Power conversion equipment

Abstract

To attain space saving of power conversion equipment.SOLUTION: Power conversion equipment (10) is provided, comprising: a converter circuit (20) which converts alternating current output from an AC power source (1) into direct current; an inverter circuit (30) which converts output of the converter circuit (20) into alternating current by switching operation of a plurality of switching elements (31a-36a) and supplies the alternating current to a compressor (2); and a capacitor (41) which is connected to between input nodes of the inverter circuit (30) and allows pulsation of an output voltage of the converter circuit (20). In the power conversion equipment, there are provided: an overvoltage protection circuit (50) including a first resistor (51) and a second switching element (52), which are connected in series with each other, and connected in parallel with the capacitor (41); and a package (90) in which the second switching element (52) is stored. A heat sink is not mounted in the package (90).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device that converts alternating current output from an AC power supply. [Background technology]

[0002] Patent Document 1 discloses a power conversion device including a converter circuit that converts AC output from an AC power source into DC, an inverter circuit having a plurality of first switching elements that converts the output of the converter circuit into AC by switching operations of the plurality of first switching elements and supplies the AC output to a load, and a first capacitor that is connected between input nodes of the inverter circuit and allows pulsation of the output voltage of the converter circuit. In this power conversion device, a diode, a resistor, and a second capacitor are connected in series between the input nodes of the inverter circuit. When the switching operation of the inverter circuit is stopped, a current flows from the load to the first and second capacitors due to magnetic energy stored in the inductance component of the load. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-20836 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, even if the size and capacity of the first capacitor are reduced, the size and capacity of the second capacitor must be increased to protect the first capacitor from overvoltage, and therefore space saving cannot be achieved.

[0005] An object of the present disclosure is to reduce the space required for a power conversion device. [Means for solving the problem]

[0006] A first aspect of the present disclosure is a power conversion device including: a converter circuit (20) that converts an AC output from an AC power supply (1) into a DC; an inverter circuit (30) having a plurality of first switching elements (31a-36a) that converts an output of the converter circuit (20) into AC by switching operation of the plurality of first switching elements (31a-36a) and supplies the AC output to a load (2); and a capacitor (41) connected between input nodes (30a, 30b) of the inverter circuit (30) and allowing pulsation of an output voltage of the converter circuit (20), wherein the power conversion device further includes an overvoltage protection circuit (50) having a resistor (51) and a second switching element (52) connected in series to each other and connected in parallel to the capacitor (41); and a package (90) that houses the second switching element (52), wherein no heat sink is attached to the package (90).

[0007] In the first aspect, when the switching operation of the inverter circuit (30) is stopped, the magnetic energy stored in the inductance component of the load (2) is consumed by the resistor (51) by controlling the second switching element (52), thereby protecting the capacitor (41) from overvoltage. Therefore, it is not necessary to provide a separate capacitor for absorbing magnetic energy in the overvoltage protection circuit (50), thereby realizing space saving. In addition, since the energy can be rapidly consumed by the resistor (51) by controlling the second switching element (52), it is possible to shorten the driving time of the second switching element (52) when the switching operation of the inverter circuit (30) is stopped, and to suppress the temperature rise of the second switching element (52). Therefore, it is not necessary to attach a heat sink to the package (90) that accommodates the second switching element (52), thereby realizing space saving.

[0008] A second aspect of the present disclosure is characterized in that in the first aspect, a terminal (91) is connected to the package (90), and the terminal (91) is connected to a substrate (80).

[0009] In the second embodiment, since a heat sink is not attached to the package (90), the package (90) can be mounted in a smaller space on the substrate (80) than if a heat sink were attached.

[0010] A third aspect of the present disclosure is characterized in that, in the first or second aspect, the length (L1) of the package (90) in a first direction is 27 mm or less, the length (L2) of the package (90) in a second direction perpendicular to the first direction is 21 mm or less, and the length (L3) of the package (90) in a third direction perpendicular to the first and second directions is 5.5 mm or less.

[0011] In the third aspect, a plurality of electronic components including the second switching element (52) can be mounted on the substrate (80) at a relatively high density.

[0012] A fourth aspect of the present disclosure is characterized in that in any one of the first to third aspects, the second switching element (52) has a larger current capacity than the first switching elements (31a to 36a).

[0013] In the fourth aspect, when the switching operation of the inverter circuit (30) is stopped, a relatively large current can be passed through the resistor (51) to rapidly consume energy. This shortens the drive time of the second switching element (52) when the switching operation of the inverter circuit (30) is stopped, and more reliably suppresses the temperature rise of the second switching element (52).

[0014] A fifth aspect of the present disclosure is characterized in that, in any one of the first to fourth aspects, the first switching element (31a to 36a) and the second switching element (52) are insulated gate bipolar transistors or insulated gate field effect transistors, and the absolute value of the gate-emitter voltage or the gate-source voltage of the second switching element (52) in the on state is greater than the absolute value of the gate-emitter voltage or the gate-source voltage of the first switching element (31a to 36a) in the on state.

[0015] In the fifth aspect, the conduction loss and switching loss of the second switching element (52) are reduced, and therefore it is easy to pass a relatively large current through the resistor (51) and rapidly consume energy when the switching operation of the inverter circuit (30) is stopped. As a result, the drive time of the second switching element (52) when the switching operation of the inverter circuit (30) is stopped can be shortened, and the temperature rise of the second switching element (52) can be more reliably suppressed.

