Power converters and air conditioners

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

[Technical Field]

[0001] This disclosure relates to power conversion devices, etc. [Background technology]

[0002] Regarding power conversion devices including inverter circuits, for example, the technology described in Patent Document 1 is known. Specifically, Patent Document 1 describes a power conversion device having a resistor and a semiconductor element connected in series, and equipped with an overvoltage protection circuit that protects the inverter circuit from overvoltage. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6421882 [Overview of the project] [Problems that the invention aims to solve]

[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 value of the resistive element and the operating conditions of the switching element. However, immediately after the switching operation of the inverter circuit stops, regenerative power is generated in the motor, and this regenerative power is consumed by the resistive element of the overvoltage protection circuit (electrical energy is converted into thermal energy), so heat is generated in the resistive element. If the amount of heat generated is too large, it can shorten the lifespan of the resistive element and may also have a thermal impact on surrounding circuit components. Therefore, in terms of improving the reliability of the power conversion device, there is room for improvement in the technology described in Patent Document 1.

[0005] Therefore, the objective of this disclosure is to provide highly reliable power conversion devices, etc. [Means for solving the problem]

[0006] To solve the aforementioned problems, the power conversion device according to this disclosure comprises: a converter circuit that converts an AC voltage applied from an AC power source 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 resistor element, and connected in parallel to the smoothing capacitor. The power conversion device also comprises an overvoltage protection control circuit that performs overvoltage protection control by switching the switching element to the ON state when the DC voltage of the smoothing capacitor reaches a predetermined value after the inverter circuit has stopped. The inverter control circuit performs winding short-circuit control by turning on all phases of one of the upper arm and lower arm of the inverter circuit while turning off all phases of the other arm, and the winding short-circuit control is started based on a predetermined state quantity that has a correlation with the cumulative heat generated by the resistor element in conjunction with the overvoltage protection control. The predetermined state quantity is the amount of decrease from the peak value when the change in the DC voltage after the start of the overvoltage protection control rises, reaches a peak value, and then starts to decline. That's what we decided. Further details will be explained within the embodiments. [Effects of the Invention]

[0007] According to this disclosure, highly reliable power conversion devices and the like can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] This is a configuration diagram of a power conversion device according to the first embodiment. [Figure 2A] This is an explanatory diagram showing an example of winding short-circuit control in a power converter according to the first embodiment. [Figure 2B] This is an explanatory diagram showing another example of winding short-circuit control in a power converter according to the first embodiment. [Figure 3] This is a flowchart showing the processing of the control unit of the power converter according to the first embodiment. [Figure 4] This is a time chart relating to overvoltage protection control and winding short-circuit control of a power converter according to the first embodiment. [Figure 5]This is a flowchart showing the processing of the control unit of the power converter according to the second embodiment. [Figure 6] This is a time chart relating to overvoltage protection control and winding short-circuit control of a power converter according to the second embodiment. [Figure 7] This is a flowchart showing the processing of the control unit of the power converter according to the third embodiment. [Figure 8] This is a time chart relating to overvoltage protection control and winding short-circuit control of a power converter according to the third embodiment. [Figure 9] This is a diagram showing the configuration of a power conversion device according to the fourth embodiment. [Figure 10] This is a flowchart showing the processing of the control unit of the power converter according to the fourth embodiment. [Figure 11] This is a time chart relating to overvoltage protection control and winding short-circuit control of the power converter according to the fourth embodiment. [Figure 12] This is a flowchart showing the processing of the control unit of the power converter according to the fifth embodiment. [Figure 13] This is a time chart relating to overvoltage protection control and winding short-circuit control of the power converter according to the fifth embodiment. [Figure 14] This is a time chart relating to overvoltage protection control and winding short-circuit control of a power converter according to the sixth embodiment. [Figure 15] This is a configuration diagram of the power converter according to the seventh embodiment. [Figure 16] This is a diagram showing the configuration of an air conditioner according to the eighth embodiment. [Modes for carrying out the invention]

[0009] ≪First Embodiment≫ <Configuration of a power converter> Figure 1 is a diagram showing the configuration of the power converter 100 according to the first embodiment. The power conversion device 100 shown in Figure 1 is a device that converts AC power supplied from an AC power source E1 into DC power, and then converts this DC power back into a predetermined AC power for output to a motor M1. The motor M1 may be, for example, a permanent magnet synchronous motor, or it may be of another type. As shown in Figure 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 the AC voltage applied from the three-phase AC power supply E1 into a DC voltage (pulsating DC voltage). In the example in Figure 1, the converter circuit 10 uses a full-wave rectifier circuit with six diodes D1 to D6 connected in a bridge configuration. A switching type converter may be used instead of the converter circuit 10 shown in Figure 1. The output side of the converter circuit 10 is connected to the inverter circuit 50 via the positive DC line K1 and also via the negative DC line K2.

[0011] The smoothing capacitor 20 is an element that smooths 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 can be used as such a smoothing capacitor 20.

[0012] Generally, film capacitors are smaller in size (volume) than large-capacity electrolytic capacitors. Therefore, by using a film capacitor as the smoothing capacitor 20, the circuit board (not shown) of the power conversion device 100 can be miniaturized. Film capacitors also have the advantage of a longer lifespan compared to electrolytic capacitors. Furthermore, since insulating plastic film is used as the dielectric in film capacitors, 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 malfunction in the film capacitor.

[0013] However, if a small-capacity film capacitor is used, taking into account the cost per unit of capacitance, the voltage of the film capacitor will be prone to fluctuations in response to changes in the amount of stored energy. 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 stops, the DC voltage E of the smoothing capacitor 20 will fluctuate. dc The voltage rises sharply. Therefore, by providing an overvoltage protection circuit 40, the DC voltage E of the smoothing capacitor 20 rises sharply. dc This is designed to suppress the rise in voltage. Note that the type of smoothing capacitor 20 is not limited to film capacitors; other types of capacitors, such as electrolytic capacitors, may also be used.

[0014] The DC voltage detection unit 30 detects the DC voltage E across the smoothing capacitor 20. dc This unit detects the DC voltage E between a pair of DC lines K1 and K2. dc It detects the DC voltage E across the smoothing capacitor 20. dc The voltage is divided by a series connection of multiple resistive elements (not shown), and the DC voltage E is calculated based on the voltage division ratio and the voltages of predetermined resistive elements. dc The detection of the DC voltage may be configured to detect it. The moment-by-moment detection value of the DC voltage detection unit 30 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 overvoltage and is connected in parallel to the smoothing capacitor 20. As shown in Figure 1, the overvoltage protection circuit 40 has a series connection of a switching element 41 and a resistor 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 the flow or interruption of current through the resistive element 42. Examples of such switching elements 41 include IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). The resistive 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 controls the DC voltage E across the smoothing capacitor 20. dc This is a power converter that converts the current into a predetermined AC voltage and applies this AC voltage to the motor M1. The inverter circuit 50 has a configuration in which the first, second, and third legs 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 and third legs). Switching elements S1 to S6 that make up the first, second, and third legs can be, for example, IGBTs or MOSFETs.

