Motor drive device and refrigeration cycle device

Abstract

A motor drive device (1) comprises: a control unit (20) that controls the operation of an inverter circuit (11); and a current sensor (22) and a BPF (13), which are detection units for detecting a ripple current flowing through a smoothing capacitor (10). The control unit (20) includes a current waveform detection unit (12) for detecting a current waveform and a current value of the ripple current, on the basis of the detection values of the detection units. The control unit (20) performs: first determination processing for performing a threshold value determination, using a first threshold value, of the current value of the ripple current detected by the current waveform detection unit (12): and second determination processing for performing a threshold value determination, using a second threshold value, of a specific frequency component included in the current waveform of the ripple current. The control unit (20) controls a torque control amount or a motor rotation speed by determining, on the basis of the results of the first and second determination processing, whether to reduce the control amount of torque control for varying the motor current in accordance with a variation in load torque of a motor (4a), or to reduce the motor rotation speed of the motor (4a).

Description

Electric motor drive device and refrigeration cycle device

[0001] The present disclosure relates to an electric motor drive device that drives an electric motor, and a refrigeration cycle apparatus that includes the electric motor drive device.

[0002] The motor drive unit installed in the refrigeration cycle equipment is equipped with a smoothing capacitor to smooth the power supply voltage applied from the AC power source. Generally, using a smoothing capacitor with a large capacity leads to an increase in the size and cost of the motor drive unit. On the other hand, if a smoothing capacitor with a small capacity is used, a current containing a large ripple component flows through the smoothing capacitor. In this article, the current flowing through the smoothing capacitor will be referred to as "ripple current."

[0003] Against the above technical background, Patent Document 1 below describes a technology in which the core temperature of a smoothing capacitor is calculated based on the pulsation amplitude of a DC bus voltage, the power supply frequency, and the output power value of an inverter, and if the calculated core temperature exceeds a preset threshold, the output frequency of the inverter is limited to suppress the ripple current flowing through the smoothing capacitor.

[0004] JP 2013-66299 A

[0005] When rotating an electric motor provided in a compressor of a refrigeration cycle device, the load torque of the electric motor fluctuates during one rotation of the motor, causing vibration of the compressor. To suppress this vibration, the electric motor drive device controls the inverter so that a current corresponding to the load torque flows to the electric motor. This control is called "torque control." Torque control fluctuates the electric motor current flowing to the electric motor according to the electric motor rotation frequency, which is correlated with the pulsation frequency of the load torque. Therefore, the ripple current of the smoothing capacitor increases with the frequency component caused by the load torque. Furthermore, if the capacity of the smoothing capacitor is small, a current component caused by the power supply frequency flows into the smoothing capacitor.

[0006] As described above, the ripple current flowing through the smoothing capacitor has a plurality of frequency components depending on the source of the ripple components, and therefore, conventional methods have the problem that the ripple current cannot be suppressed.

[0007] The present disclosure has been made in view of the above, and has an object to provide an electric motor drive device that can perform appropriate control in accordance with the source of the ripple component.

[0008] To solve the above-mentioned problems and achieve the object, an electric motor drive device according to the present disclosure includes a rectifier circuit, a smoothing capacitor, an inverter circuit, a control unit, and a detection unit. The rectifier circuit rectifies a power supply voltage applied from an AC power supply, and the smoothing capacitor smooths the voltage rectified by the rectifier circuit. The inverter circuit converts the DC voltage smoothed by the smoothing capacitor into a drive voltage for driving an electric motor provided in a compressor, which is a load. The control unit controls the operation of the inverter circuit, and the detection unit detects a ripple current flowing through the smoothing capacitor. The control unit includes a current waveform detection unit and an output frequency setting unit. The current waveform detection unit detects a current waveform and current value of the ripple current based on a value detected by the detection unit, and the output frequency setting unit sets an output frequency of the drive voltage. The control unit performs a first determination process in which the current value of the ripple current detected by the current waveform detection unit is threshold-determined using a preset first threshold, and a second determination process in which a specific frequency component included in the current waveform of the ripple current is threshold-determined using a preset second threshold. Based on the results of the first and second judgment processes, the control unit determines whether to reduce the control variable of the torque control, which varies the motor current flowing to the motor in accordance with fluctuations in the load torque of the motor, or to reduce the motor rotation speed, which is the rotational speed of the motor, and controls the control variable of the torque control or the motor rotation speed.

