Power conversion device and heat pump equipment equipped therewith

Abstract

The capacitor is protected from overvoltage not only during regenerative braking but also during lightning surges. [Solution] The power converter is provided with a protection circuit control unit that, during regenerative operation in which current flows into the first capacitor from at least one of the AC power source side and the load side of the first capacitor, changes the on threshold to a second threshold (Von2) which is higher than the first threshold (Von1) after the voltage of the first capacitor first exceeds the on threshold with the on threshold set to the first threshold (Von1). The on threshold when turning on the second switching element during the period from when the second switching element starts switching operation in which it repeatedly turns on and off in response to the regenerative operation until the second switching element stabilizes in the off state includes the second threshold (Von2).

Description

[Technical Field]

[0001] This disclosure relates to a power conversion device that converts alternating current output from an AC power source, and a heat pump device equipped with the same. [Background technology]

[0002] Patent Document 1 discloses a power conversion device comprising: a converter circuit that converts three-phase AC output from an AC power source into DC; an inverter circuit that converts the output of the converter circuit into AC and supplies it to a load; a capacitor connected between the input nodes of the inverter circuit; an overvoltage protection circuit connected in parallel with the capacitor and having resistors and switching elements connected in series with each other; and a control unit that turns on the switching elements when the voltage of the capacitor exceeds a predetermined first threshold during the period when current flows from the load to the input side of the inverter circuit. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 7492180 [Overview of the project] [Problems that the invention aims to solve]

[0004] In the power conversion device disclosed in Patent Document 1, there is a need to protect the capacitor from overvoltage not only during regenerative operation when current flows from the load to the capacitor connected to the inverter circuit or from the power supply to the capacitor, but also when no current flows from the load to the capacitor and when lightning surges are superimposed on the power supply.

[0005] The purpose of this disclosure is to protect the capacitor from overvoltage not only during regenerative operation but also when lightning surges are superimposed on the power supply. [Means for solving the problem]

[0006] A first aspect of this disclosure includes a converter circuit (20) that converts AC output from an AC power source (6) to DC, an inverter circuit (30) that converts the output of the converter circuit (20) to AC and supplies it to a load (2), a first capacitor (41) connected between the input nodes (30a, 30b) of the inverter circuit (30), reactors (42, 43a~43c) connected between the AC power source (6) and the converter circuit (20), or between the converter circuit (20) and the first capacitor (41), an overvoltage protection circuit (50) connected in parallel with the first capacitor (41) and having resistors (51) and switching elements (52) connected in series with each other, and turning on the switching elements (52) when the voltage of the first capacitor (41) is above a predetermined on threshold, and when the voltage of the first capacitor (41) is below the on threshold The system includes a control unit (70) that turns off the switching element (52) when it is below a predetermined off threshold, and during regenerative operation in which current flows into the first capacitor (41) from at least one of the AC power supply (6) side and the load (2) side of the first capacitor (41), the on threshold is set as the first threshold (Von1), and after the voltage of the first capacitor (41) first exceeds the on threshold, the on threshold is changed to a second threshold (Von2) which is higher than the first threshold (Von1), and the on threshold when the switching element (52) is turned on during the period from when the switching element (52) starts a switching operation in which it repeatedly turns on and off in response to the regenerative operation until the switching element (52) stabilizes in the off state includes the second threshold (Von2).

[0007] In the first embodiment, the first capacitor (41) can be protected from overvoltage not only during regenerative operation when current flows into the first capacitor (41) from at least one of the AC power supply (6) side or the load (2) side of the first capacitor (41), but also during lightning surge superposition, by turning on the switching element (52) in response to the voltage of the first capacitor (41) exceeding an on threshold.

[0008] A second aspect of the present disclosure is that, in the first aspect, if the reactors (42, 43a to 43c) are provided in either or both of the first section between one output terminal of the converter circuit (20) and the first capacitor (41), and the second section between the other output terminal of the converter circuit (20) and the first capacitor (41), the sum of the inductances of the reactors (42, 43a to 43c) in the first section and the second section is used as the combined inductance, and the voltage between both output terminals of the converter circuit (20) is used as the reactor input voltage, while the reactor If the reactors (42, 43a~43c) are provided in either or both of the third section between the input terminal of the first phase of the input phase of the converter circuit (20) and the AC power supply (6), and the fourth section between the input terminal of the second phase of the input phase of the converter circuit (20) which is different from the first phase and the AC power supply (6), the sum of the inductances of the reactors (42, 43a~43c) in the third section and the fourth section shall be used as the combined inductance, and the voltage between the first and second phases of the AC power supply (6) shall be used as the reactor input voltage, and the power supply voltage of the AC power supply (6) shall be set to V ac [V], the capacitance of the first capacitor (41) is C[F], and the withstand voltage of the inverter circuit (30) is V dc2 Let [V] be the minimum value of the combined inductance during surge superposition when a surge voltage with a peak voltage of 7kV generated by a surge generator compliant with IEC61000-4-5 is superimposed on the power supply voltage with the switching element (52) turned off, and let L1[H] be the minimum value of the combined inductance during surge superposition and let V be the maximum value of the reactor input voltage during surge superposition. in [V], when the surge is superimposed, the reactor input voltage exceeds the withstand voltage of the inverter circuit (30) and then √2V ac The following equation holds true when t [seconds] is the time it takes for the value to fall below [V].

[0009]

number

[0010] In the second embodiment, since the above equation holds, if the overvoltage protection circuit (50) is not activated, there is a risk that the voltage across the first capacitor (41) will exceed the breakdown voltage of the inverter circuit (30) when a surge is superimposed. However, since the control unit (70) activates the overvoltage protection circuit (50), the first capacitor (41) can be protected from overvoltage.