[0018] From another perspective, the inverter circuit 50 includes upper arm switching elements S1, S3, and S5 connected to the high-potential DC line K1, and lower arm switching elements S2, S4, and S6 connected to the low-potential DC line K2. As shown in Figure 1, the connection point between the upper arm switching element S1 and the lower arm switching element S2 of the first leg is connected via wiring to the U-phase winding (not shown) of the motor M1. Similarly, the connection point between the upper arm switching element S3 and the lower arm switching element S4 of the second leg is connected via wiring to the V-phase winding (not shown) of the motor M1. The connection point between the upper arm switching element S5 and the lower arm switching element S6 of the third leg is connected via wiring to the W-phase winding (not shown) of the motor M1.

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

[0020] The inverter control circuit 61 controls the DC voltage E dc This circuit controls the inverter circuit 50 to a predetermined state based on detected values, etc. For example, an MCU (Micro Controller Unit) is used as such an inverter control circuit 61. Although not shown in the diagram, the MCU is composed of electronic circuits including a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and various interfaces. It reads the program stored in the ROM, loads it into the RAM, and the CPU executes 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 the on / off states of the switching elements S1 to S6 at a predetermined timing based on PWM control (Pulse Width Modulation). This AC voltage is applied to each winding of the U-phase, V-phase, and W-phase of the motor M1.

[0022] The overvoltage protection control circuit 62 controls the overvoltage protection circuit 40 in a predetermined manner based on the detected value of the DC voltage E dc . Specifically, when the DC voltage E dc of the smoothing capacitor 20 reaches a predetermined value after the inverter circuit 50 stops, the overvoltage protection control circuit 62 switches the switching element 41 to the on state. Such control is referred to as "overvoltage protection control". As the overvoltage protection control circuit 62, an analog electronic circuit including a comparator (not shown) may be used, or a microcomputer may be used. The inverter control circuit 61 and the overvoltage protection control circuit 62 are collectively referred to as the control unit 60.

[0023] <Regarding Suppression of DC Voltage> For example, immediately after the inverter circuit 50 stops, the rotor of the motor M1 rotates by inertia for a while, so the motor M1 functions as a generator and a regenerative current is generated. If this regenerative current flows directly into the smoothing capacitor 20, the DC voltage E dc of the smoothing capacitor 20 increases. In particular, when a small-capacity film capacitor is used as the smoothing capacitor 20, the DC voltage E dc rapidly increases as the stored charge increases. Therefore, in the first embodiment, by providing the overvoltage protection circuit 40, the increase in the DC voltage E dc is suppressed, and the smoothing capacitor 20 is protected from overvoltage.

[0024] Note that the DC voltage E dcAnother 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 arm, thereby short-circuiting the U, V, and W phase windings. This type of control is called "winding short-circuit control." When winding short-circuit control is performed after the inverter circuit 50 has stopped, regenerative current circulates through the switched elements and three-phase windings of the ON state of either 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, resulting in a DC voltage E dc This can suppress the rise.

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

[0026] Figure 2B is an explanatory diagram showing another example of winding short-circuit control in the power converter 100. In the example shown in Figure 2B, as winding short-circuit control, the inverter control circuit 61 (see Figure 1) turns on the switching elements S1, S3, and S5 of the upper arm while turning off the switching elements S2, S4, and S6 of the lower arm. When winding short-circuit control is performed when regenerative current is generated in the motor M1 immediately after the inverter circuit 50 stops, the regenerative current circulates through the switching elements S1, S3, and S5 of the upper arm and the three-phase winding of the motor M1.

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

[0028] As described above, winding short-circuit control (see Figures 2A and 2B) is performed after the inverter circuit 50 stops, which suppresses the rise 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 any special overvoltage protection control, an excessive current may flow through 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. Also, if winding short-circuit control is stopped while the motor M1 is rotating at a high speed without any special overvoltage protection control, the regenerative current from the motor M1 will flow into the smoothing capacitor 20, causing the DC voltage E dc It will rise significantly.

[0029] Therefore, in the first embodiment, when the control unit 60 stops the inverter circuit 50, it performs overvoltage protection control for a predetermined time, and then switches to winding short-circuit control (see Figures 2A and 2B). This suppresses excessive current flow in the inverter circuit 50 while controlling the DC voltage E dc This can suppress the rise in temperature. In addition, by shortening the time during which regenerative current flows through the resistive element 42 (limiting it to a predetermined time), the amount of heat generated by the resistive element 42 can be reduced.

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

[0031] In step S101 of Figure 3, the control unit 60 stops the switching operation of the inverter circuit 50 based on PWM control using the inverter control circuit 61. Even after the switching operation stops, the rotor of the motor M1 continues to rotate due to inertia for a while, so the motor M1 functions as a generator. This regenerative current flows into the smoothing capacitor 20 via the DC line K1, causing the DC voltage E of the smoothing capacitor 20 to decrease. dc It will rise.

[0032] In step S102, the control unit 60 determines the DC voltage E of the smoothing capacitor 20. dc It is determined whether the value is greater than or equal to a predetermined value V1. Here, the predetermined value V1 is a voltage threshold that serves as the criterion for deciding 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 of the smoothing capacitor 20 dc If the value is less than the predetermined value V1 (S102: No), the control unit 60 repeats the determination process in step S103. Also, in step S102, the DC voltage E of the smoothing capacitor 20 dc If the value is greater than or equal to a predetermined value V1 (S102: Yes), the control unit 60 proceeds to step S103.

[0034] In step S103, the control unit 60 performs (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 resistor element 42, and the regenerative energy is consumed (converted into thermal energy) in the resistor element 42. As a result, the inflow of 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 rise.

[0035] Next, in step S104, the control unit 60 performs a predetermined time t onThe control unit 60 determines whether the elapsed time from the start of the overvoltage protection control has elapsed for a predetermined time t. on It is determined whether or not the predetermined time t has been reached. on This is a time threshold that serves as the criterion for deciding whether or not to initiate winding short-circuit control, and it is set in advance.

