Motor drive device for reducing switching loss during power supply regeneration

Abstract

This motor drive device comprises: a converter that selectively executes a rectification operation for converting AC power inputted from an AC power supply to DC power and outputting the DC power to a DC link, and a regeneration operation for converting the DC power of the DC link to AC power and returning the AC power to the AC power supply when a DC link voltage exceeds a regeneration start voltage; an inverter that, in accordance with a motor drive command, selectively executes an active drive operation for converting the DC power of the DC link to AC drive power and supplying the AC drive power to a motor, and a regeneration operation for converting AC regenerative power from the motor to DC power and returning the DC power to the DC link; and a converter control unit that controls the operation of the converter. The converter control unit changes the regeneration start voltage in accordance with information related to the motor drive command.

Description

Motor drive device for reducing switching loss during power regeneration

[0001] The present disclosure relates to a motor drive device for reducing switching loss during power regeneration.

[0002] In a motor drive device that drives a motor provided in a machine tool or a robot, AC power supplied from an AC power source is converted into DC power by a converter (rectifier) and output to a DC link. Further, the DC power in the DC link is converted into AC power for motor drive by an inverter and supplied to the motor. In recent years, a converter having a power regeneration function that can return the regenerative power generated during motor deceleration to the AC power source side has been used. When the motor decelerates, the regenerative power returns to the DC link via the inverter, so the DC link voltage rises. When the DC link voltage reaches a predetermined value or there is a certain voltage rise from the steady value, the regenerative power is returned to the AC power source side via the switching element in the converter.

[0003] Japanese Patent Laid-Open No. 05-336778, Japanese Patent Laid-Open No. 2004-364462, Japanese Patent Laid-Open No. 2022-017119

[0004] In a converter having a power regeneration function, switching loss occurs due to the on / off of the switching element during the regeneration operation. The larger the current flowing through the converter, the greater the switching loss generated during the regeneration operation. Therefore, a motor drive device capable of reducing the switching loss during the regeneration operation is desired.

[0005] According to one aspect of the present disclosure, the motor drive device includes a converter that selectively performs a rectification operation that converts AC power input from an AC power source into DC power and outputs it to a DC link, and a regenerative operation that converts the DC power of the DC link into AC power and returns it to the AC power source when the DC link voltage exceeds the regenerative start voltage; an inverter that selectively performs a powering operation that converts the DC power of the DC link into AC drive power and supplies it to the motor, and a regenerative operation that converts the AC regenerative power from the motor into DC power and returns it to the DC link, in accordance with a motor drive command; and a converter control unit that controls the operation of the converter, wherein the converter control unit changes the regenerative start voltage in accordance with information related to the motor drive command.

[0006] This is a circuit diagram showing a motor drive device according to an embodiment of the present disclosure. This diagram illustrates switching losses that occur during the regenerative operation of a converter, illustrating the emitter-collector voltage waveform and current waveform that occur when a switching element switches from off to on when the current flowing through the converter is small compared to a predetermined value. This diagram illustrates switching losses that occur during the regenerative operation of a converter, illustrating the emitter-collector voltage waveform and current waveform that occur when a switching element switches from off to on when the current flowing through the converter is large compared to a predetermined value. This is a block diagram showing the converter control unit in a motor drive device according to an embodiment of the present disclosure. This is a block diagram showing the inverter control unit in a motor drive device according to an embodiment of the present disclosure. This is a diagram showing the operation flow of the regenerative start voltage setting process in a first embodiment of a motor drive device according to an embodiment of the present disclosure. This is a diagram showing the operation flow of the regenerative start voltage setting process in a second embodiment of a motor drive device according to an embodiment of the present disclosure. This is a diagram showing the operation flow of the regenerative start voltage setting process in a third embodiment of a motor drive device according to an embodiment of the present disclosure. This is a diagram showing the operation flow of the regenerative start voltage setting process in a fourth embodiment of a motor drive device according to an embodiment of the present disclosure. This figure shows the operation flow of the regenerative start voltage setting process according to the fifth embodiment of the motor drive device according to the embodiments of this disclosure. This figure shows the operation flow of the regenerative start voltage setting process according to the sixth embodiment of the motor drive device according to the embodiments of this disclosure.

[0007] The following describes an embodiment of a motor drive device that reduces switching losses during power regeneration, with reference to the drawings. In the following description, components having the same or similar function are denoted by the same reference numerals. Duplication of these components may be omitted. The drawings have been scaled appropriately for ease of understanding.

[0008] Furthermore, in the following description, terms are defined in consideration of the function in the embodiments of this disclosure, and therefore terms may differ depending on the intent or convention of the user, operator, etc. For example, “connected” means “electrically connected.” A converter that converts AC power supplied from an AC power source into DC power and outputs it is also called a “rectifier,” “rectifier device,” “rectifier circuit,” or “forward converter.” An inverter that converts DC power into AC power and outputs it is also called an “inverse converter.” “DC link” refers to the circuit portion that electrically connects the DC output side of the converter and the DC input side of the inverter. “DC link” is also called “DC link section,” “DC link,” “DC link section,” “DC bus,” or “DC intermediate circuit.” “DC link voltage” refers to the potential difference between the positive potential on the positive power line of the DC link and the negative potential on the negative power line. “DC link current” refers to the current flowing through the positive or negative power line of the DC link. "Inverter current" refers to the current flowing between the inverter and the motor (windings). "Inverter current" is also called "motor current". The concept of "power elements" includes switching elements and diodes. "Power elements" are also called "power semiconductors" or "power semiconductor elements". "On" for a switching element means that the switching element closes and forms an electrical circuit through that switching element. "Off" for a switching element means that the switching element opens and blocks the electrical circuit through that switching element. "Switching loss" means the loss that occurs in a switching element when it is turned on or off. The "rotational speed" of a motor means the "rotational speed or angular velocity of the rotor or rotating shaft" of the motor. The "speed command" of a motor means the "rotational speed command or angular velocity command for the rotor or rotating shaft" of the motor. The "speed control" of a motor means the "rotational speed control or angular velocity command for the rotor or rotating shaft" of the motor. The "position" of a motor means the "rotational position or rotational angle position of the rotor or rotating shaft" of the motor. The "position command" for a motor refers to the "rotational position command or rotational angular position command relative to the rotor or rotating shaft" of the motor.Motor "position control" refers to "rotational position control or rotational angular position control relative to the rotor or rotating shaft" of the motor. "Rate of change" means "the rate of change of a certain value per unit time." Furthermore, the numerical examples provided below are merely examples, and other numerical values ​​may be used. Also, the units of each parameter may be omitted.

[0009] Furthermore, in the motor drive device according to the embodiments of this disclosure, switching elements in the converter and inverter are switched on and off. Examples of switching elements include semiconductor elements such as IGBTs, FETs, thyristors, GTOs, and transistors, but other semiconductor elements may also be used. An IGBT has a gate terminal, a collector terminal, and an emitter terminal as its terminals. A transistor has a base terminal, a collector terminal, and an emitter terminal as its terminals. An FET has a gate terminal, a drain terminal, and a source terminal as its terminals. A thyristor and a GTO have a gate terminal, an anode terminal, and a cathode terminal as its terminals. The "current inflow terminals" of the switching elements correspond to the "collector" of IGBTs and transistors, the "drain" of FETs, and the "anode" of thyristors and GTOs, respectively. The "current outflow terminals" of the switching elements correspond to the "emitter" of IGBTs and transistors, the "source" of FETs, and the "cathode" of thyristors and GTOs, respectively. The "control terminals" of switching elements correspond to the "gate" of IGBTs, FETs, thyristors, and GTOs, and the "base" of transistors, respectively.