[0016] A sixth aspect of the present disclosure is characterized in that, in any one of the first to fifth aspects, the inverter circuit (30) further includes a control unit (70) that turns on the second switching element (52) when the voltage of the capacitor (41) exceeds a predetermined first threshold value (TH1) during a period in which a current flows from the load (2) to the input side of the inverter circuit (30).

[0017] In the sixth aspect, when the voltage of the capacitor (41) exceeds the first threshold (TH1) during a period in which a current flows from the load (2) to the input side of the inverter circuit (30), the second switching element (52) is turned on to cause the resistor (51) to consume energy, thereby suppressing an increase in the voltage of the capacitor (41).

[0018] A seventh aspect of the present disclosure is characterized in that in the sixth aspect, immediately after the control unit (70) initially turns on the second switching element (52) in a state in which a current flows from the load (2) to the input side of the inverter circuit (30), the current flowing through the second switching element (52) becomes smaller than the sum of the current flowing from the load (2) to the input side of the inverter circuit (30) and the current flowing from the AC power supply (1) to the output side of the converter circuit (20).

[0019] In the seventh aspect, the resistance value of the resistor (51) can be set large so that the current flowing through the second switching element (52) is smaller than the sum immediately after the control unit (70) turns on the second switching element (52) for the first time in a state where a current flows from the load (2) to the input side of the inverter circuit (30). By setting the resistance value of the resistor (51) large, the current flowing through the second switching element (52) can be reduced, thereby reducing the conduction loss. By reducing the current flowing through the second switching element (52), the on-time of the second switching element (52) is extended, thereby reducing the number of times that the voltage value of the capacitor (41) passes through the first threshold value (TH1), i.e., the number of times that the second switching element (52) is switched, thereby reducing the switching loss.

[0020] An eighth aspect of the present disclosure is characterized in that in the sixth aspect, the control unit (70) turns on the second switching element (52) when the voltage of the capacitor (41) exceeds the first threshold (TH1), and turns off the second switching element (52) when the voltage of the capacitor (41) is equal to or lower than a predetermined second threshold (TH2) that is equal to or lower than the first threshold (TH1), so that the following formulas (1) and (2) are satisfied, where Po is an average loss of the second switching element (52), Rth is a thermal resistance between the second switching element (52) and the package (90), Tj is a maximum rated junction temperature of the second switching element (52), Ta is a maximum atmospheric temperature around the package (90) during switching operations of the plurality of first switching elements (31a to 36a), t is a time during which the second switching element (52) is continuously turned on and off, and Cth is a heat capacity of the package (90).

[0021] Po*Rth>Tj-Ta (1) Tj-Ta>Po*Rth*(1-exp[-t / (Rth*Cth)]) ···(2) In the eighth aspect, the time during which the second switching element (52) is continuously turned on and off can be shortened, thereby making it possible to prevent thermal destruction of the second switching element (52).

[0022] A ninth aspect of the present disclosure is characterized in that, in any one of the first to eighth aspects, a reactor (42) is provided between the AC power supply (1) and the capacitor (41), and when a capacitance of the capacitor (41) is C, a maximum value of a voltage that can be applied between the input nodes (30a, 30b) of the inverter circuit (30) is Vc1, a peak voltage between the input nodes (30a, 30b) during the switching operation is Vc2, a maximum magnetic energy that can be stored in the load (2) is Em, and a maximum magnetic energy that can be stored in the reactor (42) is Er, the following formula (3) is satisfied:

[0023] C(Vc1 2 -Vc2 2 ) / 2 <Em+Er ···(3) In the ninth aspect, even if formula (3) holds, the resistor (51) is caused to consume energy by controlling the second switching element (52), thereby protecting electronic components between the input nodes (30a, 30b) of the inverter circuit (30), including the capacitor (41), from overvoltage.

[0024] A tenth aspect of the present disclosure is characterized in that, in any one of the first to eighth aspects, a reactor (42) is provided between the AC power supply (1) and the capacitor (41), and when the capacitance of the capacitor (41) is C, the withstand voltage of the capacitor (41) is Vc1, the peak voltage of the capacitor (41) during the switching operation is Vc2, the maximum magnetic energy that can be stored in the load (2) is Em, and the maximum magnetic energy that can be stored in the reactor (42) is Er, the following formula (4) holds:

[0025] C(Vc1 2 -Vc2 2 ) / 2 <Em+Er ···(4) In the tenth aspect, even though formula (4) holds, the capacitor (41) can be protected from overvoltage by causing the resistor (51) to consume energy through control of the second switching element (52).

[0026] An eleventh aspect of the present disclosure is any one of the first to tenth aspects, characterized in that the resistor (51) is mounted on a substrate (80).

[0027] In the eleventh aspect, since a heat sink is not attached to the package (90), the space required for mounting the package (90) is smaller than in the case where a heat sink is attached, and therefore it is easy to mount the resistor (51) on the same substrate (80) as the package (90).

[0028] A twelfth aspect of the present disclosure is any one of the first to eleventh aspects, characterized in that the load (2) is a compressor.