[0036] Furthermore, the longer the elapsed time from the start of overvoltage protection control, the longer the time that the regenerative energy of the motor M1 is consumed as thermal energy by the resistor element 42, and consequently the cumulative heat generated by the resistor element 42 (the sum of successive heat generated values) also increases. Therefore, in the first embodiment, the elapsed time from the start of overvoltage protection control is used as a "predetermined state variable" that has a correlation with the cumulative heat generated by the resistor element 42 associated with 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 in step S104 is not reached (S104: No), the control unit 60 returns to step S103. In this case, the overvoltage protection control continues. Also, in step S104, the elapsed time since the start of the overvoltage protection control is a predetermined time t. on If this condition is reached (S104: Yes), the control unit 60 proceeds to step S105.

[0038] In step S105, the control unit 60 terminates the 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 off state. As a result, the time during which current flows through the resistive element 42 of the overvoltage protection circuit 40 is predetermined time t. on Because this is restricted, the amount of heat generated in the resistive element 42 can be reduced. Therefore, in addition to shortening the lifespan of the resistive element 42, the thermal impact on surrounding circuit components can be suppressed.

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

[0040] For example, when winding short-circuit control is performed, the regenerative current of motor M1 circulates through the ON-state switching elements and three-phase windings of the inverter circuit 50. Furthermore, the regenerative energy of motor M1 is consumed as work done against the rotational resistance of motor M1. Therefore, during winding short-circuit control, very little regenerative current flows into the smoothing capacitor 20.

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

[0042] Furthermore, the faster the rotational speed of the motor M1, the larger the regenerative current tends to be immediately after the inverter circuit 50 stops. Therefore, the inverter control circuit 61 determines whether or not to start winding short-circuit control based on a predetermined time t, which is the criterion for deciding whether or not to start winding short-circuit control, depending on the rotational speed of the motor M1 when the inverter circuit 50 stops. on The threshold value of the predetermined state variable is increased. This suppresses the flow of excessive current into the inverter circuit 50 during winding short-circuit control.

[0043] Figure 4 shows the timing charts for overvoltage protection control and winding short-circuit control (see also Figure 1 as appropriate). Note that the horizontal axis of each time chart in Figure 4 represents time. The vertical axis of each time chart in Figure 4 represents, from top to bottom, the DC voltage E of the smoothing capacitor 20. dcThis shows the cumulative heat generated by the resistive 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 in Figure 4, after the switching operation of the inverter circuit 50 based on PWM control stops (S101 in Figure 3), the voltage across 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 across the smoothing capacitor 20 rises. dc The voltage has reached a 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 resistor element 42, causing the DC voltage E dc This can suppress the rise.

[0045] After switching the overvoltage protection circuit 40 to the ON state, a predetermined time t on If the specified time has elapsed (S104 in Figure 3: Yes), at time t3, the overvoltage protection control circuit 62 switches the overvoltage protection circuit 40 to the OFF state (S105). As a result, no current flows through the overvoltage protection circuit 40, and thus the heat generation of the resistive element 42 can be suppressed.

[0046] In the example shown in Figure 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 Figure 3). Specifically, the inverter control circuit 61 turns all phases of the switching elements S1, S3, and S5 of the upper arm OFF, while turning all phases of the switching elements S2, S4, and S6 of the lower arm ON (see Figure 2A). As a result, the regenerative current of the motor M1 circulates through the ON state of the switching elements S2, S4, and S6 and the three-phase winding. Therefore, during the execution of winding short-circuit control, regenerative current hardly flows into the smoothing capacitor 20.

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

[0048] <Effects> According to the first embodiment, after the inverter circuit 50 stops, the DC voltage E of the smoothing capacitor 20 dc When the voltage reaches a predetermined value V1, overvoltage protection control is executed. Therefore, even when a small-capacity film capacitor is used as the smoothing capacitor 20, the regenerative current of the motor M1 reduces the DC voltage E dc This helps to prevent the voltage from becoming too high. Furthermore, since there is no particular need to provide a detector to detect the current flowing through the resistive element 42, the manufacturing cost of the power converter 100 can be reduced.

[0049] Furthermore, a predetermined time t from the start of overvoltage protection control on Since winding short-circuit control is initiated when the specified time has elapsed, the amount of heat generated in the resistive element 42 of the overvoltage protection circuit 40 can be reduced. Therefore, the distance between the resistive element 42 and surrounding circuit components can be shortened during the design phase of the power converter 100, which can alleviate constraints on the circuit pattern and also allow for miniaturization of the circuit board.

[0050] Furthermore, since there is no particular need to start winding short-circuit control at the same time as stopping the inverter circuit 50, it is possible to suppress excessive current flowing through the inverter circuit 50. Therefore, according to the first embodiment, a highly reliable power converter 100 can be provided.

[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 the start of overvoltage protection control. Other aspects (such as the configuration of the power converter 100: see Figure 1) are the same as in the first embodiment. Therefore, only the differences from the first embodiment will be described, and the overlapping parts will be omitted.

[0052] Figure 5 is a flowchart showing the processing of the control unit of the power converter according to the second embodiment (see also Figure 1 as appropriate). Steps S101 to S103, S105, and S106 in Figure 5 are the same as those described in the first embodiment (see Figure 3). That is, after the control unit 60 stops the switching operation of the inverter circuit 50 (S101), the DC voltage E dc If the value becomes greater than or equal to a predetermined value V1 (S102: Yes), overvoltage protection control is executed (S103).

[0053] Next, in step S204, the control unit 60 controls the DC voltage E dc The amount of decrease is the predetermined value E ON The control unit 60 determines whether the DC voltage E is above or below the specified value after the start of overvoltage protection control. dc When the change reaches a peak value from an upward trend and then begins to decline, the amount of decrease from the peak value is a predetermined value E. ON Determine whether or not the above predetermined value E ON This is a threshold value (absolute value) of the voltage drop that serves as the criterion for deciding whether or not to initiate winding short-circuit control, and it is set in advance.

[0054] Note that the DC voltage E when overvoltage protection control is performed dc The greater the decrease in the DC voltage, the greater the cumulative heat generated by the resistive element 42 tends to be. Therefore, in the second embodiment, the following state quantity is used as a "predetermined state quantity" that has a correlation with the cumulative heat generated by the resistive element 42 due to overvoltage protection control. That is, as the "predetermined state quantity", the DC voltage E after the start of overvoltage protection control is set. dc The calculation uses the amount of decrease from the peak value when the change reaches a peak value from an upward trend and then begins to decline.

