Motor drive device and air conditioner

Abstract

A motor drive device (100) is provided with: a three-phase diode bridge (10) that rectifies a three-phase AC voltage and converts the rectified three-phase AC voltage into a DC voltage; an electrolytic capacitor (3) for smoothing 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 unbalanced state of the three-phase AC voltage on the basis of a DC voltage value, which is a detection value of the DC voltage detected by the voltage detection unit (40), and that controls the inverter (20) on the basis of the detection result of the unbalanced state.

Description

Technical Field

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

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

[0003] In a motor drive device having a three-phase diode bridge structure, when the input three-phase AC voltage is unbalanced, an imbalance occurs in the input current, and pulsation also occurs in the DC voltage rectified by the three-phase diode bridge. If pulsation occurs in the rectified DC voltage, it is possible that the circuit breaker trips and components mounted on the substrate are damaged. In response to such a problem, 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 supply, and protects the circuit components by suppressing the output of the inverter when it is in an unbalanced state.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2017-22920

[0005] In the process of determining whether the three-phase AC is in an unbalanced state, the above-mentioned conventional motor drive device estimates the line voltage, and then compares the unbalance coefficient calculated based on the estimated result of the line voltage with a predetermined threshold value to detect the unbalanced state. Therefore, the conventional motor drive device needs to provide a voltage detection circuit for at least two phases of the three-phase AC, which leads to a large device, complicated processing, and increased processing load. Accordingly, it is desired to realize a motor drive device that can miniaturize the device and reduce the processing load. Summary of the invention

[0006] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to obtain a motor drive device that can achieve miniaturization of the device and reduce the processing load.

[0007] In order to solve the above-mentioned problems and achieve the purpose, the motor drive device disclosed in the present invention comprises: a three-phase diode bridge, which rectifies the three-phase AC voltage and converts it into a DC voltage; a smoothing capacitor, which smoothes the DC voltage; a DC inductor, which is arranged between the three-phase diode bridge and the smoothing capacitor; an inverter, which converts the DC voltage smoothed by the smoothing capacitor into an AC voltage and outputs it to the motor; a voltage detection unit, which detects the DC voltage output by the three-phase diode bridge; and an inverter control unit, which detects the unbalanced state of the three-phase AC voltage based on the detection value of the DC voltage detected by the voltage detection unit, that is, the DC voltage value, and controls the inverter based on the detection result of the unbalanced state.

[0008] The motor drive device disclosed herein can achieve the effect of reducing the size of the device and reducing the processing load. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a diagram showing a configuration example of the motor drive device according to the first embodiment.

[0010] Figure 2 This is a flowchart showing an example of the operation of the motor drive device according to the first embodiment.

[0011] Figure 3 This is a diagram for explaining the ripple voltage calculated by the inverter control unit according to the first embodiment.

[0012] Figure 4 This is a diagram showing a configuration example of a motor drive device according to a second embodiment.

[0013] Figure 5 This is a diagram showing an example of the relationship between the phase voltages of three-phase AC and the line voltages.

[0014] Figure 6 This is a diagram showing an example of the relationship between the voltage of each phase of three-phase AC and the DC voltage obtained by rectifying the voltage of each phase.

[0015] Figure 7 This is a diagram showing the relationship between the DC voltage and the line voltage at the zero-crossing point of the phase voltage.

[0016] Figure 8 This is a flowchart showing an example of the operation of the motor drive device according to the second embodiment.

[0017] Fig. 9 It is a diagram showing a configuration example of an air conditioner according to Embodiment 3. DETAILED DESCRIPTION

[0018] Hereinafter, a motor drive device and an air conditioner according to an embodiment of the present disclosure will be described in detail based on the drawings.

[0019] Implementation method 1.

[0020] Figure 1 1 is a diagram showing a configuration example of a motor drive device 100 according to Embodiment 1. The motor drive device 100 is connected to a power source 1 via three power lines L1 to L3, and receives a supply of three-phase AC power from the power source 1 to drive a motor 2. That is, the motor drive device 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 driving power for the motor 2. In addition, the motor 2 is a three-phase motor.