[0009] The electric motor drive device according to the present disclosure has the advantage of being able to perform appropriate control according to the source of the ripple component.

[0010] FIG. 1 is a diagram showing a configuration example of a refrigeration cycle device including an electric motor drive device according to a first embodiment. FIG. 2 is a block diagram showing a configuration example when the functions of the control unit in the first embodiment are realized by software. FIG. 3 is a block diagram showing a configuration example when the functions of the control unit in the first embodiment are realized by a processing circuit. FIG. 4 is a diagram showing an example of a control curve for torque control in the first embodiment.

[0011] Hereinafter, an electric motor drive device and a refrigeration cycle device according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. Note that various specific setting examples described in the following embodiments are merely examples, and the present disclosure is not limited to these specific examples.

[0012] 1 is a diagram showing an example of the configuration of a refrigeration cycle device 50 including an electric motor drive device 1 according to embodiment 1. The refrigeration cycle device 50 includes the electric motor drive device 1 and a refrigerant circuit 2. The refrigeration cycle device 50 can be applied to products equipped with a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters.

[0013] As shown in Fig. 1, the electric motor drive device 1 is provided between an AC power source 3 and a refrigerant circuit 2. The refrigerant circuit 2 includes a compressor 4, a condenser 5, a throttling device 6, and an evaporator 7. The compressor 4 is a load of the electric motor drive device 1 and includes an electric motor 4a. The compressor 4, the condenser 5, the throttling device 6, and the evaporator 7 are connected in a ring shape by refrigerant piping 21, and a refrigeration cycle is formed by refrigerant circulating within the refrigerant piping 21. The electric motor drive device 1 converts AC power supplied from the AC power source 3 into drive power for driving the compressor 4 and supplies the drive power to the electric motor 4a provided in the compressor 4.

[0014] The electric motor drive device 1 includes a rectifier circuit 8, a reactor 9, a smoothing capacitor 10, an inverter circuit 11, a BPF (Band Pass Filter) 13, a current sensor 22, and a control unit 20. The rectifier circuit 8 rectifies the power supply voltage applied from the AC power supply 3. Examples of the power supply voltage include AC 200V and AC 100V.

[0015] The reactor 9 is connected to the output side of the rectifier circuit 8 and is provided for power factor improvement and harmonics suppression. The smoothing capacitor 10 smoothes the voltage rectified by the rectifier circuit 8. The inverter circuit 11 converts the DC voltage smoothed by the smoothing capacitor 10 into a drive voltage for driving the electric motor 4a. The BPF 13 is connected in series with the smoothing capacitor 10, and the current sensor 22 detects the ripple current flowing between the smoothing capacitor 10 and the BPF 13. The BPF 13 and the current sensor 22 function as the detection unit in the first embodiment.

[0016] In the configuration of Fig. 1, a boost circuit may be provided between the rectifier circuit 8 and the smoothing capacitor 10. In Fig. 1, the reactor 9 is inserted between the rectifier circuit 8 and the smoothing capacitor 10, but the reactor 9 may be inserted between the AC power supply 3 and the rectifier circuit 8. In addition, the four rectifier elements constituting the rectifier circuit 8 may be switching elements.

[0017] The control unit 20 includes, as components for controlling the operation of the inverter circuit 11 in the first embodiment, a current waveform detection unit 12, a machine 1f component estimation unit 14, a motor rotation speed limiting unit 15, a torque control amount limiting unit 16, an output frequency setting unit 17, and a PWM (Pulse Width Modulation) signal calculation unit 18. The operation of each of these units will be described later.

[0018] Fig. 2 is a block diagram showing an example of a configuration when the functions of the control unit 20 in embodiment 1 are realized by software. When the functions of the control unit 20 in embodiment 1 are realized by software, as shown in Fig. 2, the configuration can include a processor 200 that performs calculations, a memory 202 that stores programs read by the processor 200, and an interface 204 that inputs and outputs signals.

