Electric motor drive systems and air conditioners

Abstract

An electric motor driving device (100) comprises a three-phase diode bridge (10) that rectifies and converts a three-phase AC voltage into a DC voltage, an electrolytic capacitor (3) that smooths the DC voltage, a DC reactor (30) provided between the three-phase diode bridge (10) and the electrolytic capacitor (3), an inverter (20) that converts the DC voltage smoothed by the electrolytic capacitor (3) into an AC voltage and outputs the AC voltage to a motor (2), a voltage detection unit (40) that detects the DC voltage output by the three-phase diode bridge (10), and an inverter control unit (50) that detects an imbalance state of the three-phase AC voltage on the basis of a DC voltage value, which is a value of the DC voltage detected by the voltage detection unit (40), and controls the inverter (20) on the basis of the result of detecting the imbalance state.

Description

Technical Field

[0001] The present disclosure relates to a motor drive device and an air conditioner.

Background Art

[0002] There exists a motor drive device that includes a three-phase AC diode bridge and an inverter, which converts the power supplied from a three-phase AC power source into three-phase AC power of a desired voltage and frequency and supplies it to a motor (for example, Patent Document 1).

[0003] In a motor drive device configured with a three-phase diode bridge, when there is an imbalance in the input three-phase AC voltage, an imbalance occurs in the input current, and a pulsation also occurs in the DC voltage after rectification by the three-phase diode bridge. When a pulsation occurs in the rectified DC voltage, there is a risk of problems such as breaker trips and damage to components mounted on the board. To address such problems, the motor drive device described in Patent Document 1 determines whether the three-phase AC is in an unbalanced state based on the line voltage of the three-phase AC power source, and if it is in an unbalanced state, protects the circuit components by suppressing the output of the inverter.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The conventional motor drive system described above detects an unbalanced state by estimating the line voltage and comparing the unbalance rate calculated based on the estimated line voltage with a predetermined threshold. Therefore, conventional motor drive systems require voltage detection circuits for at least two phases of the three-phase AC, leading to larger device size and increased processing complexity and load. For these reasons, there is a need for a motor drive system that is smaller and reduces processing load.

[0006] This disclosure has been made in view of the above, and aims to provide an electric motor drive device that can achieve miniaturization of the device and reduction of the processing load. [Means for solving the problem]

[0007] To solve the above-mentioned problems and achieve the objective, the motor drive device according to this disclosure includes a three-phase diode bridge that rectifies a three-phase AC voltage and converts it into a DC voltage, a smoothing capacitor that smooths the DC voltage, a DC reactor provided between the three-phase diode bridge and the smoothing capacitor, an inverter that converts the DC voltage smoothed by the smoothing capacitor into an AC voltage and outputs it to a motor, a voltage detection unit that detects the DC voltage output by the three-phase diode bridge, and an inverter control unit that detects an unbalanced state of the three-phase AC voltage based on the DC voltage value detected by the voltage detection unit and controls the inverter based on the detection result of the unbalanced state. A zero-crossing detection unit that detects the zero-crossing point of any one phase of the three-phase AC voltage, It is equipped with. The inverter control unit detects an unbalanced state of the three-phase AC voltage based on the DC voltage value and the zero-crossing point detected by the zero-crossing detection unit. [Effects of the Invention]

[0008] The electric motor drive device described herein has the effect of enabling miniaturization of the device and reduction of the processing load. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of the configuration of an electric motor drive device according to Embodiment 1. [Figure 2]A flowchart showing an example of the operation of the motor drive device according to Embodiment 1. [Figure 3] A diagram illustrating the ripple voltage calculated by the inverter control unit according to Embodiment 1. [Figure 4] This figure shows an example of the configuration of an electric motor drive device according to Embodiment 2. [Figure 5] This diagram shows an example of the relationship between the phase voltages of each phase of a three-phase AC system and the line voltage. [Figure 6] This diagram shows an example of the relationship between the phase voltages of a three-phase AC system and the DC voltage after rectification of those phase voltages. [Figure 7] This diagram shows the relationship between DC voltage and line voltage at the zero-crossing point of the phase voltage. [Figure 8] A flowchart showing an example of the operation of the motor drive device according to Embodiment 2. [Figure 9] A diagram showing an example configuration of an air conditioner according to Embodiment 3. [Modes for carrying out the invention]

[0010] The electric motor drive unit and air conditioner according to embodiments of this disclosure will be described in detail below with reference to the drawings.