[0029] In the twelfth aspect, the load (2) is a compressor. The compressor has a small inertia, and is hardly affected by the regenerative energy due to the rotation of the rotating part of the compressor. The only energy regenerated from the compressor to the capacitor (41) is the magnetic energy stored in the motor of the compressor. Thus, when the switching operation of the inverter circuit (30) is stopped, the second switching element (52) is controlled so that the energy regenerated from the load (2) can be easily consumed by the resistor (51) in a relatively short time. Therefore, even if a heat sink is not attached to the package (90), the temperature rise of the second switching element (52) can be easily suppressed.

[0030] A thirteenth aspect of the present disclosure, in any one of the first to twelfth aspects, is characterized in that the second switching element (52) is an element whose main material is a wide band gap semiconductor.

[0031] In the thirteenth aspect, the second switching element (52) can be operated at a higher temperature than when the main material of the second switching element (52) is a semiconductor other than a wide band gap semiconductor. [Brief description of the drawings]

[0032] [Figure 1]FIG. 1 is a circuit diagram showing a configuration of a power conversion device according to the first embodiment. [Diagram 2] FIG. 2 is a front view showing the package attached to a substrate. [Diagram 3] FIG. 3 is a side view showing the package attached to a substrate. [Figure 4] FIG. 4 is a plan view showing a package attached to a substrate. [Diagram 5] FIG. 5 is a timing chart showing the operation of the power conversion device in the first embodiment. [Figure 6] FIG. 6 is a graph showing the value of the right side of equation (2) when the heat capacity of the package is set to different first to third heat capacities. [Figure 7] FIG. 7 is a view corresponding to FIG. 1 of the second embodiment. [Figure 8] FIG. 8 is a perspective view of the package and its surroundings of a power conversion device according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] 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.

[0034] (Embodiment 1) 1 shows a power conversion device (10) according to a first embodiment of the present disclosure. The power conversion device (10) converts AC power output from an AC power source (1) into AC having a desired frequency and a desired voltage, and supplies the AC power to a compressor (2) as a load. In the first embodiment, the AC power source (1) is a three-phase AC power source.

[0035] The power conversion device (10) includes a converter circuit (20), an inverter circuit (30), a capacitor (41), a reactor (42), a voltage detection unit (43), a second resistor (44), an overvoltage protection circuit (50), an inverter control unit (60), a protection circuit control unit (70), a substrate (80), and a package (90).

[0036] The converter circuit (20) converts the AC output from the AC power supply (1) into DC and outputs it. The converter circuit (20) has first to sixth rectifier diodes (21-26) connected in a bridge shape. The rectifier diodes (21-26) have their cathodes facing the positive voltage power line (PL) and their anodes facing the negative voltage power line (NL).

[0037] The inverter circuit (30) has six (a plurality of) first switching elements (31a-36a) and six (a plurality of) free wheel diodes (31b-36b). The six first switching elements (31a-36a) are bridge-connected. More specifically, the inverter circuit (30) has three switching legs connected between a positive voltage side power line (PL) and a negative voltage side power line (NL). Each switching leg has two first switching elements (31a-36a) connected in series to each other. In each of the three switching legs, a midpoint between the first switching element (31a-33a) of the upper arm and the first switching element (34a-36a) of the lower arm is connected to a coil of each phase (coil of u-phase, v-phase, w-phase) of the compressor (2). A free wheel diode (31b-36b) is connected in anti-parallel to each of the first switching elements (31a-36a). The inverter circuit (30) converts the output of the converter circuit (20) into AC by switching operations of six first switching elements (31a-36a) and supplies the AC to the compressor (2). The first switching elements (31a-36a) are insulated gate bipolar transistors.

[0038] The six first switching elements (31a to 36a) are elements whose main material is a wide band gap semiconductor containing silicon carbide (SiC), gallium nitride (GaN) or diamond (C).

[0039] The capacitor (41) is connected between the input nodes (30a, 30b) of the inverter circuit (30) and allows pulsation in the output voltage of the converter circuit (20). The capacitance of the capacitor (41) is set so that it can hardly smooth the output voltage of the converter circuit (20) but can suppress the ripple voltage caused by the switching operation of the inverter circuit (30). The ripple voltage that is suppressed here is a voltage fluctuation corresponding to the switching frequency of the first switching elements (31a-36a).

[0040] In short, the capacitance of the capacitor (41) is set to tolerate pulsation 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 operations. More specifically, the capacitance of the capacitor (41) is set to suppress the voltage fluctuations of the capacitor (41) during a switching period to 1 / 10 or less of the average voltage of the capacitor (41). In this way, the capacitance of the capacitor (41) can be reduced to an extent that allows the pulsation in the output voltage of the converter circuit (20) to be tolerated, and therefore the capacitor (41) can be made smaller.

[0041] Here, the switching period is a period during which the first switching elements (31a to 36a) are repeatedly turned on and off. In the first embodiment, since the first switching elements (31a to 36a) are controlled by PWM control, the switching period is the carrier period of the carrier wave.

[0042] Conventionally, an electrolytic capacitor has been used as a smoothing capacitor for smoothing the output voltage of the converter circuit (20). On the other hand, the capacitance of the capacitor (41) of the present embodiment is about 0.01 to 0.1 times that of the smoothing capacitor. As an example, the capacitor (41) is a film capacitor.

[0043] When the capacitance of the 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 so as to satisfy the following formula.

[0044]

number

[0045] Therefore, pulsation occurs in the voltage of the capacitor (41) due to the frequency of the input AC supplied from the AC power source (1). Because the AC power source (1) is a three-phase power source, the frequency of the pulsation due to the frequency of the AC power source (1) is six times the frequency of the AC power source (1).

