Power conversion device, motor driving device, and air conditioner

Abstract

A power conversion device (1) comprises a smoothing unit (200) that is provided with a smoothing capacitor (210), an inverter (310) that converts a DC current smoothed by the smoothing capacitor (210) to an AC current and supplies AC power to a motor (314), and a control unit (400) that controls the inverter (310). The control unit (400) has a capacitor capacity estimation unit (401) that estimates the capacitor capacity of the smoothing capacitor (210). When the estimated value of the capacitor capacity of the smoothing capacitor (210) is equal to or less than a first threshold value, the inverter (310) is caused to stop the operation for supplying the AC power to the motor (314). When the estimated value of the capacitor capacity of the smoothing capacitor (210) is equal to or less than a second threshold value that is set in advance to a value greater than the first threshold value, the inverter (310) is caused to continue the operation for supplying the AC power to the motor (314) while limiting output.

Description

Power conversion device, motor drive device, and air conditioning device

[0001] The present disclosure relates to a power conversion device that converts power supplied from an AC power supply and outputs the converted power to a load, a motor drive device, and an air conditioner.

[0002] 2. Description of the Related Art A power conversion device that converts power supplied from an AC power source and outputs it to a load includes a converter that rectifies the AC current and outputs a DC current, and an inverter that converts the DC current into an AC current.

[0003] A smoothing capacitor is installed between the converter and the inverter, primarily to smooth the DC current output by the converter. Electrolytic capacitors are used as smoothing capacitors. Electrolytic capacitors tend to deteriorate over time and operating load, and their capacity decreases due to temperature characteristics.

[0004] It is known that a decrease in the capacitance of the smoothing capacitor leads to a deterioration in inverter controllability and can cause the smoothing capacitor to break down due to an increase in capacitor ripple current. Therefore, it is necessary to prevent the deterioration of inverter controllability and the breakdown of the smoothing capacitor by controlling the smoothing capacitor in accordance with its actual capacitance.

[0005] Patent Document 1 discloses an inverter device that measures the actual capacitance of a smoothing capacitor by discharging the smoothing capacitor while the inverter is stopped.

[0006] Japanese Patent Application Publication No. 8-80055

[0007] However, the inverter device disclosed in Patent Document 1 measures the actual capacitance of the smoothing capacitor by discharging the smoothing capacitor, so it is not possible to measure the actual capacitance of the smoothing capacitor while the inverter is operating, which poses a problem in that it is not possible to continue operation while controlling the inverter in accordance with the actual capacitance of the smoothing capacitor.

[0008] The present disclosure has been made in view of the above, and has an object to provide a power conversion device that can continue to operate while controlling an inverter in accordance with the actual capacitor capacity of a smoothing capacitor.

[0009] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes a converter that rectifies AC current input from an AC power source and outputs DC current, a smoothing unit including a smoothing capacitor that smooths the DC current output by the converter, an inverter that converts the DC current smoothed by the smoothing capacitor into AC current and supplies AC power to a motor, a voltage detection unit that detects a voltage across the smoothing capacitor, a first current detection unit that detects a current value of the DC current output from the converter, a second current detection unit that detects a current value of the DC current input to the inverter, and a control unit that controls the inverter. The control unit has a capacitor capacitance estimation unit that estimates a capacitance of the smoothing capacitor based on values ​​detected by the voltage detection unit, the first current detection unit, and the second current detection unit. The control unit stops the inverter from supplying AC power to the motor when the estimated capacitance of the smoothing capacitor is equal to or less than a predetermined first threshold, and causes the inverter to continue supplying AC power to the motor while limiting its output when the estimated capacitance of the smoothing capacitor is equal to or less than a predetermined second threshold that is greater than the first threshold.

[0010] The power conversion device according to the present disclosure has an advantage of being able to continue operation while controlling the inverter in accordance with the actual capacitance of the smoothing capacitor.

[0011] FIG. 1 shows the configuration of a power conversion device according to embodiment 1. Flowchart showing the flow of operation of a power conversion device according to embodiment 1. FIG. 1 shows the configuration of a power conversion device according to embodiment 2. FIG. 2 shows an example of power control of a power conversion device according to embodiment 3. FIG. 3 shows an example of power control of a power conversion device according to embodiment 4. FIG. 2 shows the configuration of a power conversion device according to embodiment 5. FIG. 3 shows an example of power control of a power conversion device according to embodiment 5. FIG. 4 shows an example of hardware configuration for realizing a control unit provided in a power conversion device according to any one of embodiments 1 to 5. FIG. 5 shows the configuration of an air conditioning device according to embodiment 6.