[0010] The following description will explain the case where the switching element is composed of an IGBT as an example, but the embodiments of this disclosure are also applicable to FETs, thyristors, GTOs, or transistors. Furthermore, when the switching element is composed of an FET, the current inflow terminal "collector" is read as "drain," and the current outflow terminal "emitter" is read as "source," and the embodiments of this disclosure apply accordingly. Furthermore, when the switching element is composed of a transistor, the control terminal "gate" is read as "base," and the embodiments of this disclosure apply accordingly. Furthermore, when the switching element is composed of a thyristor or GTO, the current inflow terminal "collector" is read as "anode," and the current outflow terminal "emitter" is read as "cathode," and the embodiments of this disclosure apply accordingly. The switching element performs an on / off operation when a voltage corresponding to a command is applied to the gate of the switching element.

[0011] <Overall Configuration of Motor Drive Device According to Embodiment of the Disclosure> Figure 1 is a circuit diagram showing a motor drive device according to an embodiment of the disclosure.

[0012] In the embodiments of this disclosure described below, one example is shown of a case in which a motor 3 is driven by a motor drive device 1 connected to an AC power supply 2. Examples of AC power supply 2 include a three-phase AC 400V power supply, a three-phase AC 200V power supply, a three-phase AC 600V power supply, and a single-phase AC 100V power supply. Here, as an example, the AC power supply 2 is assumed to be three-phase. The motor 3 may be either an induction motor or a synchronous motor. Furthermore, the number of phases of the motor 3 is not particularly limited to each embodiment, and may be, for example, three-phase or single-phase. Here, as an example, the motor 3 is assumed to be a three-phase AC motor. Furthermore, the number of motors 3 is not particularly limited to each embodiment, and may be multiple. Here, as an example, the motor 3 is assumed to be one. Machines in which the motor 3 is provided include, for example, machine tools and robots. The motor 3 is used, for example, as a drive source for the feed axis or spindle of a machine tool, or the arm of a robot.

[0013] As shown in Figure 1, the motor drive device 1 according to the embodiment of the present disclosure comprises a converter 11, an inverter 12, a converter control unit 13, an inverter control unit 14, a capacitor 15, and AC reactors 16R, 16S, and 16T. The motor drive device 1 also comprises an input current detection unit 21, a DC link current detection unit 22, a DC link voltage detection unit 23, an inverter current detection unit 24, and a speed detection unit 25. Power supplies for driving each of these units, such as the converter control unit 13, the inverter control unit 14, the input current detection unit 21, the DC link current detection unit 22, the DC link voltage detection unit 23, the inverter current detection unit 24, and the speed detection unit 25, are not shown in the figure.

[0014] The converter 11 selectively performs two operations in response to a command from the converter control unit 13: a rectification operation that converts the AC power input from the AC power source 2 into DC power and outputs it to the DC link 17, and a regenerative operation that converts the DC power of the DC link 17 into AC power and returns it to the AC power source 2 when the DC link voltage exceeds the regeneration start voltage. The converter 11 is configured as a three-phase bridge circuit when three-phase AC power is supplied from the AC power source 2, and as a single-phase bridge circuit when single-phase AC power is supplied from the AC power source 2. In the illustrated example, the AC power source 2 is a three-phase AC power source, so the converter 11 is configured as a three-phase bridge circuit.

[0015] Examples of converters 11 include PWM switching control type rectifiers and 120-degree energizing type rectifiers. For example, a converter 11 consisting of a PWM switching control type rectifier has a bridge circuit configuration of power elements consisting of switching elements and diodes connected in antiparallel to them. When a regenerative command is received from the converter control unit 13, the converter 11 consisting of a PWM switching control type rectifier performs regenerative operation by switching each switching element on and off, and when a rectification command is received from the converter control unit 13 but no regenerative command is received, the switching elements turn off to perform rectification. Also, for example, a converter 11 consisting of a 120-degree energizing type rectifier has a bridge circuit of power elements consisting of switching elements connected in antiparallel to each other. When a regenerative command is received from the converter control unit 13, the converter 11 consisting of a 120-degree energizing type rectifier performs regenerative operation by switching each switching element on and off, and when a rectification command is received from the converter control unit 13 but no regenerative command is received, the switching elements turn off and rectification is performed by diodes. Examples of switching elements include semiconductor elements such as IGBTs, FETs, thyristors, GTOs, and transistors, but other semiconductor elements may also be used. In the illustrated example, converter 11 is a PWM switching control type rectifier.

[0016] The converter control unit 13 controls the operation of the converter 11. If the DC link voltage exceeds the regeneration start voltage, the converter control unit 13 sends a regeneration command to the converter 11. If the DC link voltage does not exceed the regeneration start voltage, the converter control unit 13 sends a rectification command to the converter 11 instead of a regeneration command. Details of the converter control unit 13 will be described later.

[0017] AC reactors 16R, 16S, and 16T are provided on the AC input side of converter 11. Although not shown here, circuit breakers, electromagnetic contactors, etc., may also be provided on the AC input side of converter 11.

[0018] A capacitor 15 is connected to the DC link 17 between the converter 11 and the inverter 12. The capacitor 15 is sometimes referred to as a "DC link capacitor," "DC link capacitor," or "smoothing capacitor." The capacitor 15 has the function of suppressing the oscillation component of the DC output of the converter 11 and the function of storing the DC power used by the inverter 12 to generate AC power. Examples of capacitors 15 include electrolytic capacitors and film capacitors. A pre-charging circuit for pre-charging the capacitor 15 may be provided, but it is not shown in the diagram.

[0019] The inverter 12 is connected to the converter 11 via the DC link 17. The inverter 12 selectively performs two operations in response to a motor drive command from the inverter control unit 14: a powering operation in which the DC power of the DC link 17 is converted to AC drive power and supplied to the motor 3, and a regenerative operation in which the AC regenerative power from the motor 3 is converted to DC power and returned to the DC link 17. The inverter 12 is configured as a three-phase bridge circuit when the motor 3 is a three-phase AC motor, and as a single-phase bridge circuit when the motor 3 is a single-phase motor. In the illustrated example, the motor 3 is a three-phase AC motor, so the converter 11 is configured as a three-phase bridge circuit. The inverter 12 has a bridge circuit configuration of power elements consisting of switching elements and diodes connected in antiparallel thereto. Examples of switching elements include semiconductor elements such as IGBTs, FETs, thyristors, GTOs, and transistors, but other semiconductor elements may also be used. The inverter 12 selectively performs the powering operation and the regenerative operation by turning each switching element on and off in response to a motor drive command from the inverter control unit 14. As a result, the motor 3 is driven based on the AC power output from the inverter 12.

[0020] The inverter control unit 14 controls the operation of the inverter 12. The inverter control unit 14 generates motor drive commands and transmits them to the inverter 12. Upon receiving the motor drive commands, the inverter 12 selectively executes powering and regenerative braking operations. Details of the inverter control unit 14 will be described later.

[0021] The input current detection unit 21 detects the value or rate of change of the current (hereinafter referred to as "input current") flowing between the AC power supply 2 and the converter 11. In the illustrated example, since the AC power supply 2 is a three-phase AC power supply, a three-phase AC input current flows bidirectionally between the AC power supply 2 and the converter 11. However, the input current detection unit 21 detects the value or rate of change of the input current for, for example, two of the three phases. Alternatively, the input current detection unit 21 may detect the value or rate of change of the input current for all three phases. The value or rate of change of the input current detected by the input current detection unit 21 is sent to the converter control unit 13, but may also be sent to the inverter control unit 14.

[0022] The DC link current detection unit 22 detects the value or rate of change of the current flowing through the DC link 17 (hereinafter referred to as "DC link current"). In the illustrated example, the DC link current detection unit 22 detects the value or rate of change of the DC link current flowing through the positive power line of the DC link 17, but it may also detect the value or rate of change of the DC link current flowing through the negative power line of the DC link 17. The value or rate of change of the DC link current detected by the DC link current detection unit 22 is sent to the converter control unit 13 and the inverter control unit 14.

