Motor drive device for determining state of resistor discharge during regeneration

Abstract

This motor drive device includes: a converter; an inverter; a capacitor which is provided to a DC link part; a discharge circuit which has a discharge resistor and a discharge switch; an energy calculation unit which, when the discharge switch is commanded to close during regenerative operation of the inverter, estimates first energy that returns to the DC link part from a motor via the inverter during a prescribed time period, second energy that is consumed by the discharge resistor during the prescribed time period, and third energy representing the amount in increase / decrease of stored energy in the capacitor during the prescribed time period; and an abnormality determination unit which determines that the discharge circuit is normal when the difference between the first energy and the sum of the second energy and the third energy is within a prescribed range, and determines that the discharge circuit is abnormal when said difference is not within the prescribed range.

Description

Motor drive system for determining the state of resistance discharge during regeneration

[0001] This disclosure relates to a motor drive device for determining the state of resistive discharge during regeneration.

[0002] In motor drive systems that drive motors installed in machine tools and robots, AC power supplied from an AC power source is converted to DC power by a converter (rectifier) ​​and output to the DC link section. Further, an inverter converts the DC power in the DC link section back to AC power for motor drive and supplies it to the motor. When the motor decelerates, regenerative power returns to the DC link section via the inverter, causing the voltage in the DC link section to rise. When the voltage in the DC link section rises, damage to components within the motor drive system may occur. For this reason, a discharge circuit is provided in the DC link section to suppress the rise in voltage in the DC link section by consuming energy through the discharge circuit.

[0003] Japanese Patent Publication No. 2013-143830, Japanese Patent Publication No. Hei 02-188173, Japanese Patent Publication No. 2021-018566

[0004] If there is a malfunction in the discharge circuit provided in the DC link section, the voltage rise in the DC link section during the regenerative operation of the motor drive unit cannot be suppressed, which may cause damage to components within the motor drive unit. Therefore, there is a need for a space-saving and low-cost motor drive unit that can detect malfunctions in the discharge circuit that suppresses the voltage rise in the DC link section during regenerative operation.

[0005] According to one aspect of the present disclosure, a motor drive device includes a converter that converts AC power supplied from an AC power source into DC power and outputs the DC power to a DC link section, an inverter that performs a power running operation of converting the DC power in the DC link section into AC power for driving a motor and supplying the AC power to the motor, and a regeneration operation of converting AC power regenerated by the motor into DC power and returning the DC power to the DC link section, a capacitor provided in the DC link section, a discharge resistor, and a discharge circuit having a discharge switch that conducts the discharge resistor and the DC link section by closing and disconnects the discharge resistor and the DC link section by opening. An energy calculation unit that estimates a first energy returned from the motor to the DC link section via the inverter during a predetermined time, a second energy consumed by the discharge resistor during the predetermined time, and a third energy that is an increase or decrease in the stored energy of the capacitor during the predetermined time when the discharge switch is commanded to close during the regeneration operation of the inverter; and an abnormality determination unit that determines that the discharge circuit is normal when the difference between the sum of the second energy and the third energy and the first energy is within a predetermined range, and determines that the discharge circuit is abnormal when the difference is not within the predetermined range.

[0006] It is a circuit diagram showing a motor drive device according to an embodiment of the present disclosure. It is a flowchart showing an operation flow of the motor drive device according to an embodiment of the present disclosure. In an embodiment of the present disclosure, it is a diagram illustrating a voltage waveform of the DC link section when the voltages of the DC link section detected twice are the same. In an embodiment of the present disclosure, it is a diagram illustrating a voltage waveform of the DC link section when the voltage of the DC link section detected the second time is larger than the voltage of the DC link section detected the first time. In an embodiment of the present disclosure, it is a diagram illustrating a voltage waveform of the DC link section when the voltage of the DC link section detected the second time is smaller than the voltage of the DC link section detected the first time. It is a circuit diagram showing a motor drive device according to a modified example of an embodiment of the present disclosure.

[0007] The following describes an embodiment of a motor drive device for determining the state of resistance discharge during 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 may vary depending on the intent or convention of the user or operator. 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 section" refers to the circuit section that electrically connects the DC output side of the converter and the DC input side of the inverter. "DC link section" is also called a "DC link," "DC link," "DC link section," "DC bus," or "DC intermediate circuit." "Voltage of the DC link section" refers to the potential difference between the positive potential on the positive power line of the DC link section and the negative potential on the negative power line. "On operation" of a switching element means that the switching element closes and forms an electrical circuit through the switching element. "Off operation" of a switching element means that the switching element opens and the electrical circuit through that switching element is interrupted. "Closing" of a discharge switch means that the discharge switch closes and an electrical circuit through that discharge switch is formed. "Opening" of a discharge switch means that the discharge switch opens and the electrical circuit through that discharge switch is interrupted. "Angular velocity" of a motor means the "angular velocity of the rotor or rotating shaft" of the motor. The numerical examples given below are just examples, and other values ​​may be used. Also, the units of each parameter may be omitted.

[0009] <Configuration of the motor drive device according to the embodiment of the present disclosure> Figure 1 is a circuit diagram showing a motor drive device according to the embodiment of the present disclosure.

[0010] In the embodiments of the present disclosure described below, as an example, the case where the motor 3 is driven by the motor drive device 1 connected to the AC power supply 2 is shown. Examples of the 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, a single-phase AC 100V power supply, and the like. Here, as an example, the AC power supply 2 is three-phase. The machines in which the motor 3 is provided include, for example, machine tools and robots.

