Electric power conversion device and air conditioner

Abstract

Provided is, inter alia, a highly reliable electric power conversion device. The electric power conversion device (100) comprises: a converter circuit (10); a first capacitor (22); a first inverter circuit (30); a second capacitor (42) that is connected to a high-potential-side DC line (K1) with a diode (41) interposed therebetween, and that is connected to a low-potential-side DC line (K2) by a wire (K4); a second inverter circuit (50) that converts a DC voltage of the second capacitor (42) into an AC voltage; and a control unit (60), wherein the diode (41) allows the flow of an electric current flowing from the high-potential-side DC line (K1) to the second capacitor (42), and cuts off the electric current flow in the direction opposite to said the flow.

Description

Power conversion device and air conditioner

[0001] The present disclosure relates to a power conversion device and an air conditioner.

[0002] For example, Patent Documents 1 and 2 disclose known techniques for power conversion devices equipped with inverter circuits. Patent Document 1 describes a configuration in which a resistive element, a capacitive element, and a diode are connected in series in a first bypass connected in parallel to a capacitor. Patent Document 2 describes a configuration including a reactor that forms a series resonant circuit together with a smoothing capacitor, and a peak-value suppression element that suppresses the peak value of a rectified voltage.

[0003] Patent No. 4760001 Patent No. 3772898

[0004] The techniques described in Patent Documents 1 and 2 provide overvoltage protection so that the DC voltage across the smoothing capacitor does not exceed a predetermined withstand voltage, but there is room for improvement in terms of reliability.

[0005] Therefore, an object of the present disclosure is to provide a highly reliable power conversion device and the like.

[0006] In order to solve the above-mentioned problems, the power conversion device according to the present disclosure includes a converter circuit that converts an AC voltage applied from an AC power supply into a DC voltage, a first capacitor connected to a pair of DC lines on the output side of the converter circuit, a first inverter circuit that converts the DC voltage of the first capacitor into an AC voltage and applies the AC voltage to a first motor, a second capacitor that is connected to the DC line on the higher potential side of the pair of DC lines via a diode and connected to the DC line on the lower potential side via wiring, a second inverter circuit that converts the DC voltage of the second capacitor into an AC voltage and applies the AC voltage to a second motor, and a control unit that controls the first inverter circuit and the second inverter circuit, wherein the diode allows a current to flow from the DC line on the higher potential side toward the second capacitor and blocks a current flow in the opposite direction to the flow.

[0007] According to the present disclosure, a highly reliable power conversion device and the like can be provided.

[0008] FIG. 1 is a configuration diagram of a power conversion device according to a first embodiment. FIG. 2 is a flowchart of processing executed by a control unit of the power conversion device according to the first embodiment. FIG. 3 is a time chart relating to the power conversion device according to the first embodiment. FIG. 4 is a simulation result showing a change in DC voltage when the first inverter circuit is stopped in the first embodiment and a comparative example. FIG. 5 is a simulation result showing the relationship between the output of the second inverter circuit in the power conversion device according to the first embodiment and the maximum value of the DC voltage. FIG. 6 is a configuration diagram of a power conversion device according to a second embodiment. FIG. 7 is a configuration diagram of a power conversion device according to a third embodiment. FIG. 8 is a configuration diagram of a power conversion device according to a fourth embodiment. FIG. 9 is a configuration diagram of a power conversion device according to a fifth embodiment. FIG. 10 is a configuration diagram of a power conversion device according to a sixth embodiment. FIG. 11 is a configuration diagram of an air conditioner according to a seventh embodiment. FIG. 12 is a configuration diagram of a power conversion device according to a comparative example.

[0009] First Embodiment Configuration of Power Conversion Device Fig. 1 is a configuration diagram of a power conversion device 100 according to a first embodiment. The power conversion device 100 shown in Fig. 1 is a device that converts AC power supplied from an AC power source E1 into DC power, and then converts this DC power into predetermined AC power to drive a first motor M1 and a second motor M2. The first motor M1 and the second motor M2 may be, for example, permanent magnet synchronous motors, or may be other types of motors.

[0010] 1 , the power conversion device 100 includes a converter circuit 10, a reactor 21, a first capacitor 22, and a first inverter circuit 30. In addition to the above-described components, the power conversion device 100 also includes a diode 41, a second capacitor 42, a second inverter circuit 50, and a control unit 60.

[0011] The converter circuit 10 is a power converter that converts AC voltage applied from an AC power source E1 into DC voltage (pulsating DC voltage). In the example of Fig. 1, a full-wave rectifier circuit having six diodes D1 to D6 connected in a bridge configuration is used as the converter circuit 10. Note that a switching type converter may be used instead of the converter circuit 10 shown in Fig. 1.

[0012] The output side of the converter circuit 10 is connected to the first inverter circuit 30 via a positive DC line K1 and is also connected to the first inverter circuit 30 via a negative DC line K2. The output side of the converter circuit 10 is connected to the second inverter circuit 50 via (a part of) the positive DC line K1 and a wiring K3 in this order, and is also connected to the second inverter circuit 50 via (a part of) the negative DC line K2 and a wiring K4 in this order. As shown in FIG. 1 , a diode 41 is provided on the wiring K3, and details of the diode 41 will be described later.

[0013] The reactor 21 is an element for smoothing the pulsating DC voltage applied from the converter circuit 10 and suppressing inrush current at startup. As shown in Fig. 1 , the reactor 21 is provided on the positive DC line K1. More specifically, the reactor 21 is provided on the positive DC line K1 between the converter circuit 10 and a connection point between the DC line K1 and the first capacitor 22.

[0014] The first capacitor 22 is an element that smoothes the DC voltage (pulsating DC voltage) on the output side of the converter circuit 10. As shown in Fig. 1, the first capacitor 22 is connected to a pair of DC lines K1 and K2 on the output side of the converter circuit 10. Specifically, the high-potential side (one lead wire) of the first capacitor 22 is connected to the positive DC line K1, and the low-potential side (the other lead wire) is connected to the negative DC line K2. For example, a film capacitor is used as this first capacitor 22.