[0023] The DC link voltage detection unit 23 detects the value or rate of change of the DC link voltage, which is the voltage between the terminals of the DC link 17. That is, the DC link voltage detection unit 23 detects the value or rate of change of the potential difference between the positive potential appearing at the positive terminal on the DC output side of the converter 11 and the negative potential appearing at the negative terminal on the DC output side of the converter 11 as the value or rate of change of the DC link voltage. Alternatively, the DC link voltage detection unit 23 may detect the value or rate of change of the voltage applied between the positive and negative terminals of the capacitor 15 as the value or rate of change of the DC link voltage. The value or rate of change of the DC link voltage detected by the DC link voltage detection unit 23 is sent to the converter control unit 13 and the inverter control unit 14.

[0024] The inverter current detection unit 24 detects the value or rate of change of the inverter current flowing between the inverter 12 and the motor 3 (windings). In the illustrated example, since the motor 3 is a three-phase AC motor, a three-phase AC inverter current flows bidirectionally between the inverter 12 and the motor 3. However, the inverter current detection unit 24 detects the value or rate of change of the inverter current for, for example, two of the three phases. Alternatively, the inverter current detection unit 24 may detect the value or rate of change of the inverter current for all three phases. The value or rate of change of the inverter current detected by the inverter current detection unit 24 is sent to the converter control unit 13 and the inverter control unit 14.

[0025] The speed detection unit 25 detects the value or rate of change of the rotational speed of the motor 3. In the illustrated example, the speed detection unit 25 detects the value or rate of change of the rotational speed of the motor 3 via an encoder 26 attached to the rotation shaft of the motor 3. As an alternative, the encoder 26 may be omitted, and the speed detection unit 25 may detect the value or rate of change of the rotational speed of the motor 3 sensorlessly using a known calculation method. The value or rate of change of the rotational speed of the motor 3 detected by the speed detection unit 25 is sent to the converter control unit 13 and the inverter control unit 14.

[0026] <Losses Occurring During Converter Regenerative Operation> Figures 2A and 2B illustrate switching losses that occur during the regenerative operation of the converter. Figure 2A illustrates the emitter-collector voltage and current waveforms that occur when a switching element switches from off to on when the current flowing through the converter is small compared to a predetermined value, and Figure 2B illustrates the emitter-collector voltage and current waveforms that occur when a switching element switches from off to on when the current flowing through the converter is large compared to a predetermined value. Multiple switching elements are provided in the converter 11, but Figures 2A and 2B illustrate the voltage and current waveforms for one of these switching elements.

[0027] As illustrated in Figures 2A and 2B, when the switching element is off, a predetermined voltage is applied between the emitter and collector of the switching element, but no current flows. When the switching element switches from off to on, the voltage between the emitter and collector of the switching element gradually decreases and the current gradually increases. The larger the current flowing through the converter 11, the larger the current flowing between the emitter and collector of the switching element when it switches from off to on, and therefore the greater the switching loss. In other words, when the converter 11 performs regenerative operation when the current flowing through the converter 11 is large, the switching loss generated in the switching element becomes larger. Therefore, in the embodiment of this disclosure, when the current flowing through the converter 11 is large, the regeneration start voltage, which is a requirement for starting the regenerative operation of the converter 11, is set lower than usual, and regeneration is performed at a lower voltage than usual, thereby reducing the switching loss during the regenerative operation of the converter 11. Switching loss is expressed as "DC link voltage × regenerative current" during regeneration. By lowering the regeneration start voltage, regenerative operation is performed at a low DC link voltage, which reduces the current flowing between the emitter and collector of the switching element, thus reducing switching loss.

[0028] <Information related to motor drive commands> In the embodiments of this disclosure, "information related to motor drive commands" is used in the regenerative start voltage setting process. The information related to motor drive commands includes electrical information generated in response to motor drive commands, command information related to motor drive commands, and motor information generated in response to motor drive commands. Each piece of information is described in more detail below.

[0029] The electrical information generated in response to the motor drive command includes the input current flowing between the AC power supply 2 and the converter 11 in response to the motor drive command, the DC link current flowing through the DC link 17 in response to the motor drive command, the inverter current flowing between the inverter 12 and the motor 3 in response to the motor drive command, and the output voltage of the inverter 12 in response to the motor drive command. The value and rate of change of the input current are detected by the input current detection unit 21. The value and rate of change of the DC link current are detected by the DC link current detection unit 22. The value and rate of change of the inverter current are detected by the inverter current detection unit 24. The value and rate of change of the output voltage of the inverter 12 are acquired within the inverter control unit 14.

[0030] The command information related to the motor drive command includes a current command that controls the operation of the inverter 12, a voltage command that controls the operation of the inverter 12, a speed command for the motor 3, and a torque command for the motor 3. The speed command for the motor 3 includes an acceleration command and a deceleration command for the motor 3. The values ​​and rate of change of the command information are acquired within the inverter control unit 14.

[0031] The motor information generated in response to the motor drive command includes the rotational speed of motor 3 and the torque of motor 3 generated in response to the motor drive command. The value and rate of change of the rotational speed of motor 3 are detected as actual values ​​by the speed detection unit 25 via the encoder 26 or by sensorless calculation processing. The value and rate of change of the torque of motor 3 are detected as actual values ​​by the torque detection unit (not shown) or by calculation processing.

[0032] In the embodiments of this disclosure, the above-mentioned "information related to motor drive commands" is used in the process of setting the regenerative start voltage for the following reasons.

[0033] Generally, the larger the value or rate of change of the information related to the motor drive command, the larger the current flowing through the converter 11. When the converter 11 performs regenerative operation when the value or rate of change of the information related to the motor drive command is large (i.e., when the value or rate of change of the current flowing through the converter 11 is large), a large switching loss occurs. Therefore, in the embodiment of this disclosure, when the value or rate of change of the information related to the motor drive command is larger than normal (i.e., when the value or rate of change of the current flowing through the converter 11 is larger than normal), the regenerative start voltage, which is a requirement for starting the regenerative operation of the converter 11, is set lower than normal, and the DC link voltage during regenerative operation is lowered, thereby reducing the switching loss of the regenerative operation of the converter 11.

[0034] Whether the value or rate of change of information related to motor drive commands is larger than normal is determined by comparing the value or rate of change of the information related to motor drive commands with the corresponding threshold. If the value or rate of change of information related to motor drive commands exceeds the threshold, it can be said that the value or rate of change of information related to motor drive commands is larger than normal. If the value or rate of change of information related to motor drive commands does not exceed the threshold, it can be said that the value or rate of change of information related to motor drive commands is within the range observed under normal conditions.

[0035] The threshold can be set appropriately after determining in advance the relationship between the values ​​or rate of change of information related to the application environment and motor drive commands of the motor drive device 1 and the current flowing through the converter 11 that is generated in response to the motor drive command, for example, by operating the motor drive device 1 through trial operation or actual operation, or by performing computer simulations. The threshold may be stored in a rewritable memory device (not shown) and rewritable by an external device, and even after the threshold has been set, it can be changed to an appropriate value as needed.

[0036] The following is an example of how the value of electrical information related to the motor drive command is the value of the input current flowing between the AC power supply 2 and the converter 11 in response to the motor drive command. When the value of the input current detected by the input current detection unit 21 is larger than normal (i.e., when the value of the input current exceeds the threshold), a larger current than normal is flowing through the converter 11. When the converter 11 performs regenerative operation in such a situation, a large switching loss occurs. Therefore, in the embodiment of this disclosure, when the value of the input current exceeds the threshold, the regenerative start voltage, which is a requirement for starting the regenerative operation of the converter 11, is set lower than normal, and the DC link voltage when the converter 11 performs regenerative operation is lowered. The same explanation applies to values ​​of electrical information other than the value of the input current.

