WO2021240642A1

WO2021240642A1 - Harmonic suppression device and air conditioning system

Info

Publication number: WO2021240642A1
Application number: PCT/JP2020/020731
Authority: WO
Inventors: 啓佑石倉; 暁範橋本; 秀太石川
Original assignee: 三菱電機株式会社
Priority date: 2020-05-26
Filing date: 2020-05-26
Publication date: 2021-12-02
Also published as: JPWO2021240642A1

Abstract

A harmonic suppression device comprises: a rectifier in which a plurality of vertical arms are connected in parallel, an upper-side switching element and a lower-side switching element being connected in series in each vertical arm, and the phases of an AC power source being connected at a center point that is the connection point between the upper-side switching element and the lower-side switching element; a load current detection unit that detects the load current inputted to a harmonic generation load from the AC power source; a first and second drive circuit that turn the upper-side switching element and the lower-side switching element on and off; and a control device that generates a control signal for causing the first and second drive circuits to turn the upper-side switching element and the lower-side switching element on and off, the control device selecting, from among the load currents of the phases of the AC power source, the phase for which the load current is smallest as a charging phase, and turning the lower-side switching element corresponding to the charging phase in the second drive circuit on and off, whereby the bootstrap capacitor of the first drive circuit corresponding to the charging phase is charged.

Description

Harmonic suppressor and air conditioning system

The present disclosure relates to a harmonic suppression device that suppresses a harmonic component of a current flowing through a system power supply, and an air conditioning system equipped with the harmonic suppression device.

As a conventional harmonic suppression device, a drive circuit for turning on / off an upper switching element and a lower switching element constituting a rectifier has a bootstrap capacitor (see, for example, Patent Document 1). .. The upper switching element and the lower switching element are connected in series to form a leg. The rectifier is configured by connecting a plurality of legs in parallel.

In Patent Document 1, the bootstrap capacitor acts as a power source for driving the upper switching element of each leg. The bootstrap capacitor is charged from the control power supply.

In Patent Document 1, for charging the bootstrap capacitor for activating the harmonic suppression operation, the lower switching element of the phase to be charged is based on the phase of the AC power supply voltage, and the phase voltage of the AC power supply is the minimum. Always turn on when taking phase. Further, PWM control is performed when the phase voltage of the AC power supply is not the minimum phase and is negative.

In the harmonic suppression device shown in Patent Document 1, by performing the PWM control, the following effects are obtained as compared with the case where the AC power supply voltage is always turned on only when the phase is the minimum phase. That is, even when the phase of the AC power supply voltage is not the minimum phase and is negative, a power supply short-circuit current at a level that does not result in a steep large current is passed to forcibly charge the bootstrap capacitor. You can save time.

Japanese Unexamined Patent Publication No. 2012-50177

In the case of Patent Document 1 above, the bootstrap capacitor is charged based on the state of the AC power supply voltage. Therefore, if the imbalance of the AC power supply voltage is significant, or if distortion is superimposed on the power supply voltage of the AC power supply due to a large impedance on the power supply side, etc., the phase of the AC power supply voltage should be recognized correctly. I can't. As a result, charging starts in a charging period different from the original one, and there is a problem that a large current steeper than expected flows.

Further, Patent Document 1 described above describes a means for charging a bootstrap capacitor based on a reactor current after rectification of a harmonic generation load. In this case, in addition to the load current current detecting means before rectification for suppressing harmonics, a new current detecting means for the reactor after rectification is required. Further, since it is not possible to determine from which phase the detected current is derived from the reactor current alone, a means for detecting the power supply voltage and the phase is required.

This disclosure is made to solve such a problem, and obtains a harmonic suppression device capable of charging a bootstrap capacitor without being affected by an AC power source and an air conditioning system equipped with the harmonic suppression device. The purpose is.

The harmonic suppression device according to the present disclosure is a harmonic suppression device that is connected in parallel with a harmonic generation load connected to an AC power supply and suppresses the harmonics generated by the harmonic generation load, and is an upper switching element. A plurality of upper and lower arms in which the lower switching element and the lower switching element are connected in series are connected in parallel, and each phase of the AC power supply is connected to a middle point which is a connection point between the upper switching element and the lower switching element. , A rectifier, a load current detector that detects a load current input from the AC power supply to the harmonic generation load, a first drive circuit that turns the upper switching element ON / OFF, and the lower switching element. A second drive circuit that operates ON / OFF, and a control device that generates a control signal that causes the first drive circuit and the second drive circuit to perform the ON / OFF operation of the upper switching element and the lower switching element. The first drive circuit has a bootstrap condenser that acts as a power source for driving the upper switching element and a control power supply for charging the bootstrap condenser, and the control device is a control power source for each of the AC power supplies. Among the load currents of the phase, the phase having the minimum load current is selected as the charging phase, and the lower switching element corresponding to the charging phase is operated ON / OFF in the second drive circuit. , The bootstrap condenser of the first drive circuit corresponding to the charging phase is charged.

According to the harmonic suppression device according to the present disclosure, even when distortion is superimposed on the power supply voltage, the bootstrap capacitor for driving the upper switching element can be charged without being affected by the AC power supply. can.

It is a circuit block diagram which shows the schematic structure of the air conditioning system 1 provided with the harmonic suppression device 4 which concerns on Embodiment 1. FIG. It is a circuit block diagram which shows the structure of the 1st drive circuit 13r to 13t in the harmonic suppression apparatus 4 which concerns on Embodiment 1. FIG. It is a block diagram which showed the structure of the control apparatus 10 of the harmonic suppression apparatus 4 which concerns on Embodiment 1. FIG. It is a figure which shows an example of the ON / OFF operation of the lower switching element 70x to 70z which concerns on Embodiment 1. FIG. It is a figure which shows an example of the 1st drive circuit 13 which has the control voltage adjustment circuit 20 for suppressing the heat generation of the harmonic suppression apparatus 4 which concerns on Embodiment 1. FIG. It is a flowchart explaining the charge control example of the boot strap capacitor 18 of the harmonic suppression apparatus 4 which concerns on Embodiment 1. FIG. It is a flowchart explaining the charge control example of the bootstrap capacitor 18 in the harmonic suppression apparatus 4 when there is a phase which does not generate a load current in Embodiment 1. FIG. It is a figure which shows the load current of R phase, S phase, and T phase. It is a figure which shows typically the installation method of the harmonic suppression apparatus 4 which concerns on Embodiment 1. FIG. It is a figure which shows typically the installation method of the harmonic suppression apparatus 4 which concerns on Embodiment 1. FIG. It is a figure which shows typically the installation method of the harmonic suppression apparatus 4 which concerns on Embodiment 1. FIG.

