Power conversion device and air conditioner

Abstract

The present invention provides, for example, a highly reliable power conversion device. A power conversion device (100) comprises a converter circuit (10), a smoothing capacitor (20), an inverter circuit (50), an inverter control circuit (61), an overvoltage protection circuit (40), and an overvoltage protection control circuit (62) that, when a DC voltage of the smoothing capacitor (20) reaches a prescribed value after the inverter circuit (50) has stopped, performs overvoltage protection control for switching a switching element (41) to an on state, wherein: after the overvoltage protection control is initiated, the inverter control circuit (61) performs winding short-circuit control for turning on all phases of one of an upper arm and a lower arm of the inverter circuit (50) and turning off all phases of the other; and the winding short-circuit control is initiated on the basis of a prescribed state quantity correlating with the cumulative heat generation amount of a resistance element (42) accompanying the overvoltage protection control.

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. 6421882

[0004] The overvoltage protection circuit described in Patent Document 1 has the advantages of a simple circuit configuration and a high degree of freedom in setting the resistance values ​​of the resistor elements and the operating conditions of the switching elements. However, immediately after the switching operation of the inverter circuit stops, regenerative power is generated in the motor. This regenerative power is consumed by the resistor elements of the overvoltage protection circuit (electrical energy is converted into thermal energy), generating heat in the resistor elements. If the amount of this heat is too great, it may shorten the life of the resistor elements and may also have a thermal impact on 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 that 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 a motor, an inverter control circuit that controls the inverter circuit, and an overvoltage protection circuit having a series connection of a switching element and a resistive element and connected in parallel to the smoothing capacitor, and the inverter control circuit also performs overvoltage protection control by switching the switching element to an on state when the DC voltage of the smoothing capacitor reaches a predetermined value after the inverter circuit is stopped, and after the overvoltage protection control is started, the inverter control circuit performs winding short-circuit control by turning on all phases of one of the upper arm and the lower arm of the inverter circuit while turning off all phases of the other, and the winding short-circuit control is started based on a predetermined state quantity that is correlated with an integrated heat generation amount of the resistive element associated with the overvoltage protection control.

[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 an explanatory diagram showing an example of winding short-circuit control in the power conversion device according to the first embodiment. FIG. 3 is an explanatory diagram showing another example of winding short-circuit control in the power conversion device according to the first embodiment. FIG. 4 is a flowchart showing processing by a control unit of the power conversion device according to the first embodiment. FIG. 5 is a time chart relating to overvoltage protection control and winding short-circuit control of the power conversion device according to the first embodiment. FIG. 6 is a flowchart showing processing by a control unit of a power conversion device according to a second embodiment. FIG. 7 is a time chart relating to overvoltage protection control and winding short-circuit control of the power conversion device according to the second embodiment. FIG. 8 is a flowchart showing processing by a control unit of a power conversion device according to a third embodiment. FIG. 9 is a time chart relating to overvoltage protection control and winding short-circuit control of the power conversion device according to the third embodiment. FIG. 10 is a configuration diagram of a power conversion device according to a fourth embodiment. FIG. 11 is a flowchart showing processing by a control unit of a power conversion device according to the fourth embodiment. FIG. 12 is a time chart relating to overvoltage protection control and winding short-circuit control of the power conversion device according to the fourth embodiment. FIG. 13 is a flowchart showing processing by a control unit of a power conversion device according to a fifth embodiment. FIG. 14 is a time chart relating to overvoltage protection control and winding short-circuit control of the power conversion device according to the fifth embodiment. FIG. 15 is a time chart relating to overvoltage protection control and winding short-circuit control of the power conversion device according to the sixth embodiment. FIG. 16 is a configuration diagram of a power conversion device according to a seventh embodiment. FIG. 17 is a configuration diagram of an air conditioner according to an eighth embodiment.

[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 smoothing capacitor 20, a DC voltage detection unit 30, an overvoltage protection circuit 40, an inverter circuit 50, an inverter control circuit 61, and an overvoltage protection control circuit 62.

[0010] The converter circuit 10 is a power converter that converts AC voltage applied from a three-phase AC power source E1 into DC voltage (pulsating DC voltage). In the example of FIG. 1, a full-wave rectification 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. The output side of the converter circuit 10 is connected to the inverter circuit 50 via a positive DC line K1 and also via a negative DC line K2.

[0011] The smoothing capacitor 20 is an element that smoothes the DC voltage (pulsating DC voltage) on the output side of the converter circuit 10, and is connected to a pair of DC lines K1 and K2. Specifically, one end (one lead wire) of the smoothing capacitor 20 is connected to the positive DC line K1, and the other end (the other lead wire) is connected to the negative DC line K2. For example, a film capacitor is used as such a smoothing capacitor 20.

[0012] Generally, film capacitors are smaller in size (volume) than large-capacity electrolytic capacitors. Therefore, using a film capacitor as the smoothing capacitor 20 allows for the miniaturization of the circuit board (not shown) of the power conversion device 100. Film capacitors also have the advantage of having 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.

[0013] 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 the regenerative current of the motor M1 flows directly into the smoothing capacitor 20 immediately after the switching operation of the inverter circuit 50 is stopped, the DC voltage E of the smoothing capacitor 20 will ｄｃTherefore, by providing the overvoltage protection circuit 40, the DC voltage E ｄｃ The type of smoothing capacitor 20 is not limited to a film capacitor, but may be another type of capacitor such as an electrolytic capacitor.

[0014] The DC voltage detection unit 30 detects the DC voltage E ｄｃ That is, the DC voltage detection unit 30 detects the DC voltage E between the pair of DC lines K1 and K2. ｄｃ For example, the DC voltage E ｄｃ is divided by a series connection of a plurality of resistor elements (not shown), and a DC voltage E is generated based on the voltage division ratio and the voltage of a predetermined resistor element. ｄｃ The detected value of the DC voltage detector 30 at every moment is output to the inverter control circuit 61 and also to the overvoltage protection control circuit 62.

[0015] The overvoltage protection circuit 40 is a circuit for protecting the smoothing capacitor 20 from an overvoltage, and is connected in parallel to the smoothing capacitor 20. As shown in Fig. 1, the overvoltage protection circuit 40 has a series connection of a switching element 41 and a resistance element 42. This series connection is connected in parallel to the smoothing capacitor 20. 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.