[0046] The reactor (42) is connected between an output node of the converter circuit (20) on the positive voltage side power supply line (PL) and one end of the capacitor (41). In this manner, the reactor (42) is provided between the AC power supply (1) and the capacitor (41). Therefore, a current from the AC power supply (1) is input to the capacitor (41) via the reactor (42).

[0047] The voltage detection unit (43) detects the voltage of the capacitor (41), that is, the DC link voltage.

[0048] The overvoltage protection circuit (50) is connected in parallel with the capacitor (41). The overvoltage protection circuit (50) has a first resistor (51) and a second switching element (52) connected in series with each other in this order from the positive voltage side power line (PL), 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 line (PL), and the anode of the diode (53) is connected to the collector of the second switching element (52). The current capacity of the second switching element (52) is larger than the current capacity of the first switching elements (31a-36a). The absolute value of the gate-emitter voltage of the second switching element (52) in the ON state is larger than the absolute value of the gate-emitter voltage of the first switching elements (31a-36a) in the ON state. Note that the current capacity of the second switching element (52) may be made larger than the current capacity of the first switching elements (31a-36a), while the absolute value of the gate-emitter voltage of the second switching element (52) in the on state may be set to be equal to or smaller than the absolute value of the gate-emitter voltage of the first switching elements (31a-36a) in the on state. Furthermore, the absolute value of the gate-emitter voltage of the second switching element (52) in the on state may be made larger than the absolute value of the gate-emitter voltage of the first switching elements (31a-36a) in the on state, while the current capacity of the second switching element (52) may be made smaller than the current capacity of the first switching elements (31a-36a).

[0049] The second switching element (52) is an element whose main material is a wide band gap semiconductor containing silicon carbide (SiC), gallium nitride (GaN), or diamond (C). Wide band gap semiconductors can operate at high temperatures of approximately 200 degrees. Since the second switching element (52) is made mainly of a wide band gap semiconductor, the overvoltage protection circuit (50) can convert a relatively large amount of energy into heat, even though it is relatively small in size.

[0050] A second resistor (44) is connected to the negative voltage power supply line (NL) between the capacitor (41) and the overvoltage protection circuit (50).

[0051] The inverter control unit (60) and the protection circuit control unit (70) are constituted by various elements, a microcomputer, a memory, etc. An output terminal of the inverter control unit (60) is connected to the gate terminals of the first switching elements (31a-36a) in the inverter circuit (30).

[0052] The inverter control unit (60) controls the switching operation of each of the first switching elements (31a-36a). This control includes control for making the rotation speed of the compressor (2) approach a desired rotation speed. The inverter control unit (60) performs PWM control for controlling the first switching elements (31a-36a) with a switching signal corresponding to a result of comparison between the modulated wave of each phase and a carrier wave, which is a predetermined triangular wave. In more detail, if the modulated wave is larger than the carrier wave, the upper arm switching elements (31a-33a) are turned on and the lower arm switching elements (34a-36a) are turned off, whereas if the modulated wave is smaller than the carrier wave, the upper arm switching elements (31a-33a) are turned off and the lower arm switching elements (34a-36a) are turned on.

[0053] The protection circuit control unit (70) has one input terminal. The DC link voltage detected by the voltage detection unit (32) is input to this input terminal. The protection circuit control unit (70) has one output terminal. This output terminal is connected to the gate terminal of the second switching element (52). The protection circuit control unit (70) turns on the second switching element (52) when the DC link voltage exceeds a first threshold (TH1) (see FIG. 5 ). On the other hand, the protection circuit control unit (70) turns off the second switching element (52) when the DC link voltage becomes equal to or lower than a second threshold (TH2) (see FIG. 5 ) that is lower than the first threshold (TH1) while the second switching element (52) is turned on. Note that, although the second threshold (TH2) is smaller than the first threshold (TH1) in the first embodiment, it may be equal to the first threshold (TH1). In other words, the second threshold (TH2) may be equal to or lower than the first threshold (TH1).

[0054] The converter circuit (20), the inverter circuit (30), the capacitor (41), the overvoltage protection circuit (50), the inverter control unit (60), and the protection circuit control unit (70) are mounted on a common substrate (80). The converter circuit (20), the inverter circuit (30), the capacitor (41), the overvoltage protection circuit (50), the inverter control unit (60), and the protection circuit control unit (70) may be mounted separately on multiple substrates.

[0055] The second switching element (52) of the overvoltage protection circuit (50) is accommodated in a resin package (90) as shown in FIGS. 2 to 4. The package (90) is formed in a substantially rectangular plate shape. The package (90) is connected to the substrate (80) with the longitudinal direction of the main surface of the package (90) oriented perpendicular to the plate surface of the substrate (80) and the lateral and thickness directions of the main surface aligned along the surface of the substrate (80). The length (L1) of the package (90) in the longitudinal direction as a first direction is 27 mm or less. The length (L2) of the package (90) in the lateral direction of the main surface as a second direction perpendicular to the first direction is 21 mm or less. The length (L3) of the package (90) in the thickness direction as a third direction perpendicular to the first and second directions is 5.5 mm or less.

[0056] Three terminals 91 are connected to the package 90. These terminals 91 are connected to the substrate 80.

