Motor drive device

Abstract

This motor drive device comprises an inverter circuit, a single- or multi-phase motor, a computing unit, and a PWM signal generation unit. The computing unit computes a drive voltage and determines a first duty ratio of a PWM signal. The PWM signal generation unit converts the first duty ratio into a PWM signal at a carrier frequency and outputs the PWM signal. Furthermore, the computing unit selects the phase when there is only one phase or selects one or more phases randomly when there are a plurality of phases, randomly selects one or more cycles of a PWM cycle with respect to the selected phase, calculates a designated value for increasing or decreasing the first duty ratio, and sets the duty ratio of the PWM signal in the selected phase or the selected cycle as a second duty ratio that is increased or decreased from the first duty ratio by the designated value. This makes it possible to reduce a noise peak value attributed to the carrier frequency, and can be easily introduced even in a low-cost microcomputer with slow processing speed.

Description

Motor drive unit

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

[0002] Patent Document 1 discloses a PWM inverter device or a control method thereof, which aims to reduce audible noise without increasing loss and to ensure stable control performance.

[0003] Specifically, the PWM inverter device disclosed in Patent Document 1 has a configuration in which two switching means, each consisting of a switching element and a diode connected in anti-parallel, are connected in series, and a plurality of single-phase switching means, each having a connection point as an output terminal, are connected in parallel to form a multi-phase switching means, a DC power supply is connected to both ends of the multi-phase switching means, and a load is connected to the multi-phase output terminal to control the voltage of the load, and further includes a carrier frequency variation means for varying a predetermined frequency range centered on an arbitrary carrier frequency.

[0004] Japanese Patent Application Laid-Open No. 2007-20320

[0005] The PWM inverter device disclosed in Patent Document 1 decentralizes specific frequency components caused by the carrier frequency by varying the carrier frequency within a specific frequency range centered on the carrier frequency. However, varying the carrier frequency is difficult to achieve with inexpensive microcomputers with slow processing speeds.

[0006] An object of the present disclosure is to provide a motor drive device that can be easily implemented even in an inexpensive microcomputer with a slow processing speed, and that reduces noise peak values ​​caused by carrier frequencies.

[0007] In order to solve the above-mentioned problems, a motor drive device according to the present disclosure includes an inverter circuit that converts direct current to alternating current, a motor with one or more phases connected to the inverter circuit, a calculation unit, and a PWM signal generation unit, wherein the calculation unit calculates a drive voltage for driving the motor and determines a first duty ratio of a PWM signal, the PWM signal generation unit converts the first duty ratio calculated by the calculation unit into the PWM signal at a carrier frequency and outputs the PWM signal, and the calculation unit further calculates a PWM signal when the motor has only one phase. In this case, if there are multiple phases, one or more phases are irregularly selected for the phase, one or more PWM cycles are irregularly selected for the selected phase, a specified value for increasing or decreasing the first duty ratio is calculated, the duty ratio of the PWM signal in the selected cycle for the selected phase is set to a second duty ratio that is increased or decreased from the first duty ratio by the specified value, and the PWM signal generation unit is configured to convert the second duty ratio into the PWM signal and output it.

[0008] According to the above configuration, the regularity of the PWM signal is disrupted, so that frequency components of a carrier frequency different from a specific carrier frequency are applied to the motor. This disperses the frequency components of the carrier frequency. This reduces noise peaks in the frequency band of the carrier frequency. Moreover, according to the above configuration, even when carrier frequency dispersion control is performed, there is no need to change the period of other controls. Therefore, the control according to this embodiment can be easily implemented even in an inexpensive microcomputer with a slow processing speed.

[0009] 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.

[0010] The present disclosure has the advantage of being able to provide a motor drive device that reduces noise peak values ​​caused by carrier frequencies, with the above configuration, which can be easily implemented even in inexpensive microcomputers with slow processing speeds.

