Power conversion device and heat pump system having the same

Abstract

To suppress harmonics superimposed on an input current from a three-phase AC power supply.SOLUTION: A power conversion device (100) includes a rectifier circuit (110) that rectifies AC output from a three-phase AC power supply (2) into DC, an inverter circuit (120) that converts the DC output from the rectifier circuit (110) into AC by switching operations of a plurality of first switching elements (121 to 126) and supplies the AC to a motor (201), a capacitor (130) connected between input nodes of the inverter circuit (120), an overvoltage protection circuit (140) having a second switching element (142) and connected in parallel with the capacitor (130), and a reactor (150) connected in series with the rectifier circuit (110) and the inverter circuit (120), in which no capacitor element is connected in series with the second switching element (142), and the capacitance of the capacitor (130) is set to 50 μF or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion device equipped with an overvoltage protection circuit and a heat pump system having the same. [Background technology]

[0002] The power conversion device disclosed in Patent Document 1 includes a rectifier circuit that rectifies AC output from a three-phase AC power supply into DC, an inverter circuit having a plurality of switching elements that converts the DC output from the rectifier circuit into AC through the switching operation of the plurality of switching elements and supplies the AC to a motor, a capacitor connected between input nodes of the inverter circuit, an overvoltage protection circuit having a diode, a resistor, and a second capacitor connected in series and connected in parallel to the capacitor, and a reactor connected in series with the rectifier circuit and the inverter circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4391768 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the inventors of the present application have discovered that when a capacitor is provided in an overvoltage protection circuit as in Patent Document 1, the harmonics superimposed on the input current from the three-phase AC power supply become larger than when no capacitor is provided.

[0005] An object of the present disclosure is to suppress harmonics superimposed on an input current from a three-phase AC power supply. [Means for solving the problem]

[0006] A first aspect of the present disclosure is a power conversion device including: a rectifier circuit (110) that rectifies AC output from a three-phase AC power supply (2) into DC; an inverter circuit (120) having a plurality of first switching elements (121-126) that converts the DC output from the rectifier circuit (110) into AC by switching operations of the plurality of first switching elements (121-126) and supplies the AC to a motor (201); a capacitor (130) connected between input nodes of the inverter circuit (120); an overvoltage protection circuit (140) having a second switching element (142) and connected in parallel with the capacitor (130); and a reactor (150) connected in series with the rectifier circuit (110) and the inverter circuit (120), wherein no capacitor element is connected in series to the second switching element (142), and the capacitance of the capacitor (130) is 50 μF or less.

[0007] In the first aspect, since a capacitor element is not connected in series to the second switching element (142) of the overvoltage protection circuit (140), harmonics superimposed on the input current from the three-phase AC power supply (2) can be suppressed more effectively than when the capacitor elements are connected in series.

[0008] Furthermore, since the capacitance of the capacitor (130) is set to 50 μF or less, harmonics superimposed on the input current from the three-phase AC power supply (2) can be suppressed more effectively than when the capacitance is set to more than 50 μF.

[0009] A second aspect of the present disclosure is characterized in that in the first aspect, the second switching element (142) is an element whose main material is a wide bandgap semiconductor.

[0010] In the second aspect, the temperature at which the overvoltage protection circuit (140) can stably operate can be increased, and therefore the cooler for cooling the overvoltage protection circuit (140) can be made smaller.

[0011] A third aspect of the present disclosure is a circuit configuration in which, in the first or second aspect, when the capacitance of the capacitor (130) is C [F], the switching frequency of the first switching elements (121 to 126) is fc [Hz], and the inductance of the reactor (150) is L [H], the following relationship holds: fc>20*10 3 When the above equation is satisfied, the following equation is satisfied:

[0012]

number

[0013] In the third aspect, harmonics superimposed on the input current from the three-phase AC power supply (2) can be suppressed more effectively than when the above formula is not satisfied.

[0014] A fourth aspect of the present disclosure is characterized in that, in any one of the first to third aspects, the rated output of the motor (201) is 4 kW or more and 30 kW or less.

[0015] In the fourth aspect, the rated output of the motor (201) is set to 30 kW or less, and therefore, harmonics superimposed on the input current from the three-phase AC power supply (2) can be suppressed more effectively than when the rated output of the motor (201) is set to more than 30 kW.