[0015] Generally, film capacitors are smaller in size (volume) than large-capacity electrolytic capacitors. Therefore, using a film capacitor as the first capacitor 22 allows for the miniaturization of the circuit board (not shown) of the power conversion device 100. Film capacitors also have the advantage of a longer lifespan than electrolytic capacitors. Furthermore, because film capacitors use an insulating plastic film as a dielectric, there is no particular need to use an electrolyte, as in electrolytic capacitors. Therefore, there is little risk of malfunctioning of the film capacitor, even when used in high-temperature environments such as the outdoor unit of an air conditioner in the summer.

[0016] However, if a small-capacity film capacitor is used in consideration of the unit price per capacitance, the voltage of the film capacitor is likely to fluctuate with changes in the amount of stored electricity. For example, if all of the regenerative current from the first motor M1 flows directly into the first capacitor 22 immediately after the first inverter circuit 30 is stopped, the DC voltage of the first capacitor 22 will rise sharply. Therefore, in the first embodiment, a portion of the regenerative current is configured to flow into the second capacitor 42 via the diode 41. This suppresses the rise in the DC voltage of the first capacitor 22. Note that the type of the first capacitor 22 is not limited to a film capacitor, and other types of capacitors, such as an electrolytic capacitor, may also be used.

[0017] The first inverter circuit 30 is a power converter that converts the DC voltage of the first capacitor 22 into a predetermined AC voltage and applies this AC voltage to the first motor M1. The first inverter circuit 30 has a first leg, a second leg, and a third leg, and each of these legs is connected in parallel to the first capacitor 22. The first leg has a pair of switching elements 31, 32 connected in series (the same applies to the remaining second leg and third leg). The switching elements 31 to 36 that are components of the first leg, second leg, and third leg may be, for example, insulated gate bipolar transistors (IGBTs) or metal-oxide-semiconductor field-effect transistors (MOSFETs), but are not limited thereto.

[0018] In the first inverter circuit 30, the connection point between the upper arm switching element 31 and the lower arm switching element 32 of the first leg is connected to a U-phase winding (not shown) of the first motor M1 via a wire. Similarly, the connection point between the upper arm switching element 33 and the lower arm switching element 34 of the second leg is connected to a V-phase winding (not shown) of the first motor M1 via a wire. The connection point between the upper arm switching element 35 and the lower arm switching element 36 of the third leg is connected to a W-phase winding (not shown) of the first motor M1 via a wire.

[0019] Furthermore, in order to prevent destruction of the switching elements 31 to 36 due to commutation, a free wheel diode (reference numeral not shown) is connected in anti-parallel to each of the switching elements 31 to 36. If the switching elements 31 to 36 have a parasitic diode, this parasitic diode functions as the free wheel diode, and therefore there is no particular need to provide a separate free wheel diode.

[0020] The second capacitor 42 is a capacitor for absorbing a portion of the regenerative energy of the first motor M1 immediately after the switching operation of the first inverter circuit 30 is stopped. The second capacitor 42 also functions to absorb inrush current when the power is turned on, as well as surge current when power is restored after a momentary or power outage. For example, an electrolytic capacitor with a larger capacitance than the first capacitor 22 is used as this second capacitor 42. This makes it possible to sufficiently suppress an increase in the DC voltage of the second capacitor 42 when absorbing a portion of the regenerative energy of the first motor M1.

[0021] 1, the second capacitor 42 is connected to the high-potential DC line K1 of the pair of DC lines K1, K2 via a diode 41, and is connected to the low-potential DC line K2 via a wiring K4. More specifically, the positive electrode of the second capacitor 42 is connected to the high-potential DC line K1 via the diode 41. The negative electrode of the second capacitor 42 is connected to the low-potential DC line K2 via the wiring K4.

[0022] The diode 41 is an element that allows current to flow from the high-potential side DC line K1 toward the second capacitor 42 and blocks current flow in the opposite direction to the flow of the high-potential side DC line K1, and is provided on the wiring K3. The wiring K3 is a wiring that connects the high-potential side DC line K1 and the input side of the second inverter circuit 50.

[0023] 1, the anode of the diode 41 is connected to the high-potential DC line K1 via a portion of the wiring K3. The cathode of the diode 41 is connected to the positive electrode of the second capacitor 42 via a portion of the wiring K3. The diode 41 and the second capacitor 42 are connected in series. The diode 41 and the second capacitor 42 constitute an overvoltage protection circuit.

[0024] The second inverter circuit 50 is a power converter that converts the DC voltage of the second capacitor 42 into a predetermined AC voltage and applies this AC voltage to the second motor M2. The input side of the second inverter circuit 50 is connected to both ends of the second capacitor 42. As shown in FIG. 1 , the second inverter circuit 50 includes switching elements 51 to 56. The configuration of the second inverter circuit 50 is similar to that of the first inverter circuit 30, and therefore a description thereof will be omitted.

[0025] The switching elements 31 to 36 of the first inverter circuit 30 may have a larger current capacity or output capacity than the switching elements 51 to 56 of the second inverter circuit 50. For example, when the circuit board of the power conversion device 100 is installed in the outdoor unit of an air conditioner, the first motor M1 may be the drive source for the compressor, and the second motor M2 may be the drive source for the outdoor fan.

[0026] The control unit 60 has a function of controlling the first inverter circuit 30 and the second inverter circuit 50. The control unit 60 is configured to include, for example, an MCU (Micro Controller Unit: not shown) and a gate drive circuit (not shown). Regarding the control of the first inverter circuit 30, the MCU (i.e., the control unit 60) calculates a three-phase voltage command for driving the first motor M1 based on, for example, a detected value of the bus current flowing through the DC line K2, and generates a predetermined PWM signal (Pulse Width Modulation signal) based on the three-phase voltage command.

[0027] Furthermore, the gate drive circuit (i.e., the control unit 60) switches the switching elements 31 to 36 on and off in a predetermined manner based on the PWM signal generated by the MCU. This converts the DC voltage of the first capacitor 22 into a three-phase AC voltage, which is applied to the U-phase, V-phase, and W-phase windings of the first motor M1. The rotor of the first motor M1 then rotates in a predetermined manner due to magnetic attraction and repulsion. The same process is also carried out when the control unit 60 controls the second inverter circuit 50 in a predetermined manner to drive the second motor M2.

[0028] <Regarding DC voltage suppression> For example, immediately after the first inverter circuit 30 is stopped, the rotor of the first motor M1 rotates for a while due to inertia (coast), causing the first motor M1 to function as a generator. If the induced voltage of the first motor M1 becomes higher than the DC voltage of the first capacitor 22, a regenerative current is generated due to the potential difference, and the regenerative current flows from the first motor M1 through the first inverter circuit 30 to the first capacitor 22, etc.