[0011] 1 is a block diagram showing a representative configuration example of a motor drive device according to an embodiment of the present disclosure. It is a timing chart showing an example of increasing or decreasing the duty ratio in one PWM cycle in one phase in the motor drive device shown in FIG. 1. It is a timing chart showing an example that schematically explains increasing or decreasing the duty ratio in a PWM cycle in the motor drive device shown in FIG. 1. It is a flowchart showing an example of control for increasing or decreasing the duty ratio of one cycle or multiple PWM cycles in one or multiple irregularly selected phases in the motor drive device shown in FIG. 1. It is a timing chart showing an example of control for increasing or decreasing the duty ratio by the same value for all phases in one PWM cycle for all three phases in the motor drive device shown in FIG. 1. It is a flowchart showing an example of control for increasing or decreasing the duty ratio by the same value for all phases in one or multiple irregularly selected PWM cycles in the motor drive device shown in FIG. 1. It is a comparison diagram of graphs that schematically show an example of noise distribution near the motor carrier frequency with and without duty ratio increase / decrease control in the motor drive device shown in FIG. 2 is a comparison diagram of graphs showing an example of actual measurements of noise near the motor carrier frequency when duty ratio increase / decrease control is performed and when it is not performed in the motor drive device shown in FIG. 1 . FIG.

[0012] (Knowledge, etc. that formed the basis of the present disclosure) At the time the inventors came up with the idea for the present disclosure, a technique was known for suppressing noise peak values ​​caused by the carrier frequency of an inverter device, in which the carrier frequency was varied within a predetermined frequency range around an arbitrary carrier frequency, thereby dispersing specific frequency components, as in the technique disclosed in the above-mentioned Patent Document 1.

[0013] However, because varying the carrier frequency requires multiple consecutive carrier frequency settings, the calculations and control tend to become complicated. For this reason, it has been difficult to implement a configuration that varies the carrier frequency with inexpensive microcomputers that have slow processing speeds.

[0014] Furthermore, switching between multiple consecutive carrier frequencies tends to be a fixed order and involves regular switching, which makes it difficult to achieve effective noise reduction because noise reduction occurs at fixed timing.

[0015] The inventors have discovered such a problem, and have come to form the subject of the present disclosure in order to solve the problem.

[0016] Therefore, the present disclosure provides a motor drive device that can be easily implemented in an inexpensive microcomputer with a slow processing speed and that reduces noise peak values ​​caused by carrier frequencies.

[0017] 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.

[0018] 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.

[0019] [1. Configuration Example of Motor Drive Device] A configuration example of a representative motor drive device according to the present disclosure will be described with reference to Fig. 1. For example, as shown in Fig. 1, the motor drive device according to this embodiment includes an inverter device 1 and a compressor 30. That is, in this embodiment, the motor (electric motor) to be driven by the motor drive device according to the present disclosure is a brushless DC motor 31 included in the compressor 30, as shown in Fig. 1.

[0020] 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 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 position detection unit 24.

[0021] 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).

[0022] 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 the position detection unit 24 of the control unit 20.

[0023] 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 motor drive device.

[0024] The calculation unit 21 executes various calculation processes associated with the control by the control unit 20. Specific examples of the calculation processes include, for example, a process of calculating a voltage command value (drive voltage) to drive the compressor 30 and outputting it as a duty ratio of a PWM signal, as will be described later.

[0025] Carrier frequency setting unit 22 sets the carrier frequency that drives compressor 30. PWM signal generation unit 23 converts the duty ratio output from calculation unit 21 into a PWM signal. Position detection unit 24 estimates the rotor position of brushless DC motor 31 from the circuit current detected by current detection circuit 12. The estimated rotor position is used for calculation processing by calculation unit 21. That is, calculation unit 21 calculates a voltage command value appropriate for motor drive from the estimated rotor position, and outputs it as the duty ratio of the PWM signal, as described above.

[0026] 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, position detection unit 24, etc. included in the control unit 20. For example, the control unit 20 described in this embodiment may be configured with a calculation device and a storage device of a microcomputer or a microcontroller.

[0027] 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)).

[0028] 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.

[0029] 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.

[0030] 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).

[0031] The inverter device 1 configured as above is connected to the compressor 30 by one or more phase wires. 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 by supplying sinusoidal current.

[0032] 2. Operation of the Motor Drive Device The operation of the motor drive device (inverter device 1 and compressor 30) configured as above will be described below.

[0033] [2-1. Basic Operation] The operation of the inverter device 1 will be described with reference to Fig. 1. When the brushless DC motor 31 is rotating, a back electromotive force is generated due to the rotation. The back electromotive force serves as information for estimating the rotor position of the brushless DC motor 31. The circuit current value of the inverter circuit 10, which includes information on this back electromotive force, is acquired by the current detection circuit 12 and input to the position detection unit 24.