[0019] The processor 200 is an example of a computing unit. The processor 200 may be a computing unit called a microprocessor, a microcomputer, a microcontroller, a central processing unit (CPU), or a digital signal processor (DSP). Examples of the memory 202 include non-volatile or volatile semiconductor memory such as a random access memory (RAM), a read-only memory (ROM), a flash memory, an erasable programmable read-only memory (EPROM), or an electrically programmable read-only memory (EEPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, and a digital versatile disk (DVD).

[0020] The memory 202 stores a program that executes the functions of the control unit 20, which will be described later. The processor 200 exchanges necessary information via the interface 204, executes the program stored in the memory 202, and refers to the table stored in the memory 202, thereby performing the above-mentioned processing. The calculation results by the processor 200 can be stored in the memory 202.

[0021] Furthermore, when realizing the functions of the control unit 20 in the first embodiment, the configuration shown in Fig. 3 may be used. Fig. 3 is a block diagram showing an example configuration when the functions of the control unit 20 in the first embodiment are realized by a processing circuit 203. In Fig. 3, the processor 200 and memory 202 shown in Fig. 2 are replaced with a processing circuit 203. The processing circuit 203 may be a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. Information input to the processing circuit 203 and information output from the processing circuit 203 can be exchanged via an interface 204.

[0022] It is also possible that some of the processing in the control unit 20 is performed by the processing circuit 203 , and the processing that is not performed by the processing circuit 203 is performed by the processor 200 and the memory 202 .

[0023] Returning to the explanation of Fig. 1 , under the control of the control unit 20, the inverter circuit 11 converts the smoothed DC voltage into an AC voltage of a set frequency and applies it to the electric motor 4a of the compressor 4. The electric motor rotation speed, which is the rotation speed of the electric motor 4a, is controlled by the AC voltage of the set frequency. The electric motor rotation speed corresponds to the frequency of the output voltage output from the inverter circuit 11.

[0024] The compressor 4 draws in refrigerant by rotating the electric motor 4a, compresses the drawn refrigerant to a high-temperature, high-pressure state, and then discharges it. The condenser 5 exchanges heat between, for example, air and the refrigerant. During heat exchange, the refrigerant is condensed and liquefied. The expansion device 6 reduces the pressure of the refrigerant to expand it. The evaporator 7 exchanges heat between, for example, air and the refrigerant. During heat exchange, the refrigerant is evaporated and gasified.

[0025] Next, we will explain the specific frequency components that may be included in the ripple current of the smoothing capacitor. First, the voltage applied to the smoothing capacitor 10 is a voltage rectified from the AC power source 3 through the rectifier circuit 8, and therefore is a voltage resulting from the power supply frequency, which is the frequency of the power supply voltage. For example, if the AC power source 3 is single-phase 50 Hz and the rectifier circuit 8 is a full-wave rectifier circuit, a pulsating voltage of 100 Hz, which is twice the power supply frequency, is applied to the smoothing capacitor 10. Therefore, the 100 Hz current component also appears significantly in the ripple current flowing through the smoothing capacitor 10. Hereinafter, the frequency component resulting from the power supply frequency of the ripple current will be referred to as the "power supply 2f component." The power supply 2f component is a specific frequency component included in the ripple current.

[0026] When the motor rotation speed is high and the inverter power output from the inverter circuit 11 is large, the ripple of the ripple current also becomes large, and the power supply 2f component also becomes large, and the power supply 2f component becomes the main component of the ripple current. Furthermore, it is known that when the AC power supply 3 is a three-phase power supply, a frequency component six times the power supply frequency appears.

[0027] FIG. 4 is a diagram showing an example of a control curve for torque control in the first embodiment. The horizontal axis represents the motor rotation speed, and the vertical axis represents the torque control amount. Torque control is a control that suppresses vibration by varying the motor current in accordance with the load torque fluctuations per rotation of the motor. The torque control amount is the control amount for torque control. Due to torque control, the same frequency component as the motor rotation speed also appears in the ripple current. Hereinafter, the frequency component of the ripple current caused by the load torque will be referred to as the "machine 1f component."