[0016] A fifth aspect of the present disclosure provides a three-phase AC power supply (2) including a rectifier circuit (110) that rectifies AC output from a three-phase AC power supply (2) into DC; an inverter circuit (120) that has a plurality of first switching elements (121-126) and converts the DC output from the rectifier circuit (110) into AC by switching operations of the plurality of first switching elements (121-126) and supplies the AC to a motor (201); a capacitor (130) connected between input nodes of the inverter circuit (120); and an overvoltage protection circuit (142) that has a second switching element (142) and is connected in parallel with the capacitor (130). The heat pump system includes a power conversion device (100) including a protection circuit (140) and a reactor (150) connected in series with the rectifier circuit (110) and the inverter circuit (120), wherein a capacitor element is not connected in series to the second switching element (142), and the following equation is satisfied when the capacitance of the capacitor (130) is C [F], the AC voltage output from the three-phase AC power source (2) is Vac [V], and the power obtained by multiplying the larger of the power consumption during operation under rated cooling conditions and the power consumption during operation under rated heating conditions by 1.75 is P [W]:

[0017]

number

[0018] In the fifth aspect, since a capacitor element is not connected in series to the second switching element (142) of the overvoltage protection circuit (140), harmonics superimposed on the input current from the three-phase AC power supply (2) can be suppressed more effectively than when the capacitor elements are connected in series.

[0019] Furthermore, compared to when the capacitance of the capacitor (130) is made larger than the right-hand side of the above equation, harmonics superimposed on the input current from the three-phase AC power supply (2) can be suppressed.

[0020] A sixth aspect of the present disclosure provides a power supply for a motor (201), comprising: a rectifier circuit (110) that rectifies AC output from a three-phase AC power supply (2) into DC; an inverter circuit (120) that has a plurality of first switching elements (121-126) and converts the DC output from the rectifier circuit (110) into AC by switching operations of the plurality of first switching elements (121-126) and supplies the AC to a motor (201); a capacitor (130) connected between input nodes of the inverter circuit (120); and a second switching element (121-126). The power conversion device includes an overvoltage protection circuit (142) connected in parallel with the capacitor (130), and a reactor (150) connected in series with the rectifier circuit (110) and the inverter circuit (120), wherein the second switching element (142) does not have a capacitor element connected in series, and the following formula is established when the capacitance of the capacitor (130) is C [F], the AC voltage output from the three-phase AC power supply (2) is Vac [V], and the rated output power of the motor (201) is P [W].

[0021]

number

[0022] In the sixth aspect, since a capacitor element is not connected in series to the second switching element (142) of the overvoltage protection circuit (140), harmonics superimposed on the input current from the three-phase AC power supply (2) can be suppressed more effectively than when the capacitor elements are connected in series.

[0023] Furthermore, compared to when the capacitance of the capacitor (130) is made larger than the right-hand side of the above equation, harmonics superimposed on the input current from the three-phase AC power supply (2) can be suppressed. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a block diagram showing the configuration of an air conditioning system as a heat pump system according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a circuit diagram showing the configuration of the power conversion device. [Figure 3] FIG. 3 is a graph showing the relationship between the capacitance of the capacitor and the harmonics superimposed on the input current. [Figure 4] FIG. 4 is a timing chart of the input current from the three-phase AC power supply when the capacitance of the capacitor is 120 μF, and the input current from the three-phase AC power supply when the capacitance of the capacitor is 50 μF. [Figure 5] FIG. 5 is a view corresponding to FIG. 2 of the second embodiment. [Figure 6] FIG. 6 is a view equivalent to FIG. 5 of the third embodiment. [Figure 7] FIG. 7 is a timing chart showing the operation of the power conversion device according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the following embodiments are essentially preferred examples and are not intended to limit the scope of the present invention, its applications, or its uses.

[0026] (Embodiment 1) Fig. 1 shows an air conditioning system (1) as a heat pump system. The air conditioning system (1) includes an outdoor unit (10) and an indoor unit (20). The outdoor unit (10) includes a power converter (100) according to the first embodiment of the present disclosure shown in Fig. 2 and a compressor (200).

[0027] The power converter (100) converts AC power supplied from the three-phase AC power supply (2) into AC power having a desired frequency and a desired voltage, and supplies the AC power to a motor (201) of a compressor (200). The rated output of the motor (201) is 4 kW or more and 30 kW or less.

[0028] The power conversion device (100) includes a rectifier circuit (110), an inverter circuit (120), a capacitor (130), an overvoltage protection circuit (140), a reactor (150), first and second resistors (161, 162), a shunt resistor (163), a switching power supply (180), and a control circuit (190).

