Compressor driving device

Abstract

This compressor driving device comprises: an inverter device provided with an inverter circuit that converts direct current into alternating current and a control unit; and a compressor provided with an electric motor connected to the inverter circuit and a piston that is reciprocated in the cylinder by the electric motor. The control unit includes: a multi-phase PWM signal generation unit capable of setting a plurality of carrier frequencies for driving the compressor; and a bottom dead center detection unit for detecting the bottom dead center of the piston in the compressor. When the carrier frequency is switched from a high frequency to a low frequency during the rotation of the compressor, the timing of the switching is set at the bottom dead center of the compressor. As a result, it is possible to satisfactorily suppress the occurrence of an overcurrent when switching the carrier frequency.

Description

Compressor drive unit

[0001] The present disclosure relates to a compressor drive device used in various types of refrigeration and freezing equipment.

[0002] Patent Document 1 discloses an inverter control device that enables starting even when the starting load is relatively large. This inverter control device is configured to set the carrier frequency of a PWM signal during a start control period from the start of motor start until a predetermined time has elapsed higher than the carrier frequency during a steady control state after the period has elapsed.

[0003] Japanese Patent Application Laid-Open No. 2005-168196

[0004] Through careful investigations by the inventors, it has become clear that, since the base point for switching the carrier frequency from a high frequency to a low frequency while the compressor is running is time, if the switching position occurs near top dead center where the load torque fluctuation is large, an excess current will be generated, which may cause vibration, noise, etc. in the compressor.

[0005] The present disclosure has been made to solve such problems, and aims to provide a compressor driving device that can effectively suppress the generation of excess current when switching the carrier frequency.

[0006] In order to solve the above-mentioned problems, the compressor drive device of the present disclosure comprises an inverter device including an inverter circuit that converts direct current to alternating current and a control unit, an electric motor connected to the inverter circuit, and a compressor including a piston that is reciprocated within a cylinder by the electric motor, the control unit including a multi-phase PWM signal generation unit that can set multiple carrier frequencies that drive the compressor, and a bottom dead center detection unit that detects the bottom dead center of the piston in the compressor, and when the carrier frequency is switched from a high frequency to a low frequency while the compressor is rotating, the timing of the switch is set to the bottom dead center of the compressor.

[0007] According to the above configuration, when controlling multiple carrier frequencies for driving the compressor, the carrier frequency can be switched from a high frequency to a low frequency at a timing when load torque fluctuations are small. Therefore, the carrier frequency can be switched smoothly without impairing controllability, and the generation of excessive current during switching can be suppressed.

[0008] The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings.

[0009] With the above-described configuration, the present disclosure has an advantage of being able to provide a compressor driving device that can effectively suppress the generation of excess current when switching the carrier frequency.

[0010] Fig. 2 is a block diagram showing a representative configuration example of a compressor driving device according to an embodiment of the present disclosure. Fig. 3 is a schematic diagram showing an overview of the rotational position of a compressor driven by the compressor driving device shown in Fig. 1. Fig. 4 is a flowchart showing an example of control by the compressor driving device shown in Fig. 1. Fig. 5 is a timing chart showing an example of carrier frequency switching in the compressor driving device shown in Fig. 1. Fig. 6 is a timing chart showing an example of carrier frequency switching in a compressor driving device according to a conventional embodiment.

[0011] (Knowledge Forming the Basis of the Present Disclosure) At the time when the inventors arrived at the subject matter of the present disclosure, it was known that, from the viewpoint of reducing power loss in an inverter circuit when driving a compressor, a lower carrier frequency of a PWM signal that drives the compressor is more effective in reducing power loss. It was also known that, from the viewpoint of increasing the frequency of control correction and ensuring control stability during startup acceleration of the compressor, a higher carrier frequency of the PWM signal makes it easier to ensure control stability.