[0055] In step S204, the DC voltage E dc The amount of decrease is the predetermined value E ON If the value is less than (S204: No), the control unit 60 returns to step S103. In this case, overvoltage protection control continues. Also, in step S204, the DC voltage Edc The amount of decrease is the predetermined value E ON If the above is true (S204: Yes), the control unit 60 proceeds to step S105. Then, the control unit 60 terminates the overvoltage protection control (S105) and performs winding short circuit control (S106). Thus, the DC voltage E after the start of overvoltage protection control dc Based on the decrease in (predetermined state quantity), winding short-circuit control is initiated.

[0056] Furthermore, the inverter control circuit 61 determines whether or not to start winding short-circuit control based on a predetermined value E, which is the criterion for determining whether or not to start winding short-circuit control, depending on the rotational speed of the motor M1 when stopping the inverter circuit 50. ON It is advisable to increase the threshold value of the predetermined state variable. This will prevent excessive current from flowing through the inverter circuit 50.

[0057] Figure 6 shows the timing charts for overvoltage protection control and winding short-circuit control (see also Figure 1 as appropriate). Note that the horizontal and vertical axes of each time chart in Figure 6 are the same as those in Figure 4, so no explanation is given. In the example in Figure 6, the DC voltage E dc When the change from rising to a peak value E0 and then begins to fall, the amount of decrease from the peak value E0 is a predetermined value E at time t3. ON The DC voltage E has reached (S204: Yes in Figure 5). In this case, the control unit 60 terminates the overvoltage protection control (S105) and performs winding short circuit control (S106). As a result, no current flows through the overvoltage protection circuit 40, so the DC voltage E dc This method suppresses the rise in temperature while reducing the cumulative heat generated by the resistive element 42.

[0058] <Effects> According to the second embodiment, DC voltage E dc The amount of decrease is the predetermined value E ON When it reaches this point, winding short-circuit control is initiated. Also, the greater the heat generated by the resistive element 42, the greater the DC voltage E dc Since the decrease in voltage also tends to be greater, winding short-circuit control can be initiated at the appropriate timing.

[0059] ≪Third Embodiment≫ The third embodiment differs from the first embodiment in that winding short-circuit control is initiated based on the integrated value of the DC voltage drop after the start of overvoltage protection control. Other aspects (such as the configuration of the power converter 100: see Figure 1) are the same as in the first embodiment. Therefore, the differences from the first embodiment will be explained, and the overlapping parts will be omitted.

[0060] Figure 7 is a flowchart showing the processing of the control unit of the power converter according to the third embodiment (see also Figure 1 as appropriate). Note that steps S101 to S103, S105, and S106 in Figure 7 are the same as those described in the first embodiment (see Figure 3). That is, after the control unit 60 stops the switching operation of the inverter circuit 50 (S101), the DC voltage E dc If the value becomes greater than or equal to a predetermined value V1 (S102: Yes), overvoltage protection control is executed (S103).

[0061] Next, in step S304, the control unit 60 controls the DC voltage E dc The cumulative value (sequential sum) of the decrease is a predetermined value E dec The control unit 60 determines whether the DC voltage E is above or below the specified value after the start of overvoltage protection control. dc When the change from an upward trend reaches a peak value and then begins to decline, the cumulative value of the decrease from the peak value is a predetermined value E. dec Determine whether or not the above predetermined value E dec This is a threshold value of the cumulative voltage drop (absolute value) that serves as the criterion for deciding whether or not to initiate winding short-circuit control, and it is set in advance.

[0062] Note that the DC voltage E during overvoltage protection control is dc The larger the cumulative value of the decrease in voltage, the greater the cumulative heat generated by the resistive element 42 tends to be. Therefore, in the third embodiment, the following state quantity is used as a "predetermined state quantity" that has a correlation with the cumulative heat generated by the resistive element 42 due to overvoltage protection control. That is, after the start of overvoltage protection control, the DC voltage E dcThe system uses the cumulative value of the decrease from the peak value when the change reaches a peak value from an upward trend and then begins to decline as the "predetermined state variable."

[0063] In step S304, the DC voltage E dc The cumulative value of the decrease is the predetermined value E dec If the value is less than (S304: No), the control unit 60 proceeds to step S305. In step S305, the control unit 60 controls the DC voltage E dc It is determined whether or not the predetermined value V2 is less than or equal to the predetermined value V2. (Second prescribed value) This is a voltage threshold that serves as the criterion for determining whether or not to interrupt the overvoltage protection control, and is the predetermined value V1 mentioned above. (First predetermined value) It is pre-set to a value lower than that.

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

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

[0066] Then, the control unit 60 terminates the overvoltage protection control (S105) and performs winding short circuit control (S106). Thus, in the third embodiment, the DC voltage E after the termination of the overvoltage protection control is dcBased on the cumulative value of the decrease in the DC voltage E, the inverter control circuit 61 initiates winding short-circuit control. dc The cumulative value of the decrease may be reset when winding short-circuit control starts.

[0067] Furthermore, the flowchart shown in Figure 7 is just one example and is not limited to it. For example, DC voltage E dc Based on the comparison result with predetermined values ​​V1 and V2, the control unit 60 alternately switches the overvoltage protection circuit 40 on and off, while simultaneously controlling the DC voltage E dc The cumulative value of the decrease and the predetermined value E dec You may repeat the comparison with the DC voltage E. dc The cumulative value of the decrease is the predetermined value E dec If the above occurs, the control unit 60 may execute the processes in steps S105 and S106 as an interrupt process. The same effect can be achieved with this type of processing.

[0068] Furthermore, the inverter control circuit 61 determines whether or not to start winding short-circuit control based on a predetermined value E, which is the criterion for determining whether or not to start winding short-circuit control, depending on the rotational speed of the motor M1 when stopping the inverter circuit 50. dec It is advisable to increase the threshold value of the predetermined state variable. This will prevent excessive current from flowing through the inverter circuit 50.

[0069] Furthermore, during winding short-circuit control, the DC voltage E dc Even if the voltage reaches a predetermined value V1 again (i.e., even if the conditions for starting overvoltage protection control are met again), the control unit 60 may choose not to start overvoltage protection control. This suppresses the increase in the cumulative heat generated by the resistive element 42.

[0070] Figure 8 shows the timing charts for overvoltage protection control and winding short-circuit control (see also Figure 1 as appropriate). Note that the vertical axis of the second time chart from the top of the page in Figure 8 represents the DC voltage E dcIt is the integrated value of the decrease amount. Regarding the vertical axis of the remaining time chart in FIG. 8, since it is the same as that in FIG. 4, the description thereof is omitted.