[0028] As described above, the ripple current has a power supply 2f component and a machine 1f component as specific frequency components. In this paper, the power supply 2f component is sometimes referred to as the "first component" and the machine 1f component is sometimes referred to as the "second component."

[0029] In the control curve shown in Fig. 4, the operating range of the compressor 4 is divided into three ranges: "large torque control," "small torque control," and "zero torque control." That is, according to the control curve shown in Fig. 4, as the motor rotation speed increases, the torque control amount decreases and eventually becomes zero. The torque control amount becomes zero because the higher the motor rotation speed, the less torque control is required for vibration suppression.

[0030] Therefore, when the motor rotation speed is low and the inverter output power is small, the torque control amount increases, which increases the mechanical 1f component, and the mechanical 1f component becomes the main component of the ripple current. However, for example, if the compressor 4 is a twin rotary type, two periodic fluctuations occur for each load torque fluctuation of one rotation of the motor. In this case, the ripple current contains a mechanical 2f component, which is a frequency component twice the motor rotation speed. Note that this paper will explain an example in which the mechanical 1f component is the main component of the ripple current, but the control flow is similar when the mechanical 2f component is the main component of the ripple current.

[0031] From the above, the main components of the ripple current can be the power supply 2f component and the machine 1f component. When the power supply 2f component is the main component of the ripple current, the ripple current can be reduced by lowering the inverter output power, and therefore the power supply 2f component can be reduced. In this case, the output frequency of the inverter circuit 11 can be controlled to reduce the motor rotation speed. On the other hand, when the machine 1f component is the main component of the ripple current, the torque control variable does not decrease even if the inverter output power is reduced, and therefore the machine 1f component cannot be reduced. In this case, the machine 1f component is reduced by reducing the torque control variable, which is the cause of the machine 1f component. Although reducing the machine 1f component should reduce the ripple current, if the ripple current remains large, it is considered that some kind of abnormality has occurred, and operation of the compressor 4 must be stopped.

[0032] Next, a method for extracting frequency components contained in the ripple current will be described with reference to FIG. 1 . First, as described above, the current sensor 22 detects the current flowing between the smoothing capacitor 10 and the BPF 13. The current waveform detection unit 12 detects the current waveform and current value of the ripple current based on the detection value of the current sensor 22. The BPF 13 is a bandpass filter corresponding to the frequency of the power supply 2f component and extracts the power supply 2f component contained in the ripple current. As described above, the specific frequency components contained in the ripple current are dominated by the power supply 2f component and the machine 1f component. Therefore, the machine 1f component can be estimated by removing the power supply 2f component extracted by the BPF 13 from the output of the current waveform detection unit 12. Based on this method, the machine 1f component estimation unit 14 estimates the machine 1f component of the ripple current from the difference between the detection value of the ripple current output from the current waveform detection unit 12 and the extracted value of the power supply 2f component extracted by the BPF 13.

[0033] If the current value of the ripple current exceeds a set threshold and the extracted value of the power supply 2f component exceeds a set threshold, the motor rotation speed limiting unit 15 determines that the main component of the ripple current is the power supply 2f component and performs motor rotation speed limiting control to reduce the motor rotation speed.

[0034] If the current value of the ripple current exceeds a set threshold and the estimated value of the machine 1f component exceeds a set threshold, the torque control amount limiting unit 16 determines that the main component of the ripple current is the machine 1f component and performs torque control amount limiting control to reduce the torque control amount.

[0035] The output frequency setting unit 17 sets the output frequency of the inverter output power supplied by the inverter circuit 11, for example, based on an operation mode set by a user. The PWM signal calculation unit 18 calculates a PWM signal for controlling a switching element (not shown) provided in the inverter circuit 11, and outputs the PWM signal to the inverter circuit 11.

[0036] Fig. 5 is a flowchart showing a processing flow by the control unit 20 according to embodiment 1. The operation of the electric motor drive device 1 according to embodiment 1 will be described below with reference to Fig. 5. Note that the steps in Fig. 5 are processed in chronological order in the order shown, but may also be executed in parallel or individually.

