Power conversion device and air conditioner

Abstract

This power conversion device comprises: a rectifier circuit that rectifies the AC voltage of an AC power supply and converts the AC voltage into a DC voltage; an inverter circuit that converts the DC voltage converted by the rectifier circuit into an AC voltage; and a filter circuit that removes, from the DC voltage converted by the rectifier circuit, a high-frequency pulsation equal to or higher than a cutoff frequency. The filter circuit has: a positive-side voltage dividing resistor and a negative-side voltage dividing resistor that are connected in series; and an RC low-pass filter. When the resistance value of the negative-side voltage dividing resistor is denoted by R, the resistance value of the RC low-pass filter by r, the capacitance value of the RC low-pass filter by C, the power supply frequency of the AC power supply by fs, and a margin by K, the following expression (16) is satisfied.　

Description

Power conversion device and air conditioner

[0001] The present disclosure relates to a power conversion device that converts power from an AC power source and supplies the converted power to an electric motor, and an air conditioner that includes the power conversion device.

[0002] Conventionally, there has been known a power conversion device (so-called chemical capacitor-less inverter) that reduces costs by replacing the electrolytic capacitor for smoothing voltage in the main circuit with a small-capacity film capacitor (see, for example, Patent Document 1). In a chemical capacitor-less inverter, the voltage of the AC power supply is not smoothed, so the DC bus voltage pulsates at a frequency twice the number of phases of the AC power supply.

[0003] International Publication No. 2018 / 062395

[0004] In order to control the power output from an inverter circuit, it is necessary to detect a pulsating DC bus voltage. To accurately detect the DC bus voltage, a DC bus voltage detection circuit may be provided with a low-pass filter circuit that cuts out high-frequency components and removes noise. When a low-pass filter circuit is applied to the circuit of Patent Document 1, the low-pass filter circuit must pass pulsations with a frequency twice the number of phases of the AC power supply and remove noise with frequencies higher than that. However, in conventional low-pass filter circuits, even if a cutoff frequency for removing noise is set, components with frequencies lower than the cutoff frequency may also be removed.

[0005] The present disclosure has been made to solve the above-mentioned problems, and provides a power conversion device with improved noise removal accuracy and an air conditioner equipped with the power conversion device.

[0006] A power conversion device according to the present disclosure includes a rectifier circuit that rectifies an AC voltage of an AC power supply and converts it into a DC voltage, an inverter circuit that converts the DC voltage converted by the rectifier circuit into an AC voltage, and a filter circuit that removes high-frequency pulsation of a cutoff frequency or higher from the DC voltage converted by the rectifier circuit, wherein the filter circuit has a positive-side voltage dividing resistor and a negative-side voltage dividing resistor connected in series, and an RC low-pass filter, wherein the resistance value of the negative-side voltage dividing resistor is R, the resistance value of the RC low-pass filter is r, and the capacitance value of the RC low-pass filter is C, and the power supply frequency of the AC power supply is f ｓ and the margin is K, the following formula (1) is satisfied.

[0007] In the power conversion device according to the present disclosure, the filter circuit is configured to satisfy formula (1). In formula (1), the cutoff frequency is set taking into consideration that the voltage dividing resistor of the filter circuit also functions as a low-pass filter. Therefore, the power conversion device can operate the filter circuit at the target cutoff frequency, thereby improving the noise removal accuracy.

[0008] Fig. 1 is a circuit diagram showing a power conversion device according to embodiment 1. Fig. 2 is a diagram showing voltage detection accuracy and noise resistance when the value of (R+r)C is changed. Fig. 3 is a diagram showing an actual bus voltage and a bus voltage after passing through a filter circuit. Fig. 4 is a diagram showing an actual bus voltage and a bus voltage after passing through a filter circuit. Fig. 5 is a schematic diagram showing an air conditioner according to embodiment 2.

[0009] Embodiment 1. Hereinafter, an embodiment of a power conversion device 100 according to the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiment, and various modifications are possible without departing from the spirit of the present disclosure. Furthermore, the present disclosure includes all possible combinations of configurations shown in the following embodiments and their modifications. Furthermore, in each drawing, components with the same reference numerals are identical or equivalent, and this is common throughout the entire specification. Note that in each drawing, the relative dimensional relationship or shape of each component may differ from the actual one. Furthermore, hereinafter, electrical or magnetic connection may be simply referred to as "connection."

