Power conversion device and air conditioner

Abstract

The present invention provides a highly reliable power conversion device, etc. A power conversion device (100) comprises a converter circuit (10), a smoothing capacitor (30), an inverter circuit (60), an inverter control circuit (81), an overvoltage protection circuit (50), and an overvoltage protection control circuit (82), wherein: the inverter control circuit (81) performs motor deceleration control to reduce the rotational speed of a motor (M1) when there is a command to stop a switching operation of the inverter circuit (60) and the induced voltage of the motor (M1) is higher than the DC voltage of the smoothing capacitor (30); and the overvoltage protection control circuit (82) starts overvoltage protection control to turn on a switching element (51) of the overvoltage protection circuit (50) after starting the motor deceleration control and before, during, or after stopping the switching operation of the inverter circuit (60).

Description

Power conversion device and air conditioner

[0001] The present disclosure relates to a power conversion device and the like.

[0002] Regarding a power conversion device including an inverter circuit, for example, the technology described in Patent Document 1 is known. That is, Patent Document 1 describes a power conversion device equipped with an overvoltage protection circuit that has a resistor and a semiconductor element connected in series and protects the inverter circuit from overvoltage.

[0003] Patent No. 6844725

[0004] For example, if the switching operation of the inverter circuit is stopped while the motor is rotating at high speed, the induced voltage of the motor may become higher than the DC voltage, and an excessive regenerative current may flow through the overvoltage protection circuit. As a result, the amount of heat generated by the resistor element of the overvoltage protection circuit may increase, shortening the life of the resistor element and potentially thermally affecting surrounding circuit components. Therefore, the technology described in Patent Document 1 leaves room for improvement in terms of improving the reliability of the power conversion device.

[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, a 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 smoothing capacitor connected to a pair of DC lines on the output side of the converter circuit and smoothing the DC voltage on the output side of the converter circuit, an inverter circuit that converts the DC voltage of the smoothing capacitor into an AC voltage and applies the AC voltage to a motor, an inverter control circuit that controls the inverter circuit, and also includes an overvoltage protection circuit that has a switching element and is connected to the pair of DC lines, and an overvoltage protection control circuit that controls the overvoltage protection circuit, wherein when a command to stop the switching operation of the inverter circuit is received and an induced voltage of the motor is higher than the DC voltage of the smoothing capacitor, the inverter control circuit performs motor deceleration control to reduce the rotational speed of the motor, and the overvoltage protection control circuit starts overvoltage protection control to turn on the switching element of the overvoltage protection circuit after the start of the motor deceleration control, before, during, or after the switching operation of the inverter circuit is stopped.

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

[0008] 1 is a configuration diagram of a power conversion device according to a first embodiment. FIG. 2 is a flowchart showing the processing of a control unit of the power conversion device according to the first embodiment. FIG. 3 is a time chart relating to motor deceleration control and overvoltage protection control of the power conversion device according to the first embodiment. FIG. 4 is a flowchart showing the processing of a control unit of a power conversion device according to a second embodiment. FIG. 5 is a time chart relating to motor deceleration control and overvoltage protection control of the power conversion device according to the second embodiment. FIG. 6 is a flowchart showing the processing of a control unit of a power conversion device according to a third embodiment. FIG. 7 is a time chart relating to motor deceleration control and overvoltage protection control of the power conversion device according to the 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 time chart relating to 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, converts the DC power into a predetermined AC power, and outputs the converted AC power to a motor M1. The motor M1 may be, for example, a permanent magnet synchronous motor or another type of motor. As shown in Fig. 1, the power conversion device 100 includes a converter circuit 10, a reactor 20, a smoothing capacitor 30, a DC voltage detection unit 40, an overvoltage protection circuit 50, an inverter circuit 60, a shunt resistor 70, and a control unit 80.

[0010] The converter circuit 10 is a power converter that converts a three-phase AC voltage applied from an AC power source E1 into a DC voltage (pulsating DC voltage). In the example of FIG. 1, the converter circuit 10 uses a full-wave rectifier circuit configured with six diodes D1 to D6 connected in a bridge configuration. Note that a switching type converter may be used instead of the converter circuit 10 shown in FIG. 1. The output side of the converter circuit 10 is connected to the inverter circuit 60 via a positive DC line K1 and also via a negative DC line K2.

[0011] The reactor 20 and the smoothing capacitor 30 are elements that smooth the pulsating DC voltage applied from the converter circuit 10. As shown in Fig. 1, the reactor 20 is provided on the positive DC line K1. More specifically, the reactor 20 is provided on the positive DC line K1 between the converter circuit 10 and a connection point between the DC line K1 and the smoothing capacitor 30.

[0012] As described above, the smoothing capacitor 30 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 smoothing capacitor 30 is connected to a pair of DC lines K1 and K2 on the output side of the converter circuit 10. Specifically, one end (one lead wire) of the smoothing capacitor 30 is connected to the positive DC line K1, and the other end (the other lead wire) is connected to the negative DC line K2. As such a smoothing capacitor 30, for example, a film capacitor is used.

[0013] Generally, film capacitors are smaller in size (volume) than large-capacity electrolytic capacitors. Therefore, using a film capacitor as the smoothing capacitor 30 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, even when the power conversion device 100 is used in a high-temperature environment, there is almost no risk of the film capacitor failing.

[0014] 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 as the amount of stored electricity changes. For example, if the regenerative current of the motor M1 flows directly into the smoothing capacitor 30 immediately after the switching operation of the inverter circuit 60 stops, the DC voltage of the smoothing capacitor 30 will rise sharply. Therefore, the overvoltage protection circuit 50 is configured to suppress the rise in the DC voltage of the smoothing capacitor 30. Note that the type of smoothing capacitor 30 is not limited to a film capacitor, and other types of capacitors such as an electrolytic capacitor may also be used.