[0037] In step S1, the control unit 20 detects the current value of the ripple current based on the detection value of the current sensor 22. In step S2, the control unit 20 determines whether the current value of the detected ripple current exceeds a preset threshold. In this document, this process is referred to as the "first determination process" as appropriate, and the threshold used in the first determination process is referred to as the "first threshold." That is, the first determination process is a process of threshold-determining the current value of the ripple current detected by the current waveform detection unit 12 using the first threshold. If the current value of the ripple current exceeds the first threshold (step S2, Yes), the process proceeds to step S3. If the current value of the ripple current does not exceed the first threshold (step S2, No), the process proceeds to step S9, where the operation of the compressor 4 continues.

[0038] In step S3, the control unit 20 determines whether the power supply 2f component extracted by the BPF 13 exceeds a preset threshold. In this document, this process is referred to as the "second determination process" as appropriate, and the threshold used in the second determination process is referred to as the "second threshold." That is, the second determination process is a process of threshold-determining the power supply 2f component, which is a specific frequency component extracted by the BPF 13, using the second threshold. If the power supply 2f component exceeds the second threshold (step S3, Yes), the process proceeds to step S4, where the aforementioned motor rotation speed limit control is performed, and then the process proceeds to step S9, where the operation of the compressor 4 is continued. If the power supply 2f component does not exceed the second threshold (step S3, No), the process proceeds to step S5.

[0039] In step S5, the control unit 20 determines whether the machine 1f component estimated using the difference between the detected value of the ripple current and the extracted value of the power supply 2f component exceeds a preset threshold. In this document, this process is referred to as the "third determination process" as appropriate, and the threshold used in the third determination process is referred to as the "third threshold." That is, the third determination process is a process of threshold-determining the machine 1f component resulting from the power supply frequency estimated by the control unit 20 using the third threshold. If the machine 1f component exceeds the third threshold (step S5, Yes), the process proceeds to step S6, where the torque control amount limiting control described above is performed, and the process proceeds to step S7. If the machine 1f component does not exceed the third threshold (step S5, No), the process proceeds to step S10, where the operation of the compressor 4 is stopped.

[0040] In step S7, the control unit 20 detects the current value of the ripple current and proceeds to step S8. In step S8, the control unit 20 determines whether the current value of the detected ripple current exceeds a preset threshold. In this document, this process is referred to as the "fourth determination process" as appropriate, and the threshold used in the fourth determination process is referred to as the "fourth threshold." That is, the fourth determination process is a process of threshold-determining the current value of the ripple current detected by the current waveform detection unit 12 using the fourth threshold. If the current value of the ripple current does not exceed the fourth threshold (step S8, Yes), the process proceeds to step S9, where the operation of the compressor 4 continues. If the current value of the ripple current exceeds the fourth threshold (step S8, No), the process proceeds to step S10, where the operation of the compressor 4 is stopped.

[0041] A supplementary note about step S8: Reaching step S8 means that torque control amount limiting control has been performed to reduce the power supply 2f component, which is smaller than the second threshold, and the machine 1f component, which exceeds the third threshold. Even after performing such control, if the current value of the ripple current exceeds the fourth threshold, it is possible that some abnormality has occurred in the motor drive device 1. For this reason, the determination process of step S8 is provided, and if the current value of the ripple current exceeds the fourth threshold, operation of the compressor 4 is stopped.

[0042] In the above-described processing of steps S6 to S8, a determination is made as to whether to continue or stop the operation of the compressor 4 based on the result of one execution of the torque control amount limit control, but a determination as to whether to continue or stop the operation of the compressor 4 may be made based on the result of multiple executions of the torque control amount limit control. In this way, excessive control in the torque control amount limit control can be prevented.

[0043] In addition, in the determination process of step S2 described above, when the current value of the ripple current is equal to the first threshold value, the determination is made as "No," but the determination may also be made as "Yes." That is, when the current value of the ripple current is equal to the first threshold value, the determination may be made as either "Yes" or "No."

[0044] In addition, in the determination process of step S3 described above, when the power supply 2f component is equal to the second threshold, the determination is made as "No," but the determination may also be made as "Yes." That is, when the power supply 2f component is equal to the second threshold, the determination may be made as either "Yes" or "No."