[0011] Embodiment 1. Figure 1 shows an example configuration of the motor drive unit 100 according to Embodiment 1. The motor drive unit 100 is connected to a power source 1 via three power lines L1 to L3 and drives the motor 2 by receiving three-phase AC power from the power source 1. That is, the motor drive unit 100 converts the three-phase AC power supplied from the power source 1 into three-phase AC power of a desired voltage and frequency to generate the drive power for the motor 2. The motor 2 is a three-phase motor.

[0012] The motor drive unit 100 includes a three-phase diode bridge 10 that rectifies the three-phase AC voltage supplied from a power supply 1, which is a three-phase AC power supply, and converts it into a DC voltage; an electrolytic capacitor 3, which is a smoothing capacitor that smooths the DC voltage output by the three-phase diode bridge 10; an inverter 20 that converts the DC voltage after smoothing by the electrolytic capacitor 3 into a three-phase AC voltage and applies it to the motor 2; and a DC reactor 30 provided between the three-phase diode bridge 10 and the electrolytic capacitor 3 to suppress harmonic currents contained in the DC current flowing between the three-phase diode bridge 10 and the inverter 20. The motor drive unit 100 also includes a voltage detection unit 40 connected between the three-phase diode bridge 10 and the DC reactor 30 that detects the DC voltage output by the three-phase diode bridge 10; and an inverter control unit 50 that receives the DC voltage value detected by the voltage detection unit 40 as input and provides commands generated based on the input DC voltage value to the inverter 20 to generate drive power for the motor 2. Although not shown in Figure 1, the detected voltage value and voltage command output by the inverter 20 are input to the inverter control unit 50. The inverter control unit 50 generates a command for the inverter 20 based on the detected voltage value and voltage command output by the inverter 20 and the DC voltage value mentioned above. The voltage detection unit 40 is implemented, for example, by a voltage sensor. The inverter control unit 50 is implemented, for example, by a microcontroller.

[0013] Although the detailed operation will be explained separately, the motor drive unit 100 determines whether the three-phase AC voltage supplied from the power supply 1 is unbalanced based on the DC voltage detection result by the voltage detection unit 40, and if it is unbalanced, the output of the inverter 20 is suppressed.

[0014] As described above, if there is an imbalance in the input three-phase AC voltage, an imbalance occurs in the input current, and pulsation (hereinafter referred to as ripple) occurs in the DC voltage after rectification by the three-phase diode bridge 10. In other words, when the three-phase AC voltage is unbalanced, the ripple component contained in the DC voltage increases. Therefore, it is possible to detect the imbalance in the three-phase AC voltage by monitoring the DC voltage after rectification by the three-phase diode bridge 10. The inverter control unit 50 of the motor drive device 100 according to this embodiment detects the imbalance in the three-phase AC voltage by utilizing this characteristic. This eliminates the need to provide a circuit to detect the voltage of each phase of the three-phase AC input from the power supply 1, making it possible to miniaturize and reduce the cost of the device.

[0015] Furthermore, since ripple in the DC voltage occurs when the load on the inverter 20 to which the DC voltage is applied fluctuates, the motor drive unit 100 is configured to detect the DC voltage between the three-phase diode bridge 10 and the DC reactor 30, where the effect of load fluctuations is small. However, if the expected maximum fluctuation amount of the load connected to the inverter 20 is small, that is, if the ripple generated due to the load fluctuation is negligibly small compared to the ripple generated due to the imbalance of the three-phase AC voltage, the DC voltage may be detected at a location different from the DC voltage detection location shown in Figure 1 (for example, between the electrolytic capacitor 3 and the inverter 20).

[0016] Figure 2 is a flowchart illustrating an example of the operation of the motor drive unit 100 according to Embodiment 1. Specifically, the flowchart in Figure 2 shows an example of operation in which the inverter control unit 50 of the motor drive unit 100 determines whether or not there is an imbalance in the power supply voltage and performs control on the inverter 20 according to the determination result.