[0071] In the example of FIG. 8, with the stop of the inverter circuit 50, the DC voltage E reaches a predetermined value V1 at time t2 (S102: Yes in FIG. 7), and the overvoltage protection circuit 40 is switched to the ON state (S103). At time t3 thereafter, since the DC voltage E has dropped to the predetermined value V2 (S305: Yes), the overvoltage protection circuit 40 is switched to the OFF state once (S306). Note that at the time of time t3, since the integrated value of the decrease amount of the DC voltage E has not reached the predetermined value E (S304: No), the winding short-circuit control has not yet started.

[0072] After time t3 in FIG. 8, the regenerative energy of the motor M1 causes the DC voltage E to rise again, and at time t4, the DC voltage E reaches the predetermined value V1 (S102: Yes in FIG. 7), so the overvoltage protection circuit 40 is switched to the ON state again (S103). At time t5 thereafter, since the integrated value of the decrease amount of the DC voltage E has reached the predetermined value E (S304: Yes), the control unit 60 switches the overvoltage protection circuit 40 to the OFF state (S105) and starts the winding short-circuit control (S106).

[0073] <Effect> According to the third embodiment, the winding short-circuit control is started at the timing when the integrated value of the decrease amount of the DC voltage E reaches the predetermined value E. Here, the larger the integrated value of the decrease amount of the DC voltage E, the larger the integrated heat generation amount of the resistance element 42, and the smaller the regenerative energy that has not been consumed. 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 is different from the first embodiment in that the power conversion device 100A (see FIG. 9) includes a current detector 70. Further, the fourth embodiment is different from the first embodiment in that winding short-circuit control is started when the detection value of the current detector 70 reaches a predetermined value. Note that other aspects are the same as those of the first embodiment. Therefore, the parts different from the first embodiment will be described, and the description of the overlapping parts will be omitted.

[0075] FIG. 9 is a configuration diagram of the 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 each configuration described in the first embodiment (see FIG. 1). The current detector 70 detects the current flowing through the resistance element 42 and is connected in series to the resistance element 42 and the switching element 41. As such a current detector 70, for example, a shunt resistor or a current sensor is used. The detection value of the current detector 70 at each moment is output to the control unit 60.

[0076] FIG. 10 is a flowchart showing the processing of the control unit of the power conversion device (also refer to 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 dc executes overvoltage protection control when the DC voltage E is equal to or higher than a predetermined value V1 (S102: Yes) (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 higher 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 overvoltage protection control becomes equal to or higher than a predetermined value I. ON The predetermined value I described above is a current threshold value that serves as a criterion for determining whether to start winding short-circuit control and is set in advance. ON

[0078] Furthermore, the larger the current flowing through the resistor 42 when overvoltage protection control is performed, the greater the cumulative heat generated by the resistor 42 tends to be. Therefore, in the fourth embodiment, the magnitude of the current flowing through the resistor 42 after the start of overvoltage protection control is used as a "predetermined state variable" that has a correlation with the cumulative heat generated by the resistor 42 due to overvoltage protection control.

[0079] In step S404, the detected current value I is a predetermined value I ON If the value is less than (S404: No), the control unit 60 returns to step S103. In this case, overvoltage protection control continues. Also, in step S404, if the current detection value I is less than the predetermined value I ON If the above is true (S404: Yes), the control unit 60 proceeds to step S105. Then, the control unit 60 terminates the overvoltage protection control (S105) and performs winding short-circuit control (S106). In this way, winding short-circuit control is started based on the magnitude of the current flowing through the resistive element 42 (a predetermined state quantity) after the start of overvoltage protection control.

[0080] Furthermore, the inverter control circuit 61 determines whether or not to start winding short-circuit control based on a predetermined value I, which is the criterion for determining whether or not to start winding short-circuit control, depending on the rotational speed of the motor M1 when stopping the inverter circuit 50. ON It is advisable to increase the threshold value of the predetermined state variable. This will prevent excessive current from flowing through the inverter circuit 50.

[0081] Figure 11 is a time chart for overvoltage protection control and winding short-circuit control of the power converter (see also Figure 9 as appropriate). Note that the vertical axis of the second time chart from the top of the page in Figure 11 represents the current detected value in the current detector 70. The vertical axes of the remaining time charts in Figure 11 are the same as those in Figure 4, so their explanation is omitted.

[0082] In the example shown in Figure 11, the current detected by the current detector 70 reaches a predetermined value I at time t3. ONThe DC voltage E is reached (S404 in Figure 10: Yes). In this case, the overvoltage protection control circuit 62 switches the overvoltage protection circuit 40 to the OFF state (S105). As a result, current stops flowing through the overvoltage protection circuit 40, and thus the heat generation of the resistive element 42 can be suppressed. In the example in Figure 10, winding short-circuit control is started at time t3 when the overvoltage protection circuit 40 is switched to the OFF state (S106). As a result, the DC voltage E dc This allows for the consumption of regenerative energy from motor M1 while suppressing the rise in voltage.

[0083] <Effects> According to the fourth embodiment, the detected value of the current flowing through the resistive element 42 is a predetermined value I ON When this condition is reached, winding short-circuit control is initiated. Furthermore, since the amount of heat generated by the resistive element 42 tends to increase with larger current flowing through it, winding short-circuit control can be initiated 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 the integrated value of the current flowing through the resistive element 42 (see Figure 9). Other aspects (such as the configuration of the power converter 100A: see Figure 9) are the same as in the fourth embodiment. Therefore, the differences from the fourth embodiment will be explained, and the overlapping parts will be omitted.

[0085] Figure 12 is a flowchart showing the processing of the control unit of the power converter according to the fifth embodiment (see also Figure 9 as appropriate). Steps S101 to S103, S105, and S106 in Figure 12 are the same as those described in the first embodiment (see Figure 3). That is, after the control unit 60 stops the switching operation of the inverter circuit 50 (S101), the DC voltage E dc If the value is greater than or equal to a predetermined value V1 (S102: Yes), overvoltage protection control is executed (S103).

[0086] Next, in step S504, the control unit 60 checks if the integrated value (successive sum) of the current detection value I is a predetermined value I decThe control unit 60 determines whether the value of the current flowing through the resistor 42 after the start of overvoltage protection control is greater than or equal to a predetermined value I. dec Determine whether or not the above predetermined value I dec This is a threshold value of the integrated current that serves as the criterion for deciding whether or not to initiate winding short-circuit control, and it is set in advance.

[0087] Furthermore, when overvoltage protection control is performed, the larger the integrated value of the current flowing through the resistor element 42, the greater the integrated heat generated by the resistor element 42 tends to be. Therefore, in the fifth embodiment, the integrated value of the current flowing through the resistor element 42 after the start of overvoltage protection control is used as a "predetermined state variable" that has a correlation with the integrated heat generated by the resistor element 42 due to overvoltage protection control.

