Motor drive device and refrigeration circuit device

Abstract

A motor drive device (1) comprises a control unit (20) that controls the operation of an inverter circuit (11), as well as a current sensor (22) and a bandpass filter (13), which together form a sensing unit for detecting a ripple current flowing to a smoothing capacitor (10). The control unit (20) comprises a current waveform sensing unit (12) that detects a current waveform and a current value of the ripple current based on a sensing value from the sensing unit.The control unit (20) performs a first determination operation to establish a threshold for the current value of the ripple current detected by the current waveform detection unit (12), using a first threshold value. It then performs a second determination operation to establish a threshold for a specific frequency component included in the current waveform of the ripple current, using a second threshold value. Based on the results of the first and second determination operations, the control unit (20) determines whether to decrease the degree of torque control to change a motor current in accordance with a change in the load torque of a motor (4a), or whether to decrease the motor speed of the motor (4a), and controls the torque control degree or the motor speed accordingly.

Description

Technical field

[0001] The present disclosure relates to a motor drive device that drives an electric motor (hereinafter referred to simply as the motor) and a refrigeration circuit device that includes the motor drive device. background

[0002] A motor drive device installed in a refrigeration circuit includes a smoothing capacitor for smoothing a supply voltage applied by an alternating current (AC) power supply. Using a high-capacity smoothing capacitor generally results in a larger and more expensive motor drive device. Conversely, using a low-capacity smoothing capacitor results in a current with a high ripple component flowing to the smoothing capacitor. This current flowing to the smoothing capacitor is referred to as the "ripple current."

[0003] Against the foregoing technical background, the patent literature 1 mentioned below describes a technology which reduces the ripple current flowing to the smoothing capacitor such that the core temperature of the smoothing capacitor is calculated on the basis of the pulsation amplitude of the DC bus voltage, the power supply frequency and the output power value of the inverter and the output frequency of the inverter is limited when the calculated core temperature exceeds a predetermined threshold. List of patent literature

[0004] Patent literature 1: Japanese patent application publication number 2013 - 66 299 (JP 2013 - 66 299 A) Overview of the invention Problem to be solved by the invention

[0005] When the motor enclosed in the compressor of the refrigeration circuit device is rotated, the motor's load torque varies during one revolution, which can cause compressor vibration. To reduce or prevent this vibration, the motor drive device controls the inverter so that a current corresponding to the load torque flows to the motor. This control is called "torque control." Torque control causes the motor current flowing to the motor to vary according to the motor rotational frequency, which correlates with the pulsation frequency of the load torque. This increases the current with a frequency component due to the load torque in the ripple current of the smoothing capacitor. If the smoothing capacitor has a low capacitance, a current component due to the power supply frequency also flows into the smoothing capacitor.

[0006] As described above, the ripple current flowing into the smoothing capacitor comprises several frequency components, depending on the source of the ripple component. This therefore poses a problem: it is impossible to reduce the ripple current using such a conventional method.

[0007] The present disclosure was made in view of the foregoing considerations, and it is an objective of the present disclosure to provide a motor drive device capable of performing control suitable for the source of the ripple component. Means to solve the problem

[0008] To solve the problem and achieve the goal described above, a motor drive device according to the present disclosure comprises a rectifier circuit, a smoothing capacitor, an inverter circuit, a control unit, and a sensing unit. The rectifier circuit rectifies a supply voltage applied from an AC power supply. The smoothing capacitor smooths a voltage obtained by rectification, which is passed through the rectifier circuit. The inverter circuit converts a DC voltage smoothed by the smoothing capacitor into a drive voltage for driving a motor enclosed in a compressor, which is a load. Furthermore, the control unit controls the operation of the inverter circuit. The sensing unit detects a ripple current flowing to the smoothing capacitor.The control unit comprises a current waveform acquisition unit and an output frequency setting unit. The current waveform acquisition unit acquires a current waveform and current value of the ripple current based on a sensing value from the acquisition unit. The output frequency setting unit sets an output frequency of the drive voltage. The control unit performs a first determination operation and a second determination operation. The first determination operation is an operation to perform a threshold determination for the current value of the ripple current acquired by the current waveform acquisition unit using a first predetermined threshold. The second determination operation is an operation to perform a threshold determination for a specific frequency component included in the current waveform of the ripple current using a second predetermined threshold.Based on the results of the first and second determination operations, the control unit determines whether to reduce the degree of control of a torque control or to reduce the motor speed, and controls the degree of control of the torque control or the motor speed, wherein the torque control is a control to change a motor current flowing to the motor according to a change in the load torque of the motor, and wherein the motor speed is a speed of the motor. Effects of the invention