[0016] The switching element 41 is an element for switching between flow and interruption of current via the resistance element 42. For example, an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is used as the switching element 41. The resistance element 42 is an element that consumes electrical energy associated with the regenerative current of the motor M1 and converts it into thermal energy.

[0017] The inverter circuit 50 converts the DC voltage Eｄｃ The inverter circuit 50 is a power converter that converts a voltage from a power source (V) to a predetermined AC voltage and applies this AC voltage to the motor M1. The inverter circuit 50 has a configuration in which a first leg, a second leg, and a third leg are connected in parallel to the smoothing capacitor 20. The first leg has a configuration in which a pair of switching elements S1 and S2 are 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.

[0018] From another perspective, the inverter circuit 50 includes upper-arm switching elements S1, S3, and S5 connected to a high-potential DC line K1, and lower-arm switching elements S2, S4, and S6 connected to a low-potential DC line K2. As shown in FIG. 1 , a 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 wiring. Similarly, a 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 wiring. A 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 wiring.

[0019] In addition, in order to prevent breakdown of the switching elements S1 to S6 due to commutation in the inverter circuit 50, freewheeling diodes (reference numbers not shown) are connected in antiparallel to each of the switching elements S1 to S6. Note that if the switching elements S1 to S6 have parasitic diodes, these parasitic diodes function as freewheeling diodes, and therefore there is no particular need to provide separate freewheeling diodes.

[0020] The inverter control circuit 61 generates a DC voltage E ｄｃThe inverter control circuit 61 controls the inverter circuit 50 in a predetermined manner based on the detected values ​​of the inverter circuit 50. For example, an MCU (Micro Controller Unit) is used as the inverter control circuit 61. Although not shown, the MCU is configured to include electronic circuits such as a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and various interfaces, and reads out programs stored in the ROM and loads them into the RAM, allowing the CPU to execute various processes.

[0021] The inverter control circuit 61 converts the DC voltage of the smoothing capacitor 20 into a three-phase AC voltage by switching on and off the switching elements S1 to S6 in a predetermined manner based on PWM (Pulse Width Modulation) control. This AC voltage is applied to the U-phase, V-phase, and W-phase windings of the motor M1.

[0022] The overvoltage protection control circuit 62 controls the DC voltage E ｄｃ Specifically, the overvoltage protection control circuit 62 controls the DC voltage E of the smoothing capacitor 20 after the inverter circuit 50 is stopped. ｄｃ reaches a predetermined value, the switching element 41 is switched on. This type of control is called "overvoltage protection control." Note that an analog electronic circuit including a comparator (not shown) or a microcomputer may be used as the overvoltage protection control circuit 62. The inverter control circuit 61 and the overvoltage protection control circuit 62 are collectively referred to as the control unit 60.

[0023] <Regarding DC voltage suppression> For example, immediately after the inverter circuit 50 is stopped, the rotor of the motor M1 rotates for a while due to inertia (coast-force), so the motor M1 functions as a generator and generates a regenerative current. If this regenerative current flows directly into the smoothing capacitor 20, the DC voltage E of the smoothing capacitor 20 will ｄｃ In particular, when a small-capacity film capacitor is used as the smoothing capacitor 20, the DC voltage E ｄｃTherefore, in the first embodiment, the DC voltage E ｄｃ This suppresses the rise in the smoothing capacitor 20 and protects it from overvoltage.

[0024] In addition, DC voltage E ｄｃ Another method for suppressing this is to turn on all phases of one of the upper and lower arms of the inverter circuit 50 while turning off all phases of the other, thereby short-circuiting the three-phase windings of the U, V, and W phases. This type of control is called "winding short-circuit control." When winding short-circuit control is performed after the inverter circuit 50 is stopped, regenerative current circulates through the on-state switching elements and three-phase windings of the upper or lower arm of the inverter circuit 50. Therefore, almost no regenerative current flows from the three-phase windings of the motor M1 to the smoothing capacitor 20, and the DC voltage E ｄｃ This can suppress the increase in

[0025] 2A is an explanatory diagram showing an example of winding short-circuit control in the power conversion device 100. In the example of Fig. 2A, as winding short-circuit control, the inverter control circuit 61 (see Fig. 1) turns off the upper-arm switching elements S1, S3, and S5, while turning on the lower-arm switching elements S2, S4, and S6. If winding short-circuit control is performed while a regenerative current is being generated in the motor M1 immediately after the inverter circuit 50 is stopped, the regenerative current circulates through the lower-arm switching elements S2, S4, and S6 and the three-phase windings of the motor M1.

[0026] 2B is an explanatory diagram showing another example of winding short-circuit control in the power conversion device 100. In the example of FIG. 2B, as winding short-circuit control, the inverter control circuit 61 (see FIG. 1) turns on the upper-arm switching elements S1, S3, and S5 while turning off the lower-arm switching elements S2, S4, and S6. If winding short-circuit control is performed while a regenerative current is being generated in the motor M1 immediately after the inverter circuit 50 is stopped, the regenerative current circulates via the upper-arm switching elements S1, S3, and S5 and the three-phase windings of the motor M1.

[0027] In the following description (including other embodiments), winding short-circuit control will be described in which the upper arm switching elements S1, S3, and S5 are turned OFF while the lower arm switching elements S2, S4, and S6 are turned ON, as shown in FIG. 2A . However, instead of this, control as shown in FIG. 2B may be performed.

[0028] As described above, winding short-circuit control (see FIGS. 2A and 2B) is performed after the inverter circuit 50 is stopped, thereby suppressing an increase in the DC voltage of the smoothing capacitor 20. However, if winding short-circuit control is started simultaneously with the stopping of the inverter circuit 50 without performing overvoltage protection control, an excessive current may flow in the inverter circuit 50 due to the energy stored in the three-phase windings of the motor M1 and the electromotive force of the motor M1. Furthermore, if winding short-circuit control is stopped while the rotation speed of the motor M1 is high without performing overvoltage protection control, the regenerative current of the motor M1 will flow into the smoothing capacitor 20, and the DC voltage E ｄｃ increases significantly.

[0029] Therefore, in the first embodiment, when the control unit 60 stops the inverter circuit 50, the overvoltage protection control is performed for a predetermined time, and then the control is switched to the winding short-circuit control (see FIGS. 2A and 2B). This prevents an excessive current from flowing through the inverter circuit 50 while maintaining the DC voltage E ｄｃ Furthermore, by shortening the time during which the regenerative current flows through the resistance element 42 (limiting it to a predetermined time), the amount of heat generated by the resistance element 42 can be reduced.