[0029] The rectifier circuit (110) rectifies AC output from the three-phase AC power supply (2) into DC and outputs the DC to a positive voltage power line (171) and a negative voltage power line (172). The rectifier circuit (110) has first to sixth rectifier circuit diodes (111 to 116) connected in a bridge configuration. The cathodes of these rectifier circuit diodes (111 to 116) face the positive voltage power line (171) and the anodes face the negative voltage power line (172).

[0030] The inverter circuit (120) has six first switching elements (121-126) and six freewheeling diodes (FD). The six first switching elements (121-126) are bridge-connected. More specifically, the inverter circuit (120) has three switching legs connected between a positive voltage side power supply line (171) and a negative voltage side power supply line (172). Each switching leg has two first switching elements (121-126) connected in series. In each of the three switching legs, the midpoint between the first switching element (121, 123, 125) of the upper arm and the first switching element (122, 124, 126) of the lower arm is connected to a coil of each phase (coil of the u-phase, v-phase, and w-phase) of the motor (200). Each of the first switching elements (121-126) is connected in anti-parallel to a freewheeling diode (FD). The inverter circuit (120) converts the direct current output from the rectifier circuit (110) into alternating current through switching operations of the plurality of first switching elements (121-126) and supplies the alternating current to the motor (201) of the compressor (200).

[0031] The capacitor (130) is connected between the rectifier circuit (110) and the inverter circuit (120) and between the input nodes of the inverter circuit (120) (between the positive voltage side power supply line (171) and the negative voltage side power supply line (172)).

[0032] The overvoltage protection circuit (140) includes a third resistor (141) and a second switching element (142) connected in series between a positive voltage side power supply line (171) and a negative voltage side power supply line (172). The overvoltage protection circuit (140) is connected in parallel with a capacitor (130) between the rectifier circuit (110) and the inverter circuit (120). No capacitor element is connected in series with the second switching element (142). The second switching element (142) is an element whose main material is a wide bandgap semiconductor containing silicon carbide (SiC), gallium nitride (GaN), or diamond (C). Wide bandgap semiconductors can operate at high temperatures of up to approximately 300 degrees. The second switching element (142) has an on-resistance.

[0033] The overvoltage protection circuit 140 may not include the third resistor 141, and the function of the third resistor 141 may be performed by the on-resistance of the second switching element 142. The second switching element 142 may be an element mainly made of a silicon semiconductor, instead of a wide bandgap semiconductor.

[0034] The first switching element (121-126) of the inverter circuit (120) and the third resistor (141) and second switching element (142) of the overvoltage protection circuit (140) are housed in the same package (case).

[0035] The reactor (150) is connected in series with the rectifier circuit (110) and the inverter circuit (120). Specifically, the reactor (150) is connected to a positive voltage side power supply line (171) between the rectifier circuit (110) and the capacitor (130). When the capacitance of the capacitor (130) is 50 μF or less and the switching frequency of the first switching elements (121-126) is 20 kHz (20*10 3When the frequency of the capacitor (130) is higher than fc [Hz], the following equation (1) holds: In the following equation (1), the capacitance of the capacitor (130) is C [F], the switching frequency of the first switching elements (121 to 126) is fc [Hz], and the inductance of the reactor (150) is L [H].

[0036]

number

[0037] The first and second resistors (161, 162) are connected in series between the positive voltage power supply line (171) and the negative voltage power supply line (172). The first and second resistors (161, 162) are connected in parallel with the capacitor (130) between the rectifier circuit (110) and the inverter circuit (120).

[0038] The shunt resistor 163 is connected to the negative voltage side power supply line 172. The shunt resistor 163 detects the current flowing from the negative voltage side power supply line 172 to the motor 201.

[0039] The switching power supply (180) uses the voltage at the connection point of the first and second resistors (161, 162) to output a voltage required for the control circuit (190). The voltage across the second resistor (162) is input to the switching power supply (180). The voltage across the second resistor (162) is 5 to 40 V.

[0040] The control circuit (190) detects the voltage at the connection point of the first and second resistors (161, 162). The detected voltage here is a voltage obtained by dividing the voltage of the capacitor (130) and is a voltage corresponding to the voltage of the capacitor (130). The control circuit (190) operates the first switching elements (121-126) of the inverter circuit (120) based on the current detected by the shunt resistor (163) and the detected voltage corresponding to the voltage of the capacitor (130), thereby controlling the motor (201) while suppressing resonance generated by the capacitor (130) and the reactor (150). The control circuit (190) operates the first switching elements (121-126) so that the switching frequency of the first switching elements (121-126) is higher than 20 kHz. By setting the switching frequency of the first switching elements (121-126) higher than 20 kHz, which is the upper limit of the human audible range, it is possible to suppress abnormal noise generated from the inverter circuit (120).

