Harmonic suppression device and air conditioning system

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

[Technical field]

[0001] The present disclosure relates to a harmonic suppression device that suppresses harmonic components of a current flowing to a power grid, and an air conditioning system including the same. [Background technology]

[0002] In a conventional harmonic suppression device, a drive circuit for turning on / off upper and lower switching elements constituting a rectifier includes a bootstrap capacitor (see, for example, Patent Document 1). The upper and lower switching elements are connected in series to form a leg. The rectifier is configured with multiple legs connected in parallel.

[0003] In Patent Document 1, a bootstrap capacitor acts as a power supply for driving the upper switching elements of each leg. The bootstrap capacitor is charged from a control power supply.

[0004] In Patent Document 1, in order to charge a bootstrap capacitor for starting the harmonic suppression operation, the lower switching element of the phase to be charged is always ON when the phase voltage of the AC power supply is at the minimum phase based on the phase of the AC power supply voltage. Also, when the phase voltage of the AC power supply is not at the minimum phase and is negative, PWM control is performed.

[0005] The harmonic suppression device disclosed in Patent Document 1 performs PWM control to obtain the following effects compared to a case where the device is always ON only when the phase of the AC power supply voltage is the minimum phase: Even when the phase of the AC power supply voltage is not the minimum phase and is negative, a power supply short-circuit current of a level that does not become a steep large current is passed to forcibly charge the bootstrap capacitor, thereby shortening the charging time. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2012-50177 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the case of the above-mentioned Patent Document 1, the bootstrap capacitor is charged based on the state of the AC power supply voltage. Therefore, when the AC power supply voltage is significantly unbalanced, or when 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 cannot be correctly recognized. This causes a problem that charging starts at a different charging period than normal, causing a steeper current to flow than expected.

[0008] Furthermore, the above-mentioned Patent Document 1 describes a means for charging a bootstrap capacitor based on the reactor current after rectification of the harmonic generating load. In this case, in addition to a current detection means for the load current before rectification to suppress harmonics, a new means for detecting the reactor current after rectification is required. Furthermore, since it is not possible to determine which phase the detected current comes from based on the reactor current alone, a means for detecting the power supply voltage and phase is required.

[0009] The present disclosure has been made to solve such problems, and has an object to provide a harmonic suppression device and an air conditioning system equipped with the same that are capable of charging a bootstrap capacitor without being affected by the AC power supply. [Means for solving the problem]

[0010] A harmonic suppression device according to the present invention is a harmonic suppression device that is connected in parallel to a harmonic generating load connected to an AC power supply having multiple phases and suppresses harmonics generated by the harmonic generating load, the harmonic suppression device comprising a rectifier having multiple upper and lower arms connected in parallel corresponding to the multiple phases, the multiple upper and lower arms having upper switching elements and lower switching elements directly connected to the upper switching elements, the rectifier having a corresponding one of the multiple phases of the AC power supply connected to a midpoint which is a connection point between the upper switching element and the lower switching element in the multiple upper and lower arms, a load current detection unit configured to detect an instantaneous value of a load current input from each of the multiple phases of the AC power supply to the harmonic generating load, and the control device comprises: a plurality of first drive circuits provided corresponding to the plurality of upper and lower arms and configured to turn on / off the upper switching elements of the corresponding upper and lower arms among the plurality of upper and lower arms; a plurality of second drive circuits provided corresponding to the plurality of upper and lower arms and configured to turn on / off the lower switching elements of the corresponding upper and lower arms among the plurality of upper and lower arms; and a control device that generates control signals for causing the plurality of first drive circuits and the plurality of second drive circuits to perform the on / off operation of the upper switching elements and the lower switching elements, the plurality of first drive circuits having bootstrap capacitors acting as power supplies for driving the upper switching elements of the corresponding upper and lower arms among the plurality of upper and lower arms, and a control power supply that charges the bootstrap capacitor, and the control device When the harmonic generating load is in an operating state and there is no phase among the plurality of phases of the AC power supply in which a load current input to the harmonic generating load is not generated, A first charging method is implemented to charge the bootstrap capacitor of the first driving circuit, and in the first charging method ,before Multiple phases of Among them, the instantaneous value of the load current of the plurality of phases is the largest when comparing the instantaneous values ​​of the load current of the plurality of phases. Select a smaller phase as a charging phase and set the load current of the charging phase When the instantaneous value of is compared with the multiple phases other than the charging phaseDuring the period during which the minimum state continues, the second drive circuit among the plurality of second drive circuits corresponding to the charging phase is caused to turn on the lower switching elements of the upper and lower arms among the plurality of upper and lower arms corresponding to the charging phase, thereby charging the bootstrap capacitor of the first drive circuit corresponding to the charging phase. Effect of the Invention

[0011] According to the harmonic suppression device disclosed herein, even when distortion is superimposed on the power supply voltage, it is possible to charge the bootstrap capacitor for driving the upper switching element without being affected by the AC power supply. [Brief description of the drawings]