[0011] A third aspect of the present disclosure is characterized in that, in the first or second aspect, the control unit (70) changes the on threshold to the first threshold (Von1) after the switching element (52) has been turned on with the on threshold at the second threshold (Von2) and the switching element (52) has remained in the off state for a predetermined period of time.

[0012] In the third embodiment, after the switching element (52) is turned on with the ON threshold set to the second threshold (Von2), the ON threshold is changed to the first threshold (Von1) when the condition is met that the switching element (52) remains in the OFF state for a predetermined time. Thereafter, the switching element (52) can be turned on when the voltage of the first capacitor (41) exceeds the first threshold (Von1) due to the superposition of a lightning surge.

[0013] A fourth aspect of the present disclosure is characterized in that, in the third aspect, the control unit (70) includes a second capacitor (73), a charge / discharge circuit (74) that charges the second capacitor (73) when the switching element (52) is in the ON state and discharges the second capacitor (73) when the switching element (52) is in the OFF state, and a comparison circuit (75) that sets the ON threshold to a second threshold (Von2) when the voltage of the second capacitor (73) is equal to or greater than a predetermined first switching threshold (CTH1), and sets the ON threshold to a first threshold (Von1) when the voltage of the second capacitor (73) is less than a predetermined second switching threshold (CTH1) which is equal to or less than the first switching threshold (CTH1).

[0014] In the fourth aspect, after the switching element (52) is turned on in a state where the on-threshold is the second threshold (Von2), when the switching element (52) is turned off and the voltage of the second capacitor (73) becomes less than the second switching threshold (CTH1) due to discharge of the second capacitor (73), the on-threshold can be changed to the first threshold (Von1).

[0015] A fifth aspect of the present disclosure is a heat pump apparatus (1) comprising the power conversion device (10) according to any one of the first to fourth aspects and the load (2), wherein the load (2) is a compressor. [Brief Description of Drawings]

[0016] [Figure 1] Figure 1 is a schematic diagram showing the configuration of a heat pump apparatus including a power conversion device according to Embodiment 1 of the present disclosure. [Figure 2] Figure 2 is a circuit diagram showing the configuration of the power conversion device according to Embodiment 1 of the present disclosure. [Figure 3] Figure 3 is a circuit diagram showing the configuration of a protection circuit control unit. [Figure 4] Figure 4 is a timing chart illustrating a control signal of a second switching element, a voltage of a second capacitor, and a detection gain during a regenerative operation. [Figure 5] Figure 5 is a timing chart illustrating the voltage of the first capacitor and the loss of the overvoltage protection circuit during regenerative operation when the on-threshold is always set to the first threshold. [Figure 6] Figure 6 is a diagram corresponding to Figure 5 when the on-threshold is always set to the second threshold. [Figure 7] Figure 7 is a diagram corresponding to Figure 5 in Embodiment 1 of the present disclosure. [Figure 8] Figure 8 is a timing chart illustrating the voltage of the first capacitor and the control signal of the second switching element when a lightning surge is superimposed. [Figure 9]Figure 9 is a timing chart illustrating the voltage of the first capacitor, the reactor input voltage, and the reactor current during surge superposition, when a surge voltage compliant with IEC61000-4-5 is superimposed on the power supply voltage with the second switching element turned off. [Figure 10] Figure 10 is a timing chart illustrating the voltage of the first capacitor, the power supply voltage, and the control signal of the second switching element when a lightning surge is superimposed after regenerative operation. [Figure 11] Figure 11 is a diagram corresponding to Figure 3 in Embodiment 2. [Figure 12] Figure 12 is a diagram corresponding to Figure 2 in Embodiment 3. [Figure 13] Figure 13 is a circuit diagram showing the configuration between the AC power supply and the converter circuit in Embodiment 4. [Figure 14] Figure 14 is a timing chart illustrating the voltage of the first capacitor and the control signal of the second switching element during regenerative operation in Embodiment 5. [Modes for carrying out the invention]

[0017] Embodiments of this disclosure will be described below with reference to the drawings. These embodiments are essentially preferred examples and are not intended to limit the scope of the invention, its applications, or its uses.

[0018] (Embodiment 1) Figure 1 shows an air conditioner (1) as a heat pump device. This air conditioner (1) comprises a compressor (2), a condenser (3), an evaporator (4), and an expansion valve (5). The refrigerant compressed by the compressor (2) turns into a liquid in the condenser (3) while releasing heat, passes through the expansion valve (5) to be released from compression, and then absorbs heat again in the evaporator (4) to return to a gas. The compressor (2) performs the compression operation using the output power of a power converter (10) according to Embodiment 1 of this disclosure.

[0019] Figure 2 shows a power converter (10) according to Embodiment 1 of the present disclosure. The power converter (10) converts the three-phase AC output from the AC power source (6) into a predetermined three-phase AC and supplies it to the compressor (2) as a load. For example, an IPM (Interior Permanent Magnet) motor is used as the compressor (2). The power converter (10) includes a converter circuit (20), an inverter circuit (30), a first capacitor (41), a reactor (42), an overvoltage protection circuit (50), an inverter control unit (60), and a protection circuit control unit (70).

[0020] The converter circuit (20) converts the three-phase AC output from the AC power supply (6) into DC and outputs it. The converter circuit (20) has first to sixth rectifier circuit diodes (21 to 26) connected in a bridge configuration. These rectifier circuit diodes (21 to 26) have their cathodes facing the positive voltage side power line (PL) and their anodes facing the negative voltage side power line (NL).