[0034] As described above, the position detector 24 estimates the rotor position of the brushless DC motor 31. The calculator 21 calculates a voltage command value appropriate for driving the motor from the estimated rotor position and outputs it as a duty ratio of a PWM signal. The PWM signal generator 23 converts (generates) this duty ratio into a PWM signal.

[0035] The carrier frequency used when the PWM signal generating unit 23 generates a PWM signal is the frequency set in the carrier frequency setting unit 22. This carrier frequency is determined by the setting from the calculation unit 21. Typically, the carrier frequency is determined by comprehensively determining the switching loss, noise, controllability, etc. of the drive element. In this embodiment, priority is given to reducing the loss of the drive element, and the carrier frequency is set to a low frequency, for example, 1.5 kHz.

[0036] The control voltage mainly used in the inverter circuit 10 is 15 V, rather than 3.3 V or 5 V used in the control unit 20. In addition, in the inverter circuit 10, voltage conversion using a bootstrap circuit or the like is required to drive the high-side drive element.

[0037] Therefore, a drive circuit 11 is provided between the control unit 20 and the inverter circuit 10, and this drive circuit 11 converts signals. Note that some drive circuits 11 have built-in protection circuits for overcurrent protection and the like. The brushless DC motor 31 is driven by a voltage signal output from the inverter circuit 10. This allows the brushless DC motor 31 to continue rotating.

[0038] In the motor drive device according to the present disclosure, as described above, the calculation unit 21 calculates the drive voltage for driving the brushless DC motor 31 and determines the duty ratio of the PWM signal, and the PWM signal generation unit 23 generates the PWM signal from this duty ratio. Furthermore, the calculation unit 21 irregularly selects one or more PWM cycles in one or more phases of the brushless DC motor 31 and increases or decreases the duty ratio of the PWM signal in the selected cycle. The PWM signal generation unit 23 converts the increased or decreased duty ratio into a PWM signal and outputs it.

[0039] This disrupts the regularity of the PWM signal, causing frequency components different from the specific carrier frequency to be applied to brushless DC motor 31. This disperses the frequency components when brushless DC motor 31 is driven, thereby reducing noise peaks in the frequency band of the carrier frequency.

[0040] Below, we will explain the operation of reducing noise peak values ​​caused by the carrier frequency (carrier frequency dispersion operation) in the motor drive device of the present disclosure, dividing it into cases where the calculation unit 21 selects only one phase and increases or decreases the duty ratio, and where the calculation unit 21 selects one cycle of multiple phases and increases or decreases the duty ratio.

[0041] In this disclosure, for convenience of explanation, the duty ratio determined by the calculation unit 21 may be referred to as the "first duty ratio," and the duty ratio that is increased or decreased by the calculation unit 21 to reduce the noise peak value may be referred to as the "second duty ratio."

[0042] [2-2. Carrier Frequency Dispersion Operation 1 (For Each Phase)] First, an operation (carrier frequency dispersion operation 1) will be described, in which one phase (or multiple phases) of a PWM signal is selected, one or more PWM cycles are selected from the selected phase, and the duty ratio of the selected PWM cycle is increased or decreased to disperse the frequency components of the carrier frequency.

[0043] An example in which the duty ratio is increased for one PWM cycle in one phase of the brushless DC motor 31 is shown in Fig. 2. The example shown in Fig. 2 shows the carrier waveform and PWM waveform for one phase irregularly selected by the calculation unit 21. In this example, a sine wave is used as the modulating wave, and the carrier signal is modulated.

[0044] The phase for which the duty ratio is increased or decreased is selected randomly from among the phases of the brushless DC motor 31. The method for selecting a phase may be a method using an asynchronous counter or a method using a random function, but is not particularly limited in the present disclosure. Furthermore, the PWM cycle may also be selected randomly using a known method, and the selection method is not particularly limited.

[0045] In the example shown in Figure 2, the seventh PWM cycle (carrier period) from the left of the PWM waveform is irregularly selected, and the duty ratio of this PWM cycle is increased. In the figure, the shaded area (shaded area) represents the increase in pulse width corresponding to the increase in duty ratio, and the unshaded area corresponds to the pulse width before the duty ratio was increased. Therefore, in one selected PWM cycle, the unshaded area represents the pulse width corresponding to the "first duty ratio," and the combined area of ​​the unshaded area and the shaded area represents the pulse width corresponding to the "second duty ratio."