[0030] <Processing of the control unit> Figure 3 is a flowchart showing the processing of the control unit of the power conversion device (also see Figure 1 as appropriate). It is assumed that a command to stop the switching operation of the inverter circuit 50 is input at the time of "START" in Figure 3. For example, if the motor M1 is used as the drive source for the compressor of an air conditioner, a command to stop the switching operation of the inverter circuit 50 is input to the inverter control circuit 61 when a stop button on a remote control (not shown) is pressed.

[0031] 3, the control unit 60 causes the inverter control circuit 61 to stop the switching operation of the inverter circuit 50 based on PWM control. Note that even after the switching operation is stopped, the rotor of the motor M1 continues to rotate by inertia, so the motor M1 functions as a generator. This regenerative current flows into the smoothing capacitor 20 via the DC line K1, so the DC voltage E of the smoothing capacitor 20 ｄｃ increases.

[0032] In step S102, the control unit 60 detects the DC voltage E ｄｃ is equal to or greater than a predetermined value V1. The predetermined value V1 is a voltage threshold that is a criterion for determining whether or not to switch the overvoltage protection circuit 40 to the ON state, and is set in advance.

[0033] In step S102, the DC voltage E ｄｃ is less than the predetermined value V1 (S102: No), the control unit 60 repeats the determination process of step S103. ｄｃ If is equal to or greater than the predetermined value V1 (S102: Yes), the process of the control unit 60 proceeds to step S103.

[0034] In step S103, the control unit 60 executes (starts) overvoltage protection control using the overvoltage protection control circuit 62. That is, the control unit 60 switches the switching element 41 of the overvoltage protection circuit 40 to the ON state. As a result, the regenerative current of the motor M1 flows through the resistance element 42, and the regenerative energy is consumed (converted into thermal energy) in the resistance element 42. As a result, the inflow of the regenerative current to the smoothing capacitor 20 is suppressed, and the DC voltage E of the smoothing capacitor 20 is reduced. ｄｃ This can suppress the increase in

[0035] Next, in step S104, the control unit 60 ｏｎ That is, the control unit 60 determines whether the time elapsed from the start of the overvoltage protection control is equal to or greater than the predetermined time t ｏｎ It is determined whether the predetermined time t ｏｎis a preset threshold value of time that is used as a criterion for determining whether or not to start winding short-circuit control.

[0036] Note that the longer the time that has elapsed since the start of overvoltage protection control, the longer the time that the regenerative energy of the motor M1 is consumed as heat energy in the resistance element 42, and accordingly the greater the integrated heat generation amount (the value obtained by summing up the heat generation amounts over time) of the resistance element 42. Therefore, in the first embodiment, the elapsed time from the start of overvoltage protection control is used as the "predetermined state quantity" that has a correlation with the integrated heat generation amount of the resistance element 42 accompanying the overvoltage protection control.

[0037] In step S104, the elapsed time from the start of the overvoltage protection control is a predetermined time t ｏｎ If the time elapsed since the start of the overvoltage protection control is not equal to the predetermined time t (S104: No), the control unit 60 returns to step S103. In this case, the overvoltage protection control is continued. ｏｎ If it has reached (S104: Yes), the process of the control unit 60 proceeds to step S105.

[0038] In step S105, the control unit 60 ends the overvoltage protection control by the overvoltage protection control circuit 62. That is, the control unit 60 switches the switching element 41 of the overvoltage protection circuit 40 to the OFF state. As a result, the time during which a current flows through the resistance element 42 of the overvoltage protection circuit 40 is set to the predetermined time t ｏｎ This reduces the amount of heat generated by the resistance element 42. This not only reduces the life of the resistance element 42 but also suppresses the thermal influence on surrounding circuit components.

[0039] Next, in step S106, the control unit 60 executes winding short-circuit control using the inverter control circuit 61. Specifically, after the overvoltage protection control is initiated, the inverter control circuit 61 executes winding short-circuit control by turning on all phases of one of the upper and lower arms of the inverter circuit 50 while turning off all phases of the other (see FIG. 2A). In this way, in the first embodiment, the winding short-circuit control is initiated based on the elapsed time (predetermined state quantity) since the start of the overvoltage protection control.

[0040] By performing the winding short-circuit control, the regenerative current of the motor M1 circulates through the on-state switching elements and three-phase windings of the inverter circuit 50. Furthermore, the regenerative energy of the motor M1 is consumed as work performed on the rotational resistance of the motor M1. Therefore, while the winding short-circuit control is being executed, almost no regenerative current flows into the smoothing capacitor 20.

[0041] After performing the process of step S106, the control unit 60 ends the series of processes (END). Note that the duration of the winding short-circuit control may be set in advance. This duration is set, for example, to be longer than the time it takes for the rotation of the motor M1 due to inertia to stop.

[0042] Furthermore, the faster the rotation speed of the motor M1, the larger the regenerative current tends to be immediately after stopping the inverter circuit 50. Therefore, the faster the rotation speed of the motor M1 when stopping the inverter circuit 50, the longer the predetermined time t ｏｎ (the threshold value of the predetermined state quantity) is increased. This makes it possible to prevent an excessive current from flowing through the inverter circuit 50 due to the winding short-circuit control.

[0043] 4A and 4B are time charts relating to overvoltage protection control and winding short-circuit control (see also FIG. 1 as appropriate). The horizontal axis of each time chart in FIG. 4 represents time. The vertical axis of each time chart in FIG. 4 represents, from top to bottom, the DC voltage E ｄｃ , the cumulative heat generation amount of the resistance element 42, the operation of the switching element 41 of the overvoltage protection circuit 40, the operation of the switching elements S1, S3, and S5 of the upper arm of the inverter circuit 50, and the operation of the switching elements S2, S4, and S6 of the lower arm.