[0021] The inverter circuit (30) has six (or more) first switching elements (31a to 36a) and six (or more) freewheeling diodes (31b to 36b). The six first switching elements (31a to 36a) are bridge-connected. More specifically, the inverter circuit (30) has three switching legs connected between the positive voltage side power line (PL) and the negative voltage side power line (NL). Each switching leg consists of two first switching elements (31a to 36a) connected in series with each other. In each of the three switching legs, the midpoint between the first switching elements of the upper arm (31a, 33a, 35a) and the first switching elements of the lower arm (32a, 34a, 36a) is connected to the coils of each phase (u-phase, v-phase, and w-phase) of the motor of the compressor (2), respectively. Each first switching element (31a to 36a) is connected in antiparallel to one freewheeling diode (31b to 36b). The inverter circuit (30) converts the output of the converter circuit (20) into AC and supplies it to the compressor (2) through the switching operation of the six first switching elements (31a to 36a). The first switching elements (31a to 36a) are insulated-gate bipolar transistors.

[0022] The six first switching elements (31a to 36a) may be elements made primarily of silicon (Si).

[0023] Furthermore, the six first switching elements (31a to 36a) may be elements whose main material is a wide-bandgap semiconductor containing silicon carbide (SiC), gallium nitride (GaN), or diamond (C).

[0024] The first capacitor (41) is connected between the input nodes (30a, 30b) of the inverter circuit (30) and allows for pulsation of the output voltage of the converter circuit (20). The capacitance of the first capacitor (41) is set so as not to smooth the output voltage of the converter circuit (20) but to suppress the ripple voltage caused by the switching operation of the inverter circuit (30). The ripple voltage suppressed here is the voltage fluctuation corresponding to the switching frequency of the first switching elements (31a to 36a).

[0025] In short, the capacitance of the first capacitor (41) is set to tolerate pulsations in the output voltage of the converter circuit (20) and to absorb voltage fluctuations between the input nodes (30a, 30b) of the inverter circuit (30) caused by switching operation. More specifically, the capacitance of the first capacitor (41) is set to suppress the voltage fluctuation of the first capacitor (41) during the switching period to less than 1 / 10 of the average value of the voltage of the first capacitor (41). In this way, the capacitance of the first capacitor (41) can be reduced to a degree that tolerates pulsations in the output voltage of the converter circuit (20), thus allowing the first capacitor (41) to be miniaturized.

[0026] Here, the switching period is the period during which the first switching elements (31a to 36a) repeatedly switch on and off. In this embodiment 1, the first switching elements (31a to 36a) are controlled by PWM control, and the switching period becomes the carrier period of the carrier wave.

[0027] Conventionally, electrolytic capacitors are sometimes used as smoothing capacitors to smooth the output voltage of the converter circuit (20). On the other hand, the capacitance value of the first capacitor (41) in this embodiment is approximately 0.01 to 0.1 times that of this smoothing capacitor. As an example, the first capacitor (41) is made up of a film capacitor.

[0028] When the capacitance of the first capacitor (41) is C, the power supply voltage is Vac, and the maximum output power of the inverter circuit (30) is Pmax, C is set to satisfy the following equation.

[0029]

number

[0030] Therefore, the voltage across the first capacitor (41) experiences pulsations caused by the frequency of the input AC supplied from the AC power supply (6). Since the AC power supply (6) is a three-phase power supply, the frequency of the pulsations caused by the frequency of the AC power supply (6) is six times the frequency of the AC power supply (6).

[0031] The reactor (42) is connected between the output node of the converter circuit (20) on the positive voltage side power line (PL) and one end of the first capacitor (41). Thus, the reactor (42) is provided between the AC power supply (6) and the first capacitor (41). Therefore, the current from the AC power supply (6) is input to the first capacitor (41) via the reactor (42).

[0032] The overvoltage protection circuit (50) is connected in parallel with the first capacitor (41). The overvoltage protection circuit (50) includes a first resistor (51) and a second switching element (52) connected in series with each other from the positive voltage side power supply line (PL) side, and a diode (53) connected in parallel with the first resistor (51). The second switching element (52) is an insulated gate bipolar transistor. The cathode of the diode (53) is connected to the positive voltage side power supply line (PL), and the anode of the diode (53) is connected to the collector of the second switching element (52).

[0033] The second switching element (52) may be an element made primarily of silicon (Si).

[0034] Furthermore, the second switching element (52) may be 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 even at high temperatures of approximately 200 degrees Celsius. In this way, when the main material of the second switching element (52) is a wide-bandgap semiconductor, the overvoltage protection circuit (50) can convert a relatively large amount of energy into heat despite its relatively small size.

[0035] The inverter control unit (60) and the protection circuit control unit (70) are composed of various elements, a microcomputer, and memory, etc.

[0036] The inverter control unit (60) controls the switching operation of each first switching element (31a to 36a). This control includes controlling the rotational speed of the compressor (2) to approach a desired rotational speed. The inverter control unit (60) performs PWM control to control the multiple first switching elements (31a to 36a) using switching signals corresponding to the comparison result between the modulated wave of each phase and a predetermined triangular wave carrier wave. Specifically, if the modulated wave is larger than the carrier wave, the upper arm switching elements (31a, 33a, 35a) are turned on and the lower arm switching elements (32a, 34a, 36a) are turned off. Conversely, if the modulated wave is smaller than the carrier wave, the upper arm switching elements (31a, 33a, 35a) are turned off and the lower arm switching elements (32a, 34a, 36a) are turned on.

[0037] The protection circuit control unit (70) turns on the second switching element (52) when the voltage of the first capacitor (41) is above a predetermined on threshold, and turns off the second switching element (52) when the voltage of the first capacitor (41) is below a predetermined off threshold which is below the on threshold. Furthermore, during regenerative operation in which current flows into the first capacitor (41) from at least one of the AC power supply (6) side or the load (2) side of the first capacitor (41), the protection circuit control unit (70) changes the on threshold to a second threshold (Von2) which is higher than the first threshold (Von1) after the voltage of the first capacitor (41) first exceeds the on threshold with the on threshold set to the first threshold (Von1) (see Figure 10).