[0011] As shown in FIG. 1, the motor drive device 1 according to the embodiment of the present disclosure includes a converter 11, an inverter 12, a capacitor 13, a discharge circuit 30, an energy calculation unit 16, an abnormality determination unit 17, a motor control unit 18, and a resistance discharge control unit 19. The motor drive device 1 also includes a position detection unit 21 and a voltage detection unit 22. Note that the power supplies for driving each unit such as the energy calculation unit 16, the abnormality determination unit 17, the motor control unit 18, the resistance discharge control unit 19, the position detection unit 21, and the voltage detection unit 22 are not shown.

[0012] The converter 11 converts the AC power supplied from the AC power source 2 into DC power and outputs this DC power to the DC link section 40. When three-phase AC power is supplied from the AC power source 2, the converter 11 is configured as a three-phase bridge circuit, and when single-phase AC power is supplied from the AC power source 2, it is configured as a single-phase bridge circuit. 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. Examples of converters 11 include diode rectifiers, PWM switching control type rectifiers, and 120-degree energization type rectifiers. For example, a converter 11 made of a diode rectifier has a diode bridge circuit configuration. Also, for example, a converter 11 made of a PWM switching control type rectifier has a bridge circuit configuration of switching elements and diodes connected in antiparallel thereto. Also, for example, a converter 11 made of a 120-degree energization type rectifier has a bridge circuit of switching elements connected in antiparallel to each other. If the converter 11 is a PWM switching control type rectifier or a 120-degree energizing type rectifier, each switching element is controlled on / off in accordance with a drive command received from a higher-level control device (not shown) to perform AC-DC power conversion. Examples of switching elements include semiconductor elements such as FETs, IGBTs, thyristors, GTOs, and transistors, but other semiconductor elements may also be used. Diodes and switching elements provided within the converter 11 are not shown in the illustration.

[0013] Although not shown in the diagram, the AC input side of the converter 11 may also be equipped with a circuit breaker, an electromagnetic contactor, and a reactor.

[0014] A capacitor 13 is connected to the DC link section 40 between the converter 11 and the inverter 12. The capacitor 13 is sometimes referred to as a "DC link capacitor," "DC link capacitor," or "smoothing capacitor." The capacitor 13 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 13 include electrolytic capacitors and film capacitors. A pre-charging circuit for pre-charging the capacitor 13 may be provided, but it is not shown in the diagram.

[0015] The inverter 12 is connected to the converter 11 via the DC link section 40. The inverter 12 consists of a three-phase bridge circuit of switching elements and diodes connected in antiparallel thereto. Examples of switching elements include semiconductor elements such as FETs, IGBTs, thyristors, GTOs, and transistors, but other semiconductor elements may also be used. The inverter 12 receives a PWM switching command from the motor control unit 18 and switches the switching elements on and off to selectively perform a powering operation, which converts the DC power in the DC link section 40 into AC power to drive the motor 3 and outputs it to the motor 3, and a regenerative operation, which converts the AC power regenerated by the motor 3 into DC power and returns it to the DC link section 40. As a result, the motor 3 is driven based on the AC power output from the inverter 12. The switching elements and diodes provided in the inverter 12 are not shown in the diagram.

[0016] The discharge circuit 30 is provided in the DC link section 40. The discharge circuit 30 includes a discharge resistor 14 and a discharge switch 15.

[0017] The discharge resistor 14 is provided to dissipate the regenerative power from the motor 3 through resistive discharge. The discharge resistor 14 is sometimes referred to as a "regenerative discharge resistor" or "regenerative resistor".

[0018] The discharge switch 15 is connected in series with the discharge resistor 14. The discharge switch 15 is composed of, for example, a relay or a switching element. Examples of switching elements include semiconductor elements such as FETs, IGBTs, thyristors, GTOs, and transistors, but other semiconductor elements may also be used. The opening and closing of the discharge switch 15 is commanded by the resistance discharge control unit 19. If there is no abnormality in the discharge switch 15 (i.e., if it is functioning normally), the discharge switch 15 will close upon receiving a command from the resistance discharge control unit 19, thereby creating conductivity between the discharge resistor 14 and the DC link section 40. Also, if there is no abnormality in the discharge switch 15 (i.e., if it is functioning normally), the discharge switch 15 will open upon receiving a command from the resistance discharge control unit 19, thereby disconnecting the discharge resistor 14 and the DC link section 40. On the other hand, if there is an abnormality in the discharge switch 15, the discharge switch 15 will not open or close according to the command received from the resistance discharge control unit 19.

[0019] The resistive discharge control unit 19 commands the opening and closing of the discharge switch 15 during the regenerative operation of the inverter 12. The resistive discharge control unit 19 commands the opening and closing of the discharge switch 15 when the voltage of the DC link section 40 reaches the discharge start level V during the regenerative operation of the inverter 12. ths When this occurs, a command is issued to close the discharge switch 15 in order to make the discharge resistor 14 and the DC link section 40 conductive. If there is no abnormality in the discharge switch 15 (i.e., if it is functioning normally), the discharge resistor 14 and the DC link section 40 will be conductive via the discharge switch 15, and the regenerative power from the motor 3 will be consumed as heat by the discharge resistor 14. After the consumption of regenerative power by the discharge resistor 14 begins, the voltage of the DC link section 40 will reach the discharge completion level V. the When the following conditions are met, a command is issued to open the discharge switch 15 in order to disconnect the discharge resistor 14 from the DC link section 40. If there is no abnormality in the discharge switch 15 (i.e., if it is functioning normally), the discharge resistor 14 is electrically disconnected from the DC link section 40, and the consumption of regenerative power by the discharge resistor 14 ends. Note that discharge start level V ths [V] and discharge termination level V the [V] should be set considering the voltage ratings of the components in the converter 11 and inverter 12, the resistance value and voltage rating of the discharge resistor 14, the voltage rating of the discharge switch 15, etc. Generally, the discharge start level Vths [V] is the discharge termination level V the The voltage is set higher than [V].