[0021] The motor drive device 100 includes: a three-phase diode bridge 10 that rectifies and converts a three-phase AC voltage supplied from a power source 1 as a three-phase AC power source into a DC voltage; an electrolytic capacitor 3 that is a smoothing capacitor that smoothes the DC voltage output from the three-phase diode bridge 10; an inverter 20 that converts the DC voltage smoothed by the electrolytic capacitor 3 into a three-phase AC voltage and applies it to the motor 2; and a DC reactor 30 that is provided between the three-phase diode bridge 10 and the electrolytic capacitor 3 and suppresses harmonic currents included in the DC current flowing between the three-phase diode bridge 10 and the inverter 20. In addition, the motor drive device 100 includes: a voltage detection unit 40 that is connected between the three-phase diode bridge 10 and the DC reactor 30 and detects the DC voltage output from the three-phase diode bridge 10; and an inverter control unit 50 that receives a DC voltage value that is a detection value of the DC voltage detected by the voltage detection unit 40 and gives a command generated based on the input DC voltage value to the inverter 20 to generate driving power for the motor 2. In addition, although Figure 1 Although not described in the description, the detected value of the voltage output by the inverter 20 and the voltage command are input to the inverter control unit 50. The inverter control unit 50 generates a command to the inverter 20 based on the detected value of the voltage output by the inverter 20 and the voltage command and the DC voltage value. The voltage detection unit 40 is implemented by, for example, a voltage sensor. The inverter control unit 50 is implemented by, for example, a microcontroller.

[0022] The detailed operation will be described separately, but in the motor drive device 100, the inverter control unit 50 determines whether the three-phase AC voltage supplied from the power supply 1 is in an unbalanced state based on the detection result of the DC voltage detected by the voltage detection unit 40, and suppresses the output of the inverter 20 when it is in an unbalanced state.

[0023] Here, as described above, when 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) is also generated in the DC voltage rectified by the three-phase diode bridge 10. That is, if the three-phase AC voltage becomes unbalanced, the ripple component contained in the DC voltage increases. Therefore, by monitoring the DC voltage rectified by the three-phase diode bridge 10, the imbalance of the three-phase AC voltage can be detected. The inverter control unit 50 of the motor drive device 100 of the present embodiment uses such characteristics to detect the imbalance of the three-phase AC voltage. As a result, there is no need to set up a circuit for detecting the voltage of each phase of the three-phase AC input from the power supply 1, and the device can be miniaturized and cost-effective.

[0024] In addition, since ripples in the DC voltage also occur when the load of the inverter 20 to which a DC voltage is applied changes, the motor drive device 100 is configured to detect the DC voltage between the three-phase diode bridge 10, where the influence of load changes is small, and the DC reactor 30. In addition, when the assumed maximum change amount of the load connected to the inverter 20 is small, that is, when the ripples generated due to load changes are negligible compared to the ripples generated due to the imbalance of the three-phase AC voltage, it may also be configured to detect the DC voltage 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).

[0025] Figure 2 is a flowchart showing an example of the operation of the motor drive device 100 according to Embodiment 1. Specifically, Figure 2 The flowchart shows an operation example in which the inverter control unit 50 of the motor drive device 100 determines whether there is an imbalance in the power supply voltage and controls the inverter 20 according to the determination result.

[0026] When the motor drive device 100 is performing a power conversion operation for generating drive power for the motor 2, the inverter control unit 50 repeats the operation according to the Figure 2 flowchart. That is, when the motor drive device 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 period.

[0027] Specifically, first, the inverter control unit 50 acquires a DC voltage value (step S1). In detail, the inverter control unit 50 acquires the detected value of the DC voltage from the voltage detection unit 40.