Hereinafter, embodiments of the harmonic suppression device and the air conditioning system according to the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments, and can be variously modified without departing from the gist of the present disclosure. In addition, the present disclosure includes all combinations of configurations that can be combined among the configurations shown in the following embodiments and modifications thereof. Further, in each figure, those having the same reference numerals are the same or equivalent thereof, which are common to the whole text of the specification. In each drawing, the relative dimensional relationship or shape of each component may differ from the actual one.

Further, each program according to the embodiment of the present disclosure is a process performed in chronological order in the order described, but is a process that is executed in parallel or individually even if it is not necessarily processed in chronological order. May include.

Further, each function of the harmonic suppression device and the air conditioning system according to the embodiment of the present disclosure may be realized by either hardware or software. Each function in each block diagram may be realized by hardware such as a circuit device, or may be realized by software implemented on an arithmetic unit.

Embodiment 1.
FIG. 1 is a circuit block diagram showing a schematic configuration of an air conditioning system 1 provided with a harmonic suppression device 4 according to a first embodiment. In the air conditioning system 1, the harmonic suppression device 4 suppresses the harmonic component of the current flowing from the harmonic generation load 3 to the AC power supply 2. A harmonic is a wave having a frequency that is an integral multiple of the fundamental wave contained in the waveform on which distortion is superimposed.

As shown in FIG. 1, the air conditioning system 1 is connected to an AC power supply 2 that functions as a system power supply. The air conditioning system 1 includes a harmonic generation load 3, a harmonic suppression device 4, and a refrigerant circuit 5. The AC power supply 2 is, for example, a three-phase AC power supply, and supplies electric power to the harmonic generation load 3. Hereinafter, the three output lines extending from the AC power supply 2 are referred to as a first output line (R phase), a second output line (S phase), and a third output line (T phase), respectively. ..

(Structure of harmonic generation load 3)
The configuration of the harmonic generation load 3 will be described. The harmonic generation load 3 is a power conversion device including, for example, a rectifier 30, a DC reactor 31, a smoothing capacitor 32, an inverse converter (not shown), and the like, and supplies electric power to the refrigerant circuit 5. The rectifier 30 rectifies the AC voltage of the AC power supply 2 to a DC voltage. A smoothing capacitor 32 is connected in parallel to the output side of the rectifier 30 via a DC reactor 31. The smoothing capacitor 32 smoothes the DC voltage input from the rectifier 30 via the DC reactor 31. If necessary, an inverter circuit may be provided between the harmonic generation load 3 and the refrigerant circuit 5.

(Structure of Refrigerant Circuit 5)
Next, the configuration of the refrigerant circuit 5 will be described. The refrigerant circuit 5 includes, for example, a compressor 50, two

heat exchangers

51 and 52, and an expansion valve 53 connected via a refrigerant pipe 54. The refrigerant circuit 5 may further include a four-way valve, an accumulator, and the like.

The compressor 50 sucks in a low-pressure gas refrigerant, compresses it, and discharges it as a high-pressure gas refrigerant. The compressor 50 is, for example, an inverter compressor. The inverter compressor can change the amount of the refrigerant to be sent out per unit time by controlling the inverter circuit or the like.

Each of the two

heat exchangers

51 and 52 has a heat transfer tube and fins. The

heat exchangers

51 and 52 are, for example, fin-and-tube heat exchangers. Each of the

heat exchangers

51 and 52 exchanges heat between the refrigerant flowing inside the heat transfer tube and the air flowing outside the heat transfer tube. When the refrigerant circuit 5 is an air conditioner, one of the

heat exchangers

51 and 52 functions as an evaporator and the other functions as a condenser.

The expansion valve 53 decompresses the inflowing liquid refrigerant by a squeezing action and flows out so that the refrigerant liquefied by the condenser can be easily evaporated by the evaporator. Further, the expansion valve 53 adjusts the amount of the refrigerant so as to maintain an appropriate amount of the refrigerant according to the load of the evaporator. The expansion valve 53 is composed of, for example, an electronic expansion valve. As shown in FIG. 1, the expansion valve 53 is connected to the two

heat exchangers

51 and 52 by a refrigerant pipe 54.

(Structure of Harmonic Suppression Device 4)
The harmonic suppression device 4 is provided to suppress the harmonic current because the harmonic generation load 3 causes the harmonic current to flow to the AC power supply 2. The harmonic suppression device 4 is connected in parallel with the harmonic generation load 3 connected to the AC power supply 2 to suppress the harmonics generated from the harmonic generation load 3. The harmonic suppression device 4 is built in the main body of the air conditioning system 1 as shown in FIG. 9, or is externally attached to the main body of the air conditioning system 1 as shown in FIG. Alternatively, as shown in FIG. 11, the harmonic suppression device 4 may be configured separately from the air conditioning system 1 and may be placed separately. 9 to 11 are diagrams schematically showing the installation method of the harmonic suppression device 4 according to the first embodiment.

As shown in FIG. 1, the harmonic suppression device 4 includes a ripple filter 6, a switching circuit 7, a reactor 8, a capacitor 9, a control device 10, a load current detection unit 11, and a compensation current detection unit 12. have.

The ripple filter 6 suppresses the ripple component of the compensation current output from the harmonic suppression device 4. The ripple filter 6 has reactors 64a, 64b and 64c and

capacitors

65a, 65b and 65c. The reactors 64a, 64b and 64c are connected in series to the first output line (R phase), the second output line (S phase) and the third output line (T phase) of the AC power supply 2, respectively. .. Further, one end of the capacitor 65a is connected to the first output line (R phase) of the AC power supply 2, and the other end is connected to the connection point 63. One end of the capacitor 65b is connected to the second output line (S phase) of the AC power supply 2, and the other end is connected to the connection point 63. One end of the capacitor 65c is connected to the third output line (T phase) of the AC power supply 2, and the other end is connected to the connection point 63.

The reactor 8 connects the switching circuit 7 and the ripple filter 6. The reactor 8 has

reactors

8a, 8b and 8c. The

reactors

8a, 8b and 8c are connected in series to the first output line (R phase), the second output line (S phase) and the third output line (T phase) of the AC power supply 2, respectively. ..

The capacitor 9 is connected in parallel to the switching circuit 7.