[0029] In the first embodiment, the diode 41 and the second capacitor 42 are provided to promote absorption of the regenerative current. For example, when the induced voltage of the first motor M1 is higher than the DC voltages of the first capacitor 22 and the second capacitor 42, part of the regenerative current flows into the first capacitor 22 via the DC line K1, and the remainder of the regenerative current flows into the second capacitor 42 via the diode 41. As a result, the regenerative current is absorbed by the first capacitor 22, and also by the second capacitor 42.

[0030] Furthermore, in the first embodiment, the control unit 60 continues to drive the second inverter circuit 50 when the first inverter circuit 30 is stopped. This consumes the charge in the second capacitor 42 (i.e., the second capacitor 42 has a surplus of stored electricity), so that the second capacitor 42 can sufficiently absorb part of the regenerative current that flows from the first motor M1 immediately after the first inverter circuit 30 is stopped.

[0031] <Processing of the Control Unit> Figure 2 is a flowchart of the processing executed by the control unit (also see Figure 1 as appropriate). Note that at "START" in Figure 2, both the first inverter circuit 30 and the second inverter circuit 50 are operating. In step S101, the control unit 60 determines whether a stop command has been input for the device including the first motor M1 and the second motor M2. For example, if the device is an air conditioner, a predetermined stop command is input to the control unit 60 when the stop button on a remote control (not shown) is pressed.

[0032] If there is no stop command in step S101 (S101: No), the control unit 60 repeats the process of step S101 while continuing to drive the first inverter circuit 30 and the second inverter circuit 50. On the other hand, if there is a stop command in step S101 (S101: Yes), the process of the control unit 60 proceeds to step S102.

[0033] In step S102, the control unit 60 stops the first inverter circuit 30. That is, the control unit 60 stops the switching operation of the first inverter circuit 30 while allowing the second inverter circuit 50 to continue the switching operation.

[0034] In step S103, the control unit 60 determines whether a predetermined time has elapsed since the first inverter circuit 30 was stopped. This predetermined time is the time for which the second inverter circuit 50 continues to be driven after the first inverter circuit 30 was stopped, and is set in advance. If the predetermined time has not elapsed since the first inverter circuit 30 was stopped in step S103 (S103: No), the control unit 60 repeats the process of step S103. If the predetermined time has elapsed since the first inverter circuit 30 was stopped in step S103 (S103: Yes), the process of the control unit 60 proceeds to step S104.

[0035] In step S104, the control unit 60 stops the second inverter circuit 50. After performing the process of step S104, the control unit 60 ends the series of processes (END).

[0036] <Operation of Power Conversion Device and Current Flow> Figure 3 is a time chart related to the power conversion device (see also Figure 1 as appropriate). The horizontal axis of each time chart in Figure 3 represents time. The vertical axis of each time chart in Figure 3 represents, from top to bottom, the rotational speed of the first motor M1, the induced voltage of the first motor M1, the DC voltage of the first capacitor 22, the current flowing through the diode 41, the operation of the first inverter circuit 30, and the operation of the second inverter circuit 50. The DC voltage of the second capacitor 42 (omitted from Figure 3) is slightly lower than the DC voltage of the first capacitor 22 due to the voltage drop at the diode 41, but the manner of change is similar to that of the DC voltage of the first capacitor 22.

[0037] In the example of Fig. 3, a stop command is input immediately before time t1 (S101: Yes in Fig. 2), and the first inverter circuit 30 is stopped at time t1 (S102 in Fig. 2). After the first inverter circuit 30 is stopped, the rotation speed of the first motor M1 decreases and becomes substantially zero at time t3. Similarly, the induced voltage of the first motor M1 also decreases from time t1 and becomes substantially zero at time t3.

[0038] At time t1 when the first inverter circuit 30 is stopped, a regenerative current is generated in the first motor M1 because the induced voltage value V1 of the first motor M1 is higher than the DC voltage value V2 of the first capacitor 22. This regenerative current flows into the first capacitor 22 via the DC line K1 and into the second capacitor 42 via the diode 41.

[0039] 3, the DC voltage of the first capacitor 22 increases between time t1 and time t2 due to the regenerative current from the first motor M1. Also, a current (regenerative current) flows through the diode 41 between time t1 and time t2. This regenerative current flows until time t2, when the DC voltage of the first capacitor 22 becomes substantially equal to the induced voltage of the first motor M1.

[0040] Furthermore, because the regenerative current flowing through the diode 41 flows into the second capacitor 42, the DC voltage of the second capacitor 42 also rises, similar to the first capacitor 22, although this is not shown in the figure. As shown in Figure 3, the second inverter circuit 50 continues to operate for a predetermined time (the time between times t1 and t4) even after the first inverter circuit 30 has stopped. This consumes the charge in the second capacitor 42, allowing the second capacitor 42 to store more charge, thereby facilitating the absorption of the regenerative current.

[0041] In the example of FIG. 3 , the second inverter circuit 50 is stopped at time t4, a predetermined time after time t1, when the first inverter circuit 30 is stopped (S103: Yes, S104 in FIG. 2 ). Although some regenerative current is generated in the second motor M2 immediately after the second inverter circuit 50 is stopped, the flow of this regenerative current toward the DC line K1 is blocked by the diode 41. Therefore, the regenerative current from the second motor M2 rarely flows into the first capacitor 22. In other words, the DC voltage of the first capacitor 22 rarely rises immediately after the second inverter circuit 50 is stopped. The regenerative current from the second motor M2 is absorbed by the second capacitor 42.

[0042] <Simulation Results> Figure 4 shows simulation results showing changes in DC voltage when the first inverter circuit is stopped in the first embodiment and the comparative example (see also Figure 1 as appropriate). Note that the horizontal axis of Figure 4 represents time, and the vertical axis represents the DC voltage of the first capacitor 22. The solid line graph in Figure 4 represents changes in DC voltage of the first capacitor 22 in the power conversion device 100 of the first embodiment. Furthermore, the dashed line graph in Figure 4 represents changes in DC voltage of the first capacitor 22 in the power conversion device 100Z (see Figure 12) of the comparative example. Here, the configuration of the comparative example will be briefly described using Figure 12.