[0015] The DC voltage detection unit 40 detects the DC voltage across the smoothing capacitor 30. That is, the DC voltage detection unit 40 detects the DC voltage between the pair of DC lines K1 and K2. For example, the DC voltage across the smoothing capacitor 30 may be divided by a series connection of multiple resistor elements (not shown), and the DC voltage of the smoothing capacitor 30 may be detected based on the voltage division ratio or the voltage of a predetermined resistor element. The values ​​detected by the DC voltage detection unit 40 at every moment are output to an MCU 83 (Micro Controller Unit).

[0016] The overvoltage protection circuit 50 is a circuit for protecting the smoothing capacitor 30 from overvoltage, and is connected to a pair of DC lines K1 and K2. As shown in Fig. 1, the overvoltage protection circuit 50 has a series connection of a switching element 51 and a resistor element 52. One end of this series connection is connected to the positive DC line K1, and the other end is connected to the negative DC line K2. The series connection is also connected in parallel to the smoothing capacitor 30.

[0017] The switching element 51 has a function of switching between passing and blocking a current through the resistance element 52. For example, an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is used as the switching element 51. The resistance element 52 is an element that consumes electrical energy associated with a regenerative current of the motor M1 and converts it into thermal energy.

[0018] The inverter circuit 60 is a power converter that converts the DC voltage of the smoothing capacitor 30 into a predetermined AC voltage and applies this AC voltage to the motor M1. The inverter circuit 60 has a first leg, a second leg, and a third leg, and each of these legs is connected in parallel to the smoothing capacitor 30. The first leg has a pair of switching elements S1 and S2 connected in series (the same applies to the remaining second leg and third leg). The switching elements S1 to S6 that constitute the first leg, second leg, and third leg are, for example, IGBTs or MOSFETs.

[0019] In the inverter circuit 60, the connection point between the upper arm switching element S1 and the lower arm switching element S2 of the first leg is connected to a U-phase winding (not shown) of the motor M1 via a wire. Similarly, the connection point between the upper arm switching element S3 and the lower arm switching element S4 of the second leg is connected to a V-phase winding (not shown) of the motor M1 via a wire. The connection point between the upper arm switching element S5 and the lower arm switching element S6 of the third leg is connected to a W-phase winding (not shown) of the motor M1 via a wire.

[0020] In addition, to prevent breakdown of the switching elements S1 to S6 due to commutation, a free wheel diode (not shown) is connected in anti-parallel to each of the switching elements S1 to S6. If the switching elements S1 to S6 have a parasitic diode, this parasitic diode functions as the free wheel diode, so there is no need to provide a separate free wheel diode.

[0021] The shunt resistor 70 is a resistive element for detecting a current flowing through the DC line K2. In the example of Fig. 1, the shunt resistor 70 is provided between the overvoltage protection circuit 50 and the inverter circuit 60 on the negative DC line K2.

[0022] The control unit 80 includes an inverter control circuit 81, an overvoltage protection control circuit 82, and an MCU (Micro Controller Unit) 83. The inverter control circuit 81 switches the switching elements S1 to S6 on and off in a predetermined manner based on PWM (Pulse Width Modulation) control. This converts the DC voltage of the smoothing capacitor 30 into a three-phase AC voltage. This AC voltage is applied to the U-phase, V-phase, and W-phase windings of the motor M1. A predetermined gate drive circuit is used as the inverter control circuit 81.

[0023] The overvoltage protection control circuit 82 controls the overvoltage protection circuit 50 in a predetermined manner. As such an overvoltage protection control circuit 82, an analog electronic circuit including a comparator (not shown) may be used, or a digital electronic circuit based on predetermined software may be used.

[0024] Although not shown, the MCU 83 is configured to include electronic circuits such as a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), various interfaces, etc. The MCU 83 reads out programs stored in the ROM and loads them into the RAM, and the CPU executes various processes.

[0025] The MCU 83 calculates a three-phase voltage command for driving the motor M1 based on the detected value of the shunt resistor 70, etc. Based on this three-phase voltage command, the inverter control circuit 81 generates a PWM signal, which switches on and off the switching elements S1 to S6 of the inverter circuit 60 in a predetermined manner. The "inverter control unit" that controls the inverter circuit 60 is configured to include the inverter control circuit 81 and the MCU 83.

[0026] The MCU 83 also has a function of generating a command signal indicating whether or not to operate the overvoltage protection circuit 50, based on the detection value of the DC voltage detection unit 40. The overvoltage protection circuit 50 then controls the on / off of the switching element 51 based on the command signal generated by the MCU 83. The "overvoltage protection control unit" that controls the overvoltage protection circuit 50 is configured to include the overvoltage protection control circuit 82 and the MCU 83.

[0027] <Regarding DC voltage suppression> For example, immediately after the inverter circuit 60 is stopped, the rotor of the motor M1 rotates for a while due to inertia (coast-force), causing the motor M1 to function as a generator. As a result, a regenerative current is generated due to the induced voltage of the motor M1, and a predetermined current is generated by the energy stored in the three-phase windings of the motor M1 and the reactor 20.

[0028] The induced voltage of the motor M1 is calculated as the product (ω·Ke) of the rotation speed ω of the motor M1 and the induced voltage constant Ke. Since the induced voltage constant Ke is a fixed value (known value), the induced voltage is proportional to the rotation speed of the motor M1. Therefore, the faster the rotation speed of the motor M1 when the inverter circuit 60 is stopped, the higher the induced voltage.