[0057] No heat sink is attached to the package (90). Therefore, substantially all of the heat dissipated from the second switching element (52) is dissipated to the substrate (80) or directly to the atmosphere. The reason why it is said to be substantially all is that a portion of the heat dissipated from the second switching element (52) is dissipated to lead wires, etc. Furthermore, a member that contributes little to heat dissipation may be attached to the package (90).

[0058] FIG. 5 shows the states of the first switching elements (31a to 36a), the state of the second switching element (52), the DC link voltage (the voltage of the capacitor (41)), and the current flowing through the second switching element (52).

[0059] During the period T1 from time t0 to time t1, the inverter circuit 30 performs a switching operation. During this period, the DC link voltage is below the first threshold voltage TH1 and is stable.

[0060] At time t1, the inverter control unit (60) stops the switching operation of the first switching elements (31a-36a). In the first embodiment, while the switching operation is stopped, all the first switching elements (31a-36a) of the inverter circuit (30) are turned off. Then, a current flows from the compressor (2) to the input side of the inverter circuit (30) due to regeneration of the magnetic energy stored in the compressor (2), and a current flows from the AC power source (1) to the output side of the converter circuit (20) due to the magnetic energy stored in the reactor (42), etc., and the DC link voltage starts to increase. The period during which a current flows from the compressor (2) to the input side of the inverter circuit (30) and the period during which a current flows from the AC power source (1) to the output side of the converter circuit (20) may be shifted or may not overlap depending on the inductance of the reactor (42).

[0061] At time t2, the DC link voltage exceeds the first threshold value (TH1). In response to this, the protection circuit control unit (70) turns on the second switching element (52). As a result, current flows from the AC power source (1) and the compressor (2) to the second switching element (52). As a result, energy is consumed in the first resistor (51), and the increase in voltage of the capacitor (41) is suppressed. The current flowing from the AC power source (1) to the second switching element (52) also includes a current flowing from the AC power source (1) to the second switching element (52) due to the magnetic energy stored in the reactor (42). Immediately after the second switching element (52) is turned on, the rate at which the DC link voltage increases gradually decreases during the period from time t2 to time t3, but the DC link voltage continues to increase. During this time, the current flowing through the second switching element (52) is smaller than the sum of the current flowing from the compressor (2) to the input side of the inverter circuit (30) and the current flowing from the AC power supply (1) to the output side of the converter circuit (20). At time t2, the current (I1) flowing through the second switching element (52) is equal to the first threshold value (TH1) divided by the discharge resistance value (resistance of the overvoltage protection circuit (50)). The current flowing from the AC power supply (1) to the output side of the converter circuit (20) is a current flowing from the AC power supply (1) to the second switching element (52) due to magnetic energy stored in the reactor (42) or the like.

[0062] At time t3, the DC link voltage starts to decrease. During the period from time t3 to time t4, the current flowing through the second switching element (52) is greater than the sum of the current flowing from the compressor (2) to the input side of the inverter circuit (30) and the current flowing from the AC power supply (1) to the output side of the converter circuit (20).

[0063] At time t4, when the DC link voltage becomes equal to or lower than the second threshold value (TH2), the protection circuit control unit (70) turns off the second switching element (52). As a result, no current flows through the second switching element (52), and a current flows from the AC power source (1) and the compressor (2) to the capacitor (41), causing the DC link voltage to increase. The current (I2) flowing through the second switching element (52) at time t4 is equal to the second threshold value (TH2) divided by the discharge resistance value (the resistance of the overvoltage protection circuit (50)).

[0064] At time t5, when the DC link voltage exceeds the first threshold value (TH1) again, the second switching element (52) is turned on, and the DC link voltage decreases.

[0065] Thereafter, at time t6, when the DC link voltage becomes equal to or lower than the second threshold value (TH2), the protection circuit control unit (70) turns off the second switching element (52). As a result, no current flows through the second switching element (52), and a current flows from the AC power source (1) and the compressor (2) to the capacitor (41), causing the DC link voltage to increase. When the magnetic energy stored in the compressor (2) and the reactor (42) is exhausted, the DC link voltage becomes constant from time t7.

[0066] In Fig. 5, during a period in which currents flow from the compressor (2) and the AC power source (1) to the capacitor (41), the protection circuit control unit (70) also turns on the second switching element (52) when the voltage of the capacitor (41) exceeds the first threshold value (TH1). Although not shown in Fig. 5, during a period in which no current flows from the compressor (2) to the capacitor (41) but current flows from the AC power source (1) to the capacitor (41), the protection circuit control unit (70) also turns on the second switching element (52) when the voltage of the capacitor (41) exceeds the first threshold value (TH1). Note that during a period in which no current flows from the compressor (2) to the capacitor (41) but current flows from the AC power source (1) to the capacitor (41), the protection circuit control unit (70) may not turn on the second switching element (52) even if the voltage of the capacitor (41) exceeds the first threshold value (TH1).