[0044] In the example of FIG. 4, after the switching operation of the inverter circuit 50 based on PWM control is stopped (S101 in FIG. 3), the voltage of the smoothing capacitor 20 rises sharply from time t1. This is because a regenerative current is generated by the induced voltage of the motor M1, and this regenerative current flows into the smoothing capacitor 20. Then, at time t2, the DC voltage E of the smoothing capacitor 20 ｄｃhas reached the predetermined value V1 (S102: Yes). In this case, the overvoltage protection control circuit 62 switches the overvoltage protection circuit 40 to the ON state (S103). As a result, the regenerative current of the motor M1 flows through the resistance element 42, and the DC voltage E ｄｃ This can suppress the increase in

[0045] A predetermined time t after the overvoltage protection circuit 40 is switched on ｏｎ If the time has elapsed (S104 in FIG. 3: Yes), the overvoltage protection control circuit 62 switches the overvoltage protection circuit 40 to the OFF state at time t3 (S105). This prevents current from flowing through the overvoltage protection circuit 40, thereby suppressing heat generation in the resistance element 42.

[0046] In the example of FIG. 4 , winding short-circuit control by the inverter control circuit 61 is initiated at time t3 when the overvoltage protection circuit 40 is switched to the OFF state (S106 in FIG. 3 ). Specifically, the inverter control circuit 61 turns OFF all phases of the upper-arm switching elements S1, S3, and S5, while turning ON all phases of the lower-arm switching elements S2, S4, and S6 (see FIG. 2A ). As a result, regenerative current from the motor M1 circulates through the ON-state switching elements S2, S4, and S6 and the three-phase windings. Therefore, during the winding short-circuit control, almost no regenerative current flows into the smoothing capacitor 20.

[0047] Although not shown in FIG. 1, a discharge resistor is connected in parallel to the smoothing capacitor 20, and therefore, a current flows out of the smoothing capacitor 20 through the discharge resistor during the winding short-circuit control. As a result, the DC voltage E of the smoothing capacitor 20 ｄｃ continues to decrease.

[0048] <Effects> According to the first embodiment, the DC voltage E of the smoothing capacitor 20 after the inverter circuit 50 is stopped ｄｃ When the DC voltage E reaches the predetermined value V1, the overvoltage protection control is executed. Therefore, even if a small-capacity film capacitor is used as the smoothing capacitor 20, the DC voltage E ｄｃMoreover, since there is no particular need to provide a detector for detecting the current flowing through the resistance element 42, the manufacturing cost of the power conversion device 100 can be reduced.

[0049] In addition, a predetermined time t ｏｎ Since winding short-circuit control is initiated when the time elapses, it is possible to reduce the amount of heat generated in the resistance element 42 of the overvoltage protection circuit 40. Therefore, the distance between the resistance element 42 and the surrounding circuit components can be shortened at the design stage of the power conversion device 100, which not only alleviates restrictions on the circuit pattern but also enables the miniaturization of the circuit board.

[0050] Furthermore, since there is no particular need to start the winding short-circuit control at the same time as stopping the inverter circuit 50, it is possible to prevent an excessive current from flowing through the inverter circuit 50. Therefore, according to the first embodiment, it is possible to provide a highly reliable power conversion device 100.

[0051] Second Embodiment The second embodiment differs from the first embodiment in that winding short-circuit control is initiated based on the amount of DC voltage drop after overvoltage protection control is initiated. Other aspects (such as the configuration of the power conversion device 100: see FIG. 1 ) are similar to those of the first embodiment. Therefore, only the differences from the first embodiment will be described, and overlapping aspects will not be described.

[0052] 5 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 needed). Note that steps S101 to S103, S105, and S106 in FIG. 5 are the same as those described in the first embodiment (see FIG. 3). That is, after stopping the switching operation of the inverter circuit 50 (S101), the control unit 60 ｄｃ becomes equal to or greater than the predetermined value V1 (S102: Yes), the overvoltage protection control is executed (S103).

[0053] Next, in step S204, the control unit 60 controls the DC voltage E ｄｃ The decrease amount is a predetermined value E ＯＮ That is, the control unit 60 determines whether the DC voltage E ｄｃWhen the change in the value of the voltage Vcc reaches a peak value and then starts to decrease, the amount of decrease from the peak value is equal to a predetermined value E ＯＮ It is determined whether the value is equal to or greater than the predetermined value E ＯＮ is a threshold value of the voltage drop amount (absolute value) that serves as a criterion for determining whether or not to start winding short-circuit control, and is set in advance.

[0054] In addition, when the overvoltage protection control is being executed, the DC voltage E ｄｃ The larger the amount of decrease in DC voltage E, the larger the integrated heat generation amount of the resistor element 42. Therefore, in the second embodiment, the following state quantity is used as the "predetermined state quantity" that has a correlation with the integrated heat generation amount of the resistor element 42 accompanying the overvoltage protection control. That is, as the "predetermined state quantity", ｄｃ The amount of decrease from the peak value when the change in the value of the signal changes from an increase to a peak value and then changes to a decrease is used.

[0055] In step S204, the DC voltage E ｄｃ The decrease amount is a predetermined value E ＯＮ If the DC voltage E is less than the threshold voltage E (S204: No), the process of the control unit 60 returns to step S103. In this case, the overvoltage protection control is continued. ｄｃ The decrease amount is a predetermined value E ＯＮ If the DC voltage E is equal to or greater than the threshold voltage (S204: Yes), the control unit 60 proceeds to step S105. Then, the control unit 60 ends the overvoltage protection control (S105) and executes the winding short-circuit control (S106). In this way, the DC voltage E after the start of the overvoltage protection control ｄｃ Based on the amount of decrease (predetermined state amount) of the winding, the winding short-circuit control is started.

[0056] The inverter control circuit 61 determines whether or not to start winding short-circuit control by adjusting the predetermined value E as the rotation speed of the motor M1 increases when the inverter circuit 50 is stopped. ＯＮ It is preferable to increase the threshold value of the predetermined state quantity. This makes it possible to prevent an excessive current from flowing through the inverter circuit 50.

[0057] 6 is a time chart relating to overvoltage protection control and winding short-circuit control (see also FIG. 1 as appropriate). The horizontal and vertical axes of each time chart in FIG. 6 are the same as those in FIG. 4, and therefore will not be described here. In the example of FIG. 6, the DC voltage E ｄｃ When the change in the value of E1 reaches a peak value E0 from the rise and then turns to a fall, the amount of fall from the peak value E0 reaches a predetermined value E ＯＮ (S204 in FIG. 5: Yes). In this case, the control unit 60 ends the overvoltage protection control (S105) and executes the winding short-circuit control (S106). As a result, no current flows through the overvoltage protection circuit 40, and the DC voltage E ｄｃ The cumulative heat generation amount of the resistance element 42 can be reduced while suppressing the increase in the temperature.