[0029] Furthermore, when the induced voltage of the motor M1 is higher than the DC voltage of the smoothing capacitor 30, this potential difference generates a regenerative current, which flows from the motor M1 to the smoothing capacitor 30 and other components via the inverter circuit 60. As described above, the faster the rotation speed of the motor M1 when the inverter circuit 60 is stopped, the higher the induced voltage becomes, and accordingly the potential difference between the DC voltage of the smoothing capacitor 30 and the induced voltage also becomes larger, resulting in a large regenerative current easily flowing. Therefore, in order to suppress the rise in the DC voltage of the smoothing capacitor 30 due to the regenerative current of the motor M1, the overvoltage protection circuit 50 is provided.

[0030] However, if the switching operation of the inverter circuit 60 were to be stopped while the motor M1 was rotating at high speed, an excessively large regenerative current would flow through the resistor element 41 of the overvoltage protection circuit 50, potentially causing considerable heat to be generated in the resistor element 52. This could shorten the life of the resistor element 52 and could have a thermal effect on surrounding circuit components. In short, if the inverter circuit 60 were to be stopped while the motor M1 was rotating at high speed, a state would occur in which "DC voltage < induced voltage," generating an excessively large regenerative current, which would increase the electrical and thermal load on the overvoltage protection circuit 50.

[0031] Therefore, in the first embodiment, if the DC voltage is less than the induced voltage when a command to stop the inverter circuit 60 is input, the control unit 80 decelerates the motor M1, stops the inverter circuit 60, and then switches on the overvoltage protection circuit 50. This prevents an excessive regenerative current from flowing through the overvoltage protection circuit 50, and ultimately prevents a shortened lifespan of the resistance element 52.

[0032] <Processing of Control Unit> Figure 2 is a flowchart showing the processing of the control unit of the power conversion device (see also Figure 1 as appropriate). It is assumed that, at the time of "START" in Figure 2, the motor M1 is driven by the switching operation of the inverter circuit 60. In step S101, the control unit 80 determines whether or not a command to stop the switching operation of the inverter circuit 60 has been input to the MCU 83. For example, if the motor M1 is used as a drive source for the compressor of an air conditioner, a command to stop the switching operation of the inverter circuit 60 is input to the MCU 83 when a stop button on a remote control (not shown) is pressed.

[0033] If there is no command to stop the switching operation of the inverter circuit 60 in step S101 (S101: No), the control unit 80 repeats the determination process of step S101 while continuing to drive the inverter circuit 60. On the other hand, if there is a command to stop the switching operation of the inverter circuit 60 in step S101 (S101: Yes), the process of the control unit 80 proceeds to step S102.

[0034] In step S102, the control unit 80 determines whether the induced voltage of the motor M1 is higher than the DC voltage of the smoothing capacitor 30. As described above, the induced voltage of the motor M1 is calculated as the product (ω·Ke) of the rotation speed ω of the motor M1 and the induced voltage constant Ke. Note that the induced voltage constant Ke is assumed to be a known value. The DC voltage of the smoothing capacitor 30 is detected by the DC voltage detection unit 40.

[0035] If the induced voltage of the motor M1 is higher than the DC voltage of the smoothing capacitor 30 in step S102 (S102: Yes), the control unit 80 proceeds to step S103. In step S103, the control unit 80 decelerates the motor M1 using the inverter control circuit 81. In this manner, when a command to stop the switching operation of the inverter circuit 60 is received (S101: Yes) and the induced voltage of the motor M1 is higher than the DC voltage of the smoothing capacitor 30 (S102: Yes), the control unit 80 (inverter control unit) performs "motor deceleration control" to reduce the rotational speed of the motor M1 (S103). Note that the rate of reduction in the rotational speed over time when the inverter control circuit 81 decelerates the motor M1 is preset.

[0036] In step S104, the control unit 80 stops the switching operation of the inverter circuit 60 based on PWM control by the inverter control circuit 81. Note that even after the switching operation is stopped, the rotor of the motor M1 continues to rotate by inertia for a while, and the motor M1 functions as a generator, but the rotation speed of the motor M1 is kept low by the motor deceleration control (S103).

[0037] 2, the magnitude relationship between the induced voltage of the motor M1 and the DC voltage of the smoothing capacitor 30 may be used as a trigger for the control unit 80 to terminate the motor deceleration control (i.e., to stop the switching operation of the inverter circuit 60). Specifically, the control unit 80 (inverter control unit) may continue the motor deceleration control until the induced voltage of the motor M1 becomes equal to or less than the DC voltage of the smoothing capacitor 30 (induced voltage≦DC voltage). When the induced voltage of the motor M1 is equal to or less than the DC voltage of the smoothing capacitor 30, almost no regenerative current flows, and therefore, when the overvoltage protection circuit 50 is subsequently switched on, the current flowing through the resistance element 41 can be suppressed.

[0038] Furthermore, for example, the control unit 80 may continue the motor deceleration control until the induced voltage of the motor M1 decreases to or below a predetermined value as the motor M1 decelerates. The predetermined value is a threshold value of the induced voltage that serves as a criterion for determining whether or not to terminate the motor deceleration control, and is set in advance. Alternatively, for example, the control unit 80 may terminate the motor deceleration control when the duration of the motor deceleration control reaches a predetermined time.

[0039] Next, in step S105, the control unit 80 switches the overvoltage protection circuit 50 to the ON state using the overvoltage protection control circuit 82. That is, the control unit 80 (overvoltage protection control unit) performs "overvoltage protection control" by switching the switching element 51 of the overvoltage protection circuit 50 to the ON state based on the detection value of the DC voltage detection unit 40. By performing overvoltage protection control in this manner, the regenerative current of the motor M1 and the current due to the energy of the reactor 20, etc., flow through the resistance element 52 and are consumed as heat energy by the resistance element 52. This makes it possible to suppress an increase in the DC voltage of the smoothing capacitor 30.