[0046] A more detailed explanation of the increase and decrease in the duty ratio within a PWM cycle is shown in FIG. 3. As shown in FIG. 3, a PWM waveform is determined by comparing the magnitude of a carrier signal and a modulated wave. The calculation unit 21 increases or decreases the duty ratio of the determined PWM waveform within a selected PWM cycle. In FIG. 3, as in FIG. 2, the solid area indicates the pulse width corresponding to the "first duty ratio," and the combined area of ​​the solid area and the shaded area indicates the pulse width corresponding to the "second duty ratio."

[0047] Methods for increasing or decreasing the duty ratio include, but are not limited to, a method of increasing or decreasing a fixed value, a method of calculating based on the current value, a method of determining a numerical value using an asynchronous counter, a method using a random function, etc. However, the duty ratio is increased or decreased so as not to exceed the upper or lower limit value range of the duty ratio.

[0048] In the examples shown in Figures 2 and 3, the duty ratio is increased or decreased before the high period of the PWM waveform, but the method for increasing or decreasing the duty ratio is not limited to this. The duty ratio may be increased or decreased after the high period of the PWM waveform, or may be distributed to both sides. The examples shown in Figures 2 and 3 illustrate an example in which the duty ratio is increased (the pulse width corresponding to the first duty ratio is smaller than the pulse width corresponding to the second duty ratio). In addition, while the simple comparison method is used to generate the PWM waveform in this embodiment, other methods such as space vector modulation and intermediate voltage 1 / 2 addition may also be used.

[0049] FIG. 4 shows a specific example of control in which one or more phases are selected, one or more PWM cycles of the selected phases are selected, and the duty ratio of the PWM cycles is increased or decreased.

[0050] First, as described above, the current value (circuit current) of the inverter circuit 10 acquired by the current detection circuit 12 is output to the position detection unit 24 of the control unit 20. In the control unit 20, the position detection unit 24 estimates the rotor position of the brushless DC motor 31 from this current value (step S101).

[0051] The calculation unit 21 of the control unit 20 calculates a voltage command value (drive voltage) based on the estimated rotor position of the brushless DC motor 31 (step S102). The control unit 20 reflects the calculated voltage command value in the duty ratio (step S103). That is, the calculation unit 21 of the control unit 20 determines the first duty ratio of the PWM signal from the calculated drive voltage.

[0052] When the calculation unit 21 outputs the first duty ratio, the control unit 20 selects one or more phases of the brushless DC motor 31 (step S104), and then randomly selects one or more PWM cycles for the selected one or more phases (step S105). The calculation unit 21 then calculates a designated value for increasing or decreasing the first duty ratio, thereby determining the increase or decrease amount for the previously calculated first duty ratio (step S106). This determination of the increase or decrease amount (step S106) is performed for each selected phase.

[0053] The control unit 20 reflects the determined increase / decrease value in the first duty ratio (step S107). That is, the calculation unit 21 of the control unit 20 increases or decreases the duty ratio in the PWM cycle (carrier period) selected for the selected phase from the first duty ratio calculated previously (steps S102 to S103) by the specified value (based on the increase / decrease value), sets it as the second duty ratio, and outputs it to the PWM signal generation unit 23 as a voltage command.

[0054] Based on this voltage command, the PWM signal generator 23 generates a PWM signal including a PWM cycle reflecting the second duty ratio (step S108). The generated PWM signal is converted into a voltage signal that drives the brushless DC motor 31 via the drive circuit 11 and the inverter circuit 10. As a result, the brushless DC motor 31 continues to rotate.

[0055] In this way, in the motor drive device according to the present disclosure, as a carrier frequency dispersion operation, the calculation unit 21 of the control unit 20 can employ a configuration in which it irregularly selects one or more of the phases of the brushless DC motor 31, irregularly selects one or more of the PWM cycles of the selected phases, and sets the duty ratio of the PWM signal in the selected PWM cycle of the selected phase to a second duty ratio that is increased or decreased by a specified value from the first duty ratio.