[0041] Furthermore, when the operation of the inverter circuit (120) is stopped for the purpose of protection against overcurrent and overvoltage, i.e., when the motor (201) is not being controlled, the control circuit (190) turns on the second switching element (142) to operate the overvoltage protection circuit (140). The control circuit (190) turns on the second switching element (142) only when the operation of the inverter circuit (120) is stopped.

[0042] In the power conversion device (100) configured as described above, when the control circuit (190) stops the operation of the first switching elements (121 to 126) from the state where the first switching elements (121 to 126) are operated at a switching frequency higher than 20 kHz, the second switching element (142) is turned on. As a result, the operation of the inverter circuit (120) stops, and regenerative energy from the motor (201) flows into the capacitor (130). At this time, the regenerative energy from the motor (201) is consumed by the third resistor (141) of the overvoltage protection circuit (140). Therefore, it is possible to suppress the increase in the voltage of the capacitor (130) due to the regenerative energy from the motor (201).

[0043] Hereinafter, as a method for setting the capacitance of the capacitor (130), the first and second setting methods will be described. It is preferable to set the capacitance of the capacitor (130) by selecting and using either the first or second setting method.

[0044] First, the first setting method is a method of setting the capacitance of the capacitor (130) such that the following formula (2) holds. Here, let the capacitance of the capacitor (130) be C [F], the AC voltage output from the three-phase AC power supply (2) be Vac [V], the rated output power of the motor (201) be P [W], the frequency that is n times the frequency f of the three-phase AC power supply (2) be fn [Hz], and the target ratio value of the n-th component with respect to the fundamental wave component be K (0 < K < 1). Note that the fundamental wave component indicates the frequency component of the AC output from the three-phase AC power supply (2). Hereinafter, the case where the fundamental wave component is a frequency component of 50 Hz will be described, but the fundamental wave component may be a frequency component of 60 Hz.

[0045]

Equation

[0046] When the loss of the inverter circuit (120) is small and the rated output power of the motor (201) is approximately equal to the input power of the inverter circuit (120), the following formula (3) holds. Here, the inductance of the reactor (150) is L [H], the capacitance of the capacitor (130) is C [F], the AC voltage output from the three-phase AC power supply (2) is Vac [V], the rated output power of the motor (201) is P [W], the frequency that is n times the frequency f of the three-phase AC power supply (2) is fn [Hz], and the target ratio value of the nth component with respect to the fundamental wave component is K (0 < K < 1). The rated output power of the motor (201) is the mechanical output that can be continuously used. Note that instead of the rated output power of the motor (201), the power obtained by multiplying by 1.75 the larger of the power consumption during operation under the cooling rated conditions and the power consumption during operation under the heating rated conditions may be used as P [W].

[0047]

Number

[0048] The reactor (150) and the capacitor (130) constitute an LC filter. The denominator on the left side of formula (3) represents the impedance [Ω] at fn [Hz]. Therefore, the left side of formula (3) is the value obtained by dividing the AC voltage output from the three-phase AC power supply (2) by the impedance, that is, the value of the nth component of the input current from the three-phase AC power supply (2). The right side of formula (3) is the value obtained by multiplying the target ratio value of the nth component by the fundamental wave current, that is, it represents the target value of the harmonic current at fn [Hz].

[0049] Since the capacitance C [F] of the capacitor (130) in the denominator on the left side of formula (3) is small, as shown below, the impedance of the capacitor (130) becomes dominant with respect to the overall impedance.

[0050]

Number

[0051] Therefore, formula (3) can be rewritten as follows.

[0052]

number

[0053] This formula can be transformed into the above formula (2).

[0054] Furthermore, substituting K=0.15 and fn=250 into the above formula (2) results in the following formula (4).

[0055]

number

[0056] In equation (4), when P=30 kW and Vac=200 V, the ratio of the fifth-order component to the fundamental wave component can be reduced to less than the target ratio value by setting the capacitance of the capacitor (130) to less than approximately 71.25 μF.