[0040] 2, the overvoltage protection control circuit 82 may continue the overvoltage protection control until the DC voltage of the smoothing capacitor 30 falls below a predetermined value. Alternatively, the overvoltage protection control circuit 82 may continue the overvoltage protection control for a predetermined period of time. This makes it possible to suppress an increase in the DC voltage of the smoothing capacitor 30.

[0041] Furthermore, if the induced voltage of the motor M1 is equal to or less than the DC voltage of the smoothing capacitor 30 in step S102 (S102: No), the control unit 80 proceeds to step S106. In step S106, the control unit 80 causes the inverter control circuit 81 to stop the switching operation of the inverter circuit 60. In this case, since the induced voltage is equal to or less than the DC voltage (S102: No), almost no regenerative current flows. Therefore, there is no particular need to switch the overvoltage protection circuit 50 to the ON state. After performing the process of step S105 or S106, the control unit 80 ends the series of processes (END).

[0042] 3 is a time chart relating to motor deceleration control and overvoltage protection control (see also FIG. 1 as appropriate). The horizontal axis of each time chart in FIG. 3 represents time. The vertical axis of each time chart in FIG. 3 represents, from top to bottom, the rotation speed of motor M1, the induced voltage of motor M1, the DC voltage of smoothing capacitor 30, the integrated heat generation amount of resistor element 52 of overvoltage protection circuit 50, the operation of inverter circuit 60, and the operation of overvoltage protection circuit 50. Assume also that a stop command for inverter circuit 60 is input to control unit 80 at time t1 in FIG. 3 (S101: Yes in FIG. 2).

[0043] In the example of Fig. 3, at time t1 when a stop command is input to the inverter circuit 60, the induced voltage value V1 of the motor is higher than the DC voltage value V2 of the smoothing capacitor 30 (S102: Yes in Fig. 2). Therefore, the control unit 80 starts motor deceleration control from time t1 to reduce the rotational speed of the motor (S103). In the example of Fig. 3, at time t2 when the rotational speed of the motor M1 has decreased from value N1 to value N2, the induced voltage of the motor M1 has decreased to value V2, which is equal to the DC voltage of the smoothing capacitor 30.

[0044] Therefore, at time t2, the control unit 80 ends the motor deceleration control, stops the inverter circuit 60, and starts overvoltage protection control (S104, S105 in FIG. 2). That is, the control unit 80 switches the switching element 51 of the overvoltage protection circuit 50 to the ON state. In this way, in the example of FIG. 3, the overvoltage protection control is started at time t2, which is after the start of the motor deceleration control (i.e., after time t1) and when the switching operation of the inverter circuit 60 stops. In other words, since the overvoltage protection control is started immediately when the inverter circuit 60 stops, an increase in the DC voltage of the smoothing capacitor 30 can be suppressed.

[0045] 3, after the overvoltage protection control is started at time 2, the DC voltage of smoothing capacitor 30 increases once and then starts to decrease. This is because a current due to the energy stored in the three-phase windings of motor M1 and reactor 20 flows into overvoltage protection circuit 50, but the integrated heat generation amount of resistance element 52 is kept to a relatively small value Q1.

[0046] <Comparative Example> Fig. 12 is a time chart relating to a power conversion device according to a comparative example. Note that the configuration of the power conversion device according to the comparative example is the same as that shown in Fig. 1, but differs from the first embodiment in that motor deceleration control is not performed. Furthermore, the horizontal and vertical axes of each time chart in Fig. 12 are the same as those in Fig. 3, and therefore description thereof will be omitted.

[0047] In the comparative example shown in FIG. 12 , at time t11 when a stop command is input to the inverter circuit 60, the induced voltage value V1 of the motor is higher than the DC voltage value V2 of the smoothing capacitor 30. Furthermore, because deceleration control is not performed in the comparative example, the inverter circuit 60 is switched OFF and the overvoltage protection circuit 50 is switched ON at time t11. Therefore, overvoltage protection control is initiated in a state in which the induced voltage value V1 of the motor M1 is significantly higher than the DC voltage value V2 of the smoothing capacitor 30. As a result, an excessive current flows through the resistor element 52 of the overvoltage protection circuit 50, and the integrated heat generation value of the resistor element 52 reaches a relatively large value Q2. Such processing may shorten the life of the resistor element 52 and may also have a thermal impact on surrounding circuit components.

[0048] <Effects> In contrast, in the first embodiment, as described above, if the "induced voltage is greater than the DC voltage" when a stop command is input to the inverter circuit 60 (S102: Yes in FIG. 2), the control unit 80 performs motor deceleration control, stops the inverter circuit 60, and performs overvoltage protection control (S103 to S105). This prevents an excessive regenerative current from flowing through the resistance element 52 of the overvoltage protection circuit 50, thereby reducing the amount of heat generated by the resistance element 52. It also prevents an excessive current from flowing through the switching element 51 of the overvoltage protection circuit 50. Therefore, according to the first embodiment, it is possible to prevent a shortening of the lifespan of the switching element 51 and the resistance element 52, and it is also possible to suppress the thermal impact on circuit components around the resistance element 52.

[0049] Furthermore, the magnitude of the regenerative current generated in the motor M1 depends on the induced voltage constant and inertia (moment of inertia) of the motor M1. In other words, the magnitude of the regenerative current varies depending on the specifications of the motor M1. However, as described above, in the first embodiment, the regenerative current flowing through the overvoltage protection circuit 50 is significantly suppressed. Therefore, when a designer designs the circuit of the power conversion device 100, there is no need to select (tune) switching elements 51 and resistor elements 52 with a sufficient rated current for each specification of the motor M1. In other words, even when motors M1 with different specifications are used in multiple types of equipment, it is possible to use common switching elements 51 and resistor elements 52, which simplifies the work of designing the circuit of the power conversion device 100.