[0012] Generally, the sampling interval for capturing the drive status to control the compressor is synchronized with the carrier frequency of the PWM signal. Therefore, when the carrier frequency is switched from a high frequency to a low frequency while the compressor is running, the sampling interval becomes longer than the short period, and correction becomes slower.

[0013] When switching near the top dead center where load torque fluctuations are large, delayed correction may not be able to provide sufficient feedback control to keep up with the load fluctuations, and the drive may not follow. In particular, if the torque falls short of the required amount, an excess current proportional to the shortfall will be generated, causing vibration and noise in the compressor.

[0014] The present inventors independently discovered this problem and have come up with the subject matter of the present disclosure to solve this problem. That is, the compressor drive device according to the present disclosure makes it possible to suppress the generation of excess current when switching the carrier frequency from a high frequency to a low frequency, while achieving both control stability during startup acceleration such as when starting the compressor and reduced power loss during steady-state operation.

[0015] Hereinafter, embodiments will be described in detail with reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters or redundant description of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Furthermore, in the following description, identical or corresponding elements are designated by the same reference numerals throughout all drawings, and redundant description thereof will be omitted.

[0016] The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0017] [1. Configuration Example of Compressor Drive Device] A configuration example of a representative compressor drive device according to the present disclosure will be described with reference to Fig. 1. For example, as shown in Fig. 1, the compressor drive device according to this embodiment includes an inverter device 1 and a compressor 30. In this embodiment, the inverter device 1 includes an inverter circuit 10, a drive circuit 11, a current detection circuit 12, and a control unit 20. In addition, in this embodiment, the control unit 20 includes a calculation unit 21, a carrier frequency setting unit 22, a PWM signal generation unit 23, and a bottom dead center detection unit 24.

[0018] The inverter circuit 10 outputs a signal for driving a brushless DC motor 31 included in the compressor 30. The inverter circuit 10 is a circuit including a driving element such as an IGBT (Insulated Gate Bipolar Transistor) or an FET (Field Effect Transistor), and in this embodiment, includes a temperature sensor 13 such as an NTC (Negative Temperature Coefficient) thermistor, as schematically shown in FIG.

[0019] The drive circuit 11 converts the signal output from the control unit 20 into a signal suited to the inverter circuit 10. The drive circuit 11 may have a built-in protection circuit for overcurrent protection, etc. The current detection circuit 12 periodically obtains a current value (circuit current) from the inverter circuit 10 and outputs it to a bottom dead center detection unit 24 of the control unit 20.

[0020] The control unit 20 controls the driving of the compressor 30 via the inverter circuit 10. The control unit 20 may also be configured to perform various controls other than the driving of the compressor 30 depending on the specific configuration of the compressor driving device.

[0021] The calculation unit 21 executes various calculation processes associated with the control by the control unit 20. A specific example of the calculation process is the calculation of a voltage command value for driving the compressor 30, as will be described later.

[0022] Carrier frequency setting unit 22 sets a plurality of carrier frequencies for driving compressor 30. PWM signal generation unit 23 converts the voltage command value calculated by calculation unit 21 into a PWM signal. Bottom dead center detection unit 24 estimates the rotation phase of brushless DC motor 31 from the circuit current detected by current detection circuit 12, and estimates the position of the bottom dead center.

[0023] Here, there are no particular limitations on the specific configuration of the control unit 20 and the configurations of the calculation unit 21, carrier frequency setting unit 22, PWM signal generation unit 23, bottom dead center detection unit 24, etc. included in the control unit 20. For example, the control unit 20 described in this embodiment may be configured by an arithmetic unit and a storage device of a microcomputer or a microcontroller.

[0024] The storage device constituting the control unit 20 may be configured as an internal memory of a microcomputer or microcontroller, or may be configured as an independent memory or storage. The storage device does not need to be a single device, and may be configured as multiple storage devices (for example, an internal memory and an external hard disk drive or SSD (Solid State Drive)).

