step S130.

Next, step S340 is performed in the same manner as step S140.

Next, step S350 is performed in the same manner as step S150.

If it is determined that the charging completion period t1 has not elapsed, the determination in step S350 is No, and the control unit 11 repeats step S350. If it is determined that the charging completion period t1 has elapsed, the determination in step S350 is Yes, and the process proceeds to step S360.

In step S360, the control unit 11 performs control to turn on the third relay 22, that is, control to open the third relay 22. The third relay 22 is opened according to the control of the control section 11 .

In step S370, the control unit 11 determines whether or not a predetermined period of time t3 has elapsed after the control for turning on the third relay 22, that is, after the control for opening the third relay 22 was performed. do. A period t<b>3 is a standby period in which the switching timing of the switching of the third relay 22 and the switching of the second relay 10 are to be different. That is, the period t3 is a waiting time for preventing the third relay 22 and the second relay 10 from turning on at the same time. In a broad sense, the period t3 can be said to be a stabilization period during which the switching of the third relay 22 waits until the influence of the switching of the third relay 22 on the circuit of the power converter 1 stabilizes. If it is determined that the period t3 has not elapsed, the determination in step S370 is No, and the control unit 11 repeats step S370. If it is determined that the period t3 has elapsed, the determination in step S370 is Yes, and the process proceeds to step S380.

In step S380, the control unit 11 performs control to turn on the second relay 10, that is, control to close the second relay 10. The second relay 10 is closed under the control of the controller 11 .

In step S390, the second smoothing capacitor 7 is charged by the output from the converter 5 as the second relay 10 is closed.

Here, since the third relay 22 is in an open circuit state, when the second relay 10 is turned on in step S380, that is, when the second relay 10 is closed, the second relay 10 is applied through the first smoothing capacitor 6. Short-circuit current flowing through relay 10 and second smoothing capacitor 7 can be suppressed. For this reason, in the time chart shown in FIG. 7, the first smoothing capacitor 7 is caused by the short-circuit current flowing through the first smoothing capacitor 6 to the second relay 10 and the second smoothing capacitor 7 shown in the time chart shown in FIG. 6 does not drop in potential. Also, since the third relay 22 is in an open circuit state, no current flows through the first smoothing capacitor 6 .

By suppressing the short-circuit current flowing through the second relay 10 and the second smoothing capacitor 7 through the first smoothing capacitor 6, the specifications of the second relay 10 can be suppressed, the cost of the second relay 10 can be reduced, and the second relay 10 and the weight of the second relay 10 can be reduced. As a result, the power converter 1b can be reduced in cost, size, and weight.

Also, by suppressing the short-circuit current flowing through the first smoothing capacitor 6 to the second relay 10 and the second smoothing capacitor 7, the life of the second smoothing capacitor 7 can be extended. Thereby, the life of the power conversion device 1b can be extended.

In step S400, the control unit 11 determines whether or not the potential of the second smoothing capacitor 7 has reached a predetermined threshold value B. Specifically, the voltage detector 9 detects the voltage across the second smoothing capacitor 7 and outputs the detected voltage value to the controller 11 . Based on the voltage value of the voltage across the second smoothing capacitor 7 obtained from the voltage detector 9, the control unit 11 determines whether or not the potential of the second smoothing capacitor 7 has reached a predetermined threshold value B. . The threshold B is a threshold for the control unit 11 to determine whether or not charging of the second smoothing capacitor 7 has temporarily ended. The threshold B is determined in advance and stored in the controller 11 . The threshold B in the third embodiment is the target voltage V1.

If it is determined that the potential of the second smoothing capacitor 7 has not reached the predetermined threshold value B, the result is No in step S400, and the control unit 11 determines that the charging of the second smoothing capacitor 7 has not been provisionally terminated. It determines and repeats step S400. If it is determined that the potential of the second smoothing capacitor 7 has reached the predetermined threshold value B, the result is Yes in step S400, and the control unit 11 determines that the charging of the second smoothing capacitor 7 has been provisionally terminated. , go to step S410. That is, when the potential of the second smoothing capacitor 7 reaches a predetermined threshold value B, the control unit 11 detects temporary termination of charging of the second smoothing capacitor 7 .