[0012] A power conversion device, a motor drive device, and an air conditioner according to embodiments will be described in detail below with reference to the drawings.

[0013] 1 is a diagram showing the configuration of a power conversion device according to a first embodiment. The power conversion device 1 is connected between an AC power supply 110 and a motor 314. The power conversion device 1 converts first AC power supplied from the AC power supply 110 into second AC power and supplies the second AC power to the motor 314. The second AC power may be different from the first AC power in at least one of the amplitude and phase, or may be the same as the first AC power in both the amplitude and phase.

[0014] The power conversion device 1 includes a converter 130 that rectifies AC current input from an AC power supply 110 and outputs DC current, a smoothing unit 200 that includes a smoothing capacitor 210 that smooths the DC current output by the converter 130, an inverter 310 that converts the DC current smoothed by the smoothing unit 200 into AC current and supplies AC power to a motor 314 that is a load, a voltage detection unit 502 that detects the voltage across the smoothing capacitor 210, a first current detection unit 601 that detects the current value of the DC current output from the converter 130, a second current detection unit 602 that detects the current value of the DC current input to the inverter 310, and a control unit 400 that controls the inverter 310.

[0015] The control unit 400 has a capacitor capacitance estimation unit 401 that estimates the capacitor capacitance of the smoothing capacitor 210 based on the detection values ​​of the voltage detection unit 502, the first current detection unit 601, and the second current detection unit 602, and a control signal output unit 402 that outputs a control signal to the inverter 310.

[0016] The motor 314 and the power conversion device 1 constitute a motor drive device 2 .

[0017] The reactor 120 removes harmonic components. The reactor 120 is connected between the AC power supply 110 and the converter 130. The converter 130 has a bridge circuit configured with rectifying elements 131, 132, 133, and 134. The converter 130 rectifies and outputs the first AC power supplied from the AC power supply 110. In the power conversion device 1 according to the first embodiment, the converter 130 performs full-wave rectification. 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 smoothing unit 200 is connected to the output terminal of the converter 130 via the voltage detection unit 502. The smoothing unit 200 has a smoothing capacitor 210, which is a smoothing element, and smoothes the power rectified by the converter 130. The smoothing capacitor 210 is, for example, an electrolytic capacitor or a film capacitor. Smoothing capacitor 210 has a capacity to smooth the power rectified by converter 130, and the voltage generated in smoothing capacitor 210 due to the smoothing is not a full-wave rectified waveform of AC power supply 110, but a waveform in which a voltage ripple corresponding to the frequency of AC power supply 110 is superimposed on a DC component, and does not pulsate significantly.

[0018] The inverter 310 is connected to both ends of the smoothing capacitor 210 included in the smoothing unit 200. The inverter 310 has switching elements 311a, 311b, 311c, 311d, 311e, and 311f and freewheeling diodes 312a, 312b, 312c, 312d, 312e, and 312f. The inverter 310 turns on and off the switching elements 311a, 311b, 311c, 311d, 311e, and 311f under the control of the control unit 400, converts the power output from the converter 130 and the smoothing unit 200 into second AC power, and outputs the second AC power to the motor 314. The motor 314 rotates in accordance with the amplitude and phase of the second AC power supplied from the inverter 310, and performs a compression operation.

[0019] Note that, in the power conversion device 1, the arrangement of the components shown in Fig. 1 is one example, and the arrangement of the components is not limited to the example shown in Fig. 1. For example, the reactor 120 may be arranged in a stage subsequent to the converter 130.

[0020] The control unit 400 acquires the voltage value of the power rectified by the converter 130 from the voltage detection unit 502. The control unit 400 uses the detection value detected by the voltage detection unit 502 to control the operation of the inverter 310, specifically, the on / off of the switching elements 311a, 311b, 311c, 311d, 311e, and 311f included in the inverter 310.

[0021] When the estimated capacitor capacity value is equal to or less than a first threshold value, which is a threshold value for determining whether or not an abnormality exists, the control signal output unit 402 outputs a control signal to the inverter 310 to stop the supply of AC power to the motor 314. When the estimated capacitor capacity value is equal to or less than a second threshold value, which is a threshold value for determining whether or not load reduction is necessary, the control signal output unit 402 causes the inverter 310 to continue the operation of supplying AC power to the motor 314 while limiting the output. The second threshold value is set to a value greater than the first threshold value.