[0012] [Figure 1] 1 is a circuit block diagram showing a schematic configuration of an air conditioning system 1 equipped with a harmonic suppression device 4 according to a first embodiment. [Diagram 2] 2 is a circuit diagram showing a configuration of first drive circuits 13r to 13t in a harmonic suppression device 4 according to the first embodiment. FIG. [Diagram 3] 1 is a block diagram showing a configuration of a control device 10 of a harmonic suppression device 4 according to a first embodiment. [Figure 4] 5 is a diagram showing an example of an ON / OFF operation of lower switching elements 70x to 70z according to the first embodiment. FIG. [Diagram 5] 2 is a diagram showing an example of a first drive circuit 13 having a control voltage adjustment circuit 20 for suppressing heat generation in a harmonic suppression device 4 according to the first embodiment. FIG. [Figure 6] 5 is a flowchart illustrating an example of charging control of a bootstrap capacitor 18 of the harmonic suppression device 4 according to the first embodiment. [Figure 7] 5 is a flowchart illustrating an example of charging control of the bootstrap capacitor 18 in the harmonic suppression device 4 in the first embodiment when there is a phase in which no load current is generated. [Figure 8] FIG. 13 is a diagram showing R-phase, S-phase, and T-phase load currents. [Figure 9] 2 is a diagram showing a schematic diagram of a method of installing a harmonic suppression device 4 according to the first embodiment. FIG. [Figure 10] 2 is a diagram showing a schematic diagram of a method of installing a harmonic suppression device 4 according to the first embodiment. FIG. [Figure 11] 2 is a diagram showing a schematic diagram of a method of installing a harmonic suppression device 4 according to the first embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of a harmonic suppression device and an 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 embodiment, and various modifications can be made without departing from the spirit of the present disclosure. The present disclosure also includes all combinations of possible configurations among the configurations shown in the following embodiment and its modified examples. In each drawing, the same reference numerals are used to denote the same or equivalent items, and this is common throughout the entire specification. In each drawing, the relative dimensional relationship or shape of each component may differ from the actual ones.

[0014] In addition, each program according to the embodiments of the present disclosure is a process that is performed chronologically in the order described, but it does not necessarily have to be processed chronologically, and may include processes that are executed in parallel or individually.

[0015] Furthermore, 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 executed on a computing device.

[0016] Embodiment 1 1 is a circuit block diagram showing a schematic configuration of an air conditioning system 1 equipped with a harmonic suppression device 4 according to embodiment 1. In the air conditioning system 1, the harmonic suppression device 4 suppresses harmonic components of a current flowing from a harmonic generating load 3 to an AC power source 2. A harmonic is a wave that has a frequency that is an integer multiple of a fundamental wave and is included in a waveform with superimposed distortion.

[0017] As shown in Fig. 1, an 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 generating 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 power to the harmonic generating load 3. Hereinafter, 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.

[0018] (Configuration of harmonic generating load 3) The configuration of the harmonic generating load 3 will be described. The harmonic generating load 3 is, for example, a power conversion device including a rectifier 30, a DC reactor 31, a smoothing capacitor 32, an inverter (not shown), and the like, and supplies power to the refrigerant circuit 5. The rectifier 30 rectifies the AC voltage of the AC power source 2 to a DC voltage. A smoothing capacitor 32 is connected in parallel to the output side of the rectifier 30 via the DC reactor 31. The smoothing capacitor 32 smoothes the DC voltage input from the rectifier 30 via the DC reactor 31. Note that an inverter circuit may be provided between the harmonic generating load 3 and the refrigerant circuit 5, as necessary.

[0019] (Configuration of refrigerant circuit 5) Next, a configuration of the refrigerant circuit 5 will be described. The refrigerant circuit 5 is configured, for example, by connecting a compressor 50, two heat exchangers 51 and 52, and an expansion valve 53 via a refrigerant pipe 54. The refrigerant circuit 5 may further include a four-way valve, an accumulator, and the like.

[0020] The compressor 50 draws in low-pressure gas refrigerant, compresses it, and discharges it as high-pressure gas refrigerant. The compressor 50 is, for example, an inverter compressor. The inverter compressor can change the amount of refrigerant delivered per unit time by controlling an inverter circuit or the like.

[0021] 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.

[0022] The expansion valve 53 reduces the pressure of the liquid refrigerant that has been introduced by throttling, and then discharges it so that the refrigerant liquefied in the condenser can be easily evaporated in the evaporator. The expansion valve 53 also adjusts the amount of refrigerant to maintain an appropriate amount of refrigerant according to the load of the evaporator. The expansion valve 53 is, for example, an electronic expansion valve. As shown in FIG. 1, the expansion valve 53 is connected between two heat exchangers 51 and 52 by a refrigerant pipe 54.

[0023] (Configuration of harmonic suppression device 4) The harmonic suppression device 4 is provided to suppress harmonic currents that flow from the harmonic generating load 3 to the AC power source 2. The harmonic suppression device 4 is connected in parallel with the harmonic generating load 3 connected to the AC power source 2, and suppresses harmonics generated from the harmonic generating load 3. The harmonic suppression device 4 is built into 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. 10. Alternatively, the harmonic suppression device 4 may be configured as a separate body and placed separately from the air conditioning system 1 as shown in FIG. 11. Note that FIGS. 9 to 11 are diagrams that diagrammatically show a method of installing the harmonic suppression device 4 according to the first embodiment.

[0024] 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.

[0025] 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 source 2, respectively. One end of the capacitor 65a is connected to the first output line (R phase) of the AC power source 2, and the other end is connected to a connection point 63. One end of the capacitor 65b is connected to the second output line (S phase) of the AC power source 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 source 2, and the other end is connected to the connection point 63.

[0026] The reactor 8 connects the switching circuit 7 and the ripple filter 6. The reactor 8 includes reactors 8a, 8b, and 8c. The reactors 8a, 8b, and 8c are connected in series to a first output line (R phase), a second output line (S phase), and a third output line (T phase) of the AC power supply 2, respectively.

[0027] The capacitor 9 is connected in parallel to the switching circuit 7 .

[0028] 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 each have a diode 71 connected in anti-parallel to them. Hereinafter, this configuration will be called an arm. In addition, the arm is configured by connecting two arms in series, and will be called an upper and lower arm below. The three upper and lower arms are connected in parallel. Furthermore, a capacitor 9 is connected in parallel to these upper and lower arms. The connection point between the switching element 70r and the switching element 70x, the connection point between the switching element 70s and the switching element 70y, and the connection point between the switching element 70t and the switching element 70z will be called midpoints 72a, 72b, and 72c, respectively.