[0038] Specifically, as shown in Figure 3, the protection circuit control unit (70) includes a comparator (71), a voltage source (72), a second capacitor (73), a charge / discharge circuit (74), and a comparison circuit (75).

[0039] The non-inverting input terminal of the comparator (71) is connected to the output of the comparator circuit (75), which will be described later, and the inverting input terminal of the comparator (71) is connected to a voltage source (72) that outputs a predetermined voltage. The output terminal of the comparator (71) is connected to the gate of the second switching element (52). The comparator (71) has hysteresis characteristics. That is, the output voltage of the comparator circuit (75) when the output of the comparator (71) switches from a low level to a high level is higher than the output voltage of the comparator circuit (75) when the output of the comparator (71) switches from a high level to a low level.

[0040] One end of the second capacitor (73) is connected to the negative voltage side power line (NL), and the other end of the second capacitor (73) is connected to the signal input of the comparator circuit (75), which will be described later. The capacitance of the second capacitor (73) is set to, for example, 0.1 μF.

[0041] The charge / discharge circuit (74) charges the second capacitor (73) when the second switching element (52) is ON, and discharges the second capacitor (73) when the second switching element (52) is OFF by using the energy to turn on the third switching element (75d) of the comparator circuit (75), which will be described later. Specifically, the charge / discharge circuit (74) has a charge / discharge diode (74a) and a second resistor (74b). The anode of the charge / discharge diode (74a) is connected to the output terminal of the comparator (71) and the gate of the second switching element (52). One end of the second resistor (74b) is connected to the cathode of the charge / discharge diode (74a), and the other end of the second resistor (74b) is connected to the other end of the second capacitor (73) and the signal input of the comparator circuit (75), which will be described later.

[0042] The comparator circuit (75) sets the ON threshold to the second threshold (Von2) when the voltage of the second capacitor (73) is equal to or greater than a predetermined first switching threshold (CTH1) (see Figure 4), while setting the ON threshold to the first threshold (Von1) when the voltage of the second capacitor (73) is less than the first switching threshold (CTH1). Specifically, the comparator circuit (75) includes a third resistor (75a), a fourth resistor (75b), a fifth resistor (75c), and a third switching element (75d).

[0043] The third resistor (75a) and the fourth resistor (75b) are connected in series with each other between the positive voltage power line (PL) and the negative voltage power line (NL).

[0044] One end of the fifth resistor (75c) is connected to the connection point of the third resistor (75a) and the fourth resistor (75b) via the third switching element (75d). The other end of the fifth resistor (75c) is connected to the negative voltage power line (NL).

[0045] The third switching element (75d) turns on when the voltage across the second capacitor (73) is equal to or greater than a predetermined first switching threshold (CTH1), and turns off when the voltage across the second capacitor (73) is less than the first switching threshold (CTH1). Specifically, the gate of the third switching element (75d) is connected to the other end of the second capacitor (73). The collector of the third switching element (75d) is connected to the connection point of the third resistor (75a) and the fourth resistor (75b). The emitter of the third switching element (75d) is connected to one end of the fifth resistor (75c). The gate of the third switching element (75d) is the signal input of the comparator circuit (75), and the voltage at the connection point of the third resistor (75a) and the fourth resistor (75b) is the output of the comparator circuit (75).

[0046] Figure 4 illustrates the control signal (gate signal) of the second switching element (52), the voltage of the second capacitor (73), and the detection gain during regenerative operation.

[0047] In the protection circuit control unit (70) configured as described above, with the ON threshold set to the first threshold (Von1), when the voltage of the first capacitor (41) rises due to regenerative operation with the third switching element (75d) turned off, the output of the comparator circuit (75) rises, and the output of the comparator (71) becomes high level. As a result, the second switching element (52) turns on. Also, the charge / discharge diode (74a) conducts, and charging of the second capacitor (73) begins. When the voltage of the second capacitor (73) becomes equal to or greater than the first switching threshold (CTH1), the third switching element (75d) turns on.

[0048] Here, let the output voltage of the comparator circuit (75) be Vc, the voltage across the first capacitor (41) be Vdc, and with the third switching element (75d) turned off, assume that the following equation (α) holds true. A is approximately the value obtained by dividing the resistance of the fourth resistor (75b) by the sum of the resistances of the third resistor (75a) and the fourth resistor (75b).

[0049] Vc = Vdc * A ... (α) When the third switching element (75d) is turned on, the following equation (β) holds true. B is approximately the value obtained by dividing the combined resistance of the fourth resistor (75b) and the fifth resistor (75c) by the sum of the resistance of the third resistor (75a) and the combined resistance. B is smaller than A.

[0050] Vc = Vdc * B ... (β) If the resistance value of the fourth resistor (75b) is RL1 and the resistance value of the fifth resistor (75c) is RL2, then the combined resistance of the fourth resistor (75b) and the fifth resistor (75c) is:

[0051]

number

[0052] This is the result.

[0053] Therefore, when the third switching element (75d) is turned on, the detection gain of the voltage across the first capacitor (41) decreases compared to when it was turned off. Specifically, the voltage across the first capacitor (41), i.e., the on threshold, rises from the first threshold (Von1) to the second threshold (Von2) when the output of the comparator (71) switches from a low level to a high level. The detection gain when the third switching element (75d) is turned off is value A in equation (α), and the detection gain when the third switching element (75d) is turned on is value B in equation (β).