[0017] While the motor drive unit 100 is performing a power conversion operation to generate drive power for the motor 2, the inverter control unit 50 repeats the operation according to the flowchart in Figure 2. That is, when the motor drive unit 100 drives the motor 2, the inverter control unit 50 repeatedly executes a series of processes from start to end shown in Figure 2 at a predetermined cycle.

[0018] Specifically, the inverter control unit 50 first acquires a DC voltage value (step S1). More specifically, the inverter control unit 50 acquires the detected DC voltage value from the voltage detection unit 40.

[0019] The inverter control unit 50 then calculates the ripple voltage based on the DC voltage value obtained in step S1 (step S2). The ripple voltage calculated by the inverter control unit 50 in step S2 will be explained using Figure 3. Figure 3 is a diagram for explaining the ripple voltage calculated by the inverter control unit 50 according to Embodiment 1. In Figure 3, V dc This indicates the DC voltage detected by the voltage detection unit 40, V L1 , V L2 and V L3 Figure 3 shows the voltage of each phase of the three-phase AC power input to the motor drive unit 100 from each of the three power lines L1 to L3. The horizontal axis represents time and the vertical axis represents voltage. Figure 3 shows the voltage of each phase of the three-phase AC power V L1 , V L2 and V L3 and DC voltage V dc This shows an example of the correspondence between the two. As shown in Figure 3, the ripple voltage calculated by the inverter control unit 50 is the difference in magnitude between adjacent ripples included in the DC voltage, that is, the voltage difference between adjacent peaks. In step S2, the inverter control unit 50 detects the peaks of the ripple by analyzing the latest DC voltage value obtained from the voltage detection unit 40 and previously obtained DC voltage values, and calculates the ripple voltage from the detected peaks. For example, when the inverter control unit 50 analyzes the DC voltage value and detects the latest ripple peak, it calculates the difference between the detected peak and the previously detected ripple peak, and uses this difference as the ripple voltage.

[0020] The inverter control unit 50 then compares the ripple voltage calculated in step S2 with a predetermined unbalance detection threshold (hereinafter referred to as the unbalance detection threshold) (step S3). The unbalance detection threshold is determined in advance by performing an operation simulation of the motor drive unit 100.

[0021] If the ripple voltage is greater than the unbalance detection threshold (step S3: Yes), the inverter control unit 50 determines that the three-phase AC voltage is in an unbalanced state and suppresses the output of the inverter 20 (step S4). For example, the inverter control unit 50 controls the inverter 20 so that its maximum output does not exceed N% of its normal maximum output. Note that N < 100, and normal state means that the three-phase AC voltage is not unbalanced. The above N may be a variable value. For example, if the ripple voltage and the unbalance detection threshold are significantly different, N may be changed to a small value. Alternatively, multiple different unbalance detection thresholds and corresponding values ​​of N may be prepared, and the value of N to be used may be determined based on the comparison result between the ripple voltage and each unbalance detection threshold.

[0022] If the ripple voltage is below the unbalance detection threshold (step S3: No), the inverter control unit 50 determines that the three-phase AC voltage is not in an unbalanced state, that is, that the three-phase AC voltage is in a normal state, and continues normal operation of the inverter 20 (step S5). In normal operation, the inverter control unit 50 controls the voltage output by the inverter 20 so that it follows the voltage command.

[0023] As described above, the motor drive device 100 according to this embodiment includes a voltage detection unit 40 that detects a DC voltage between the three-phase diode bridge 10 and the DC reactor 30, and an inverter control unit 50 that detects an unbalanced state of the three-phase AC voltage based on the ripple of the DC voltage detected by the voltage detection unit 40. When the inverter control unit 50 detects an unbalanced state of the three-phase AC voltage, it suppresses the output of the inverter 20. According to this embodiment, it is possible to realize a motor drive device 100 that can prevent malfunctions such as breaker tripping and damage to components mounted on the circuit board when an unbalanced state of the three-phase AC voltage occurs, and it is also possible to miniaturize the device and reduce the processing load.