[0029] In the switching circuit 7, a first output line (R phase) of the AC power supply 2 is connected to a midpoint 72a via a reactor 64a and a reactor 8a of the ripple filter 6. A second output line (S phase) of the AC power supply 2 is connected to a midpoint 72b via a reactor 64b and a reactor 8b of the ripple filter 6. Similarly, a third output line (T phase) of the AC power supply 2 is connected to a midpoint 72c via a reactor 64c and a reactor 8c of the ripple filter 6.

[0030] In the switching circuit 7, a diode 71 is connected in anti-parallel to each of the switching elements 70r-70t and 70x-70z. Furthermore, the switching elements 70r-70t and 70x-70z are provided with drive circuits 13r-13t and 13x-13z that output drive signals for turning the switching elements 70r-70t and 70x-70z on and off, respectively. The drive circuits 13r-13t and 13x-13z are connected to the control device 10, receive a control signal 61 from the control device 10, and perform the on / off operation of the corresponding switching element based on the control signal 61.

[0031] In the following, of the six switching elements 70r-70t and 70x-70z, the switching elements 70r-70t are referred to as upper switching elements, and the switching elements 70x-70z are referred to as lower switching elements. In the following, the drive circuits 13r-13t that drive the upper switching elements 70r-70t are referred to as first drive circuits 13r-13t, and the drive circuits 13x-13z that drive the lower switching elements 70x-70z are referred to as second drive circuits 13x-13z.

[0032] The diodes 71 connected in anti-parallel to the switching elements 70r-70t and 70x-70z of the three upper and lower arms connected in parallel form the "rectifier" of the harmonic suppression device 4 according to embodiment 1. That is, the "rectifier" of the harmonic suppression device 4 according to embodiment 1 is the switching circuit 7 in FIG. 1 minus the first drive circuits 13r-13t and the second drive circuits 13x-13z.

[0033] FIG. 2 is a circuit 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 simplicity, 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 has 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 source 16 via the diode 15. The drive IC 17 is powered by the voltage across the bootstrap capacitor 18. The drive IC 17 receives a 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 to turn 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.

[0034] The second drive circuits 13x-13z that drive the lower switching elements 70x-70z, respectively, basically have the same configuration as the first drive circuits 13r-13t shown in Fig. 2. However, the second drive circuits 13x-13z do not need to be provided with the diode 15. The reason for this will be explained below. The second drive circuits 13x-13z are configured to eliminate the need for the diode 15 because the negative electrode of the capacitor 9 can be shared as shown in Fig. 1, and the bootstrap capacitor 18 is constantly charged.

[0035] Returning to the description of FIG. 1, the control device 10 outputs a control signal 61 for controlling the ON / OFF operation of the switching elements 70r-70t and 70x-70z to the first drive circuits 13r-13t and the second drive circuits 13x-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 determination unit 10a determines the phase for charging the bootstrap capacitor 18 from among the upper switching elements 70r-70t of the R phase, S phase, and T phase. The control signal generation unit 10b generates the control signal 61 for suppressing the harmonic current.

[0036] 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 a memory. The control device 10 has a memory. The memory is a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, or an EPROM (Erasable Programmable ROM), or a disk such as a magnetic disk, a flexible disk, or an optical disk.

[0037] 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 generating load 3. The load current detection unit 11 has load current detection units 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 detects the load current flowing through the third output line (T phase) of the AC power supply 2. The load current detection units 11r and 11t are connected to the control device 10 and transmit current information of the detected load current to the control device 10. Note that, in the example of FIG. 1, a load current detection unit for detecting the load current is not provided in the second output line (S phase) of the AC power supply 2. The load current flowing through the second output line (S phase) is calculated by the control device 10 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). A load current detection unit that detects a load current flowing through the second output line (S phase) may be provided in the second output line (S phase) of the AC power supply 2. The load current detection unit 11 is composed of, for example, a current sensor.

[0038] 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 generating 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. 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 current information of the detected compensation current to the control device 10. Note that, 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 calculates the S-phase compensation current flowing between the reactor 8b and the midpoint 72b based on the R-phase compensation current detected by the compensation current detection unit 12a and the T-phase compensation current detected by the compensation current detection unit 12c. Note that, without being limited to this, a compensation current detection unit may also be provided between the reactor 8b and the midpoint 72b (S-phase). Note that the compensation current detection unit 12 is composed of, for example, a current sensor.

[0039] (Bootstrap capacitor 18 charging operation) Hereinafter, a description will be given of an operation of the harmonic suppression device 4 according to the first embodiment to charge the bootstrap capacitor 18. The harmonic suppression device 4 drives the lower switching elements 70x-70z of the switching circuit 7 to ON, thereby charging the bootstrap capacitors 18 of the first drive circuits 13r-13t that drive the upper switching elements 70r-70t.

[0040] First, an operation of the harmonic suppression device 4 to charge the bootstrap capacitor 18 when a load current is generated by the harmonic generating load 3 will be described. In the following, for the sake of simplicity, the upper switching elements 70r-70t of the phase to be charged will be simply referred to as the upper switching elements 70, and the lower switching elements 70x-70z of the same phase will be simply referred to as the lower switching elements 70. The phase to be charged will be referred to as the charging phase. Furthermore, the first drive circuits 13r-13t of the upper switching elements 70r-70t will be simply referred to as the drive circuits 13.

[0041] 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 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. To achieve this, a current is caused to flow through the diode 71 connected in anti-parallel to the lower switching element 70 of the charging phase, or the lower switching element 70 is driven to be 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.