[0010] FIG. 1 is a circuit diagram showing a power conversion device 100 according to a first embodiment. As shown in FIG. 1, the power conversion device 100 according to the first embodiment is connected to an AC power supply 1, which is a power source, and an electric motor 2, which is a load. The AC power supply 1 is, for example, a three-phase commercial power supply having U, V, and W phases. The AC power supply 1 is connected to the power conversion device 100 via a power terminal block (not shown). The electric motor 2 is, for example, a three-phase permanent magnet synchronous motor having U, V, and W phases, and is supplied with power from the power conversion device 100. The electric motor 2 is mounted, for example, in a compressor of an air conditioner.

[0011] The power conversion device 100 converts the voltage and frequency of AC power supplied from an AC power source 1 and supplies the converted power to a motor 2. The power conversion device 100 includes a rectifier circuit 3, a bus-to-bus capacitor 4, an inverter circuit 5, a current detection unit 6, an inverter control unit 7, and a filter circuit 80.

[0012] The rectifier circuit 3 rectifies the AC voltage of the AC power supply 1 and converts it into a DC voltage. A bus capacitor 4 is connected to the output side of the rectifier circuit 3.

[0013] The busbar capacitor 4 is, for example, a film capacitor having a smaller capacitance than an electrolytic capacitor. In other words, the power conversion device 100 of the first embodiment is a so-called chemical capacitor-less inverter in which a small-capacity film capacitor is used as the capacitor of the main circuit instead of a conventional electrolytic capacitor. Unlike conventional electrolytic capacitors, the busbar capacitor 4 does not smooth the waveform of the low-order harmonic components of the DC voltage output from the rectifier circuit 3. The capacitance of the busbar capacitor 4 is designed so as not to remove low-order harmonic components that pulsate significantly at frequencies two or six times the power supply frequency of the AC power supply 1, for example, but to remove the carrier frequency component of the inverter circuit 5.

[0014] In a chemical capacitor-less inverter, the voltage of the AC power supply is not smoothed, so the DC bus voltage pulsates at a frequency twice the number of phases of the AC power supply. In other words, the DC voltage rectified by the rectifier circuit 3 contains low-order harmonic components that pulsate at a frequency six times the power supply frequency of the three-phase AC power supply 1 (twice the number of phases).

[0015] The inverter circuit 5 converts the DC voltage rectified by the rectifier circuit 3 into an AC voltage in accordance with a switching signal and outputs the AC voltage to the electric motor 2. The electric motor 2 is connected to the output side of the inverter circuit 5. The inverter circuit 5 is configured, for example, as a full-bridge circuit including six semiconductor switches (not shown). The semiconductor switches are switching elements such as insulated gate bipolar transistors (IGBTs), metal-oxide-semiconductor field effect transistors (MOSFETs), or high electron mobility transistors (HEMTs). The inverter circuit 5 controls the path of current flowing through the electric motor 2 by switching the semiconductor switches on and off, thereby driving the electric motor 2. The inverter circuit 5 functions to change the voltage value and frequency of the AC current supplied to the electric motor 2.

[0016] The current detection unit 6 is provided between the inverter circuit 5 and the electric motor 2, detects the current flowing from the inverter circuit 5 to the electric motor 2, and outputs current information to the inverter control unit 7. The current detection unit 6 is, for example, a current sensor using an instrument current transformer called a CT (Current Transformer). The current detection unit 6 may use a method called a one-shunt current detection method, which uses a shunt resistor provided in the negative-side DC link of the power conversion device 100. Alternatively, the current detection unit 6 may use a method called a three-shunt current detection method, which uses a shunt resistor provided in series with a switching element on the lower side of the inverter circuit 5.

[0017] The inverter control unit 7 outputs switching signals to the inverter circuit 5 based on speed commands and torque commands input from, for example, an external control device (not shown) that controls the air conditioner. As a method for controlling the speed and torque, the inverter control unit 7 performs vector control, for example, using a dq coordinate system to perform feedback control of the current flowing through the electric motor 2. Note that the inverter control unit 7 may be configured to perform constant V / f control, which outputs a voltage proportional to the operating frequency of the electric motor 2, or direct torque control, which controls the magnetic flux and torque of the electric motor 2.

[0018] The filter circuit 80 has a positive-side voltage dividing resistor 81, a negative-side voltage dividing resistor 82, and an RC low-pass filter 83. The positive-side voltage dividing resistor 81 and the negative-side voltage dividing resistor 82 are directly connected to the bus. The RC low-pass filter 83 has an RC filter resistor 84 and an RC filter capacitor 85. The filter circuit 80 inputs the DC bus voltage divided by the positive-side voltage dividing resistor 81 and the negative-side voltage dividing resistor 82 to the inverter control unit 7 through the RC low-pass filter 83. The resistance value of the positive-side voltage dividing resistor 81 is sufficiently larger than the resistance value of the negative-side voltage dividing resistor 82.