[0054] In this embodiment 1, when the ON threshold is at the second threshold (Von2) and the voltage of the second capacitor (73) falls below the first switching threshold (CTH1), the ON threshold is set to the first threshold (Von1). In other words, the threshold (second switching threshold) when changing the ON threshold from the second threshold (Von2) to the first threshold (Von1) is equal to the threshold (first switching threshold) when switching the ON threshold from the first threshold (Von1) to the second threshold (Von2). However, the threshold (second switching threshold) when changing the ON threshold from the state where the ON threshold is at the second threshold (Von2) to the first threshold (Von1) may be set to a threshold lower than the first switching threshold (CTH1) when switching the ON threshold from the first threshold (Von1) to the second threshold (Von2). In other words, the gate voltage threshold when switching the third switching element (75d) from the ON state to the OFF state may be lower than the gate voltage threshold when switching the third switching element (75d) from the OFF state to the ON state.

[0055] When the second switching element (52) is turned on, current flows from the first capacitor (41) to the first resistor (51), causing the voltage across the first capacitor (41) to decrease. When the voltage across the first capacitor (41) falls below a predetermined off threshold, the output of the comparator (71) becomes low, and the second switching element (52) turns off. At the same time, the charge / discharge diode (74a) becomes non-conductive, the charge in the second capacitor (73) is released, and the voltage across the second capacitor (73) decreases.

[0056] Subsequently, if current continues to flow into the first capacitor (41) from at least one of the sides of the AC power supply (6) and the compressor (2) side of the first capacitor (41), the voltage of the first capacitor (41) rises again. When the voltage of the first capacitor (41) exceeds the second threshold (Von2), the output of the comparator (71) becomes high, and the second switching element (52) turns on. In this way, the second switching element (52) repeatedly turns on and off during regenerative operation. After the regenerative operation ends, the second switching element (52) stabilizes in the off state. As a result, the charge / discharge diode (74a) becomes non-conductive, the charge in the second capacitor (73) is released, and the voltage of the second capacitor (73) decreases.

[0057] Thus, in this embodiment 1, the second threshold (Von2) is included in the on threshold when the second switching element (52) is turned on during the period from when current flows into the first capacitor (41) from at least one of the AC power supply (6) side or the compressor (2) side of the first capacitor (41) until the second switching element (52) stabilizes in the off state, after the second switching element (52) begins switching operation by repeatedly turning on and off in response to the current flowing into the first capacitor (41) from at least one of the AC power supply (6) side or the compressor (2) side of the first capacitor (41)

[0058] When the second switching element (52) remains in the off state for a predetermined time (indicated by the symbol T1 in Figure 4) and the voltage across the second capacitor (73) falls below the first switching threshold (CTH1), the third switching element (75d) turns off. This increases the detection gain of the voltage across the first capacitor (41) compared to when it was on. Specifically, the voltage across the first capacitor (41), i.e., the on threshold, switches from the second threshold (Von2) to the first threshold (Von1) when the output of the comparator (71) switches from a low level to a high level. The predetermined period indicated by T1 in Figure 3 is the time from when the second switching element (52) finishes its switching operation of repeatedly turning on and off until the second switching element (52) stabilizes in the off state, for example, set to 600 μs.

[0059] Figure 5 illustrates the voltage of the first capacitor (41) and the loss of the overvoltage protection circuit (50) during regenerative operation when the ON threshold is always set to the first threshold (Von1). Figure 6 is the equivalent of Figure 5 when the ON threshold is always set to the second threshold (Von2).

[0060] In Figure 5, the switching cycle of the second switching element (52) is greater than in Figure 6, resulting in a greater switching loss for the second switching element (52). Therefore, when the ON threshold is always set to the first threshold (Von1), the loss of the overvoltage protection circuit (50) is greater than when the ON threshold is always set to the second threshold (Von2). In Figure 5, T2 is 0.798 ms, and in Figure 6, T3 is 0.62 ms.

[0061] Specifically, if a second switching element (52) with a permissible temperature range of -40 to 175°C and a permissible power dissipation of 649W is used, and the ON threshold is always set to 870V, the device temperature of the second switching element (52) during regenerative operation at an ambient temperature of 65°C will be 201°C, which is outside the permissible temperature range. If the ON threshold is always set to 930V, the device temperature of the second switching element (52) during regenerative operation at an ambient temperature of 65°C will be 125.2°C, which is within the permissible temperature range.

[0062] Figure 7 is a diagram corresponding to Figure 5 in Embodiment 1 of this disclosure.

[0063] In this embodiment 1, during regenerative operation, when the voltage of the first capacitor (41) exceeds the first threshold (Von1) for the first time while the ON threshold is set to the first threshold (Von1), the ON threshold is changed to a second threshold (Von2) which is higher than the first threshold (Von1). Therefore, compared to Figure 5, the number of switching cycles of the second switching element (52) can be reduced, and the switching loss of the second switching element (52) can be reduced. Therefore, in this embodiment 1, the loss of the overvoltage protection circuit (50) can be reduced compared to when the ON threshold is always set to the first threshold (Von1). In Figure 7, T4 is 0.70 ms.

[0064] In this embodiment 1, a second switching element (52) with an allowable temperature range of -40 to 175°C and an allowable power dissipation of 649W is used, and the first threshold (Von1) is set to 870V and the second threshold (Von2) to 930V. Then, when regenerative operation is performed at an ambient temperature of 65°C, the device temperature of the second switching element (52) becomes 126.1°C, which falls within the allowable temperature range.