The configuration of the switching circuit 7 will be described. In the switching circuit 7, the

switching elements

70r, 70s and 70t arranged on the upper side and the

switching elements

70x, 70y and 70z arranged on the lower side have a diode 71 connected in antiparallel to each other. Hereinafter, this configuration is referred to as an arm. Further, the arm is configured by connecting two arms in series, and hereinafter, this is referred to as an upper and lower arm. The three upper and lower arms are connected in parallel. Further, a capacitor 9 is connected in parallel to these upper and lower arms. The connection points between the switching element 70r and the switching element 70x, the connection points between the switching element 70s and the switching element 70y, and the connection points between the switching element 70t and the switching element 70z are referred to as

midpoints

72a, 72b, and 72c, respectively. ..

In the switching circuit 7, the first output line (R phase) of the AC power supply 2 is connected to the midpoint 72a via the reactor 64a and the reactor 8a of the ripple filter 6. Further, the second output line (S phase) of the AC power supply 2 is connected to the midpoint 72b via the reactor 64b and the reactor 8b of the ripple filter 6. Similarly, the third output line (T phase) of the AC power supply 2 is connected to the midpoint 72c via the reactor 64c and the reactor 8c of the ripple filter 6.

Further, in the switching circuit 7, the diode 71 is connected in antiparallel to each of the switching elements 70r to 70t and 70x to 70z. Further, drive circuits 13r to 13t and 13x to 13z for outputting drive signals for performing these ON / OFF operations are installed in each of the switching elements 70r to 70t and 70x to 70z, respectively. The drive circuits 13r to 13t and 13x to 13z are connected to the control device 10, receive a control signal 61 from the control device 10, and perform an ON / OFF operation of the corresponding switching element based on the control signal 61. ..

Further, in the following, among the six switching elements 70r to 70t and 70x to 70z, the switching elements 70r to 70t are referred to as upper switching elements, and the switching elements 70x to 70z are referred to as lower switching elements. In the following, the drive circuits 13r to 13t for driving the upper switching elements 70r to 70t are referred to as first drive circuits 13r to 13t, and the drive circuits 13x to 13z for driving the lower switching elements 70x to 70z are referred to as second drive circuits. It is called 13x to 13z.

The diodes 71 connected in antiparallel to the switching elements 70r to 70t and 70x to 70z of the three upper and lower arms connected in parallel constitute the "rectifier" of the harmonic suppression device 4 according to the first embodiment. There is. That is, the switching circuit 7 of FIG. 1 from which the first drive circuits 13r to 13t and the second drive circuits 13x to 13z are removed is the "rectifier" of the harmonic suppression device 4 according to the first embodiment.

FIG. 2 is a circuit configuration diagram showing the configuration of the first drive circuits 13r to 13t in the harmonic suppression device 4 according to the first embodiment. Here, for the sake of simplification of the description, the first drive circuits 13r to 13t are collectively referred to as the first drive circuit 13. The first drive circuit 13 drives the upper switching elements 70r to 70t, respectively. As shown in FIG. 2, the first drive circuit 13 includes a current limiting resistor 14, a diode 15, a bootstrap capacitor 18, and a drive IC (Integrated Circuit) 17. The bootstrap capacitor 18 acts as a power source for driving the upper switching elements 70r to 70t. The bootstrap capacitor 18 is charged from the control power supply 16 via the diode 15. The drive IC 17 is powered by the voltage across the bootstrap capacitor 18. The drive IC 17 receives the control signal 61 from the control device 10. The drive IC 17 outputs a drive signal 62 to each of the

upper switching elements

70r, 70s and 70t based on the control signal 61, and turns on / off each of the

upper switching elements

70r, 70s and 70t. The current limiting resistor 14 limits the current from the control power supply 16. As shown in FIG. 2, the current limiting resistor 14 is connected to the anode side of the diode 15, but is not limited to this, and may be connected to the cathode side.

The second drive circuits 13x to 13z for driving the lower switching elements 70x to 70z have basically the same configuration as the first drive circuits 13r to 13t shown in FIG. However, in the second drive circuit 13x to 13z, the diode 15 may not be provided. The reason will be explained. As shown in FIG. 1, the second drive circuits 13x to 13z are configured to eliminate the need for the diode 15 because the negative electrode of the capacitor 9 can be shared, and the bootstrap capacitor 18 is constantly charged.

Return to the explanation in Fig. 1. The control device 10 outputs a control signal 61 for turning on / off the switching elements 70r to 70t and 70x to 70z to the first drive circuits 13r to 13t and the second drive circuits 13x to 13z. As shown in FIG. 3, the control device 10 includes a charging phase determination unit 10a and a control signal generation unit 10b. FIG. 3 is a block diagram showing the configuration of the control device 10 of the harmonic suppression device 4 according to the first embodiment. The charging phase determining unit 10a determines the phase for charging the bootstrap capacitor 18 from the upper switching elements 70r to 70t of the R phase, the S phase, and the T phase. The control signal generation unit 10b generates a control signal 61 for suppressing the harmonic current.

Here, the hardware configuration of the control device 10 will be described. The control device 10 is composed of a processing circuit. The processing circuit is composed of dedicated hardware or a processor. The dedicated hardware is, for example, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The processor executes a program stored in memory. The control device 10 has a memory. The memory is a non-volatile or volatile semiconductor memory such as RAM (RandomAccessMemory), ROM (ReadOnlyMemory), flash memory, EPROM (ErasableProgrammableROM), or a disk such as a magnetic disk, flexible disk, or optical disk. Is.

Further, the load current detection unit 11 shown in FIG. 1 detects the load current input from the AC power supply 2 to the harmonic generation load 3. The load current detection unit 11 has a load

current detection unit

11r and 11t. The load current detection unit 11r detects the load current flowing through the first output line (R phase) of the AC power supply 2, and the load current detection unit 11t flows through the third output line (T phase) of the AC power supply 2. Detect load current. The load

current detection units

11r and 11t are connected to the control device 10, and transmit the current information of the detected load current to the control device 10. In the example of FIG. 1, the second output line (S phase) of the AC power supply 2 is not provided with a load current detection unit for detecting the load current. The load current flowing through the second output line (S phase) is based on the load current flowing through the first output line (R phase) and the load current flowing through the third output line (T phase) by the control device 10. , Obtained by calculation. The second output line (S phase) of the AC power supply 2 may be provided with a load current detection unit for detecting the load current flowing through the second output line (S phase). The load current detection unit 11 is composed of, for example, a current sensor.