[0020] The position detection unit 21 detects information regarding the rotational angular velocity of the motor 3 via the encoder 20 installed on the motor 3.

[0021] The voltage detection unit 22 detects the voltage of the DC link unit 40. That is, the voltage detection unit 22 detects the potential difference between the positive potential on the positive power line of the DC link unit 40 and the negative potential on the negative power line as the voltage of the DC link unit 40. Alternatively, the voltage detection unit 22 may detect the voltage applied between the positive and negative terminals of the capacitor 13 as the voltage of the DC link unit 40.

[0022] The motor control unit 18 generates commands to control the rotational angular velocity, position, or torque of the motor 3's rotor based on the rotational angular velocity of the motor 3 detected by the position detection unit 21, the current flowing through the motor 3's windings, rotational angular velocity commands, torque commands, position commands, and the motor 3's operation program. The commands generated by the motor control unit 18 are transmitted to each switching element in the inverter 12, and the inverter 12 performs power conversion operations in response. The commands generated by the motor control unit 18 include commands to cause the inverter 12 to perform powering operations and commands to cause regenerative operations. Note that the configuration of the motor control unit 18 defined here is merely an example, and the configuration of the motor control unit 18 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.

[0023] The energy calculation unit 16 estimates the following three energies during a predetermined time interval, based on the voltage of the DC link section 40 and the rotational angular velocity of the motor 3, which are detected at predetermined time intervals when the resistance discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of the inverter 12. Specifically, the energy calculation unit 16 estimates a first energy E1 that is expected to return from the motor 3 to the DC link section 40 via the inverter 12 during a predetermined time interval when the resistance discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of the inverter 12. The energy calculation unit 16 also estimates a second energy E2 that is expected to be consumed by the discharge resistor 14 during the same predetermined time interval when the resistance discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of the inverter 12. Furthermore, the energy calculation unit 16 estimates a third energy E3, which is the estimated increase or decrease in the stored energy of the capacitor 13 during the predetermined time period when the resistive discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of the inverter 12.

[0024] The first energy E1, the second energy E2, and the third energy E3 can be estimated, for example, as follows: Let t1 [s] be the start time and t2 [s] be the end time of the predetermined time when the resistance discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of the inverter 12. Let ω1 [rad / s] be the rotational angular velocity of the motor 3 detected by the position detection unit 21 at the start time t1 of the predetermined time, and V1 [V] be the voltage of the DC link unit 40 detected by the voltage detection unit 22. Let ω2 [rad / s] be the rotational angular velocity of the motor 3 detected by the position detection unit 21 at the end time t2 of the predetermined time, and V2 [V] be the voltage of the DC link unit 40 detected by the voltage detection unit 22. Let J [kg・m] be the rotor moment of inertia of the motor 3. 2 Let the resistance value of the discharge resistor 14 be R [Ω]. Let the capacitance of the capacitor 13 be C [F].

[0025] The first energy E1 [J] that is expected to return from the motor 3 to the DC link section 40 via the inverter 12 during a predetermined time period (between t1 and t2) can be expressed, for example, by equation 1.

[0026]

[0027] As a variation, the first energy E1 may be estimated by considering the influence of the potential energy of the actuator driven by the motor 3. In this case, the first energy E1 can be obtained by adding the potential energy of the actuator driven by the motor 3 to the kinetic energy of the motor 3, which is based on the rotational angular velocity of the motor 3 expressed on the right-hand side of Equation 1. The potential energy of the actuator can be estimated, for example, based on the mass and height of the actuator and the acceleration due to gravity.

[0028] As an alternative, the first energy E1 may be estimated by taking into account the influence of the frictional energy possessed by the motor 3. In this case, the first energy E1 can be obtained by subtracting the frictional energy possessed by the motor 3 from the kinetic energy of the motor 3, which is based on the rotational angular velocity of the motor 3 expressed on the right-hand side of Equation 1.

[0029] As an alternative, the first energy E1 may be estimated by considering the influence of the potential energy of the actuator driven by the motor 3 and the frictional energy of the motor 3. In this case, the first energy E1 can be obtained by adding the potential energy of the actuator driven by the motor 3 to the kinetic energy of the motor 3 based on the rotational angular velocity of the motor 3 expressed on the right-hand side of Equation 1, and subtracting the frictional energy of the motor 3.

[0030] The second energy E2 [J] that is expected to be consumed by the discharge resistor 14 during a predetermined time period (between t1 and t2) can be expressed, for example, by equation 2.

[0031]

[0032] In equation 2, V(t) is expressed in equation 3.

[0033]

[0034] In Formula 3, α and β are represented by Formula 4.

[0035]

[0036] The third energy E3 [J], which is the estimated increase or decrease in the stored energy of the capacitor 13 during a predetermined time period (from t1 to t2), can be expressed, for example, by Formula 5.