[0022] 2 is a flowchart showing the flow of operation of the power conversion device according to embodiment 1. In step S1, the capacitor capacity estimation unit 401 acquires detected voltage values ​​and detected current values ​​from the voltage detection unit 502, the first current detection unit 601, and the second current detection unit 602. In step S2, the capacitor capacity estimation unit 401 estimates the capacitance of the smoothing capacitor 210 based on the detected voltage values ​​and detected current values ​​acquired from the voltage detection unit 502, the first current detection unit 601, and the second current detection unit 602.

[0023] In step S3, the control signal output unit 402 determines whether the estimated capacitance value of the smoothing capacitor 210 is equal to or less than the first threshold. If the estimated capacitance value of the smoothing capacitor 210 is equal to or less than the first threshold, the answer in step S3 is Yes, and the process proceeds to step S4. If the estimated capacitance value of the smoothing capacitor 210 is not equal to or less than the first threshold, the answer in step S3 is No, and the process proceeds to step S5.

[0024] In step S4, the control signal output unit 402 outputs a stop signal to the inverter 310 to stop the supply of AC power to the motor 314. In step S5, the control signal output unit 402 determines whether the estimated capacitance value of the smoothing capacitor 210 is equal to or less than the second threshold. If the estimated capacitance value of the smoothing capacitor 210 is equal to or less than the second threshold, the answer in step S5 is Yes, and the process proceeds to step S6. If the estimated capacitance value of the smoothing capacitor 210 is not equal to or less than the second threshold, the answer in step S5 is No, and the process proceeds to step S7.

[0025] In step S6, the control signal output unit 402 causes the inverter 310 to continue supplying AC power to the motor 314 while limiting the output. In step S7, the control signal output unit 402 causes the inverter 310 to continue supplying AC power to the motor 314 without limiting the output.

[0026] The power conversion device 1 according to the first embodiment estimates the capacitance of the smoothing capacitor 210 based on the detection results of the voltage detection unit 502, the first current detection unit 601, and the second current detection unit 602, and therefore can estimate the capacitance of the smoothing capacitor 210 without stopping operation. Furthermore, when the estimated capacitor capacitance value becomes equal to or less than the second threshold value, the power conversion device 1 according to the first embodiment causes the inverter 310 to continue supplying AC power to the motor 314 while limiting the output, thereby reducing the operating load of the smoothing capacitor 210 and suppressing deterioration of the smoothing capacitor 210.

[0027] 3 is a diagram showing the configuration of a power conversion device according to embodiment 2. The power conversion device 1 according to embodiment 2 differs from the power conversion device 1 according to embodiment 1 in that the control unit 400 includes a capacitor life prediction unit 403.

[0028] The capacitor life prediction unit 403 predicts the remaining life of the smoothing capacitor 210 based on the difference between the initial value of the capacitance of the smoothing capacitor 210 and the estimated capacitance value, or based on the amount of decrease in the capacitance of the smoothing capacitor 210 over a preset period.

[0029] When predicting the remaining life of the smoothing capacitor 210 based on the difference between the initial value of the capacitance of the smoothing capacitor 210 and the estimated value of the capacitance of the smoothing capacitor 210, the estimated value of the capacitance of the smoothing capacitor 210 at the time of initial startup of the power conversion device 1 or the nominal capacitance value of the smoothing capacitor 210 is stored in advance in the capacitor life prediction unit 403 as the initial value of the capacitance of the smoothing capacitor 210. In addition, the allowable minimum capacitance value of the smoothing capacitor 210 is specified in advance and stored in the capacitor life prediction unit 403. For example, a capacitance value that is −20% of the nominal capacitance value of the smoothing capacitor 210, or the minimum capacitance value required for stable operation of the motor based on design, is specified as the allowable minimum capacitance value and stored in the capacitor life prediction unit 403.

[0030] The capacitor life prediction unit 403 estimates the remaining life of the smoothing capacitor 210 by calculating the ratio corresponding to the estimated capacitor capacity value estimated by the capacitor capacity estimation unit 401 during operation of the motor 314, after corresponding the initial capacitor capacity value to 100% and the minimum allowable capacity value to 0%. For example, if the initial capacitor capacity value is 12.5 μF, the minimum allowable capacity value is 10 μF, and the estimated capacitor capacity value is 11 μF, the capacitor life prediction unit 403 predicts that the remaining life of the smoothing capacitor 210 is 40%.