[0043] Fig. 12 is a configuration diagram of a power conversion device 100Z according to a comparative example. The power conversion device 100Z of the comparative example shown in Fig. 12 includes a series connection of a diode 101 and a second capacitor 102 as an overvoltage protection circuit. This series connection is connected in parallel to the first capacitor 22. The capacitance of the first capacitor 22 is 90 [μF], and the capacitance of the second capacitor 102 is 390 [μF]. A load resistor 103 consuming power equivalent to 10 [W] is connected in parallel to the second capacitor 102.

[0044] 4, the capacitance of the first capacitor 22 (see FIG. 1) is 90 μF, and the capacitance of the second capacitor 42 (see FIG. 1) is 390 μF. In addition, to simulate the second inverter circuit 50 consuming power equivalent to 340 W, a load resistor (not shown) consuming power equivalent to 340 W is connected in parallel to the second capacitor 42 (see FIG. 1).

[0045] That is, when performing a simulation using the configuration of the first embodiment, a predetermined load resistor is used instead of the second inverter circuit 50 (see FIG. 1 ). The reason why the power consumption (340 W) of the load resistor (not shown) in the first embodiment is set to be larger than the power consumption (10 W) of the load resistor in the comparative example is to simulate the second inverter circuit 50 continuing to operate when the first inverter circuit 30 is stopped in the first embodiment (i.e., large power consumption). Note that motor constants such as the induced voltage constant and the inductance of each motor are set to approximately the same values ​​in the first embodiment and the comparative example.

[0046] Returning to Fig. 4 , the explanation will be continued. In the first inverter circuit 30 of each of the first embodiment and the comparative example, when drive (switching operation) is stopped at time t1, the DC voltage of the first capacitor 22 immediately rises due to the regenerative current of the first motor M1. Then, in both the first embodiment and the comparative example, after the DC voltage of the first capacitor 22 reaches a maximum value (peak value) at time t2, the change in its value changes from rising to falling.

[0047] 4, the maximum value of the DC voltage at time t2 is lower in the first embodiment than in the comparative example. This is because power is consumed by a load resistor (not shown) equivalent to 340 W, reducing the amount of charge in the second capacitor 42, which allows the second capacitor 42 to absorb regenerative energy. Note that in the simulation, a load resistor (not shown) with high power consumption is connected in parallel to the second capacitor 42. However, the same effect can be achieved even if the second inverter circuit 50 continues to operate when the first inverter circuit 30 is stopped.

[0048] 5 shows the results of a simulation showing the relationship between the output of the second inverter circuit 50 and the maximum value of the DC voltage in the power conversion device according to the first embodiment (see also FIG. 1 as appropriate). The horizontal axis of FIG. 5 represents the output of the second inverter circuit 50, and the vertical axis represents the maximum value of the DC voltage of the first capacitor 22. Here, the "maximum value of the DC voltage" refers to the peak value when the DC voltage of the first capacitor 22 changes from increasing to decreasing immediately after the first inverter circuit 30 is stopped.

[0049] The solid line graph in Figure 5 shows the case where the capacitance of the second capacitor 42 is 200 [μF]. The dashed line graph shows the case where the capacitance of the second capacitor 42 is 400 [μF]. The dashed-dotted line graph shows the case where the capacitance of the second capacitor 42 is 600 [μF]. Note that in all of the solid, dashed, and dashed-dotted line graphs, the capacitance of the first capacitor 22 is 90 [μF]. Also, it is assumed that the motor constants and operating conditions are approximately the same in each graph.

[0050] As shown in Fig. 5, the higher the output of the second inverter circuit 50, the lower the maximum value of the DC voltage of the first capacitor 22. This is because the higher the output of the second inverter circuit 50, the more charge is consumed by the second capacitor 42, creating a surplus in the second capacitor 42 for absorbing regenerative energy. Also, as shown in Fig. 5, the larger the capacitance of the second capacitor 42, the lower the maximum value of the DC voltage. This is because the larger the capacitance of the second capacitor 42, the more regenerative energy is absorbed by the second capacitor 42.

[0051] For example, in the comparative example described above, let us assume that the capacitance of second capacitor 102 (see FIG. 12) is set to 600 μF and that load resistor 103 (see FIG. 12) consumes power equivalent to 10 W. In this case, using the data in FIG. 5 , it can be seen that the maximum DC voltage of first capacitor 22 in the comparative example is approximately 377 V, based on the value at an output of 10 W in the dashed-dotted line graph.

[0052] On the other hand, in the configuration of the first embodiment, even if the capacitance of the second capacitor 42 (see FIG. 1) is set to 200 μF, which is one-third of the aforementioned 600 μF, if the output of the second inverter circuit 50 (see FIG. 1) is set to 1000 W, the maximum DC voltage of the first capacitor 22 (see FIG. 1) will be approximately 375 V. In other words, in the first embodiment, even if the capacitance of the second capacitor 42 is set to one-third of that of the comparative example, the maximum DC voltage can be set to a value equivalent to that of the comparative example by driving the second inverter circuit 50 (see FIG. 1) in a predetermined manner. In short, in the first embodiment, even if the capacitance of the second capacitor 42 is set to a relatively small value, the increase in the DC voltage of the first capacitor 22 can be appropriately suppressed.

[0053] <Effects> According to the first embodiment, the regenerative current immediately after the first inverter circuit 30 is stopped flows to the first capacitor 22, and also flows to the second capacitor 42 via the diode 41. This makes it possible to suppress an increase in DC voltage due to the regenerative current even when the capacitance of the first capacitor 22 is reduced. As a result, malfunctions in the circuit elements can be prevented, thereby improving the reliability of the power conversion device 100.

[0054] Furthermore, the control unit 60 continues to drive the second inverter circuit 50 when the first inverter circuit 30 is stopped. As a result, charge continues to be consumed in the second capacitor 42 even immediately after the first inverter circuit 30 is stopped, so that regenerative energy can be sufficiently absorbed even if the capacitance of the second capacitor 42 is relatively small.

[0055] Furthermore, because the diode 41 has a rectifying function, discharge from the second capacitor 42 to the DC line K1 is not particularly performed. In other words, the second capacitor 42 hardly ever experiences ripples in the DC voltage due to repeated alternating charging and discharging. Therefore, it is possible to use an inexpensive capacitor with a small ripple tolerance and a small capacitance as the second capacitor 42. In this way, since the capacitance of the second capacitor 42 can be reduced in addition to that of the first capacitor 22, the power conversion device 100 can be made smaller and less expensive.