[0056] [2-3. Carrier Frequency Dispersion Operation 2 (Increasing or Decreasing the Same Value for All Phases)] Next, an operation (carrier frequency dispersion operation 2) will be described in which all phases of the PWM signal are selected, and the duty ratio of the selected PWM cycle is increased or decreased by the same value for all phases to disperse the frequency components of the carrier frequency.

[0057] 5 shows an example in which, when the brushless DC motor 31 has three phases, U, V, and W, one PWM cycle is selected irregularly for all three phases, and the duty ratio of the selected PWM cycle for each phase is increased by the same value. The example shown in FIG. 5 shows a carrier waveform, modulated waves for all three phases, and PWM waveforms for all three phases. In the example shown in FIG. 5, a sine wave is used as the modulating wave, and the carrier signal is modulated.

[0058] In the example shown in FIG. 5, the tenth PWM cycle (carrier period) from the left of the illustrated PWM waveform is irregularly selected, and the duty ratio of the selected PWM cycle is increased by the same value for all three phases, U phase, V phase, and W phase.

[0059] 2 and 3, in each of the U, V, and W phases, the shaded areas indicate the increase in pulse width corresponding to the increase in duty ratio, and the unshaded areas indicate the pulse width before the duty ratio was increased. Therefore, in each of the three phases, in a selected PWM cycle, the unshaded areas indicate the pulse width corresponding to the "first duty ratio," and the sum of the unshaded and shaded areas indicates the pulse width corresponding to the "second duty ratio."

[0060] In the example shown in FIG. 5 , in the selected PWM cycle (carrier period), the first duty ratio has the smallest value in the order of the duty ratio of the U phase, the duty ratio of the V phase, and the duty ratio of the W phase, but the same increase value is reflected for each of the different first duty ratios in the three phases.

[0061] In this manner, in the present disclosure, the duty ratio of the PWM waveform can be increased or decreased by the same value for all of the multiple phases within one or more selected PWM cycles, i.e., one or more carrier periods. Note that methods for increasing or decreasing the duty ratio include, but are not limited to, a method of increasing or decreasing by a fixed value, a method of calculating based on a current value, a method of determining a value using an asynchronous counter, and a method using a random function.

[0062] A typical example of a method for increasing or decreasing the duty ratio will be described. In this embodiment, for example, a method of calculating an increase or decrease in the duty ratio based on a current value will be described. The voltage command values, i.e., duty ratios of the three phases calculated by the calculation unit 21 are assumed to be, for example, as follows: U phase = 20%, V phase = 60%, W phase = 70%.

[0063] When increasing the duty ratio, the duty ratio must not exceed 100%. When adding the same value to all phases, if the duty ratio of the phase with the highest duty ratio does not exceed 100%, the duty ratio of the remaining phases will not exceed 100%. Therefore, the value to be added is calculated based on the phase with the highest duty ratio.

[0064] In the example shown in Figure 5, the phase with the largest duty ratio is the W phase, which has a value of 70%. In this example, the duty ratio is increased by half of the difference up to 100% (100% - 70% = 30%). In this case, the value (specified value) by which the duty ratio is increased is as follows: (100 - 70) x (1 / 2) = 15

[0065] In this way, if the designated value is 15, the calculation unit 21 will increase the duty ratio of each phase by 15. As a result, the recalculated duty ratios of each phase will be as follows: U phase = 35%, V phase = 75%, W phase = 85%

[0066] FIG. 6 shows a specific example of control in which one or more PWM cycles are selected for all phases of the brushless DC motor 31 and the duty ratio of the selected PWM cycle is increased or decreased.

[0067] First, as described above, the current value (circuit current) of the inverter circuit 10 acquired by the current detection circuit 12 is output to the position detection unit 24 of the control unit 20. In the control unit 20, the position detection unit 24 estimates the rotor position of the brushless DC motor 31 from the current value (step S201).

[0068] The calculation unit 21 of the control unit 20 calculates a voltage command value (drive voltage) based on the estimated rotor position of the brushless DC motor 31 (step S202). The control unit 20 reflects the calculated voltage command value in the duty ratio (step S203). That is, the calculation unit 21 of the control unit 20 determines the first duty ratio of the PWM signal from the calculated drive voltage.