[0042] When the lower switching element 70 is driven to be ON, the charging phase determination unit 10a of the control device 10 selects a phase in which the load current is the smallest based on the load current of the harmonic generating load 3 detected by the load current detection unit 11. 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 specifies the duty ratio of the lower switching element 70 of the charging phase in a range of 0%<duty ratio≦100%. As a result, even if 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, a charging period for the bootstrap capacitor 18 of each phase exists during one cycle of the load current, and the start-up performance of the upper switching element 70 is improved.

[0043] 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 elements 70x to 70z needs to be set to a range exceeding 0%. This range is a range in which the charge amount of the bootstrap capacitor 18 decreases little.

[0044] Next, an operation of the harmonic suppressor 4 for charging the bootstrap capacitor 18 when the AC power supply 2 is unbalanced will be described.

[0045] The control device 10 judges whether or not an unbalance 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 the phases to judge whether or not the ratio between the phase in which the load current has the maximum value and the phase in which the load current has the minimum value is equal to or greater than a threshold value U. If the ratio is less than the threshold value U, it is judged that no unbalance has occurred in the AC power supply 2. On the other hand, if the ratio is equal to or greater than the threshold value U, it is judged that an unbalance has occurred in the AC power supply 2. In this case, the threshold value U may be changed depending on the magnitude of the load current, or may be a predetermined fixed value.

[0046] Furthermore, when the AC power supply 2 is unbalanced, depending on the condition of the unbalance, a phase in which almost no current flows may occur in the harmonic generating load 3. In this case, the load current detection unit 11 cannot detect the load current 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 phases, and determines the charging phase based on the phase in which charging was performed in the period immediately before the period. Thereafter, 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.

[0047] For this purpose, the charging phase determination unit 10a uses the magnitude of the effective value or the average value of the absolute value of the load current of each phase to determine whether or not the ratio of the magnitude of the phase in which the magnitude is maximum to the phase in which the magnitude is minimum is equal to or greater than a preset threshold value P. That is, it determines whether or not the result of dividing the magnitude of the maximum phase by the magnitude of the minimum phase is equal to or greater than the threshold value P. If the ratio of the magnitude of the maximum phase to 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 a first period. The charging phase determination unit 10a determines the charging phase based on the phase in which charging was performed in the period immediately before the first period. Here, the load currents of the R phase, S phase, and T phase change periodically as shown in FIG. 8. FIG. 8 is a diagram showing an example of the load currents of the R phase, S phase, and T phase of a rectifier to which a three-phase AC power source having a DC reactor and a smoothing capacitor is input. In FIG. 8, the horizontal axis indicates the phase, and the vertical axis indicates the load current. Moreover, a solid line 80 indicates the load current of the R phase, a dashed line 81 indicates the load current of the S phase, and a dotted line 82 indicates 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 smallest, the period (2) is the period in which the load current of the R phase is the smallest, and the period (3) is the period in which the load current of the S phase is the smallest. In this way, the load currents of the R phase, S phase, and T phase change periodically, and the phases in which the load current becomes the smallest are the R phase, the S phase, the T phase, the R phase, the S phase, . . . Therefore, when the phase in which charging was performed in the 0th period immediately before the first period is the R phase, the phase in which the load current becomes the next smallest is the S phase, and therefore the charging phase determination unit 10a determines the charging phase of the first period to be the S phase. Also, if the phase in which charging was performed in the 0th period immediately before the first period is the S phase, the phase in which the load current becomes the next smallest is the T phase, so the charging phase determination unit 10a determines the charging phase for the first period to be the T phase. Similarly, if the phase in which charging was performed in the 0th period immediately before the first period is the T phase, the phase in which the load current becomes the next smallest is the R phase, so the charging phase determination unit 10a determines the charging phase for the first period to be the R phase. Here, FIG. 4 is a diagram showing an example of the load currents of the R phase, S phase, and T phase and the ON / OFF operation of the lower switching elements 70x to 70z when the AC power supply 2 is balanced. In FIG. 4(a), the horizontal axis indicates the phase, and the vertical axis indicates the load current. Also, in FIG. 4(b), the horizontal axis indicates the phase, and the vertical axis indicates the ON / OFF operation.The dotted lines indicate the timing of switching of the phase at which the load current becomes the minimum. In Fig. 4, period (1) is the period when the load current of the T phase is the minimum, period (2) is the period when the load current of the R phase is the minimum, and period (3) is the period when the load current of the S phase is the minimum. Therefore, in order to charge the bootstrap capacitor 18 of the first drive circuit 13, it is sufficient to generate a control signal with a duty ratio in the range of 0%<duty ratio≦100% during these periods.

[0048] The control signal generating unit 10b generates 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 in the first period. As a result, the bootstrap capacitor 18 is charged even in a phase in which no load current flows, and a charging period for the bootstrap capacitor 18 exists in each phase. FIG. 4 is a diagram showing an example of the ON / OFF operation of the lower switching elements 70x to 70z according to the first embodiment. Among these, FIG. 4(a) is a waveform diagram showing the waveform of the load current generated by the harmonic generating load 3 flowing in the AC power source 2. FIG. 4(b) is a waveform diagram showing the operation waveforms of the drive signals 62x, 62y, and 62z for turning the lower switching elements 70x to 70z ON / OFF.