[0009] A motor drive device according to the present disclosure provides an advantageous effect with respect to the ability to perform a control suitable for the source of the ripple component. Brief description of the drawings Fig. Figure 1 is a diagram showing an exemplary configuration of a refrigeration circuit device including a motor drive device according to a first embodiment. Fig. Figure 2 is a block diagram showing an exemplary configuration when a function of a control unit in the first embodiment is implemented in software. Fig. Figure 3 is a block diagram showing an exemplary configuration when the function of the control unit in the first embodiment is implemented in a processing circuit. Fig. Figure 4 is a diagram showing an example of a control curve for the torque control performed in the first embodiment. Fig. Figure 5 is a flowchart showing a process flow carried out by the control unit of the first embodiment. Fig. 6 is a flowchart that shows one of the ones in Fig. The process sequence shown in section 5 differs from that of the control unit of the first embodiment. Fig. Figure 7 is a diagram showing an exemplary configuration of a refrigeration circuit device including a motor drive device according to a second embodiment. Description of the embodiments

[0010] A motor drive device and a refrigeration circuit device according to embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. It should be noted that the various specific examples of settings described in the following embodiments are only examples and the settings are not limited to these specific examples. First embodiment.

[0011] Fig. Figure 1 is a diagram showing an exemplary configuration of a refrigeration circuit device 50, including a motor drive device 1, according to a first embodiment. The refrigeration circuit device 50 comprises the motor drive device 1 and a refrigerant circuit 2. The refrigeration circuit device 50 is applicable to products that include a refrigeration circuit, such as an air conditioner, a refrigerator, a freezer, and a heat pump water heater.

[0012] As in Fig. As shown in Figure 1, the motor drive device 1 is arranged between an AC power supply 3 and the refrigerant circuit 2. The refrigerant circuit 2 comprises a compressor 4, a condenser 5, an expansion device 6, and an evaporator 7. The compressor 4 is a load for the motor drive device 1 and includes a motor 4a. The components of the compressor 4, the condenser 5, the expansion device 6, and the evaporator 7 are connected to each other in a ring-shaped configuration by a refrigerant line 21. The circulation of a refrigerant in the refrigerant line 21 forms a refrigeration cycle. The motor drive device 1 converts the AC power supplied by the AC power supply 3 into drive power to drive the compressor 4 and delivers this drive power to the motor 4a enclosed within the compressor 4.

[0013] The motor drive device 1 comprises a rectifier circuit 8, an inductor 9, a smoothing capacitor 10, an inverter circuit 11, a bandpass filter (BPF) 13, a current sensor 22, and a control unit 20. The rectifier circuit 8 rectifies a supply voltage applied by the AC power supply 3. Examples of the supply voltage are 200 V AC and 100 V AC.

[0014] The choke 9 is connected to the output side of the rectifier circuit 8. The choke 9 serves to improve the power factor and reduce harmonics. The smoothing capacitor 10 smooths a voltage obtained by the rectification of the rectifier circuit 8. The inverter circuit 11 converts a DC voltage smoothed by the smoothing capacitor 10 into a drive voltage for driving the motor 4a. The bandpass filter 13 is connected in series with the smoothing capacitor 10. The current sensor 22 detects a ripple current flowing between the smoothing capacitor 10 and the bandpass filter 13. In the first embodiment, the bandpass filter 13 and the current sensor 22 together function as a detection unit.

[0015] It should be noted that in the configuration of Fig. 1. A step-up circuit may be provided between the rectification circuit 8 and the smoothing capacitor 10. Although in Fig. 1. The choke 9 is arranged between the rectification circuit 8 and the smoothing capacitor 10; the choke 9 can also be arranged between the AC power supply 3 and the rectification circuit 8. Furthermore, the rectification circuit 8 comprises four rectifier elements, which can be switching elements.

[0016] The control unit 20 comprises a component for controlling the operation of the inverter circuit 11 in the first embodiment. This component includes a current waveform detection unit 12, a mechanical 1f component estimation unit 14, a motor speed limiting unit 15, a torque control degree limiting unit 16, an output frequency setting unit 17, and a pulse width modulation (PWM) signal calculation unit 18. The operation of these components will be described later.