[0025] The arithmetic device constituting the control unit 20 may be a general-purpose processor, a dedicated processor, an integrated circuit, an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuits), a GPU, etc., either alone or in combination of two or more types, and may be configured to operate to realize the functions of the control unit 20 in accordance with a program stored in a storage device.

[0026] A processor as an arithmetic device is a circuit (or processing circuit) as hardware because it includes a circuit configured with a large number of transistors, memories, etc. An integrated circuit or ASIC is also a circuit as hardware because it includes a processor or processing block such as a CPU. An FPGA is a circuit as hardware because it includes a large number of integrated logic circuits (functional blocks). A GPU is a circuit as hardware because it includes a large number of arithmetic circuits (cores) mounted in parallel. Software such as programs stored in a storage device is used to configure a circuit (processor, integrated circuit, FPGA, ASIC, GPU, etc.) as hardware. Alternatively, an arithmetic device may be configured as a logic circuit or the like using known switching elements, subtractors, comparators, etc.

[0027] Furthermore, the specific configurations of the inverter circuit 10, drive circuit 11, current detection circuit 12, etc. described in this embodiment are not particularly limited, and known configurations can be suitably used. For example, as described above, the inverter circuit 10 may be a circuit including an IGBT or FET as a switching element (drive element).

[0028] The inverter device 1 configured as described above is connected to the compressor 30 via multi-phase connection lines. A voltage is supplied to the inverter device 1 from a DC voltage source 32. The compressor 30 includes a brushless DC motor 31. The brushless DC motor 31 is driven by a voltage signal output from the inverter circuit 10 of the inverter device 1. Specific driving methods include, for example, two-phase modulation control and three-phase modulation control, which perform control using sinusoidal wave energization, and square wave control, which is control using square wave energization.

[0029] Next, the configuration of the main parts of the compressor 30 will be described with reference to Fig. 2. As shown schematically in Fig. 2, the brushless DC motor 31 is provided with a crank mechanism 33, and a piston 34 is connected to the crank mechanism 33. The piston 34 reciprocates within a cylinder 35. The space within the cylinder 35 defined by the piston 34 is a compression chamber.

[0030] The specific configuration of compressor 30 is not particularly limited as long as it includes an electric motor such as brushless DC motor 31, piston 34, and cylinder 35. A typical configuration example of compressor 30 is one in which compressor 30 includes a crankshaft having a main shaft and an eccentric shaft as crank mechanism 33, in which the main shaft is fixed to brushless DC motor 31 and the eccentric shaft is connected to piston 34 by a connecting means (e.g., a connecting rod) or the like.

[0031] When the crankshaft is rotated by the rotation of the brushless DC motor 31, a piston 34 connected to an eccentric shaft reciprocates within a cylinder 35. In Fig. 2, the rotation phases of the top dead center and bottom dead center of the piston 34 in the crank mechanism 33 are indicated by black circles.

[0032] 2. Example of Operation of Compressor Driving Device The operation of the compressor driving device configured as above will be described below.

[0033] 2-1. Compressor Start-Up Operation 1 (Immediately After Start-Up) The basic operation of the inverter device 1 will be described with reference to Fig. 1. When accelerating the start-up of the brushless DC motor 31, the calculation unit 21 in the control unit 20 calculates a voltage command value appropriate for start-up.

[0034] When it is assumed that the pressure state of the compressor 30 is in a balanced state, no preparatory operation is performed before startup, and therefore sufficient back electromotive force information cannot be obtained from the brushless DC motor 31 in the low rotation range at the start of startup. This makes it difficult to estimate the rotor position of the brushless DC motor 31. Therefore, immediately after the start of startup, forced commutation driving is performed without estimating the rotor position.

[0035] On the other hand, for example, in a system incorporating the compressor 30, if the pressure immediately before shutdown is maintained in order to reduce power loss, the pressure state at startup will be unbalanced, which may make startup with forced commutation drive difficult.