[0049] In the above charging method when a load current is generated from the harmonic generating load 3, the charging phase is determined based on the load current, so that when the AC power source 2 is unbalanced, the period during which the current flows in one cycle is shorter than when it is balanced. Therefore, the control device 10 obtains the ratio of the difference between the phase in which the load current is maximum and the phase in which the load current is minimum to the average of the load currents of all phases from the load currents of each phase as the unbalance rate. Then, the control device 10 limits the charging period for the phase in which the load current is the smallest based on the effective value of the load current by the unbalance rate. This allows the bootstrap capacitor 18 to be charged without a steep large current. If the amount of charge in one cycle is insufficient, charging is repeatedly performed over a period of multiple cycles until the amount of charge in the bootstrap capacitor 18 becomes equal to or greater than the threshold H (first threshold). This allows the amount of charge to be secured. If the unbalance of the power source caused by the operation of the harmonic generating load 3 other than the air conditioning system 1 is eliminated, the unbalance rate of the load current becomes smaller, and the limit on the charging period is released, thereby shortening the charging time. Furthermore, if the charging period that can be limited is increased, the capacity of the bootstrap capacitor 18 will increase, so it is desirable to limit the charging period to a range in which the decrease in the charge amount is small according to the capacity of the bootstrap capacitor 18.

[0050] Furthermore, when the load current is large and the harmonic current to be 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 generates heat compared to when the harmonic current is small. Fig. 5 is a diagram showing an example of a first drive circuit 13 having a control voltage adjustment circuit 20 for suppressing heat generation in the harmonic suppression device 4 according to the first embodiment.

[0051] The first drive circuit 13 shown in FIG. 5 has a control voltage adjusting circuit 20, a memory 21, a bootstrap control circuit 24, and a switching circuit 25 added to the configuration of FIG.

[0052] The control voltage adjustment circuit 20 receives a switching signal determined based on the operating state of the harmonic suppression device 4 from the control device 10. The control voltage adjustment circuit 20 determines the maximum voltage to charge 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 greater than the threshold G (third threshold), the amount of heat generated by the switching element is large, and therefore the control device 10 outputs a first switching signal based on the value of the load current. The control voltage adjustment circuit 20 increases the control voltage of the control power supply 16 by, for example, a fixed amount based on the first switching signal. This suppresses loss in the switching element. On the other hand, when the load current is less than the threshold G, the amount of heat generated by the switching element becomes relatively small, and therefore there is a temperature margin during operation. In this case, the control device 10 outputs a second switching signal based on the value of the load current. The control voltage adjustment circuit 20 decreases the control voltage of the control power supply 16 by, for example, a fixed amount based on the second switching signal. This increases switching loss, but can reduce noise during switching. Here, the adjustment by the control voltage adjustment circuit 20 is made in two stages, above the threshold and below the threshold. However, it may be further divided according to the value of the load current or the operating state of the harmonic suppression device 4.

[0053] The memory 21 stores a plurality of charging methods for 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 a first charging method and a second storage unit 23 that stores a 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 generating load 3 is in an operating state and the AC power source 2 is unbalanced or the power source impedance is greater than a 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 source voltage of the AC power source 2 (see, for example, Patent Document 1). The second charging method is applied when the AC power source 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 that exceeds 0% based on the phase of the AC power source 2, and the corresponding lower switching element is switched. This charges the bootstrap capacitor 18 of the drive circuit 13 for the upper switching element. Details of the first charging method will be described later with reference to the flowcharts of FIGS.

[0054] The control device 10 selects whether to charge the battery using the first charging method or the second charging method by a switching signal input to the switching circuit 25. The control device 10 may output the switching signal based only on the load current, but when other parameters such as the state of the AC power source 2 and the value of the power source impedance are also used for the judgment, a judgment table may be stored in advance in the memory. In that case, the control device 10 stores in the memory a judgment table that predetermines what conditions are satisfied for outputting the first switching signal and what conditions are satisfied for outputting the second switching signal. Then, the control device 10 may output the switching signal based on the judgment table. The switching circuit 25 reads out the first charging method from the first storage unit 22 or the second charging method from the second storage unit 23 in accordance with the switching signal. As a result, the bootstrap control circuit 24 outputs a control signal to the driving IC 17 for charging the bootstrap capacitor 18 using the selected charging method and the detection value corresponding to the selected charging method among the detection value of the load current or the detection value of the power source voltage.

[0055] In this way, the first charging method stored in the first storage unit 22 is applied when the load current is detected while the harmonic generating load 3 is in an operating state, and the AC power source 2 is unbalanced or has a large power source impedance. The second charging method stored in the second storage unit 23 is applied when the power source of the AC power source 2 is normal or when a load current is not detected. In this way, by switching between the first charging method and the second charging method depending on the state of the AC power source 2 or the load current, it is possible to charge the bootstrap capacitor 18 regardless of the state of the AC power source 2 and the state of the load current of the harmonic generating load 3. Note that, in this embodiment, the first charging method stored in the first storage unit 22 is applied when a load current is generated, but the second charging method stored in the second storage unit 23 may be applied in any case. However, from the viewpoint of stabilizing control, the charging method switching operation 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 the bootstrap capacitor 18 is being charged.

[0056] In the first embodiment, as in the above configuration and operation, when no load current flows, the bootstrap capacitor 18 of the charging phase is charged based on the power supply voltage. Also, when a load current flows, the bootstrap capacitor 18 of the charging phase is charged based on the load current. This makes it possible to minimize the influence of distortion superimposed on the voltage of the AC power supply 2 or the influence of the AC power supply 2 becoming unbalanced, so that the harmonic suppression device 4 can be started smoothly. Also, in the first embodiment, the harmonic suppression device 4 cannot start due to a steep large current flow caused by the harmonic suppression device 4 being unable to correctly recognize the phase of the AC power supply 2, and this problem is solved. Therefore, even when the air conditioning system 1 and the harmonic suppression device 4 are operating in cooperation with each other, the problem of the operation of the air conditioning system 1 being hindered due to the harmonic suppression device 4 being unable to start is no longer caused.