[0017] Fig. Figure 2 is a block diagram showing an exemplary configuration when a function of the control unit 20 in the first embodiment is implemented in software. When the function of the control unit 20 in the first embodiment is implemented in software, the control unit 20 can, as shown in Fig. 2 shown, configured to include a processor 200 that performs calculations, a memory 202 that stores a program to be read by the processor 200, and an interface 204 that inputs and outputs signals.

[0018] The Processor 200 is an example of a computing device. The Processor 200 can be a computing device referred to as a microprocessor, microcomputer, microcontroller, central processing unit (CPU), or digital signal processor (DSP). Furthermore, the Memory 202 can be represented by a non-volatile or volatile semiconductor memory such as random-access memory (RAM), read-only memory (ROM), flash memory, erasable programmable ROM (EPROM), or electrically erasable programmable ROM (EEPROM) (registered trademark); a magnetic disk, a flexible disk, an optical disk, a compact disc, a miniDisc, or a digital versatile disc (DVD).

[0019] Memory 202 stores a program for executing the function of control unit 20 described later. Processor 200 is capable of performing the processing described above by providing and receiving necessary information via interface 204, executing a program stored in memory 202, and looking up a table stored in memory 202. A calculation result performed by processor 200 can be stored in memory 202.

[0020] The function of the control unit 20 in the first embodiment can meanwhile be described in a Fig. The configuration shown in 3 will be implemented. Fig. Figure 3 is a block diagram showing an exemplary configuration when the function of the control unit 20 in the first embodiment is implemented in a processing circuit 203. Fig. 3 will be in Fig. The processor 200 and memory 202 shown in Figure 2 are replaced by the processing circuit 203. The processing circuit 203 is a single circuit, a set of multiple circuits, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination thereof. Information to be inputted to and output from the processing circuit 203 can be received and provided via the interface 204.

[0021] It should be noted that some of the processing in the control unit 20 can be carried out in the processing circuit 203, and the processing not carried out by the processing circuit 203 can be carried out by the combination of the processor 200 and the memory 202.

[0022] Back to the description with reference to Fig. 1. The inverter circuit 11 converts the smoothed DC voltage, controlled by the control unit 20, into an AC voltage with a set frequency and applies the AC voltage to the motor 4a of the compressor 4. The motor speed in motor 4, which is the speed of motor 4a, is controlled by the AC voltage with the set frequency. The motor speed corresponds to the frequency of the output voltage provided by the inverter circuit 11.

[0023] The compressor 4 draws in the refrigerant according to the rotation of the motor 4a, compresses the refrigerant to a state of high temperature and high pressure, and releases the refrigerant in this state. The condenser 5 exchanges heat, for example, between the air and the refrigerant. This heat exchange causes the refrigerant to condense and liquefy. The expansion device 6 decompresses and expands the refrigerant. The evaporator 7 exchanges heat, for example, between the air and the refrigerant. This heat exchange causes the refrigerant to evaporate and vaporize.

[0024] Next, a specific frequency component that may be included in the ripple current of the smoothing capacitor is described. First, the voltage applied to the smoothing capacitor 10 is a voltage supplied by the AC power supply 3 and then rectified by the rectifier circuit 8, and therefore a voltage generated based on the power supply frequency, i.e., the frequency of the supply voltage. For example, if the AC power supply 3 outputs a single-phase voltage at 50 Hz and the rectifier circuit 8 is a full-wave rectifier, the smoothing capacitor 10 receives a pulsation voltage at 100 Hz, which is twice the power supply frequency. Accordingly, the ripple current flowing to the smoothing capacitor 10 also includes a high current component at 100 Hz.The frequency component of the ripple current caused by the power supply frequency is referred to below as the "power supply 2f component". The power supply 2f component is a specific frequency component included in the ripple current.

[0025] When the motor speed is high and the inverter power from inverter circuit 11 is high, the ripple current has a large pulsation and thus a large power supply 2f component. This results in the power supply 2f component being the main component of the ripple current. If the AC power supply 3 is a three-phase power supply, a frequency component is known to occur that is six times the power supply frequency.

[0026] Fig. Figure 4 is a diagram showing an example of a torque control curve implemented in the first embodiment. The horizontal axis represents the motor speed, and the vertical axis represents the torque control ratio. Torque control is a control mechanism used to reduce or prevent vibration by varying the motor current in response to changes in load torque that occur during one motor revolution. The torque control ratio is the degree of control applied by the torque control. Torque control causes the ripple current to also have a frequency component corresponding to the motor speed. This frequency component of the ripple current, caused by the load torque, is referred to below as the "mechanical 1f component."