[0057] In addition, a second setting method is to set the capacitance of the capacitor (130) to 50 μF or less, which can suppress harmonics superimposed on the input current from the three-phase AC power supply (2) more effectively than when the capacitance of the capacitor (130) is set to more than 50 μF.

[0058] 3 is a graph showing the relationship between the capacitance of the capacitor 130 and the harmonics superimposed on the input current from the three-phase AC power supply 2. The vertical axis of the graph in FIG. 3 represents the ratio of the nth-order component to the fundamental wave component.

[0059] As shown in Fig. 3, the smaller the capacitance of the capacitor (130), the more effectively the harmonics superimposed on the input current from the three-phase AC power supply (2) are suppressed. In Fig. 3, the target ratio of the nth-order component to the fundamental wave component is set to 15%. When the capacitance of the capacitor (130) is set to 50 µF, the ratios of the 250 Hz, 350 Hz, and 550 Hz frequency components superimposed on the input current from the three-phase AC power supply (2) to the fundamental wave component can be made less than the target ratio.

[0060] FIG. 4 is a timing chart of the input current from the three-phase AC power supply (2) when the capacitance of the capacitor (130) is 120 μF and when the capacitance of the capacitor (130) is 50 μF.

[0061] As shown in FIG. 4, when the capacitance of the capacitor (130) is 50 μF, the harmonics superimposed on the input current from the three-phase AC power supply (2) are reduced compared to when the capacitance of the capacitor (130) is 120 μF.

[0062] Therefore, according to the first embodiment, since a capacitor element is not connected in series to the second switching element (142) of the overvoltage protection circuit (140), harmonics superimposed on the input current from the three-phase AC power supply (2) can be suppressed more effectively than when capacitor elements are connected in series.

[0063] As shown in Table 1 below, when the overvoltage protection circuit (140) is configured with a diode, a resistor, and a 200 μF capacitor element connected in series, the ratio of the 250 Hz frequency component superimposed on the input current from the three-phase AC power supply (2) to the fundamental component is 15.4%. In the first embodiment, the overvoltage protection circuit (140) is configured with a third resistor (141) and a second switching element (142) connected in series. That is, no capacitor element is connected in series to the second switching element (142) of the overvoltage protection circuit (140). When the overvoltage protection circuit (140) is configured with the third resistor (141) and the second switching element (142) connected in series, the ratio of the 250 Hz frequency component superimposed on the input current from the three-phase AC power supply (2) to the fundamental component is 15.0%. The values ​​in Table 1 are based on the assumption that the rated output of the motor (201) is 30 kW and the capacitance of the capacitor (130) is 50 μF. In this way, by configuring the overvoltage protection circuit (140) with the third resistor (141) and the second switching element (142) connected in series with each other, the fundamental component of the 250 Hz frequency component superimposed on the input current can be reduced compared to when a capacitor element is provided in the overvoltage protection circuit (140).

[0064] [Table 1]

[0065] Table 2 below shows the target values ​​for the ratio of each order frequency component of a six-pulse converter to the fundamental wave component as stated in the "Guidelines for Harmonic Suppression Measures for Customers Receiving High Voltage or Extra-High Voltage Power."

[0066] [Table 2]

[0067] By configuring the overvoltage protection circuit 140 with the third resistor 141 and the second switching element 142 connected in series, the 250 Hz (5th order) frequency component can be reduced to 15.0% of the fundamental wave component, as shown in Table 1. Therefore, the 250 Hz (5th order) frequency component can be comfortably reduced to or below 17.5%, which is the target value of the guidelines listed in Table 2.

[0068] According to the first embodiment, the first switching elements (121-126) of the inverter circuit (120) and the third resistor (141) and the second switching element (142) of the overvoltage protection circuit (140) are housed in a common package, and thus a common cooling device is used for these elements, which facilitates downsizing of the power conversion device (100). Furthermore, the third resistor (141) is cooled in the same manner as the first switching elements (121-126) and the second switching element (142), thereby suppressing heat generation from the third resistor (141).

[0069] Therefore, in the first embodiment, the control circuit (190) turns on the second switching element (142) only when the operation of the inverter circuit (120) is stopped. Therefore, when the motor (201) is controlled by turning on and off the inverter circuit (120), the operation of the overvoltage protection circuit (140) does not change the power supplied to the motor (201) and does not affect the harmonics superimposed on the input current from the three-phase AC power supply (2).