[0037] The following is an example of how the rate of change of electrical information, which is information related to the motor drive command, can be described, taking the case where it is the rate of change of the output voltage of the inverter 12 that occurs in response to the motor drive command. When the rate of change of the output voltage of the inverter 12 is larger than normal (i.e., when the rate of change of the output voltage of the inverter 12 exceeds a threshold), a larger current than normal flows through the converter 11. When the converter 11 performs regenerative operation in such a case, a large switching loss occurs. Therefore, in the embodiment of this disclosure, when the rate of change of the output voltage of the inverter 12 exceeds a threshold, the regeneration start voltage, which is the requirement for starting the regenerative operation of the converter 11, is set lower than normal, and the DC link voltage when the converter 11 performs regenerative operation is lowered. The same explanation applies to the rate of change of electrical information other than the rate of change of the output voltage of the inverter 12.

[0038] The following is an example of how the value of the command information, which is information related to the motor drive command, can be used to explain the case where the value of the speed command for motor 3 is the value of the speed command. When motor 3 is rotating, if a speed command to rapidly decelerate in the next stage is output to motor 3, motor 3 rapidly decelerates and a large amount of regenerative power is returned to the DC link 17, causing the DC link voltage to rise significantly. As a result, the DC link voltage is more likely to exceed the regeneration start voltage, increasing the likelihood that the converter 11 will perform regenerative operation. When the converter 11 performs regenerative operation in such a situation, a large switching loss occurs. Therefore, in the embodiment of this disclosure, when the value of the speed command (deceleration command) for motor 3 exceeds a threshold, the regeneration start voltage, which is the requirement for starting the regenerative operation of the converter 11, is set lower than usual, thereby lowering the DC link voltage when the converter 11 performs regenerative operation. The same explanation applies to the values ​​of other command information besides the speed command value.

[0039] The following explanation takes the case where the rate of change of the command information, which is information related to the motor drive command, is the rate of change of the current command that controls the operation of the inverter 12. When the motor 3 is accelerating, staying at a constant speed, or decelerating, if a current command is output to further rapidly decelerate the motor 3 in the next stage, the motor 3 decelerates rapidly and a large amount of regenerative power is returned to the DC link 17, causing the DC link voltage to rise sharply. As a result, the DC link voltage is more likely to exceed the regeneration start voltage, increasing the likelihood that the converter 11 will perform regenerative operation. When the converter 11 performs regenerative operation in such a situation, a large switching loss occurs. Therefore, in the embodiment of this disclosure, when the rate of change of the current command exceeds a threshold, the regeneration start voltage, which is the requirement for starting the regenerative operation of the converter 11, is set lower than usual, thereby lowering the DC link voltage when the converter 11 performs regenerative operation. The same explanation applies to the rate of change of other command information besides the rate of change of the current command.

[0040] The following explanation takes the case where the value of the motor information, which is information related to the motor drive command, is the value of the rotational speed of motor 3. When the value of the rotational speed of motor 3 is greater than normal (i.e., when the value of the rotational speed exceeds the threshold), when motor 3 decelerates in the next stage, a large amount of regenerative power is returned from motor 3 to the DC link 17, causing the DC link voltage to rise significantly. As a result, the DC link voltage is more likely to exceed the regeneration start voltage, increasing the likelihood that the converter 11 will perform regenerative operation. When the converter 11 performs regenerative operation in such a situation, a large switching loss occurs. Therefore, in the embodiment of this disclosure, when the value of the rotational speed of motor 3 exceeds the threshold, the regeneration start voltage, which is the requirement for starting the regenerative operation of the converter 11, is set lower than normal, and the DC link voltage when the converter 11 performs regenerative operation is lowered. The same explanation applies to other motor information values ​​other than the value of rotational speed (i.e., the torque of motor 3).

[0041] The following explanation takes the case where the rate of change of motor information, which is information related to the motor drive command, is the rate of change of motor 3's torque. When the rate of change of motor 3's torque is larger than normal (i.e., when the rate of change of torque exceeds a threshold), when motor 3 decelerates in the next stage, a large amount of regenerative power is returned from motor 3 to the DC link 17, causing the DC link voltage to rise significantly. As a result, the DC link voltage is more likely to exceed the regeneration start voltage, increasing the likelihood that the converter 11 will perform regenerative operation. When the converter 11 performs regenerative operation in such a situation, a large switching loss occurs. Therefore, in the embodiment of this disclosure, when the rate of change of motor 3's torque exceeds a threshold, the regeneration start voltage, which is the requirement for starting the regenerative operation of the converter 11, is set lower than normal, and the DC link voltage when the converter 11 performs regenerative operation is lowered. The same explanation applies to other motor information rates of change (i.e., the rate of change of the rotational speed of motor 3) other than the rate of change of torque.

[0042] <Converter control unit in a motor drive device according to an embodiment of the present disclosure> Figure 3 is a block diagram showing the converter control unit in a motor drive device according to an embodiment of the present disclosure.

[0043] The process of changing the regeneration start voltage according to the information related to the motor drive command by the converter control unit 13 may be executed in any state during the rectification operation and the regeneration operation of the converter 11, or may be executed only when the converter 11 is in the rectification operation.

[0044] The converter control unit 13 includes an acquisition unit 131, a storage unit 132, a comparison unit 133, a setting unit 134, and a regeneration command generation unit 135 in order to change the regeneration start voltage according to the information related to the motor drive command.

[0045] The acquisition unit 131 acquires, as the value or change rate of the information related to the motor drive command, the value or change rate of the electrical information generated according to the motor drive command, the value or change rate of the command information related to the motor drive command, and / or the value or change rate of the motor information generated according to the motor drive command. The acquisition unit 131 may acquire only one piece of information related to the motor drive command from the value or change rate of the electrical information, the value or change rate of the command information, or the value or change rate of the motor information, or may acquire a plurality of pieces of information from the value or change rate of the electrical information, the value or change rate of the command information, and / or the value or change rate of the motor information.

[0046] The storage unit 132 stores the threshold value used in the comparison process of the comparison unit 133. The threshold value stored in the storage unit 132 corresponds to the value or change rate of the information related to the motor drive command acquired by the acquisition unit 131. For example, when the acquisition unit 131 acquires the value of the DC link current, it is a threshold value related to the value of the DC link current, and when the acquisition unit 131 acquires the change rate of the rotation speed of the motor 3, it is a threshold value related to the change rate of the rotation speed of the motor 3. When there are a plurality of values or change rates of the information related to the motor drive command acquired by the acquisition unit 131, a plurality of threshold values corresponding to each of them are stored in the storage unit 132. The storage unit 132 may be a rewritable storage device. According to this, even after the threshold value is once stored in the storage unit 132, it can be changed to an appropriate value as needed.

[0047] The comparison unit 133 compares the value or change rate of the information related to the motor drive command acquired by the acquisition unit 131 with the threshold value stored in the storage unit 132. When there are a plurality of values or change rates of the information related to the motor drive command acquired by the acquisition unit 131, each of the values or change rates of the information related to the motor drive command is compared with the corresponding threshold value respectively.

[0048] The setting unit 134 sets the regeneration start voltage based on the comparison result by the comparison unit 133.

[0049] The regeneration command generation unit 135 generates a command for controlling the operation of the converter 11 based on the regeneration start voltage set by the setting unit 134 and the DC link voltage detected by the DC link voltage detection unit 23. When the DC link voltage exceeds the regeneration start voltage, the regeneration command generation unit 135 generates a regeneration command and transmits it to the converter 11. When the DC link voltage does not exceed the regeneration start voltage, the regeneration command generation unit 135 generates a rectification command and transmits it to the converter 11. When the converter 11 consists of a PWM switching control type rectifier, when receiving a regeneration command from the converter control unit 13, each switching element turns on and off to execute the regeneration operation. When receiving a rectification command without receiving a regeneration command from the converter control unit 13, each switching element turns on and off to execute the rectification operation. When the converter 11 consists of a 120-degree conduction type rectifier, when receiving a regeneration command from the converter control unit 13, each switching element turns on and off to execute the regeneration operation. When receiving a rectification command without receiving a regeneration command from the converter control unit 13, each switching element turns off to execute the rectification operation.