[0027] As described above, the ripple current exhibits the power supply 2f component and the mechanical 1f component, each as a specific frequency component. It should be noted that the power supply 2f component can be referred to here as the "first component" and the mechanical 1f component as the "second component".

[0028] The in Fig. The control curve shown in Figure 4 represents an operating range of compressor 4, which is divided into three ranges: "Torque control: high", "Torque control: low", and "Torque control: no". That is, the... Fig. Figure 4 shows that the torque control ratio decreases with increasing engine speed and eventually reaches zero. The torque control ratio eventually reaches zero because, as engine speed increases, the need for torque control to reduce or prevent vibrations decreases.

[0029] Therefore, if the motor speed is low and the inverter output power is low, the torque control ratio will be higher, and the higher torque control ratio results in a larger mechanical 1f component, making the mechanical 1f component the main component of the ripple current. It should be noted that, for example, if compressor 4 is a twin-rotor type, two cyclic changes corresponding to a load torque change will occur during one motor revolution. In this case, the ripple current will have a mechanical 2f component, which is a frequency component with a frequency twice that of the motor speed. It should be noted that while this is an example of the case where the mechanical 1f component is the main component of the ripple current, a similar control flow also applies to the case where the mechanical 2f component is the main component of the ripple current.

[0030] As described above, the power supply 2f component and the mechanical 1f component can be the main components of the ripple current. If the power supply 2f component is the main component of the ripple current, reducing the inverter output power can decrease the ripple current and thereby decrease the power supply 2f component. This can be achieved by controlling the output frequency of inverter circuit 11 to reduce the motor speed. Conversely, if the mechanical 1f component is the main component of the ripple current, reducing the inverter output power is ineffective in reducing the torque control factor and therefore ineffective in reducing the mechanical 1f component. In this case, the mechanical 1f component is reduced by reducing the torque control factor, which is the cause of the mechanical 1f component.Even though reducing the mechanical 1f component should decrease the ripple current, a case where the ripple current remains high may indicate an anomaly and therefore requires the shutdown of compressor 4.

[0031] Next, with reference to Fig. A method for extracting a frequency component contained in the ripple current is described. First, as described above, the current sensor 22 detects a current flowing between the smoothing capacitor 10 and the bandpass filter 13. The current waveform detection unit 12 detects a current waveform and a current value of the ripple current based on a detection value from the current sensor 22. The bandpass filter 13 is a bandpass filter matched to the frequency of the power supply 2f component and thus extracts the power supply 2f component contained in the ripple current. As described above, the power supply 2f component and the mechanical 1f component are dominant components with respect to the specific frequency components contained in the ripple current.This means that by removing the power supply 2f component extracted by the bandpass filter 13 from the output of the current waveform acquisition unit 12, the mechanical 1f component can be estimated. According to this procedure, the mechanical 1f component estimator 14 estimates the mechanical 1f component in the ripple current from the difference between the acquisition value of the ripple current output by the current waveform acquisition unit 12 and the extraction value of the power supply 2f component extracted by the bandpass filter 13.

[0032] If the current value of the ripple current is greater than a predetermined threshold and the extraction value of the power supply 2f component is greater than a predetermined threshold, the motor speed limiting unit 15 determines that the power supply 2f component is the main component of the ripple current and thus performs motor speed limiting control to reduce the motor speed.

[0033] If the current value of the ripple current is greater than the predetermined threshold and the estimated value of the mechanical 1f component is greater than a predetermined threshold, the torque control rate limiting unit 16 determines that the mechanical 1f component is the main component of the ripple current and thus performs a torque control rate limiting control to reduce the torque control rate.

[0034] The output frequency setting unit 17 sets the output frequency of the inverter output power to be supplied by the inverter circuit 11, for example, based on a user-defined operating mode and / or the like. The PWM signal calculation unit 18 calculates a PWM signal for controlling switching elements (not shown) included in the inverter circuit 11 and outputs the PWM signal to the inverter circuit 11.

[0035] Fig. Figure 5 is a flowchart showing a process sequence executed by the control unit 20 of the first embodiment. Next, with reference to Fig. 5. Operation of the motor drive device 1 according to the first embodiment is described. It should be noted that the steps of Fig. The 5 steps can be performed sequentially in the order shown, but can also be performed in parallel or separately.