[0045] In addition, in the determination process of step S5 described above, the case where the machine 1f component is equal to the third threshold is determined as "No," but the case where the machine 1f component is equal to the third threshold may be determined as "Yes." That is, the case where the machine 1f component is equal to the third threshold may be determined as either "Yes" or "No."

[0046] In addition, in the determination process of step S8 described above, when the current value of the ripple current is equal to the fourth threshold, the determination is made as "Yes," but the determination may also be made as "No." That is, when the current value of the ripple current is equal to the fourth threshold, the determination may be made as either "Yes" or "No."

[0047] Fig. 6 is a flowchart showing a processing flow by the control unit 20 of the first embodiment, which is different from that shown in Fig. 5. In the flowchart of Fig. 5, a determination process is performed in step S2 to compare the current value of the ripple current with a first threshold, and then a determination process is performed in step S3 to compare the power supply 2f component with a second threshold. In contrast, in the flowchart of Fig. 6, a determination process is performed in step S12 to compare the current value of the ripple current with a first threshold, and then a determination process is performed in step S13 to compare the machine 1f component with a second threshold.

[0048] 5, after the determination process of comparing the power supply 2f component with the second threshold in step S3, the determination process of comparing the machine 1f component with the third threshold is performed in step S5. In contrast, in the flowchart of FIG. 6, after the determination process of comparing the machine 1f component with the second threshold in step S13, the determination process of comparing the power supply 2f component with the third threshold is performed in step S15. As explained here, in this paper, the threshold used in the determination processes of steps S3 and S13 is called the "second threshold," and the threshold used in the determination processes of steps S5 and S15 is called the "third threshold."

[0049] The processes of steps S11 and S17 to S20 in Fig. 6 correspond to the processes of steps S1 and S7 to S10 in Fig. 5. The process of step S14 in Fig. 6 corresponds to the process of step S6 in Fig. 5, and the process of step S16 in Fig. 6 corresponds to the process of step S4 in Fig. 5. Although the process flow is different, the individual process contents are the same, and further explanation will be omitted here.

[0050] A supplementary note about step S18: Reaching step S18 means that the motor rotation speed limiting control has been performed to reduce the power supply 2f component, which is smaller than the second threshold and exceeds the third threshold. If the current value of the ripple current exceeds the fourth threshold even after performing such control, it is possible that some abnormality has occurred in the motor drive device 1. For this reason, the determination process of step S18 is provided, and if the current value of the ripple current exceeds the fourth threshold, the operation of the compressor 4 is stopped.

[0051] In the above-described processing of steps S16 to S18, the determination of whether to continue or stop the operation of the compressor 4 is made based on the result of one execution of the motor rotation speed limit control, but the determination of whether to continue or stop the operation of the compressor 4 may be made based on the results of multiple executions of the motor rotation speed limit control. In this way, excessive control in the motor rotation speed limit control can be prevented.

[0052] As described above, the electric motor drive device according to the first embodiment includes a control unit that controls the operation of the inverter circuit and a detection unit that detects a ripple current flowing through the smoothing capacitor. The control unit also includes a current waveform detection unit that detects a current waveform and a current value of the ripple current based on a value detected by the detection unit. The control unit performs a first determination process that performs a threshold determination of the current value of the ripple current detected by the current waveform detection unit using a preset first threshold, and a second determination process that performs a threshold determination of a specific frequency component included in the current waveform of the ripple current using a preset second threshold. Based on the results of the first and second determination processes, the control unit determines whether to reduce a control variable of torque control that varies the motor current flowing through the electric motor in accordance with fluctuations in the load torque of the electric motor, or to reduce the electric motor rotation speed, which is the rotational speed of the electric motor, and controls the control variable of torque control or the electric motor rotation speed. In an electric motor drive device configured in this manner, when the ripple current detected by the current waveform detector is large and exceeds the first threshold, the second threshold is used to determine whether a specific frequency component contained in the current waveform of the ripple current is a component caused by the power supply frequency or a component caused by fluctuations in the load torque of the electric motor, and appropriate control can be selected based on the determination result. This makes it possible to obtain an electric motor drive device that can perform appropriate control according to the source of the ripple component. Furthermore, using an electric motor drive device with such a function can slow the rate of deterioration of the smoothing capacitor provided in the electric motor drive device, thereby extending the product life.