[0019] As mentioned above, in a chemical-capacitor-less inverter connected to a three-phase power supply, the DC voltage rectified by the rectifier circuit 3 pulsates at a frequency six times the power supply frequency. The inverter control unit 7 detects this low-frequency pulsation and uses it for control. For this reason, the filter circuit 80 passes low-frequency pulsation below the cutoff frequency and inputs it to the inverter control unit 7, while removing high-frequency pulsation above the cutoff frequency as noise.

[0020] In the first embodiment, an improvement is made to the conventional method of calculating the cutoff frequency, thereby aiming to remove noise with high accuracy in the filter circuit 80. By removing noise with high accuracy in the filter circuit 80, the bus voltage can be detected with high accuracy in the inverter control unit 7. Before describing the method of calculating the cutoff frequency in the first embodiment, a general method of calculating the cutoff frequency will be described.

[0021] RC low-pass filter cutoff frequency f １ It has been known that can be found by the following equation (2): where r is the resistance value of the RC low-pass filter (the resistance value of the RC filter resistor), and C is the capacitance value of the RC low-pass filter (the capacitance value of the RC filter capacitor).

[0022]

[0023] However, in reality, in the above circuit configuration, the DC bus voltage signal V ｏｕｔ The cutoff frequency f １ may be smaller than that of equation (2). This is because the positive-side voltage dividing resistor 81 and the negative-side voltage dividing resistor 82 of the DC bus voltage also function as low-pass filters.

[0024] Next, a method for calculating the cutoff frequency f in the first embodiment will be described. First, the DC bus voltage signal V ｏｕｔ Calculate the DC bus voltage as V ｄｃ , the voltage between the positive-side voltage dividing resistor 81 and the negative-side voltage dividing resistor 82 is V １ At this time, the DC bus voltage signal V ｏｕｔ is V １is a voltage obtained by dividing the voltage between the RC filter resistor 84 and the RC filter capacitor 85 of the RC low-pass filter 83, so the following equation (3) holds: where s is a Laplace operator.

[0025]

[0026] The combined impedance Z of the negative-side voltage dividing resistor 82, the RC filter resistor 84, and the RC filter capacitor 85 is expressed by the following equation (4). In the following, R is the resistance value of the negative-side voltage dividing resistor 82. Note that the resistance value R of the negative-side voltage dividing resistor 82 is greater than the resistance value r of the RC filter resistor of the RC low-pass filter 83. In particular, the resistance value R of the negative-side voltage dividing resistor 82 is five times or more the resistance value r of the RC filter resistor of the RC low-pass filter 83.

[0027]

[0028] Furthermore, V １ is V ｄｃ is a voltage divided by the positive side voltage dividing resistor 81 and the synthetic impedance Z calculated by equation (4), so the resistance value of the positive side voltage dividing resistor 81 is R １ Then, the following equation (5) holds.

[0029]

[0030] In this case, by rearranging the formulas (3) to (5), the following formula (6) is obtained.

[0031]

[0032] That is, when the positive-side voltage dividing resistor 81, the negative-side voltage dividing resistor 82, and the RC low-pass filter 83 are taken into consideration, the DC bus voltage signal V ｏｕｔ The gain of is R / (R １ +R), and the cutoff frequency f is given by the following equation (7).

[0033]

[0034] Here, R １ >>R, r, so R / R １ ≒0, (R × r) / R １≈0. Note that "≈" is a symbol indicating that both sides are approximately equal. Therefore, equation (7) can be approximated as equation (8) below. That is, in the first embodiment, the cutoff frequency f is calculated as shown in equation (8) using the resistance value R of the negative-side voltage dividing resistor 82, the resistance value r of the RC filter resistor 84 of the RC low-pass filter 83, and the capacitance value C of the RC filter capacitor 85 of the RC low-pass filter 83.

[0035]

[0036] As described above, when considering the removal of high-frequency pulsations above the cutoff frequency as noise, the following inequality (9) is obtained for the resistance R of the negative-side voltage dividing resistor 82, the resistance r of the RC low-pass filter 83, and the capacitance C of the capacitor of the RC low-pass filter 83. ｓ is the power supply frequency, and K is the margin for separating the cutoff frequency from the frequency to be passed.