[0028] Next, the inverter control unit 50 calculates a ripple voltage based on the DC voltage value acquired in step S1 (step S2). Figure 3 is used to explain the ripple voltage calculated by the inverter control unit 50 in Embodiment 1. 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 represents the DC voltage detected by the voltage detection unit 40, and V L1 , V L2 and V L3 represent the voltages of the respective phases of the three-phase AC input to the motor drive device 100 from each of the three power lines L1 to L3. The horizontal axis represents time, and the vertical axis represents voltage. Figure 3 represents the voltages V L1 and V L2and V L3 With DC voltage V dc An example of the corresponding relationship. Figure 3 As shown, the ripple voltage calculated by the inverter control unit 50 refers to the difference in size between adjacent ripples contained in the DC voltage, that is, the voltage difference between adjacent vertices. In step S2, the inverter control unit 50 detects the vertex of the ripple by analyzing the latest DC voltage value obtained from the voltage detection unit 40 and the DC voltage value obtained in the past, and calculates the ripple voltage based on the detected vertex. For example, when the inverter control unit 50 analyzes the DC voltage value to detect the vertex of the latest ripple, it finds the difference between the detected vertex and the vertex of the ripple detected last time, and uses the difference as the ripple voltage.

[0029] Next, the inverter control unit 50 compares the ripple voltage calculated in step S2 with a predetermined threshold value for imbalance detection (hereinafter referred to as imbalance detection threshold value) (step S3). The imbalance detection threshold value is predetermined by performing an operation simulation of the motor drive device 100 or the like.

[0030] When the ripple voltage is greater than the threshold value for imbalance detection (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 the maximum output of the inverter 20 does not exceed N% of the maximum output under normal conditions. In addition, N < 100, which means that the three-phase AC voltage is not unbalanced under normal conditions. The above-mentioned N can be a variable value. For example, when the ripple voltage is greatly different from the threshold value for imbalance detection, N can also be changed so that N becomes a smaller value. In addition, it is also possible to prepare a plurality of different imbalance detection thresholds and the value of N corresponding to each imbalance detection threshold, and determine the value of N to be used based on the comparison result between the ripple voltage and each imbalance detection threshold.

[0031] When the ripple voltage is below the unbalanced 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, the three-phase AC voltage is in a normal state, and the inverter 20 continues to operate normally (step S5). In addition, in the case of normal operation, the inverter control unit 50 controls so that the voltage output by the inverter 20 follows the voltage command.

[0032] As described above, the motor drive device 100 of the present 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, and 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 the present embodiment, it is possible to realize the motor drive device 100 that can prevent the occurrence of unfavorable conditions such as circuit breaker tripping and damage to components mounted on the substrate when an unbalanced three-phase AC voltage occurs, and it is possible to realize miniaturization of the device and reduction of processing load.

[0033] Implementation method 2.

[0034] The motor drive device 100 of the above-mentioned first embodiment determines whether the three-phase AC voltage is in an unbalanced state 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 threshold value for imbalance detection. In contrast, in this embodiment, a motor drive device 100a that can detect imbalance with high accuracy even when the DC voltage fluctuates greatly due to the influence of the fluctuation of the load connected to the inverter 20 is described.

[0035] Figure 4 FIG. 1 is a diagram showing a configuration example of a motor drive device 100a according to Embodiment 2. Figure 4 In, with Figure 1 The same reference numerals are used to denote the common components of the motor drive device 100 of the first embodiment. Figure 1 The description of components denoted by the same reference numerals will be omitted.

[0036] The motor drive device 100 a has a configuration in which the inverter control unit 50 of the motor drive device 100 of the first embodiment is replaced with the inverter control unit 50 a and a zero-crossing detection unit 60 is added.

[0037] The zero-crossing detection unit 60 monitors any one phase of the three-phase AC voltage 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. Figure 4 In the structure shown, the zero-crossing detection unit 60 detects the voltage V L1 The zero-crossing detection unit 60 is implemented by, for example, a voltage sensor, a logic circuit that determines the sign of a voltage detection value using the voltage sensor, and the like.