[0037]

[0038] In Formula 5, when the stored energy of the capacitor 13 does not change during the predetermined time period (from t1 to t2), the third energy E3 is 0; when the stored energy of the capacitor 13 increases during the predetermined time period (from t1 to t2), the third energy E3 takes a positive value; and when the stored energy of the capacitor 13 decreases during the predetermined time period (from t1 to t2), the third energy E3 takes a negative value.

[0039] Note that the rotor inertia moment J [kg·m 2 ] of the motor 3 is the moment of the motor 3 alone as J m [kg·m 2 ], and when the moment due to inertia is I [kg·m 2 ], it can be expressed, for example, by Formula 6.

[0040]

[0041] Alternatively, for the rotor inertia moment J [kg·m 2 ] of the motor 3, an estimated value calculated by a known inertia estimation method may be used.

[0042] Based on the first energy E1, the second energy E2, and the third energy E3 estimated as described above, the abnormality determination unit 17 determines whether the discharge circuit 30 is normal or abnormal. Failures of the discharge circuit 30 include, for example, an open failure and a short - circuit failure of the discharge switch 15, a breakage of the discharge resistor 14, and a short - circuit between both terminals of the discharge resistor 14.

[0043] For example, if the discharge circuit 30 is functioning normally, the first energy E1 that is expected to return from the motor 3 to the DC link section 40 via the inverter 12 over a predetermined period of time should be approximately equal to the sum of the second energy E2 that is expected to be consumed by the discharge resistor 14 over the predetermined period of time and the third energy E3, which is the estimated increase or decrease in the stored energy of the capacitor 13 over the predetermined period of time. On the other hand, if there is any abnormality in the discharge circuit 30, the first energy E1 that is expected to return from the motor 3 to the DC link section 40 via the inverter 12 over a predetermined period of time should be significantly different from the sum of the second energy E2 that is expected to be consumed by the discharge resistor 14 over the predetermined period of time and the third energy E3, which is the estimated increase or decrease in the stored energy of the capacitor 13 over the predetermined period of time. Therefore, in the embodiment of the present disclosure, the abnormality determination unit 17 determines that the discharge circuit 30 is normal if the difference between the sum "E2 + E3" consisting of the second energy E2 and the third energy E3 and the first energy E1, "E1 - (E2 + E3)", is within a predetermined range, and determines that the discharge circuit 30 is abnormal if it is outside the predetermined range.

[0044] Furthermore, the "predetermined range" used in processing by the abnormality determination unit 17 should be set in advance, taking into account the detection errors of the position detection unit 21 and the voltage detection unit 22. For example, the motor drive device 1 is test-driven to ensure that the discharge circuit 30 is functioning correctly, and the first energy E during the test-driven operation is... ref1 , the second energy E ref2 , and the third energy E ref3 Calculate or measure in advance, and "E ref1 - (E ref2 +E ref3 The abnormality determination unit 17 can then set the above-mentioned "predetermined range" used for processing by referring to the above. For example, when A and B are positive values, if the upper limit of the "predetermined range" is set to A and the lower limit of the predetermined range is set to -B, then the range defined from -B to A is the "predetermined range". For example, "E ref1 - (E ref2 +E ref3 The value 1.1 times the absolute value of ) is set as the upper limit A of the "predetermined range", and "E ref1 - (Eref2 +E ref3 The upper limit of the "specified range" -B may be set as a value obtained by adding a minus sign to 1.1 times the absolute value of )). Note that the numbers listed here are just examples, and other numbers may also be used.

[0045] The abnormality detection unit 17's determination result is notified to the motor control unit 18. If the abnormality detection unit 17 determines that the discharge circuit 30 is abnormal, the motor control unit 18 executes control to stop the motor 3. The control to stop the motor 3 can be implemented using known methods. However, if the motor control unit 18 stops the motor 3 abruptly, a large amount of regenerative power may be returned from the motor 3 to the DC link unit 40, potentially causing the DC link unit 40 to rise significantly. Therefore, when stopping the motor 3 in the event of an abnormality in the discharge circuit 30, the motor control unit 18 performs control to gradually decelerate the motor 3 over time and finally stop it.

[0046] Furthermore, the determination result from the abnormality detection unit 17 may be notified to the worker by a notification unit (not shown), such as a display device, audio device, or printer. Based on the notification, the worker can quickly and reliably determine whether or not there is an abnormality in the discharge circuit 30.

[0047] Examples of display devices include standalone display monitors, display monitors attached to the motor drive unit 1, display monitors attached to a higher-level control device (not shown) that controls the motor drive unit 1, and display monitors attached to personal computers and mobile terminals. Alternatively, the display device may be composed of light-emitting elements such as LEDs or lamps. For example, the light-emitting element may not emit light when the discharge circuit 30 is functioning normally, and may emit light when there is an abnormality in the discharge circuit 30.

[0048] For example, the sound equipment may not emit sound when the discharge circuit 30 is functioning normally, but may emit sound when there is a problem with the discharge circuit 30. Examples of sound equipment include speakers, buzzers, and chimes.

[0049] For example, if there is an abnormality in the discharge circuit 30, the date and time of the abnormality may be printed out on paper or the like.

[0050] Furthermore, each time a determination result is obtained by the abnormality determination unit 17, it can be stored in the memory unit (recording unit) and accumulated, creating a database that can be used for maintenance work, parts ordering work, and other purposes.