[0056] Furthermore, according to the first embodiment, by appropriately adjusting the output value of the second inverter circuit 50 when the first inverter circuit 30 is stopped at the design stage, it is possible to adjust the amount of regenerative energy that can be absorbed by the second capacitor 42. Therefore, for example, when using the specifications of an off-the-shelf power conversion device (not shown) as the power conversion device 100, there is no particular need to finely adjust motor constants such as the induced voltage constant or the motor inductance, or to change the capacitance of the first capacitor 22, etc., and it is only necessary to adjust the output value of the second inverter circuit 50, which makes the circuit design work easier.

[0057] Furthermore, by appropriately setting the output of the second inverter circuit 50 when the first inverter circuit 30 is stopped, it is possible to suppress an increase in DC voltage caused by errors in the motor constants, etc., thereby ensuring sufficient reliability.

[0058] Second Embodiment The second embodiment differs from the first embodiment in that the input side of a switching power supply circuit 71 (see FIG. 6) is connected to both ends of a second capacitor 42 (see FIG. 6). The other configurations are the same as those of the first embodiment. Therefore, only the differences from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0059] Fig. 6 is a configuration diagram of a power conversion device 100A according to the second embodiment. As shown in Fig. 6, the power conversion device 100A includes a switching power supply circuit 71. The switching power supply circuit 71 is a power supply circuit for applying a predetermined voltage to the gates of the switching elements of the first inverter circuit 30 and the second inverter circuit 50. As shown in Fig. 6, the switching power supply circuit 71 is connected to both ends of the second capacitor 42. The DC voltage of the second capacitor 42 is applied to the input side of the switching power supply circuit 71.

[0060] For example, when the capacitance of the second capacitor 42 is larger than the capacitance of the first capacitor 22, the DC voltage fluctuation is smaller in the second capacitor 42. Therefore, as shown in Fig. 6, connecting the switching power supply circuit 71 to the second capacitor 42 allows a more stable supply of DC voltage to the switching power supply circuit 71 than connecting it to the first capacitor 22.

[0061] Furthermore, after the first inverter circuit 30 and the second inverter circuit 50 are successively stopped, the charge stored in the second capacitor 42 is quickly consumed as thermal energy by a passive element (such as a resistor element, not shown) of the switching power supply circuit 71. Therefore, the next startup of the power conversion device 100A can be performed without any charge stored in the second capacitor 42, thereby stabilizing operation.

[0062] <Effects> According to the second embodiment, a DC voltage can be stably supplied from the second capacitor 42 having a large capacitance to the switching power supply circuit 71. Furthermore, after the first inverter circuit 30 and the second inverter circuit 50 are successively stopped, the charge in the second capacitor 42 can be quickly consumed as heat energy in the switching power supply circuit 71.

[0063] Third Embodiment The third embodiment differs from the first embodiment in that a discharge resistor 72 (see FIG. 7) is connected in parallel to the second capacitor 42 (see FIG. 7). The other configurations are the same as those of the first embodiment. Therefore, only the differences from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0064] Fig. 7 is a configuration diagram of a power conversion device 100B according to the third embodiment. As shown in Fig. 7, the power conversion device 100B includes a discharge resistor 72. The discharge resistor 72 is a resistive element for consuming the charge stored in the second capacitor 42 as thermal energy after the first inverter circuit 30 and the second inverter circuit 50 are successively stopped. As shown in Fig. 7, the discharge resistor 72 is connected in parallel to the second capacitor 42. One end of the discharge resistor 72 (i.e., the wiring K4) is assumed to be grounded.

[0065] <Effects> According to the third embodiment, after the first inverter circuit 30 and the second inverter circuit 50 are successively stopped, the charge in the second capacitor 42 is quickly consumed as thermal energy by the discharge resistor 72. Therefore, the next startup of the power conversion device 100B can be performed in a state where no charge is stored in the second capacitor 42.

[0066] Fourth Embodiment The fourth embodiment differs from the first embodiment in that a limiting resistor 73 (see FIG. 8) is connected in series with a diode 41 (see FIG. 8) and a second capacitor 42 (see FIG. 8). The other configurations are the same as those of the first embodiment. Therefore, only the parts that are different from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0067] Fig. 8 is a configuration diagram of a power conversion device 100C according to the fourth embodiment. As shown in Fig. 8, the power conversion device 100C includes a limiting resistor 73. The limiting resistor 73 is a resistive element for suppressing an inrush current when the power is turned on and a regenerative current immediately after the first inverter circuit 30 is stopped. As shown in Fig. 8, the limiting resistor 73 is provided on the wiring K3 and connected in series to the diode 41.

[0068] 8, a limiting resistor 73 is provided on the wiring K3 between the connection point between the DC line K1 and the wiring K3 and the anode of the diode 41. The limiting resistor 73 may be provided on the cathode side of the diode 41.

[0069] <Effects> According to the fourth embodiment, by connecting the limiting resistor 73 in series with the diode 41, it is possible to suppress the surge current when the power is turned on and the regenerative current immediately after the first inverter circuit 30 is stopped. This suppresses damage to electronic components due to overcurrent, thereby improving reliability.

[0070] Fifth Embodiment The fifth embodiment differs from the first embodiment in that a third inverter circuit 80 (see FIG. 9) is connected in parallel to the input side of a second inverter circuit 50 (see FIG. 9). The other configurations are the same as those of the first embodiment. Therefore, only the parts that are different from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0071] Fig. 9 is a configuration diagram of a power conversion device 100D according to a fifth embodiment. As shown in Fig. 9, the power conversion device 100D includes a third inverter circuit 80 (another inverter circuit). The third inverter circuit 80 is a power converter that converts the DC voltage of the second capacitor 42 into a predetermined AC voltage and applies this AC voltage to the third motor M3. As shown in Fig. 9, the input side of the third inverter circuit 80 (another inverter circuit) is connected to both ends of the second capacitor 42.