[0024] Embodiment 2. The motor drive device 100 according to Embodiment 1 described above determines whether the three-phase AC voltage is unbalanced by comparing the ripple voltage calculated based on the DC voltage detected by the voltage detection unit 40 provided between the three-phase diode bridge 10 and the DC reactor 30 with a predetermined unbalance detection threshold. In contrast, this embodiment describes a motor drive device 100a that can accurately detect unbalance even when the DC voltage fluctuations due to fluctuations in the load connected to the inverter 20 are large.

[0025] Figure 4 shows an example configuration of the motor drive device 100a according to Embodiment 2. In Figure 4, the same reference numerals are used for components that are common to the motor drive device 100 according to Embodiment 1 shown in Figure 1. The components that are given the same reference numerals as in Figure 1 will not be described.

[0026] The motor drive unit 100a is configured by replacing the inverter control unit 50 of the motor drive unit 100 according to Embodiment 1 with an inverter control unit 50a and adding a zero-crossing detection unit 60.

[0027] The zero-crossing detection unit 60 monitors any one of the three-phase AC voltages input from the power supply 1 to the motor drive device 100a, detects the zero-crossing point of the voltage, and outputs the detection result to the inverter control unit 50a. In the configuration shown in FIG. 4, the zero-crossing detection unit 60 detects the zero-crossing point of the voltage V L1 on the power line L1. The zero-crossing detection unit 60 is realized by, for example, a voltage sensor, a logic circuit that determines the sign of the voltage detection value by the voltage sensor, and the like.

[0028] The inverter control unit 50a generates a command for the inverter 20 based on the DC voltage value detected by the voltage detection unit 40 and the zero-crossing point detected by the zero-crossing detection unit 60. Specifically, the inverter control unit 50a calculates the voltage of each phase of the three-phase AC voltage input to the motor drive device 100a (hereinafter, the voltage of one phase is referred to as the phase voltage) based on the DC voltage value and the zero-crossing point. Then, the inverter control unit 50a determines whether the three-phase AC voltage is in an unbalanced state based on the effective value of each calculated phase voltage, and controls the output of the inverter 20 according to the determination result. For the sake of simplicity of explanation, in the following description, the effective value of the phase voltage is referred to as the "phase voltage".

[0029] Here, a method for the inverter control unit 50a to calculate the voltage of each phase of the three-phase AC voltage based on the DC voltage value and the zero-crossing point will be described.

[0030] The phase voltages V L1 , V L2 and V L3 of the three-phase AC and the line voltages V L1-L2 , V L2-L3 and V L3-L1 have the relationship shown in FIG. 5. Here, the line voltage V L1-L2 is the potential difference between the power lines L1 and L2, the line voltage V L2-L3 is the potential difference between the power lines L2 and L3, and the line voltage V L3-L1 is the potential difference between the power lines L3 and L1. Note that FIG. 5 is a diagram showing an example of the relationship between each phase voltage and the line voltage of the three-phase AC.

[0031] Also, the phase voltage V of three-phase AC L1 , V L2 and V L3 And the DC voltage V obtained by rectifying these phase voltages dc The relationship between them is shown in Figure 6. Figure 6 is an example of the relationship between the phase voltages of a three-phase AC and the DC voltage after rectification of each phase voltage. As shown in Figure 6, the DC voltage V dc Ripple is generated by the influence of each phase voltage, and each ripple peaks at the timing when each phase voltage crosses zero. Phase voltage V L1 The peak at the point where it equals 0 is the phase voltage V L2 and V L3 This is due to the influence of the DC voltage V at this timing. dc (Peak value) is the line voltage V L2-L3 It can be considered identical to the same. Similarly, the phase voltage V L2 The peak at the point where it equals 0 is the phase voltage V L3 and V L1 This is due to the influence of the DC voltage V at this timing. dc (Peak value) is the line voltage V L3-L1 It can be considered identical to the following. Phase voltage V L3 The peak at the point where it equals 0 is the phase voltage V L1 and V L2 This is due to the influence of the DC voltage V at this timing. dc (Peak value) is the line voltage V L1-L2 It can be considered identical to the DC voltage V. dc The peak value of each ripple can be determined from the relationship between the phase voltages if the zero-crossing point of any one phase of the three-phase AC is known. For this reason, the zero-crossing detection unit 60 of the motor drive unit 100a detects the zero-crossing point of one phase.