The compensation current detection unit 12 shown in FIG. 1 detects the compensation current output from the harmonic suppression device 4 in order to suppress the harmonic current generated from the harmonic generation load 3. The compensation current detection unit 12 has compensation current detection units 12a and 12c. The compensation current detection unit 12a is provided between the reactor 8a and the midpoint 72a (R phase), and detects the compensation current flowing therethrough. Further, the compensation current detection unit 12c is provided between the reactor 8c and the midpoint 72c (T phase), and detects the compensation current flowing therethrough. The compensation current detection units 12a and 12c are connected to the control device 10, and transmit the current information of the detected compensation current to the control device 10. In the example of FIG. 1, a compensation current detection unit for detecting the compensation current flowing therethrough is not provided between the reactor 8b and the midpoint 72b (S phase). Therefore, the control device 10 flows between the reactor 8b and the midpoint 72b based on the compensation current of the R phase detected by the compensation current detection unit 12a and the compensation current of the T phase detected by the compensation current detection unit 12c. The S-phase compensation current is calculated. Not limited to this, a compensation current detection unit may be provided between the reactor 8b and the midpoint 72b (S phase). The compensation current detection unit 12 is composed of, for example, a current sensor.

(Charging operation of boot strap capacitor 18)
Hereinafter, the operation of the harmonic suppression device 4 according to the first embodiment to charge the bootstrap capacitor 18 will be described. The harmonic suppression device 4 turns on the lower switching elements 70x to 70z of the switching circuit 7 to charge the bootstrap capacitors 18 of the first drive circuits 13r to 13t that drive the upper switching elements 70r to 70t.

First, an operation in which the harmonic suppression device 4 charges the bootstrap capacitor 18 when a load current is generated from the harmonic generation load 3 will be described. In the following, for the sake of brevity, the upper switching elements 70r to 70t of the phase to be charged are simply referred to as upper switching elements 70, and the lower switching elements 70x to 70z of the phase are simply referred to as lower switching elements. It will be called 70. Further, the phase to be charged is referred to as a charging phase. Further, the first drive circuits 13r to 13t of the upper switching elements 70r to 70t are simply referred to as drive circuits 13.

In order to charge the bootstrap capacitor 18 of the drive circuit 13 that drives the upper switching element 70 of the charging phase, it is necessary to lower the potential of the midpoint 72 of the upper and lower arms of the charging phase to near the negative electrode potential of the capacitor 9. By doing so, the control voltage of the control power supply 16 becomes higher than the potential of the midpoint 72. For this purpose, the current may flow through the diode 71 connected in antiparallel to the lower switching element 70 of the charging phase, or the lower switching element 70 may be driven ON. As a result, power is supplied from the control power supply 16 to the bootstrap capacitor 18 via the current limiting resistor 14 and the diode 15.

When the lower switching element 70 is driven ON, the charge phase determination unit 10a of the control device 10 minimizes the load current based on the load current of the harmonic generation load 3 detected by the load current detection unit 11. Select a phase. The selected phase becomes the charging phase. The control signal generation unit 10b of the control device 10 generates a control signal 61 for driving the lower switching element corresponding to the charging phase in order to charge the bootstrap capacitor 18 of the charging phase. The control signal 61 designates the duty ratio of the lower switching element 70 of the charging phase in the range of 0% <duty ratio ≦ 100%. As a result, even when an element that affects the determination of the power supply voltage phase such as distortion is superimposed on the output of the AC power supply 2, the charging period of the bootstrap capacitor 18 of each phase is set during one cycle of the load current. It becomes present, and the startability of the upper switching element 70 is improved.

Here, if the charge amount of the bootstrap capacitor 18 decreases, it affects the operation of the upper switching elements 70r to 70t. Therefore, the duty ratio of the lower switching element 70x to 70z needs to be set in the range exceeding 0%. This range is a range in which the decrease in the charge amount of the bootstrap capacitor 18 is small.

Next, when the AC power supply 2 is unbalanced, the operation of the harmonic suppression device 4 to charge the bootstrap capacitor 18 will be described.

The control device 10 determines whether or not an imbalance has occurred in the AC power supply 2 as follows. That is, the control device 10 compares the effective values of the load currents of each phase, and determines whether or not the ratio of the phase having the maximum value and the phase having the minimum value of the load current is equal to or greater than the threshold U. When the ratio is less than the threshold value U, it is determined that no imbalance has occurred in the AC power supply 2. On the other hand, when the ratio is equal to or higher than the threshold value U, it is determined that an imbalance has occurred in the AC power supply 2. At this time, the threshold value U may be changed depending on the magnitude of the load current. Alternatively, it may be a predetermined fixed value.

Further, when the AC power supply 2 is unbalanced, a phase in which almost no current flows may occur in the harmonic generating load 3 depending on the unbalanced condition. At this time, the load current cannot be detected by the load current detection unit 11 for the phase in which almost no current flows. In this case, the charging phase determination unit 10a of the control device 10 detects a period in which almost no current flows in all the phases, and the charging phase is based on the phase charged in the period immediately before the period. To determine. After that, the control signal generation unit 10b needs to generate a control signal 61 for driving the lower switching element 70 of the charging phase to charge the bootstrap capacitor 18 of the upper switching element 70 of the charging phase.

For this purpose, the charging phase determination unit 10a uses the size of the effective value or the average value of the absolute values of the load currents of each phase, and the size of the phase having the maximum value and the phase having the minimum value. It is determined whether or not the ratio of the current is equal to or higher than the preset threshold value P. That is, it is determined whether or not the division result obtained by dividing the maximum phase size by the minimum phase size is equal to or greater than the threshold value P. When the ratio of the magnitudes of the maximum phase and the minimum phase is equal to or greater than the threshold value P, the charging phase determination unit 10a determines a period in which almost no current flows. This period is called the first period. The charging phase determination unit 10a determines the charging phase based on the phase charged in the period immediately before the first period. Here, the load currents of the R phase, the S phase, and the T phase change periodically as shown in FIG. FIG. 8 is a diagram showing an example of load currents of R-phase, S-phase, and T-phase of a rectifier to which a three-phase AC power supply having a DC reactor and a smoothing capacitor is input. In FIG. 8, the horizontal axis represents the phase and the vertical axis represents the load current. Further, the solid line 80 shows the load current of the R phase, the broken line 81 shows the load current of the S phase, and the dotted line 82 shows the load current of the T phase. In FIG. 8, the period (1) is the period in which the load current of the T phase is the minimum, the period (2) is the period in which the load current of the R phase is the minimum, and the period (3) is the period in which the load current of the S phase is the minimum. The minimum period. In this way, the load currents of the R phase, S phase, and T phase change periodically, and the phases that minimize the load current are the R phase, S phase, T phase, R phase, S phase, and so on. It becomes in order. Therefore, when the phase charged in the 0th period immediately before the 1st period is the R phase, the phase with the smallest load current is the S phase, so that the charging phase determination unit 10a is the first phase. The charging phase of the period is determined to be the S phase. Further, when the phase charged in the 0th period immediately before the 1st period is the S phase, the phase in which the load current is minimized next is the T phase, so that the charging phase determination unit 10a is the first phase. The charging phase of the period is determined to be the T phase. Similarly, when the phase charged in the 0th period immediately before the 1st period is the T phase, the phase with the smallest load current is the R phase, so that the charging phase determination unit 10a is the first. The charging phase for one period is determined to be the R phase. Here, FIG. 4 is a diagram showing an example of ON / OFF operation of the load currents of the R phase, the S phase, and the T phase and the lower switching elements 70x to 70z when the AC power supply 2 is in equilibrium. In FIG. 4A, the horizontal axis represents the phase and the vertical axis represents the load current. Further, in FIG. 4B, the horizontal axis indicates the phase and the vertical axis indicates the ON / OFF operation. The dotted line indicates the timing at which the phase with the minimum load current is switched. In FIG. 4, the period (1) is the period in which the load current of the T phase is the minimum, the period (2) is the period in which the load current of the R phase is the minimum, and the period (3) is the period in which the load current of the S phase is the minimum. The minimum period. Therefore, in order to charge the bootstrap capacitor 18 of the first drive circuit 13, a control signal having a duty ratio in the range of 0% <duty ratio ≦ 100% may be generated during this period.