[0036] Countermeasures include calculating the rotor position in advance by performing a preliminary operation such as reverse rotation before starting, or implementing control before this process to stop the rotor at a position away from top dead center where a large load torque is required.

[0037] After startup, the voltage command value calculated by the calculation unit 21 is converted into a PWM signal by the PWM signal generation unit 23. The carrier frequency at this time is the frequency set by the carrier frequency setting unit 22. The frequency is determined by the setting from the calculation unit 21.

[0038] To generate a PWM signal, it is necessary to periodically obtain a current value from the compressor 30 using the current detection circuit 12. The sampling intervals for obtaining this current value are synchronized with the carrier frequency, and the next voltage command value is calculated by the calculation unit 21 based on the sampled value, and is converted into a PWM signal by the PWM signal generation unit 23.

[0039] During startup, the pressure state of the compressor 30 also fluctuates as the compressor accelerates from a stopped state to a predetermined rotation speed. Therefore, control using a short sampling interval is required. Therefore, a sampling interval that can adequately track load fluctuations due to pressure fluctuations, in addition to speed fluctuations due to acceleration, is required. Therefore, the carrier frequency is set to, for example, 6 kHz or higher.

[0040] As described above, signals for driving the brushless DC motor 31 are output from the inverter circuit 10. As described above, typical driving methods for the brushless DC motor 31 include, for example, sine wave control (two-phase modulation control, three-phase modulation control) and square wave control. In such control, the control voltage mainly used in the inverter circuit 10 is 15 V, rather than the 3.3 V or 5 V used in the control unit 20. Furthermore, voltage conversion using a bootstrap circuit or the like is required to drive the high-side elements. Therefore, a drive circuit 11 is provided between the control unit 20 and the inverter circuit 10, and signal conversion is performed by the drive circuit 11.

[0041] [2-2. Compressor startup operation 2 (during acceleration)] When brushless DC motor 31 starts to rotate, a back electromotive force is generated by the rotation. Based on this back electromotive force, control unit 20 estimates the rotor position of brushless DC motor 31, and further, control unit 20 outputs a voltage command value corresponding to this rotor position.

[0042] Specifically, the calculation unit 21 of the control unit 20 estimates and calculates the rotor position based on the circuit current value of the inverter circuit 10 obtained by the current detection circuit 12. Thereafter, the calculation unit 21 continuously calculates an appropriate voltage command value according to the rotation phase obtained by the rotor position estimation calculation. As a result, the calculation unit 21 (control unit 20) continues to output this voltage command value. As a result, the brushless DC motor 31 continues to rotate.

[0043] [2-3. Operation of Transitioning to Steady-State Drive of Compressor] When the rotation speed of the brushless DC motor 31 reaches the target value and stabilizes, the control unit 20 starts changing the carrier frequency. The procedure for this will be described.

[0044] The bottom dead center detector 24 included in the control unit 20 estimates the rotational phase of the brushless DC motor 31 from the circuit current of the inverter circuit 10 detected by the current detection circuit 12, and estimates the bottom dead center position of the piston 34. Here, in controlling the compressor 30, it is difficult to directly detect the bottom dead center or estimate a point where the load torque fluctuation is small, but as shown in Figure 2, the bottom dead center of the piston 34 is mechanically opposite to the top dead center. The load torque fluctuation is large at the top dead center of the piston 34.

[0045] Therefore, in this embodiment, the bottom dead center detection unit 24 detects the top dead center of the piston 34 and indirectly estimates the sum of top dead center and mechanical angle 180° as the bottom dead center of the piston 34. That is, in this embodiment, in the control of the control unit 20, estimating the position of the bottom dead center of the piston 34 is considered to be substantially synonymous with directly detecting the bottom dead center.

[0046] The bottom dead center position of the piston 34 detected (estimated) by the bottom dead center detection unit 24 is output to the calculation unit 21. The calculation unit 21 issues a command to the carrier frequency setting unit 22 to switch the carrier frequency at the estimated bottom dead center position. At this time, the carrier frequency is set to a lower frequency than the carrier frequency at startup, for example, 1.5 kHz. Upon receiving the command to switch the carrier frequency, the carrier frequency setting unit 22 switches the carrier frequency based on the command and sends a command to the PWM signal generation unit 23.