[0037]

[0038] Here, the power supply frequency f ｓ By substituting specific values ​​for the resistance R of the negative voltage dividing resistor 82, the resistance r of the RC low-pass filter 83, and the capacitance C of the RC low-pass filter 83, the conditions are determined that satisfy to be able to remove high frequency pulsations above the cutoff frequency as noise. The power supply frequency currently used around the world is 50 Hz or 60 Hz. Here, f is set so that the range of (R+r)C that satisfies the inequality is wider. ｓ = 60 Hz. The margin can be determined by observing the filter effect of an actual signal mixed with noise, but it is generally known that the high voltage section of the power conversion device 100 functions with K = 5. Therefore, f is added to equation (9). ｓ = 60 Hz and K = 5, we obtain equation (10).

[0039]

[0040] FIG. 2 shows the voltage detection accuracy and noise immunity when the value of (R+r)C is changed. The voltage detection accuracy indicates the degree to which the bus voltage, when filtered through an RC low-pass filter, captures pulsations at a frequency six times the power supply frequency. The noise immunity indicates the degree to which noise input to the inverter control unit 7 is avoided. FIG. 2 also shows the results of evaluating the voltage detection accuracy and noise immunity when the value of (R+r)C is changed. An evaluation result of "x" indicates poor voltage detection accuracy or noise immunity. An evaluation result of "o" indicates good voltage detection accuracy or noise immunity. An evaluation result of "double circle" indicates particularly good voltage detection accuracy or noise immunity.

[0041] In FIG. 2, the value of (R+r)C is 88.4×10 －６ While the voltage detection accuracy decreases when the value of (R+r)C is greater than 88.4×10 －６ It has been shown that the voltage detection accuracy is good when the value is as follows: As described above, the upper limit of the value of (R+r)C in equation (10) is recognized to be effective from the viewpoint of voltage detection accuracy.

[0042] However, even if the value of (R+r)C is made infinitely small, the effect in terms of voltage detection accuracy saturates, and pulsation becomes excessively large. Furthermore, if (R+r)C is extremely small, high-frequency components also pass through, resulting in noise being input to the inverter control unit 7. In other words, noise resistance deteriorates, and a voltage different from the actual voltage is detected, resulting in unstable control. Therefore, the lower limit of equation (11) is determined from the perspective of achieving a balance that does not reduce the noise filter effect (noise resistance) within a range that maintains voltage detection accuracy and ensures control stability through pulsation extraction. Figure 2 shows that when the value of (R+r)C is 4.42 × 10 －６Therefore, the lower limits of the resistance R of the negative-side voltage dividing resistor 82, the resistance r of the RC low-pass filter 83, and the capacitance C of the RC low-pass filter 83 may be limited as shown in equation (11).

[0043]

[0044] 2, taking into consideration values ​​that are considered to be particularly good in both voltage detection accuracy and noise immunity, the range of (R+r)C may be limited as shown in formula (12). In the first embodiment, for example, the range of (R+r)C=15.8×10 that satisfies formula (12) is (R+r)C=15.8×10 －６ will be adopted.

[0045]

[0046] 3 and 4 are diagrams showing the actual bus voltage and the bus voltage after passing through the filter circuit 80. The effects of the first embodiment will be described with reference to FIGS. 3 and 4. In both FIGS. 3 and 4, the dashed line indicates the actual bus voltage before passing through the filter circuit 80, and the solid line indicates the bus voltage after passing through the RC low-pass filter. However, FIG. 3 shows an example in which the time constant is 1 ms and the filter circuit does not satisfy equation (10). FIG. 4 shows an example in which the time constant is 0.05 ms and the filter circuit 80 satisfies equations (10) and (11). In FIGS. 3 and 4, the actual bus voltage before passing through the filter circuit 80 is the same. The time constant is calculated by (R+r)C. That is, when the time constant is 0.05 ms, (R+r)C=50.0×10 －６ is.

[0047] As shown by the dashed line in Figure 3, if equation (10) is not satisfied, the pulsation of the bus voltage, which is six times the power supply frequency, that is, the pulsation that occurs every 2.8 [ms], which corresponds to 6f (frames) of 60 Hz, cannot be fully captured when the RC low-pass filter in Figure 3 is applied. Specifically, it can be seen that the bus voltage that has passed through the filter circuit in Figure 3 exhibits a phase delay and a smaller gain compared to the actual bus voltage.