In the first period, the control signal generation unit 10b drives the lower switching element 70 of the charging phase to generate a control signal 61 for charging the bootstrap capacitor 18 of the upper switching element 70. As a result, the bootstrap capacitor 18 is charged even in the phase in which the load current does not flow, and each phase has a charging period for the bootstrap capacitor 18. FIG. 4 is a diagram showing an example of ON / OFF operation of the lower switching elements 70x to 70z according to the first embodiment. Of these, FIG. 4A is a waveform diagram showing the waveform of the load current generated by the harmonic generation load 3 flowing through the AC power supply 2. Further, FIG. 4B is a waveform diagram showing the operation waveforms of the drive signals 62x, 62y and 62z for turning on / off the lower switching elements 70x to 70z.

Further, in the above charging method when the load current is generated from the harmonic generation load 3, the charging phase is determined based on the load current, so that one cycle occurs when the AC power supply 2 is unbalanced. Of these, the period during which current flows is shorter than at equilibrium. Therefore, the control device 10 obtains the ratio of the difference between the phase having the maximum load current and the phase having the minimum load current to the average of the load currents of all the phases from the load current of each phase as the unbalance rate. Then, the control device 10 limits the charging period by the unbalance rate for the phase having the smallest load current based on the effective value of the load current. As a result, the bootstrap capacitor 18 can be charged without a steep large current. When the charge amount in one cycle is not sufficient, charging is repeatedly performed over a period of a plurality of cycles until the charge amount of the bootstrap capacitor 18 becomes equal to or higher than the threshold value H (first threshold value). As a result, the amount of charge can be secured. If the imbalance of the power supply caused by the operation of the harmonic generation load 3 other than the air conditioning system 1 is eliminated, the unbalance rate of the load current becomes smaller and the limitation of the charging period is lifted. The charging time can be shortened. Further, if the charge period that can be limited is increased, the capacity of the bootstrap capacitor 18 becomes large. Therefore, it is desirable to limit the charge amount within a range where the decrease in the charge amount is small according to the capacity of the bootstrap capacitor 18.

Further, when the load current is large and the harmonic current suppressed by the harmonic suppression device 4 is large, the compensation current for suppressing the harmonic current becomes large, and the switching element of the harmonic suppression device 4 increases the harmonic current. It generates heat compared to the case where there is little. FIG. 5 is a diagram showing an example of a first drive circuit 13 having a control voltage adjusting circuit 20 for suppressing heat generation of the harmonic suppression device 4 according to the first embodiment.

In the first drive circuit 13 shown in FIG. 5, a control voltage adjusting circuit 20, a memory 21, a bootstrap control circuit 24, and a switching circuit 25 are added to the configuration of FIG.

A switching signal determined based on the operating state of the harmonic suppression device 4 is input from the control device 10 to the control voltage adjustment circuit 20. The control voltage adjustment circuit 20 determines the maximum voltage for charging the bootstrap capacitor 18 based on the switching signal. At this time, when the load current detected by the load current detection unit 11 is equal to or higher than the threshold value G (third threshold value), the amount of heat generated by the switching element is large, so that the control device 10 has a first load current value. Output the switching signal. The control voltage adjustment circuit 20 raises the control voltage of the control power supply 16 by, for example, a certain amount, based on the first switching signal. This suppresses the loss of the switching element. On the other hand, when the load current is less than the threshold value G, the calorific value of the switchon element is relatively small, so that there is a temperature margin in operation. In this case, the control device 10 outputs the second switching signal based on the value of the load current. The control voltage adjustment circuit 20 lowers the control voltage of the control power supply 16 by, for example, a certain amount, based on the second switching signal. As a result, although the switching loss increases, the noise during switching can be reduced. Here, the adjustment in the control voltage adjustment circuit 20 is divided into two stages, one above the threshold value and one below the threshold value, but the adjustment may be further subdivided according to the value of the load current or the operating state of the harmonic suppression device 4.

The memory 21 stores a plurality of charging methods as the charging method of the bootstrap capacitor 18 of the harmonic suppression device 4. In the example of FIG. 5, the memory 21 has a first storage unit 22 that stores the first charging method and a second storage unit 23 that stores the second charging method. The first charging method stored in the first storage unit 22 is a charging method for the bootstrap capacitor 18 based on the load current. The first charging method is applied when the harmonic generation load 3 is in an operating state and the AC power supply 2 is unbalanced or the power supply impedance is larger than the threshold value I. The second charging method stored in the second storage unit 23 is a charging method for the bootstrap capacitor 18 based on the power supply voltage of the AC power supply 2 (see, for example, Patent Document 1). The second charging method is applied when the AC power supply 2 is normal or when the load current detection unit 11 does not detect the load current. In the second charging method, the duty ratio of the corresponding lower switching element is limited to 100% or less, which exceeds 0%, based on the phase of the AC power supply 2, and the lower switching element is switched. As a result, the bootstrap capacitor 18 of the drive circuit 13 of the upper switching element is charged. The details of the first charging method will be described later with reference to the flowchart of FIG. 6 and the flowchart of FIG. 7.