[0057] In this embodiment, there are two types of charging methods, the first charging method and the second charging method, but the number of charging methods may be three or more. Specifically, a charging method in which some steps are 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, may be prepared. In this case, these charging methods are stored in advance in the memory 21 as the third charging method, the fourth charging method, etc., and one of them is selected and used in response to a switching signal from the control device 10.

[0058] The switching elements 70r to 70t and 70x to 70z of the harmonic suppression device 4 according to the first embodiment may be made of a wide band gap semiconductor, such as GaN (gallium nitride), SiC (silicon carbide), or diamond.

[0059] The effect of the upper switching elements 70r to 70t and the lower switching elements 70x to 70z being made of wide band gap semiconductors will be described. Wide band gap 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, the semiconductor module incorporating such switching elements 70r to 70t and 70x to 70z can also be miniaturized. In addition, since the wide band gap semiconductor has good heat resistance, the heat sink for the switching elements 70r to 70t and 70x to 70z can also be miniaturized. Furthermore, when the wide band gap 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, the amount of gate charge required is also small, so the charging time of the bootstrap capacitor 18 is shortened.

[0060] (Operation of the First Embodiment) Fig. 6 is a flowchart for explaining an example of charging 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 phases, that is, the R phase, the S phase, and the T phase. That is, the flow in Fig. 6 corresponds to the first charging method stored in the first storage unit 22 shown in Fig. 5. The flow in Fig. 6 is applied when a load current flows in all phases.

[0061] (Step S1) The control device 10 determines whether the effective values ​​of the load currents of the R, S, and T phases are greater than a threshold A. The threshold A is a preset value, and is a charge start threshold for determining whether charging should be started or not. If the effective value of the load current exceeds the threshold 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 A, the process of FIG. 6 ends as it is.

[0062] (Step S2) The control device 10 detects the phase having the smallest load current from among the R phase, the S phase, and the T phase.

[0063] (Step S3) The control device 10 sets a threshold value B of the load current at which charging of each phase is started based on the minimum value of the load current of the previous charging phase. Note that, without being limited to this, the threshold value B may be a fixed value set in advance.

[0064] (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. If the load current of the R phase is the smallest, the control device 10 proceeds to step S5. On the other hand, if the load current of the R phase is not the smallest, the control device 10 proceeds to step S7.

[0065] (Step S5) The control device 10 determines whether the R-phase load current is below the threshold value B. If the R-phase load current is below the threshold value B, the control device 10 proceeds to step S6. On the other hand, if the R-phase load current is not below the threshold value B, the control device 10 ends the process.

[0066] (Step S6) The control device 10 outputs a control signal 61 for charging the bootstrap capacitor 18 of the R-phase drive circuit 13r. This causes the drive IC 17 to output a drive signal 62 for driving the lower switching element 70x. This causes the lower switching element 70x to be turned ON, and the bootstrap capacitor 18 of the R-phase drive circuit 13r is charged.

[0067] (Step S7) The control device 10 determines whether the load current of the S phase is the smallest among the R phase, S phase, and T phase. If the load current of the S phase is the smallest, the control device 10 proceeds to step S8. On the other hand, if the load current of the S phase is not the smallest, the control device 10 proceeds to step S10.

[0068] (Step S8) The control device 10 determines whether the S-phase load current is below the threshold value B. If the S-phase load current is below the threshold value B, the control device 10 proceeds to step S9. On the other hand, if the S-phase load current is not below the threshold value B, the control device 10 ends the process.

[0069] (Step S9) The control device 10 outputs a control signal 61 for charging the bootstrap capacitor 18 of the S-phase drive circuit 13s. This causes the drive IC 17 to output a drive signal 62 for driving the lower switching element 70y. This causes the lower switching element 70y to be turned ON, and the bootstrap capacitor 18 of the S-phase drive circuit 13s is charged.

[0070] (Step S10) The control device 10 determines whether the T-phase load current is below the threshold value B. If the T-phase load current is below the threshold value B, the control device 10 proceeds to step S11. On the other hand, if the T-phase load current is not below the threshold value B, the control device 10 ends the process.

[0071] (Step S11) The control device 10 outputs a control signal 61 for charging the bootstrap capacitor 18 of the T-phase drive circuit 13t. This causes the drive IC 17 to output a drive signal 62 for driving the lower switching element 70z. This causes the lower switching element 70z to be turned ON, and the bootstrap capacitor 18 of the T-phase drive circuit 13t is charged.

[0072] Fig. 7 is a flowchart for explaining an example of charging control of the bootstrap capacitor 18 in the harmonic suppression device 4 in the case where there is a phase in which no load current is generated according to the first embodiment. That is, the flow in Fig. 7 corresponds to the first charging method stored in the second storage unit 22 shown in Fig. 5. The flow in Fig. 7 is applied to the case where there is a phase in which no load current flows.

[0073] (Step S21) The control device 10 selects the phase with the maximum effective value and the phase with the minimum effective value from the effective values ​​of the load currents of the R phase, S phase, and T phase. Hereinafter, the effective value of the maximum phase will be referred to as the maximum effective value, and the effective value of the minimum phase will be referred to as the minimum effective value. The control device 10 determines whether or not the ratio between the maximum effective value and the minimum effective value is equal to or greater than a threshold value P. If the ratio is equal to or greater than the threshold value P, the control device 10 proceeds to step S22. On the other hand, if the ratio is less than the threshold value P, the control device 10 ends the process.

[0074] (Step S22) The control device 10 determines whether the load currents of all the R, S, and T phases are equal to or less than a preset threshold value Q (second threshold value). If the load currents of all the R, S, and T phases are equal to or less than the threshold value Q, the control device 10 proceeds to step S23. On the other hand, if the load current of at least one of the R, S, and T phases exceeds the threshold value Q, the control device 10 ends the process.