[0032] Using this relationship, the inverter control unit 50a calculates the phase voltage of the three-phase AC voltage using the method shown below.

[0033] The inverter control unit 50a first controls the phase A shown in Figure 7, that is, the phase voltage V L3 Phase voltage V at the zero-crossing pointL1 Calculate the phase A. Note that the phase voltage V L3 At the zero-crossing point, the phase voltage V L3 Since = 0, the DC voltage at this time V dc The phase voltage is V L1 and V L2 Depends on the DC voltage V dc = Line voltage V L1-L2 The following holds true. Figure 7 shows the phase voltage V L3 DC voltage V at the zero-crossing point dc and line voltage V L1-L2 This is a diagram showing the relationship between the two.

[0034] The inverter control unit 50a then determines the intersection point L1 shown in Figure 7. Specifically, the inverter control unit 50a finds the coordinates (x,y) of the intersection point L1 of the two lines obtained by substituting the calculated phase A into the following equations (1) and (2).

[0035] y = tan(A) × x …(1) y = tan(120°-A) × x + V dc …(2)

[0036] The inverter control unit 50a then substitutes the phase A into equation (3) to find the x of the intersection point L1 shown in Figure 7, and then substitutes the found x into equation (1) to find y.

[0037] x=V dc / (tan(A)+tan(120°-A)) …(3)

[0038] The inverter control unit 50a then substitutes the x and y obtained above into equation (4) to obtain the phase voltage V L1 We seek.

[0039] V L1 =√(x^2+y^2) …(4)

[0040] Furthermore, the inverter control unit 50a uses the phase A and phase voltage V obtained above. L1 Using equations (5) and (6), the phase voltage V L2 We seek.

[0041] V dc =V L1 ×sin(A)-V L2 ×sin(A-120°) …(5) V L2 =(V L1 ×sin(A)-V dc ) / sin(A-120°) …(6)

[0042] The inverter control unit 50a controls the phase voltage V in a similar manner. L3 Specifically, the inverter control unit 50a determines the phase voltage V L2 Phase voltage V at the zero-crossing point L1 Calculate the phase B, and the calculated phase B and the phase voltage V L1 Then, using equations (7) and (8), the phase voltage V L3 We seek.

[0043] V dc =V L3 ×sin(B-240°)-V L1 ×sin(B) …(7) V L3 =(V L1 ×sin(B)-V dc ) / sin(B-240°) …(8)

[0044] In this embodiment, the zero-crossing detection unit 60 is configured to detect the zero-crossing point of the phase voltage of any one of the three-phase AC voltages. However, the inverter control unit 50a may also be configured to have a zero-crossing point detection function. That is, a means for detecting the instantaneous value of the phase voltage of any one of the three-phase AC voltages (for example, a voltage sensor) may be provided, and the inverter control unit 50a may detect the zero-crossing point based on the detection result.

[0045] Next, the operation of the motor drive device 100a according to this embodiment will be described. Figure 8 is a flowchart showing an example of the operation of the motor drive device 100a according to Embodiment 2. In Figure 8, the same step numbers as in Figure 2 indicate the same process. The process with the same step numbers as in Figure 2 will not be explained.

[0046] After the inverter control unit 50a acquires the DC voltage value in step S1, the zero-crossing detection unit 60 detects the phase voltage V L1 The zero-crossing point is detected (step S11). Next, the inverter control unit 50a calculates the above-mentioned phase A from the zero-crossing point detected by the zero-crossing detection unit 60 (step S12).

[0047] Next, the inverter control unit 50a receives the DC voltage V detected by the voltage detection unit 40. dc The phase voltages of the three-phase AC are calculated based on the maximum value and phase A (step S13). Here, the DC voltage V dc The maximum value is the DC voltage V dc This is the peak voltage of each ripple. The inverter control unit 50a controls each phase voltage (V) in the manner described above. L1 ,V L2 ,V L3 Calculate ).