[0038] The inverter control unit 50a generates an instruction to 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 based on the DC voltage value and the zero crossing point (hereinafter, the voltage of one phase is referred to as phase voltage). Then, the inverter control unit 50a determines whether the three-phase AC voltage is in an unbalanced state based on the calculated effective value of each phase voltage, and controls the output of the inverter 20 according to the determination result. In addition, in order to simplify the description, the effective value of the phase voltage is recorded as "phase voltage" in the following description.

[0039] Here, a method in which the inverter control unit 50a calculates 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.

[0040] The phase voltage V of the three-phase AC L1 、V L2 and V L3 With line voltage V L1-L2 、V L2-L3 and V L3-L1 There exists Figure 5 Here, the line voltage V L1-L2 is the potential difference between power lines L1 and L2, the line voltage V L2-L3 is the potential difference between power lines L2 and L3, the line voltage V L3-L1 is the potential difference between power lines L3 and L1. In addition, Figure 5 This is a diagram showing an example of the relationship between the phase voltages of three-phase AC and the line voltages.

[0041] In addition, the phase voltage V L1 、V L2 and V L3 The DC voltage V obtained by rectifying these phase voltages dc There exists Figure 6 In addition, Figure 6 : is a diagram showing an example of the relationship between the voltage of each phase of three-phase AC and the DC voltage after rectification of each phase voltage. Figure 6 As shown, the DC voltage V dc The ripples are generated due to the influence of each phase voltage, and each ripple becomes a peak value when the phase voltage passes through zero. L1 = 0 is due to the phase voltage V L2 and V L3 The timing of the DC voltage V dc (peak value) is considered to be the same as the line voltage V L2-L3 Similarly, the phase voltage VL2 = 0 is due to the phase voltage V L3 and V L1 The timing of the DC voltage V dc (peak value) is considered to be the same as the line voltage V L3-L1 Same. Phase voltage V L3 = 0 is due to the phase voltage V L1 and V L2 The timing of the DC voltage V dc (peak value) is considered to be the same as the line voltage V L1-L2 In addition, as long as the zero crossing point of any phase in the three-phase AC is known, the DC voltage V can be derived from the relationship between the phase voltages. dc Therefore, the zero-crossing detection unit 60 of the motor drive device 100a detects the zero-crossing point of one phase.

[0042] Using such a relationship, the inverter control unit 50a calculates each phase voltage of the three-phase AC voltage by the method described below.

[0043] First, the inverter control unit 50a calculates Figure 7 Phase A shown, that is, phase voltage V L3 The phase voltage V at the zero crossing point L1 Phase A. In addition, due to the phase voltage V L3 The phase voltage V at the zero crossing point L3 =0, so the DC voltage V dc Depends on the phase voltage V L1 and V L2 , DC voltage V dc = Line voltage V L1-L2 Established. Figure 7 It represents the phase voltage V L3 The DC voltage V at the zero crossing point dc With line voltage V L1-L2 Graph of the relationship.

[0044] Next, the inverter control unit 50a obtains Figure 7 Specifically, the inverter control unit 50a obtains the coordinates (x, y) of the intersection point L1 of two lines obtained by substituting the calculated phase A into the following equations (1) and (2).

[0045] y=tan(A)××…(1)

[0046] y=tan(120°-A)×x+V dc …(2)

[0047] Next, the inverter control unit 50a substitutes the phase A into the following equation (3) to obtain Figure 7 The x of the intersection point L1 shown is substituted into equation (1) to obtain y.

[0048] x=V dc / (tan(A)+tan(120°-A))…(3)

[0049] Next, the inverter control unit 50a substitutes the obtained x and y into the following equation (4) to obtain the phase voltage V L1 .

[0050]

[0051] In addition, the inverter control unit 50a uses the phase A and phase voltage V obtained above. L1 The phase voltage V is obtained by using the following equations (5) and (6): L2 .

[0052] V dc =V L1 ×sin(A)-V L2 ×sin(A-120°)…(5)

[0053] V L2 =(V L1 ×sin(A)-V dc ) / sin(A-120°)…(6)

[0054] The inverter control unit 50a obtains the phase voltage V by the same method. L3 Specifically, the inverter control unit 50a calculates the phase voltage V L2 The phase voltage V at the zero crossing point L1 Phase B, using the calculated phase B, phase voltage V L1 And the following equations (7) and (8) are used to calculate the phase voltage V L3 .