[0070] Furthermore, since the second switching element (142) is primarily made of a wide bandgap semiconductor, the temperature at which the overvoltage protection circuit (140) can stably operate is increased, and the cooler for cooling the overvoltage protection circuit (140) can be made smaller.

[0071] Furthermore, since the first switching elements (121-126) of the inverter circuit (120) and the third resistor (141) and second switching element (142) of the overvoltage protection circuit (140) are housed in the same package (case), they can easily share a cooling device such as a heat sink. This facilitates miniaturization of the power conversion device (100). Furthermore, by cooling the third resistor (141) together with the first switching elements (121-126) and the second switching element (142), heat generation by the third resistor (141) can be suppressed.

[0072] Furthermore, since the rated output of the motor (201) is set to 30 kW or less, harmonics superimposed on the input current from the three-phase AC power supply (2) can be suppressed compared to when the rated output of the motor (201) is set to more than 30 kW.

[0073] (Embodiment 2) FIG. 5 is a diagram corresponding to FIG. 2 of the second embodiment. In the second embodiment, the overvoltage protection circuit (140) does not include a third resistor (141). A first temperature sensor (143) for detecting the temperature near the second switching element (142) of the overvoltage protection circuit (140) is provided near the second switching element (142). A current sensor (144) for detecting the current flowing through the second switching element (142) is connected to the second switching element (142). In the second embodiment, the first switching elements (121-126) of the inverter circuit (120) and the second switching element (142) of the overvoltage protection circuit (140) are also housed in the same package (case).

[0074] The control circuit (190) controls the second switching element (142) based on the value detected by the first temperature sensor (143) so that the second switching element (142) operates at a temperature that will not cause the second switching element (142) to fail. Specifically, when the value detected by the first temperature sensor (143) is equal to or higher than a predetermined temperature threshold while the second switching element (142) is on, the control circuit (190) repeatedly turns the second switching element (142) off for a predetermined short time (instant) and then turns it on again.

[0075] Furthermore, the control circuit (190) controls the second switching element (142) based on the detection value of the current sensor (144) so ​​as to prevent a large current that may destroy the second switching element (142) from flowing through the second switching element (142). Specifically, when the detection value of the current sensor (144) is equal to or greater than a predetermined current threshold value while the second switching element (142) is on, the control circuit (190) turns off the second switching element (142).

[0076] In the second embodiment, when the inverter circuit (120) is stopped from operating and the second switching element (142) of the overvoltage protection circuit (140) is turned on, the regenerative energy from the motor (201) is consumed mainly by the on-resistance of the second switching element (142).

[0077] The other configurations are the same as those in the first embodiment, so detailed explanations thereof will be omitted.

[0078] Therefore, according to the second embodiment, the control circuit (190) controls the second switching element (142) based on the value detected by the first temperature sensor (143), thereby reducing the possibility of failure of the second switching element (142), thereby improving the reliability of the power conversion device (100).

[0079] Furthermore, since the control circuit (190) controls the second switching element (142) based on the value detected by the current sensor (144), the possibility of failure of the second switching element (142) can be reduced, thereby improving the reliability of the power conversion device (100).

[0080] Furthermore, since the first switching elements (121-126) of the inverter circuit (120) and the second switching element (142) of the overvoltage protection circuit (140) are housed in the same package (case), they can easily share a cooling device such as a heat sink, which facilitates miniaturization of the power conversion device (100).

[0081] (Embodiment 3) 6 is a diagram corresponding to FIG. 5 of the third embodiment. In the third embodiment, the overvoltage protection circuit (140) does not include a current sensor (144). In addition, a second temperature sensor (127) is provided near the first switching elements (122, 124, 126) of the lower arms of the inverter circuit (120) to detect the temperatures near the first switching elements (122, 124, 126) of the lower arms.

[0082] The first switching elements (121-126) and the second temperature sensor (127) of the inverter circuit (120) and the second switching element (142) and the first temperature sensor (143) of the overvoltage protection circuit (140) are housed in the same package (case) to form a power module.

[0083] Furthermore, when the control circuit (190) stops the operation of the inverter circuit (120), it first starts operation in a first mode in which only the second switching element (142) is turned on to operate the overvoltage protection circuit (140). Then, when the detection value of the first temperature sensor (143) becomes equal to or greater than a predetermined temperature threshold while operating in the first mode, the control circuit (190) starts operation in a second mode in which the second switching element (142) is turned off and the first switching elements (121-126) of the inverter circuit (120) are turned on. When the detection value of the second temperature sensor (127) becomes equal to or greater than a predetermined temperature threshold while operating in the second mode, the control circuit (190) switches operation to the first mode.