[0069] When the calculation unit 21 outputs the first duty ratio, the control unit 20 selects all phases of the brushless DC motor 31 (step S204) and randomly selects one or more PWM cycles for all phases (step S205). The calculation unit 21 then calculates a designated value for increasing or decreasing the first duty ratio, thereby determining the increase or decrease value for the previously calculated first duty ratio (step S206). At this time, the same value (same increase or decrease value, same designated value) is used for all phases.

[0070] The control unit 20 reflects the determined same increase / decrease value in the first duty ratio of each phase (step S207). That is, the calculation unit 21 of the control unit 20 increases or decreases the duty ratio in the PWM cycle (carrier period) selected for all phases by the specified value (based on the increase / decrease value) compared to the first duty ratio calculated previously (steps S202 to S203), to obtain a second duty ratio, and outputs the second duty ratio to the PWM signal generation unit 23 as a voltage command.

[0071] Based on this voltage command, the PWM signal generator 23 generates a PWM signal including a PWM cycle reflecting the second duty ratio (step S208). The generated PWM signal is converted into a voltage signal that drives the brushless DC motor 31 via the drive circuit 11 and the inverter circuit 10. As a result, the brushless DC motor 31 continues to rotate.

[0072] In this way, in the motor drive device according to the present disclosure, as a carrier frequency dispersion operation, the calculation unit 21 of the control unit 20 can employ a configuration in which one or more PWM cycles are irregularly selected for all phases of the brushless DC motor 31, and the duty ratio of the PWM signal in the selected PWM cycle of the selected phase is set to a second duty ratio that is increased or decreased by a specified value from the first duty ratio.

[0073] [3. Effects, etc.] [3-1. Main effects, etc. of this embodiment] As described above, the motor 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 position detection unit 24. The compressor 30 includes a brushless DC motor 31. The inverter device 1 is connected to the compressor 30 by one or more phase wires. The DC voltage source 32 supplies a voltage to the inverter device 1.

[0074] The calculation unit 21 calculates a drive voltage for driving the brushless DC motor 31 and determines a duty ratio (first duty ratio) of the PWM signal. The PWM signal generation unit 23 converts the first duty ratio calculated by the calculation unit 21 into a PWM signal at a carrier frequency and outputs the PWM signal.

[0075] Furthermore, in the motor drive device according to this embodiment, in the above configuration, calculation unit 21 further randomly selects one or more PWM cycles in one or more phases of brushless DC motor 31 and calculates a specified value for increasing or decreasing the first duty ratio. Calculation unit 21 sets the duty ratio of the PWM signal in the selected cycle in the selected phase to a second duty ratio that is increased or decreased from the first duty ratio by the specified value. PWM signal generation unit 23 converts the second duty ratio into a PWM signal and outputs it.

[0076] This disrupts the regularity of the PWM signal, causing frequency components of a carrier frequency different from the specific carrier frequency to be applied to the motor, dispersing the frequency components of the carrier frequency and reducing noise peaks in the frequency band of the carrier frequency.

[0077] On the other hand, this distributed control of the carrier frequency only needs to be performed for one or more randomly selected PWM cycles, and does not need to be performed for all PWM cycles. Furthermore, because the period of the PWM signal does not change, there is no need to change the period for controls other than the distributed control of the carrier frequency, such as the timing of obtaining current values ​​and reflecting voltage command values.

[0078] In conventional methods that vary the carrier frequency, it is necessary to continuously change the settings of multiple carrier frequencies. Furthermore, because the PWM cycle changes each time, the timing of acquiring the current value and reflecting the voltage command value, etc., may need to be adjusted in response to the change in the PWM cycle. In such conventional methods, the calculation processing or control itself tends to be complicated. Therefore, the conventional method may be difficult to implement on inexpensive, slow-processing microcontrollers.

[0079] In contrast to this, in this embodiment, even if the distributed control of the carrier frequency is performed, there is no need to change the cycle of other controls, as described above. Therefore, the control according to this embodiment can be easily introduced even in an inexpensive microcomputer with a slow processing speed.

[0080] Furthermore, in the motor drive device according to this embodiment, the specified value for increasing or decreasing the first duty ratio may be an irregular, different value. This allows for more irregular and natural frequency distribution compared to methods that calculate the duty ratio. This makes it possible to achieve a more even noise distribution and further reduce noise peaks.