[0050] Furthermore, even when a small-capacity film capacitor is used as the smoothing capacitor 30, it is possible to prevent the DC voltage of the smoothing capacitor 30 from becoming too high due to the regenerative current of the motor M1, etc. Therefore, it is possible to reduce the cost, size, and life of the smoothing capacitor 30, and to improve the reliability of the power conversion device 100.

[0051] Second Embodiment The second embodiment differs from the first embodiment in that overvoltage protection control is initiated when the DC voltage of the smoothing capacitor 30 (see FIG. 1) reaches a predetermined value after the inverter circuit 60 (see FIG. 1) is stopped. Note that the other features (such as the configuration of the power conversion device 100: see FIG. 1) are the same as those of the first embodiment. Therefore, only the differences from the first embodiment will be described, and descriptions of overlapping features will be omitted.

[0052] 4 is a flowchart showing the processing of the control unit of the power conversion device according to the second embodiment (see also FIG. 1 as appropriate). The processing of steps S201 to S204, S206, and S208 in FIG. 4 is the same as steps S101 to S104, S105, and S106 in FIG. 2 according to the first embodiment, in this order, and therefore will not be described in detail again. When a stop command for the inverter circuit 60 is issued (S201: Yes), if the induced voltage of the motor M1 is higher than the DC voltage of the smoothing capacitor 30 (S202: Yes), the control unit 80 stops the switching operation of the inverter circuit 60 after the motor M1 has decelerated (S203, S204).

[0053] Even when the switching operation of the inverter circuit 60 is stopped after the motor M1 is decelerated, the DC voltage of the smoothing capacitor 30 often rises temporarily due to the current caused by the energy stored in the three-phase windings of the motor M1 and the reactor 20. Therefore, in the second embodiment, the control unit 80 determines in step S205 whether the DC voltage of the smoothing capacitor 30 is equal to or greater than a predetermined value Vsh. The predetermined value Vsh is a voltage threshold that serves as a criterion for determining whether the control unit 80 should start overvoltage protection control (S206), and is set in advance.

[0054] If the DC voltage of the smoothing capacitor 30 is equal to or greater than the predetermined value Vsh in step S205 (S205: Yes), the control unit 80 proceeds to step S206. In step S206, the control unit 80 switches the overvoltage protection circuit 50 to the ON state via the overvoltage protection control circuit 82. That is, if the DC voltage of the smoothing capacitor 30 is equal to or greater than the predetermined value Vsh after the switching operation of the inverter circuit 60 has stopped (S205: Yes), the control unit 80 (overvoltage protection control unit) starts overvoltage protection control (S206). As a result, the regenerative current of the motor M1 and the current due to the energy of the reactor 20, etc., flow through the resistance element 52 and are consumed as thermal energy, thereby suppressing an increase in the DC voltage of the smoothing capacitor 30.

[0055] If the DC voltage of the smoothing capacitor 30 is less than the predetermined value Vsh in step S205 (S205: No), the control unit 80 proceeds to step S207. In step S207, the control unit 80 determines whether a predetermined time has elapsed since the switching operation of the inverter circuit 60 was stopped. This predetermined time is a threshold value that serves as a criterion for determining whether the control unit 80 should end the series of processes without performing overvoltage protection control (S206), and is set in advance.

[0056] In step S207, if the predetermined time has not elapsed since the switching operation of the inverter circuit 60 was stopped (S207: No), the control unit 80 returns to step S205. In addition, in step S207, if the predetermined time has elapsed since the switching operation of the inverter circuit 60 was stopped (S207: Yes), the control unit 80 ends the series of processes (END) without performing overvoltage protection control (S206).

[0057] 5 is a time chart relating to motor deceleration control and overvoltage protection control (see also FIG. 1 as appropriate). Note that the horizontal and vertical axes of each time chart in FIG. 5 are the same as those in FIG. 3, and therefore will not be described here. In the example of FIG. 5, at time t4 when the induced voltage of motor M1 has decreased to value V2, which is equal to the DC voltage of smoothing capacitor 30, due to motor deceleration control (S203 in FIG. 4), the operation of inverter circuit 60 is switched to the OFF state (S204).

[0058] As the inverter circuit 60 stops, a current due to the energy stored in the three-phase windings of the motor M1 and the reactor 20 flows through the smoothing capacitor 30, causing the DC voltage of the smoothing capacitor 30 to rise once from time t4 and reach the predetermined value Vsh at time t5 (S205: Yes in FIG. 4). In this case, the control unit 80 switches the switching element 51 of the overvoltage protection circuit 50 to the ON state (S206).

[0059] In this way, the overvoltage protection control starts at time t5, which is after the start of the motor deceleration control (after time t3 in FIG. 5 ) and after the switching operation of the inverter circuit 60 has stopped (after time t4 in FIG. 5 ). This allows current to flow through the overvoltage protection circuit 50, thereby suppressing an increase in the DC voltage of the smoothing capacitor 30.

[0060] <Effects> According to the second embodiment, even after the switching operation of the inverter circuit 60 is stopped, if the DC voltage of the smoothing capacitor 30 does not reach the predetermined value Vsh, overvoltage protection control is not performed. Therefore, the operation frequency of the overvoltage protection circuit 50 is reduced, and as a result, the electrical and thermal loads on the resistance element 52 are reduced compared to the first embodiment. This makes it possible to extend the life of the resistance element 52.

