Electric motor drive system and refrigeration cycle system

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

Technical Field

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[0001] The present disclosure relates to a motor drive device for driving a motor and a refrigeration cycle device provided with the motor drive device.

Background Art

[0002] In a motor drive device mounted on a refrigeration cycle device, a smoothing capacitor is provided to smooth the power supply voltage applied from an AC power supply. Generally, using a smoothing capacitor with a large capacitance leads to an increase in the size and cost of the motor drive device. On the other hand, using a smoothing capacitor with a small capacitance results in a large amount of current containing a large ripple component flowing through the smoothing capacitor. Hereinafter, in this document, the current flowing through the smoothing capacitor is referred to as "ripple current".

[0003] Under the above technical background, Patent Document 1 below describes a technique for calculating the core temperature of a smoothing capacitor based on the pulsation width of the DC bus voltage, the power supply frequency, and the output power value of the inverter, and suppressing the ripple current flowing through the smoothing capacitor by restricting the output frequency of the inverter when the calculated core temperature exceeds a preset threshold value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When rotating an electric motor in a refrigeration cycle compressor, the motor's load torque fluctuates during one rotation, causing vibrations in the compressor. To suppress these vibrations, the motor drive system controls the inverter so that a current corresponding to the load torque flows to the motor. This control is called "torque control." In torque control, the motor current flowing to the motor is varied according to the motor rotation frequency, which is correlated with the pulsation frequency of the load torque. As a result, the ripple current in the smoothing capacitor increases due to the frequency component caused by the load torque. Furthermore, if the smoothing capacitor has a small capacitance, a current component caused by the power supply frequency flows into the smoothing capacitor.

[0006] As described above, the ripple current flowing through a smoothing capacitor has multiple frequency components depending on the source of the ripple component, so there is a problem in that conventional methods cannot suppress the ripple current.

[0007] This disclosure has been made in view of the above, and aims to provide an electric motor drive device that can implement appropriate control according to the source of the ripple component. [Means for solving the problem]

[0008] To solve the above-mentioned problems and achieve the objective, the motor drive device according to this disclosure comprises a rectifier circuit, a smoothing capacitor, an inverter circuit, a control unit, and a detection unit. The rectifier circuit rectifies the power supply voltage applied from the 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 the motor provided in the compressor, which is the load. The control unit controls the operation of the inverter circuit, and the detection unit detects the ripple current flowing through the smoothing capacitor. The control unit comprises a current waveform detection unit and an output frequency setting unit. The current waveform detection unit detects the current waveform and current value of the ripple current based on the detection value of the detection unit, and the output frequency setting unit sets the 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 thresholded using a preset first threshold, and a second determination process in which specific frequency components included in the current waveform of the ripple current are thresholded using a preset second threshold. Based on the results of the first and second determination processes, the control unit decides whether to reduce the amount of torque control, which varies the motor current flowing through the motor in accordance with fluctuations in the motor's load torque, or to reduce the motor speed, which is the rotational speed of the motor, and controls either the amount of torque control or the motor speed. [Effects of the Invention]

[0009] The electric motor drive device described herein has the effect of enabling appropriate control according to the source of the ripple component. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example of the configuration of a refrigeration cycle system including an electric motor drive unit according to Embodiment 1. [Figure 2] Block diagram showing an example configuration when the functions of the control unit in Embodiment 1 are implemented in software. [Figure 3] Block diagram showing an example configuration when the functions of the control unit in Embodiment 1 are implemented by a processing circuit. [Figure 4]This figure shows an example of a control curve for torque control in Embodiment 1. [Figure 5] Flowchart showing the processing flow by the control unit of Embodiment 1 [Figure 6] A flowchart showing a different processing flow from Figure 5 by the control unit of Embodiment 1. [Figure 7] This figure shows an example configuration of a refrigeration cycle system including an electric motor drive unit according to Embodiment 2. [Modes for carrying out the invention]

[0011] The electric motor drive system and refrigeration cycle system according to the embodiments of this disclosure will be described in detail below with reference to the attached drawings. Note that the various specific setting examples described in the following embodiments are merely examples and are not limited to these specific examples.