[0031] If the period from the initial capacitance value of the capacitor to the minimum allowable capacitance value is estimated in advance, such as at the time of design, the remaining life may be calculated based on the calculated ratio. For example, if the period from the initial capacitance value of the capacitor to the minimum allowable capacitance value is estimated to be 10 years and the ratio of the estimated capacitance value is 80%, the remaining life can be predicted to be 8 years.

[0032] On the other hand, when predicting the remaining life of the smoothing capacitor 210 based on the amount of decrease in the capacitance of the smoothing capacitor 210 over a predetermined period, the minimum allowable capacitance value of the smoothing capacitor 210 is specified in advance and stored in the capacitor life prediction unit 403. For example, a capacitance value that is -20% of the nominal capacitance value of the smoothing capacitor 210, or the minimum capacitance value required for stable operation of the motor based on design, is specified as the minimum allowable capacitance value and stored in the capacitor life prediction unit 403. The capacitor life prediction unit 403 calculates the slope of the change in capacitance over a predetermined period based on the estimated capacitance value during operation of the motor 314, which is acquired at regular intervals. Furthermore, the capacitor life prediction unit 403 calculates the period in which the current estimated capacitance value will reach the minimum allowable capacitance value based on the slope of the change in capacitance, and predicts the remaining life of the smoothing capacitor 210.

[0033] When the predicted remaining life of the smoothing capacitor 210 becomes shorter than a preset value, the control unit 400 may limit the output of the inverter 310 to suppress the rate at which the remaining life of the smoothing capacitor 210 decreases. Furthermore, the control unit 400 may notify the user that the remaining life of the smoothing capacitor 210 has decreased by displaying a warning message on a display (not shown) that the remaining life of the smoothing capacitor 210 has become shorter than a preset value.

[0034] The power conversion device 1 according to the second embodiment predicts the remaining life of the smoothing capacitor 210 based on the actual change in the estimated capacitor capacitance value during operation, and is therefore able to highly accurately predict the remaining life of the smoothing capacitor 210. Furthermore, when the predicted remaining life becomes smaller than a preset value, the output of the inverter 310 is limited, or a display (not shown) is displayed to warn that the remaining life of the smoothing capacitor 210 has become smaller than the preset value, thereby preventing the smoothing capacitor 210 from failing in a period short of its expected life.

[0035] Embodiment 3 The configuration of the power conversion device 1 according to embodiment 3 is the same as that of the power conversion device 1 according to embodiment 1. In the power conversion device 1 according to embodiment 3, the control unit 400 increases the AC power supplied from the inverter 310 to the motor 314 when the estimated capacitance value of the smoothing capacitor 210 becomes equal to or greater than a third threshold, which is a threshold for determining operational stability that is preset based on the minimum capacitance of the smoothing capacitor 210 that allows the motor 314 to operate stably. For example, the control unit 400 increases the AC power supplied from the inverter 310 to the motor 314 by increasing the rotation speed of the motor 314. Here, the rotation speed of the motor 314 is the number of rotations per unit time, i.e., the rotation speed of the motor 314.

[0036] 4 is a diagram illustrating an example of power control of the power conversion device according to embodiment 3. The control unit 400 keeps the motor rotation speed constant during the period from t10 to t11 when the estimated capacitance value of the smoothing capacitor 210 is less than the third threshold, and increases the motor rotation speed after t11 when the estimated capacitance value of the smoothing capacitor 210 becomes equal to or greater than the third threshold.

[0037] The power conversion device 1 according to the third embodiment can perform and continue a certain operation even when the estimated capacitance value of the smoothing capacitor 210 is smaller than the third threshold, and can transition to high-capacity operation when the estimated capacitance value of the smoothing capacitor 210 is equal to or greater than the third threshold. Therefore, the power conversion device 1 according to the third embodiment can prevent the occurrence of abnormalities in operation or failure of the motor 314, which would occur if a high-load operation were performed when the actual capacitance of the smoothing capacitor 210 is small, thereby improving the continuity of operation.