[0072] Furthermore, the input side of the third inverter circuit 80 is connected in parallel to the input side of the second inverter circuit 50. That is, of the pair of wirings K5 and K6 on the input side of the third inverter circuit 80, the positive side wiring K5 is connected to the wiring K3 on the input side of the second inverter circuit 50. Similarly, the negative side wiring K6 is connected to the wiring K4 on the input side of the second inverter circuit 50. Incidentally, there is no particular need to separately provide a diode on the wiring K5. This is because the flow of current toward the DC line K1 via the wiring K5 and (part of) the wiring K3 in this order is blocked by the diode 41, even without providing a diode on this wiring K5.

[0073] As shown in FIG. 9 , the third inverter circuit 80 includes switching elements 81 to 86. The configuration of the third inverter circuit 80 is similar to that of the first inverter circuit 30 and the second inverter circuit 50, and therefore a description thereof will be omitted. For example, when the circuit board of the power conversion device 100D is installed in the outdoor unit of an air conditioner, the first motor M1 may be the drive source for the compressor, the second motor M2 may be the drive source for the first outdoor fan, and the third motor M3 may be the drive source for the second outdoor fan. For example, the outdoor unit of a multi-air conditioner for a building may be equipped with multiple outdoor fans.

[0074] The control unit 60 continues to drive the second inverter circuit 50 and the third inverter circuit 80 when the first inverter circuit 30 is stopped. As a result, the charge of the second capacitor 42 continues to be consumed in accordance with the outputs of the second inverter circuit 50 and the third inverter circuit 80, which increases the margin for absorbing the regenerative energy of the first motor M1 in the second capacitor 42.

[0075] The control unit 60 then stops the second inverter circuit 50 after a first predetermined time has elapsed since the first inverter circuit 30 was stopped. The control unit 60 also stops the third inverter circuit 80 after a second predetermined time has elapsed since the first inverter circuit 30 was stopped. The first predetermined time and the second predetermined time may be set so that one is longer than the other, or may be substantially the same length. The regenerative energy of the second motor M2 and the third motor M3 is absorbed by the second capacitor 42.

[0076] The number of "another inverter circuits" whose input sides are connected across the second capacitor 42 is not limited to one (i.e., the third inverter circuit 80 in FIG. 9 ) and may be multiple. In this case, the control unit 60 continues to drive the second inverter circuit 50 while the first inverter circuit 30 is stopped, and also continues to drive at least one of the one or more "another inverter circuits." This causes the charge in the second capacitor 42 to continue to be consumed by the second inverter circuit 50 and the "another inverter circuits," thereby accelerating the absorption of regenerative energy by the second capacitor 42.

[0077] <Effects> According to the fifth embodiment, the input side of the third inverter circuit 80 is connected to both ends of the second capacitor 42, and the second inverter circuit 50 and the third inverter circuit 80 continue to be driven when the first inverter circuit 30 is stopped. This increases the amount of regenerative energy that can be absorbed by the second capacitor 42 compared to the first embodiment, thereby improving the reliability of the power conversion device 100D.

[0078] Sixth Embodiment The sixth embodiment differs from the first embodiment in that a DC voltage detection unit 74 (see FIG. 10), a comparator 75 (see FIG. 10), and a protection circuit 76 (see FIG. 10) are provided. Note that the other configurations are the same as those of the first embodiment. Therefore, only the parts that are different from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0079] Fig. 10 is a configuration diagram of a power conversion device 100E according to the sixth embodiment. As shown in Fig. 10, the power conversion device 100E includes a DC voltage detection unit 74, a comparator 75, and a protection circuit 76. The DC voltage detection unit 74 detects the DC voltage across the first capacitor 22. The detected value of the DC voltage detection unit 74 is output to the comparator 75.

[0080] The comparator 75 has a function of comparing the DC voltage of the first capacitor 22 with a predetermined value. When the DC voltage of the first capacitor 22 reaches or exceeds the predetermined value, the comparator 75 switches on the switching element 76a of the protection circuit 76. The predetermined value is a threshold value that serves as a criterion for determining whether to switch on the switching element 76a, and is a voltage value that is set in advance depending on the purpose, etc.

[0081] It is preferable that the comparator 75 be configured as an analog electronic circuit. Here, an "analog electronic circuit" is a circuit in which the processing of signals (voltage and current) is continuous (analog). The analog electronic circuit does not particularly include microcomputers that process signals digitally. An analog electronic circuit is configured with elements such as resistors, capacitors, coils, and transistors.

[0082] By using an analog electronic circuit for the comparator 75, even if the microcomputer (not shown) of the control unit 60 is reset due to the influence of noise or the like and is unable to perform normal operation, the comparator 75 can switch the switching element 76a to the on state. This allows the charge stored in the second capacitor 42 to be consumed as heat energy by the resistance element 76b.

[0083] The protection circuit 76 is a circuit for protecting circuit elements from overvoltage in the event of an abnormality, and is configured to include a series connection of a switching element 76 a and a resistance element 76 b. This series connection is connected in parallel to the second capacitor 42.

[0084] The switching element 76a is an element that switches between flowing and blocking of current through the resistance element 76b. For example, an IGBT or a MOSFET is used as the switching element 76a. The resistance element 76b is an element that converts the electrical energy of the current flowing through the switching element 76a into thermal energy.

[0085] For example, if an abnormality such as a power outage or a reset of the microcomputer (hardware of the control unit 60) occurs, the operation of the first inverter circuit 30 and the second inverter circuit 50 stops. If the DC voltage of the first capacitor 22 exceeds a predetermined value due to regenerative energy generated during the abnormality, the comparator 75 switches the switching element 76a to the ON state. As a result, the charge stored in the second capacitor 42 flows through the switching element 76a to the resistor element 76b, where it is consumed as heat energy. This suppresses the rise in the DC voltage of the second capacitor 42, preventing malfunctions of the circuit elements.

[0086] <Effects> According to the sixth embodiment, even if the first inverter circuit 30 or the second inverter circuit 50 stops due to an abnormality, the charge in the second capacitor 42 can be consumed as heat energy by the resistance element 76 b, thereby preventing malfunctions in the circuit elements.