[0081] Furthermore, the motor drive device according to this embodiment may increase or decrease the duty ratio by the same specified value for one or more randomly selected PWM cycles for all phases. This increases or decreases the same voltage for all phases, so the inter-phase voltage does not change and the motor current generated by the inter-phase voltage is not affected. This allows noise peaks to be reduced while minimizing the effect on motor control of increasing or decreasing the duty ratio.

[0082] [3-2. Example of Specific Effects] Next, the effects obtained by the motor drive device according to this embodiment will be specifically described with reference to FIGS. 7 and 8. FIG.

[0083] First, FIG. 7 is a comparison diagram of graphs that schematically show the change in noise level when the duty ratio of each phase is increased or decreased with the same value for each phase for one PWM cycle that is irregularly selected when all phases are selected.

[0084] In the case of sinusoidal wave drive, if the carrier frequency is fc [kHz], the main frequency component of the interphase voltage applied to the brushless DC motor 31 is centered around the motor carrier frequency 2fc [kHz], which is twice the carrier frequency.

[0085] The two graphs shown in Fig. 7 each show a noise distribution near the motor carrier frequency, with the horizontal axis representing frequency [kHz] and the vertical axis representing noise level [dB]. Graph I on the left side of Fig. 7 is a graph that schematically shows the change in noise level when "no duty ratio increase / decrease control" is not performed, i.e., when the above-mentioned carrier frequency dispersion operation is not performed, and graph II on the right side is a graph that schematically shows the change in noise level when "duty ratio increase / decrease control is performed," i.e., when the above-mentioned carrier frequency dispersion operation is performed.

[0086] When duty ratio increase / decrease control is not performed, the noise distribution has a sharp peak at the motor carrier frequency 2fc, as shown schematically in graph I.

[0087] In contrast, when duty ratio increase / decrease control is performed, the frequency components of the carrier frequency are dispersed by irregularly increasing or decreasing the duty ratio. As a result, as shown schematically in Graph II, frequency components near the motor carrier frequency 2fc are also dispersed. As a result, as is clear from the comparison of the dashed lines between Graph I and Graph II in Figure 7, the peak value of noise at the motor carrier frequency 2fc can be reduced.

[0088] Next, Fig. 8 shows an example of the results of actually measuring noise components, i.e., a representative embodiment of the present disclosure. As in Fig. 7, graph I on the left side of Fig. 8 is a graph showing changes in the actual measured values ​​of noise in an embodiment "without duty ratio increase / decrease control," i.e., in which the above-mentioned carrier frequency dispersion operation is not performed, and graph II on the right side is a graph showing changes in the actual measured values ​​of noise in an embodiment "with duty ratio increase / decrease control," i.e., in which the above-mentioned carrier frequency dispersion operation is performed.

[0089] In this embodiment, as in the schematic example shown in FIG. 7, the increase / decrease of the duty ratio in one PWM cycle selected irregularly is controlled for all phases.

[0090] In this example, as shown in Figure 8, it can be seen that the noise peak value at the motor carrier frequency 2fc is clearly suppressed in Graph II, which shows "without duty ratio control," compared to Graph I, which shows "with duty ratio control." The suppression level at this time was approximately 4 dB. As such, it can be seen that the results of the example shown in Figure 8 show a similar tendency to the schematic model shown in Figure 7.

[0091] It goes without saying that the effects of the present embodiment described above can be realized in a motor drive device according to the claims of the present disclosure, and are not limited to the configuration of the present embodiment or examples described above.

[0092] (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.

[0093] Specifically, for example, in the above-described embodiment, the rotor position of the brushless DC motor 31 is estimated using the circuit current detected by the current detection circuit 12. However, the estimation of the rotor position in the present disclosure is not limited to detection of the circuit current by the current detection circuit 12, and known methods can be suitably used. For example, the rotor position may be estimated using a sensor such as a Hall element built into the brushless DC motor 31.

[0094] Alternatively, in the above-described embodiment, current detection is performed using a one-shunt configuration using the current detection circuit 12. However, in the present disclosure, the configuration for current detection using the current detection circuit 12 is not limited to this, and may be, for example, a three-shunt system for detecting currents of each phase.