Whether to charge by the first charging method or the second charging method is selected by the switching signal input from the control device 10 to the switching circuit 25. The control device 10 may output a switching signal based only on the load current, but when other parameters such as the state of the AC power supply 2 and the value of the power supply impedance are also used for the determination, the determination table is stored in advance in the memory. You may remember it in. In that case, the control device 10 determines in advance what conditions are satisfied to output the first switching signal and what conditions are satisfied to output the second switching signal. Is stored in the memory. Then, the switching signal may be output based on the determination table. The switching circuit 25 reads the first charging method from the first storage unit 22 or reads the second charging method from the second storage unit 23 according to the switching signal. As a result, the bootstrap control circuit 24 uses the selected charging method and the detected value corresponding to the charging method among the detected values of the load current or the power supply voltage to make the bootstrap capacitor 18. A control signal for charging is output to the drive IC 17.

As described above, the first charging method stored in the first storage unit 22 is applied when the load current is detected while the harmonic generation load 3 is in operation and the AC power supply 2 is unbalanced or has a large power supply impedance. .. The second charging method stored in the second storage unit 23 is applied when the power supply of the AC power supply 2 is normal or when the load current is not detected. In this way, by switching between the first charging method and the second charging method according to the state of the AC power supply 2 or the load current, the state of the AC power supply 2 and the load current of the harmonic generation load 3 can be changed. The bootstrap capacitor 18 can be charged regardless of the state. Here, when the load current is generated, the first charging method stored in the first storage unit 22 is applied, but the second charging method stored in the second storage unit 23 is not limited to that case. A charging method may be applied. However, from the viewpoint of stabilizing the control, the operation of switching the charging method is not performed while the bootstrap capacitor 18 is being charged. Therefore, the control device 10 does not change the output of the switching signal while charging the bootstrap capacitor 18.

In the first embodiment, when the load current does not flow as in the above configuration and operation, the bootstrap capacitor 18 of the charging phase is charged based on the power supply voltage. When the load current flows, the bootstrap capacitor 18 of the charging phase is charged based on the load current. As a result, the influence of the distortion superimposed on the voltage of the AC power supply 2 or the influence of the imbalance of the AC power supply 2 can be suppressed to the minimum, so that the harmonic suppression device 4 can be started smoothly. can do. Further, in the first embodiment, there is a problem that the harmonic suppression device 4 cannot be started due to the flow of a steep large current due to the fact that the harmonic suppression device 4 cannot correctly recognize the phase of the AC power supply 2. It will be resolved. Therefore, even when the air conditioning system 1 and the harmonic suppression device 4 are operating in cooperation with each other, there is no problem that the operation of the air conditioning system 1 is hindered by the inability to start the harmonic suppression device 4.

Here, there are two types of charging methods, a first charging method and a second charging method, but the number of charging methods may be three or more. Specifically, a charging method in which a part of the steps is deleted from the flow of FIG. 6 or FIG. 7 described later, or a charging method in which some steps are added to the flow of FIG. 6 or FIG. 7 described later are also prepared. May be good. In that case, those charging methods are stored in the memory 21 in advance as the third charging method, the fourth charging method, and the like, and one of them is selected by the switching signal from the control device 10. Use.

The switching elements 70r to 70t and 70x to 70z of the harmonic suppression device 4 according to the first embodiment may be composed of a wide bandgap semiconductor. The wide bandgap semiconductor is, for example, GaN (gallium nitride), SiC (silicon carbide), or diamond.

The effect when the upper switching elements 70r to 70t and the lower switching elements 70x to 70z are composed of a wide bandgap semiconductor will be described. Wide bandgap semiconductors have a high withstand voltage and a high allowable current density. Therefore, the switching elements 70r to 70t and 70x to 70z can be miniaturized. As a result, it is possible to reduce the size of the semiconductor module incorporating such switching elements 70r to 70t and 70x to 70z. Further, since the wide bandgap semiconductor has good heat resistance, the heat sink for the switching elements 70r to 70t and 70x to 70z can be miniaturized. Further, when the wide bandgap semiconductor is applied to the switching elements 70r to 70t and 70x to 70z, the on-resistance is low, the conduction loss is small, and the switching loss is also small. In addition, since the amount of gate charge required is also small, the charging time of the bootstrap capacitor 18 is shortened.

(Operation of Embodiment 1)
FIG. 6 is a flowchart illustrating an example of charge control of the bootstrap capacitor 18 of the harmonic suppression device 4 according to the first embodiment. FIG. 6 shows a flow when a load current is generated in all of the R phase, the S phase, and the T phase. That is, the flow of FIG. 6 corresponds to the first charging method stored in the first storage unit 22 shown in FIG. The flow of FIG. 6 is applied when the load current is flowing in all phases.

(Step S1)
The control device 10 determines whether the effective value of the load currents of the R phase, the S phase, and the T phase is larger than the threshold value A. The threshold value A is a preset value, and is a charging start threshold value for determining whether or not charging is started. If the effective value of the load current exceeds the threshold value A, the harmonic suppression device 4 proceeds to step S2. On the other hand, if the effective value of the load current does not exceed the threshold value A, the process of FIG. 6 is terminated as it is.

(Step S2)
The control device 10 detects the phase having the smallest load current from the R phase, the S phase, and the T phase.

(Step S3)
The control device 10 sets a threshold value B of the load current for starting charging of each phase based on the minimum value of the load current of the previous charging phase. Not limited to this, the threshold value B may be a preset fixed value.

(Step S4)
The control device 10 determines whether the load current of the R phase is the smallest among the R phase, the S phase, and the T phase. The control device 10 proceeds to step S5 when the load current of the R phase is the smallest. On the other hand, if the load current of the R phase is not the smallest, the process proceeds to step S7.

(Step S5)
The control device 10 determines whether the load current of the R phase is below the threshold value B. If the load current of the R phase is below the threshold value B, the control device 10 proceeds to step S6. On the other hand, if the load current of the R phase is not lower than the threshold value B, the process is terminated as it is.

(Step S6)
The control device 10 outputs a control signal 61 for charging the bootstrap capacitor 18 of the R-phase drive circuit 13r. As a result, the drive IC 17 outputs a drive signal 62 for driving the lower switching element 70x. As a result, the lower switching element 70x is driven ON, and the bootstrap capacitor 18 of the R-phase drive circuit 13r is charged.

(Step S7)
The control device 10 determines whether the load current of the S phase is the smallest among the R phase, the S phase, and the T phase. The control device 10 proceeds to step S8 when the load current of the S phase is the smallest. On the other hand, if the load current of the S phase is not the smallest, the process proceeds to step S10.

(Step S8)
The control device 10 determines whether the load current of the S phase is below the threshold value B. The control device 10 proceeds to step S9 when the load current of the S phase is below the threshold value B. On the other hand, if the load current of the S phase is not lower than the threshold value B, the process is terminated as it is.