[0038] Fourth Embodiment The configuration of the power conversion device 1 according to the fourth embodiment is the same as that of the power conversion device 1 according to the first embodiment. In the power conversion device 1 according to the fourth embodiment, when the estimated capacitor capacitance value of the smoothing capacitor 210 becomes equal to or less than a fourth threshold value, which is a preset threshold value for determining whether or not a capacity increase is required and is greater than the first threshold value and less than the second threshold value, the control unit 400 changes the AC power supplied from the inverter 310 to the motor 314 to increase the capacitor current, which is the current flowing through the smoothing capacitor 210. For example, the control unit 400 increases the capacitor current by increasing at least one of the frequency and current of the AC power supplied to the motor 314. The fourth threshold value is set in advance based on the capacitor capacitance of the smoothing capacitor 210 that allows the motor 314 to operate stably.

[0039] 5 is a diagram illustrating an example of power control of a power conversion device according to embodiment 4. The control unit 400 keeps the motor rotation speed constant during the period from t20 to t21 when the estimated capacitor capacitance value is greater than the fourth threshold, and increases the motor rotation speed to increase the capacitor current after t21 when the estimated capacitor capacitance value of the smoothing capacitor 210 becomes equal to or less than the fourth threshold.

[0040] The power conversion device 1 according to the fourth embodiment increases the capacitor current when the capacitance of the smoothing capacitor 210 decreases, thereby warming the smoothing capacitor 210 and increasing the actual capacitance of the smoothing capacitor 210. As a result, the power conversion device 1 according to the fourth embodiment can ensure that the capacitance of the smoothing capacitor 210 is equal to or greater than the capacitance required to operate the motor 314, thereby improving the continuity of operation.

[0041] The power conversion device 1 according to the fourth embodiment makes a judgment based on a decrease in the actual capacitor capacity, and therefore can prevent the operating load from being increased when the capacitor capacity of the smoothing capacitor 210 is equal to or greater than the capacitor capacity required to operate the motor 314, thereby preventing a loss of energy saving properties.

[0042] Fifth Embodiment Fig. 6 is a diagram showing the configuration of a power conversion device according to a fifth embodiment. The power conversion device 1 according to the fifth embodiment differs from the power conversion device 1 according to the first embodiment in that it includes an outside air temperature detection unit 603. The outside air temperature detection unit 603 detects the outside air temperature and outputs the detection result to the control unit 400. The power conversion device 1 according to the fifth embodiment increases the AC power supplied from the inverter 310 to the motor 314 when the estimated capacitor capacitance of the smoothing capacitor 210 is equal to or less than a fourth threshold, which is a threshold for determining whether or not a capacity increase is necessary and is a preset value that is greater than the first threshold and less than the second threshold, and when the outside air temperature is equal to or less than a fifth threshold, which is an outside air temperature threshold that is preset based on the lowest temperature at which the inverter 310 can operate stably.

[0043] 7 is a diagram illustrating an example of power control of a power conversion device according to the fifth embodiment. The control unit 400 maintains the motor rotation speed constant during the period from t30 to t31, when the estimated capacitor capacitance value is greater than the fourth threshold. During the period from t31 to t32, the estimated capacitor capacitance value is equal to or less than the fourth threshold, but the outside air temperature is greater than the fifth threshold, so the control unit 400 maintains the motor rotation speed without increasing it. During the period from t32 onward, the estimated capacitor capacitance value is equal to or less than the fourth threshold and the outside air temperature is equal to or less than the fifth threshold, so the control unit 400 increases the motor rotation speed to increase the capacitor current.

[0044] Under operating conditions where the outside air temperature is low and the capacitance of the smoothing capacitor 210 is reduced, the power conversion device 1 according to the fifth embodiment increases the AC power supplied from the inverter 310 to the motor 314 to increase the capacitor current, thereby warming the smoothing capacitor 210 and increasing the actual capacitance of the smoothing capacitor 210. As a result, the power conversion device 1 according to the fifth embodiment can ensure that the capacitance of the smoothing capacitor 210 is equal to or greater than the capacitance required for stable operation of the inverter 310, thereby improving continuity of operation.

[0045] Next, a description will be given of the hardware configuration of the control unit 400 included in the power conversion device 1. Fig. 8 is a diagram showing an example of a hardware configuration realizing the control unit included in the power conversion devices according to embodiments 1 to 5. The control unit 400 is realized by a processing circuit including a processor 91 that executes various processes, a memory 92 that is a main memory, and a storage device 93 that stores information.