[0088] After the process in step S504 is completed, the control unit 60 terminates 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 of the current flowing through the resistor element 42 (a predetermined state quantity) after the start of the overvoltage protection control. The integrated value of the current flowing through the resistor element 42 may be reset when the winding short-circuit control is started.

[0089] Furthermore, the inverter control circuit 61 determines whether or not to start winding short-circuit control based on a predetermined value I, which is the criterion for determining whether or not to start winding short-circuit control, depending on the rotational speed of the motor M1 when stopping the inverter circuit 50. dec It is advisable to increase the threshold value of the predetermined state variable. This will prevent excessive current from flowing through the inverter circuit 50.

[0090] Figure 13 shows the timing charts for overvoltage protection control and winding short-circuit control (see also Figure 9 as appropriate). Note that 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 the 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 is omitted.

[0091] In the example in Figure 13, while the overvoltage protection circuit 40 is ON (times t2 to t3), current flows through the current detector 70, causing the moment-by-moment current detection value to be greater than zero, resulting in a monotonically increasing cumulative value of the current detection value. The cumulative value of the current detection value then increases to a predetermined value I dec If this condition is reached (S504: Yes in Figure 12), the overvoltage protection circuit 40 is switched to the OFF state at time t3 (S105), and winding short-circuit control is started (S106).

[0092] <Effects> According to the fifth embodiment, the integrated value of the detected current is a predetermined value I dec Winding short-circuit control is initiated when the current reaches a certain point. Here, the larger the integrated value of the detected current, the greater the integrated heat generated by the resistive element 42, and the smaller the amount of regenerative energy that has not been fully consumed tends to be. Therefore, according to the fifth embodiment, winding short-circuit control can be initiated at an even 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 the overvoltage protection control is completed. Other aspects (such as the configuration of the power converter 100: see Figure 1) are the same as in the first embodiment. Therefore, the differences from the first embodiment will be explained, and the overlapping parts will be omitted.

[0094] Figure 14 is a time chart relating to overvoltage protection control and winding short-circuit control of the power converter according to the sixth embodiment (see also Figure 1 as appropriate). Note that the horizontal and vertical axes of each time chart in Figure 14 are the same as those in Figure 4, so no explanation is provided. In the example in Figure 14, the DC voltage E dc When the voltage reaches a predetermined value V1 at time t2, the overvoltage protection circuit 40 is switched to the ON state, and for the period from time t2 to t4 (i.e., the predetermined time t ONDuring this period, the overvoltage protection circuit 40 remains in the ON state. Meanwhile, the switching elements S2, S4, and S6 of the lower arm 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 at which the overvoltage protection control ends (time t4).

[0095] <Effects> According to the sixth embodiment, since the winding short-circuit control is started before the overvoltage protection control ends, the execution times of the overvoltage protection control and the winding short-circuit control overlap in part. As a result, the DC voltage E of the smoothing capacitor 20 dc This can speed up the rate of decrease.

[0096] ≪Seventh Embodiment≫ The seventh embodiment differs from the first embodiment in the configuration of the overvoltage protection circuit 40B (see Figure 15), but otherwise it is the same as the first embodiment. Therefore, the parts that differ from the first embodiment will be described, and the overlapping parts will be omitted from the explanation.

[0097] Figure 15 is a diagram showing the configuration of the power converter 100B according to the seventh embodiment. As shown in Figure 15, the overvoltage protection circuit 40B of the power converter 100B includes a first parallel connection, which consists of a resistor 42, a capacitor 43, and a diode 44 connected in parallel. Furthermore, the overvoltage protection circuit 40B includes a second parallel connection, which consists of a switching element 41, a resistor 45, and a diode 46 connected in parallel. The first parallel connection and the second parallel connection are connected in series. 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.

[0098] The capacitor 43 shown in Figure 15 is an element that stores charge when the switching element 41 is turned on, and is connected in parallel with the resistive element 42, etc. For example, an electrolytic capacitor can be used as such a capacitor 43. Note that the circuit configuration shown in Figure 15 is also included in the fact that the overvoltage protection circuit 40B has a series connection of the switching element 41 and the resistive element 42.

[0099] Diodes 44 and 46 are elements that form a current path when a reverse voltage is applied to the switching element 41. One diode 44 has its cathode connected to the positive DC line K1 and its anode connected to the negative DC line K2 via a second parallel connector. The other diode 46 has its anode connected to the negative DC line K2 and its cathode connected to the positive DC line K1 via a first parallel connector. The resistor 45 is a high-impedance resistor that stabilizes 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 this power is consumed by the resistive element 42. Therefore, abrupt changes in the current flowing through the resistive element 42 can be suppressed, and the temperature rise of the resistive element 42 can also be suppressed. In addition, by providing diodes 44 and 46, a current path can be formed when a reverse voltage is applied to the switching element 41.

[0101] ≪Eighth Embodiment≫ In the eighth embodiment, an air conditioner W1 (see Figure 16) equipped with a power converter 100 (see Figure 1) having the configuration described in the first embodiment will be described. Note that the configuration and processing details of the power converter 100 are the same as in the first embodiment, so their description will be omitted.

[0102] Figure 16 is a diagram showing the configuration of the air conditioner W1 according to the eighth embodiment. The solid arrows in Figure 16 indicate the flow of refrigerant during the heating cycle. Furthermore, the dashed arrows in Figure 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 Figure 16, the air conditioner W1 has an outdoor unit U1 which includes 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 has an indoor unit U2 which includes an indoor heat exchanger 96 and an indoor fan 97.

[0103] Although not shown in Figure 16, the air conditioner W1 is equipped with a power converter 100 (see Figure 1) having the same configuration as in the first embodiment. The power converter 100 is mounted on the circuit board (not shown) of the outdoor unit U1.

[0104] The compressor 91 is a device that compresses low-temperature, low-pressure gaseous refrigerant and discharges it as high-temperature, high-pressure gaseous refrigerant. Although not shown in Figure 16, an accumulator for separating the refrigerant into gas and liquid is connected to the suction side of the compressor 91. The motor M1, which is the driving source for the compressor 91, is connected to the output side of the inverter circuit 50 (see Figure 1) of the power conversion device 100 (see Figure 1).