[0047] The PWM signal generating unit 23 converts the voltage command value output by the calculation unit 21 into a PWM signal at the switched carrier frequency. The drive circuit 11 converts this PWM signal into a signal suitable for input to the inverter circuit 10. The inverter circuit 10 then outputs a voltage signal at the set carrier frequency to drive the brushless DC motor 31.

[0048] Such a change in carrier frequency is executed as a control by the control unit 20. An example of the control by the control unit 20 will be described with reference to the block diagram of FIG. 1 and the flowchart of FIG.

[0049] First, the control unit 20 detects the circuit current of the inverter circuit 10 using the current detection circuit 12 (step S1). Next, the bottom dead center detection unit 24 of the control unit 20 detects (estimates) the bottom dead center position of the piston 34 from the detected circuit current (step S2). The bottom dead center detection unit 24 determines whether the piston 34 is located at the bottom dead center from the circuit current (step S3).

[0050] When bottom dead center detector 24 detects that piston 34 is at bottom dead center (YES in step S3), calculator 21 of controller 20 outputs a command to carrier frequency setting unit 22 of controller 20 to switch the carrier frequency from a high carrier frequency to a low carrier frequency, i.e., a command to switch from the high carrier frequency to the low carrier frequency (step S4). In response to this command, carrier frequency setting unit 22 switches from the high carrier frequency to the low carrier frequency (step S5).

[0051] The PWM signal generating unit 23 of the control unit 20 generates a PWM signal from the voltage command value from the calculation unit 21 at the low carrier frequency switched by the carrier frequency setting unit 22 (step S6). On the other hand, if the bottom dead center detecting unit 24 cannot detect that the piston 34 is at the bottom dead center (No in step S3), the PWM signal generating unit 23 generates a PWM signal from the voltage command value from the calculation unit 21 at the high carrier frequency before the switching (step S6).

[0052] 1, the control unit 20 inputs the PWM signal generated by the PWM signal generation unit 23 to the inverter circuit 10 via the drive circuit 11. As a result, the inverter circuit 10 drives the brushless DC motor 31 using the voltage signal with the switched low carrier frequency or the voltage signal with the high carrier frequency before the switching.

[0053] The timing for switching the carrier frequency will now be described with reference to Figures 4 and 5. The upper part of Figure 4 or Figure 5 shows changes in the load torque of brushless DC motor 31 (compressor 30), with the vertical axis representing the magnitude of the load torque and the horizontal axis representing the rotational phase of the rotor of brushless DC motor 31. The black dots on the load torque change graphs are sampling points for control by control unit 20. The lower part of Figure 4 or Figure 5 shows a carrier waveform corresponding to changes in the load torque of brushless DC motor 31. Figure 4 corresponds to a compressor driving device according to an embodiment of the present disclosure, and Figure 5 corresponds to a compressor driving device according to a conventional embodiment.

[0054] 4, as the rotor rotation phase approaches the top dead center of the piston 34, the load torque gradually increases, reaches a maximum value, and then gradually decreases. When the top dead center is reached, the load torque decreases sufficiently, reaches a minimum value shortly after passing the top dead center, and after the load torque increases once, the amount of change is small and a stable state continues. This stable state continues until the piston 34 reaches the bottom dead center, after which the load torque gradually increases.

[0055] As described above, compared to the vicinity of the top dead center, the vicinity of the bottom dead center of the piston 34 is a stable region where the range of change in the load torque of the brushless DC motor 31 is small. Therefore, as shown in Fig. 4, even if the carrier frequency is switched from a high carrier frequency to a low carrier frequency and the sampling interval becomes wider, the vicinity of the bottom dead center is less susceptible to the change in load torque when the sampling interval becomes wider than the vicinity of the top dead center.