[0058] <Effects> According to the second embodiment, the DC voltage E ｄｃ The decrease amount is a predetermined value E ＯＮ The winding short-circuit control is started when the DC voltage E ｄｃ Since the amount of decrease in the winding current also tends to be large, winding short-circuit control can be started at an appropriate timing.

[0059] Third Embodiment The third embodiment differs from the first embodiment in that winding short-circuit control is initiated based on an integrated value of the amount of DC voltage drop after the start of overvoltage protection control. Other aspects (such as the configuration of the power conversion device 100: see FIG. 1 ) are similar to those of the first embodiment. Therefore, only the differences from the first embodiment will be described, and overlapping aspects will not be described.

[0060] 7 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 needed). Note that steps S101 to S103, S105, and S106 in FIG. 7 are the same as those described in the first embodiment (see FIG. 3). That is, after stopping the switching operation of the inverter circuit 50 (S101), the control unit 60 ｄｃ becomes equal to or greater than the predetermined value V1 (S102: Yes), the overvoltage protection control is executed (S103).

[0061] Next, in step S304, the control unit 60 controls the DC voltage E ｄｃ The cumulative value of the decrease (the value obtained by sequentially adding up the values) is equal to the predetermined value E ｄｅｃ That is, the control unit 60 determines whether the DC voltage E ｄｃ When the change in the value of the voltage Vcc reaches a peak value and then starts to decrease, the integrated value of the decrease from the peak value is a predetermined value E ｄｅｃ It is determined whether the value is equal to or greater than the predetermined value E ｄｅｃ is a threshold value of the integrated value of the voltage drop amount (absolute value) that serves as a criterion for determining whether or not to start winding short-circuit control, and is set in advance.

[0062] In addition, the DC voltage E ｄｃ Therefore, in the third embodiment, the following state quantity is used as a "predetermined state quantity" that has a correlation with the integrated heat generation amount of the resistance element 42 accompanying the overvoltage protection control. That is, after the start of the overvoltage protection control, the DC voltage E ｄｃ The integrated value of the decrease from the peak value when the change in the state changes from an increase to a peak value and then changes to a decrease is used as the "predetermined state amount."

[0063] In step S304, the DC voltage E ｄｃ The cumulative value of the decrease in the amount of ｄｅｃ If the DC voltage E ｄｃ is equal to or less than a predetermined value V2. The predetermined value V2 is a voltage threshold that serves as a criterion for determining whether or not to suspend overvoltage protection control, and is preset to a value lower than the predetermined value V1.

[0064] In step S305, the DC voltage E ｄｃ is higher than the predetermined value V2 (S305: No), the control unit 60 repeats the determination process of step S305. ｄｃis equal to or less than the predetermined value V2 (S305: Yes), the process of the control unit 60 returns to step S102. ｄｃ Based on this, the overvoltage protection circuit 40 is alternately switched on (S103) and off (S306).

[0065] In step S304, the DC voltage E ｄｃ The cumulative value of the decrease in the amount of ｄｅｃ If so (S304: Yes), the process of the control unit 60 proceeds to step S105. In this case, since a predetermined amount of regenerative energy has already been consumed by the resistance element 42, there is no particular risk of an excessive current flowing through the inverter circuit 50 even if the winding short-circuit control is started.

[0066] Then, the control unit 60 ends the overvoltage protection control (S105) and executes the winding short-circuit control (S106). ｄｃ The inverter control circuit 61 starts winding short-circuit control based on the integrated value of the decrease in the DC voltage E ｄｃ The integrated value of the decrease amount may be reset when the winding short-circuit control is started.

[0067] 7 is an example, and the present invention is not limited to this. For example, when the DC voltage E ｄｃ Based on the comparison result between the DC voltage E ｄｃ The integrated value of the decrease amount and the predetermined value E ｄｅｃ The comparison with the DC voltage E ｄｃ The cumulative value of the decrease in the amount of ｄｅｃ If this occurs, the control unit 60 may execute the processes of steps S105 and S106 as an interrupt process. This process also provides the same effect.

[0068] In addition, the inverter control circuit 61 determines whether or not to start winding short-circuit control by adjusting the predetermined value E as the rotation speed of the motor M1 increases when the inverter circuit 50 is stopped.ｄｅｃ It is preferable to increase the threshold value of the predetermined state quantity. This makes it possible to prevent an excessive current from flowing through the inverter circuit 50.

[0069] In addition, during the winding short circuit control, the DC voltage E ｄｃ reaches the predetermined value V1 again (i.e., even if the condition for starting the overvoltage protection control is satisfied again), the control unit 60 may be configured not to start the overvoltage protection control. This makes it possible to suppress an increase in the integrated heat generation amount of the resistance element 42.

[0070] 8 is a time chart relating to overvoltage protection control and winding short-circuit control (see also FIG. 1 as appropriate). The vertical axis of the second time chart from the top of the page in FIG. 8 is the DC voltage E ｄｃ The vertical axes of the remaining time charts in Fig. 8 are the same as those in Fig. 4, and therefore the explanation will be omitted.

[0071] In the example of FIG. 8, the DC voltage E ｄｃ Since the DC voltage E reaches the predetermined value V1 (S102 in FIG. 7: Yes), the overvoltage protection circuit 40 is switched to the ON state (S103). ｄｃ Since the DC voltage E has decreased to the predetermined value V2 (S305: Yes), the overvoltage protection circuit 40 is temporarily switched to the OFF state (S306). ｄｃ The cumulative value of the decrease in the amount of ｄｅｃ has not yet been reached (S304: No), the winding short-circuit control has not yet been started.

[0072] After time t3 in FIG. 8, the DC voltage E ｄｃ rises again, and at time t4, the DC voltage E ｄｃ Since the DC voltage E reaches the predetermined value V1 (S102 in FIG. 7: Yes), the overvoltage protection circuit 40 is switched to the ON state again (S103). ｄｃ The cumulative value of the decrease in the amount of ｄｅｃ, (S304: Yes), the control unit 60 switches the overvoltage protection circuit 40 to the OFF state (S105) and starts winding short-circuit control (S106).