[0105] The outdoor heat exchanger 92 is a heat exchanger in which heat exchange takes place between the refrigerant flowing through its heat transfer tubes and the outside air supplied by the outdoor fan 93. The outdoor fan 93 is a fan that supplies outside air to the outdoor heat exchanger 92. The outdoor fan 93 has an outdoor fan motor 93a as its driving 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" (either the outdoor heat exchanger 92 or the indoor heat exchanger 96). The refrigerant reduced in pressure by the expansion valve 94 is then led to the "evaporator" (the other of the outdoor heat exchanger 92 or the indoor heat exchanger 96). The indoor heat exchanger 96 is a heat exchanger in which heat exchange takes place between the refrigerant flowing through its heat transfer tubes (not shown) and the indoor air (air from the air-conditioned room) supplied by the indoor fan 97. The indoor fan 97 is a fan that supplies indoor air to the indoor heat exchanger 96. The indoor fan 97 is equipped with an indoor fan motor 97a, which is its driving source, and is installed near the indoor heat exchanger 96.

[0107] The four-way valve 95 is a valve that switches the flow path of the refrigerant according to the operating mode of the air conditioner W1. For example, during cooling operation (see dashed arrow in Figure 16), the refrigerant circulates sequentially through the compressor 91, outdoor heat exchanger 92 (condenser), expansion valve 94, and indoor heat exchanger 96 (evaporator). Similarly, during heating operation (see solid arrow in Figure 16), the refrigerant circulates sequentially through the compressor 91, indoor heat exchanger 96 (condenser), expansion valve 94, and outdoor heat exchanger 92 (evaporator). The air that has exchanged heat with the refrigerant flowing through the indoor heat exchanger 96 is then blown out from the indoor unit U2 into the air conditioning room.

[0108] <Effects> According to the eighth embodiment, the air conditioner W1 is equipped with a power converter 100 (see Figure 1) having the same configuration as in the first embodiment, thereby increasing the reliability of the air conditioner W1.

[0109] ≪Variations≫ Although the power converters 100, 100A, 100B and the air conditioner W1 related to this disclosure have been described in detail in each embodiment, the invention is not limited to these descriptions, and various modifications can be made. For example, in the first embodiment (see Figure 4), the case in which winding short-circuit control is started at the same time as the overvoltage protection control is completed was described, but this is not the only case. That is, winding short-circuit control may be started after a predetermined time has elapsed from the time the overvoltage protection control is completed. The same applies to the second to fifth embodiments.

[0110] Furthermore, while each embodiment describes a case where the overvoltage protection control circuit 62 (see Figure 1) is composed of an analog electronic circuit including a comparator or a microcomputer, it is not limited to these cases. For example, the overvoltage protection control circuit 62 may be configured by combining a predetermined analog electronic circuit and a microcomputer. Furthermore, the configurations of the overvoltage protection circuits 40 and 40B described in each embodiment (see Figures 1 and 15) are merely examples and are not limited thereto. In other words, any circuit that has the function of protecting the smoothing capacitor 20 from overvoltage may be used.

[0111] Furthermore, although the embodiments described the case where the AC power supply E1 (see Figure 1) is a three-phase AC power supply, the invention is not limited to this, and a single-phase AC power supply may also be used. Furthermore, although each embodiment has described a configuration in which no reactors are specifically provided on the DC lines K1 and K2 (see Figure 1), the configuration is not limited to this. That is, a reactor may be provided on at least one of the DC lines K1 and K2. For example, in the positive DC line K1, a reactor may be provided between the connection point between the DC line K1 and the smoothing capacitor 20 and the converter circuit 10 (the same applies to the reactor on the negative DC line K2).

[0112] Furthermore, although each embodiment has described the case where there is one smoothing capacitor 20 (see Figure 1), it is not limited to this. That is, a smoothing capacitor may be formed by multiple 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 DC lines K1 and K2) when the capacitances of the multiple capacitors described above are combined and considered as a single smoothing capacitor. The same applies to the second to seventh embodiments.

[0113] Furthermore, in the seventh embodiment, the overvoltage protection circuit 40B (see Figure 15) was described as comprising a first parallel connection of a resistor 42, a capacitor 43, and a diode 44, and a second parallel connection of a switching element 41, a resistor 45, and a diode 46, but it is not limited to this configuration. That is, the switching element 41 may be connected in series to the parallel connection of the resistor 42 and the capacitor 43, and the remaining elements may be omitted as appropriate.

[0114] Furthermore, each embodiment can be combined as appropriate. For example, one of the first to fifth embodiments may be combined with the sixth embodiment (see Figure 14) so ​​that winding short-circuit control is started before the overvoltage protection control ends. Alternatively, one of the first to sixth embodiments may be combined with the seventh embodiment (see Figure 15), and the overvoltage protection circuit 40B may be configured as shown in Figure 15. Furthermore, any of the first to seventh embodiments may be combined with the eighth embodiment (see Figure 16) so that the motor M1 connected to the inverter circuit 50 is used as a drive source for the compressor of the air conditioner.

[0115] Furthermore, while the eighth embodiment (see Figure 16) describes a configuration in which the power converter 100 (see Figure 1) is connected to the motor M1 of the compressor 91, the embodiment is not limited to this. For example, the power converter 100 may be connected to the outdoor fan motor 93a (see Figure 16). Alternatively, the power converter 100 may be connected to both the motor M1 of the compressor 91 and the outdoor fan motor 93a.

[0116] Furthermore, while the eighth embodiment (see Figure 16) describes a configuration in which the air conditioner W1 is equipped with a four-way valve 95, the invention is not limited to this configuration. That is, the four-way valve 85 may be omitted as appropriate, and the air conditioner may be configured for cooling only or heating only. Furthermore, the eighth embodiment (see Figure 16) can be applied to various types of air conditioning equipment, including not only room air conditioners but also commercial air conditioners and multi-split air conditioners for buildings. In addition, the eighth embodiment can be applied to other equipment such as water heaters, refrigerators, and air conditioning and water heating systems.

[0117] Furthermore, each embodiment is described in detail for the purpose of clearly illustrating this disclosure and is not necessarily limited to having all the configurations described. In addition, it is possible to add, delete, or replace some of the configurations in each embodiment with other configurations. Furthermore, the mechanisms and configurations described above are those deemed necessary for explanatory purposes and do not necessarily represent all of the mechanisms and configurations shown in the actual product. [Explanation of Symbols]

[0118] 10 Converter Circuits 20 Smoothing Capacitors 30 DC voltage detection unit 40,40B Overvoltage Protection Circuit 41 Switching elements 42 Resistor elements 43 Capacitors 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 Converter E1 AC power supply M1 Motor S1, S3, S5 Switching elements (upper arm) S2, S4, S6 switching elements (lower arm) W1 Air Conditioner

Claims

1. A converter circuit that converts AC voltage applied from an AC power source into DC voltage, A smoothing capacitor for 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 the motor, An inverter control circuit that controls the inverter circuit, The system includes an overvoltage protection circuit having a series connection of switching elements and resistive elements, and connected in parallel to the smoothing capacitor, The inverter circuit is equipped with an overvoltage protection control circuit that performs overvoltage protection control by switching the switching element to the ON state if the DC voltage of the smoothing capacitor reaches a predetermined value after the inverter circuit has stopped. After the overvoltage protection control is initiated, the inverter control circuit performs winding short-circuit control, which turns on all phases of one of the upper and lower arms of the inverter circuit while turning off all phases of the other arm. The winding short-circuit control is initiated based on a predetermined state variable that has a correlation with the cumulative heat generated by the resistive element in conjunction with the overvoltage protection control. The predetermined state quantity is the amount of decrease from the peak value when the change in the DC voltage reaches a peak value after the start of the overvoltage protection control and then begins to decrease, in a power conversion device.