[0056] In the conventional embodiment shown in Figure 5, the timing for switching the carrier frequency is not specified, so the carrier frequency may be switched in the region near top dead center, i.e., in the region where the load torque fluctuates significantly. In this case, the point where the sampling interval becomes wider overlaps with the region where the load torque fluctuates significantly, which may cause unstable control. The compressor drive device according to this embodiment can avoid the unstable situation shown in Figure 5.

[0057] 3. Effects, etc. As described above, the compressor drive device according to this embodiment includes the inverter device 1 and the compressor 30. The inverter device 1 includes the inverter circuit 10, the drive circuit 11, the current detection circuit 12, and the control unit 20. The control unit 20 includes the calculation unit 21, the carrier frequency setting unit 22, the PWM signal generation unit 23, and the bottom dead center detection unit 24. The compressor 30 includes the brushless DC motor 31. The inverter device 1 is connected to the compressor 30 by a polyphase connection line. The DC voltage source 32 supplies a voltage to the inverter device 1. In this configuration, when the carrier frequency is switched from a high frequency to a low frequency while the brushless DC motor 31 is rotating, the timing is set to the bottom dead center of the compressor 30.

[0058] This allows the carrier frequency to be switched at a timing when the load torque of the brushless DC motor 31 is stable, thereby effectively suppressing the generation of excessive current or vibration of the compressor 30 due to the switching of the carrier frequency.

[0059] Furthermore, in the compressor drive device according to this embodiment, as in this embodiment, the carrier frequency may be set high during startup acceleration of brushless DC motor 31, and after compressor 30 has transitioned to steady rotation, the carrier frequency may be set lower than the carrier frequency during startup acceleration. In other words, in the compressor drive device, control unit 20 may be configured to set the carrier frequency during startup acceleration of compressor 30 higher than the carrier frequency during steady rotation after acceleration has ended.

[0060] During startup acceleration of the compressor 30, it is difficult to determine the regularity of control due to factors such as pressure conditions or load fluctuations. In contrast, with the compressor drive device according to this embodiment, the carrier frequency during startup acceleration is set high due to the configuration described above, so that high-frequency sampling according to the high carrier frequency is possible even in a state where the regularity of control is difficult to determine. Therefore, highly reliable startup is possible even during startup acceleration of the compressor 30.

[0061] Moreover, in the above configuration, the carrier frequency is set lower during steady rotation of the compressor 30 than during startup acceleration. Therefore, the carrier frequency is switched from a high to a low frequency at the bottom dead center of the compressor 30, making it possible to switch the carrier frequency while effectively suppressing the occurrence of excess current or vibration of the compressor 30. This makes it possible to achieve both highly reliable startup performance and reduced power loss during steady rotation.

[0062] Furthermore, in the compressor driving device according to this embodiment, when the rotation speed of an electric motor such as the brushless DC motor 31 reaches or exceeds a predetermined rotation speed (rotation speed threshold), or when the input power value to the inverter device 1 reaches or exceeds a predetermined value (input power threshold), the control unit 20 may set the carrier frequency to a value higher than the carrier frequency during steady rotation.

[0063] As described above, in the compressor drive device according to this embodiment, the control unit 20 may be configured to control the rotation speed by switching between at least two or more carrier frequencies after starting the compressor 30. In the above configuration example, when the carrier frequency during steady rotation is set to the first carrier frequency, the carrier frequency when the rotation speed exceeds the rotation speed threshold or input power threshold can be set to the second carrier frequency. Furthermore, three or more frequencies, such as a third carrier frequency, may be set in advance depending on the setting of the rotation speed threshold or input power threshold.

[0064] In addition, in a configuration in which two or more types of carrier frequencies are switched, the control unit 20 may be configured to determine the switching between two or more types of carrier frequencies based on at least one of the actual rotation speed of the compressor 30 (electric motor) and the input power to the inverter device 1. A typical configuration for this switching is one in which the carrier frequency set by the control unit 20 increases as the actual rotation speed or the input power increases.