[0036] In step S1, the control unit 20 detects a current value of the ripple current based on the reading from the current sensor 22. In step S2, the control unit 20 determines whether the detected current value of the ripple current exceeds a predetermined threshold. This operation is also referred to here as the "first determination operation," and the threshold used in the first determination operation is also referred to here as the "first threshold." That is, the first determination operation is an operation in which a threshold determination is performed for 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 (yes in step S2), the control unit 20 causes the process to continue with step S3.If the current value of the ripple current does not exceed the first threshold (No in step S2), the control unit 20 causes the process to continue with step S9 and allows the compressor 4 to continue running.

[0037] In step S3, the control unit 20 determines whether the power supply 2f component extracted by the bandpass filter 13 exceeds a predetermined threshold. This operation is also referred to here as the "second determination operation," and the threshold used in the second determination operation is also referred to here as the "second threshold." That is, the second determination operation is an operation in which a threshold determination is performed for the power supply 2f component extracted by the bandpass filter 13, which is a specific frequency component, using the second threshold. If the power supply 2f component exceeds the second threshold (yes in step S3), the control unit 20 causes the process to continue with step S4, performs the motor speed limiting control described above, causes the process to continue with step S9, and allows the compressor 4 to continue running.If the power supply 2f component does not exceed the second threshold (No in step S3), the control unit 20 causes the process to continue with step S5.

[0038] In step S5, the control unit 20 determines whether the mechanical 1f component, estimated using the difference between the ripple current measurement and the power supply 2f extraction value, exceeds a predetermined threshold. This operation is also referred to here as the "third determination operation," and the threshold used in the third determination operation is also referred to here as the "third threshold." That is, the third determination operation is an operation in which a threshold determination for the mechanical 1f component, which is due to the power supply frequency and estimated by the control unit 20, is performed using the third threshold.If the mechanical 1f component exceeds the third threshold (Yes in step S5), control unit 20 causes the process to continue to step S6, performs the torque control rate limitation control described above, and causes the process to continue to step S7. If the mechanical 1f component does not exceed the third threshold (No in step S5), control unit 20 causes the process to continue to step S10 and causes compressor 4 to stop operating.

[0039] In step S7, the control unit 20 detects the current value of the ripple current and then causes the process to continue to step S8. In step S8, the control unit 20 determines whether the detected current value of the ripple current exceeds a predefined threshold. This operation is referred to here as the "fourth determination operation," and the threshold used in the fourth determination operation is referred to here as the "fourth threshold." That is, the fourth determination operation is an operation in which a threshold determination is performed for 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 (yes in step S8), the control unit 20 causes the process to continue to step S9 and allows the compressor 4 to continue running.If the current value of the ripple current exceeds the fourth threshold (No in step S8), the control unit 20 causes the process to continue with step S10 and causes the compressor 4 to stop operating.

[0040] Next, a supplementary description of step S8 is provided. Reaching step S8 means that the power supply 2f component is below the second threshold and the torque control rate limiting control has been performed to reduce the mechanical 1f component, which exceeds the third threshold. A ripple current value that still exceeds the fourth threshold even after such control may indicate an anomaly in the motor drive device 1. Accordingly, the determination operation in step S8 is performed, and if the ripple current value exceeds the fourth threshold, the control unit 20 causes the compressor 4 to cease operation.

[0041] It should be noted that several of the preceding operations in steps S6 to S8 are performed such that the decision to continue or discontinue operation of compressor 4 is based on the result of a single execution of the torque control rate limiting control. However, the decision to continue or discontinue operation of compressor 4 can also be made based on the results of two or more executions of the torque control rate limiting control. Performing such an operation can prevent excessive control that may occur during the torque control rate limiting control.

[0042] Although the preceding determination operation in step S2 provides a determination result of "No" if the current value of the ripple current corresponds to the first threshold, such a case can be determined as "Yes". That is, if the current value of the ripple current corresponds to the first threshold, the determination result can be either "Yes" or "No".

[0043] Although the preceding determination operation in step S3 provides a determination result of "No" if the benefit provision 2f component corresponds to the second threshold, such a case can be determined as "Yes". That is, if the benefit provision 2f component corresponds to the second threshold, the determination result can be either "Yes" or "No".

[0044] Although the preceding determination operation in step S5 provides a determination result of "No" if the mechanical 1f component corresponds to the third threshold, such a case can be determined as "Yes". That is, if the mechanical 1f component corresponds to the third threshold, the determination result can be either "Yes" or "No".