[0046] The processor 91 may be a computing device such as an arithmetic unit, a microprocessor, a microcomputer, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor). The memory 92 may be a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Only Memory), or an EEPROM (Electrically Erasable Programmable Read Only Memory). The storage device 93 stores programs for controlling the inverter 310, estimating the capacitor capacitance, predicting the capacitor life, increasing the motor rotation speed, and increasing the motor load. The processor 91 reads the programs stored in the storage device 93 into the memory 92 and executes them. The processor 91 reads the programs stored in the storage device 93 into the memory 92 and executes them, thereby realizing the functions of the control unit 400.

[0047] Sixth Embodiment Fig. 9 is a diagram showing the configuration of an air conditioner according to a sixth embodiment. The air conditioner 50 includes an indoor unit 3 and an outdoor unit 4. The outdoor unit 4 includes a power conversion device 1 according to any one of the first to fifth embodiments, a compressor 315, a four-way valve 36, an outdoor heat exchanger 33 that transfers heat of the refrigerant to air, and refrigerant piping 6.

[0048] The indoor unit 3 has an expansion device 34, an indoor heat exchanger 35 that transfers heat of the refrigerant to air, and refrigerant piping 6. The expansion device 34 controls the flow rate of the refrigerant by expanding and decompressing the refrigerant. Note that the expansion device 34 may be included in the outdoor unit 4 instead of the indoor unit 3.

[0049] The compressor 315 includes a motor 314 and a compression element 31. That is, the compressor 315 includes therein the compression element 31, which is a compression mechanism that compresses the refrigerant, and the motor 314, which is a compressor motor that operates the compression element 31.

[0050] In the air conditioning apparatus 50, a refrigerant circuit in which a refrigerant circulates is configured, with the compressor 315, four-way valve 36, outdoor heat exchanger 33, expansion device 34, indoor heat exchanger 35, four-way valve 36, and compressor 315 connected in this order by refrigerant piping 6. In this manner, the refrigerant circuit in the air conditioning apparatus 50 includes the compressor 315, four-way valve 36, outdoor heat exchanger 33, expansion device 34, indoor heat exchanger 35, and refrigerant piping 6. The four-way valve 36 is a valve that switches the path of the refrigerant circuit. Note that the configuration of the refrigerant circuit shown in FIG. 9 is an example, and the configuration of the refrigerant circuit of the air conditioning apparatus 50 does not necessarily have to be the same as the configuration of the refrigerant circuit shown in FIG. 9.

[0051] The power conversion device 1 applies a voltage to the compressor 315 to control the compressor 315. Specifically, the power conversion device 1 controls the motor 314 of the compressor 315.

[0052] The motor 314 is connected to the compression element 31. The motor 314 is a three-phase motor having windings for three phases: U phase, V phase, and W phase. The compressor 315 compresses the refrigerant by the motor 314 and the compression element 31.

[0053] Here, a case where the air conditioner 50 performs cooling operation will be described. Prior to the start of cooling operation, the four-way valve 36 is switched in advance so that the refrigerant discharged from the compressor 315 flows toward the outdoor heat exchanger 33, and the refrigerant flowing out of the indoor heat exchanger 35 flows toward the compressor 315. Note that although a detailed description of the heating operation will be omitted here, switching between cooling operation and heating operation is performed by switching the flow path in the four-way valve 36.

[0054] In the air conditioning apparatus 50, the power conversion device 1 drives the motor 314 to rotate, causing the compression element 31 connected to the motor 314 to compress the refrigerant, and the compressor 315 to discharge the high-temperature, high-pressure refrigerant. The high-temperature, high-pressure refrigerant discharged from the compressor 315 flows into the outdoor heat exchanger 33 via the four-way valve 36, where it exchanges heat with the air and dissipates heat.

[0055] The refrigerant flowing out of the outdoor heat exchanger 33 is expanded and decompressed by the expansion device 34, becoming a low-temperature, low-pressure, two-phase gas-liquid refrigerant, which flows into the indoor heat exchanger 35, exchanges heat with the air in the space to be air-conditioned, evaporates, and becomes a low-temperature, low-pressure gas refrigerant, which flows out of the indoor heat exchanger 35. The gas refrigerant flowing out of the indoor heat exchanger 35 passes through the four-way valve 36 and is drawn into the compressor 315, where it is compressed again. The air conditioning apparatus 50 performs cooling operation by repeating the above operations.