[0065] In this way, by configuring multiple carrier frequencies and switching between the multiple carrier frequencies based on the rotation speed or the input power, or both the rotation speed and the input power, it is possible to achieve driving of the compressor 30 (electric motor) during steady rotation and driving at higher speeds by switching between the multiple carrier frequencies. Moreover, even when switching the carrier frequency, it is possible to effectively avoid or suppress noise or vibration of the compressor 30 or the generation of excessive current to the compressor drive device (inverter device 1). Therefore, it is possible to achieve both reduced power loss during steady rotation and stable control during higher speeds.

[0066] 1, the compressor driving device according to this embodiment may be configured such that inverter circuit 10 includes temperature sensor 13. In this configuration, when temperature sensor 13 detects that the temperature of a driving element included in inverter circuit 10 has reached a set temperature or higher, control unit 20 controls the carrier frequency to be set so as not to be higher than the current value.

[0067] As a result, for example, when the set temperature is set to the rated temperature of the drive element, the temperature rise of the drive element caused by increasing the carrier frequency can be suppressed to within the rated temperature of the drive element, thereby effectively suppressing performance degradation and damage to the drive element in the inverter circuit 10.

[0068] (Other Embodiments or Modifications) As described above, the above-described embodiments have been described as examples of the technology disclosed in this application. However, the technology according to the present disclosure is not limited to these embodiments, and can be applied to other embodiments in which modifications, substitutions, additions, omissions, etc. are made. In other words, the present disclosure also encompasses modifications of the above-described embodiments. Furthermore, the technology according to the present disclosure can also be made into new embodiments by combining the components described in the above-described embodiments.

[0069] Specifically, for example, in the above-described embodiment, the circuit current detected by the current detection circuit 12 is used to estimate the position of the bottom dead center of the piston 34. However, the estimation of the position of the bottom dead center is not limited to detection of the circuit current by the current detection circuit 12. For example, the bottom dead center of the piston 34 may be estimated using a sensor such as a Hall element built into the brushless DC motor 31, or the position of the bottom dead center or top dead center of the piston 34 may be estimated from the rotational speed of the rotor of the brushless DC motor 31.

[0070] Alternatively, in the above-described embodiment, in order to generate a PWM signal, it is necessary for the current detection circuit 12 to periodically acquire a current value from the compressor 30, and the sampling interval for acquiring this current value is configured to be synchronized with the carrier frequency. However, the number of times the current value is acquired is not limited to once in synchronization with the carrier frequency, and may be multiple times. Furthermore, the sampling interval may be configured to be asynchronous and not synchronized with the PWM signal.

[0071] Alternatively, in the above-described embodiment, the current detection circuit 12 has a single shunt configuration that detects the circuit current from the DC portion of the inverter circuit 10, but the detection of the circuit current is not limited to this. For example, a three-shunt circuit that detects the current of each of the three phases from the inverter circuit 10 may be used.

[0072] Alternatively, in the above-described embodiment, the timing for switching the carrier frequency is set to the bottom dead center of the piston 34, but the position of the bottom dead center is a target value, and variations may occur depending on various conditions such as control accuracy and various tolerances. Therefore, the timing for switching the carrier frequency is not limited to the bottom dead center of the piston 34. For example, the timing for switching the carrier frequency may be set to a position (estimated position) where the fluctuation in load torque is smaller than that at top dead center, with bottom dead center as the reference.

[0073] (Additional Notes) Based on the descriptions of the above embodiments, the present specification discloses the following technologies: (Technology 1) A compressor drive device comprising: an inverter device including an inverter circuit that converts direct current to alternating current and a control unit; an electric motor connected to the inverter circuit; and a compressor including a piston that is reciprocated within a cylinder by the electric motor, wherein the control unit includes a polyphase PWM signal generation unit that can set a plurality of carrier frequencies that drive the compressor, and a bottom dead center detection unit that detects the bottom dead center of the piston in the compressor, and wherein when the carrier frequency is switched from a high frequency to a low frequency while the compressor is rotating, the switching timing is set to the bottom dead center of the compressor.