[0045] Furthermore, although the preceding determination operation in step S8 provides a determination result of "Yes" if the current value of the ripple current corresponds to the fourth threshold, such a case can be determined as "No". That is, if the current value of the ripple current corresponds to the fourth threshold, the determination result can be either "Yes" or "No".

[0046] Fig. 6 is a flowchart that shows one of the ones in Fig. Figure 5 shows the different process flow, which is carried out by the control unit 20 of the first embodiment. In the flowchart of Fig. 5. After the determination operation in step S2, in which the current value of the ripple current is compared with the first threshold value, a determination operation is carried out in step S3, in which the power supply 2f component is compared with the second threshold value. In contrast, the flowchart of Fig. 6 is modified so that after the determination in step S12 to compare the current value of the ripple current with the first threshold, a determination is carried out in step S13 to compare the mechanical 1f component with a second threshold.

[0047] Furthermore, the flowchart of Fig. 5. Following the determination operation in step S3, where the power supply 2f component is compared with the second threshold, a determination operation is performed in step S5 to compare the mechanical 1f component with the third threshold. In contrast, the flowchart of Fig. 6 is modified such that, following the determination operation in step S13, in which the mechanical 1f component is compared with the second threshold, a determination operation is performed in step S15 to compare the power supply 2f component with a third threshold. It should be noted that, as described above, the thresholds used in the determination operations in steps S3 and S13 are here each referred to as the "second threshold," and the thresholds used in the determination operations in steps S5 and S15 are here each referred to as the "third threshold."

[0048] The companies in steps S11 and S17 to S20 in Fig. 6 correspond to the companies in steps S1 and S7 to S10 in Fig. 5. Furthermore, the operation in step S14 corresponds to Fig. 6 the operation in step S6 in Fig. 5, and the operation in step S16 in Fig. 6 corresponds to the operation in step S4 in Fig. 5. Despite the different process flows, each operation is similar to the corresponding operation, which is why a further description is omitted here.

[0049] Next, a supplementary description for step S18 is given. Reaching step S18 means that the mechanical 1f component is below the second threshold and the motor speed limiting control has been performed to reduce the power supply 2f component, which exceeds the third threshold. If, after such control, the ripple current still exceeds the fourth threshold, this may indicate an anomaly in the motor drive device 1. Accordingly, the determination operation in step S18 is performed, and if the ripple current exceeds the fourth threshold, the control unit 20 causes the compressor 4 to stop operating.

[0050] It should be noted that several of the preceding operations in steps S16 to S18 are performed such that the decision to continue or discontinue operation of compressor 4 is based on the result of a single execution of the engine speed limit control. However, the decision to continue or discontinue operation of compressor 4 can also be made based on the results of two or more executions of the engine speed limit control. Performing such an operation can prevent excessive control that may occur during engine speed limit control.

[0051] As described above, a motor drive device according to the first embodiment comprises a control unit that controls the operation of the inverter circuit and a sensing unit that detects a ripple current flowing to the smoothing capacitor. The control unit further comprises a current waveform sensing unit that detects a current waveform and current value of the ripple current based on a sensing value from the sensing unit. The control unit performs a first determination operation to determine a threshold for the current value of the ripple current detected by the current waveform sensing unit using a first predetermined threshold, and performs a second determination operation to determine a threshold for a specific frequency component included in the current waveform of the ripple current using a second predetermined threshold.Based on the results of the first and second determination operations, the control unit determines whether to reduce the degree of torque control (i.e., the control to change the motor current flowing to the motor according to a change in the motor's load torque) or the motor speed (i.e., the motor's rotational speed), and controls either the degree of torque control or the motor speed. Using the second threshold, the motor drive device, as described above, determines whether the specific frequency component included in the ripple current waveform is due to the power supply frequency or due to a change in the motor's load torque when the ripple current value detected by the waveform sensing unit is high and exceeds the first threshold.This allows a suitable control process to be selected based on the result of this determination. This, in turn, enables the provision of a motor drive device capable of performing appropriate control for the source of the ripple component. Using a motor drive device with such a function can also delay the deterioration of the smoothing capacitor within the motor drive device, thus extending the product's service life. Second embodiment.