[0065] Figure 8 illustrates, with solid lines, the voltage of the first capacitor (41) and the control signal of the second switching element (52) during a lightning surge superimposed, when a clamp circuit is connected between the positive voltage side power line (PL) and the negative voltage side power line (NL) in a power conversion device (10) according to Embodiment 1 of the present disclosure, and the first threshold (Von1) is set to 870V. The clamp circuit is a circuit in which a diode with its anode pointed towards the positive voltage side power line (PL), a resistor, and a capacitor are connected in series with each other. In Figure 8, the solid line graph represents the graph when the capacitance of the capacitor in the clamp circuit is set to 90μF. In Figure 8, the dashed line represents the graph corresponding to the solid line graph when the on threshold is always set to 930V and the capacitance of the capacitor in the clamp circuit is set to 135μF.

[0066] In Figure 8, the solid and dashed lines show that the voltage peaks of the first capacitor (41) during lightning surge superposition can be suppressed to a similar extent. Thus, when the on-threshold at which the voltage of the first capacitor (41) first exceeds the on-threshold is set to 870V, the capacitance of the capacitor in the clamp circuit can be reduced compared to when it is set to 930V.

[0067] In this embodiment 1, even when a lightning surge is superimposed, the on-threshold at which the voltage of the first capacitor (41) first exceeds the on-threshold is set to a first threshold (Von1) that is lower than the second threshold (Von2). This makes it possible to reduce the capacitance of the capacitor in the clamp circuit necessary to suppress overvoltage when a lightning surge is superimposed. Furthermore, it becomes possible to miniaturize the first capacitor (41) and the reactor (42).

[0068] Next, we will explain the capacitance of the first capacitor (41) and the inductance of the reactor (42).

[0069] Here, the voltage between both output terminals of the converter circuit (20) is defined as the reactor input voltage, and the power supply voltage of the AC power supply (6) is defined as V ac [V], the capacitance of the first capacitor (41) is defined as C[F], and the withstand voltage of the inverter circuit (30) is defined as V dc2 [V]. Further, in a state where the second switching element (52) is turned off, at the time of surge superposition in which a surge voltage having a peak voltage of 7 kV generated by a surge generator conforming to IEC61000-4-5 is superimposed on the power supply voltage, the minimum value of the inductance of the reactor (42) is defined as L1[H], and the maximum value of the reactor input voltage at the time of the surge superposition is defined as V in [V], and the time from when the reactor input voltage exceeds the withstand voltage of the inverter circuit (30) to when the reactor input voltage falls below √2V at the time of the surge superposition is defined as t[seconds]. The power conversion device (10) is designed such that the following expression (1) holds. ac [V] is defined as t[seconds]. The power conversion device (10) is designed such that the following expression (1) holds.

[0070]

Equation

[0071] FIG. 9 exemplifies the voltage of the first capacitor (41), the reactor input voltage, and the current of the reactor (42) at the time of the surge superposition. Here, the inductance of the reactor (42) is denoted by L, and the voltage of the first capacitor (41) is denoted by V dc , the reactor input voltage is denoted by V L , and the current of the reactor (42) is denoted by i L . At point P1, the inductance of the reactor (42) is 30 μH which is the minimum value, and at point P2, the inductance of the reactor (42) is 125 μH which is the maximum value.

[0072] When the output voltage of the converter circuit (20) is defined as V in , the voltage V of the first capacitor (41) dc is as shown in the following expression (2).

[0073] V dc =Vin ―V L (2) V L V L Since it is expressed by the formula =L*di / dt, the larger the inductance of the reactor (42), i.e., L, the larger V L As it increases, from equation (2), V dc It becomes smaller.

[0074] Voltage V of the first capacitor (41) before surge application dc The initial value of is expressed by the following equation (3).

[0075] V dc =√2·V ac (3) After the surge is approved, The current flowing through the reactor (42) charges the first capacitor (41). The voltage across the first capacitor (41) is expressed by the following equation (4).

[0076]

number

[0077] If the charge in the first capacitor (41) is Q and the current flowing through the first capacitor (41) is I, then the following equation (5) holds true.

[0078] Q = I * t (5) Regarding the current flowing through reactor (42), equation (6) is obtained from equations (2) and (3).

[0079]

number

[0080] Since the current flowing through the first capacitor (41) is equal to the current flowing through the reactor (42), the following equation (7) holds true.

[0081]

number

[0082] From equations (4) and (5), the voltage of the first capacitor (41) is expressed by the following equation (8).

[0083]

number

[0084] From equation (8), the inductance of reactor (42) is expressed as shown in equation (9) below.

[0085]

number

[0086] Therefore, the condition under which the voltage across the first capacitor (41) may exceed the breakdown voltage of the inverter circuit (30) when the overvoltage protection circuit (50) is not activated (when the second switching element (52) is not turned on) is expressed by the following equation (10).

[0087]

number

[0088] Therefore, in this embodiment 1, since equation (1) holds true, if the overvoltage protection circuit (50) is not activated, there is a risk that the voltage across the first capacitor (41) will exceed the breakdown voltage of the inverter circuit (30) when a surge is superimposed. However, since the overvoltage protection circuit (50) is activated by the protection circuit control unit (70), the first capacitor (41) can be protected from overvoltage.

[0089] Figure 10 illustrates the voltage of the first capacitor (41), the power supply voltage, and the control signal of the second switching element (52) when a lightning surge is superimposed after regenerative operation.

[0090] First, when regenerative operation begins, at timing t1, if the voltage of the first capacitor (41) exceeds the first threshold (Von1), the protection circuit control unit (70) turns on the second switching element (52). Subsequently, the on threshold is switched to the second threshold (Von2), and from timing t2, the second switching element (52) repeatedly turns on and off multiple times. After the second switching element (52) turns on with the on threshold set to the second threshold (Von2), the protection circuit control unit (70) changes the on threshold from the second threshold (Von2) to the first threshold (Von1) when the condition is met that the second switching element (52) remains in the off state for a predetermined time T1. Then, at timing t3, if a lightning surge occurs, the voltage of the first capacitor (41) exceeds the first threshold (Von1), and the protection circuit control unit (70) turns on the second switching element (52).