[0053] Second Embodiment Fig. 7 is a diagram showing a configuration example of a refrigeration cycle apparatus 50A including an electric motor drive device 1A according to a second embodiment. Comparing Fig. 7 with Fig. 1, in the electric motor drive device 1A shown in Fig. 7, the control unit 20 is replaced with a control unit 20A, and the BPF 13 is deleted from the configuration of Fig. 1. Furthermore, in the control unit 20A shown in Fig. 7, the machine 1f component estimator 14 is deleted, and instead, a specific frequency component calculator 19 is added. The other configuration is the same as or equivalent to that of Fig. 1, and the same or equivalent components are denoted by the same reference numerals, and redundant description will be omitted.

[0054] Next, the operation of the electric motor drive device 1A according to the second embodiment will be described. As in the first embodiment, the current waveform detection unit 12 detects the current waveform and current value of the ripple current based on the detection value of the current sensor 22. The specific frequency component calculation unit 19 receives the current waveform output from the current waveform detection unit 12 as an input signal, and performs a Fourier transform on the current waveform to calculate the power supply 2f component and machine 1f component, which are specific frequency components contained in the ripple current. The subsequent processing is the same as in the first embodiment.

[0055] In the second embodiment, the frequency components of the ripple current are calculated by Fourier transform, so that the distribution of frequency components other than the power supply 2f component and the machine 1f component can also be obtained. The frequency components other than the power supply 2f component and the machine 1f component are useful for analyzing the cause of an abnormal shutdown when the current value of the ripple current exceeds the threshold but neither the power supply 2f component nor the machine 1f component exceeds the threshold.

[0056] As described above, according to the electric motor drive device of the second embodiment, the control unit includes a specific frequency component calculation unit that calculates specific frequency components contained in the ripple current based on the current waveform detected by the current waveform detection unit. The specific frequency component calculation unit calculates the first component caused by the power supply frequency and the second component caused by fluctuations in the load torque of the electric motor as specific frequency components through a single calculation process, so that appropriate control can be performed according to the source of the ripple components, as in the first embodiment. Furthermore, according to the electric motor drive device of the second embodiment, the distribution of frequency components other than the power supply 2f component and the machine 1f component can also be obtained, so that it is possible to analyze the cause of an abnormal stop when both the power supply 2f component and the machine 1f component do not exceed their thresholds.

[0057] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0058] 1, 1A electric motor drive device, 2 refrigerant circuit, 3 AC power supply, 4 compressor, 4a electric motor, 5 condenser, 6 throttling device, 7 evaporator, 8 rectifier circuit, 9 reactor, 10 smoothing capacitor, 11 inverter circuit, 12 current waveform detection unit, 13 BPF, 14 machine 1f component estimator, 15 electric motor rotation speed limiter, 16 torque control amount limiter, 17 output frequency setting unit, 18 PWM signal calculation unit, 19 specific frequency component calculation unit, 20, 20A control unit, 21 refrigerant piping, 22 current sensor, 50, 50A refrigeration cycle device, 200 processor, 202 memory, 203 processing circuit, 204 interface.

Claims

1. a rectifier circuit that rectifies a power supply voltage applied from an AC power supply; a smoothing capacitor that smoothes the voltage rectified by the rectifier circuit; an inverter circuit that converts the DC voltage smoothed by the smoothing capacitor into a drive voltage for driving a motor provided in a compressor, which is a load; a control unit that controls the operation of the inverter circuit; a detection unit that detects a ripple current flowing through the smoothing capacitor, The control unit a current waveform detection unit that detects a current waveform and a current value of the ripple current based on a detection value of the detection unit; an output frequency setting unit that sets the output frequency of the drive voltage; The control unit a first determination process for determining a current value of the ripple current detected by the current waveform detection unit based on a first threshold value set in advance, and a second determination process for determining a specific frequency component included in the current waveform of the ripple current based on a second threshold value set in advance; Based on the results of the first and second determination processes, it is determined whether to reduce a control amount of torque control that varies the motor current flowing through the motor in accordance with fluctuations in the load torque of the motor, or to reduce the motor rotation speed, which is the rotation speed of the motor, and control the control amount of torque control or the motor rotation speed. Electric motor drive unit.