[0012] Embodiment 1. Figure 1 shows an example configuration of a refrigeration cycle device 50 including an electric motor drive unit 1 according to Embodiment 1. The refrigeration cycle device 50 comprises an electric motor drive unit 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 Figure 1, the motor drive unit 1 is installed between the AC power supply 3 and the refrigerant circuit 2. The refrigerant circuit 2 comprises a compressor 4, a condenser 5, a throttle device 6, and an evaporator 7. The compressor 4 is the load for the motor drive unit 1 and is equipped with an electric motor 4a. The compressor 4, condenser 5, throttle device 6, and evaporator 7 are connected in a ring by refrigerant piping 21, and a refrigerant cycle is formed by the circulation of refrigerant within the refrigerant piping 21. The motor drive unit 1 converts the AC power supplied from the AC power supply 3 into drive power to drive the compressor 4 and supplies it to the electric motor 4a equipped in the compressor 4.

[0014] The 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 AC200V and AC100V.

[0015] The reactor 9 is connected to the output side of the rectifier circuit 8 and is provided for power factor improvement and harmonic suppression. The smoothing capacitor 10 smooths 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 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 a detection unit in Embodiment 1.

[0016] In the configuration of FIG. 1, a boost circuit may be provided between the rectifier circuit 8 and the smoothing capacitor 10. Also, in FIG. 1, a 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. Further, the four rectifier elements constituting the rectifier circuit 8 may be switching elements.

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

[0018] FIG. 2 is a block diagram showing a configuration example 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, a configuration including a processor 200 that performs calculations, a memory 202 in which a program read by the processor 200 is stored, and an interface 204 that inputs and outputs signals can be adopted.

[0019] The processor 200 is an example of an arithmetic unit. The processor 200 may be an arithmetic unit called a microprocessor, a microcomputer, a microcontroller, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor). Also, examples of the memory 202 include non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), and EEPROM (registered trademark) (Electrically EPROM), magnetic disks, flexible disks, optical disks, compact disks, mini-disks, and DVDs (Digital Versatile Discs).

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

[0021] Furthermore, when realizing the functions of the control unit 20 in Embodiment 1, the configuration shown in Figure 3 may also be used. Figure 3 is a block diagram showing an example configuration when the functions of the control unit 20 in Embodiment 1 are realized by the processing circuit 203. In Figure 3, the processor 200 and memory 202 shown in Figure 2 are replaced by the 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 the interface 204.

[0022] Alternatively, some of the processing in the control unit 20 may be performed by the processing circuit 203, while the processing not performed by the processing circuit 203 may be performed by the processor 200 and memory 202.

[0023] Returning to the explanation of Figure 1, the control unit 20 controls the inverter circuit 11 to convert the smoothed DC voltage into an AC voltage of a set frequency and apply it to the motor 4a of the compressor 4. The motor speed, which is the rotational speed of the motor 4a, is controlled by the AC voltage of the set frequency. The motor speed corresponds to the frequency of the output voltage output from the inverter circuit 11.

[0024] The compressor 4 draws in refrigerant through the rotation of the electric motor 4a, compresses the drawn-in refrigerant to a high-temperature, high-pressure state, and then discharges it. The condenser 5 performs heat exchange between, for example, air and the refrigerant. During heat exchange, the refrigerant is condensed and liquefied. The throttling device 6 reduces the pressure of the refrigerant and causes it to expand. The evaporator 7 performs heat exchange between, for example, air and the refrigerant. During heat exchange, the refrigerant evaporates and turns into a gas.