[0061] Third Embodiment The third embodiment differs from the first embodiment in that overvoltage protection control is initiated before the switching operation of the inverter circuit 60 (see FIG. 1 ) is stopped. Other aspects (such as the configuration of the power conversion device 100: see FIG. 1 ) are the same as those of the first embodiment. Therefore, only the differences from the first embodiment will be described, and a description of overlapping aspects will be omitted.

[0062] 6 is a flowchart showing the processing of the control unit of the power conversion device according to the third embodiment (see also FIG. 1 as appropriate). Note that the processing of steps S301 to S303, S305, and S306 in FIG. 6 is the same as steps S101 to S103, S105, and S106 in FIG. 2 according to the first embodiment, in this order, and therefore detailed description thereof will be omitted. When a stop command for the inverter circuit 60 has been issued (S301: Yes), and the induced voltage of the motor M1 is higher than the DC voltage of the smoothing capacitor 30 (S302: Yes), the control unit 80 decelerates the motor M1 (S303).

[0063] Next, in step S304, the control unit 80 switches the overvoltage protection circuit 50 to the ON state using the overvoltage protection control circuit 82. As a result, the regenerative current of the motor M1 and the current due to the energy of the reactor 20, etc., flow through the resistance element 52 and are consumed as thermal energy, thereby suppressing an increase in the DC voltage of the smoothing capacitor 30.

[0064] As described above, in the third embodiment, the control unit 80 switches the overvoltage protection circuit 50 to the ON state (S304) before stopping the switching operation (S305) of the inverter circuit 60. This prevents a delay in the start timing of overvoltage protection control from being affected even if a delay occurs in the processing of the inverter control circuit 81.

[0065] Although not shown in Fig. 6, the following conditions may be used as triggers for starting the overvoltage protection control (S304). That is, the overvoltage protection control (S304) may be started when the induced voltage of the motor M1 drops to a predetermined value (a value higher than the DC voltage of the smoothing capacitor 30). The overvoltage protection control (S304) may also be started when the duration of the motor deceleration control (S303) reaches a predetermined value.

[0066] Next, in step S305, the control unit 80 causes the inverter control circuit 81 to stop the switching operation of the inverter circuit 60. Although not shown in Fig. 6 , the motor deceleration control (S303) is also stopped at the timing when the switching operation of the inverter circuit 60 is stopped (S305).

[0067] 7 is a time chart relating to motor deceleration control and overvoltage protection control. The horizontal and vertical axes of each time chart in FIG. 7 are the same as those in FIG. 3 , and therefore will not be described here. In the example of FIG. 7 , motor deceleration control (S303 in FIG. 6 ) is performed, and at time t8, when the induced voltage of motor M1 drops to value V2, which is equal to the DC voltage of smoothing capacitor 30, the operation of inverter circuit 60 is switched to the OFF state (S305).

[0068] Furthermore, the operation of the overvoltage protection circuit 50 is initiated at time t7 (S304), which is before the timing (time t8) at which the operation of the inverter circuit 60 is switched to the OFF state. That is, the overvoltage protection control is initiated at time t7, which is after the start of the motor deceleration control (after time t6 in FIG. 7 ) and before the switching operation of the inverter circuit 60 is stopped (before time t8 in FIG. 7 ). This prevents a delay in the timing at which the overvoltage protection circuit 50 is switched to the ON state, even if a delay occurs in the processing of the inverter control circuit 81 and the DC voltage of the smoothing capacitor 30 suddenly rises. Therefore, the rise in the DC voltage of the smoothing capacitor 30 can be reliably suppressed.

[0069] <Effects> According to the third embodiment, the overvoltage protection control is started before the switching operation of the inverter circuit 60 is stopped, and therefore it is possible to prevent a delay in the start of the overvoltage protection control due to a delay in the processing of the inverter control circuit 81. Therefore, it is possible to reliably suppress an increase in the DC voltage of the smoothing capacitor 30.

[0070] Fourth Embodiment In the fourth embodiment, the configuration of the overvoltage protection circuit 50A (see FIG. 8) is different from that of the first embodiment, but other configurations and processing contents are similar to 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. 8 is a configuration diagram of a power conversion device 100A according to the fourth embodiment. As shown in FIG. 8, an overvoltage protection circuit 50A of the power conversion device 100A includes a series connection of a switching element 51 and a capacitor 53. The capacitor 53 is an element that stores electric charge when the switching element 51 is turned on. For example, an electrolytic capacitor is used as the capacitor 53. The capacitance of the capacitor 53 may be larger than the capacitance of the smoothing capacitor 30. This makes it easier for regenerative current from the motor M1 to flow into the capacitor 53 of the overvoltage protection circuit 50A than into the smoothing capacitor 30.

[0072] 8, one end of the series connection of the switching element 51 and the capacitor 53 is connected to the positive DC line K1 and the other end is connected to the negative DC line K2. More specifically, the positive electrode of the capacitor 53 is connected to the positive DC line K1, and the negative electrode of the capacitor 53 is connected to the negative DC line K2 via the switching element 51.

[0073] For example, when overvoltage protection control is performed after deceleration of motor M1 and switching element 51 is switched on, regenerative currents and the like flow into smoothing capacitor 30 and capacitor 53 at a ratio corresponding to the ratio of their capacitances. Therefore, by appropriately adjusting the capacitance of capacitor 53 at the design stage, it is possible to prevent overvoltage from being applied to smoothing capacitor 30.

[0074] <Effects> According to the fourth embodiment, by configuring the overvoltage protection circuit 50A to include a series connection of the capacitor 53 and the switching element 51, it is possible to prevent an overvoltage from being applied to the smoothing capacitor 30. Furthermore, since there is no particular need to provide a high-resistance resistor element in the overvoltage protection circuit 50A to consume the regenerative current from the motor M1, etc., procurement of electronic components is easier than in the first embodiment.