[0087] Seventh Embodiment In the seventh embodiment, an air conditioner W1 (see FIG. 11) including the power conversion device 100 (see FIG. 1) configured as described in the first embodiment will be described. Note that the configuration and processing content of the power conversion device 100 are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0088] FIG. 11 is a configuration diagram of an air conditioner W1 according to a seventh embodiment. The solid arrows in FIG. 11 indicate the flow of refrigerant in the heating cycle. The dashed arrows in FIG. 11 indicate the flow of refrigerant in the cooling cycle. The air conditioner W1 is a device that performs air conditioning, such as cooling and heating. The air conditioner W1 includes, as components provided in the outdoor unit U1, a compressor 91, an outdoor heat exchanger 92, an outdoor fan 93, an expansion valve 94, and a four-way valve 95. The air conditioner W1 also includes, as components provided in the indoor unit U2, an indoor heat exchanger 96 and an indoor fan 97.

[0089] The air conditioner W1 also includes a power conversion device 100 having the same configuration as that of the first embodiment. The power conversion device 100 is mounted on a circuit board (not shown) of the outdoor unit U1.

[0090] The compressor 91 is a device that compresses a low-temperature, low-pressure gas refrigerant and discharges it as a high-temperature, high-pressure gas refrigerant. Although not shown in Fig. 11 , an accumulator for separating the refrigerant into gas and liquid is connected to the suction side of the compressor 91. A first motor M1, which is a drive source of the compressor 91, is connected to the output side of the first inverter circuit 30 (see Fig. 1 ) of the power conversion device 100.

[0091] The outdoor heat exchanger 92 is a heat exchanger in which heat is exchanged between the refrigerant flowing through its heat transfer tubes and the outside air sent in from the outdoor fan 93. The outdoor fan 93 is a fan that sends outside air to the outdoor heat exchanger 92, and is installed near the outdoor heat exchanger 92. A second motor M2 that is a drive source for the outdoor fan 93 is connected to the output side of the second inverter circuit 50 (see FIG. 1 ) of the power conversion device 100.

[0092] The expansion valve 94 is a valve that reduces the pressure of the refrigerant condensed in the "condenser" (one of the outdoor heat exchanger 92 and the indoor heat exchanger 96). The refrigerant reduced in pressure by the expansion valve 94 is guided to the "evaporator" (the other of the outdoor heat exchanger 92 and the indoor heat exchanger 96). The indoor heat exchanger 96 is a heat exchanger that exchanges heat between the refrigerant flowing through its heat transfer tube (not shown) and indoor air (air in the air-conditioned room) sent in by an indoor fan 97. The indoor fan 97 is a fan that sends indoor air to the indoor heat exchanger 96. The indoor fan 97 has an indoor fan motor 97a that serves as a drive source, and is installed near the indoor heat exchanger 96.

[0093] The four-way valve 95 switches the refrigerant flow path depending on the operating mode of the air conditioner W1. For example, in the cooling cycle (see the dashed arrow in FIG. 11 ), the refrigerant circulates sequentially through the compressor 91, the outdoor heat exchanger 92 (condenser), the expansion valve 94, and the indoor heat exchanger 96 (evaporator). In the heating cycle (see the solid arrow in FIG. 11 ), the refrigerant circulates sequentially through the compressor 91, the indoor heat exchanger 96 (condenser), the expansion valve 94, and the outdoor heat exchanger 92 (evaporator). Air that has exchanged heat with the refrigerant flowing through the indoor heat exchanger 96 is then blown out of the indoor unit U2 into the air-conditioned room.

[0094] <Effects> According to the seventh embodiment, the air conditioner W1 is provided with the power conversion device 100 having the same configuration as that of the first embodiment, and therefore the reliability of the air conditioner W1 can be improved.

[0095] <<Modifications>> The power conversion device 100 and the air conditioner W1 according to the present disclosure have been described above in various embodiments. However, they are not limited to these descriptions and various modifications can be made. For example, in the various embodiments, the control unit 60 (see FIG. 1 ) continues to drive the second inverter circuit 50 while the first inverter circuit 30 is stopped. However, this is not limiting. That is, the control unit 60 may stop the second inverter circuit 50 when the first inverter circuit 30 is stopped. Specifically, the first inverter circuit 30 and the second inverter circuit 50 may be stopped substantially simultaneously, or the first inverter circuit 30 may be stopped after the second inverter circuit 50 is stopped. Even in this case, the first capacitor 22 and the second capacitor 42 are connected in parallel via the diode 41, resulting in a larger combined capacitance (combined capacitance value) than when the first capacitor 22 is used alone. Therefore, the increase in the DC voltage of the first capacitor 22 is suppressed, thereby ensuring the reliability of the power conversion device 100.

[0096] In addition, although the embodiments have been described with reference to the case where one diode 41 is provided on the wiring K3 (see FIG. 1 ), this is not limiting. In other words, any other circuit configuration may be used as long as it allows current to flow from the high-potential DC line K1 toward the second capacitor 42 and blocks current flow in the opposite direction to the allowed current flow.

[0097] In addition, in each embodiment, the case where the second capacitor 42 (see FIG. 1) has a larger capacitance than the first capacitor 22 (see FIG. 1) has been described, but this is not limiting. For example, the second capacitor 42 may have a smaller capacitance than the first capacitor 22, or the capacitances of the first capacitor 22 and the second capacitor 42 may be substantially equal.

[0098] In addition, in each embodiment, a film capacitor is used as the first capacitor 22 (see FIG. 1 ) and an electrolytic capacitor is used as the second capacitor 42 (see FIG. 1 ). However, this is not limiting. For example, the first capacitor 22 and the second capacitor 42 may each be a film capacitor. Alternatively, the first capacitor 22 and the second capacitor 42 may each be an electrolytic capacitor. Alternatively, other predetermined types of capacitors may be used as appropriate.

[0099] Furthermore, in the fifth embodiment, the case where both the second inverter circuit 50 and the third inverter circuit 80 continue to be driven when the first inverter circuit 30 (see FIG. 9 ) is stopped has been described, but this is not limiting. For example, when the first inverter circuit 30 is stopped, one of the second inverter circuit 50 and the third inverter circuit 80 may be driven, while the other may be maintained in a stopped state. Furthermore, in a configuration in which multiple "other inverter circuits" (such as the third inverter circuit 80 in FIG. 9 ) are connected to both ends of the second capacitor 42, each of the multiple "other inverter circuits" may continue to be driven when the first inverter circuit 30 is stopped. Furthermore, when the first inverter circuit 30 is stopped, all of the multiple "other inverter circuits" may be maintained in a stopped state.