[0025] Next, we will explain the specific frequency components that may be present in the ripple current of a smoothing capacitor. First, the voltage applied to the smoothing capacitor 10 is the voltage rectified from the AC power supply 3 through the rectifier circuit 8, and therefore it is a voltage that is caused by the power supply frequency, which is the frequency of the power supply voltage. For example, if the AC power supply 3 is single-phase 50Hz and the rectifier circuit 8 is a full-wave rectifier circuit, a pulsating voltage of 100Hz, which is twice the power supply frequency, is applied to the smoothing capacitor 10. Therefore, a large 100Hz current component appears in the ripple current flowing through the smoothing capacitor 10. Hereafter, the frequency component of the ripple current caused by the power supply frequency will be called 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 high, the pulsation of the ripple current also increases, so the 2f component of the power supply also increases, and the 2f component of the power supply becomes the main component of the ripple current. Furthermore, it is well 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] Figure 4 shows an example of a control curve for torque control in Embodiment 1. The horizontal axis represents the motor speed, and the vertical axis represents the torque control amount. Torque control is a control method that suppresses vibration by varying the motor current in accordance with the load torque fluctuations per revolution of the motor. The torque control amount is the control amount for torque control. Due to torque control, the ripple current also exhibits the same frequency components as the motor speed. Hereinafter, the frequency component of the ripple current caused by the load torque will be called the "mechanical 1f component".

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

[0029] In the control curve shown in Figure 4, the operating range of the compressor 4 is divided into three categories: "torque control: high," "torque control: low," and "torque control: zero." In other words, according to the control curve shown in Figure 4, as the motor speed increases, the amount of torque control decreases and eventually becomes zero. The reason the amount of torque control becomes zero is that at higher motor speeds, torque control for vibration suppression becomes unnecessary.

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

[0031] From the above, the main components of the ripple current are the power supply 2f component and the machine 1f component. If 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, thus reducing the power supply 2f component. In this case, the output frequency of the inverter circuit 11 should be controlled to lower the motor speed. On the other hand, if the machine 1f component is the main component of the ripple current, the torque control amount will not decrease even if the inverter output power is lowered, so the machine 1f component cannot be reduced. In this case, the machine 1f component can be reduced by decreasing the torque control amount, which is the cause of the machine 1f component. Although the ripple current should also decrease when the machine 1f component is reduced, if the ripple current remains large, it is thought that some kind of abnormality has occurred, and it is necessary to stop the operation of the compressor 4.

[0032] Next, the method for extracting frequency components contained in the ripple current will be explained with reference to Figure 1. First, as mentioned 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 value detected by 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 mentioned above, the dominant components of the specific frequency components contained in the ripple current are the power supply 2f component and the mechanical 1f component. Therefore, by removing the power supply 2f component extracted by the BPF 13 from the output of the current waveform detection unit 12, the mechanical 1f component can be estimated. Based on this method, the mechanical 1f component estimation unit 14 estimates the mechanical 1f component of the ripple current from the difference between the detected 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] The motor speed limiting unit 15 determines that the main component of the ripple current is the power supply 2f component when the current value of the ripple current exceeds a set threshold and the extracted value of the power supply 2f component also exceeds a set threshold, and performs motor speed limiting control to reduce the motor speed.

[0034] The torque control amount limiting unit 16 determines that the main component of the ripple current is the mechanical 1f component if the current value of the ripple current exceeds a set threshold and the estimated value of the mechanical 1f component also exceeds a set threshold, 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 the operating mode set by the user. The PWM signal calculation unit 18 calculates a PWM signal to control the switching elements (not shown) provided in the inverter circuit 11 and outputs it to the inverter circuit 11.