2. A converter circuit that converts AC voltage applied from an AC power source into DC voltage, A smoothing capacitor for 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 the motor, An inverter control circuit that controls the inverter circuit, The system includes an overvoltage protection circuit having a series connection of switching elements and resistive elements, and connected in parallel to the smoothing capacitor, The inverter circuit is equipped with an overvoltage protection control circuit that performs overvoltage protection control by switching the switching element to the ON state if the DC voltage of the smoothing capacitor reaches a predetermined value after the inverter circuit has stopped. After the overvoltage protection control is initiated, the inverter control circuit performs winding short-circuit control, which turns on all phases of one of the upper and lower arms of the inverter circuit while turning off all phases of the other arm. The winding short-circuit control is initiated based on a predetermined state variable that has a correlation with the cumulative heat generated by the resistive element in conjunction with the overvoltage protection control. The predetermined state quantity is the cumulative value of the decrease from the peak value when the change in the DC voltage rises, reaches a peak value, and then starts to decline after the start of the overvoltage protection control, in a power converter.

3. A converter circuit that converts AC voltage applied from an AC power source into DC voltage, A smoothing capacitor for 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 the motor, An inverter control circuit that controls the inverter circuit, The system includes an overvoltage protection circuit having a series connection of switching elements and resistive elements, and connected in parallel to the smoothing capacitor, The inverter circuit is equipped with an overvoltage protection control circuit that performs overvoltage protection control by switching the switching element to the ON state if the DC voltage of the smoothing capacitor reaches a predetermined value after the inverter circuit has stopped. After the overvoltage protection control is initiated, the inverter control circuit performs winding short-circuit control, which turns on all phases of one of the upper and lower arms of the inverter circuit while turning off all phases of the other arm. The winding short-circuit control is initiated based on a predetermined state variable that has a correlation with the cumulative heat generated by the resistive element in conjunction with the overvoltage protection control. A power converter in which the predetermined state quantity is the magnitude of the current flowing through the resistive element after the start of the overvoltage protection control.

4. A converter circuit that converts AC voltage applied from an AC power source into DC voltage, A smoothing capacitor for 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 the motor, An inverter control circuit that controls the inverter circuit, The system includes an overvoltage protection circuit having a series connection of switching elements and resistive elements, and connected in parallel to the smoothing capacitor, The inverter circuit is equipped with an overvoltage protection control circuit that performs overvoltage protection control by switching the switching element to the ON state if the DC voltage of the smoothing capacitor reaches a predetermined value after the inverter circuit has stopped. After the overvoltage protection control is initiated, the inverter control circuit performs winding short-circuit control, which turns on all phases of one of the upper and lower arms of the inverter circuit while turning off all phases of the other arm. The winding short-circuit control is initiated based on a predetermined state variable that has a correlation with the cumulative heat generated by the resistive element in conjunction with the overvoltage protection control. A power converter in which the predetermined state quantity is the integrated value of the current flowing through the resistive element after the start of the overvoltage protection control.

5. A converter circuit that converts AC voltage applied from an AC power source into DC voltage, A smoothing capacitor for 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 the motor, An inverter control circuit that controls the inverter circuit, The system includes an overvoltage protection circuit having a series connection of switching elements and resistive elements, and connected in parallel to the smoothing capacitor, The inverter circuit is equipped with an overvoltage protection control circuit that performs overvoltage protection control by switching the switching element to the ON state if the DC voltage of the smoothing capacitor reaches a predetermined value after the inverter circuit has stopped. After the overvoltage protection control is initiated, the inverter control circuit performs winding short-circuit control, which turns on all phases of one of the upper and lower arms of the inverter circuit while turning off all phases of the other arm. The winding short-circuit control is initiated based on a predetermined state variable that has a correlation with the cumulative heat generated by the resistive element in conjunction with the overvoltage protection control. The inverter control circuit is a power conversion device that increases the threshold value of a predetermined state quantity, which is the criterion for determining whether or not to start the winding short-circuit control, as the rotational speed of the motor when the inverter circuit is stopped increases.

6. A converter circuit that converts AC voltage applied from an AC power source into DC voltage, A smoothing capacitor for 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 the motor, An inverter control circuit that controls the inverter circuit, The system includes an overvoltage protection circuit having a series connection of switching elements and resistive elements, and connected in parallel to the smoothing capacitor, The inverter circuit is equipped with an overvoltage protection control circuit that performs overvoltage protection control by switching the switching element to the ON state if the DC voltage of the smoothing capacitor reaches a predetermined value after the inverter circuit has stopped. After the overvoltage protection control is initiated, the inverter control circuit performs winding short-circuit control, which turns on all phases of one of the upper and lower arms of the inverter circuit while turning off all phases of the other arm. The winding short-circuit control is initiated based on a predetermined state variable that has a correlation with the cumulative heat generated by the resistive element in conjunction with the overvoltage protection control. The overvoltage protection control circuit in the power converter does not restart the overvoltage protection control even if the DC voltage of the smoothing capacitor reaches the predetermined value again after the completion of the overvoltage protection control and while the winding short-circuit control is being executed.

7. The overvoltage protection control circuit performs the overvoltage protection control when the DC voltage of the smoothing capacitor reaches a first predetermined value after the inverter circuit has stopped, and switches the switching element to the off state when the DC voltage of the smoothing capacitor falls below a second predetermined value as a result of the overvoltage protection control. The second predetermined value is a value lower than the first predetermined value. The overvoltage protection control circuit alternately switches the switching element on and off based on the first predetermined value and the second predetermined value. A power conversion device according to any one of claims 1 to 5, characterized by the following:

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

9. The overvoltage protection circuit includes a capacitor connected in parallel with the resistive element. A power conversion device according to any one of claims 1 to 6, characterized by the following:

10. The power conversion device is provided according to any one of claims 1 to 6, It comprises a compressor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger. The motor is an air conditioner, which is the driving source for the compressor.

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