2. The detection unit a bandpass filter connected in series to the smoothing capacitor; a current sensor that detects a current flowing between the smoothing capacitor and the band-pass filter. The electric motor drive device according to claim 1 .

3. the detection unit includes a current sensor that detects a current flowing through the smoothing capacitor, The control unit includes a specific frequency component calculation unit that calculates the specific frequency component included in the ripple current based on the current waveform detected by the current waveform detection unit. The electric motor drive device according to claim 1 .

4. The specific frequency component is a first component resulting from a power supply frequency, which is the frequency of the power supply voltage. The electric motor drive device according to claim 1 .

5. When the first determination process determines that the current value of the ripple current exceeds the first threshold value, and the second determination process determines that the first component exceeds the second threshold value, The control unit controls the output frequency to reduce the rotation speed of the electric motor.

5. The electric motor drive device according to claim 4.

6. When the first determination process determines that the current value of the ripple current exceeds the first threshold value and the second determination process determines that the first component does not exceed the second threshold value, the control unit performs a third determination process in which a second component caused by a fluctuation in load torque of the motor is subjected to a threshold determination using a preset third threshold value; When it is determined by the third determination process that the second component exceeds the third threshold, The control unit reduces a control amount of the torque control that is set based on the output frequency.

6. The electric motor drive device according to claim 5.

7. the control unit, after reducing the control amount of the torque control, further performs a fourth determination process of determining the current value of the ripple current using a preset fourth threshold value; When it is determined by the fourth determination process that the current value of the ripple current exceeds the fourth threshold value, the control unit stops the operation of the compressor.

7. The electric motor drive device according to claim 6.

8. the control unit, after reducing the control amount of the torque control, further performs a fourth determination process of determining the current value of the ripple current using a preset fourth threshold value; When it is determined by the fourth determination process that the current value of the ripple current does not exceed the fourth threshold value, the control unit continues operation of the compressor.

7. The electric motor drive device according to claim 6.

9. When it is determined in the third determination process that the second component does not exceed the third threshold value, the control unit stops the operation of the compressor.

7. The electric motor drive device according to claim 6.

10. The specific frequency component is a second component caused by fluctuations in the load torque of the motor. The electric motor drive device according to claim 1 .

11. When the first determination process determines that the current value of the ripple current exceeds the first threshold value, and the second determination process determines that the second component exceeds the second threshold value, The control unit reduces a control amount of the torque control that is set based on the output frequency. The electric motor drive device according to claim 10.

12. When the first determination process determines that the current value of the ripple current exceeds the first threshold value and the second determination process determines that the second component does not exceed the second threshold value, the control unit performs a third determination process in which a first component caused by a power supply frequency, which is the frequency of the power supply voltage, is determined based on a preset third threshold value; If it is determined by the third determination process that the first component exceeds the third threshold, The control unit controls the output frequency to reduce the rotation speed of the electric motor. The electric motor drive device according to claim 11.

13. the control unit controls the output frequency to reduce the number of revolutions of the electric motor, and then performs a fourth determination process of determining a current value of the ripple current using a preset fourth threshold value; When it is determined by the fourth determination process that the current value of the ripple current exceeds the fourth threshold value, the control unit stops the operation of the compressor.

13. The electric motor drive device according to claim 12.

14. the control unit controls the output frequency to reduce the number of revolutions of the electric motor, and then performs a fourth determination process of determining a current value of the ripple current using a preset fourth threshold value; When it is determined by the fourth determination process that the current value of the ripple current does not exceed the fourth threshold value, the control unit continues operation of the compressor.

13. The electric motor drive device according to claim 12.

15. When it is determined in the third determination process that the first component does not exceed the third threshold value, the control unit stops the operation of the compressor.

13. The electric motor drive device according to claim 12.

16. A refrigeration cycle apparatus comprising the motor drive device according to any one of claims 1 to 15, wherein the compressor operates a refrigeration cycle.

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