[0036] Figure 5 is a flowchart showing the processing flow by the control unit 20 of Embodiment 1. The operation of the motor drive device 1 according to Embodiment 1 will be described below with reference to Figure 5. Note that each step in Figure 5 is processed chronologically in the order described, but they 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 value detected by the current sensor 22. In step S2, the control unit 20 determines whether the detected ripple current value exceeds a preset threshold. In this paper, this process will be appropriately referred to as the "first determination process," and the threshold used in the first determination process will be appropriately referred to as the "first threshold." That is, the first determination process is a process in which the current value of the ripple current detected by the current waveform detection unit 12 is subjected to threshold determination using the first threshold. If the ripple current value exceeds the first threshold (step S2, Yes), the process proceeds to step S3. If the ripple current value does not exceed the first threshold (step S2, No), the process proceeds to step S9, and 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 paper, this process will be appropriately referred to as the "second determination process," and the threshold used in the second determination process will be appropriately referred to as the "second threshold." That is, the second determination process is a process that uses the second threshold to determine whether the power supply 2f component, which is a specific frequency component extracted by the BPF 13, exceeds the second threshold. If the power supply 2f component exceeds the second threshold (step S3, Yes), the process proceeds to step S4, where the motor speed limit control described above is implemented, and then to step S9, where the operation of the compressor 4 continues. 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 ripple current value and the extracted power supply 2f component, exceeds a preset threshold. In this paper, this process is appropriately referred to as the "third determination process," and the threshold used in the third determination process is appropriately referred to as the "third threshold." That is, the third determination process is a process in which the machine 1f component, which is caused by the power supply frequency estimated by the control unit 20, is threshold-determined 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 limit control described above is implemented, 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 detected current value of the ripple current exceeds a preset threshold. In this paper, this process will be appropriately referred to as the "fourth determination process," and the threshold used in the fourth determination process will be appropriately referred to as the "fourth threshold." That is, the fourth determination process is a process in which the current value of the ripple current detected by the current waveform detection unit 12 is subjected to threshold determination 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, and 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, and the operation of the compressor 4 is stopped.

[0041] Let me elaborate on step S8. Reaching step S8 means that the 2f component of the power supply is at the second threshold. The following Furthermore, this means that torque control amount limiting control has been implemented to reduce the machine 1f component that exceeds the third threshold. Even with such control, if the current value of the ripple current exceeds the fourth threshold, it is possible that some kind of abnormality has occurred in the motor drive unit 1. For this reason, a determination process in step S8 is provided, and if the current value of the ripple current exceeds the fourth threshold, the operation of the compressor 4 is stopped.

[0042] In steps S6 to S8 described above, the decision to continue or stop the operation of the compressor 4 is made based on the result of a single torque control limit control. However, the decision to continue or stop the operation of the compressor 4 may also be made based on the results of multiple torque control limit control operations. Doing so can prevent excessive control in the torque control limit control.

[0043] Furthermore, in the determination process of step S2 described above, the case where the current value of the ripple current is equal to the first threshold is determined as "No," but it may also be determined as "Yes." In other words, the case where the current value of the ripple current is equal to the first threshold may be determined as either "Yes" or "No."

[0044] Furthermore, in the determination process of step S3 described above, the case where the power supply 2f component and the second threshold are equal is determined as "No," but it may also be determined as "Yes." In other words, the case where the power supply 2f component and the second threshold are equal may be determined as either "Yes" or "No."

[0045] Furthermore, in the determination process of step S5 described above, the case where the machine 1f component and the third threshold are equal is determined as "No," but it may also be determined as "Yes." In other words, the case where the machine 1f component and the third threshold are equal may be determined as either "Yes" or "No."

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

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

[0048] Furthermore, in the flowchart of Figure 5, in step S3, a determination process is performed to compare the power supply 2f component with the second threshold, and then in step S5, a determination process is performed to compare the machine 1f component with the third threshold. In contrast, in the flowchart of Figure 6, in step S13, a determination process is performed to compare the machine 1f component with the second threshold, and then in step S15, a determination process is performed to compare the power supply 2f component with the third threshold. 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] Step S11 in Figure 6, S12, The process in S17~S20 is step S1 in Figure 5. S2, This corresponds to the processing in S7 to S10. Also, the processing in step S14 in Figure 6 corresponds to the processing in step S6 in Figure 5, and the processing in step S16 in Figure 6 corresponds to the processing in step S4 in Figure 5. Although the processing flow is different, the content of each individual process is the same, so further explanation is omitted here.

[0050] Let me elaborate on step S18. Reaching step S18 means that the machine 1f component is at the second threshold. The followingFurthermore, this means that motor speed limiting control has been implemented to reduce the power supply 2f component that exceeds the third threshold. Even with such control, if the ripple current value exceeds the fourth threshold, it is possible that some kind of abnormality has occurred in the motor drive unit 1. For this reason, a determination process in step S18 is provided, and if the ripple current value exceeds the fourth threshold, the operation of the compressor 4 is stopped.