[0048] Next, the inverter control unit 50a checks whether the difference in the phase voltages of each phase of the three-phase AC is greater than a predetermined unbalance detection threshold (step S14). Note that the unbalance detection threshold used in step S14 is different from the unbalance detection threshold used in step S3 shown in Figure 2, which was described in Embodiment 1. In step S14, the inverter control unit 50a checks the phase voltage V L1 and V L2 The difference between the phase voltages V L2 and V L3 The difference between and the phase voltage V L3 and V L1 The inverter control unit 50a calculates the difference between the two values, and if one or more of the calculated differences are greater than the unbalance detection threshold, it determines that the three-phase AC voltage is in an unbalanced state (Step S14: Yes), and suppresses the output of the inverter 20 (Step S4). If all of the calculated differences are less than or equal to the unbalance detection threshold, the inverter control unit 50a determines that the three-phase AC voltage is not in an unbalanced state (Step S14: No), and continues normal operation of the inverter 20 (Step S5).

[0049] As described above, the motor drive device 100a according to this embodiment includes a voltage detection unit 40 that detects a DC voltage between the three-phase diode bridge 10 and the DC reactor 30, a zero-crossing detection unit 60 that monitors any one phase of the three-phase AC voltage input from the power supply 1 and detects the zero-crossing point of the voltage, and an inverter control unit 50a that calculates the phase voltage (effective value) of the three-phase AC voltage based on the DC voltage detected by the voltage detection unit 40 and the zero-crossing point detected by the zero-crossing detection unit 60, and detects an unbalanced state of the three-phase AC voltage based on the difference between the phase voltages. When the inverter control unit 50a detects an unbalanced state of the three-phase AC voltage, it suppresses the output of the inverter 20. According to this embodiment, it is possible to realize a motor drive device 100a that can prevent malfunctions such as breaker tripping and damage to components mounted on the circuit board when an unbalanced state of the three-phase AC voltage occurs, and it is also possible to miniaturize the device. Furthermore, since the phase voltage of the three-phase AC voltage is calculated and it is determined whether or not there is an unbalanced state based on the phase voltage, the unbalanced state can be detected with high accuracy.

[0050] Embodiment 3. Embodiment 3 describes application examples of the electric motor drive devices 100 and 100a described in Embodiments 1 and 2.

[0051] Figure 9 shows an example configuration of the air conditioner 200 according to Embodiment 3. The air conditioner 200 shown in Figure 9 is realized by applying the motor drive unit 100 described in Embodiment 1. The air conditioner 200 is an example of a refrigeration cycle device realized by applying the motor drive unit 100. Note that the configuration may also be one in which the motor drive unit 100 is replaced with the motor drive unit 100a described in Embodiment 2.

[0052] The air conditioner 200 comprises an electric motor drive unit 100 connected to a power supply 1 that outputs three-phase AC power, a compressor 71, a four-way valve 72, an outdoor heat exchanger 73, an expansion valve 74, an indoor heat exchanger 75, and refrigerant piping 76. The compressor 71 includes a motor 2 driven by three-phase AC power supplied from the electric motor drive unit 100, and a compression mechanism 77 that compresses the refrigerant. The motor 2 operates the compression mechanism 77.

[0053] The refrigeration cycle is formed by the circulation of refrigerant through the compressor 71, four-way valve 72, outdoor heat exchanger 73, expansion valve 74, indoor heat exchanger 75, and refrigerant piping 76.

[0054] The air conditioner 200 is not limited to a separate-type air conditioner in which the outdoor unit is separated from the indoor unit, but may also be an integrated-type air conditioner in which the compressor 71, indoor heat exchanger 75, and outdoor heat exchanger 73 are provided in a single housing.

[0055] Although an air conditioner 200 was used as an example of a refrigeration cycle device equipped with an electric motor drive unit 100, the refrigeration cycle device is not limited to an air conditioner 200, and may be a refrigerator, a heat pump water heater, or the like.

[0056] Furthermore, in this embodiment, a configuration example has been described in which a motor 2 is used as the drive source for the compressor 71, and the motor 2 is driven by the motor drive device 100. However, a motor 2 driven by the motor drive device 100 may also be used as a drive source for the indoor unit blower and the outdoor unit blower (not shown) provided in the air conditioner 200. Alternatively, a motor 2 driven by the motor drive device 100 may be used as the drive source for the indoor unit blower, the outdoor unit blower, and the compressor 71, respectively.