[0050] <Inverter control unit in the motor drive device according to the embodiment of the present disclosure> Fig. 4 is a block diagram showing the inverter control unit in the motor drive device according to the embodiment of the present disclosure.

[0051] The inverter control unit 14 includes a speed command generation unit 141, a current command generation unit 142, a voltage command generation unit 143, and a switching command generation unit 144 in order to generate a switching command which is a motor drive command for controlling the rotational angular velocity, position and / or torque of the rotor of the motor 3.

[0052] The speed command generation unit 141 generates a speed command based on the position command and the value of the motor 3's rotational speed detected by the speed detection unit 25 (speed feedback). The current command generation unit 142 generates a current command based on the speed command and the value of the inverter current detected by the inverter current detection unit 24 (current feedback). The voltage command generation unit 143 generates a voltage command based on the current command. The switching command generation unit 144 generates a switching command based on the voltage command and transmits it to the inverter 12. The inverter 12 selectively performs a powering operation, which converts the DC power of the DC link 17 into AC drive power and supplies it to the motor 3, and a regenerative operation, which converts the AC regenerative power from the motor 3 into DC power and returns it to the DC link 17, in response to the motor drive command (switching command) from the inverter control unit 14. Note that the configuration of the inverter control unit 14 defined here is merely an example, and the configuration of the inverter control unit 14 may be defined to include terms such as position command generation unit, torque command generation unit, current control unit, position control unit, and torque control unit. Alternatively, the configuration of the inverter control unit 14 may be defined by omitting any of the speed command generation unit 141, current command generation unit 142, voltage command generation unit 143, switching command generation unit 144, position command generation unit, torque command generation unit, current control unit, position control unit, and torque control unit. Alternatively, the configuration of the inverter control unit 14 may be defined by appropriately integrating multiple of the speed command generation unit 141, current command generation unit 142, voltage command generation unit 143, switching command generation unit 144, position command generation unit, torque command generation unit, current control unit, position control unit, and torque control unit.

[0053] <Setting process for regenerative start voltage according to the first embodiment> Figure 5 is a diagram showing the operation flow of the setting process for regenerative start voltage according to the first embodiment in the motor drive device according to the embodiment of the present disclosure.

[0054] In the first embodiment, the converter control unit 13 sets the regenerative start voltage to a first voltage, which is the normal voltage, if the value of the information related to the motor drive command does not exceed a threshold, and sets the regenerative start voltage to a voltage lower than the normal voltage (first voltage) (second voltage) if the value of the information related to the motor drive command exceeds a threshold.

[0055] Here, we will explain, as an example, the case where the value of the information related to the motor drive command is the value of the electrical information. The following explanation is also applicable when the value of the information related to the motor drive command is the value of the command information or the value of the motor information.

[0056] In step S101, the acquisition unit 131 in the converter control unit 13 acquires the value of electrical information. In step S102, the comparison unit 133 in the converter control unit 13 compares the value of electrical information with a threshold value. If it is determined in step S102 that the value of electrical information does not exceed the threshold value, in step S103, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to the normal voltage (first voltage). If it is determined in step S102 that the value of electrical information exceeds the threshold value, in step S104, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to a voltage lower than the normal voltage (second voltage). The processes in steps S101 to S104 are repeatedly executed at predetermined intervals. The regeneration command generation unit 135 generates a command to control the operation of the converter 11 based on the regeneration start voltage set by the setting unit 134 and the DC link voltage detected by the DC link voltage detection unit 23.

[0057] For example, when the electrical information value is the DC link current value, if the DC link current value does not exceed the threshold, the regenerative start voltage is set to the normal voltage. If the DC link current value exceeds the threshold, the regenerative start voltage is set to a voltage lower than the normal voltage.

[0058] In the example described above, the converter control unit 13 set the regenerative start voltage based on the value of information related to one motor drive command. However, as a modification, the converter control unit 13 may set the regenerative start voltage based on the values ​​of information related to multiple motor drive commands.

[0059] <Setting process for regenerative start voltage according to the second embodiment> Figure 6 is a diagram showing the operation flow of the setting process for regenerative start voltage according to the second embodiment in the motor drive device according to the embodiment of the present disclosure.

[0060] In the second embodiment, the converter control unit 13 sets the regenerative start voltage to the first voltage, which is the normal voltage, if the value of the information related to the motor drive command does not exceed a threshold, and changes the regenerative start voltage to a value that decreases as the value of the information related to the motor drive command increases, within a range that does not exceed the first voltage, which is the normal voltage.

[0061] Here, as an example, we will explain the case where the value of the information related to the motor drive command is the value of the command information. The following explanation is also applicable when the value of the information related to the motor drive command is the value of the electrical information or the value of the motor information.

[0062] In step S201, the acquisition unit 131 in the converter control unit 13 acquires the value of the command information. In step S202, the comparison unit 133 in the converter control unit 13 compares the value of the command information with a threshold value. If it is determined in step S202 that the value of the command information does not exceed the threshold value, in step S203, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to the normal voltage (first voltage). If it is determined in step S202 that the value of the command information exceeds the threshold value, in step S204, the setting unit 134 in the converter control unit 13 calculates the voltage for the loss reduction mode. The voltage for the loss reduction mode is a value that does not exceed the normal voltage (first voltage), and is a value that decreases as the value of the command information increases. For example, in the trial run of the motor drive unit 1, a table or calculation formula showing the relationship that the voltage for the loss reduction mode decreases as the value of the command information increases is acquired in advance. In step S204, the setting unit 134 within the converter control unit 13 calculates the loss reduction mode voltage corresponding to the command information value by referring to a table or using a calculation formula.

[0063] In step S205, following step S204, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to the voltage for loss reduction mode.

[0064] The processes in steps S201 to S205 are repeatedly executed at predetermined intervals. The regenerative command generation unit 135 generates commands to control the operation of the converter 11 based on the regenerative start voltage set in the setting unit 134 and the DC link voltage detected by the DC link voltage detection unit 23.

[0065] For example, when the value of the command information is the value of the voltage command, if the value of the voltage command does not exceed the threshold, the regeneration start voltage is set to the normal voltage, and if the value of the voltage command exceeds the threshold, the regeneration start voltage is set to the voltage for loss reduction mode.

[0066] In the example described above, the converter control unit 13 set the regenerative start voltage based on the value of information related to one motor drive command. However, as a modification, the converter control unit 13 may set the regenerative start voltage based on the values ​​of information related to multiple motor drive commands.

[0067] <Setting process for regenerative start voltage according to the third embodiment> Figure 7 is a diagram showing the operation flow of the setting process for regenerative start voltage according to the third embodiment in the motor drive device according to the embodiment of the present disclosure.

[0068] In the third form, N thresholds (where N is an integer greater than or equal to 2) are set as multiple thresholds of different sizes. The k-th threshold from the smallest of the N thresholds is called the k-th threshold (where 1 ≤ k ≤ N). Therefore, the values ​​increase in the order of the first threshold, ..., to the Nth threshold.

[0069] Furthermore, multiple threshold ranges are set, defined by a certain threshold among multiple thresholds and the next largest threshold among the multiple thresholds. For example, a first threshold range defined by a first threshold and a second threshold, a second threshold range defined by a second threshold and a third threshold, ..., and an N-1 threshold range defined by the N-1th threshold and the Nth threshold are set.

[0070] Furthermore, multiple voltage values ​​(loss reduction mode voltages) with magnitudes corresponding to multiple threshold ranges are set. For example, a first loss reduction mode voltage corresponding to a first threshold range, a second loss reduction mode voltage corresponding to a second threshold range, ..., and an N-1th loss reduction mode voltage corresponding to the N-1th threshold range are set. The voltage values ​​increase in the order of the first loss reduction mode voltage, the second loss reduction mode voltage, ..., and the N-1th loss reduction mode voltage. The loss reduction mode voltages are set within a range that does not exceed the normal voltage. As the center value of each threshold range increases, the set loss reduction mode voltages also increase.