(Step S9)
The control device 10 outputs a control signal 61 for charging the bootstrap capacitor 18 of the S-phase drive circuit 13s. As a result, the drive IC 17 outputs a drive signal 62 for driving the lower switching element 70y. As a result, the lower switching element 70y is driven ON, and the bootstrap capacitor 18 of the S-phase drive circuit 13s is charged.

(Step S10)
The control device 10 determines whether the load current of the T phase is below the threshold value B. The control device 10 proceeds to step S11 when the load current of the T phase is below the threshold value B. On the other hand, if the load current of the T phase is not lower than the threshold value B, the process is terminated as it is.

(Step S11)
The control device 10 outputs a control signal 61 for charging the bootstrap capacitor 18 of the T-phase drive circuit 13t. As a result, the drive IC 17 outputs a drive signal 62 for driving the lower switching element 70z. As a result, the lower switching element 70z is driven ON, and the bootstrap capacitor 18 of the T-phase drive circuit 13t is charged.

FIG. 7 is a flowchart illustrating an example of charge control of the bootstrap capacitor 18 in the harmonic suppression device 4 when there is a phase in which the load current does not occur in the first embodiment. That is, the flow of FIG. 7 corresponds to the first charging method stored by the second storage unit 22 shown in FIG. The flow of FIG. 7 is applied when there is a phase in which the load current does not flow.

(Step S21)
The control device 10 selects a phase having the largest effective value and a phase having the smallest effective value from the effective values of the load currents of the R phase, the S phase, and the T phase. In the following, the effective value of the maximum phase is referred to as the maximum effective value, and the effective value of the minimum phase is referred to as the minimum effective value. The control device 10 determines whether or not the ratio of the maximum effective value to the minimum effective value is equal to or greater than the threshold value P. When the ratio is equal to or higher than the threshold value P, the control device 10 proceeds to step S22. On the other hand, when the ratio is less than the threshold value P, the control device 10 ends the process as it is.

(Step S22)
The control device 10 determines whether or not the load currents of all the phases of the R phase, the S phase, and the T phase are equal to or less than the preset threshold value Q (second threshold value). The control device 10 proceeds to step S23 when the load currents of all the phases of the R phase, the S phase, and the T phase are equal to or less than the threshold value Q. On the other hand, if the load current of at least one of the R phase, the S phase and the T phase exceeds the threshold value Q, the control device 10 ends the process as it is.

(Step S23)
The control device 10 detects the first period in which the load currents of all the phases of the R phase, the S phase, and the T phase are equal to or less than the threshold value Q. The control device 10 determines whether the charged phase is the R phase when the load current in the period immediately before the first period is flowing. The control device 10 proceeds to step S24 when the charged phase is the R phase. On the other hand, if it is not the R phase, the process proceeds to step S25.

(Step S24)
The control device 10 sets the S phase as the charging phase of the bootstrap capacitor 18.

(Step S25)
The control device 10 determines whether the charged phase is the S phase when the load current in the period immediately before the first period is flowing. The control device 10 proceeds to step S26 when the charged phase is the S phase. On the other hand, if it is not the S phase, the process proceeds to step S27.

(Step S26)
The control device 10 sets the T phase as the charging phase of the bootstrap capacitor 18.

(Step S27)
The control device 10 determines whether the charged phase is the T phase when the load current in the period immediately before the first period is flowing. The control device 10 proceeds to step S28 when the charged phase is the T phase. On the other hand, if it is not the T phase, the process is terminated as it is.

(Step S28)
The harmonic suppression device 4 sets the R phase as the charging phase of the bootstrap capacitor 18.

(Step S29)
The control device 10 determines whether the charging start delay time has elapsed in order to charge the bootstrap capacitor 18 of the charging phase at the timing of wanting to charge while the load current of all the phases is below the threshold value Q and hardly flows. do. If the charging start delay time has elapsed, the control device 10 proceeds to step S30. On the other hand, if the charge start delay time has not elapsed, the process ends as it is.

(Step S30)
The control device 10 charges the bootstrap capacitor 18 of the charging phase.

In the first embodiment, as shown in FIG. 6, the control device 10 detects the phase having the smallest load current as the charging phase. The control device 10 charges the bootstrap capacitor when the load current of the charging phase falls below the threshold value B determined based on the minimum value of the load current of the previous charging phase.

Further, in the first embodiment, as shown in FIG. 7, when a phase in which the load current does not flow is generated among the R phase, the S phase, and the T phase, the control device 10 uses the R phase. The maximum effective value and the minimum effective value are selected from the effective values of the load currents of the S phase and the T phase. When the ratio of the maximum effective value to the minimum effective value is equal to or greater than the threshold value P, the control device 10 determines the first period in which almost no current flows in all the phases. The control device 10 determines the phase detected in the period immediately before the first period, and determines the charging phase based on the phase.

As described above, the harmonic suppression device 4 of the first embodiment charges based on the load current when the load current flows, and charges based on the power supply voltage when the load current does not flow. Distortion may be superimposed on the power supply voltage of the AC power supply 2 because the voltage imbalance of the AC power supply 2 is significant or the power supply impedance is large. In the first embodiment, even in such a case, the bootstrap capacitor 18 for driving the upper switching element can be charged without being affected by the AC power supply 2. As a result, the harmonic suppression device 4 can be stably started.

As a conventional charging method, a method of detecting the power supply voltage and the phase to determine the charging phase can be considered, but when distortion is superimposed on the power supply voltage, the phase of the AC power supply 2 is correctly recognized. Can't. In that case, in the worst case, the harmonic suppression device 4 may not be activated. In the first embodiment, the problem can be solved, and as described above, the harmonic suppression device 4 can be stably started.

Further, when the phase voltage of the AC power supply 2 is unbalanced or the power supply voltage distortion is large, the phase information of the AC power supply 2 is not stable by the conventional charging method. In that case, if the bootstrap capacitor 18 is charged using the phase information of the power supply, the power supply phase information is not stable, so that the charging timing is deviated and the harmonic suppression device 4 may not be started due to the overcurrent. In the first embodiment, since the charging timing of the bootstrap capacitor 18 is determined from the load current, such an overcurrent problem can be avoided.