[0067] 5, in a state in which a current flows from the compressor (2) into the input side of the inverter circuit (30) and a current flows from the AC power source (1) into the output side of the converter circuit (20), immediately after the protection circuit control unit (70) turns on the second switching element (52) for the first time, the current flowing through the second switching element (52) becomes smaller than the sum of the current flowing from the compressor (2) into the input side of the inverter circuit (30) and the current flowing from the AC power source (1) into the output side of the converter circuit (20). However, if the switching operation of the first switching elements (31a-36a) is stopped in a state in which the magnetic energy stored in the compressor (2) is relatively small, immediately after the protection circuit control unit (70) turns on the second switching element (52) for the first time, the current flowing through the second switching element (52) does not become smaller than the sum of the current flowing from the compressor (2) into the input side of the inverter circuit (30) and the current flowing from the AC power source (1) into the output side of the converter circuit (20).

[0068] In the first embodiment, the following formulas (1) and (2) are satisfied when the average loss of the second switching element (52) is Po, the thermal resistance between the second switching element (52) and the package (90) is Rth, the maximum rated junction temperature of the second switching element (52) is Tj, the maximum ambient temperature around the package (90) during the switching operation of the first switching elements (31a-36a) is Ta, the time during which the second switching element (52) is continuously turned on and off is t, and the heat capacity of the package (90) is Cth. Here, the on / off operation refers to an operation of turning the second switching element (52) on and off based on a comparison result between the voltage value of the capacitor (41) and the first and second threshold values ​​(TH1 and TH2). During the period during which the on / off operation is not performed, the second switching element (52) is turned off.

[0069] Po*Rth>Tj-Ta (1) Tj-Ta>Po*Rth*(1-exp[-t / (Rth*Cth)]) ···(2) In FIG. 6, G1 is a graph showing the value on the right side of the above formula (2) when the heat capacity of the package (90) is set to the first heat capacity, G2 is a graph showing the value on the right side of the above formula (2) when the heat capacity of the package (90) is set to the second heat capacity, and G3 is a graph showing the value on the right side of the above formula (2) when the heat capacity of the package (90) is set to the third heat capacity. When the first heat capacity is Cth1, the second heat capacity is Cth2, and the third heat capacity is Cth3, Cth1 < Cth2 < Cth3. G4 is the value on the left side of formula (2), that is, Tj - Ta. The second switching element (52) performs an on-off operation only when formula (2) holds, that is, only during the period surrounded by the thick-line square in FIG. 6. Therefore, compared with the case where the second switching element (52) is also turned on when formula (2) does not hold, the time for continuously performing the on-off operation of the second switching element (52) can be shortened, so thermal breakdown of the second switching element (52) can be suppressed.

[0070] Also, in the first embodiment, when the capacitance of the capacitor (41) is C, the withstand voltage of the capacitor (41) is Vc1, the peak voltage of the capacitor (41) during the switching operation of the first switching elements (31a to 36a) is Vc2, the maximum magnetic energy stored in the compressor (2) is Em, and the maximum magnetic energy stored in the reactor (42) is Er, the following formula (3) holds.

[0071] C(Vc1 2 -Vc2 2 ) / 2 < Em + Er ···(3) Here, when the inductance of the motor of the compressor (2) is Lm and the maximum motor current (for example, the current corresponding to the overcurrent threshold value) when the motor stops is Im, the maximum magnetic energy Em stored in the compressor (2) is represented by the following formula (4).

[0072] Em = (1 / 2)*Lm*Im 2 ···(4) In addition, when the inductance of the reactor (42) is Lr and the maximum current flowing through the reactor (42) when the motor is stopped (for example, the current at the timing when the instantaneous value of the power supply current is maximum under the condition that the load of the compressor (2) is maximum) is Ir, the maximum magnetic energy Er that can be stored in the reactor (42) is expressed by the following equation (5).

[0073] Er = (1 / 2)*Lr*Ir 2 (5) In the first embodiment, the voltage of the capacitor (41) is approximately equal to the voltage between the input nodes (30a, 30b) of the inverter circuit (30). In the first embodiment, the following formula (6) also holds when the capacitance of the capacitor (41) is C, the maximum value of the voltage that can be applied between the input nodes (30a, 30b) of the inverter circuit (30) is Vc1, the peak voltage between the input nodes (30a, 30b) during the switching operation of the first switching elements (31a-36a) is Vc2, the maximum magnetic energy that can be stored in the compressor (2) is Em, and the maximum magnetic energy that can be stored in the reactor (42) is Er. Here, the voltage that can be applied between the input nodes (30a, 30b) of the inverter circuit (30) refers to the limit value of voltage that does not destroy any of the converter circuit (20), the inverter circuit (30), the capacitor (41), and the overvoltage protection circuit (50), i.e., the minimum withstand voltage of the converter circuit (20), the inverter circuit (30), the capacitor (41), and the overvoltage protection circuit (50).

[0074] C(Vc1 2 -Vc2 2 ) / 2 <Em+Er ···(6) In the first embodiment, even though formulas (3) and (6) hold, the capacitor (41) can be protected from overvoltage by causing the first resistor (51) to consume energy through control of the second switching element (52).

[0075] Therefore, according to the first embodiment, when the switching operation of the inverter circuit (30) is stopped, the magnetic energy stored in the inductance component of the compressor (2) and the magnetic energy stored in the reactor (42) are consumed by the first resistor (51) by controlling the second switching element (52), thereby protecting the capacitor (41) from overvoltage. Therefore, it is not necessary to provide a separate capacitor for absorbing magnetic energy in the overvoltage protection circuit (50), thereby realizing space saving. In addition, since the energy can be rapidly consumed by the first resistor (51) by controlling the second switching element (52), it is possible to shorten the driving time of the second switching element (52) when the switching operation of the inverter circuit (30) is stopped, and to suppress the temperature rise of the second switching element (52). Therefore, it is not necessary to attach a heat sink to the package (90) that accommodates the second switching element (52), thereby realizing space saving.