[0051] <Operation of the motor drive device according to the embodiment of the present disclosure> Figure 2 is a flowchart showing the operation flow of the motor drive device according to the embodiment of the present disclosure.

[0052] When the motor drive unit 1 is operating, in step S101, it is determined whether or not the motor drive unit 1 is performing regenerative operation. The determination of whether or not the motor drive unit 1 is performing regenerative operation is performed, for example, by the abnormality determination unit 17, the motor control unit 18, the resistance discharge control unit 19, and / or a higher-level control unit (not shown).

[0053] If it is determined in step S101 that the motor drive unit 1 is performing regenerative operation, then in step S102 the resistance discharge control unit 19 determines that the voltage of the DC link unit 40 detected by the voltage detection unit 22 is at the discharge start level V ths It is determined whether the voltage of the DC link section 40 is above the discharge start level V. ths If it is determined that the above has occurred, proceed to step S103, and the voltage of the DC link section 40 is at the discharge start level V. ths If it is not determined that the above conditions have been met, return to step S101.

[0054] In step S103, the resistance discharge control unit 19 issues a command to close the discharge switch 15 in order to make the discharge resistor 14 and the DC link unit 40 conductive.

[0055] In step S104, the voltage detection unit 22 detects the voltage of the DC link unit 40. In step S105, the position detection unit 21 detects the rotational angular velocity of the motor 3. The processes in step S104 and step S105 are executed at the same time.

[0056] In step S106, the energy calculation unit 16 determines whether the detection process for the processes in step S104 and step S105 was performed twice. If the detection process for the processes in step S104 and step S105 was performed only once, the unit returns to step S104. If the detection process for the processes in step S104 and step S105 was performed twice, the unit proceeds to step S107. The time determined between the execution timing (t1) of the first execution of the processes in step S104 and step S105 and the execution timing (t2) of the second execution of the processes in step S104 and step S105 is the "predetermined time" mentioned above.

[0057] In step S107, the energy calculation unit 16 estimates the first energy E1, the second energy E2, and the third energy E3.

[0058] In step S108, the abnormality determination unit 17 determines whether the difference between the sum of the second energy E2 and the third energy E3, "E2 + E3", and the first energy E1, "E1 - (E2 + E3)", is within a predetermined range. If, in step S108, the energy difference "E1 - (E2 + E3)" is determined to be within the predetermined range, then in S111, the abnormality determination unit 17 determines that the discharge circuit 30 is normal.

[0059] In step S112 following step S111, the resistive discharge control unit 19 determines that the voltage of the DC link unit 40 is at the discharge termination level V the It is determined whether the following conditions are met: The voltage of the DC link section 40 is at the discharge termination level V. the If it is determined that the following conditions are met, proceed to step S113, and the voltage of the DC link section 40 is determined to be discharge termination level V. the If it is not determined that the following conditions apply, return to step S104.

[0060] In step S113, the resistance discharge control unit 19 issues a command to open the discharge switch 15 in order to disconnect the discharge resistor 14 and the DC link unit 40. Then, the process returns to step S101.

[0061] On the other hand, if the energy difference "E1 - (E2 + E3)" is not determined to be within a predetermined range in step S108, the abnormality determination unit 17 determines in S109 that the discharge circuit 30 is abnormal.

[0062] In step S110, the motor control unit 18 executes a control to stop the motor 3. Although not shown in the diagram, in conjunction with the process in step S110, the result of the abnormality determination unit 17 may be notified to the worker by a notification unit such as a display device, audio device, or printer. After that, the process ends.

[0063] The series of processes in steps S101 to S113 are repeatedly executed at a predetermined control cycle. The control cycle may be changed as appropriate.

[0064] Next, the third energy E3, which is the estimated increase or decrease in the stored energy of the capacitor 13 when the resistive discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of the inverter 12, will be explained with reference to Figures 3 to 5. In Figures 3 to 5, the detection timings of the voltage of the DC link section 40 and the rotational angular velocity of the motor 3 when the resistive discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of the inverter 12 are denoted as t1 [s] and t2 [s]. At the start of the predetermined time t1, the rotational angular velocity of the motor 3 detected by the position detection unit 21 is denoted as ω1 [rad / s], and the voltage of the DC link section 40 detected by the voltage detection unit 22 is denoted as V1 [V]. At the end of the predetermined time t2, the rotational angular velocity of the motor 3 detected by the position detection unit 21 is denoted as ω2 [rad / s], and the voltage of the DC link section 40 detected by the voltage detection unit 22 is denoted as V2 [V]. The third energy E3 is calculated according to Equation 5.

[0065] Figure 3 illustrates the voltage waveform of the DC link section when the voltage of the DC link section detected twice is the same, according to an embodiment of the present disclosure.

[0066] As illustrated in Figure 3, at time 0, when the motor 3 decelerates and regenerative power begins to return to the DC link section 40 via the inverter 12, the voltage of the DC link section 40 gradually increases. At time t0, the voltage of the DC link section 40 reaches the discharge start level V. ths When this is reached, the resistance discharge control unit 19 issues a command to close the discharge switch 15 in order to make the discharge resistor 14 and the DC link unit 40 conductive. At time t1, the voltage detection unit 22 detects the voltage V1 of the DC link unit 40, and the position detection unit 21 detects the rotational angular velocity ω1 of the motor 3. At time t2, the voltage detection unit 22 detects the voltage V2 of the DC link unit 40, and the position detection unit 21 detects the rotational angular velocity ω2 of the motor 3. Subsequently, the voltage of the DC link unit 40 gradually decreases, and at time t3, the voltage of the DC link unit 40 reaches the discharge end level V the When this is reached, the resistive discharge control unit 19 issues a command to open the discharge switch 15 in order to disconnect the discharge resistor 14 and the DC link section 40. As shown in Figure 3, when the voltage of the DC link section 40 fluctuates, even if the regenerative power of the motor 3 is returned to the DC link section 40 via the inverter 12, the third energy E3, which is the estimated increase or decrease in the stored energy of the capacitor 13, is 0. In other words, no new energy is stored in the capacitor 13, and the current stored energy is maintained.