In step S410, the control unit 11 determines whether or not a predetermined charging completion period t4 has elapsed. In the charging completion period t4, the second smoothing capacitor 7 is fully charged from the point in time when the potential of the second smoothing capacitor 7 reaches a predetermined threshold value B, and charging of the second smoothing capacitor 7 is completed. This is a waiting period until the voltage and charge of the smoothing capacitor 7 are stabilized, and is predetermined and stored in the control section 11 . The charging completion period t4 can be rephrased as a second smoothing capacitor voltage stabilization period, which is a period until the voltage of the second smoothing capacitor 7 is stabilized.

If it is determined that the charging completion period t4 has not elapsed, the determination in step S410 is No, and the control unit 11 repeats step S410. If it is determined that the charging completion period t4 has elapsed, the determination in step S410 is Yes, and the process proceeds to step S420.

In step S420, the control unit 11 performs control to turn off the third relay 22, that is, control to close the third relay 22. The third relay 22 is closed under the control of the control section 11 .

In step S430, the control unit 11 determines whether or not a predetermined stabilization period t5 has elapsed. The stabilization period t5 is a period until the influence on the circuit of the power converter 1 such as chattering when the third relay 22 is closed is stabilized, and is predetermined and stored in the control unit 11 . If it is determined that the stabilization period t5 has not elapsed, the determination in step S430 is No, and the control unit 11 repeats step S430. If it is determined that the stabilization period t5 has elapsed, the determination in step S430 is Yes, and the process proceeds to step S440.

In step S440, the control unit 11 performs control to close the first relay 2. The first relay 2 is closed under the control of the controller 11 .

As described above, in the power conversion device 1b according to the third embodiment, by including the third relay 22, the inrush current is suppressed in the same manner as the power conversion device 1 and the power conversion device 1a described above, and the power conversion device As in 1a, the short-circuit current flowing through the second relay 10 and the second smoothing capacitor 7 through the first smoothing capacitor 6 can be suppressed when the second relay 10 is closed.

Also, the third relay 22 used in the power converter 1b according to the third embodiment has a smaller conduction loss than the backflow prevention diode 21. Therefore, the power conversion device 1b according to the third embodiment can suppress loss more than the power conversion device 1a described above.

FIG. 9 is a diagram showing the processor 301 when the functions of the control unit 11 in

Embodiments

1, 2, and 3 described above are implemented by the processor 301. FIG. That is, at least part of the functions of the control unit 11 may be realized by the processor 301 executing programs stored in the memory 302 . The processor 301 is a microcomputer, CPU (Central Processing Unit), processing device, arithmetic device, microprocessor, or DSP (Digital Signal Processor). Memory 302 is also shown in FIG.

When at least part of the function of the control unit 11 is realized by the processor 301, the part of the function is realized by a combination of the processor 301 and software, firmware, or software and firmware. Software or firmware is written as a program and stored in memory 302 . The processor 301 implements at least part of the functions of the control unit 11 by reading and executing programs stored in the memory 302 .

That is, when at least part of the function of the control unit 11 is realized by the processor 301, the control unit 11 stores a program that results in the execution of steps executed by at least part of the control unit 11. It has a memory 302 for It can also be said that the program stored in the memory 302 causes the computer to execute the procedure or method executed by at least part of the control unit 11 .

The memory 302 is non-volatile such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), EEPROM (registered trademark) (Electrically Erasable Programmable Read-Only Memory), etc. Alternatively, it may be a volatile semiconductor memory, magnetic disk, flexible disk, optical disk, compact disk, mini disk, DVD (Digital Versatile Disk), or the like.

FIG. 10 is a diagram showing the processing circuit 303 when at least part of the functions of the control unit 11 according to the first, second, and third embodiments are realized by the processing circuit 303. FIG. That is, at least part of the control unit 11 may be implemented by the processing circuit 303 .