[0048] On the other hand, as shown by the dashed line in Figure 4, when equations (10) and (11) are satisfied, it can be seen that when the RC low-pass filter in Figure 4 is applied, the bus voltage corresponds to pulsation at a frequency six times the power supply frequency.

[0049] As described above, in the power conversion device 100 according to the first embodiment, the filter circuit is configured to satisfy the formula (1). In the formula (1), the cutoff frequency is set taking into consideration that the voltage dividing resistor of the filter circuit also functions as a low-pass filter. Therefore, the power conversion device 100 can operate the filter circuit at the target cutoff frequency, thereby improving the accuracy of noise removal.

[0050] Embodiment 2 In Embodiment 2, the power conversion device 100 is applied to an air conditioner. Fig. 5 is a schematic diagram showing an air conditioner 400 according to Embodiment 2. The air conditioner 400 adjusts the temperature, humidity, etc. of the air in a space to be air-conditioned. The air conditioner 400 includes a refrigeration cycle device 300 and a blower 401.

[0051] The refrigeration cycle apparatus 300 includes a refrigerant compression device 200, a condenser 301, an expansion valve 302, and an evaporator 303. The refrigerant compression device 200 includes a compressor 201 and a power conversion apparatus 100. The compressor 201, the condenser 301, the expansion valve 302, and the evaporator 303 are connected by refrigerant piping, and the refrigerant circulates through the refrigerant. The compressor 201 draws in the refrigerant flowing through the refrigerant piping. The compressor 201 compresses the drawn refrigerant and discharges it into the refrigerant piping. The compressor 201 is an inverter-type compressor 201 equipped with an electric motor 2 and whose flow rate is adjusted. The condenser 301 condenses the refrigerant by exchanging heat between the refrigerant flowing therethrough and air. The expansion valve 302 is a pressure-reducing device that reduces the pressure of the refrigerant and is, for example, an electronic expansion valve. The evaporator 303 exchanges heat between the refrigerant flowing therethrough and air to evaporate the refrigerant. In the refrigeration cycle device 300, the refrigerant circulates through the compressor 201, the condenser 301, the expansion valve 302, and the evaporator 303 in this order, whereby the refrigerant repeatedly undergoes compression, condensation, expansion, and evaporation.

[0052] The blower 401 is for sending air to either or both of the condenser 301 and the evaporator 303 to promote heat exchange. The air volume of the blower 401 is adjusted by controlling the rotation speed of an electric motor (not shown).

[0053] The electric motor 2 is variably controlled by the power conversion device 100 described in embodiment 1. The power conversion device 100 controls the rotation speed of the electric motor 2 based on an operation command from a control device (not shown) of the air conditioner 400. In this way, the flow rate of the compressor 201 is adjusted.

[0054] In the second embodiment, the power conversion device 100 described in the first embodiment is applied to the air conditioner 400. Therefore, the power conversion device 100 of the air conditioner 400 of the second embodiment can also improve the noise removal accuracy. Therefore, in the air conditioner 400 of the second embodiment, the variable speed control of the motor 2, and therefore the adjustment of the flow rate of the compressor 201, can be performed with high accuracy.

[0055] Furthermore, in recent years, demand for air conditioners has been increasing in emerging countries, and there is a need to provide inexpensive air conditioners that use power conversion device 100 to control the speed of electric motor 2. According to the second embodiment, a chemical capacitor-less inverter in which electrolytic capacitors are replaced with film capacitors is used as power conversion device 100. Therefore, according to the second embodiment, component costs can be reduced and an inexpensive air conditioner can be provided.

[0056] Although the above is a description of the embodiment, the power conversion device 100 and the air conditioner 400 of the present disclosure can be modified as appropriate without departing from the spirit thereof. For example, according to the second embodiment, the power conversion device 100 has been described as controlling the variable speed of the electric motor 2 of the compressor 201, but it may also be configured to control the rotation speed of the electric motor of the blower 401.

[0057] In the first embodiment, the power conversion device 100 is described as a chemical capacitor-less inverter using a small-capacity film capacitor as the bus-bar capacitor 4. However, a conventional electrolytic capacitor may be used as the bus-bar capacitor 4.