[0075] (Step S23) The control device 10 detects a first period in which the load currents of all phases, 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 flows in the period immediately before the first period. If the charged phase is the R phase, the control device 10 proceeds to step S24. On the other hand, if the charged phase is not the R phase, the control device 10 proceeds to step S25.

[0076] (Step S24) The control device 10 sets the S phase as the charging phase for the bootstrap capacitor 18 .

[0077] (Step S25) When the load current flows in the period immediately before the first period, the control device 10 determines whether the charged phase is the S phase. If the charged phase is the S phase, the control device 10 proceeds to step S26. On the other hand, if the charged phase is not the S phase, the control device 10 proceeds to step S27.

[0078] (Step S26) The control device 10 sets the T phase as the charging phase for the bootstrap capacitor 18 .

[0079] (Step S27) When the load current flows in the period immediately before the first period, the control device 10 determines whether the charged phase is the T phase. If the charged phase is the T phase, the control device 10 proceeds to step S28. On the other hand, if the charged phase is not the T phase, the process ends.

[0080] (Step S28) The harmonic suppressor 4 sets the R phase as the charging phase of the bootstrap capacitor 18 .

[0081] (Step S29) In a period in which the load currents of all phases are barely flowing, being equal to or less than the threshold Q, 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 a desired timing. If the charging start delay time has elapsed, the control device 10 proceeds to step S30. On the other hand, if the charging start delay time has not elapsed, the control device 10 ends the process.

[0082] (Step S30) The controller 10 charges the bootstrap capacitor 18 of the charge phase.

[0083] In the first embodiment, the control device 10 detects the phase in which the load current is the smallest as the charging phase, as shown in Fig. 6. The control device 10 charges the bootstrap capacitor when the load current in the charging phase falls below a threshold B determined based on the minimum value of the load current in the previous charging phase.

[0084] In the first embodiment, as shown in Fig. 7, when there is a phase in which no load current flows among the R, S, and T phases, the control device 10 selects the maximum effective value and the minimum effective value from the effective values ​​of the load currents of the R, S, and T phases. When the ratio between the maximum effective value and the minimum effective value is equal to or greater than a threshold value P, the control device 10 determines a first period in which almost no current flows in any of 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 that phase.

[0085] As described above, the harmonic suppression device 4 of the first embodiment charges based on the load current when a load current flows, and charges based on the power supply voltage when no load current flows. There are cases where distortion is superimposed on the power supply voltage of the AC power supply 2 due to significant voltage imbalance of the AC power supply 2 or large power supply impedance. 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. This allows the harmonic suppression device 4 to be started up stably.

[0086] In addition, as a conventional charging method, a method of detecting the power supply voltage and phase to determine the charging phase can be considered, but if distortion is superimposed on the power supply voltage, the phase of the AC power supply 2 cannot be correctly recognized. In such a case, in the worst case, the harmonic suppression device 4 may not be able to start up. In the first embodiment, this problem can be solved, and the harmonic suppression device 4 can be stably started up as described above.

[0087] Furthermore, when there is a phase voltage imbalance in the AC power supply 2 or when the power supply voltage distortion is large, the phase information of the AC power supply 2 is unstable in the conventional charging method. In that case, if the bootstrap capacitor 18 is charged using the power supply phase information, the power supply phase information is unstable, and the charging timing is shifted, and there are cases where the harmonic suppression device 4 cannot be started due to an overcurrent. In the first embodiment, the charging timing of the bootstrap capacitor 18 is determined from the load current, so that such an overcurrent problem can be avoided.

[0088] In the first embodiment, the charging of the bootstrap capacitor 18 of the harmonic suppression device 4 is performed when the load current of the phase in which the load current is the minimum falls below a threshold value B determined from the minimum value of the previous load current. At this time, the load current at which the charging of the bootstrap capacitor 18 starts may be a predetermined fixed value. Also, when a phase in which no load current flows occurs, a ratio between the phase in which the load current flows and the effective value current of the phase in which no load current flows is obtained. When the ratio is equal to or greater than a threshold value P, the charging phase is determined based on the phase charged immediately before the period in which almost no load current flows, and charging is performed. As a result, even if an element that affects the determination of the power supply voltage phase, such as distortion, is superimposed on the AC power supply 2, the harmonic suppression device 4 is not affected by the element. Therefore, the harmonic suppression device 4 can charge the bootstrap capacitor 18 without short-circuiting the power supply. [Explanation of symbols]

[0089] 1 air conditioning system, 2 AC power supply, 3 harmonic generating load, 4 harmonic suppression device, 5 refrigerant circuit, 6 ripple filter, 7 switching circuit, 8 reactor, 8a reactor, 8b reactor, 8c reactor, 9 capacitor, 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 first drive circuit, 13s first drive circuit, 13t first drive circuit, 13x second drive circuit, 13y second drive circuit, 13z second drive circuit, 14 current limiting resistor, 15 diode, 16 control power supply, 18 bootstrap capacitor, 20 control voltage adjustment circuit, 21 memory, 22 First memory unit, 23 Second memory 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 piping, 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