[0055] V dc =V L3 ×sin(B-240°)-V L1 ×sin(B)…(7)

[0056] V L3 =(V L1 ×sin(B)-V dc ) / sin(B-240°)…(8)

[0057] In addition, in the present embodiment, the zero-crossing detection unit 60 is configured to detect the zero-crossing point of the phase voltage of any phase in the three-phase AC voltage, but the inverter control unit 50a may also be configured to have a zero-crossing detection function. That is, a unit (such as a voltage sensor) that detects the instantaneous value of the phase voltage of any phase in the three-phase AC voltage may also be provided, and the inverter control unit 50a detects the zero-crossing point based on the detection result.

[0058] Next, the operation of the motor drive device 100 a according to the present embodiment will be described. Figure 8 2 is a flowchart showing an example of the operation of the motor drive device 100a according to the second embodiment. Figure 8 In, with Figure 2 The same step numbers indicate the same processing. Figure 2 The description of the processes with the same step numbers is omitted.

[0059] After the inverter control unit 50a obtains the DC voltage value in step S1, the zero-crossing detection unit 60 detects the phase voltage V L1 Next, the inverter control unit 50a calculates the phase A based on the zero-crossing point detected by the zero-crossing detection unit 60 (step S12).

[0060] Next, the inverter control unit 50a controls the DC voltage V detected by the voltage detection unit 40. dc The maximum value and phase A of the three-phase AC are used to calculate the voltage of each phase (step S13). dc The maximum value refers to the DC voltage V dc The inverter control unit 50a calculates the voltage of each phase (V L1 、V L2 、V L3 ).

[0061] Next, the inverter control unit 50a checks whether the difference between the phase voltages of the three-phase AC is greater than a predetermined unbalance detection threshold value (step S14). The unbalance detection threshold value used in step S14 is the same as that described in the first embodiment. Figure 2 The unbalance detection threshold used in step S3 shown in FIG. 1 is different. In step S14, the inverter control unit 50a calculates the phase voltage V L1 With V L2 The difference between the phase voltage V L2 With V L3 The difference between the phase voltage V L3 With V L1When the calculated differences are all below the unbalanced detection threshold, the inverter control unit 50a determines that the three-phase AC voltage is not in an unbalanced state (step S14: No), and the inverter 20 continues to operate normally (step S5).

[0062] As described above, the motor drive device 100a of the present embodiment includes: the voltage detection unit 40 that detects the DC voltage between the three-phase diode bridge 10 and the DC reactor 30; the 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 the 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 the unbalanced state of the three-phase AC voltage based on the difference between the phase voltages, and the inverter control unit 50a suppresses the output of the inverter 20 when the unbalanced state of the three-phase AC voltage is detected. According to the present embodiment, the motor drive device 100a can be realized that can prevent the occurrence of malfunctions such as circuit breaker tripping and damage to components mounted on the substrate when the three-phase AC voltage is unbalanced, and can achieve miniaturization of the device. Furthermore, since the phase voltages of the three-phase AC voltages are calculated and whether or not an unbalanced state is present is determined based on the phase voltages, the unbalanced state can be detected with high accuracy.

[0063] Implementation method 3.

[0064] In the third embodiment, application examples of the motor drive devices 100 and 100 a described in the first and second embodiments will be described.

[0065] Fig. 9 This is a diagram showing a configuration example of an air conditioner 200 according to Embodiment 3. Fig. 9 The air conditioner 200 shown is realized by applying the motor drive device 100 described in Embodiment 1. The air conditioner 200 is an example of a refrigeration cycle device realized by applying the motor drive device 100. In addition, the motor drive device 100 may be replaced with the motor drive device 100a described in Embodiment 2.

[0066] The air conditioner 200 includes a motor drive device 100 connected to a power source 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 a refrigerant pipe 76. The compressor 71 includes a motor 2 driven by three-phase AC power supplied from the motor drive device 100 and a compression mechanism 77 that compresses refrigerant. The motor 2 operates the compression mechanism 77.