[0058] In this case, by configuring the filter circuit 80 to satisfy Equation (10), capacitance loss in the electrolytic capacitor can be accurately detected. Specifically, it is known that as the capacitance of an electrolytic capacitor decreases due to degradation or failure, the electrolytic capacitor's ability to smooth the bus voltage weakens. Therefore, in a three-phase AC power supply, the frequency component six times the power supply frequency indicated by the bus voltage becomes large. In this case, a filter circuit 80 that satisfies Equation (10) can accurately filter out noise and pass the frequency component six times the power supply frequency of the bus voltage. Therefore, by having the inverter control unit 7 monitor the intensity of the frequency component six times the power supply frequency, the accuracy of detecting capacitance loss in the electrolytic capacitor can be improved, leading to preventive maintenance. Specifically, the inverter control unit 7 determines that capacitance loss has occurred if the intensity of the frequency component six times the power supply frequency is equal to or greater than a threshold, and determines that capacitance loss has not occurred if the intensity of the frequency component six times the power supply frequency is less than the threshold. The threshold can be determined in advance through experiments, etc.

[0059] Similarly, by configuring the filter circuit 80 to satisfy Equation (10), damage to electrolytic capacitors and other elements can be suppressed when the AC power supply is unbalanced. Specifically, when the three-phase AC power supply 1 is unbalanced, a frequency component twice the power supply frequency is superimposed on the bus voltage (power supply pulsation occurs). If the three-phase AC power supply 1 is unbalanced and the electric motor 2 continues to operate at high output, the temperature may rise, damaging the electrolytic capacitors and other elements. In this case, a filter circuit 80 that satisfies Equation (10) can accurately filter out noise and pass the frequency component twice the power supply frequency superimposed on the bus voltage. The inverter control unit 7 detects the occurrence of the frequency component twice the power supply frequency, and when the occurrence of the frequency component twice the power supply frequency is detected, controls the inverter circuit 5 to reduce the output to the electric motor 2. This suppresses the occurrence of power supply pulsation and reduces damage to the electrolytic capacitors and other elements.

[0060] REFRIGERATION CYCLE DEVICE, 2 AC power supply, 3 Rectifier circuit, 4 Busbar capacitor, 5 Inverter circuit, 6 Current detection unit, 7 Inverter control unit, 80 Filter circuit, 81 Positive side voltage dividing resistor, 82 Negative side voltage dividing resistor, 83 RC low pass filter, 84 RC filter resistor, 85 RC filter capacitor, 100 Power conversion device, 200 Refrigerant compression device, 201 Compressor, 300 Refrigeration cycle device, 301 Condenser, 302 Expansion valve, 303 Evaporator, 400 Air conditioner, 401 Fan.

Claims

1. a rectifier circuit that rectifies the AC voltage of the AC power supply and converts it into a DC voltage; an inverter circuit that converts the DC voltage converted by the rectifier circuit into an AC voltage; a filter circuit that removes high-frequency pulsation equal to or higher than a cutoff frequency from the DC voltage converted by the rectifier circuit, The filter circuit comprises: a positive voltage dividing resistor and a negative voltage dividing resistor connected in series; an RC low-pass filter; The resistance value of the negative voltage dividing resistor is R, the resistance value of the RC low-pass filter is r, the capacitance value of the RC low-pass filter is C, and the power supply frequency of the AC power supply is f ｓ and the margin is K, the following equation (13) is satisfied: [0013] Power conversion device.

2. The filter circuit satisfies the following formula (14): [0014] The power conversion device according to claim 1 .

3. The filter circuit satisfies the following formula (15): [Equation 15] The power conversion device according to claim 1 or 2.

4. the power conversion device is connected to a three-phase AC power supply; The filter circuit passes a component of the DC voltage that is six times the power supply frequency. The power conversion device according to claim 1 or 2.

5. a bus-bar capacitor provided between the rectifier circuit and the inverter circuit; an inverter control unit that controls the inverter circuit, The busbar capacitor is an electrolytic capacitor, The inverter control unit The capacitance loss of the busbar capacitor is detected based on the intensity of the frequency component six times the power supply frequency. The power conversion device according to claim 4.

6. a bus-bar capacitor provided between the rectifier circuit and the inverter circuit; an inverter control unit that controls the inverter circuit, The busbar capacitor is an electrolytic capacitor, The inverter control unit Detecting the occurrence of a frequency component twice the power supply frequency, When the occurrence of a frequency component twice the power supply frequency is detected, the inverter circuit is controlled to reduce the output to the motor. The power conversion device according to claim 4.

7. a bus-to-bus capacitor provided between the rectifier circuit and the inverter circuit, The inter-bus capacitor is a film capacitor. The power conversion device according to claim 1 or 2.

8. The power conversion device according to claim 1 or 2; an electric motor supplied with power by the power conversion device; Air conditioner.

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