[0067] Figure 4 illustrates the voltage waveform of the DC link section in an embodiment of the present disclosure when the voltage of the DC link section detected a second time is greater than the voltage of the DC link section detected a first time.

[0068] As illustrated in Figure 4, at time 0, when the motor 3 decelerates and regenerative power begins to return to the DC link section 40 via the inverter 12, the voltage of the DC link section 40 gradually increases. At time t0, the voltage of the DC link section 40 reaches the discharge start level V. thsWhen this is reached, the resistance discharge control unit 19 issues a command to close the discharge switch 15 in order to make the discharge resistor 14 and the DC link unit 40 conductive. At time t1, the voltage detection unit 22 detects the voltage V1 of the DC link unit 40, and the position detection unit 21 detects the rotational angular velocity ω1 of the motor 3. At time t2, the voltage detection unit 22 detects the voltage V2 of the DC link unit 40, and the position detection unit 21 detects the rotational angular velocity ω2 of the motor 3. Subsequently, the voltage of the DC link unit 40 gradually decreases, and at time t3, the voltage of the DC link unit 40 reaches the discharge end level V the When this is reached, the resistance discharge control unit 19 issues a command to open the discharge switch 15 in order to disconnect the discharge resistor 14 and the DC link section 40. As shown in Figure 4, when the voltage of the DC link section 40 fluctuates, the regenerative power of the motor 3 is returned to the DC link section 40 via the inverter 12, and new energy is stored in the capacitor 13. That is, the third energy E3, which is the estimated increase or decrease in the stored energy of the capacitor 13, takes a positive value.

[0069] Figure 5 illustrates the voltage waveform of the DC link section in an embodiment of the present disclosure when the voltage of the DC link section detected a second time is smaller than the voltage of the DC link section detected a first time.

[0070] As illustrated in Figure 5, at time 0, when the motor 3 decelerates and regenerative power begins to return to the DC link section 40 via the inverter 12, the voltage of the DC link section 40 gradually increases. At time t0, the voltage of the DC link section 40 reaches the discharge start level V. ths When this is reached, the resistance discharge control unit 19 issues a command to close the discharge switch 15 in order to make the discharge resistor 14 and the DC link unit 40 conductive. At time t1, the voltage detection unit 22 detects the voltage V1 of the DC link unit 40, and the position detection unit 21 detects the rotational angular velocity ω1 of the motor 3. At time t2, the voltage detection unit 22 detects the voltage V2 of the DC link unit 40, and the position detection unit 21 detects the rotational angular velocity ω2 of the motor 3. Subsequently, the voltage of the DC link unit 40 gradually decreases, and at time t3, the voltage of the DC link unit 40 reaches the discharge end level V theWhen this is reached, the resistive discharge control unit 19 issues a command to open the discharge switch 15 in order to disconnect the discharge resistor 14 and the DC link section 40. As shown in Figure 5, if the voltage of the DC link section 40 fluctuates, even if the regenerative power of the motor 3 is returned to the DC link section 40 via the inverter 12, the stored energy of the capacitor 13 decreases, meaning that the third energy E3, which is the estimated increase or decrease in the stored energy of the capacitor 13, takes a negative value.

[0071] Thus, in Figure 3, where the stored energy of the capacitor 13 does not change during a predetermined time (between t1 and t2), the third energy E3 is 0. In Figure 4, where the stored energy of the capacitor 13 increases during a predetermined time (between t1 and t2), the third energy E3 takes a positive value. In Figure 5, where the stored energy of the capacitor 13 decreases during a predetermined time (between t1 and t2), the third energy E3 takes a negative value. The value of the third energy E3 depends on the capacitance C of the capacitor 13, the resistance R of the discharge resistor 14, the magnitude of the voltage at the DC link section 40 at the start of the regenerative operation of the motor drive device 1, and the magnitude of the regenerative power of the motor 3.

[0072] <Modifications of Embodiments of the Present Disclosure> Embodiments of the present disclosure are applicable to motor drive devices equipped with multiple inverters for driving multiple motors. Generally, in motor drive devices, one converter is often provided for multiple inverters in order to reduce the cost and space occupied by the motor drive device. That is, a converter that converts AC power supplied from an AC power source into DC power is used as a common power supply unit for multiple inverters, and these multiple inverters use the DC power output from the converter, which is the common power supply unit, to generate AC power for driving each motor.

[0073] Figure 6 is a circuit diagram showing a motor drive device according to a modified embodiment of the present disclosure. Here, as an example, a case in which two motors indicated by reference numerals 3-1 and 3-2 are driven by the motor drive device 1 according to a modified embodiment of the present disclosure will be described. An inverter 12-1 is provided corresponding to motor 3-1, and an inverter 12-2 is provided corresponding to motor 3-2. Note that the number of motors is not particularly limited to the modified embodiment of the present disclosure, and there may be three or more motors.