[0057] As described above, the air conditioner 200 according to this embodiment can detect voltage imbalance in the power supply 1 without being affected by fluctuations in the load connected to the inverter 20 by using the motor drive unit 100 according to Embodiment 1 or the motor drive unit 100a according to Embodiment 2. Furthermore, when voltage imbalance is detected, the output of the inverter 20 can be suppressed, preventing malfunctions such as breaker tripping and damage to components mounted on the circuit board. This maintains the reliability and product life of the air conditioner 200. The same effects as those of the air conditioner 200 can be achieved when the motor drive unit 100 or 100a described in Embodiment 1 or 2 is applied to refrigeration cycle devices other than the air conditioner 200.

[0058] The configurations shown in the above embodiments are examples only, and it is possible to combine them with other known technologies, combine different embodiments, and omit or modify parts of the configuration without departing from the gist of the invention. [Explanation of Symbols]

[0059] 1 Power supply, 2 Motor, 3 Electrolytic capacitor, 10 Three-phase diode bridge, 20 Inverter, 30 DC reactor, 40 Voltage detection unit, 50, 50a Inverter control unit, 60 Zero-cross detection unit, 71 Compressor, 72 Four-way valve, 73 Outdoor heat exchanger, 74 Expansion valve, 75 Indoor heat exchanger, 76 Refrigerant piping, 77 Compression mechanism, 100, 100a Motor drive unit, 200 Air conditioner.

Claims

1. A three-phase diode bridge rectifies a three-phase AC voltage and converts it into a DC voltage, A smoothing capacitor for smoothing the DC voltage, A DC reactor is provided between the three-phase diode bridge and the smoothing capacitor, An inverter that converts the DC voltage smoothed by the smoothing capacitor into an AC voltage and outputs it to a motor, A voltage detection unit for detecting the DC voltage output by the three-phase diode bridge, An inverter control unit detects an unbalanced state of the three-phase AC voltage based on the DC voltage value detected by the voltage detection unit, and controls the inverter based on the detection result of the unbalanced state. A zero-crossing detection unit that detects the zero-crossing point of any one phase of the three-phase AC voltage, Equipped with, The inverter control unit detects the unbalanced state of the three-phase AC voltage based on the DC voltage value and the zero-crossing point detected by the zero-crossing detection unit. Electric motor drive system.

2. A three-phase diode bridge that rectifies a three-phase AC voltage and converts it to a DC voltage, A smoothing capacitor for smoothing the DC voltage, A DC reactor is provided between the three-phase diode bridge and the smoothing capacitor, An inverter that converts the DC voltage smoothed by the smoothing capacitor into an AC voltage and outputs it to a motor, A voltage detection unit for detecting the DC voltage output by the three-phase diode bridge, An inverter control unit detects an unbalanced state of the three-phase AC voltage based on the DC voltage value detected by the voltage detection unit, and controls the inverter based on the detection result of the unbalanced state. Equipped with, The inverter control unit detects the peaks of ripple included in the DC voltage output by the three-phase diode bridge based on the DC voltage value, and determines that the three-phase AC voltage is unbalanced if the difference between adjacent ripple peaks is greater than a predetermined threshold. Electric motor drive system.

3. The inverter control unit determines whether the three-phase AC voltage is in an unbalanced state based on the ripple included in the DC voltage and the zero-crossing point. The electric motor drive device according to claim 1.

4. When the inverter control unit detects an imbalance in the three-phase AC voltage, it suppresses the output of the inverter, making it smaller than the output when the three-phase AC voltage is in a normal state. The electric motor drive device according to claim 1 or 2.

5. The inverter control unit detects the peak of the ripple included in the DC voltage output by the three-phase diode bridge based on the DC voltage value, calculates the voltage of each phase of the three-phase AC voltage based on the detected peak and the zero-crossing point, and detects an unbalanced state of the three-phase AC voltage by comparing the calculated voltages of each phase. The electric motor drive device according to claim 1 or 3.

6. The motor drive device according to claim 1 or 2, The motor drive device generates the power to operate the motor that operates the compression mechanism that compresses the refrigerant circulating in the refrigeration cycle. Air conditioner.

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