[0076] In addition, since no heat sink is attached to the package (90), the package (90) can be mounted in a smaller space on the board (80) than if a heat sink were attached. In addition, since the space required to mount the package (90) is reduced, it is easier to mount the first resistor (51) on the same board (80) as the package (90). In addition, heat from the first resistor (51) can be dissipated to the board (80).

[0077] Furthermore, the longitudinal length (L1) of the package (90) is set to 27 mm or less, the lateral length (L2) of the main surface of the package (90) is set to 21 mm or less, and the thickness direction length (L3) of the package (90) is set to 5.5 mm or less. This makes it possible to mount multiple electronic components including the second switching element (52) on the substrate (80) at a relatively high density.

[0078] In addition, since the current capacity of the second switching element (52) is set to be larger than the current capacity of the first switching elements (31a-36a), a relatively large current can be passed through the first resistor (51) when the switching operation of the inverter circuit (30) is stopped, thereby allowing energy to be consumed rapidly. As a result, the drive time of the second switching element (52) when the switching operation of the inverter circuit (30) is stopped can be shortened, and the temperature rise of the second switching element (52) can be more reliably suppressed.

[0079] In addition, since the absolute value of the gate-emitter voltage of the second switching element (52) in the on state is set to be greater than the absolute value of the gate-emitter voltage of the first switching elements (31a-36a) in the on state, the conduction loss and switching loss of the second switching element (52) are reduced, and it becomes easy to cause a relatively large current to flow through the first resistor (51) and to rapidly consume energy when the switching operation of the inverter circuit (30) is stopped. As a result, the drive time of the second switching element (52) when the switching operation of the inverter circuit (30) is stopped can be shortened, and the temperature rise of the second switching element (52) can be more reliably suppressed.

[0080] In addition, the resistance value of the first resistor (51) can be set large so that the current flowing through the second switching element (52) is smaller than the sum of the current flowing from the compressor (2) to the input side of the inverter circuit (30) and the current flowing from the AC power source (1) to the output side of the converter circuit (20) immediately after the protection circuit control unit (70) turns on the second switching element (52) for the first time in a state in which a current flows from the compressor (2) to the input side of the inverter circuit (30) and a current flows from the AC power source (1) to the output side of the converter circuit (20). By setting the resistance value of the first resistor (51) large, the current flowing through the second switching element (52) can be reduced, thereby reducing the conduction loss. By reducing the current flowing through the second switching element (52), the number of times the voltage value of the capacitor (41) passes through the first threshold value (TH1), i.e., the number of times the second switching element (52) is switched, can be reduced, thereby reducing the switching loss.

[0081] In addition, since the load (2) is a compressor that generates a relatively small amount of regenerative energy, the regenerative energy can be easily consumed in the first resistor (51) in a relatively short time by controlling the second switching element (52) when the switching operation of the inverter circuit (30) is stopped. Therefore, it is easy to suppress a temperature rise in the second switching element (52) without attaching a heat sink to the package (90).

[0082] Furthermore, the second switching element (52) can be operated at a higher temperature than when the main material of the second switching element (52) is a semiconductor other than a wide band gap semiconductor.

[0083] (Embodiment 2) FIG. 7 is a diagram corresponding to FIG. 1 of the second embodiment. In the second embodiment, the AC power supply (1) is a single-phase AC power supply. The converter circuit (20) has only the first to fourth rectifier diodes (21 to 24). A reactor (42) is connected between the AC power supply (1) and one of the input terminals of the converter circuit (20). In this case, the pulsating component of the DC link voltage corresponding to the frequency of the power supply voltage has a frequency approximately twice as high as that of the power supply voltage. The DC link voltage pulsates so that its maximum value is at least twice its minimum value.

[0084] The other configurations and operations are the same as those in the first embodiment, so detailed description thereof will be omitted.

[0085] (Other embodiments) In the above-mentioned embodiments 1 and 2, the longitudinal direction of the main surface of the package (90) is oriented in a direction perpendicular to the surface of the substrate (80). However, as shown in FIG. 8, the package (90) may be connected to the substrate (80) so that the main surface of the package (90) faces the substrate (80).

[0086] In the first and second embodiments, the first switching element (31a-36a) and the second switching element (52) are insulated gate bipolar transistors, but they may be insulated gate field effect transistors. In this case, by setting the absolute value of the gate-source voltage of the second switching element (52) in the on state to be larger than the absolute value of the gate-source voltage of the first switching elements (31a-36a) in the on state, the drive time of the second switching element (52) when the switching operation of the inverter circuit (30) is stopped can be shortened and the temperature rise of the second switching element (52) can be more reliably suppressed.

[0087] In the above first and second embodiments, while the switching operation is stopped, all of the first switching elements (31a-36a) of the inverter circuit (30) are turned off. However, among the six first switching elements (31a-36a), the first switching elements (31a-36a) connected in parallel to the free wheel diodes (31b-36b) through which a current flows due to the energy regenerated from the compressor (2) may be turned on.