[0074] As shown in Figure 6, the motor drive device 1 according to the embodiment of the present disclosure comprises a converter 11, inverters 12-1 and 12-2, a capacitor 13, a discharge circuit 30, an energy calculation unit 16, an abnormality determination unit 17, a motor control unit 18, a resistance discharge control unit 19, a position detection unit 21, and a voltage detection unit 22. Power supplies for driving each of these units, such as the energy calculation unit 16, the abnormality determination unit 17, the motor control unit 18, the resistance discharge control unit 19, and the voltage detection unit 22, are not shown in the figure.

[0075] The AC power supply 2, converter 11, capacitor 13, discharge circuit 30, resistance discharge control unit 19, position detection unit 21, and voltage detection unit 22 are as described in the embodiment with reference to Figures 1 to 5.

[0076] Inverters 12-1 and 12-2 are connected to the converter 11 via the DC link section 40. Inverter 12-1 performs a powering operation, converting the DC power in the DC link section 40 into AC power to drive motor 3-1 and outputting it to motor 3-1, and a regenerative operation, converting the AC power regenerated by motor 3-1 back into DC power and returning it to the DC link section 40. As a result, motor 3-1 is driven based on the AC power output from inverter 12-1. Inverter 12-2 performs a powering operation, converting the DC power in the DC link section 40 into AC power to drive motor 3-2 and outputting it to motor 3-2, and a regenerative operation, converting the AC power regenerated by motor 3-2 back into DC power and returning it to the DC link section 40. As a result, motor 3-2 is driven based on the AC power output from inverter 12-2. The configurations of inverters 12-1 and 12-2 are as described for inverter 12.

[0077] The position detection unit 21 detects information regarding the rotational angular velocity of motor 3-1 via encoder 20-1 installed on motor 3-1. The position detection unit 21 also detects information regarding the rotational angular velocity of motor 3-2 via encoder 20-2 installed on motor 3-2.

[0078] The motor control unit 18 generates commands to control the rotational angular velocity, position, or torque of the rotor of the motor 3-1 based on the rotational angular velocity of the motor 3-1 detected by the position detection unit 21, the current flowing through the windings of the motor 3-1, the rotational angular velocity command, the torque command, the position command, and the operation program of the motor 3-1. The commands generated by the motor control unit 18 are transmitted to each switching element in the inverter 12-1, and in response, the inverter 12-1 performs power conversion operations. The commands generated by the motor control unit 18 include commands to cause the inverter 12-1 to perform power operation and commands to cause regenerative operation.

[0079] Furthermore, the motor control unit 18 generates commands to control the rotational angular velocity, position, or torque of the rotor of the motor 3-2 based on the rotational angular velocity of the motor 3-2 detected by the position detection unit 21, the current flowing through the windings of the motor 3-2, the rotational angular velocity command, the torque command, the position command, and the operation program of the motor 3-2. The commands generated by the motor control unit 18 are transmitted to each switching element in the inverter 12-2, and in response, the inverter 12-2 performs power conversion operations. The commands generated by the motor control unit 18 include commands to cause the inverter 12-2 to perform power operation and commands to cause regenerative operation.

[0080] The configuration of the motor control unit 18 defined herein is merely an example, and the configuration of the motor control unit 18 may also be defined by including terms such as position command generation unit, torque command generation unit, current control unit, position control unit, and torque control unit.

[0081] The energy calculation unit 16 estimates the following three energies during the same time period when the resistive discharge control unit 19 commands the discharge switch 15 to close while the inverter 12-1 and / or 12-2 are in regenerative operation. More specifically, if at least one of the inverters 12-1 and 12-2 is in regenerative operation, the energy calculation unit 16 estimates the first energy E1, the second energy E2, and the third energy E3 during the predetermined time period based on the voltage of the DC link section 40 and the rotational angular velocity of the motor 3 detected at predetermined time intervals when the resistive discharge control unit 19 commands the discharge switch 15 to close.

[0082] The energy calculation unit 16 estimates, according to equations 2 to 4, the second energy E2 that is expected to be consumed by the discharge resistor 14 during a predetermined time when the resistance discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of the inverter 12-1 and / or 12-2.

[0083] Furthermore, the energy calculation unit 16 estimates a third energy E3, which is the estimated increase or decrease in the stored energy of the capacitor 13 during the predetermined time period when the resistive discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of the inverter 12-1 and / or 12-2, according to Equation 5.

[0084] Furthermore, the energy calculation unit 16 calculates the first energy E that returns from motor 3-1 to DC link unit 40 during the predetermined time when the resistance discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of inverter 12-1 and / or 12-2. 11 The first energy E is estimated to return from motor 3-2 to DC link section 40 during the predetermined time. 21 We estimate the following. More details are as follows:

[0085] When the number of motors driven by the motor drive device 1 is n (where n is an integer of 2 or more), i can take values ​​from 1 to n. In particular, in the example shown in Figure 6, n = 2. The rotational angular velocity of motor 3-i detected by the position detection unit 21 at the start time t1 of a predetermined time is ω i1 Let [rad / s] be the rotational angular velocity of motor 3-i detected by the position detection unit 21 at the end of the predetermined time t2, and ω i2 Let [rad / s] be the rotor moment of inertia of motor 3-i. i [kg・m 2 The energy calculation unit 16 calculates the first energy E that returns from the motor 3-i to the DC link unit 40 during the predetermined time when the resistance discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of the inverter 12-i. i1 This is estimated for each motor 3-i according to Equation 7.