[0073] <Effects> According to the third embodiment, the DC voltage E ｄｃ The cumulative value of the decrease in the amount of ｄｅｃ When the DC voltage E ｄｃ As the integrated value of the decrease in the resistance value increases, the integrated heat generation amount of the resistance element 42 increases, and the amount of regenerative energy that is not fully consumed tends to decrease. Therefore, according to the third embodiment, the winding short-circuit control can be started at a more appropriate timing than in the second embodiment.

[0074] Fourth Embodiment The fourth embodiment differs from the first embodiment in that the power conversion device 100A (see FIG. 9) includes a current detector 70 (see FIG. 9). The fourth embodiment also differs from the first embodiment in that winding short-circuit control is initiated when the detection value of the current detector 70 reaches a predetermined value. Note that the rest of the fourth embodiment is the same as the first embodiment. Therefore, only the parts that differ from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0075] Fig. 9 is a configuration diagram of a power conversion device 100A according to the fourth embodiment. The power conversion device 100A shown in Fig. 9 includes a current detector 70 in addition to the components described in the first embodiment (see Fig. 1). The current detector 70 detects the current flowing through the resistive element 42 and is connected in series to the resistive element 42 and the switching element 41. For example, a shunt resistor or a current sensor is used as this current detector 70. The momentary detected value of the current detector 70 is output to the control unit 60.

[0076] 10 is a flowchart showing the processing of the control unit of the power conversion device (see also FIG. 9 as appropriate). Note that steps S101 to S103, S105, and S106 in FIG. 10 are the same as those described in the first embodiment (see FIG. 3). That is, after stopping the switching operation of the inverter circuit 50 (S101), the control unit 60 ｄｃis equal to or greater than the predetermined value V1 (S102: Yes), the overvoltage protection control is executed (S103).

[0077] Next, in step S404, the control unit 60 determines whether the current detection value I (the detection value of the current detector 70) is equal to or greater than a predetermined value I ＯＮ That is, the control unit 60 determines whether the magnitude of the current flowing through the resistance element 42 after the start of the overvoltage protection control is equal to or greater than the predetermined value I ＯＮ It is determined whether the predetermined value I ＯＮ is a preset current threshold value that is used as a criterion for determining whether or not to start winding short-circuit control.

[0078] It should be noted that the larger the current flowing through the resistance element 42 when overvoltage protection control is being executed, the larger the integrated heat generation amount of the resistance element 42. Therefore, in the fourth embodiment, the magnitude of the current flowing through the resistance element 42 after the start of overvoltage protection control is used as the "predetermined state quantity" that has a correlation with the integrated heat generation amount of the resistance element 42 accompanying the overvoltage protection control.

[0079] In step S404, the detected current value I is equal to the predetermined value I ＯＮ If the detected current value I is less than the predetermined value I (S404: No), the process of the control unit 60 returns to step S103. In this case, the overvoltage protection control is continued. ＯＮ If so (S404: Yes), the control unit 60 proceeds to step S105. The control unit 60 then terminates the overvoltage protection control (S105) and executes winding short-circuit control (S106). In this way, the winding short-circuit control is started based on the magnitude of the current (predetermined state quantity) flowing through the resistance element 42 after the start of the overvoltage protection control.

[0080] The inverter control circuit 61 determines whether or not to start winding short-circuit control by adjusting the predetermined value I ＯＮ It is preferable to increase the threshold value of the predetermined state quantity. This makes it possible to prevent an excessive current from flowing through the inverter circuit 50.

[0081] Fig. 11 is a time chart relating to overvoltage protection control and winding short-circuit control of the power conversion device (see also Fig. 9 as appropriate). The vertical axis of the second time chart from the top of the page in Fig. 11 represents the current detection value of the current detector 70. The vertical axes of the remaining time charts in Fig. 11 are the same as those in Fig. 4, and therefore will not be described here.

[0082] In the example of FIG. 11, the current detected by the current detector 70 reaches a predetermined value I ＯＮ (S404 in FIG. 10: Yes). In this case, the overvoltage protection control circuit 62 switches the overvoltage protection circuit 40 to the OFF state (S105). This prevents current from flowing through the overvoltage protection circuit 40, thereby suppressing heat generation in the resistance element 42. In the example of FIG. 10, the winding short-circuit control is started at time t3 when the overvoltage protection circuit 40 is switched to the OFF state (S106). This reduces the DC voltage E ｄｃ The regenerative energy of the motor M1 can be consumed while suppressing the increase in the current.

[0083] <Effects> According to the fourth embodiment, the detected value of the current flowing through the resistance element 42 is equal to or exceeds the predetermined value I ＯＮ Furthermore, since the amount of heat generated by the resistance element 42 tends to increase as the current flowing through the resistance element 42 increases, the winding short-circuit control can be started at an appropriate timing.

[0084] Fifth Embodiment The fifth embodiment differs from the fourth embodiment in that winding short-circuit control is initiated based on an integrated value of a current flowing through a resistance element 42 (see FIG. 9 ). Other aspects (such as the configuration of the power conversion device 100A: see FIG. 9 ) are the same as those of the fourth embodiment. Therefore, only the differences from the fourth embodiment will be described, and a description of overlapping aspects will be omitted.

[0085] 12 is a flowchart showing the processing of the control unit of the power conversion device according to the fifth embodiment (see also FIG. 9 as needed). Note that steps S101 to S103, S105, and S106 in FIG. 12 are the same as those described in the first embodiment (see FIG. 3). That is, after stopping the switching operation of the inverter circuit 50 (S101), the control unit 60ｄｃ is equal to or greater than the predetermined value V1 (S102: Yes), the overvoltage protection control is executed (S103).

[0086] Next, in step S504, the control unit 60 determines whether the integrated value (successive sum) of the current detection value I is equal to or exceeds a predetermined value I ｄｅｃ That is, the control unit 60 determines whether the integrated value of the current flowing through the resistance element 42 after the start of the overvoltage protection control is equal to or greater than the predetermined value I ｄｅｃ It is determined whether the predetermined value I ｄｅｃ is a threshold value of the current integrated value that is a criterion for determining whether or not to start winding short-circuit control, and is set in advance.

[0087] It should be noted that the larger the integrated value of the current flowing through the resistance element 42 when overvoltage protection control is being executed, the larger the integrated amount of heat generated by the resistance element 42. Therefore, in the fifth embodiment, the integrated value of the current flowing through the resistance element 42 after the start of overvoltage protection control is used as the "predetermined state quantity" that has a correlation with the integrated amount of heat generated by the resistance element 42 due to overvoltage protection control.