[0100] In the sixth embodiment, the comparator 75 (see FIG. 10) is an analog electronic circuit, but the present invention is not limited to this. That is, the comparator 75 may include a digital electronic circuit such as a microcomputer (e.g., MCU).

[0101] Although each embodiment has been described with reference to a case where three-phase AC power is supplied from the AC power supply E1 (see FIG. 1 ), the present invention is not limited to this. For example, each embodiment can also be applied to a case where single-phase AC power is supplied from the AC power supply.

[0102] Although each of the embodiments has been described with reference to a case where one first capacitor 22 (see FIG. 1 ) and one second capacitor 42 (see FIG. 1 ) are provided, this is not a limitation. That is, the first capacitor and the second capacitor may be formed by a plurality of capacitors connected in series, parallel, or series-parallel. Furthermore, each of the embodiments has been described with reference to a process (S104) in which the control unit 60 stops the second inverter circuit 50 after a predetermined time has elapsed since the first inverter circuit 30 was stopped (S102, S103: Yes in FIG. 2 ). However, this is not a limitation. That is, the control unit 60 may stop the second inverter circuit 50 based on a predetermined condition other than the elapsed time since the first inverter circuit 30 was stopped. For example, after the first inverter circuit 30 is stopped, the control unit 60 may stop the second inverter circuit 50 when the load on the compressor 91 (the load torque of the first motor M1) becomes equal to or less than a predetermined value. Furthermore, for example, after the first inverter circuit 30 has been stopped, when the differential pressure between the suction side and the discharge side of the compressor 91 becomes equal to or less than a predetermined value, the control unit 60 may stop the second inverter circuit 50. In addition, the conditions for stopping the second inverter circuit 50 may be changed as appropriate.

[0103] Furthermore, the respective embodiments can be combined as appropriate. For example, the second embodiment (see FIG. 6) and the third embodiment (see FIG. 7) may be combined, connecting the switching power supply circuit 71 across the second capacitor 42 (second embodiment) and connecting the discharge resistor 72 in parallel (third embodiment). Furthermore, any of the first to sixth embodiments may be combined with the seventh embodiment (see FIG. 11), using the first motor M1 as the drive source for the compressor 91 and the second motor M2 as the drive source for the outdoor fan 93. Various other combinations of the first to seventh embodiments are also possible.

[0104] Furthermore, in the seventh embodiment (see FIG. 11 ), a configuration in which the air conditioner W1 includes a four-way valve 95 has been described, but this is not limiting. That is, the four-way valve 95 may be omitted as appropriate to configure an air conditioner dedicated to cooling or heating. Furthermore, the seventh embodiment (see FIG. 11 ) can be applied to various types of air conditioners, such as commercial air conditioners and multi-air conditioners for buildings, in addition to room air conditioners. Furthermore, the seventh embodiment can be applied to other devices (refrigeration cycle devices) such as water heaters, air-conditioning water heaters, and chillers.

[0105] Furthermore, each embodiment has been described in detail to clearly explain the present disclosure, and is not necessarily limited to having all of the described configurations. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. Furthermore, the above-described mechanisms and configurations are those considered necessary for explanation, and do not necessarily represent all mechanisms and configurations of the product.

[0106] 10 Converter circuit 21 Reactor 22 First capacitor 30 First inverter circuit 41 Diode 42 Second capacitor 50 Second inverter circuit 60 Control unit 71 Switching power supply circuit 72 Discharge resistor 73 Limiting resistor 74 DC voltage detection unit 75 Comparator 76 Protection circuit 76a Switching element 76b Resistance element 80 Third inverter circuit (another inverter circuit) 91 Compressor 92 Outdoor heat exchanger 93 Outdoor fan 94 Expansion valve 95 Four-way valve 96 Indoor heat exchanger 97 Indoor fan 100, 100A, 100B, 100C, 100D, 100E Power conversion device E1 AC power supply K1 DC line (DC line on high potential side) K2 DC line (DC line on low potential side) K4 Wiring M1 First motor M2 Second motor W1 Air conditioner

Claims

1. A power conversion device comprising: a converter circuit that converts AC voltage applied from an AC power source into DC voltage; a first capacitor connected to a pair of DC lines on the output side of the converter circuit; a first inverter circuit that converts the DC voltage of the first capacitor into AC voltage and applies the AC voltage to a first motor; a second capacitor that is connected to the DC line on the higher potential side of the pair of DC lines via a diode and is connected to the DC line on the lower potential side via wiring; a second inverter circuit that converts the DC voltage of the second capacitor into AC voltage and applies the AC voltage to a second motor; and a control unit that controls the first inverter circuit and the second inverter circuit, wherein the diode allows current to flow from the DC line on the higher potential side toward the second capacitor and blocks current flow in the opposite direction to the flow.

2. The power conversion device according to claim 1, wherein the control unit continues to drive the second inverter circuit when the first inverter circuit is stopped.

3. The power conversion device according to claim 1, characterized in that the second capacitor has a larger capacitance than the first capacitor.

4. The power conversion device according to claim 1, further comprising a switching power supply circuit connected across the second capacitor, wherein the DC voltage of the second capacitor is applied to the input side of the switching power supply circuit.

5. The power conversion device according to claim 1, further comprising a discharge resistor connected in parallel to the second capacitor.

6. The power conversion device according to claim 1, further comprising a limiting resistor connected in series with the diode.

7. The power conversion device according to claim 1, further comprising one or more other inverter circuits, the input side of said other inverter circuits being connected to both ends of said second capacitor, and said control unit continuing to drive said second inverter circuit when said first inverter circuit is stopped, and continuing to drive at least one of said one or more other inverter circuits.

8. The power conversion device according to claim 1, further comprising a protection circuit having a series connection of a switching element and a resistance element, said series connection being connected in parallel to said second capacitor, and a comparator which compares the DC voltage of said first capacitor with a predetermined value, and switches said switching element to an ON state when the DC voltage of said first capacitor becomes equal to or greater than said predetermined value.

9. An air conditioner comprising: a power conversion device according to any one of claims 1 to 8; a compressor; an outdoor heat exchanger; an expansion valve; and an indoor heat exchanger; an outdoor fan installed near the outdoor heat exchanger; and an indoor fan installed near the indoor heat exchanger; wherein the first motor is a drive source for the compressor; and the second motor is a drive source for the outdoor fan.

Images