The processing circuit 303 is dedicated hardware. The processing circuit 303 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. is. Part of the control unit 11 may be dedicated hardware separate from the rest.

The configurations shown in the above embodiments are only examples, and can be combined with other known techniques, or can be combined with other embodiments, without departing from the scope of the invention. It is also possible to omit or change part of the configuration.

1, 1a, 1b power converter, 2 first relay, 3 inrush current prevention element, 4 rectifier, 5 converter, 6 first smoothing capacitor, 7 second smoothing capacitor, 8 inverter, 9 voltage detector, 10 second relay , 11 control unit, 12 inrush current prevention circuit, 21 backflow prevention diode, 22 third relay, 51 AC power supply, 52 load, 301 processor, 302 memory, 303 processing circuit.

Claims

a rectifier that converts an AC voltage supplied from an AC power supply to a DC voltage;
an inverter that converts the output from the rectifier into alternating current;
a first smoothing capacitor and a second smoothing capacitor connected in parallel between the rectifier and the inverter for smoothing and charging the output of the rectifier;
an inrush current prevention circuit configured by connecting in parallel a first relay and an inrush current prevention element that suppresses an inrush current on the AC input side of the rectifier, and suppressing an inrush current to the rectifier;
a second relay connected in series with the second smoothing capacitor;
a control unit that controls the first relay and the second relay;
A power conversion device comprising:
The control unit charges the first smoothing capacitor when the first relay and the second relay are open, and closes the second relay after charging of the first smoothing capacitor to perform the second smoothing. to control the charging of the capacitor,
The power converter according to claim 1.
The first smoothing capacitor is arranged on the inverter side,
The second smoothing capacitor is arranged on the rectifier side,
Between the first smoothing capacitor and the second smoothing capacitor, a backflow prevention diode is provided with the first smoothing capacitor side as the cathode side,
The power converter according to claim 2.
The first smoothing capacitor is arranged on the inverter side,
The second smoothing capacitor is arranged on the rectifier side,
A third relay disposed between the first smoothing capacitor and the second smoothing capacitor,
The power converter according to claim 2.
The control unit charges the first smoothing capacitor while the first relay and the second relay are open and the third relay is closed, and after the charging of the first smoothing capacitor is completed, the Control to open a third relay and close the second relay to charge the second smoothing capacitor;
The power converter according to claim 4.
A rectifier that converts an AC voltage supplied from an AC power supply to a DC voltage, an inverter that converts an output from the rectifier to an AC voltage, and a device that smoothes and charges the output of the rectifier, the rectifier and the inverter. A first smoothing capacitor and a second smoothing capacitor connected in parallel between the rectifier, and a rush current prevention element for suppressing a rush current on the AC input side of the rectifier and a first relay are connected in parallel. an inrush current prevention circuit that suppresses inrush current to the second smoothing capacitor, a second relay that suppresses inrush current connected in series with the second smoothing capacitor, and a control unit that controls the first relay and the second relay; An inrush current suppression method in a power conversion device comprising:
charging the first smoothing capacitor with the first relay and the second relay open;
closing the second relay to charge the second smoothing capacitor after the charging of the first smoothing capacitor is completed;
A method for suppressing an inrush current in a power conversion device comprising:
The first smoothing capacitor is arranged on the inverter side,
The second smoothing capacitor is arranged on the rectifier side,
Between the first smoothing capacitor and the second smoothing capacitor, a backflow prevention diode is provided with the first smoothing capacitor side as the cathode side,
The inrush current suppression method in the power converter according to claim 6.
The first smoothing capacitor is arranged on the inverter side,
The second smoothing capacitor is arranged on the rectifier side,
A third relay disposed between the first smoothing capacitor and the second smoothing capacitor,
the control unit charging the first smoothing capacitor while the first relay and the second relay are open and the third relay is closed;
opening the third relay and closing the second relay to charge the second smoothing capacitor after charging the first smoothing capacitor;
The inrush current suppression method in the power converter according to claim 6, comprising: