Power conversion device and air conditioner

Abstract

A power conversion device (1) comprises: a converter (130) that rectifies first AC power supplied from a power supply (110); a capacitor (210) that is connected to an output end of the converter (130); an inverter (310) that is connected to both ends of the capacitor (210) and generates second AC power; and a control unit (400) that controls the inverter (310). The control unit (400) includes: an abnormality determination unit (430) that performs abnormality determination for determining whether or not a capacitor current value, which is the value of the current flowing through the capacitor (210), is an abnormal value, and determines the output stop or output reduction of the inverter (310) when the capacitor current value is an abnormal value; and an abnormality determination execution determination unit (420) that determines whether or not the abnormality determination unit (430) executes the abnormality determination.

Description

Power conversion device and air conditioner

[0001] The present disclosure relates to a power conversion device that converts AC power supplied from a power source into desired power, and an air conditioner.

[0002] When AC power is converted to the desired power, it is converted to DC power. This conversion to DC power is performed using a rectifier circuit, but it is difficult to extract only the DC component from AC power, so smoothing using an electrolytic capacitor is performed to suppress the remaining AC component.

[0003] Electrolytic capacitors can deteriorate or fail depending on the duration of use and the load. The decrease in capacitance due to deterioration leads to poor controllability and increases the ripple current flowing through the electrolytic capacitor, which is known to lead to the destruction of the electrolytic capacitor.

[0004] As a technique related to this problem, Patent Document 1 proposes suppressing the pulsating voltage by reducing the output of the inverter when the pulsating voltage of the smoothing capacitor becomes excessive.

[0005] Japanese Patent Application Laid-Open No. 2007-259629

[0006] However, the technology described in Patent Document 1 reduces the inverter output even at times when protection is not actually required, which may result in an air conditioner equipped with a compressor driven by the output power from the inverter being unable to operate as desired.

[0007] The present disclosure has been made in view of the above, and has an object to provide a power conversion device that can perform a protection operation for a smoothing capacitor at an appropriate timing.

[0008] In order to solve the above-mentioned problems and achieve the object, the power conversion device according to the present disclosure includes a converter that rectifies first AC power supplied from a power source, a smoothing capacitor connected to the output terminal of the converter, an inverter connected to both ends of the smoothing capacitor and generating second AC power, and a control unit that controls the inverter, wherein the control unit performs an abnormality determination that determines whether a capacitor current value, which is the value of the current flowing through the smoothing capacitor, is an abnormal value, and if the capacitor current value is an abnormal value, the control unit includes an abnormality determination unit that decides to stop or reduce the output of the inverter, and an abnormality determination implementation decision unit that decides whether the abnormality determination unit should perform an abnormality determination.

[0009] The power conversion device according to the present disclosure has an advantage that it is possible to perform a protection operation for the smoothing capacitor at an appropriate timing.

[0010] FIG. 1 is a diagram showing a configuration example of a power conversion device according to a first embodiment; FIG. 2 is a flowchart showing an example of an abnormality detection operation by a control unit of the power conversion device according to the first embodiment; FIG. 3 is a diagram showing a configuration example of a control unit included in the power conversion device according to the first embodiment; FIG. 4 is a diagram showing a configuration example of an abnormality determination implementation determining unit of a control unit included in the power conversion device according to the first embodiment;

[0011] A power conversion device and an air conditioner according to embodiments of the present disclosure will be described in detail below with reference to the drawings.

[0012] 1 is a diagram illustrating a configuration example of a power conversion device according to a first embodiment. The power conversion device 1 is connected between a power supply 110 and a compressor 315. The power conversion device 1 converts first AC power supplied from the power supply 110 into second AC power and supplies the second AC power to the compressor 315. The second AC power may be different from the first AC power in at least one of the amplitude and the phase, or may be the same as the first AC power in both the amplitude and the phase.

[0013] The power conversion device 1 includes a voltage / current detection unit 501, a converter 130, a voltage detection unit 502, a current detection unit 503, a smoothing unit 200, an inverter 310, current detection units 313a and 313b, and a control unit 400. The compressor 315 is a load device that includes a motor 314 for driving the compressor, to which power is supplied from the power conversion device 1. The motor 314 included in the compressor 315 and the power conversion device 1 constitute a motor drive device 2.

[0014] The voltage / current detection unit 501 is configured, for example, by a voltage sensor and a current sensor. The voltage / current detection unit 501 detects the voltage and current values ​​of the first AC power supplied from the power supply 110 and outputs the detected voltage and current values ​​to the control unit 400. The voltage of the first AC power is the power supply voltage. The converter 130 rectifies the first AC power supplied from the power supply 110 and outputs the rectified power. The converter 130 is configured, for example, by a bridge circuit including multiple rectifying elements such as diodes. In addition to the bridge circuit, the converter 130 may also include a boost circuit that changes the voltage value of the DC power by controlling the switching of switching elements. The voltage detection unit 502 is configured, for example, by a voltage sensor. The voltage detection unit 502 detects the voltage value of the power rectified by the converter 130 and outputs the detected voltage value to the control unit 400. The current detection unit 503 is configured, for example, by a current sensor. Current detection unit 503 detects the value of the current flowing from converter 130 to inverter 310 and outputs the detected current value to control unit 400. Smoothing unit 200 is connected to the output terminal of converter 130 via voltage detection unit 502 and current detection unit 503. Smoothing unit 200 is configured with capacitor 210, which is a smoothing capacitor, and smoothes the power rectified by converter 130. Capacitor 210 is, for example, an electrolytic capacitor or a film capacitor.

[0015] The inverter 310 is connected to both ends of the capacitor 210 included in the smoothing unit 200. The inverter 310 is a typical inverter circuit including a switching element and a freewheeling diode. The inverter 310 turns on and off the switching element under the control of the control unit 400, converts the DC power supplied from the converter 130 via the smoothing unit 200 into second AC power, and outputs the second AC power to the compressor 315. Each of the current detection units 313a and 313b detects the current value of one phase of the three-phase current output from the inverter 310 and outputs the detected current value to the control unit 400. The control unit 400 can calculate the current value of the remaining one phase output from the inverter 310 by acquiring the current values ​​of two phases of the three-phase current output from the inverter 310. The motor 314 rotates in accordance with the amplitude and phase of the second AC power supplied from the inverter 310, thereby performing a compression operation. For example, when the compressor 315 is a hermetic compressor used in an air conditioner or the like, the load torque of the compressor 315 can often be considered as a constant torque load.

[0016] In the following description, voltage / current detection unit 501, voltage detection unit 502, current detection unit 503, and current detection units 313a and 313b may be collectively referred to as detection units. Furthermore, the voltage value and current value detected by voltage / current detection unit 501, the voltage value detected by voltage detection unit 502, the current value detected by current detection unit 503, and the current value detected by current detection units 313a and 313b may be referred to as detection values.

[0017] The control unit 400 acquires the voltage and current values ​​of the first AC power from the voltage and current detection unit 501, the voltage value of the power rectified by the converter 130 from the voltage detection unit 502, the current value of the power rectified by the converter 130 from the current detection unit 503, and the current values ​​of the two predetermined phases of the second AC power from the current detection units 313a and 313b. The control unit 400 uses the detection values ​​detected by each detection unit to control the operation of the inverter 310, specifically, the on / off of each switching element of the inverter 310. Furthermore, if the converter 130 includes a boost circuit, the control unit 400 controls the on / off of the switching elements included in the boost circuit. Furthermore, the control unit 400 has an abnormality detection function for the power conversion device 1, specifically, a function to detect a state in which the current flowing through the capacitor 210 (hereinafter, this current will be referred to as the capacitor current) exceeds a predetermined upper limit. That is, the control unit 400 compares the capacitor current with the upper limit value, and determines that an abnormality has occurred if the capacitor current is greater than the upper limit value. When the control unit 400 detects an abnormality in the power conversion device 1, the control unit 400 limits the output of the inverter 310 or stops the output of the inverter 310, thereby reducing the current flowing through the capacitor 210 to or below the upper limit value.

[0018] The operation of the control unit 400 to detect an abnormality in the power conversion device 1 will be described below.

[0019] 2 is a flowchart showing an example of an abnormality detection operation by the control unit 400 of the power conversion device 1 according to the first embodiment. The control unit 400 repeatedly executes a series of processes shown in the flowchart of FIG. 2 at a predetermined timing.

[0020] First, the control unit 400 acquires the capacitor current (step S11). The method for acquiring the capacitor current is not important. The capacitor current may be measured directly or calculated from other measured values.

[0021] The control unit 400 then determines whether or not to perform an abnormality determination based on the capacitor current acquired in step S11 (step S12). Specifically, the control unit 400 checks whether or not a predetermined condition for not performing an abnormality determination is met, and if the condition is met, the control unit 400 does not perform an abnormality determination, and if the condition is not met, the control unit 400 performs an abnormality determination. Details of the conditions for not performing an abnormality determination will be described later. Note that a condition for performing an abnormality determination may be set instead of a condition for not performing an abnormality determination.

[0022] If the control unit 400 does not perform the abnormality determination (step S12: No), the control unit 400 ends the operation. On the other hand, if the control unit 400 performs the abnormality determination (step S12: Yes), the control unit 400 determines whether the abnormality determination, specifically, the capacitor current value acquired in step S11, is an abnormal value (step S13). That is, the control unit 400 determines whether the capacitor current value is greater than an upper limit value, which is a predetermined threshold value.

[0023] If the capacitor current value is normal (step S13: No), the control unit 400 ends the operation. On the other hand, if the capacitor current value is abnormal (step S13: Yes), the control unit 400 changes the output of the inverter 310 (step S14). That is, the control unit 400 reduces or stops the output of the inverter 310 so that the capacitor current is equal to or less than the threshold value. For example, the control unit 400 stops the output of the inverter 310 if the capacitor current does not become equal to or less than the threshold value even after detecting an abnormality in the capacitor current and performing an operation to reduce the output of the inverter 310 a predetermined number of times.

[0024] 3 is a diagram illustrating an example of the configuration of the control unit 400 included in the power conversion device 1 according to the first embodiment. The control unit 400 includes a capacitor current obtaining unit 410, an abnormality determination execution determining unit 420, an abnormality determination unit 430, and an inverter control unit 440.

[0025] The capacitor current acquisition unit 410 acquires the capacitor current. That is, the capacitor current acquisition unit 410 executes the process of step S11 shown in Fig. 2. The capacitor current acquisition unit 410 outputs the acquired capacitor current to the abnormality determination unit 430.

[0026] The abnormality determination execution determining unit 420 determines whether the abnormality determination unit 430 should perform an abnormality determination. That is, the abnormality determination execution determining unit 420 executes the process of step S12 shown in FIG. 2 . When the capacitor current is unstable and the capacitor current acquiring unit 410 cannot acquire a highly reliable capacitor current value, the abnormality determination execution determining unit 420 determines not to cause the abnormality determination unit 430 to perform an abnormality determination. A highly reliable capacitor current value is a capacitor current value with small fluctuations, and an unreliable capacitor current value is a capacitor current value with large fluctuations over a short period of time. For example, the abnormality determination execution determining unit 420 determines not to cause the abnormality determination unit 430 to perform an abnormality determination immediately after the power conversion device 1 starts a power conversion operation to convert the first AC power to the second AC power. Immediately after the start of the power conversion operation, the current flowing into the capacitor 210 is unstable and may temporarily become excessively large. Performing an abnormality determination in this state increases the likelihood of an incorrect determination. Therefore, the abnormality determination execution determining unit 420 determines not to cause the abnormality determination unit 430 to perform abnormality determination for a period from the start of the power conversion operation until a predetermined time has elapsed. The abnormality determination execution determining unit 420 outputs an abnormality determination execution determination signal indicating the determination result to the abnormality determination unit 430. The abnormality determination execution determining unit 420 outputs the abnormality determination execution determination signal, which, for example, becomes an H (High) level when abnormality determination is to be performed and becomes an L (Low) level when abnormality determination is not to be performed. As shown in FIG. 4 , the abnormality determination execution determining unit 420 includes an abnormality determination start determining unit 421 that determines the timing to start abnormality determination, and the abnormality determination start determining unit 421 outputs the abnormality determination execution determination signal. Note that FIG. 4 is a diagram illustrating an example configuration of the abnormality determination execution determining unit 420 of the control unit 400 included in the power conversion device 1 according to the first embodiment. The abnormality determination start determining unit 421 determines to start abnormality determination when a highly reliable capacitor current value can be acquired.

[0027] When the abnormality determination execution determining unit 420 determines to perform the abnormality determination, the abnormality determination unit 430 determines whether the capacitor current value acquired by the capacitor current acquiring unit 410 is an abnormal value. That is, the abnormality determination unit 430 executes the process of step S13 shown in FIG. 2 . The abnormality determination unit 430 generates an inverter operation limiting signal based on the determination result and outputs it to the inverter control unit 440. Specifically, when the capacitor current value is an abnormal value, the abnormality determination unit 430 determines to reduce or stop the output of the inverter 310, and outputs an inverter operation limiting signal instructing the inverter control unit 440 to operate in accordance with the determination result. On the other hand, when the capacitor current value is a normal value, the abnormality determination unit 430 determines not to reduce or stop the output of the inverter 310, and outputs an inverter operation limiting signal instructing the inverter control unit 440 to operate in accordance with the determination result, i.e., an inverter operation limiting signal instructing the inverter control unit 440 to operate normally. The abnormality determination unit 430 outputs an inverter operation limiting signal that is at H level when instructing to reduce or stop the output of the inverter 310, and is at L level when instructing normal operation of the inverter 310. Whether to reduce or stop the output of the inverter 310 may be set in advance, or the abnormality determination unit 430 may determine this based on the capacitor current value.

[0028] The inverter control unit 440 performs on / off control of each switching element included in the inverter 310 to generate second AC power that drives the motor 314 of the compressor 315. At this time, if the inverter operation limiting signal input from the abnormality determination unit 430 has a value that instructs a reduction in the output of the inverter 310, the inverter control unit 440 controls each switching element of the inverter 310 so that the output of the inverter 310 is lower than normal. Furthermore, if the inverter operation limiting signal has a value that instructs a stop of the output of the inverter 310, the inverter control unit 440 stops the on / off control of each switching element of the inverter 310, thereby stopping the output of the inverter 310. The inverter control unit 440 may reduce the output of the inverter 310 by controlling a reduction in the rotation speed of the compressor 315 connected to the inverter 310.

[0029] Fig. 5 is a time chart showing an example of the operation timing of the power conversion device 1 according to the first embodiment. Fig. 5 shows, from top to bottom, a time chart of the output signal of the abnormality determination execution determining unit 420, the output signal of the abnormality determination unit 430, the output of the inverter 310, and the capacitor current.

[0030] In the example shown in FIG. 5 , the output signal (abnormality determination execution determination signal) of the abnormality determination execution determination unit 420 is initially at an L level, indicating that abnormality determination will not be performed. Therefore, the abnormality determination unit 430 does not perform abnormality determination. Therefore, although the capacitor current is an abnormal value greater than the threshold value (capacitor current abnormality threshold), it is not determined to be abnormal, and the output signal of the abnormality determination unit 430 is at an L level (=0). As a result, the output of the inverter 310 remains high without changing. After that, when the output signal of the abnormality determination execution determination unit 420 becomes an H level (=1), indicating that abnormality determination will be performed, the abnormality determination unit 430 performs abnormality determination. In the example shown in FIG. 5 , since the capacitor current value is an abnormal value, the abnormality determination unit 430 determines that an abnormality has occurred and switches the output signal (inverter operation limit signal) to an H level. When the inverter operation limit signal becomes an H level, the inverter control unit 440 controls the inverter 310 to reduce its output, resulting in the capacitor current decreasing to a value below the threshold.

[0031] The power conversion device 1 may include a control unit 400a having the configuration shown in Fig. 6. Fig. 6 is a diagram illustrating an example of the configuration of another control unit 400a included in the power conversion device 1 according to the first embodiment. The control unit 400a includes a capacitor current obtaining unit 410, an abnormality determination implementation determining unit 420a, an abnormality determination unit 430, and an inverter control unit 440. The capacitor current obtaining unit 410, the abnormality determination unit 430, and the inverter control unit 440 of the control unit 400a are the same as the capacitor current obtaining unit 410, the abnormality determination unit 430, and the inverter control unit 440 of the control unit 400 shown in Figs. 3 and 4 , and therefore description thereof will be omitted.

[0032] The abnormality determination execution determining unit 420a of the control unit 400a includes an abnormality determination termination determining unit 422 that determines when to terminate the abnormality determination, and the abnormality determination termination determining unit 422 outputs an abnormality determination execution determination signal. While the abnormality determination unit 430 is performing the abnormality determination, the abnormality determination termination determining unit 422 repeatedly checks whether a preset termination condition for the abnormality determination is satisfied. When the termination condition is satisfied, the abnormality determination termination determining unit 422 outputs an abnormality determination execution determination signal instructing the termination of the abnormality determination. The termination condition is when a highly reliable capacitor current value cannot be obtained. In other words, the abnormality determination termination determining unit 422 determines to terminate the abnormality determination when a highly reliable capacitor current value cannot be obtained and a high possibility of an erroneous determination occurs.

[0033] Fig. 7 is a time chart showing an example of the operation timing of the power conversion device 1 including the control unit 400a shown in Fig. 6. Fig. 7 shows, from top to bottom, a time chart of the output signal of the abnormality determination execution determining unit 420a, the output signal of the abnormality determination unit 430, the output of the inverter 310, and the capacitor current.

[0034] In the example shown in FIG. 7 , initially, the output signal (abnormality determination execution decision signal) of the abnormality determination execution decision unit 420a is at an H level indicating that abnormality determination is to be executed, and the output signal (inverter operation limiting signal) of the abnormality determination unit 430 is at an H level indicating that an abnormality has been detected. Therefore, the output of the inverter 310 decreases, and the capacitor current also decreases. When the output signal of the abnormality determination execution decision unit 420a subsequently becomes an L level indicating that abnormality determination is not to be executed, the abnormality determination unit 430 ends the abnormality determination and changes its output signal to an L level. As a result, the output of the inverter 310 increases, and the capacitor current also increases. At this time, the capacitor current is greater than the threshold value, but because the abnormality determination has been terminated, no abnormality is determined, and the output of the inverter 310 is not reduced.

[0035] In this embodiment, the abnormality judgment implementation decision unit 420 including the abnormality judgment start decision unit 421 and the abnormality judgment implementation decision unit 420a including the abnormality judgment end decision unit 422 have been described, but the abnormality judgment implementation decision unit 420 may also be configured to include both the abnormality judgment start decision unit 421 and the abnormality judgment end decision unit 422 and determine the start and end of abnormality judgment.

[0036] An example of the operation of the abnormality determination execution determining unit 420 will be described when the abnormality determination execution determining unit 420 is configured to include both the abnormality determination start determining unit 421 and the abnormality determination end determining unit 422. Here, as an example, an example of the operation will be described when the compressor 315 connected to the power conversion device 1 is a compressor for an air conditioner.

[0037] The abnormality determination execution determining unit 420 determines not to perform abnormality determination when the air conditioner equipped with the compressor 315 is operating in a special operation mode, for example, in defrosting operation, rather than in normal air conditioning operation. That is, in the abnormality determination execution determining unit 420, the abnormality determination termination determining unit 422 determines to stop abnormality determination when the air conditioner starts defrosting operation, and the abnormality determination start determining unit 421 determines to start abnormality determination when the air conditioner ends defrosting operation.

[0038] Furthermore, the abnormality determination execution determining unit 420 determines not to perform abnormality determination when the load connected to the power conversion device 1 suddenly changes, for example, in a transient state in which the rotation speed of the compressor 315 suddenly changes. For example, suppose the temperature of a room where an air conditioner equipped with the compressor 315 is installed suddenly changes due to the opening and closing of a door or window. In this case, the air conditioner rapidly increases its output through PAM (Pulse Amplitude Modulation) control to restore the room temperature (to approach the set value). Specifically, the power conversion device 1 drives the boost circuit provided in the converter 130 to increase the voltage output from the converter 130. This significantly changes the current flowing through the capacitor 210. In such a case, the abnormality determination execution determining unit 420 determines not to perform abnormality determination. That is, the abnormality determination execution determining unit 420 determines to stop abnormality determination when the air conditioner suddenly increases its output, and determines to start abnormality determination when a predetermined time has elapsed since the air conditioner suddenly increased its output.

[0039] The abnormality determination execution determining unit 420 may also determine whether to perform abnormality determination based on the amount of change in the capacitance of the capacitor 210 to be protected, for which the abnormality determination unit 430 performs abnormality determination. For example, the abnormality determination execution determining unit 420 may determine to perform abnormality determination when the capacitance of the capacitor 210 decreases due to deterioration of the capacitor 210. That is, the abnormality determination execution determining unit 420 determines to start abnormality determination when the capacitance of the capacitor 210 falls below a predetermined value or when the amount of capacitance decrease exceeds a threshold. The abnormality determination execution determining unit 420 may also determine to start abnormality determination when the capacitance of the capacitor 210 decreases by a predetermined percentage (e.g., 5%) from the initial capacitance at the start of use of the capacitor 210. The capacitance of the capacitor 210 is acquired by a known method. Note that, since the pulsation of the voltage applied to the capacitor 210 (hereinafter referred to as the capacitor voltage) increases as the capacitance of the capacitor 210 decreases, the abnormality determination execution determining unit 420 may determine to start abnormality determination when the pulsation of the capacitor voltage reaches a predetermined magnitude. By making the determination using the amount of pulsation in the capacitor voltage, it is not necessary to provide a circuit or the like for acquiring the capacitance of the capacitor 210 .

[0040] As described above, the power conversion device 1 according to the first embodiment includes the abnormality determination unit 430 that determines whether or not the current flowing through the capacitor 210, which is a smoothing capacitor, is an abnormal value, and the abnormality determination execution determination units 420, 420a that determine whether or not the abnormality determination unit 430 will perform abnormality determination. As a result, the power conversion device 1 can perform abnormality detection of the capacitor current flowing through the capacitor 210 at appropriate timing, and can perform a protective operation of suppressing the capacitor current by reducing or stopping the output of the inverter 310.

[0041] Second Embodiment A power conversion device according to a second embodiment has a configuration in which the control unit 400 of the power conversion device 1 according to the first embodiment is replaced with a control unit 400b shown in Fig. 8. Therefore, in this embodiment, the control unit 400b, which is different from that of the first embodiment, will be described, and descriptions of the other parts will be omitted.

[0042] 8 is a diagram illustrating a configuration example of a control unit 400b included in the power conversion apparatus according to the second embodiment. The control unit 400b includes a capacitor current obtaining unit 410, an abnormality determination execution determining unit 420, an abnormality determination unit 430, an inverter control unit 440, and an abnormality determination reset unit 450. The capacitor current obtaining unit 410, the abnormality determination execution determining unit 420, the abnormality determination unit 430, and the inverter control unit 440 of the control unit 400 according to the first embodiment are similar to the capacitor current obtaining unit 410, the abnormality determination execution determining unit 420, the abnormality determination unit 430, and the inverter control unit 440, and therefore detailed description thereof will be omitted.

[0043] Abnormality determination reset unit 450 determines whether to perform an abnormality determination reset that initializes the operations of capacitor current obtaining unit 410 and abnormality determination unit 430, based on the determination result by abnormality determination implementation determining unit 420. Abnormality determination reset unit 450 outputs an abnormality determination reset signal indicating the determination result to abnormality determination unit 430 and capacitor current obtaining unit 410.

[0044] For example, when the abnormality determination execution determination unit 420 determines not to perform abnormality determination, the abnormality determination reset unit 450 initializes (resets) the capacitor current acquisition unit 410 and the abnormality determination unit 430. An example of initialization will be described. For example, if the abnormality determination unit 430 detects a state in which the capacitor current value is greater than the threshold N times in a row (N is a positive integer) and determines that the capacitor current is abnormal and decides to limit the output of the inverter 310, the abnormality determination reset unit 450 instructs the abnormality determination unit 430 to reset the number of consecutive detections of a state in which the capacitor current value is greater than the threshold. At the same time, the abnormality determination reset unit 450 instructs the capacitor current acquisition unit 410 to discard the capacitor current value information that it has acquired and stored up to that point. Furthermore, if the abnormality determination unit 430 determines that the capacitor current is abnormal, and then the abnormality determination reset unit 450 resets the abnormality determination, and the abnormality determination implementation decision unit 420 decides to implement the abnormality determination, the abnormality determination unit 430 considers that the abnormality in the capacitor current has been resolved, and restarts the abnormality determination operation from the beginning.

[0045] Fig. 9 is a time chart showing an example of the operation timing of the power conversion device 1 according to the second embodiment. Fig. 9 shows, from top to bottom, a time chart of the output signal of the abnormality determination reset unit 450, the output signal of the abnormality determination unit 430, the output of the inverter 310, and the capacitor current.

[0046] 9 , (1) while the output of inverter 310 is increasing, some factor causes the capacitor current to momentarily increase to an abnormal value, and (2) abnormality determination unit 430 determines that an abnormality has occurred. (3) In response to the abnormality determination by abnormality determination unit 430, inverter control unit 440 stops increasing the output of inverter 310. Thereafter, (4) when the capacitor current falls below the abnormal value, (5) abnormality determination reset unit 450 resets the abnormality determination, and inverter control unit 440 increases the output of inverter 310 again.

[0047] As described above, the control unit 400b of the power conversion device 1 according to the second embodiment includes an abnormality determination reset unit 450 for initializing (resetting) the operation of the capacitor current acquisition unit 410 and the abnormality determination unit 430. According to the power conversion device 1 according to the second embodiment, by resetting the abnormality determination, it is possible to acquire the capacitor current with good tracking ability for different abnormality determination values ​​and perform abnormality determination. For example, when switching the PAM control of an air conditioner on and off, the PAM control may switch quickly, but the effective value of the capacitor current may only be updated slowly. In such cases, it is possible to quickly determine an abnormality by resetting the capacitor current acquired by the capacitor current acquisition unit 410 and the value in the abnormality determination unit 430.

[0048] Third Embodiment A power conversion device according to a third embodiment has a configuration in which the control unit 400 of the power conversion device 1 according to the first embodiment is replaced with a control unit 400c shown in Fig. 10. Therefore, in this embodiment, the control unit 400c, which is different from that of the first embodiment, will be described, and descriptions of the other parts will be omitted.

[0049] 10 is a diagram illustrating a configuration example of a control unit 400c included in the power conversion apparatus according to the third embodiment. The control unit 400c includes a capacitor current obtaining unit 410, an abnormality determination execution determining unit 420, an instantaneous current abnormality determining unit 431, and an inverter control unit 440. The capacitor current obtaining unit 410, the abnormality determination execution determining unit 420, and the inverter control unit 440 of the control unit 400 according to the first embodiment are similar to the capacitor current obtaining unit 410, the abnormality determination execution determining unit 420, and the inverter control unit 440, and therefore detailed description thereof will be omitted.

[0050] The abnormality determination unit 430 included in the control unit 400 of the power conversion device 1 according to the first embodiment performs abnormality determination based on the effective value of the capacitor current. In contrast, the instantaneous current abnormality determination unit 431 included in the control unit 400c of the power conversion device 1 according to the third embodiment performs abnormality determination based on the instantaneous value of the capacitor current. That is, the instantaneous current abnormality determination unit 431 determines an abnormality when the abnormality determination execution determination unit 420 determines that an abnormality determination is to be executed and the instantaneous value of the capacitor current exceeds a predetermined threshold, and instructs the inverter control unit 440 to reduce or stop the output of the inverter 310. Note that, in order to prevent erroneous determination, an abnormality may be determined when the instantaneous value continues to exceed the threshold, for example, when the instantaneous value exceeds the threshold a certain number of times in succession.

[0051] When an abnormality determination is performed based on the effective value of the capacitor current, even if the effective value is within a normal range, the instantaneous value may greatly exceed the threshold for determining an abnormality, which may result in a malfunction of the capacitor 210. The control unit 400c includes the instantaneous current abnormality determination unit 431, which makes it possible to detect cases in which the capacitor current momentarily increases, which is difficult to detect using the effective value of the capacitor current, and prevent malfunction of the capacitor 210. Furthermore, the instantaneous current abnormality determination unit 431 performs an abnormality determination when the abnormality determination execution decision unit 420 decides to execute an abnormality determination, thereby preventing unnecessary restrictions on the operation of the inverter 310.

[0052] Fig. 11 is a time chart showing an example of the operation timing of the power conversion device 1 according to the third embodiment. Fig. 11 shows, from top to bottom, a time chart of the output signal of the abnormality determination execution determining unit 420, the output signal of the instantaneous current abnormality determination unit 431, the output of the inverter 310, the effective value of the capacitor current, and the instantaneous value of the capacitor current.

[0053] 11 , the effective value of the capacitor current is below the threshold (capacitor current abnormality threshold), but the instantaneous value of the capacitor current continues to exceed the threshold (abnormality threshold) for abnormality determination in accordance with the pulsation period of the compressor 315, so the instantaneous current abnormality determination unit 431 determines that the capacitor current is abnormal. When the instantaneous current abnormality determination unit 431 determines that the capacitor current is abnormal, it sets the inverter operation limit signal to an H level. As a result, the inverter control unit 440 reduces the output of the inverter 310 to protect the capacitor 210.

[0054] Fig. 12 is a time chart showing another example of the operation timing of the power conversion device 1 according to the third embodiment. Fig. 12 shows, from top to bottom, a time chart of the same signals as those in Fig. 11 , namely, the output signal of the abnormality determination execution determining unit 420, the output signal of the instantaneous current abnormality determining unit 431, the output of the inverter 310, the effective value of the capacitor current, and the instantaneous value of the capacitor current.

[0055] In the example shown in Figure 12, the bus voltage momentarily rises due to pulsation in the system power supply, causing the instantaneous value of the capacitor current to exceed the threshold. However, since the instantaneous value of the capacitor current does not continue to exceed the threshold and the effective value of the capacitor current is below the threshold, the instantaneous current abnormality determination unit 431 determines that the capacitor current is normal. In this case, the inverter control unit 440 does not reduce the output of the inverter 310.

[0056] As described above, the control unit 400c of the power conversion device 1 according to the third embodiment includes an instantaneous current abnormality determination unit 431 that determines an abnormality based on the instantaneous value of the capacitor current. According to the power conversion device 1 according to the third embodiment, even when the instantaneous value of the capacitor current exceeds the capacitor current abnormality threshold but the effective value of the capacitor current is below the capacitor current abnormality threshold, an abnormality is determined to have occurred, and the capacitor 210 can be protected.

[0057] Next, a description will be given of the hardware configuration of each control unit (control units 400, 400a, 400b, 400c) included in each power conversion device 1 described in the first to third embodiments. Note that the hardware configuration of each control unit is the same.

[0058] 13 is a diagram illustrating an example of a hardware configuration for realizing the control units 400, 400a, 400b, and 400c included in the power conversion device 1 according to each embodiment. The control units 400, 400a, 400b, and 400c of the power conversion device 1 are realized by, for example, a processor 91 and a memory 92 illustrated in FIG.

[0059] The processor 91 is a CPU (Central Processing Unit, also called a processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor)). The memory 92 is a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory), or the like.

[0060] The memory 92 stores programs for operating as the control units 400, 400a, 400b, and 400c of the power conversion device 1. The control units 400, 400a, 400b, and 400c of the power conversion device 1 are realized by the processor 91 reading and executing the programs stored in the memory 92. The programs stored in the memory 92 may be provided to a user or the like in a state written on a storage medium such as a CD (Compact Disc)-ROM or a DVD (Digital Versatile Disc)-ROM, or may be provided via a network.

[0061] The control units 400, 400a, 400b, and 400c can also be realized by dedicated processing circuits, such as a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a circuit that combines these.

[0062] Embodiment 4 In this embodiment, a device that can be realized by applying the power conversion devices 1 described in Embodiments 1 to 3 will be described. As an example, an air conditioner that can be realized by applying the power conversion device 1 described in Embodiment 1 will be described.

[0063] 14 is a diagram showing a configuration example of an air conditioner 900 according to the fourth embodiment. The air conditioner 900 according to the fourth embodiment includes the power conversion device 1 described in the first embodiment.

[0064] The air conditioner 900 also includes a refrigeration cycle in which a four-way valve 902 , a compressor 315 , a heat exchanger 906 , an expansion valve 908 , and a heat exchanger 910 are attached via refrigerant piping 912 .

[0065] The compressor 315 is provided with a compression mechanism 904 that compresses the refrigerant circulating in the refrigerant pipe 912 , and a motor 314 that operates the compression mechanism 904 .

[0066] The air conditioner 900 according to the fourth embodiment includes an abnormality determination execution determining unit 420 that determines whether or not to perform abnormality determination by the abnormality determination unit 430. Therefore, the power conversion device 1 can be continuously operated while maintaining a high output without excessively protecting the smoothing capacitor (capacitor 210), and continuous operation of the compressor 315 and the air conditioner 900 can be realized.

[0067] 15 is a diagram showing a configuration example of a control unit 400d included in a power conversion device according to a fifth embodiment. The control unit 400d has a configuration in which an information transmission unit 460 is added to the control unit 400 of the power conversion device 1 according to the first embodiment. The capacitor current acquisition unit 410, the abnormality determination implementation determination unit 420, the abnormality determination unit 430, and the inverter control unit 440 of the control unit 400 according to the first embodiment are similar to the capacitor current acquisition unit 410, the abnormality determination implementation determination unit 420, the abnormality determination unit 430, and the inverter control unit 440 of the control unit 400 according to the first embodiment, and therefore detailed description thereof will be omitted.

[0068] The information transmission unit 460 is connected to the server 600 via a communication network (not shown), and transmits the determination result by the abnormality determination unit 430 to the server 600. The information transmission unit 460 transmits the result of the abnormality determination of the capacitor current repeatedly performed by the abnormality determination unit 430 to the server 600. The result of the abnormality determination of the capacitor current includes, for example, information on whether the capacitor current value is a normal value or an abnormal value, and information on the time when the abnormality determination was performed.

[0069] For example, when the power conversion device 1 according to the fifth embodiment is used in an air conditioner, by analyzing the information stored in the server 600, it is possible to know how much the usage period of the air conditioner and the lifespan of the capacitor 210 differ from the design assumptions, which may lead to design optimization and cost reduction. Also, it may be possible to perform maintenance before a failure occurs and prevent customer disadvantages.

[0070] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0071] 1 Power conversion device, 2 Motor drive device, 110 Power supply, 130 Converter, 200 Smoothing unit, 210 Capacitor, 310 Inverter, 313a, 313b, 503 Current detection unit, 314 Motor, 315 Compressor, 400, 400a, 400b, 400c, 400d Control unit, 410 Capacitor current acquisition unit, 420, 420a Abnormality judgment implementation decision unit, 421 Abnormality judgment start decision unit, 422 Abnormality judgment end decision unit, 430 Abnormality judgment unit, 431 Instantaneous current abnormality judgment unit, 440 Inverter control unit, 450 Abnormality judgment reset unit, 460 Information transmission unit, 501 Voltage current detection unit, 502 Voltage detection unit, 600 Server, 900 Air conditioner, 902 Four-way valve, 904 Compression mechanism, 906, 910 Heat exchanger, 908 expansion valve, 912 refrigerant piping.

Claims

1. A converter that rectifies the first AC power supplied from the power source, A smoothing capacitor connected to the output terminal of the converter, An inverter connected to both ends of the smoothing capacitor generates a second AC power, A control unit that controls the inverter, Equipped with, The control unit, An abnormality determination unit performs an abnormality determination to determine whether the capacitor current value, which is the value of the current flowing through the smoothing capacitor, is an abnormal value, and if the capacitor current value is an abnormal value, it determines to stop the output of the inverter or reduce the output. An abnormality determination unit determines whether or not to perform the abnormality determination, and Equipped with, The abnormality determination execution decision unit is a power conversion device that determines whether or not the abnormality determination unit will perform the abnormality determination when the decrease in the capacitance of the smoothing capacitor exceeds a threshold.

2. A converter for rectifying a first AC power supplied from a power source, A smoothing capacitor connected to the output terminal of the converter, An inverter connected to both ends of the smoothing capacitor generates a second AC power, A control unit that controls the inverter, Equipped with, The control unit, An abnormality determination unit performs an abnormality determination to determine whether the capacitor current value, which is the value of the current flowing through the smoothing capacitor, is an abnormal value, and if the capacitor current value is an abnormal value, it determines to stop the output of the inverter or reduce the output. An abnormality determination unit determines whether or not to perform the abnormality determination, and Equipped with, The abnormality determination execution decision unit is a power conversion device that determines whether or not the abnormality determination unit will perform the abnormality determination based on the amount of pulsation of the capacitor voltage of the smoothing capacitor.

3. The abnormality determination unit decides to perform the abnormality determination if it can obtain a highly reliable capacitor current value. The power conversion device according to claim 1 or 2.

4. The aforementioned abnormality determination execution unit, An abnormality determination start determination unit determines the start of the abnormality determination by the abnormality determination unit when it becomes possible to obtain a highly reliable capacitor current value. A power conversion device according to claim 1 or 2, comprising:

5. The aforementioned abnormality determination execution unit, An abnormality determination termination determination unit determines the termination of the abnormality determination by the abnormality determination unit when it becomes impossible to obtain a reliable capacitor current value. A power conversion device according to claim 1 or 2, comprising:

6. The abnormality determination unit decides not to perform the abnormality determination if the load connected to the inverter changes suddenly. The power conversion device according to claim 1 or 2.

7. The converter includes a boost circuit, The abnormality determination unit decides not to perform the abnormality determination if the converter changes the output voltage. The power conversion device according to claim 1 or 2.

8. An abnormality determination reset unit initializes the operation of the abnormality determination unit when the abnormality determination unit changes from a state in which it performs abnormality determination to a state in which it does not perform abnormality determination. A power conversion device according to claim 1 or 2, comprising:

9. The instantaneous value of the current flowing through the smoothing capacitor is defined as the capacitor current value. The power conversion device according to claim 1 or 2.

10. An information transmission unit that transmits the determination result from the abnormality determination unit to the server. A power conversion device according to claim 1 or 2, comprising:

11. A compressor is connected to the inverter. The control unit, when the abnormality determination unit determines that the output of the inverter should be reduced, implements control to reduce the rotational speed of the compressor. The power conversion device according to claim 1 or 2.

12. An air conditioner equipped with the power conversion device described in claim 1 or 2.