[0071] The converter control unit 13 sets the regeneration start voltage to the first voltage, which is the normal voltage, if the value of the information related to the motor drive command does not exceed the minimum threshold (first threshold) among a plurality of thresholds. If the value of the information related to the motor drive command exceeds the minimum threshold (first threshold), it sets the regeneration start voltage to a voltage value corresponding to the threshold range in which the information related to the motor drive command falls.

[0072] Here, as an example, we will explain the case where the value of the information related to the motor drive command is the value of the motor information. The following explanation is also applicable when the value of the information related to the motor drive command is the value of the electrical information or the value of the command information.

[0073] In step S301, the acquisition unit 131 in the converter control unit 13 acquires the motor information value. In step S302, the comparison unit 133 in the converter control unit 13 compares the motor information value with the minimum threshold (first threshold).

[0074] If it is determined in step S302 that the value of the command information does not exceed the threshold, then in step S303, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to the normal voltage (first voltage).

[0075] If it is determined in step S302 that the value of the command information exceeds the minimum threshold, then in step S304, the setting unit 134 in the converter control unit 13 determines which threshold range the value of the motor information falls within. In step S305, following step S304, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to a loss reduction mode voltage corresponding to the threshold range in which the value of the motor information falls.

[0076] The processes in steps S301 to S305 are repeatedly executed at predetermined intervals. The regenerative command generation unit 135 generates commands to control the operation of the converter 11 based on the regenerative start voltage set in the setting unit 134 and the DC link voltage detected by the DC link voltage detection unit 23.

[0077] For example, when the motor information value is the rotational speed of motor 3, if the rotational speed value does not exceed the minimum threshold (first threshold), the regeneration start voltage is set to the normal voltage. If the rotational speed value exceeds the minimum threshold (first threshold), it is determined which threshold range the rotational speed value falls into. For example, if the rotational speed value falls into the first threshold range defined by the first threshold and the second threshold, the regeneration start voltage is set to the first loss reduction mode voltage corresponding to the first threshold range. For example, if the rotational speed value falls into the (n-1)th threshold range defined by the (n-1)th threshold and the (n)th threshold, the regeneration start voltage is set to the (n-1)th loss reduction mode voltage corresponding to the (n-1)th threshold range.

[0078] In the example described above, the converter control unit 13 set the regenerative start voltage based on the value of information related to one motor drive command. However, as a modification, the converter control unit 13 may set the regenerative start voltage based on the values ​​of information related to multiple motor drive commands.

[0079] <Setting process for regenerative start voltage according to the fourth embodiment> Figure 8 is a diagram showing the operation flow of the setting process for regenerative start voltage according to the fourth embodiment in the motor drive device according to the embodiment of the present disclosure.

[0080] The fourth embodiment is a modification of the first embodiment. In the first embodiment, the converter control unit 13 set the regenerative start voltage based on the comparison result between the value of the information related to the motor drive command and a threshold value. In the fourth embodiment, the converter control unit 13 sets the regenerative start voltage based on the comparison result between the rate of change of the information related to the motor drive command and a threshold value.

[0081] Here, as an example, we will explain the case where the rate of change of information related to motor drive commands is the rate of change of electrical information. The following explanation is also applicable when the rate of change of information related to motor drive commands is the rate of change of command information or the rate of change of motor information.

[0082] In step S401, the acquisition unit 131 in the converter control unit 13 acquires the rate of change of electrical information. In step S402, the comparison unit 133 in the converter control unit 13 compares the rate of change of electrical information with a threshold. If it is determined in step S402 that the rate of change of electrical information does not exceed the threshold, in step S403, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to the normal voltage (first voltage). If it is determined in step S402 that the rate of change of electrical information exceeds the threshold, in step S404, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to a voltage lower than the normal voltage (second voltage). The processes in steps S401 to S404 are repeatedly executed at predetermined intervals. The regeneration command generation unit 135 generates a command to control the operation of the converter 11 based on the regeneration start voltage set by the setting unit 134 and the DC link voltage detected by the DC link voltage detection unit 23.

[0083] For example, when the electrical information value is the rate of change of the inverter current, if the value of the inverter current does not exceed a threshold, the regenerative start voltage is set to the normal voltage. If the rate of change of the inverter current exceeds the threshold, the regenerative start voltage is set to a voltage lower than the normal voltage.

[0084] In the example described above, the converter control unit 13 set the regenerative start voltage based on the rate of change of information related to one motor drive command. However, as a modified example, the converter control unit 13 may set the regenerative start voltage based on the rate of change of information related to multiple motor drive commands.

[0085] <Setting process for regenerative start voltage according to the fifth embodiment> Figure 9 is a diagram showing the operation flow of the setting process for regenerative start voltage according to the fifth embodiment in the motor drive device according to the embodiment of the present disclosure.

[0086] The fifth embodiment is a modification of the second embodiment. In the second embodiment, the converter control unit 13 set the regenerative start voltage based on the comparison result between the value of the information related to the motor drive command and a threshold value, but in the fifth embodiment, the regenerative start voltage is set based on the comparison result between the rate of change of the information related to the motor drive command and a threshold value.

[0087] Here, as an example, we will explain the case where the rate of change of information related to motor drive commands is the rate of change of command information. The following explanation is also applicable when the rate of change of information related to motor drive commands is the rate of change of electrical information or the rate of change of motor information.

[0088] In step S501, the acquisition unit 131 in the converter control unit 13 acquires the rate of change of command information. In step S502, the comparison unit 133 in the converter control unit 13 compares the rate of change of command information with a threshold value. If it is determined in step S502 that the rate of change of command information does not exceed the threshold value, in step S503, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to the normal voltage (first voltage). If it is determined in step S502 that the rate of change of command information exceeds the threshold value, in step S504, the setting unit 134 in the converter control unit 13 calculates the voltage for the loss reduction mode. The voltage for the loss reduction mode is a value that does not exceed the normal voltage (first voltage), and is a value that decreases as the rate of change of command information increases. For example, in the trial run of the motor drive unit 1, a table or calculation formula showing the relationship in which the voltage for the loss reduction mode decreases as the rate of change of command information increases is acquired in advance. In step S504, the setting unit 134 within the converter control unit 13 calculates the voltage for the loss reduction mode corresponding to the rate of change of the command information by referring to a table or using a calculation formula.

[0089] In step S505, following step S504, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to the voltage for loss reduction mode.

[0090] The processes in steps S501 to S505 are repeatedly executed at predetermined intervals. The regenerative command generation unit 135 generates commands to control the operation of the converter 11 based on the regenerative start voltage set in the setting unit 134 and the DC link voltage detected by the DC link voltage detection unit 23.

[0091] For example, when the rate of change of the command information is the rate of change of the torque command, if the rate of change of the torque command does not exceed a threshold, the regeneration start voltage is set to the normal voltage. If the rate of change of the torque command exceeds the threshold, the regeneration start voltage is set to the voltage for loss reduction mode.

[0092] In the example described above, the converter control unit 13 set the regenerative start voltage based on the rate of change of information related to one motor drive command. However, as a modified example, the converter control unit 13 may set the regenerative start voltage based on the rate of change of information related to multiple motor drive commands.

[0093] <Setting process for regenerative start voltage according to the sixth embodiment> Figure 10 is a diagram showing the operation flow of the setting process for regenerative start voltage according to the sixth embodiment in the motor drive device according to the embodiment of the present disclosure.

[0094] The sixth embodiment is a modification of the third embodiment. In the third embodiment, the converter control unit 13 set the regenerative start voltage based on the comparison result between the value of the information related to the motor drive command and a threshold value, but in the sixth embodiment, the converter control unit 13 sets the regenerative start voltage based on the comparison result between the rate of change of the information related to the motor drive command and a threshold value.