[0088] 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 appropriately combined or substituted as long as the functions of the subject of the present disclosure are not impaired. [Industrial Applicability]

[0089] The present disclosure is useful as a power conversion device that converts AC output from an AC power supply. [Explanation of symbols]

[0090] 1 AC power supply 2 Compressor (load) 10 Power conversion device 20 Converter circuit 30 Inverter circuit 30a, 30b Input nodes 31a to 36a First switching elements 41 Capacitor 42 Reactor 50 Overvoltage protection circuit 51 1st resistance 52 Second switching element 70 Protection circuit control section 80 Substrate 90 Packages 91 Terminal L1, L2, L3 Length TH1 First Threshold TH2 Second Threshold

Claims

1. a converter circuit (20) that converts AC output from an AC power source (1) into DC; an inverter circuit (30) having a plurality of first switching elements (31a-36a) for converting an output of the converter circuit (20) into AC by switching operations of the plurality of first switching elements (31a-36a) and supplying the AC output to a load (2); a capacitor (41) connected between input nodes (30a, 30b) of the inverter circuit (30) for allowing pulsation of the output voltage of the converter circuit (20), an overvoltage protection circuit (50) having a resistor (51) and a second switching element (52) connected in series with each other and connected in parallel with the capacitor (41); a package (90) that houses the second switching element (52), A power conversion device characterized in that no heat sink is attached to the package (90).

2. 2. The power conversion device according to claim 1, A terminal (91) is connected to the package (90), The power conversion device, wherein the terminal (91) is connected to a substrate (80).

3. 3. The power conversion device according to claim 2, a length (L1) of the package (90) in a first direction is 27 mm or less, a length (L2) of the package (90) in a second direction perpendicular to the first direction is 21 mm or less, and a length (L3) of the package (90) in a third direction perpendicular to the first direction and the second direction is 5.5 mm or less.

4. 2. The power conversion device according to claim 1, The power conversion device is characterized in that the second switching element (52) has a larger current capacity than the first switching elements (31a-36a).

5. 2. The power conversion device according to claim 1, the first switching elements (31a to 36a) and the second switching element (52) are insulated gate bipolar transistors or insulated gate field effect transistors; an absolute value of a gate-emitter voltage or a gate-source voltage of the second switching element (52) in an on state is greater than an absolute value of a gate-emitter voltage or a gate-source voltage of the first switching elements (31a-36a) in an on state.

6. 2. The power conversion device according to claim 1, a control unit (70) that turns on the second switching element (52) when the voltage of the capacitor (41) exceeds a predetermined first threshold (TH1) during a period in which a current flows from the load (2) to the input side of the inverter circuit (30).

7. 7. The power conversion device according to claim 6, the control unit (70) turns on the second switching element (52) for the first time in a state in which a current flows from the load (2) to the input side of the inverter circuit (30), the current flowing through the second switching element (52) is smaller than the sum of the current flowing from the load (2) to the input side of the inverter circuit (30) and the current flowing from the AC power supply (1) to the output side of the converter circuit (20).

8. 7. The power conversion device according to claim 6, the control unit (70) turns on the second switching element (52) when the voltage of the capacitor (41) exceeds the first threshold (TH1), and turns off the second switching element (52) when the voltage of the capacitor (41) is equal to or lower than a predetermined second threshold (TH2) that is equal to or lower than the first threshold (TH1); When an average loss of the second switching element (52) is Po, a thermal resistance between the second switching element (52) and the package (90) is Rth, a maximum rated junction temperature of the second switching element (52) is Tj, a maximum atmospheric temperature around the package (90) during switching operations of the plurality of first switching elements (31a-36a) is Ta, a time during which the second switching element (52) is continuously turned on and off is t, and a thermal capacity of the package (90) is Cth, A power conversion device characterized in that the following formulas (1) and (2) hold. Po*Rth>Tj-Ta...(1) Tj-Ta>Po*Rth*(1-exp[-t / (Rth*Cth)])...(2)

9. 2. The power conversion device according to claim 1, A reactor (42) is provided between the AC power supply (1) and the capacitor (41). a maximum voltage that can be applied between the input nodes (30a, 30b) of the inverter circuit (30) is Vc1; a peak voltage between the input nodes (30a, 30b) during the switching operation is Vc2; a maximum magnetic energy that can be stored in the load (2) is Em; and a maximum magnetic energy that can be stored in the reactor (42) is Er. This power conversion device is characterized in that the following formula (3) holds: C(Vc1) ２ -Vc2 ２ ) / 2<E+E2・・・(3)

10. 2. The power conversion device according to claim 1, A reactor (42) is provided between the AC power supply (1) and the capacitor (41). The power conversion device is characterized in that the following formula (4) holds when the capacitance of the capacitor (41) is C, the withstand voltage of the capacitor (41) is Vc1, the peak voltage of the capacitor (41) during the switching operation is Vc2, the maximum magnetic energy that can be stored in the load (2) is Em, and the maximum magnetic energy that can be stored in the reactor (42) is Er: C(Vc1) ２ -Vc2 ２ ) / 2<E+E2・・・(4)

11. 2. The power conversion device according to claim 1, The power conversion device is characterized in that the resistor (51) is mounted on a substrate (80).

12. 2. The power conversion device according to claim 1, The power conversion device, wherein the load (2) is a compressor (2).

13. 2. The power conversion device according to claim 1, The power conversion device, wherein the second switching element (52) is an element whose main material is a wide band gap semiconductor.

Images