[0075] Fifth Embodiment In the fifth embodiment, the configuration of the overvoltage protection circuit 50B (see FIG. 9 ) is different from that of the fourth embodiment, but other configurations and processing contents are similar to those of the fourth embodiment. Therefore, only the parts that are different from the fourth embodiment will be described, and a description of the overlapping parts will be omitted.

[0076] Fig. 9 is a configuration diagram of a power conversion device 100B according to the fifth embodiment. As shown in Fig. 9, an overvoltage protection circuit 50B of the power conversion device 100B includes a switching element 51, a capacitor 53, a first resistor element 54, and a second resistor element 55. The capacitor 53 is an element that stores electric charge when the switching element 51 is turned on. In the example of Fig. 9, the positive electrode of the capacitor 53 is connected to the positive DC line K1, and the negative electrode of the capacitor 53 is connected to the negative DC line K2 via the switching element 51.

[0077] The first resistor element 54 is an element for adjusting the magnitude of the current that flows into the capacitor 53 when the switching element 51 is switched to the on state, and is connected in series to one side (positive electrode) of the capacitor 53. The second resistor element 55 is an element for consuming (converting into thermal energy) the charge stored in the capacitor 53, and is connected in parallel to the capacitor 53. The switching element 51 is an element for switching whether or not to allow a current to flow through the first resistor element 54, and is connected in series to the other side (negative electrode) of the capacitor 53.

[0078] As shown in FIG. 9, one end of a series connection of a first resistor element 54, a capacitor 53, and a switching element 51 is connected to a positive DC line K1, and the other end is connected to a negative DC line K2.

[0079] <Effects> According to the fifth embodiment, the magnitude of the current flowing through the capacitor 53 when the switching element 51 is switched to the on state can be adjusted by the first resistor element 54. In other words, by appropriately adjusting the resistance value of the first resistor element 54 at the circuit design stage, it is possible to prevent an excessive current from flowing through the capacitor 53. In addition, the charge stored in the capacitor 53 can be consumed by the second resistor element 55.

[0080] Sixth Embodiment In the sixth embodiment, the configuration of an overvoltage protection circuit 50C (see FIG. 10) is different from that of the fifth embodiment (see FIG. 9), but other configurations and processing contents are similar to those of the fifth embodiment. Therefore, only the differences from the fifth embodiment will be described, and a description of overlapping portions will be omitted.

[0081] Fig. 10 is a configuration diagram of a power conversion device 100C according to the sixth embodiment. As shown in Fig. 10, an overvoltage protection circuit 50C of the power conversion device 100C includes a capacitor 53, a switching element 51, a first resistor element 54, a second resistor element 55, a third resistor element 56, and diodes 57 and 58. Note that the connections of the capacitor 53, the first resistor element 54, and the second resistor element 55 are the same as those in the fifth embodiment (see Fig. 9), and therefore will not be described here.

[0082] 10 is a high-impedance resistor for stabilizing the voltage applied to the switching element 51. One end of the third resistor element 56 is connected to the negative electrode of the capacitor 53, and the other end is connected to the negative DC line K2. Diodes 57 and 58 are elements for forming a current path when a reverse voltage is applied to the switching element 51.

[0083] One of the diodes, 57, and the third resistor element 56, are connected in parallel to the switching element 51. The diode 57 has an anode connected to the negative DC line K2 and a cathode connected to the negative electrode of the capacitor 53. The other diode 58 has an anode connected to the negative DC line K2 via the switching element 51 and a cathode connected to the positive DC line K1.

[0084] <Effects> According to the sixth embodiment, the provision of the third resistor element 56 can stabilize the voltage of the switching element 51. Furthermore, the provision of the diodes 57 and 58 can form a current path when a reverse voltage is applied to the switching element 51.

[0085] 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.

[0086] 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. As shown in FIG. 11 , 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.

[0087] Although not shown in Fig. 11, the air conditioner W1 is equipped with a power conversion device 100 (see Fig. 1) having the same configuration as that of the first embodiment. This power conversion device 100 is mounted on a circuit board (not shown) of the outdoor unit U1.

[0088] 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 motor M1 that is a drive source of the compressor 91 is connected to the output side of the inverter circuit 60 (see Fig. 1) of the power conversion device 100 (see Fig. 1).

[0089] 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 the outside air to the outdoor heat exchanger 92. The outdoor fan 93 has an outdoor fan motor 93a that serves as a drive source, and is installed near the outdoor heat exchanger 92.

[0090] 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.

[0091] The four-way valve 95 switches the refrigerant flow path depending on the operating mode of the air conditioner W1. For example, during cooling operation (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). During heating operation (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.

[0092] <Effects> According to the seventh embodiment, the air conditioner W1 is provided with the power conversion device 100 (see FIG. 1) having the same configuration as in the first embodiment, and therefore the reliability of the air conditioner W1 can be improved.

[0093] <<Modifications>> The power conversion devices 100, 100A, 100B, and 100C and the air conditioner W1 according to the present disclosure have been described above in the various embodiments, but they are not limited to these descriptions and various modifications can be made. For example, in the various embodiments, the overvoltage protection control circuit 82 (see FIG. 1) is configured as an analog electronic circuit including a comparator or a software-based digital electronic circuit. However, this is not limiting. In other words, the overvoltage protection control circuit 82 may be configured by combining a predetermined analog electronic circuit and a digital electronic circuit.

[0094] 2 in the first embodiment, if the induced voltage of the motor M1 is equal to or lower than the DC voltage of the smoothing capacitor 30 (S102: No), the control unit 80 may stop the switching operation of the inverter circuit 60 (S106) and then perform overvoltage protection control. This allows the current associated with the energy stored in the three-phase windings of the motor M1 and the reactor 20 to be consumed by the resistance element 41, thereby suppressing an increase in the DC voltage of the smoothing capacitor 30. The same applies to the second embodiment (see FIG. 4) and the third embodiment (see FIG. 6).