[0095] The converter control unit 13 sets the regenerative start voltage to the first voltage, which is the normal voltage, if the rate of change of the information related to the motor drive command does not exceed the minimum threshold (first threshold) among a plurality of thresholds. If the rate of change of the information related to the motor drive command exceeds the minimum threshold (first threshold), it sets the regenerative start voltage to a voltage value corresponding to the threshold range in which the rate of change of the information related to the motor drive command falls.

[0096] Here, as an example, we will explain the case where the rate of change of information related to motor drive commands is the rate of change of motor information. The following explanation is also applicable when the rate of change of information related to motor drive commands is the rate of change of electrical information or the rate of change of command information.

[0097] In step S601, the acquisition unit 131 in the converter control unit 13 acquires the rate of change of motor information. In step S602, the comparison unit 133 in the converter control unit 13 compares the rate of change of motor information with the minimum threshold (first threshold).

[0098] If it is determined in step S602 that the rate of change of the command information does not exceed the threshold, then in step S603, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to the normal voltage (first voltage).

[0099] If it is determined in step S602 that the rate of change of the command information exceeds the minimum threshold, then in step S604, the setting unit 134 in the converter control unit 13 determines which threshold range the rate of change of the motor information falls within. In step S605, following step S604, the setting unit 134 in the converter control unit 13 sets the regeneration start voltage to a loss reduction mode voltage corresponding to the threshold range within which the rate of change of the motor information falls.

[0100] The processes in steps S601 to S605 are repeatedly executed at predetermined intervals. The regenerative command generation unit 135 generates commands to control the operation of the converter 11 based on the regenerative start voltage set in the setting unit 134 and the DC link voltage detected by the DC link voltage detection unit 23.

[0101] For example, when the rate of change of motor information is the rate of change of the rotational speed of motor 3, if the rate of change of rotational speed does not exceed the minimum threshold (first threshold), the regeneration start voltage is set to the normal voltage. If the rate of change of rotational speed exceeds the minimum threshold (first threshold), it is determined which threshold range the rate of change of rotational speed falls into. For example, if the rate of change of rotational speed falls into the first threshold range defined by the first threshold and the second threshold, the regeneration start voltage is set to the first loss reduction mode voltage corresponding to the first threshold range. For example, if the rate of change of rotational speed falls into the (n-1)th threshold range defined by the (n-1)th threshold and the Nth threshold, the regeneration start voltage is set to the (n-1)th loss reduction mode voltage corresponding to the (n-1)th threshold range.

[0102] In the example described above, the converter control unit 13 set the regenerative start voltage based on the rate of change of information related to one motor drive command. However, as a modified example, the converter control unit 13 may set the regenerative start voltage based on the rate of change of information related to multiple motor drive commands.

[0103] <Processor and Memory> The motor drive device 1 is provided with at least one processor, which is an arithmetic processing unit. Examples of arithmetic processing units include ICs, LSIs, CPUs, MPUs, and DSPs. The arithmetic processing unit has a converter control unit 13, an inverter control unit 14, an input current detection unit 21, a DC link current detection unit 22, a DC link voltage detection unit 23, an inverter current detection unit 24, a speed detection unit 25, and other processing units. Each of these parts of the arithmetic processing unit is a functional module realized by a program executed on the processor, for example. For example, if the converter control unit 13, inverter control unit 14, input current detection unit 21, DC link current detection unit 22, DC link voltage detection unit 23, inverter current detection unit 24, speed detection unit 25, and other processing units are constructed in program format, the functions of each part can be realized by operating the arithmetic processing unit according to this program. The programs for executing each process in the converter control unit 13, inverter control unit 14, input current detection unit 21, DC link current detection unit 22, DC link voltage detection unit 23, inverter current detection unit 24, speed detection unit 25, and other processing units may be provided in the form of a program product stored (recorded) on a computer-readable storage medium (recording medium), such as a semiconductor memory, magnetic storage medium (magnetic recording medium), or optical storage medium (optical recording medium). Alternatively, the converter control unit 13, inverter control unit 14, input current detection unit 21, DC link current detection unit 22, DC link voltage detection unit 23, inverter current detection unit 24, speed detection unit 25, and other processing units may be implemented as semiconductor integrated circuits on which programs that realize the functions of each unit are written.

[0104] Furthermore, the motor drive unit 1 is provided with at least one memory, which is a storage device (recording device). The memory includes the converter control unit 13, the inverter control unit 14, the input current detection unit 21, the DC link current detection unit 22, the DC link voltage detection unit 23, the inverter current detection unit 24, the speed detection unit 25, and various other storage units (recording units) within the processing unit. The memory may be an electrically erasable and recordable non-volatile memory such as EEPROM (registered trademark), or a high-speed read / write random access memory such as DRAM or SRAM. The storage device may also have a configuration such as an HDD (hard disk drive) or an SSD (solid state drive). The memory stores a program for operating the converter control unit 13, the inverter control unit 14, the input current detection unit 21, the DC link current detection unit 22, the DC link voltage detection unit 23, the inverter current detection unit 24, the speed detection unit 25, and the other processing units. Furthermore, the memory stores the value or rate of change of the input current detected by the input current detection unit 21, the value or rate of change of the DC link current detected by the DC link current detection unit 22, the value or rate of change of the DC link voltage detected by the DC link voltage detection unit 23, the value or rate of change of the inverter current detected by the inverter current detection unit 24, the value or rate of change of the output voltage of the inverter 12 acquired in the inverter control unit 14, the value or rate of change of the rotational speed of the motor 3 detected by the speed detection unit 25, and the value or rate of change of the torque detected by the torque detection unit. The memory also stores threshold values. The memory also stores threshold ranges. The memory also stores values ​​or rates of change of information related to motor drive commands acquired by the acquisition unit 131. The memory also stores comparison results from the comparison unit 133. The memory also stores the loss reduction mode voltage calculated or set by the setting unit 134. The memory also stores tables and formulas showing the relationship that the loss reduction mode voltage decreases as the value or rate of change of information related to motor drive commands increases. The memory stores commands generated by the regenerative command generation unit 135. The memory also stores speed commands generated by the speed command generation unit 141.The memory stores current commands generated by the current command generation unit 142. The memory stores voltage commands generated by the voltage command generation unit 143. The memory stores switching commands generated by the switching command generation unit 144. The memory stores various programs and data related to the converter control unit 13. The memory stores various programs and data related to the converter 11. The memory stores various programs and data related to the inverter control unit 14. The memory stores various programs and data related to the inverter 12. The memory stores various programs and data related to the motor drive unit 1.

[0105] <Advantages of Embodiments and Modifications of the Disclosure> According to embodiments and modifications of the disclosure, a motor drive device can be realized that can reduce switching losses during regenerative operation.

[0106] In converters with a power regeneration function, switching losses occur during regenerative operation. The larger the current flowing through the converter during regenerative operation, the greater the switching losses. However, if switching elements are selected considering, for example, the maximum loss generated by the switching elements, the switching elements become larger and the cost increases. According to the embodiments of this disclosure and their modifications, when the current flowing through the converter is large, the regeneration start voltage, which is a requirement for starting the converter's regenerative operation, is set lower than usual, thereby lowering the DC link voltage when the converter performs regenerative operation. This reduces the switching losses generated by the switching elements. Therefore, according to the embodiments of this disclosure and their modifications, the switching elements can be made larger and the cost increases can be avoided.

[0107] Although the present disclosure has been described in detail above, it is not limited to the individual embodiments and modifications described above. These embodiments and modifications can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the gist of the present disclosure or from the spirit of the present disclosure derived from the claims and their equivalents. Furthermore, these embodiments and modifications can be implemented in combination. For example, the order of operations and processes in the embodiments and modifications described above are shown as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments and modifications described above.

[0108] <Note> The following additional information is disclosed regarding the above embodiments and modifications.