[0091] (Embodiment 2) Figure 11 is a diagram corresponding to Figure 3 of Embodiment 2. In Embodiment 2, the function of the protection circuit control unit (70) of Embodiment 1 is realized by the third resistor (75a), the fourth resistor (75b), and the microcomputer (76).

[0092] Since the other components are the same as in Embodiment 1, the same reference numerals are used for common components and their detailed descriptions are omitted.

[0093] (Embodiment 3) Figure 12 is a diagram corresponding to Figure 2 of Embodiment 3. In this Embodiment 3, there is no reactor (42) between the converter circuit (20) and the first capacitor (41). A first reactor (43a) is connected between the R-phase input terminal of the converter circuit (20) and the AC power supply (6) (third section, fourth section). A second reactor (43b) is connected between the S-phase input terminal of the converter circuit (20) and the AC power supply (6) (third section, fourth section). A third reactor (43c) is connected between the T-phase input terminal of the converter circuit (20) and the AC power supply (6) (third section, fourth section).

[0094] Then, the sum of the first reactor (43a) and the second reactor (43b) is taken as the combined inductance, and the voltage between the R phase and S phase of the AC power supply (6) is taken as the reactor input voltage. Then, if the minimum value of the combined inductance when the surge is superimposed between the R phase and S phase of the AC power supply (6) is L1 [H], then equation (1) holds true.

[0095] Furthermore, even when the sum of the second reactor (43b) and the third reactor (43c) is taken as the combined inductance, and the voltage between the S phase and T phase of the AC power supply (6) is taken as the reactor input voltage, equation (1) still holds true when the surge is superimposed between the R phase and S phase of the AC power supply (6).

[0096] Furthermore, even when the sum of the first reactor (43a) and the third reactor (43c) is taken as the combined inductance, and the voltage between the R phase and T phase of the AC power supply (6) is taken as the reactor input voltage, equation (1) also holds true when the surge is superimposed between the R phase and S phase of the AC power supply (6).

[0097] Since the other components are the same as in Embodiment 1, the same reference numerals are used for common components and their detailed descriptions are omitted.

[0098] (Embodiment 4) Figure 13 shows the configuration between the AC power supply (6) and the converter circuit (20) in Embodiment 4. In Embodiment 4, instead of the first reactor (43a), a first common mode choke coil (44a) and a first normal mode choke coil (46a) are connected in order from the AC power supply (6) side between the R phase input terminal of the converter circuit (20) and the AC power supply (6) (third section, fourth section). Instead of the second reactor (43b), a second common mode choke coil (44b) and a second normal mode choke coil (46b) are connected in order from the AC power supply (6) side between the S phase input terminal of the converter circuit (20) and the AC power supply (6) (third section, fourth section). Between the T-phase input terminal of the converter circuit (20) and the AC power supply (6) (third section, fourth section), a third common-mode choke coil (44c) and a third normal-mode choke coil (46c) are connected in order from the AC power supply (6) side, replacing the third reactor (43c). One end of the first R-phase capacitor (45a) is connected to the connection point between the AC power supply (6) and the first common-mode choke coil (44a). One end of the first S-phase capacitor (45b) is connected to the connection point between the AC power supply (6) and the second common-mode choke coil (44b). One end of the first T-phase capacitor (45c) is connected to the connection point between the AC power supply (6) and the third common-mode choke coil (44c). The other end of the first R-phase capacitor (45a), the other end of the first S-phase capacitor (45b), and the other end of the first T-phase capacitor (45c) are connected to each other.

[0099] One end of the second R-phase capacitor (47a) is connected to the connection point between the first common-mode choke coil (44a) and the first normal-mode choke coil (46a). One end of the second S-phase capacitor (47b) is connected to the connection point between the second common-mode choke coil (44b) and the second normal-mode choke coil (46b). One end of the second T-phase capacitor (47c) is connected to the connection point between the third common-mode choke coil (44c) and the third normal-mode choke coil (46c). The other end of the second R-phase capacitor (47a), the other end of the second S-phase capacitor (47b), and the other end of the second T-phase capacitor (47c) are connected to each other.

[0100] Since the other components are the same as in Embodiment 3, the same reference numerals are used for common components and their detailed descriptions are omitted.

[0101] Furthermore, composite coils such as those shown in Japanese Patent Publication No. 6593834 may be used as the common mode choke coils (44a, 44b, 44c) and normal mode choke coils (46a, 46b, 46c).

[0102] In other words, a composite coil may be used in which multiple coils are wound around a single core, thereby incorporating the functions of a first common-mode choke coil (44a) and a first normal-mode choke coil (46a), a second common-mode choke coil (44b) and a second normal-mode choke coil (46b), and a third common-mode choke coil (44c) and a third normal-mode choke coil (46c).

[0103] (Embodiment 5) Figure 14 illustrates the voltage of the first capacitor (41) and the control signal of the second switching element (52) during regenerative operation in Embodiment 5. In Embodiment 5, during regenerative operation, the protection circuit control unit (70) changes the ON threshold to a second threshold (Von2) which is higher than the first threshold (Von1), and then further changes the ON threshold to a third threshold (Von3) which is lower than the first threshold (Von1).

[0104] The other components are the same as in Embodiment 1, so a detailed explanation will be omitted.