[0084] FIG. 7 is a timing chart showing the operation of the power conversion device (100) in the third embodiment.

[0085] At time 1, the control circuit (190) stops the operation of the inverter circuit (120) and starts operation in the first mode, with the first switching elements (121-126) of the inverter circuit (120) operating at a switching frequency higher than 20 kHz. That is, at time 1, the control circuit (190) turns off the first switching elements (121-126) and turns on the second switching element (142). This stops the operation of the inverter circuit (120), and regenerative energy from the motor (201) flows to the capacitor (130). Furthermore, as indicated by arrow X1 in FIG. 6 , the regenerative energy is consumed by the on-resistance of the second switching element (142) of the overvoltage protection circuit (140). Because the overvoltage protection circuit (140) does not include a resistive element, the voltage of the motor (201), which is the load, is short-circuited and remains at approximately 0 V during the first mode. As a result, substantially all of the voltage of the three-phase AC power supply (2) is applied to the second switching element (142), and substantially all of the current from the three-phase AC power supply (2) flows through it. Therefore, the second switching element (142) generates a large amount of heat, and the temperature of the second switching element (142) rises rapidly. When the value detected by the first temperature sensor (143) reaches or exceeds a predetermined temperature threshold, the control circuit (190) starts operating in the second mode at time 2. That is, at time 2, the control circuit (190) turns off the second switching element (142) and turns on the first switching elements (122, 124, 126) of the lower arm of the inverter circuit (120). In the second mode, regenerative energy flows as indicated by arrow X2 in FIG. 6 , and the regenerative energy of the motor (201) is consumed using the resistance of the motor (201). When a predetermined time T2 has elapsed after the start of the second mode operation, at time 3, the control circuit (190) turns off the first switching elements (121-126) of the inverter circuit (120).

[0086] The time T1 during which the first mode continues is within the short-circuit withstand capability of the second switching element 142. The short-circuit withstand capability is the time it takes for the second switching element 142 to break down when the motor (load) 201 is short-circuited.

[0087] Tomoyuki Shoji, "Research on the Cosmic Ray Damage Resistance of Power Devices", [online], 2016, University of Tsukuba, [Retrieved March 19, 2024], Internet<https: / / core.ac.uk / download / pdf / 56664253.pdf> The short-circuit energy density of SiC (silicon carbide) at room temperature of 20°C is 10.57 J / cm 2 It is described that the regenerative energy of a 30 kW inverter circuit (120) is about 60 J. Therefore, in order to consume the regenerative energy of a 30 kW inverter circuit (120) with SiC (silicon carbide), 6 cm 2 Therefore, it is preferable to use a SiC chip measuring 2.4 cm x 2.4 cm as the second switching element (142). The first switching elements (121-126) constituting the inverter circuit (120) that outputs 30 kW of power typically use SiC chips with a rated current capacity of 100 A and a chip size of 0.8 cm x 0.8 cm. Based on the chip area, it can be assumed that a 2.4 cm x 2.4 cm SiC chip can pass a current of 300 A, which is three times 100 A. Therefore, when a 2.4 cm x 2.4 cm SiC chip is used as the second switching element (142), the rated current capacity of the second switching element (142) of the overvoltage protection circuit (140) is more than three times the rated current capacity of the first switching elements (121-126).

[0088] The other configurations are the same as those in the second embodiment, so detailed explanations thereof will be omitted.

[0089] According to the third embodiment, when the detection value of the first temperature sensor (143) becomes equal to or greater than a predetermined temperature threshold value while the power supply is operating in the first mode, the control circuit (190) switches the operation to the second mode, so that the duration T1 of the first mode is within the short-circuit withstand capability of the second switching element (142). This prevents damage to the second switching element (142) and improves reliability.

[0090] Furthermore, when the detection value of the second temperature sensor (127) becomes equal to or greater than a predetermined temperature threshold value while the inverter is operating in the second mode, the control circuit (190) switches the operation to the first mode, thereby preventing damage to the first switching elements (122, 124, 126) of the lower arm and improving reliability.

[0091] Furthermore, since the first switching elements (121-126) and the second temperature sensor (127) of the inverter circuit (120) and the second switching element (142) and the first temperature sensor (143) of the overvoltage protection circuit (140) are housed in the same package (case), it is easy to share a cooling device such as a heat sink, which facilitates miniaturization of the power conversion device (100).