[0109] (Note 1) A motor drive device comprising: a converter that selectively performs a rectification operation that converts AC power input from an AC power source into DC power and outputs it to a DC link, and a regenerative operation that converts the DC power of the DC link into AC power and returns it to the AC power source when the DC link voltage exceeds the regenerative start voltage; an inverter that selectively performs a power operation that converts the DC power of the DC link into AC drive power and supplies it to a motor, and a regenerative operation that converts the AC regenerative power from the motor into DC power and returns it to the DC link, in accordance with a motor drive command; and a converter control unit that controls the operation of the converter, wherein the converter control unit changes the regenerative start voltage in accordance with information related to the motor drive command. (Note 2) The motor drive device according to Note 1, wherein the converter control unit sets the regenerative start voltage to a first voltage if the value of the information related to the motor drive command does not exceed a threshold, and sets the regenerative start voltage to a second voltage lower than the first voltage if the information related to the motor drive command exceeds a threshold. (Note 3) The motor drive device as described in Note 1, wherein the converter control unit sets the regenerative start voltage to a first voltage if the value of the information related to the motor drive command does not exceed a threshold, and if the value of the information related to the motor drive command exceeds a threshold, it changes the regenerative start voltage to a lower value as the value of the information related to the motor drive command increases, within a range that does not exceed the first voltage. (Note 4) The motor drive device as described in Note 1, wherein multiple thresholds of different magnitudes are set, multiple threshold ranges are set which are defined by one threshold among the multiple thresholds and the next largest threshold among the multiple thresholds, and multiple voltage values ​​having magnitudes corresponding to the multiple threshold ranges are set, wherein the converter control unit sets the regenerative start voltage to a first voltage if the value of the information related to the motor drive command does not exceed the smallest threshold among the multiple thresholds, and if the value of the information related to the motor drive command exceeds the smallest threshold, it sets the regenerative start voltage to a voltage value corresponding to the threshold range in which the value of the information related to the motor drive command falls. (Note 5) The motor drive device as described in Note 1, wherein the converter control unit sets the regenerative start voltage to a first voltage if the rate of change of information related to the motor drive command does not exceed a threshold, and sets the regenerative start voltage to a second voltage lower than the first voltage if the information related to the motor drive command exceeds a threshold.(Note 6) The motor drive device as described in Note 1, wherein the converter control unit sets the regenerative start voltage to a first voltage if the rate of change of the information related to the motor drive command does not exceed a threshold, and if the rate of change of the information related to the motor drive command exceeds a threshold, it changes the regenerative start voltage to a lower value as the rate of change of the information related to the motor drive command increases, within a range that does not exceed the first voltage. (Note 7) The motor drive device as described in Note 1, wherein a plurality of thresholds of different magnitudes are set, a plurality of threshold ranges are set which are defined by a certain threshold among the plurality of thresholds and the next largest threshold among the plurality of thresholds, a plurality of voltage values ​​having magnitudes corresponding to the plurality of threshold ranges are set, and the converter control unit sets the regenerative start voltage to a first voltage if the rate of change of the information related to the motor drive command does not exceed the smallest threshold among the plurality of thresholds, and if the rate of change of the information related to the motor drive command exceeds the smallest threshold, it sets the regenerative start voltage to a voltage value corresponding to the threshold range in which the rate of change of the information related to the motor drive command is contained. (Note 8) The motor drive device described in any one of Notes 1 to 7, wherein the information related to the motor drive command is at least one of the following: input current flowing between the AC power supply and the converter generated in response to the motor drive command, DC link current flowing through the DC link generated in response to the motor drive command, inverter current flowing between the inverter and the motor generated in response to the motor drive command, output voltage of the inverter generated in response to the motor drive command, rotational speed of the motor generated in response to the motor drive command, torque of the motor generated in response to the motor drive command, current command controlling the operation of the inverter, voltage command controlling the operation of the inverter, speed command for the motor, and torque command for the motor.

[0110] 1 Motor drive unit 2 AC power supply 3 Motor 11 Converter 12 Inverter 13 Converter control unit 14 Inverter control unit 15 Capacitors 16R, 16S, 16T AC reactor 17 DC link 21 Input current detection unit 22 DC link current detection unit 23 DC link voltage detection unit 24 Inverter current detection unit 25 Speed ​​detection unit 26 Encoder 131 Acquisition unit 132 Storage unit 133 Comparison unit 134 Setting unit 135 Regenerative command generation unit 141 Speed ​​command generation unit 142 Current command generation unit 143 Voltage command generation unit 144 Switching command generation unit

Claims

1. A motor drive device comprising: a converter that selectively performs a rectification operation to convert AC power input from an AC power source into DC power and output it to a DC link, and a regenerative operation to convert the DC power of the DC link into AC power and return it to the AC power source when the DC link voltage exceeds the regenerative start voltage; an inverter that selectively performs a power operation to convert the DC power of the DC link into AC drive power and supply it to a motor, and a regenerative operation to convert the AC regenerative power from the motor into DC power and return it to the DC link, in accordance with a motor drive command; and a converter control unit that controls the operation of the converter, wherein the converter control unit changes the regenerative start voltage in accordance with information related to the motor drive command.

2. The motor drive device according to claim 1, wherein the converter control unit sets the regenerative start voltage to a first voltage if the value of the information related to the motor drive command does not exceed a threshold, and sets the regenerative start voltage to a second voltage lower than the first voltage if the value of the information related to the motor drive command exceeds the threshold.

3. The motor drive device according to claim 1, wherein the converter control unit sets the regenerative start voltage to a first voltage if the value of the information related to the motor drive command does not exceed a threshold, and changes the regenerative start voltage to a lower value as the value of the information related to the motor drive command increases, within a range that does not exceed the first voltage.

4. A motor drive device according to claim 1, wherein a plurality of thresholds of different magnitudes are set, a plurality of threshold ranges are set defined by a certain threshold among the plurality of thresholds and the next largest threshold among the plurality of thresholds, a plurality of voltage values ​​having magnitudes corresponding to the plurality of threshold ranges are set, and the converter control unit sets the regeneration start voltage to a first voltage if the value of the information related to the motor drive command does not exceed the smallest threshold among the plurality of thresholds, and sets the regeneration start voltage to a voltage value corresponding to the threshold range in which the value of the information related to the motor drive command falls if the value of the information related to the motor drive command exceeds the smallest threshold.

5. The motor drive device according to claim 1, wherein the converter control unit sets the regenerative start voltage to a first voltage if the rate of change of the information related to the motor drive command does not exceed a threshold, and sets the regenerative start voltage to a second voltage lower than the first voltage if the rate of change of the information related to the motor drive command exceeds the threshold.

6. The motor drive device according to claim 1, wherein the converter control unit sets the regenerative start voltage to a first voltage if the rate of change of the information related to the motor drive command does not exceed a threshold, and changes the regenerative start voltage to a lower value as the rate of change of the information related to the motor drive command increases, within a range that does not exceed the first voltage.

7. A motor drive device according to claim 1, wherein a plurality of thresholds of different magnitudes are set, a plurality of threshold ranges are set which are defined by a certain threshold among the plurality of thresholds and the next largest threshold among the plurality of thresholds, a plurality of voltage values ​​having magnitudes corresponding to the plurality of threshold ranges are set, and the converter control unit sets the regeneration start voltage to a first voltage if the rate of change of the information related to the motor drive command does not exceed the smallest threshold among the plurality of thresholds, and sets the regeneration start voltage to a voltage value corresponding to the threshold range in which the rate of change of the information related to the motor drive command is contained if the rate of change of the information related to the motor drive command exceeds the smallest threshold.

8. The motor drive device according to any one of claims 1 to 7, wherein the information related to the motor drive command is at least one of the following: an input current flowing between the AC power supply and the converter generated in response to the motor drive command; a DC link current flowing through the DC link generated in response to the motor drive command; an inverter current flowing between the inverter and the motor generated in response to the motor drive command; an output voltage of the inverter generated in response to the motor drive command; the rotational speed of the motor generated in response to the motor drive command; the torque of the motor generated in response to the motor drive command; a current command controlling the operation of the inverter; a voltage command controlling the operation of the inverter; a speed command for the motor; and a torque command for the motor.

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