[0105] In the embodiment 1 described above, the reactor (42) was provided only in the first section between one output terminal of the converter circuit (20) and the first capacitor (41). However, the reactor may also be provided in both the first section and the second section between the other output terminal of the converter circuit (20) and the first capacitor (41). In this case, if L1 [H] is the minimum value of the sum of the inductances of the reactor in the first section and the second section (composite inductance) during surge superposition, the condition under which the voltage of the first capacitor (41) can become higher than the breakdown voltage of the inverter circuit (30) when the overvoltage protection circuit (50) is not activated is expressed by equation (1).

[0106] Furthermore, although the present invention was applied to a power converter (10) for a three-phase power supply in embodiments 1 to 5 described above, the present invention can also be applied to a power converter for a single-phase power supply.

[0107] Furthermore, although the present invention was applied to an air conditioner (1) in the embodiments 1 to 5 described above, the present invention can also be applied to other heat pump equipment such as chillers and water heaters.

[0108] While embodiments have been described above, it will be understood that various modifications to the 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 they do not impair the functions covered by this disclosure. [Industrial applicability]

[0109] This disclosure is useful as a power conversion device that converts AC output from an AC power source and as a heat pump device equipped therewith. [Explanation of Symbols]

[0110] 1. Air conditioners (heat pump equipment) 2. Compressor (Load) 6 AC power supply 10 Power converter 20 Converter Circuits 30 Inverter Circuit 30a, 30b Input nodes 41. First Capacitor 42 Reactor 43a First Reactor 43b Second Reactor 43c Third Reactor 50 Overvoltage protection circuit 51 1st resistance 52. Related to the second switching. 70 Protection Circuit Control Unit 73 Second Capacitor 74 Charge / discharge circuit 75 Comparison circuit Von1 First threshold Von2 Second threshold CTH1 First switching threshold (Second switching threshold)

Claims

1. A converter circuit (20) that converts the AC output from the AC power supply (6) to DC, An inverter circuit (30) converts the output of the converter circuit (20) into AC and supplies it to the load (2), The first capacitor (41) connected between the input nodes (30a, 30b) of the inverter circuit (30), A reactor (42, 43a to 43c) connected between the AC power supply (6) and the converter circuit (20), or between the converter circuit (20) and the first capacitor (41), An overvoltage protection circuit (50) is connected in parallel with the first capacitor (41), and has a resistor (51) and a switching element (52) connected in series with each other. The switching element (52) is turned on when the voltage of the first capacitor (41) is above a predetermined on threshold, while the switching element (52) is turned off when the voltage of the first capacitor (41) is below a predetermined off threshold which is below the on threshold. During regenerative operation in which current flows into the first capacitor (41) from at least one of the sides of the AC power supply (6) and the load (2) side of the first capacitor (41), the control unit (70) changes the on threshold to a second threshold (Von2) which is higher than the first threshold (Von1) after the voltage of the first capacitor (41) first exceeds the on threshold with the on threshold set to a first threshold (Von1). A power converter in which, after the switching element (52) starts a switching operation in which it repeatedly turns on and off in response to the regenerative operation, the second threshold (Von2) is included in the on threshold when the switching element (52) is turned on during the period until the switching element (52) stabilizes in the off state.

2. In the power conversion device according to claim 1, If the reactors (42, 43a to 43c) are provided in either or both of the following sections: the first section between one output terminal of the converter circuit (20) and the first capacitor (41), and the second section between the other output terminal of the converter circuit (20) and the first capacitor (41), the sum of the inductances of the reactors (42, 43a to 43c) in the first section and the second section shall be used as the combined inductance, and the voltage between both output terminals of the converter circuit (20) shall be used as the reactor input voltage, If the reactors (42, 43a to 43c) are provided in either or both of the third section between the input terminal of the first phase of the input phase of the converter circuit (20) and the AC power supply (6), and the fourth section between the input terminal of the second phase of the input phase of the converter circuit (20) which is different from the first phase and the AC power supply (6), the sum of the inductances of the reactors (42, 43a to 43c) in the third section and the fourth section shall be used as the combined inductance, and the voltage between the first phase and the second phase of the AC power supply (6) shall be used as the reactor input voltage. The power supply voltage of the AC power supply (6) is set to V ａｃ [V], the capacitance of the first capacitor (41) is C[F], and the withstand voltage of the inverter circuit (30) is V ｄｃ２ Let [V] be the case. With the switching element (52) turned off, the minimum value of the combined inductance during surge superposition, when a surge voltage having a peak voltage of 7 kV generated by a surge generator compliant with IEC 61000-4-5 is superimposed on the power supply voltage, is L. １ [H] The maximum value of the reactor input voltage when the surge is superimposed is V ｉｎ [V], when the reactor input voltage exceeds the withstand voltage of the inverter circuit (30) during surge superposition, then √2V ａｃ A power converter such that the following equation holds true, where t [seconds] is the time it takes for the voltage to fall below [V]. [Math 1]

3. In the power conversion device according to claim 1, The control unit (70) is a power conversion device that changes the on threshold to the first threshold (Von1) when the switching element (52) is turned on while the on threshold is the second threshold (Von2), and the switching element (52) remains in the off state for a predetermined time.

4. In the power conversion device according to claim 3, The control unit (70) The second capacitor (73) and A charge / discharge circuit (74) charges the second capacitor (73) when the switching element (52) is in the ON state, and discharges the second capacitor (73) when the switching element (52) is in the OFF state, A power converter having a comparison circuit (75) which sets the ON threshold as the second threshold (Von2) when the voltage of the second capacitor (73) is equal to or greater than a predetermined first switching threshold (CTH1), and sets the ON threshold as the first threshold (Von1) when the voltage of the second capacitor (73) is less than a predetermined second switching threshold (CTH1) which is equal to or less than the first switching threshold (CTH1).

5. A power conversion device according to any one of claims 1 to 4, The above load (2) is provided, The aforementioned load (2) is a heat pump device, which is a compressor.

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