[0088] After performing the process of step S504, the control unit 60 ends the overvoltage protection control (S105) and executes the winding short-circuit control (S106). In this way, the winding short-circuit control is started based on the integrated value (predetermined state quantity) of the current flowing through the resistance element 42 after the start of the overvoltage protection control. Note that the integrated value of the current flowing through the resistance element 42 may be reset when the winding short-circuit control is started.

[0089] In addition, the inverter control circuit 61 determines whether or not to start winding short-circuit control by adjusting the predetermined value I as the rotation speed of the motor M1 when the inverter circuit 50 is stopped. ｄｅｃ It is preferable to increase the threshold value of the predetermined state quantity. This makes it possible to prevent an excessive current from flowing through the inverter circuit 50.

[0090] Figure 13 is a time chart relating to overvoltage protection control and winding short-circuit control (see also Figure 9 as appropriate). The vertical axis of the third time chart from the top of the page in Figure 13 represents the integrated value of the current detected by current detector 70. The vertical axes of the remaining time charts in Figure 13 are the same as those in Figure 11, so their explanation will be omitted.

[0091] In the example of Figure 13, while the overvoltage protection circuit 40 is in the ON state (time t2 to t3), a current flows through the current detector 70, so the current detection value becomes greater than zero from time to time, and as a result, the integrated value of the current detection value increases monotonically. ｄｅｃ (S504 in FIG. 12: Yes), the overvoltage protection circuit 40 is switched to the OFF state at time t3 (S105), and the winding short-circuit control is started (S106).

[0092] <Effects> According to the fifth embodiment, the integrated value of the current detection value is equal to or exceeds the predetermined value I ｄｅｃ The winding short-circuit control is initiated when the integrated value of the current detection value reaches . Here, the larger the integrated value of the current detection value, the larger the integrated heat generation amount of the resistance element 42 and the smaller the amount of regenerative energy that has not been consumed. Therefore, according to the fifth embodiment, the winding short-circuit control can be initiated at a more appropriate timing than in the fourth embodiment.

[0093] Sixth Embodiment The sixth embodiment differs from the first embodiment in that winding short-circuit control is initiated before overvoltage protection control ends. Other aspects (such as the configuration of the power conversion device 100: see FIG. 1 ) are similar to those of the first embodiment. Therefore, only the differences from the first embodiment will be described, and overlapping aspects will not be described.

[0094] 14 is a time chart relating to overvoltage protection control and winding short-circuit control of the power conversion device according to the sixth embodiment (see also FIG. 1 as appropriate). The horizontal and vertical axes of each time chart in FIG. 14 are the same as those in FIG. 4, and therefore will not be described here. In the example of FIG. 14, the DC voltage E ｄｃWhen the voltage V reaches the predetermined value V1 at time t2, the overvoltage protection circuit 40 is switched to the ON state, and the voltage V is maintained for a period from time t2 to time t4 (i.e., a predetermined time t ＯＮ The overvoltage protection circuit 40 remains in the ON state during this period (time t1). Meanwhile, the lower arm switching elements S2, S4, and S6 are switched to the ON state at time t3. In other words, the winding short-circuit control is started at time t3, which is before the timing (time t4) when the overvoltage protection control is ended.

[0095] <Effects> According to the sixth embodiment, the winding short-circuit control is started before the overvoltage protection control is ended, so that the execution times of the overvoltage protection control and the winding short-circuit control partially overlap. ｄｃ The rate of decrease can be increased.

[0096] Seventh Embodiment The seventh embodiment differs from the first embodiment in the configuration of an overvoltage protection circuit 40B (see FIG. 15 ), but is otherwise similar to the first embodiment. Therefore, only the differences from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0097] Fig. 15 is a configuration diagram of a power conversion device 100B according to the seventh embodiment. As shown in Fig. 15, an overvoltage protection circuit 40B of the power conversion device 100B includes a first parallel-connected body configured by connecting a resistor element 42, a capacitor 43, and a diode 44 in parallel. The overvoltage protection circuit 40B further includes a second parallel-connected body configured by connecting a switching element 41, a resistor element 45, and a diode 46 in parallel. The first parallel-connected body and the second parallel-connected body are connected in series. One end of this series-connected body is connected to the positive DC line K1, and the other end is connected to the negative DC line K2.

[0098] 15 is an element that stores electric charge when the switching element 41 is turned on, and is connected in parallel to the resistance element 42, etc. For example, an electrolytic capacitor is used as this capacitor 43. Note that the circuit configuration shown in FIG. 15 is also included in the fact that the overvoltage protection circuit 40B has a series connection of the switching element 41 and the resistance element 42.

[0099] The diodes 44 and 46 are elements for forming a current path when a reverse voltage is applied to the switching element 41. One of the diodes 44 has a cathode connected to the positive DC line K1 and an anode connected to the negative DC line K2 via the second parallel connection. The other diode 46 has an anode connected to the negative DC line K2 and a cathode connected to the positive DC line K1 via the first parallel connection. The resistive element 45 is a high-impedance resistor for stabilizing the voltage applied to the switching element 41.

[0100] <Effects> According to the seventh embodiment, when the switching element 41 is switched to the on state, power is stored in the capacitor 43 and then consumed by the resistance element 42. Therefore, it is possible to suppress a sudden change in the current flowing through the resistance element 42 and also to suppress a temperature rise in the resistance element 42. Furthermore, by providing the diodes 44 and 46, it is possible to form a current path when a reverse voltage is applied to the switching element 41.

[0101] Eighth Embodiment In the eighth embodiment, an air conditioner W1 (see FIG. 16) 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.

[0102] FIG. 16 is a configuration diagram of an air conditioner W1 according to an eighth embodiment. The solid arrows in FIG. 16 indicate the flow of refrigerant in the heating cycle. The dashed arrows in FIG. 16 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. 16 , 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.

[0103] Although not shown in Fig. 16, 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. The power conversion device 100 is mounted on a circuit board (not shown) of the outdoor unit U1.

[0104] 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. 16, 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 50 (see Fig. 1) of the power conversion device 100 (see Fig. 1).

[0105] 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.

[0106] 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 is equipped with an indoor fan motor 97a that serves as a drive source, and is installed near the indoor heat exchanger 96.