[0052] Fig. Figure 7 is a diagram showing an exemplary configuration of a refrigeration circuit device 50A with a motor drive device 1A according to a second embodiment. In comparison between Fig. 7 and Fig. 1 includes the in Fig. 7 Motor drive device 1A shown, a control unit 20A instead of the control unit 20, and the bandpass filter 13 was taken from the configuration of Fig. 1 removed. Furthermore, the following includes: Fig. The control unit 20A shown in Figure 7 no longer includes the mechanical 1f component estimating unit 14, but instead additionally comprises a calculation unit 19 for certain frequency components. The other part of the configuration is the same as, or equivalent to, the corresponding part of Figure 7. Fig. 1. Identical or equivalent components are given identical reference symbols, and duplicate descriptions are omitted.

[0053] Next, the operation of the motor drive device 1A according to the second embodiment is described. Similar to the first embodiment, the current waveform acquisition unit 12 acquires a current waveform and a current value of the ripple current based on a sensing value from the current sensor 22. The calculation unit 19 for specific frequency components performs a Fourier transform of the current waveform output by the current waveform acquisition unit 12, using this current waveform as an input signal to calculate the power supply 2f component and the mechanical 1f component, which are the specific frequency components included in the ripple current. Further operation is similar to the corresponding operation of the first embodiment.

[0054] In the second embodiment, frequency components of the ripple current are calculated using a Fourier transform, which yields a frequency distribution different from the power supply 2f component and the mechanical 1f component. This different frequency component can be used for root cause analysis when the compressor unexpectedly stops if the ripple current exceeds the threshold value, but neither the power supply 2f component nor the mechanical 1f component exceeds the applicable threshold.

[0055] As described above, the control unit of the motor drive device according to the second embodiment includes a specific frequency component calculation unit that calculates a specific frequency component 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 based on the power supply frequency and the second component based on a change in the motor's load torque as specific frequency components in a single calculation operation. This allows, similar to the first embodiment, suitable control tailored to the source of the ripple component.Furthermore, the motor drive device according to the second embodiment enables a distribution of a frequency component that differs from the power supply 2f component and the mechanical 1f component, making it possible to perform root cause analysis in a case where the compressor stops unexpectedly, even if neither the power supply 2f component nor the mechanical 1f component is greater than the applicable threshold.

[0056] The configurations described in the preceding embodiments are merely examples. These configurations can be combined with other known technologies, and configurations of different embodiments can be combined with one another. Furthermore, such configurations can be partially omitted and / or modified without deviating from the core principle. Reference symbol list 1, 1A Motor drive device; 2 Refrigerant circuit; 3 AC power supply; 4 compressor; 4a Motor; 5 Capacitor; 6 Throttle device; 7 evaporators; 8 Rectifier circuit; 9 Throttle; 10 Smoothing capacitor; 11 Inverter circuit; 12 Current waveform detection unit; 13 bandpass filters; 14 mechanical 1f component estimation units; 15 Engine speed limiter unit; 16 Torque control degree limiting unit; 17 Output frequency setting unit; 18 PWM signal processing units; 19 Calculation unit for specific frequency components; 20, 20A control unit; 21 Refrigerant line; 22 Current sensor; 50, 50A refrigeration cycle device; 200 processor; 202 storage spaces; 203 Processing circuit; 204 Interface QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2013 - 66 299

[0004] JP 2013 - 66 299 A

[0004]