[0056] In an air conditioning apparatus 50 including a power conversion device 1 according to any one of the first to fifth embodiments, instead of increasing the motor current, the AC power supplied from the inverter 310 to the motor 314 may be increased by changing the compression conditions of the refrigerant in the compression element 31 to increase the load on the compressor 315. Furthermore, in addition to increasing the motor current, the AC power supplied from the inverter 310 to the motor 314 may be increased by changing the compression conditions of the refrigerant in the compression element 31 to increase the load on the compressor 315.

[0057] The air conditioning device 50 of embodiment 6 is equipped with a power conversion device 1 of any of embodiments 1 to 5, and therefore can suppress failure of the power conversion device 1 due to destruction of the smoothing capacitor 210, and prevent a state in which air conditioning operation cannot be performed.

[0058] The configurations shown in the above embodiments are merely examples of the content, and may be combined with other known technologies, or parts of the configurations may be omitted or modified without departing from the spirit of the invention.

[0059] REFERENCE SIGNS LIST 1 Power conversion device, 2 Motor drive device, 3 Indoor unit, 4 Outdoor unit, 6 Refrigerant piping, 31 Compression element, 33 Outdoor heat exchanger, 34 Expansion device, 35 Indoor heat exchanger, 36 Four-way valve, 50 Air conditioner, 91 Processor, 92 Memory, 93 Storage device, 110 AC power source, 120 Reactor, 130 Converter, 131, 132, 133, 134 Rectifying element, 200 Smoothing unit, 210 Smoothing capacitor, 310 Inverter, 311a, 311b, 311c, 311d, 311e, 311f Switching elements, 312a, 312b, 312c, 312d, 312e, 312f Freewheel diodes, 314 Motor, 315 Compressor, 400 Control unit, 401 Capacitor capacity estimation unit, 402 Control signal output unit, 403 capacitor life prediction unit, 502 voltage detection unit, 601 first current detection unit, 602 second current detection unit, 603 outside air temperature detection unit.

Claims

1. A converter that rectifies the AC current input from an AC power source and outputs a DC current, A smoothing unit equipped with a smoothing capacitor for smoothing the DC current output by the converter, An inverter that converts the DC current smoothed by the smoothing capacitor into AC current and supplies AC power to the motor, A voltage detection unit for detecting the voltage across the smoothing capacitor, A first current detection unit detects the current value of the DC current output from the converter, A second current detection unit detects the current value of the DC current input to the inverter, The system includes a control unit that controls the inverter, The control unit has a capacitor capacity estimation unit that estimates the capacitor capacity of the smoothing capacitor based on the detected values ​​of the voltage detection unit, the first current detection unit, and the second current detection unit. When the estimated capacitor capacity of the smoothing capacitor falls below a preset first threshold, the inverter stops supplying AC power to the motor. When the estimated capacitor capacity of the smoothing capacitor falls below a preset second threshold that is greater than the first threshold, the inverter continues to supply AC power to the motor while limiting the output. When the estimated capacitor capacity becomes greater than or equal to a preset third threshold based on the minimum capacitor capacity required to stably operate the motor, the inverter increases the AC power supplied to the motor.

2. The power conversion device according to claim 1, wherein the control unit has a capacitor life prediction unit that predicts the life of the smoothing capacitor based on the difference between the initial value of the capacitor capacitance of the smoothing capacitor and the estimated value of the capacitor capacitance, or the amount of decrease in the capacitor capacitance of the smoothing capacitor over a preset period.

3. The power conversion device according to claim 1, wherein the control unit changes the AC power supplied from the inverter to the motor such that the capacitor current, which is the current flowing through the smoothing capacitor, increases when the estimated capacitor capacitance becomes less than or equal to a fourth threshold value that is set to be greater than the first threshold value and less than the second threshold value.

4. It is equipped with an outside air temperature detection unit that detects the outside air temperature, The power conversion device according to claim 1, wherein the control unit increases the AC power supplied from the inverter to the motor when the estimated capacitor capacitance is greater than the first threshold and less than the second threshold, and the ambient temperature is less than the fifth threshold, which is set in advance based on the lowest temperature at which the inverter can operate stably.

5. Motor and, A motor drive device comprising a power conversion device according to any one of claims 1 to 4 that supplies power to the motor.

6. A compression mechanism that compresses the refrigerant and A motor that operates the compression mechanism, An air conditioning system comprising a power conversion device according to any one of claims 1 to 4 that supplies power to the motor.