[0107] 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. 16 ), 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. 16 ), 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.

[0108] <Effects> According to the eighth 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 is improved.

[0109] <<Modifications>> While the power conversion devices 100, 100A, 100B and the air conditioner W1 according to the present disclosure have been described in the above embodiments, they are not limited to these descriptions and various modifications can be made. For example, in the first embodiment (see FIG. 4 ), a case was described in which winding short-circuit control is started when overvoltage protection control is terminated, but this is not limiting. That is, winding short-circuit control may be started after a predetermined time has elapsed since overvoltage protection control was terminated. The same can be said for the second to fifth embodiments.

[0110] In addition, in each embodiment, the overvoltage protection control circuit 62 (see FIG. 1) is described as being configured with an analog electronic circuit including a comparator or a microcomputer, but this is not limiting. For example, the overvoltage protection control circuit 62 may be configured by combining a predetermined analog electronic circuit with a microcomputer. Furthermore, the configurations of the overvoltage protection circuits 40, 40B (see FIGS. 1 and 15) described in each embodiment are merely examples, and the present invention is not limited to these. In other words, any other configuration may be used as long as the circuit has the function of protecting the smoothing capacitor 20 from overvoltage.

[0111] In addition, in each embodiment, a case where the AC power supply E1 (see FIG. 1 ) is a three-phase AC power supply has been described, but this is not a limitation, and a single-phase AC power supply may also be used. In addition, in each embodiment, a configuration has been described in which no reactor is particularly provided in the DC lines K1, K2 (see FIG. 1 ), but this is not a limitation. That is, a reactor may be provided in at least one of the DC lines K1, K2. For example, in the positive-side DC line K1, a reactor may be provided between the connection point between this DC line K1 and the smoothing capacitor 20 and the converter circuit 10 (the same applies to the reactor in the negative-side DC line K2).

[0112] Furthermore, in each embodiment, the case where the number of smoothing capacitors 20 (see FIG. 1) is one has been described, but this is not limiting. That is, a 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 one smoothing capacitor. The same applies to the second to seventh embodiments.

[0113] In the seventh embodiment, the overvoltage protection circuit 40B (see FIG. 15 ) is described as including a first parallel connection of the resistive element 42, the capacitor 43, and the diode 44, and a second parallel connection of the switching element 41, the resistive element 45, and the diode 46. However, the present invention is not limited to this. That is, the overvoltage protection circuit 40B may be configured such that the switching element 41 is connected in series to the parallel connection of the resistive element 42 and the capacitor 43, and the remaining elements may be omitted as appropriate.

[0114] Furthermore, the embodiments can be combined as appropriate. For example, any of the first to fifth embodiments may be combined with the sixth embodiment (see FIG. 14 ), so that winding short-circuit control is initiated before the end of overvoltage protection control. Furthermore, any of the first to sixth embodiments may be combined with the seventh embodiment (see FIG. 15 ), so that the overvoltage protection circuit 40B has the configuration shown in FIG. 15 . Furthermore, any of the first to seventh embodiments may be combined with the eighth embodiment (see FIG. 16 ), so that the motor M1 connected to the inverter circuit 50 is used as the drive source for the compressor of the air conditioner.

[0115] In the eighth embodiment (see FIG. 16 ), 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. 16 ). 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.

[0116] Furthermore, in the eighth embodiment (see FIG. 16 ), 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 eighth embodiment (see FIG. 16 ) 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 eighth embodiment can be applied to other devices such as water heaters, refrigerators, and air-conditioning and hot water supply systems.

[0117] 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.

[0118] REFERENCE SIGNS LIST 10 Converter circuit 20 Smoothing capacitor 30 DC voltage detection unit 40, 40B Overvoltage protection circuit 41 Switching element 42 Resistance element 43 Capacitor 50 Inverter circuit 60 Control unit 61 Inverter control circuit 62 Overvoltage protection control 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 Power conversion device E1 AC power supply M1 Motor S1, S3, S5 Switching element (upper arm) S2, S4, S6 Switching element (lower arm) W1 Air conditioner

Claims

1. A power conversion device comprising: a converter circuit that converts an AC voltage applied from an AC power source into a DC voltage; a smoothing capacitor that smoothes 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; an overvoltage protection circuit having a series connection body of a switching element and a resistance element and connected in parallel to the smoothing capacitor; and an overvoltage protection control circuit that performs overvoltage protection control to switch the switching element to an on state when the DC voltage of the smoothing capacitor reaches a predetermined value after the inverter circuit stops. The inverter control circuit performs winding short-circuit control to turn on all phases of one of the upper arm and the lower arm of the inverter circuit and turn off all phases of the other after the overvoltage protection control is started. The winding short-circuit control is started based on a predetermined state quantity that has a correlation with the integrated heat generation amount of the resistance element associated with the overvoltage protection control.

2. The power conversion device according to claim 1, wherein the predetermined state quantity is the elapsed time from the start of the overvoltage protection control.

3. The power conversion device according to claim 1, wherein the predetermined state quantity is the amount of decrease from the peak value when the change in the DC voltage reaches the peak value from an increase and then turns to a decrease after the start of the overvoltage protection control.

4. The power conversion device according to claim 1, wherein the predetermined state quantity is the integrated value of the amount of decrease from the peak value when the change in the DC voltage reaches the peak value from an increase and then turns to a decrease after the start of the overvoltage protection control.

5. The power conversion device according to claim 1, wherein the predetermined state quantity is the magnitude of the current flowing through the resistance element after the start of the overvoltage protection control.

6. The power conversion device according to claim 1, wherein the predetermined state quantity is the integrated value of the current flowing through the resistance element after the start of the overvoltage protection control.

7. The power conversion device according to any one of claims 1 to 6, wherein the inverter control circuit increases the threshold value of the predetermined state quantity that serves as a criterion for determining whether to start the winding short-circuit control as the rotational speed of the motor when stopping the inverter circuit is higher.

8. The power conversion device according to any one of claims 1 to 6, characterized in that the winding short-circuit control is started before the end of the overvoltage protection control.

9. The power conversion device according to any one of claims 1 to 6, characterized in that the overvoltage protection circuit has a capacitor connected in parallel with the resistance element.

10. An air conditioner comprising the power conversion device according to any one of claims 1 to 6, and further comprising a compressor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger, wherein the motor is a drive source of the compressor.

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