Claims

[1] Motor drive device comprising: a rectifier circuit for rectifying a supply voltage applied by an AC power supply; a smoothing capacitor for smoothing a voltage obtained by rectification carried out by the rectifier circuit; an inverter circuit for converting a DC voltage smoothed by the smoothing capacitor into a drive voltage, where the drive voltage is a voltage for driving a motor enclosed in a compressor, where the compressor is a load; a control unit for controlling the operation of the inverter circuit; and a detection unit for detecting a ripple current flowing to the smoothing capacitor, the control unit includes: a current waveform detection unit for detecting a current waveform and current value of the ripple current based on a detection value from the detection unit, and an output frequency setting unit for setting an output frequency of the drive voltage, and wherein the control unit performs a first destination operation and a second destination operation, wherein the first determination operation is an operation to perform a threshold determination for the current value of the ripple current detected by the current waveform detection unit using a first predetermined threshold, and wherein the second determination operation is an operation to perform a threshold determination for a specific frequency component included in the current waveform of the ripple current using a second predetermined threshold, and wherein the control unit determines, based on results from the first and second determination operations, whether to reduce the degree of control of a torque control or to reduce an engine speed, and the degree of control of the torque control or which controls the engine speed where torque control is a control to change a motor current flowing to the motor in accordance with a change in a load torque of the motor, and where the motor speed is the speed of the engine. [2] Motor drive device according to claim 1, wherein the detection unit is configured to include the following: a bandpass filter connected in series with the smoothing capacitor, and a current sensor to detect a current flowing between the smoothing capacitor and the bandpass filter. [3] Motor drive device according to claim 1, wherein the sensing unit is configured to include a current sensor for sensing a current flowing to the smoothing capacitor, and wherein the control unit includes a calculation unit for specific frequency components to calculate the specific frequency component included in the ripple current on the basis of the current waveform detected by the current waveform sensing unit. [4] Motor drive device according to one of claims 1 to 3, where the specific frequency component is a first component due to a power supply frequency, and where the power supply frequency is a frequency of the supply voltage. [5] Motor drive device according to claim 4, wherein, when the first determination operation determines that the current value of the ripple current exceeds the first threshold, and the second determination operation determines that the first component exceeds the second threshold, the control unit controls the output frequency to reduce the motor speed. [6] Motor drive device according to claim 5, wherein, if the first determination operation determines that the current value of the ripple current exceeds the first threshold, and the second determination operation determines that the first component does not exceed the second threshold, the control unit performs a third determination operation, wherein the third determination operation is an operation to perform a threshold determination for a second component due to the change in the load torque of the engine using a predetermined third threshold, and where, if the third determining operation determines that the second component exceeds the third threshold, the control unit reduces the degree of control of the torque control, where the degree of control is set based on the output frequency. [7] Motor drive device according to claim 6, wherein, after the control unit has reduced the degree of control of the torque control, the control unit further performs a fourth determination operation, wherein the fourth determination operation is an operation to perform a threshold determination for the current value of the ripple current using a predetermined fourth threshold, and wherein, if the fourth determination operation determines that the current value of the ripple current exceeds the fourth threshold, the control unit causes the compressor to stop operating. [8] Motor drive device according to claim 6, wherein, after the control unit has reduced the degree of control of the torque control, the control unit further performs a fourth determination operation, wherein the fourth determination operation is an operation to perform a threshold determination for the current value of the ripple current using a predetermined threshold, and wherein, if the fourth determination operation determines that the current value of the ripple current does not exceed the fourth threshold, the control unit causes the compressor to continue operating. [9] Motor drive device according to claim 7 or 8, wherein, if the third determination operation determines that the second component does not exceed the third threshold, the control unit causes the compressor to stop operating. [10] Motor drive device according to one of claims 1 to 3, wherein the determined frequency component is a second component due to the change in the load torque of the motor. [11] Motor drive device according to claim 10, wherein, if the first determination operation determines that the current value of the ripple current exceeds the first threshold, and the second determination operation determines that the second component exceeds the second threshold, the control unit reduces the degree of control of the torque control, where the degree of control is set based on the output frequency. [12] Motor drive device according to claim 11, wherein, if the first determination operation determines that the current value of the ripple current exceeds the first threshold, and the second determination operation determines that the second component does not exceed the second threshold, the control unit performs a third determination operation, wherein the third determination operation is an operation to perform a threshold determination for a first component based on a power supply frequency using a predetermined third threshold, where the power supply frequency is a frequency of the supply voltage, and where, if the third determining operation determines that the first component exceeds the third threshold, the control unit controls the output frequency to reduce the motor speed. [13] Motor drive device according to claim 12, wherein, after the control unit has controlled the output frequency to reduce the motor speed, the control unit further performs a fourth determination operation, wherein the fourth determination operation is an operation to perform a threshold determination for the current value of the ripple current using a fourth predetermined threshold, and wherein, if the fourth determination operation determines that the current value of the ripple current exceeds the fourth threshold, the control unit causes the compressor to stop operating. [14] Motor drive device according to claim 12, wherein, after the control unit has controlled the output frequency to reduce the motor speed, the control unit further performs a fourth determination operation, wherein the fourth determination operation is an operation to perform a threshold determination for the current value of the ripple current using a fourth predetermined threshold, and wherein, if the fourth determination operation determines that the current value of the ripple current does not exceed the fourth threshold, the control unit causes the compressor to continue operating. [15] Motor drive device according to claim 13 or 14, wherein, if the third determination operation determines that the first component does not exceed the third threshold, the control unit causes the compressor to stop operating. [16] Refrigeration circuit device comprising the motor drive device according to any one of claims 1 to 15 to operate a refrigeration circuit through the compressor.

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