[0067] The refrigerant circulates through the compressor 71, the four-way valve 72, the outdoor heat exchanger 73, the expansion valve 74, the indoor heat exchanger 75, and the refrigerant pipe 76, thereby forming a refrigeration cycle.

[0068] The air conditioner 200 is not limited to a split-type air conditioner in which the outdoor unit and the indoor unit are separated, and may also be an integrated air conditioner in which the compressor 71, the indoor heat exchanger 75, and the outdoor heat exchanger 73 are provided in one housing.

[0069] In addition, as a refrigeration cycle device including the motor drive device 100, the air conditioner 200 has been described as an example. However, the refrigeration cycle device is not limited to the air conditioner 200, and may also be a refrigerator, a heat pump hot water supply device, or the like.

[0070] In addition, in the present embodiment, a configuration example in which the motor 2 is applied as a drive source of the compressor 71 and the motor 2 is driven by the motor drive device 100 has been described. However, as a drive source for driving an indoor unit blower and an outdoor unit blower (not shown) included in the air conditioner 200, the motor 2 driven by the motor drive device 100 may also be applied. In addition, as a drive source for each of the indoor unit blower, the outdoor unit blower, and the compressor 71, the motor 2 driven by the motor drive device 100 may also be applied.

[0071] As described above, the air conditioner 200 of the present embodiment can detect the voltage imbalance of the power source 1 without being affected by the variation of the load connected to the inverter 20 by using the motor drive device 100 of Embodiment 1 or the motor drive device 100a of Embodiment 2. In addition, when a voltage imbalance is detected, the output of the inverter 20 can be suppressed, and abnormal conditions such as a circuit breaker trip and damage to components mounted on the substrate can be prevented. Thereby, the reliability and product life of the air conditioner 200 can be maintained. When the motor drive device 100 or 100a described in Embodiment 1 or 2 is applied to a refrigeration cycle device other than the air conditioner 200, the same effects as those of the air conditioner 200 can also be achieved.

[0072] The structures shown in the above embodiments represent an example, and can be combined with other known technologies, or the embodiments can be combined with each other. Within the scope not departing from the gist, a part of the structure can also be omitted or changed.

[0073] Description of Reference Numerals

[0074] 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-crossing 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 device; 200...air conditioner.

Claims

1. A motor drive device, It is characterized in that have: A three-phase diode bridge that rectifies the three-phase AC voltage and converts it into a DC voltage; a smoothing capacitor for smoothing the DC voltage; a DC reactor disposed 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 the AC voltage to a motor; a voltage detection unit, which detects the DC voltage output by the three-phase diode bridge; as well as The inverter control unit detects an unbalanced state of the three-phase AC voltage based on a DC voltage value which is a detection value of the DC voltage detected by the voltage detection unit, and controls the inverter based on a detection result of the unbalanced state.

2. The motor drive device according to claim 1, It is characterized in that When the inverter control unit detects an unbalanced state of the three-phase AC voltage, it suppresses the output of the inverter to be lower than the output when the three-phase AC voltage is in a normal state.

3. The motor drive device according to claim 1 or 2, It is characterized in that The inverter control unit detects the apex of ripples 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 in an unbalanced state when a difference between adjacent ripple apexes is greater than a predetermined threshold.

4. The motor drive device according to claim 1 or 2, It is characterized in that A zero-crossing detection unit is provided, which detects a zero-crossing point of any phase of the three-phase AC voltage, 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.

5. The motor drive device according to claim 4, It is characterized in that The inverter control unit detects the apex of the ripple contained 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 apex and the zero crossing point, and compares the calculated voltages of each phase to detect an unbalanced state of the three-phase AC voltage.

6. An air conditioner, It is characterized in that A motor drive device according to any one of claims 1 to 5, The electric motor driving device generates driving power for a motor that operates a compression mechanism that compresses refrigerant circulating in a refrigeration cycle.

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