[0051] In steps S16 to S18 described above, the decision to continue or stop the operation of the compressor 4 is made based on the result of a single motor speed limit control. However, the decision to continue or stop the operation of the compressor 4 may also be made based on the results of multiple motor speed limit control operations. Doing so can prevent excessive control in the motor speed limit control.

[0052] As described above, the motor drive device according to Embodiment 1 includes a control unit that controls the operation of an inverter circuit and a detection unit that detects the ripple current flowing through a smoothing capacitor. The control unit also includes a current waveform detection unit that detects the current waveform and current value of the ripple current based on the value detected by the detection unit. The control unit performs a first determination process in which it determines the current value of the ripple current detected by the current waveform detection unit using a preset first threshold, and a second determination process in which it determines the threshold 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 the control amount of the torque control that varies the motor current flowing through the motor in accordance with the fluctuation of the motor's load torque, or to reduce the motor speed, which is the rotational speed of the motor, and controls the control amount of the torque control or the motor speed. In this motor drive system, if the current value of the ripple current detected by the current waveform detection unit is large and exceeds the first threshold, the second threshold is used to determine whether a specific frequency component in the ripple current waveform is due to the power supply frequency or to fluctuations in the motor's load torque. Based on this determination, appropriate control can be selected. This makes it possible to obtain a motor drive system that can implement appropriate control according to the source of the ripple component. Furthermore, by using a motor drive system with such a function, the rate of deterioration of the smoothing capacitor in the motor drive system can be slowed down, thereby extending the product's lifespan.

[0053] Embodiment 2. Figure 7 shows an example configuration of a refrigeration cycle device 50A including an electric motor drive device 1A according to Embodiment 2. Comparing Figure 7 with Figure 1, in the electric motor drive device 1A shown in Figure 7, the control unit 20 is replaced by a control unit 20A, and the BPF 13 is removed from the configuration in Figure 1. Also, in the control unit 20A shown in Figure 7, the machine 1f component estimation unit 14 is removed, and instead, a specific frequency component calculation unit 19 is added. Other configurations are the same as or equivalent to those in Figure 1, and the same or equivalent components are denoted by the same reference numerals, and redundant explanations are omitted.

[0054] Next, the operation of the motor drive device 1A according to Embodiment 2 will be described. Similar to Embodiment 1, the current waveform detection unit 12 detects the current waveform and current value of the ripple current based on the detected value of the current sensor 22. The specific frequency component calculation unit 19 takes 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 specific frequency components included in the ripple current, namely the power supply 2f component and the machine 1f component. The subsequent processing is the same as in Embodiment 1.

[0055] In Embodiment 2, the frequency components of the ripple current are calculated using the Fourier transform, so 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 ripple current value exceeds the threshold, but both the power supply 2f component and the machine 1f component do not exceed the threshold.

[0056] As described above, according to the motor drive device of Embodiment 2, the control unit includes a specific frequency component calculation unit that calculates specific frequency components included in the ripple current based on the current waveform detected by the current waveform detection unit. The specific frequency component calculation unit calculates a first component caused by the power supply frequency and a second component caused by fluctuations in the motor load torque as specific frequency components in a single calculation process, so that, as with Embodiment 1, it is possible to perform appropriate control according to the source of the ripple component. Furthermore, according to the motor drive device of Embodiment 2, it is also possible to obtain the distribution of frequency components other than the power supply 2f component and the machine 1f component, so it is possible to perform cause analysis when an abnormal stop occurs without both the power supply 2f component and the machine 1f component exceeding a threshold.

[0057] The configurations shown in the above embodiments are merely examples, 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]

[0058] 1, 1A Motor drive unit, 2 Refrigerant circuit, 3 AC power supply, 4 Compressor, 4a Motor, 5 Condenser, 6 Throttle device, 7 Evaporator, 8 Rectifier circuit, 9 Reactor, 10 Smoothing capacitor, 11 Inverter circuit, 12 Current waveform detection unit, 13 BPF, 14 Mechanical 1f component estimation unit, 15 Motor rotation speed limiting unit, 16 Torque control amount limiting unit, 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 unit, 200 Processor, 202 Memory, 203 Processing circuit, 204 Interface.