[0092] (Modification of the third embodiment) In the third embodiment, the first mode and the second mode are switched when the value detected by the first temperature sensor (143) or the second temperature sensor (127) satisfies a predetermined condition. However, the first mode may be switched to the second mode after a predetermined first predetermined time has elapsed since the start of the first mode. Similarly, the second mode may be switched to the first mode after a predetermined second predetermined time has elapsed since the start of the second mode. In this case, the first predetermined time is set to be within the short-circuit resistance of the second switching element (142).

[0093] Although the embodiments have been described above, it will be understood that various modifications of form and details are possible without departing from the spirit and scope of the claims. Furthermore, the above embodiments and modifications may be combined or substituted as appropriate as long as the functionality of the subject matter of the present disclosure is not impaired. [Industrial Applicability]

[0094] The present disclosure is useful as a power conversion device equipped with an overvoltage protection circuit. [Explanation of symbols]

[0095] 1. Air conditioning system (heat pump system) 2 Three-phase AC power supply 110 Rectifier circuit 120 Inverter circuit 121, 122, 123, 124, 125, 126 First switching element 130 Capacitor 140 Overvoltage protection circuit 142 second switching element 150 reactor 201 Motor

Claims

1. a rectifier circuit (110) that rectifies AC output from a three-phase AC power supply (2) into DC; an inverter circuit (120) having a plurality of first switching elements (121-126) for converting a direct current output from the rectifier circuit (110) into an alternating current by switching operations of the plurality of first switching elements (121-126) and supplying the alternating current to a motor (201); a capacitor (130) connected between input nodes of the inverter circuit (120); an overvoltage protection circuit (140) having a second switching element (142) and connected in parallel with the capacitor (130); a power conversion device including a reactor (150) connected in series with the rectifier circuit (110) and the inverter circuit (120), No capacitor element is connected in series to the second switching element (142), The power conversion device is characterized in that the capacitance of the capacitor (130) is 50 μF or less.

2. The power conversion device according to claim 1, The power conversion device, wherein the second switching element (142) is an element whose main material is a wide bandgap semiconductor.

3. 3. The power conversion device according to claim 1, When the capacitance of the capacitor (130) is C [F], the switching frequency of the first switching elements (121 to 126) is fc [Hz], and the inductance of the reactor (150) is L [H], fc>20*10 ３ A power conversion device characterized in that the following formula is satisfied when: [Equation 7]

4. 3. The power conversion device according to claim 1, The rated output of the motor (201) is 4 kW or more and 30 kW or less. A power conversion device characterized by:

5. a rectifier circuit (110) that rectifies AC output from a three-phase AC power supply (2) into DC; an inverter circuit (120) having a plurality of first switching elements (121-126) for converting a direct current output from the rectifier circuit (110) into an alternating current by switching operations of the plurality of first switching elements (121-126) and supplying the alternating current to a motor (201); a capacitor (130) connected between input nodes of the inverter circuit (120); an overvoltage protection circuit (140) having a second switching element (142) and connected in parallel with the capacitor (130); A heat pump system having a power converter (100) including a reactor (150) connected in series with the rectifier circuit (110) and the inverter circuit (120), No capacitor element is connected in series to the second switching element (142), The heat pump system is characterized in that the following formula is established, where C [F] is the capacity of the capacitor (130), Vac [V] is the AC voltage output from the three-phase AC power supply (2), and P [W] is the power obtained by multiplying the larger of the power consumption during operation under cooling rated conditions and the power consumption during operation under heating rated conditions by 1.75: [Equation 8]

6. a rectifier circuit (110) that rectifies AC output from a three-phase AC power supply (2) into DC; an inverter circuit (120) having a plurality of first switching elements (121-126) for converting a direct current output from the rectifier circuit (110) into an alternating current by switching operations of the plurality of first switching elements (121-126) and supplying the alternating current to a motor (201); a capacitor (130) connected between input nodes of the inverter circuit (120); an overvoltage protection circuit (140) having a second switching element (142) and connected in parallel with the capacitor (130); a power conversion device including a reactor (150) connected in series with the rectifier circuit (110) and the inverter circuit (120), No capacitor element is connected in series to the second switching element (142), When the capacitance of the capacitor (130) is C [F], the AC voltage output from the three-phase AC power supply (2) is Vac [V], and the rated output power of the motor (201) is P [W], A power conversion device characterized in that the following formula is satisfied. [Equation 9]

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