[0095] Furthermore, in each embodiment, the AC power supply E1 (see FIG. 1) is described as a three-phase AC power supply, but this is not a limitation, and a single-phase AC power supply may also be used. Furthermore, in each embodiment, the number of smoothing capacitors 30 (see FIG. 1) is described as one, but this is not a limitation. That is, the smoothing capacitor may be formed by a plurality of capacitors connected in series, parallel, or series-parallel. In this case, the "DC voltage of the smoothing capacitor" refers to the voltage across the smoothing capacitor (the DC voltage between the DC lines K1 and K2) when the capacitances of the plurality of capacitors are combined and considered as a single smoothing capacitor. The same applies to the second to seventh embodiments.

[0096] Furthermore, the respective embodiments can be combined as appropriate. For example, any of the first to third embodiments may be combined with the fourth embodiment (see FIG. 8 ), so that an overvoltage protection circuit 50A having the configuration shown in FIG. 8 is used. Similarly, the first to third embodiments may be combined with the overvoltage protection circuit 50B (fifth embodiment) shown in FIG. 9 or the overvoltage protection circuit 50C (sixth embodiment) shown in FIG. 10 . Furthermore, any of the first to sixth embodiments may be combined with the seventh embodiment (see FIG. 11 ), so that the motor M1 connected to the inverter circuit 60 is used as the drive source for the compressor 91 of the air conditioner W1.

[0097] In the seventh embodiment (see FIG. 11 ), the power conversion device 100 (see FIG. 1 ) is connected to the motor M1 of the compressor 91, but the present invention is not limited to this. For example, the power conversion device 100 may be connected to the outdoor fan motor 93 a (see FIG. 11 ). Furthermore, the power conversion device 100 may be connected to the motor M1 of the compressor 91, and the power conversion device 100 may be connected to the outdoor fan motor 93 a.

[0098] 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 85 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 such as water heaters, refrigerators, and air-conditioning and hot water supply systems.

[0099] 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.

[0100] 10 Converter circuit 20 Reactor 30 Smoothing capacitor 40 DC voltage detection unit 50, 50A, 50B, 50C Overvoltage protection circuit 51 Switching element 52 Resistance element 53 Capacitor 54 First resistance element 55 Second resistance element 56 Third resistance element 57, 58 Diode 60 Inverter circuit 70 Shunt resistor 80 Control unit 81 Inverter control circuit (inverter control unit) 82 Overvoltage protection control circuit (overvoltage protection control unit) 83 MCU (inverter control unit, overvoltage protection control unit) 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 Power conversion device E1 AC power supply K1, K2 DC line M1 Motor Steps S103, S203, S303 (motor deceleration control) Steps S105, S206, S304 (overvoltage protection control) W1 Air conditioner

Claims

1. A converter circuit that converts AC voltage applied from an AC power source into DC voltage, A smoothing capacitor is connected to a pair of DC lines on the output side of the converter circuit and smooths the DC voltage on the output side of the converter circuit. An inverter circuit that converts the DC voltage of the smoothing capacitor into an AC voltage and applies the AC voltage to the motor, It comprises an inverter control unit that controls the inverter circuit, An overvoltage protection circuit having a switching element and connected to a pair of DC lines, The system includes an overvoltage protection control unit that controls the overvoltage protection circuit, When the inverter control unit receives a command to stop the switching operation of the inverter circuit, and the induced voltage of the motor is higher than the DC voltage of the smoothing capacitor, it performs motor deceleration control to reduce the rotational speed of the motor. The inverter control unit stops the switching operation of the inverter circuit after terminating the motor deceleration control. The power converter is configured such that the overvoltage protection control unit initiates overvoltage protection control after the motor deceleration control has started, and before, during, or after the switching operation of the inverter circuit has stopped, turning on the switching element of the overvoltage protection circuit.

2. The inverter control unit continues the motor deceleration control until the induced voltage of the motor falls below the DC voltage of the smoothing capacitor. The power conversion device according to claim 1, characterized by the following:

3. The overvoltage protection control unit continues the overvoltage protection control until the DC voltage of the smoothing capacitor falls below a predetermined value. The power conversion device according to claim 1, characterized by the following:

4. The overvoltage protection control unit shall continue the overvoltage protection control for a predetermined period of time. The power conversion device according to claim 1, characterized by the following:

5. The overvoltage protection control unit starts the overvoltage protection control when the DC voltage of the smoothing capacitor exceeds a predetermined value after the switching operation of the inverter circuit has stopped. The power conversion device according to claim 1, characterized by the following:

6. The overvoltage protection circuit has a series connection of the switching element and the resistive element, The series connector has one end connected to the positive DC line and the other end connected to the negative DC line. The power conversion device according to claim 1, characterized by the following:

7. The overvoltage protection circuit has a series connection of the switching element and the capacitor, The series connector has one end connected to the positive DC line and the other end connected to the negative DC line. The power conversion device according to claim 1, characterized by the following:

8. The overvoltage protection circuit comprises a capacitor, a first resistive element connected in series with one side of the capacitor, a second resistive element connected in parallel with the capacitor, and the switching element connected in series with the other side of the capacitor. The series connection of the first resistor, the capacitor, and the switching element is such that one end is connected to the positive DC line and the other end is connected to the negative DC line. The power conversion device according to claim 1, characterized by the following:

9. The power conversion device is provided according to any one of claims 1 to 8, It comprises a compressor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger. An air conditioner in which the motor, which is the driving source for the compressor, is connected to the output side of the inverter circuit.