Claims

1. A rectifier circuit that rectifies the power supply voltage applied from an AC power source, A smoothing capacitor that smooths 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 an electric motor equipped in a compressor, which is a load, A control unit that controls the operation of the inverter circuit, The system includes a detection unit for detecting the ripple current flowing through the smoothing capacitor, The control unit, A current waveform detection unit that detects the current waveform and current value of the ripple current based on the detected value of the detection unit, The system includes an output frequency setting unit for setting the output frequency of the drive voltage. The control unit, The current waveform detection unit performs a first determination process to determine the current value of the ripple current detected by the current waveform detection unit using a preset first threshold, and a second determination process to determine the threshold 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, it is determined whether to reduce the control amount of the torque control that varies the motor current flowing through the motor in accordance with the fluctuation of the motor's load torque, or to reduce the motor speed, which is the rotational speed of the motor, and the control amount of the torque control or the motor speed is controlled accordingly. Electric motor drive system.

2. The detection unit is A bandpass filter connected in series with the smoothing capacitor, The system is configured to include a current sensor that detects the current flowing between the smoothing capacitor and the bandpass filter. The electric motor drive device according to claim 1.

3. The detection unit is configured to have a current sensor that detects the 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 aforementioned specific frequency component is a first component resulting from the power supply frequency, which is the frequency of the power supply voltage. The electric motor drive device according to claim 1.

5. If the first determination process determines that the current value of the ripple current exceeds the first threshold, and the second determination process determines that the first component exceeds the second threshold, The control unit controls the output frequency to reduce the motor rotation speed. The electric motor drive device according to claim 4.

6. If the first determination process determines that the current value of the ripple current exceeds the first threshold, and the second determination process determines that the first component does not exceed the second threshold, the control unit performs a third determination process to determine the second component caused by fluctuations in the load torque of the electric motor using a preset third threshold. If the third determination process determines that the second component exceeds the third threshold, The control unit reduces the amount of torque control set based on the output frequency. The electric motor drive device according to claim 5.

7. After reducing the control amount of the torque control, the control unit further performs a fourth determination process to determine the current value of the ripple current using a preset fourth threshold. If the fourth determination process determines that the current value of the ripple current exceeds the fourth threshold, the control unit stops the operation of the compressor. The electric motor drive device according to claim 6.

8. After reducing the control amount of the torque control, the control unit further performs a fourth determination process to determine the current value of the ripple current using a preset fourth threshold. If the fourth determination process determines that the current value of the ripple current does not exceed the fourth threshold, the control unit continues to operate the compressor. The electric motor drive device according to claim 6.

9. If the third determination process determines that the second component does not exceed the third threshold, the control unit stops the operation of the compressor. The electric motor drive device according to claim 6.

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

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

12. If the first determination process determines that the current value of the ripple current exceeds the first threshold, and the second determination process determines that the second component does not exceed the second threshold, the control unit performs a third determination process to determine the threshold of the first component, which is the power supply frequency, using a preset third threshold. If the third determination process determines that the first component exceeds the third threshold, The control unit controls the output frequency to reduce the motor rotation speed. The electric motor drive device according to claim 11.

13. The control unit controls the output frequency to reduce the motor speed, and then performs a fourth determination process to determine the current value of the ripple current using a preset fourth threshold. If the fourth determination process determines that the current value of the ripple current exceeds the fourth threshold, the control unit stops the operation of the compressor. The electric motor drive device according to claim 12.

14. The control unit controls the output frequency to reduce the motor speed, and then performs a fourth determination process to determine the current value of the ripple current using a preset fourth threshold. If the fourth determination process determines that the current value of the ripple current does not exceed the fourth threshold, the control unit continues to operate the compressor. The electric motor drive device according to claim 12.

15. If the third determination process determines that the first component does not exceed the third threshold, the control unit stops the operation of the compressor. The electric motor drive device according to claim 12.

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

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