[0095] Alternatively, in the above-described embodiment, the motor drive device is configured to drive the brushless DC motor 31 provided in the compressor 30. However, the motor (electric motor) to be driven in the present disclosure is not limited to this, and may be a motor provided in various known devices. Also, while the brushless DC motor 31 is three-phase in the above-described embodiment, the present disclosure is not limited to this, and may be single-phase, two-phase, four-phase, five-phase, or any other multiple-phase.

[0096] (Additional Note) Based on the description of the above embodiments, the following techniques are disclosed in this specification. (Technology 1) A motor drive device including an inverter circuit that converts direct current to alternating current, a motor with one or more phases connected to the inverter circuit, a calculation unit, and a PWM signal generation unit, wherein the calculation unit calculates a drive voltage for driving the motor and determines a first duty ratio of a PWM signal, the PWM signal generation unit converts the first duty ratio calculated by the calculation unit into the PWM signal at a carrier frequency and outputs the PWM signal, the calculation unit further selects the phase if there is only one phase, or one or more phases if there are multiple phases, irregularly selects one or more PWM cycles for the selected phase, calculates a specified value by which to increase or decrease the first duty ratio, and sets the duty ratio of the PWM signal for the selected phase in the selected cycle to a second duty ratio that is increased or decreased by the specified value from the first duty ratio, and the PWM signal generation unit converts the second duty ratio into the PWM signal and outputs it.

[0097] (Technology 2) The motor drive device according to Technology 1, wherein the cycle of increasing or decreasing the first duty ratio calculated by the calculation unit is irregular, and the designated value is an irregular, different value.

[0098] (Technology 3) The motor drive device according to Technology 1 or Technology 2, wherein the specified value for increasing or decreasing the first duty ratio calculated by the calculation unit for the selected phase is the same within the same PWM cycle.

[0099] (Technology 4) The motor drive device according to any one of Technology 1 to Technology 3, wherein the calculation unit selects and applies a designated value for increasing or decreasing the first duty ratio to all phases.

[0100] 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.

[0101] 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.

[0102] The present disclosure can be suitably used in a wide range of fields, including motor drive devices that drive various motors using PWM control, and various appliances equipped with motors. In particular, the present disclosure can be applied to motor drive devices that drive motors equipped in compressors of various refrigeration and freezing appliances (e.g., refrigerators, air conditioners, etc.). Therefore, the present disclosure can be suitably used not only in the field of various appliances equipped with motors, but also in the field of various refrigeration and freezing appliances.

[0103] 1: Inverter device 10: Inverter circuit 11: Drive circuit 12: Current detection circuit 20: Control unit 21: Calculation unit 22: Carrier frequency setting unit 23: PWM signal generation unit 24: Position detection unit 30: Compressor 31: Brushless DC motor 32: DC voltage source

Claims

1. A power supply comprising: an inverter circuit for converting direct current to alternating current; a motor with one or more phases connected to the inverter circuit; a calculation unit; and a PWM signal generation unit, wherein the calculation unit calculates a drive voltage for driving the motor and determines a first duty ratio of a PWM signal; the PWM signal generation unit converts the first duty ratio calculated by the calculation unit into the PWM signal at a carrier frequency and outputs the PWM signal; the calculation unit further: selects the phase when there is only one phase, or irregularly selects one or more phases when there are multiple phases, and irregularly selects one or more PWM cycles for the selected phase; calculates a designated value for increasing or decreasing the first duty ratio; sets the duty ratio of the PWM signal in the selected cycle of the selected phase to a second duty ratio that is increased or decreased by the designated value from the first duty ratio; and the PWM signal generation unit converts the second duty ratio into the PWM signal and outputs it. Motor drive device.

2. The motor drive device according to claim 1, wherein the cycle for increasing or decreasing the first duty ratio calculated by the calculation unit is irregular, and the designated value is an irregular and different value.

3. The motor drive device according to claim 1 or 2, wherein the designated value for increasing or decreasing the first duty ratio calculated by the calculation unit for the selected phase is the same within the same PWM cycle.

4. The motor drive device according to claim 1 or 2, wherein the calculation unit selectively applies a designated value for increasing or decreasing the first duty ratio to all phases.

5. The motor drive device according to claim 3, wherein the calculation unit selectively applies a designated value for increasing or decreasing the first duty ratio to all phases.

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