[0074] (Technology 2) The compressor driving device according to Technology 1, wherein, when starting the compressor, the control unit sets a carrier frequency during acceleration higher than a carrier frequency during steady driving after acceleration ends.

[0075] (Technology 3) The compressor driving device according to Technology 1 or Technology 2, wherein the control unit controls the rotation speed by switching between at least two or more types of carrier frequencies after starting the compressor.

[0076] (Technology 4) The compressor drive device according to any one of Technology 1 to Technology 3, wherein the control unit determines switching between two or more types of carrier frequencies based on at least one of an actual rotation speed of the compressor and input power to the inverter device.

[0077] (Technology 5) The compressor driving device according to Technology 4, wherein the control unit sets a higher carrier frequency as the actual rotation speed or the input power to the inverter device increases.

[0078] (Technology 6) The compressor drive device according to any one of Technology 1 to Technology 5, wherein the inverter circuit has a temperature sensor, and when the temperature sensor detects that a temperature of a drive element included in the inverter circuit is equal to or higher than a set temperature, the control unit does not set a carrier frequency higher than a current value.

[0079] It should be noted that the present disclosure is not limited to the description of the above-described embodiment. Various modifications of the present disclosure are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments or multiple modifications are also included in the technical scope of the present disclosure.

[0080] Furthermore, many modifications and other embodiments of the present invention will be apparent to those skilled in the art from the above description. Therefore, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. Details of the structure and / or function thereof may be substantially changed without departing from the spirit of the present invention.

[0081] The present disclosure can be suitably used widely in the field of driving compressors used in various refrigeration appliances, and particularly in the field of compressor driving devices provided in refrigeration appliances such as refrigerators and air conditioners.

[0082] 1: Inverter device 10: Inverter circuit 11: Drive circuit 12: Current detection circuit 13: Temperature sensor 20: Control unit 21: Calculation unit 22: Carrier frequency setting unit 23: PWM signal generation unit 24: Bottom dead center detection unit 30: Compressor 31: Brushless DC motor (electric motor) 32: DC voltage source 33: Crank mechanism 34: Piston 35: Cylinder

Claims

1. A compressor drive device comprising: an inverter device having an inverter circuit that converts direct current to alternating current and a control unit; and a compressor having an electric motor connected to the inverter circuit and a piston that reciprocates within a cylinder by the electric motor, wherein the control unit includes: a multi-phase PWM signal generation unit that can set a plurality of carrier frequencies that drive the compressor; and a bottom dead center detection unit that detects the bottom dead center of the piston in the compressor, wherein when the carrier frequency is switched from a high frequency to a low frequency while the compressor is rotating, the switching timing is set to the bottom dead center of the compressor.

2. The compressor drive device according to claim 1, wherein, when starting the compressor, the control unit sets a carrier frequency during acceleration higher than a carrier frequency during steady-state driving after the end of acceleration.

3. The compressor drive device according to claim 1, wherein the control unit controls the rotation speed by switching between at least two types of carrier frequencies after starting the compressor.

4. The compressor drive device according to claim 1, wherein the control unit determines whether to switch between two or more types of carrier frequencies based on at least one of an actual rotation speed of the compressor and an input power to the inverter device.

5. The compressor driving device according to claim 4, wherein the control unit sets a higher carrier frequency as the actual rotation speed or the input power to the inverter device increases.

6. A compressor driving device according to any one of claims 1 to 5, wherein the inverter circuit has a temperature sensor, and when the temperature sensor detects that the temperature of a driving element included in the inverter circuit has reached a set temperature or higher, the control unit does not set the carrier frequency higher than a current value.

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