1. A harmonic suppression device that is connected in parallel with a harmonic generating load that is connected to an AC power source having multiple phases and suppresses harmonics generated by the harmonic generating load, a rectifier in which a plurality of upper and lower arms corresponding to the plurality of phases are connected in parallel, the plurality of upper and lower arms each having an upper switching element and a lower switching element directly connected to the upper switching element, and a corresponding one of the plurality of phases of the AC power supply is connected to a midpoint of the plurality of upper and lower arms which is a connection point between the upper switching element and the lower switching element; a load current detection unit configured to detect an instantaneous value of a load current input from each of the plurality of phases of the AC power supply to the harmonic generating load; a plurality of first drive circuits provided corresponding to the plurality of upper and lower arms, each of which controls ON / OFF of the upper switching element of the corresponding upper or lower arm among the plurality of upper and lower arms; a plurality of second drive circuits provided corresponding to the plurality of upper and lower arms, each of which controls ON / OFF of the lower switching element of the corresponding upper or lower arm among the plurality of upper and lower arms; a control device that generates control signals for causing the first drive circuits and the second drive circuits to perform the ON / OFF operations of the upper switching element and the lower switching element; Equipped with The plurality of first drive circuits include a bootstrap capacitor acting as a power source for driving the upper switching element of the corresponding upper or lower arm among the plurality of upper and lower arms; a control power supply for charging the bootstrap capacitor; having the control device implements a first charging method for charging the bootstrap capacitor of the first drive circuit when the harmonic generating load is in an operating state and there is no phase among the multiple phases of the AC power supply that does not generate a load current input to the harmonic generating load, In the first charging method, Among the plurality of phases, a phase having the smallest instantaneous value of the load current when comparing the instantaneous values ​​of the load current of the plurality of phases is selected as a charging phase, and during a period during which the instantaneous value of the load current of the charging phase is the smallest when compared with the plurality of phases other than the charging phase, The bootstrap capacitor of the first drive circuit corresponding to the charging phase is charged by causing the lower switching elements of the upper and lower arms corresponding to the charging phase among the plurality of upper and lower arms to be operated ON in the second drive circuit corresponding to the charging phase among the plurality of second drive circuits. Harmonic suppression device.

2. When the load current detection unit detects the instantaneous value of the load current input from the AC power supply to the harmonic generating load in all of the multiple phases, The control device includes: In the first charging method, among the load currents of the multiple phases of the AC power supply, a phase having the smallest instantaneous value of the load current when instantaneous values ​​of the load currents of the multiple phases at any phase of the AC power supply are compared is selected as the charging phase, and during a period during which a state in which the instantaneous value of the load current of the charging phase is smallest when compared with the multiple phases other than the charging phase continues, the second drive circuit among the multiple second drive circuits corresponding to the charging phase is caused to turn on the lower side switching element corresponding to the charging phase at 0%<duty ratio≦100%, thereby charging the bootstrap capacitor of the first drive circuit corresponding to the charging phase; The harmonic suppression device according to claim 1 .

3. The control device includes: calculating a ratio of a difference between the effective value of the load current of a phase among the plurality of phases in which the effective value of the load current is maximum and the effective value of the load current of a phase among the plurality of phases in which the effective value of the load current is minimum, to an average of the effective values ​​of the load current of all of the plurality of phases; limiting a period for charging the bootstrap capacitor of the first drive circuit corresponding to the charging phase based on the ratio; The bootstrap capacitor is repeatedly charged over a period of a plurality of cycles in which the charging phase is a charging target until a charge amount of the bootstrap capacitor becomes equal to or greater than a first threshold value. The harmonic suppression device according to claim 1 or 2.

4. The control device includes: When the harmonic generating load is in an operating state and there is a phase among the plurality of phases of the AC power supply in which a load current input to the harmonic generating load is not generated, If there is a period during which the effective value of the load current of each phase is equal to or less than a second threshold, the period is determined to be a first period; A second charging method is implemented in which the charging phase of the first period is determined based on the phase that was the charging phase in the period immediately before the first period. The harmonic suppression device according to claim 3.

5. the first drive circuit has a memory that stores a plurality of charging methods including the first charging method as a charging method for the bootstrap capacitor; The control device includes: outputting, to the first drive circuit, a switching signal for selecting one of the plurality of charging methods based on whether or not the instantaneous values ​​of the load currents of the plurality of phases have been detected by the load current detection unit, or based on whether the AC power supply is balanced or unbalanced; the first drive circuit reads out from the memory a charging method designated by the switching signal, and charges the bootstrap capacitor using the charging method; The harmonic suppression device according to any one of claims 1 to 4.

6. The control device includes: While the bootstrap capacitor is being charged, the output of the switching signal is not changed. The harmonic suppression device according to claim 5.

7. The first drive circuit is a control voltage adjusting circuit that adjusts a control voltage that charges the bootstrap capacitor of the control power supply; The control voltage adjustment circuit includes: When the load current of the plurality of phases detected by the load current detection unit has a phase whose effective value is equal to or greater than a third threshold value, the control voltage of the control power supply supplied to the first drive circuit corresponding to the phase is increased; When the load current of the plurality of phases detected by the load current detection unit has a phase whose effective value is less than the third threshold value, the control voltage of the control power supply supplied to the first drive circuit corresponding to the phase is reduced. The harmonic suppression device according to any one of claims 3, 4, 5 which recites claim 3 or 4, and 6 which recites claim 5 which recites claim 3 or 4.

8. The upper switching element and the lower switching element are made of a wide band gap semiconductor. The harmonic suppression device according to any one of claims 1 to 7.

9. The wide band gap semiconductor is GaN (gallium nitride), SiC (silicon carbide), or diamond; The harmonic suppression device according to claim 8.

10. the AC power supply is a three-phase AC power supply, The rectifier is configured by connecting three upper and lower arms in parallel, the upper and lower arms being 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.

11. a refrigerant circuit in which a compressor, a heat exchanger, and an expansion valve are connected via a refrigerant pipe; The harmonic generating load that drives the refrigerant circuit; A harmonic suppression device according to any one of claims 1 to 10, which suppresses harmonic currents generated by the harmonic generating load. Equipped with an air conditioning system.

12. The harmonic suppression device is built into the main body of the air conditioning system. The air conditioning system of claim 11.

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