In the first embodiment, the boot strap capacitor 18 of the harmonic suppression device 4 is charged when the load current of the phase having the minimum load current falls below the threshold value B determined from the minimum value of the previous load current. implement. At this time, the load current for starting charging of the bootstrap capacitor 18 may be a predetermined fixed value. Further, when a phase in which the load current does not flow is generated, the ratio of the effective value current of the phase having the maximum effective value among the phases in which the load current flows and the phase in which the load current does not flow is obtained. When the ratio is equal to or higher than the threshold value P, the charging phase is determined based on the phase charged immediately before the period in which the load current hardly flows, and charging is performed. As a result, the harmonic suppression device 4 is not affected even when an element that affects the determination of the power supply voltage phase such as distortion is superimposed on the AC power supply 2. Therefore, the harmonic suppression device 4 can charge the bootstrap capacitor 18 without short-circuiting the power supply.

1 air conditioning system, 2 AC power supply, 3 harmonic generation load, 4 harmonic suppression device, 5 refrigerant circuit, 6 ripple filter, 7 switching circuit, 8 reactor, 8a reactor, 8b reactor, 8c reactor, 9 condenser, 10 control Device, 10a Charging phase determination unit, 10b Control signal generation unit, 11 Load current detection unit, 11r Load current detection unit, 11t Load current detection unit, 12 Compensation current detection unit, 12a Compensation current detection unit, 12c Compensation current detection unit, 13 drive circuit, 13r 1st drive circuit, 13s 1st drive circuit, 13t 1st drive circuit, 13x 2nd drive circuit, 13y 2nd drive circuit, 13z 2nd drive circuit, 14 current limiting resistance, 15 diode, 16 control Power supply, 18 bootstrap capacitor, 20 control voltage adjustment circuit, 21 memory, 22 1st storage unit, 23 2nd storage unit, 24 bootstrap control circuit, 25 switching circuit, 30 rectifier, 31 DC reactor, 32 smoothing capacitor, 50 Compressor, 51 heat exchanger, 52 heat exchanger, 53 expansion valve, 54 refrigerant pipe, 61 control signal, 62 drive signal, 62x drive signal, 62y drive signal, 62z drive signal, 63 connection point, 64 reactor, 64a reactor , 64b reactor, 64c reactor, 65 capacitor, 65a capacitor, 65b capacitor, 65c capacitor, 70 switching element, 70r upper switching element, 70s upper switching element, 70t upper switching element, 70x lower switching element, 70y lower switching element, 70z lower switching element, 71 diode, 72 midpoint, 72a midpoint, 72b midpoint, 72c midpoint.

Claims

A harmonic suppression device that is connected in parallel with a harmonic generation load connected to an AC power supply and suppresses the harmonics generated by the harmonic generation load.
A plurality of upper and lower arms in which an upper switching element and a lower switching element are connected in series are connected in parallel, and each phase of the AC power supply is located at a middle point which is a connection point between the upper switching element and the lower switching element. Connected, rectifier and
A load current detector that detects the load current input from the AC power supply to the harmonic generating load, and
The first drive circuit that turns on / off the upper switching element and
The second drive circuit that turns on / off the lower switching element, and
A control device for generating a control signal for causing the first drive circuit and the second drive circuit to perform the ON / OFF operation of the upper switching element and the lower switching element is provided.
The first drive circuit is
A bootstrap capacitor that acts as a power source to drive the upper switching element,
It has a control power supply to charge the bootstrap capacitor and
The control device is
Among the load currents of each phase of the AC power supply, the phase having the minimum load current is selected as the charging phase, and the lower switching element corresponding to the charging phase is turned on / in the second drive circuit. By operating the OFF operation, the bootstrap capacitor of the first drive circuit corresponding to the charging phase is charged.
Harmonic suppressor.
When the load current detection unit detects the load current,
The control device is
Among the load currents of each phase of the AC power supply, the phase having the minimum load current is selected as the charging phase, and the second drive circuit is used during the period when the load current of the charging phase is minimized. The lower switching element corresponding to the charging phase is turned ON / OFF to charge the bootstrap capacitor of the first drive circuit corresponding to the charging phase.
The harmonic suppression device according to claim 1.
When the AC power supply becomes unbalanced,
The control device is
The ratio of the period during which the load current flows during the unbalance to the period during which the load current flows during the equilibrium of the AC power supply is determined as the unbalance rate.
The period for charging the bootstrap capacitor of the first drive circuit corresponding to the charging phase is limited based on the unbalance rate.
The bootstrap capacitor is repeatedly charged over a period of a plurality of cycles until the charge amount of the bootstrap capacitor becomes equal to or higher than the first threshold value.
The harmonic suppression device according to claim 1 or 2.
When the load current detector does not detect the load current,
The control device is
The period in which the load current of each phase is equal to or less than the second threshold value is determined as the first period.
The charging phase of the first period is determined based on the phase that was the charging phase in the period immediately preceding the first period.
The harmonic suppression device according to any one of claims 1 to 3.
The first drive circuit has a memory for storing a plurality of charging methods as a charging method for the bootstrap capacitor.
The control device is
The first drive circuit outputs a switching signal for selecting one from the plurality of charging methods based on whether or not the load current is detected by the load current detection unit, or whether the AC power supply is balanced or unbalanced. Output to
The first drive circuit reads the charging method specified by the switching signal from the memory and charges the bootstrap capacitor by the charging method.
The harmonic suppression device according to any one of claims 1 to 4.
The control device is
While charging the bootstrap capacitor, the output of the switching signal is not changed.
The harmonic suppression device according to claim 5.
The first drive circuit is
It has a control voltage adjustment circuit that adjusts the control voltage of the control power supply.
The control voltage adjustment circuit is
When the load current detected by the load current detection unit is equal to or higher than the third threshold value, the control voltage of the control power supply is increased.
When the load current detected by the load current detection unit is less than the third threshold value, the control voltage of the control power supply is lowered.
The harmonic suppression device according to any one of claims 1 to 6.
The upper switching element and the lower switching element are composed of a wide bandgap semiconductor.
The harmonic suppression device according to any one of claims 1 to 7.
The wide bandgap semiconductor is GaN (gallium nitride), SiC (silicon carbide), or diamond.
The harmonic suppression device according to claim 8.
The AC power supply is a three-phase AC power supply.
The rectifier is configured by connecting three upper and lower arms in parallel, which are installed corresponding to each phase of the three-phase AC power supply.
The harmonic suppression device according to any one of claims 1 to 9.
A refrigerant circuit in which a compressor, a heat exchanger, and an expansion valve are connected via a refrigerant pipe,
The harmonic generation load that drives the refrigerant circuit and
An air conditioning system including the harmonic suppression device according to any one of claims 1 to 10, wherein the harmonic current generated by the harmonic generation load is suppressed.
The harmonic suppression device is built in the main body of the air conditioning system.
The air conditioning system according to claim 11.