[0086]

[0087] As a variation, the first energy E i1This may be estimated by taking into account the influence of the potential energy of the actuator driven by motor 3-i. In this case, the first energy E is obtained by adding the potential energy of the actuator driven by motor 3-i to the kinetic energy of motor 3-1 based on the rotational angular velocity of motor 3-i, which is expressed on the right-hand side of equation 7. i1 The potential energy of an actuator can be calculated. For example, the potential energy of an actuator can be estimated based on the actuator's mass and height and the acceleration due to gravity.

[0088] Furthermore, as a variation, the first energy E i1 This can also be estimated by taking into account the influence of the frictional energy possessed by motor 3-i. In this case, the first energy E can be obtained by subtracting the frictional energy possessed by motor 3-i from the kinetic energy of motor 3-i based on the rotational angular velocity of motor 3 expressed on the right side of equation 7. i1 It is possible to find this.

[0089] Furthermore, as a variation, the first energy E i1 This can be estimated by considering the influence of the potential energy of the actuator driven by motor 3-i and the frictional energy of motor 3-i. In this case, the first energy E is obtained by adding the potential energy of the actuator driven by motor 3-i to the kinetic energy of motor 3-i based on the rotational angular velocity of motor 3-i expressed on the right side of equation 7, and subtracting the frictional energy of motor 3-i. i1 It is possible to find this.

[0090] When the resistive discharge control unit 19 commands the discharge switch 15 to close during the regenerative operation of the inverter 12-i, the first energy E returns from the motor 3-i to the DC link unit 40 during the predetermined time. i1 The sum E sum1 This can be expressed as shown in Equation 8.

[0091]

[0092] The abnormality detection unit 17 calculates the sum "E2 + E3" consisting of the second energy E2 and the third energy E3, and the sum of the first energies for each motor 3-i. sum1 The difference is "E sum1 If "-(E2 + E3)" is within a predetermined range, the discharge circuit 30 is determined to be normal; if it is outside the predetermined range, the discharge circuit 30 is determined to be abnormal.

[0093] In the modified example, the "predetermined range" used for processing by the abnormality determination unit 17 should be set in advance, taking into account the detection errors of the position detection unit 21 and the voltage detection unit 22. For example, the motor drive device 1 is test-driven to ensure that the discharge circuit 30 is functioning correctly, and the sum of the first energies E during the test-driven operation is... sumref1 , the second energy E ref2 , and the third energy E ref3 Calculate or measure in advance, and "E sumref1 - (E ref2 +E ref3 The abnormality determination unit 17 can then set the above-mentioned "predetermined range" used for processing by referring to the above. For example, when A and B are positive values, if the upper limit of the "predetermined range" is set to A and the lower limit of the predetermined range is set to -B, then the range defined from -B to A is the "predetermined range". For example, "E sumref1 - (E ref2 +E ref3 The value 1.1 times the absolute value of ) is set as the upper limit A of the "predetermined range", and "E sumref1 - (E ref2 +E ref3 The upper limit of the "specified range" -B may be set as a value obtained by adding a minus sign to 1.1 times the absolute value of )). Note that the numbers listed here are just examples, and other numbers may also be used.

[0094] Thus, if at least one of the inverters 12-1 and 12-2 is performing regenerative operation, the energy calculation unit 16 estimates the three energies for the same time period when the discharge switch 15 is commanded to close. For example, when inverter 12-1 is performing regenerative operation and inverter 12-2 is performing power operation, the first energy E11 It takes a positive value, and the first energy E 21 It takes a negative value. The abnormality determination unit 17 determines the first energy E 11 and the first energy E 21 The sum of E sum1 Then, using the second energy E2 and the third energy E3, the anomaly detection process described above is performed.

[0095] Note that the flowchart in Figure 2 is executed with the following substitutions for steps S101, S107, and S108. In step S101, it is determined whether at least one of the multiple inverters 12-i of the motor drive unit 1 is performing regenerative operation. In step S107, the energy calculation unit 16 estimates the first energy E1, the second energy E2, and the third energy E3 for each motor 3-i. In step S108, the abnormality determination unit 17 calculates the sum of the second energy E2 and the third energy E3, "E2 + E3", and the total sum of the first energies for each motor 3-i. sum1 The difference is "E sum1 If "-(E2 + E3)" is within a predetermined range, the discharge circuit 30 is determined to be normal; if it is outside the predetermined range, the discharge circuit 30 is determined to be abnormal.

[0096] <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 an energy calculation unit 16, an abnormality determination unit 17, a motor control unit 18, a resistance discharge control unit 19, a position detection unit 21, a voltage detection unit 22, and other processing units. Each of these units in the arithmetic processing unit is a functional module realized by a program executed on the processor. For example, if the energy calculation unit 16, abnormality determination unit 17, motor control unit 18, resistance discharge control unit 19, position detection unit 21, voltage detection unit 22, and other processing units are constructed in program format, the functions of each unit can be realized by operating the arithmetic processing unit according to this program. The programs for executing each process in the energy calculation unit 16, the abnormality determination unit 17, the motor control unit 18, the resistance discharge control unit 19, the position detection unit 21, the voltage detection unit 22, 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, a magnetic storage medium (magnetic recording medium), or an optical storage medium (optical recording medium). Alternatively, the energy calculation unit 16, the abnormality determination unit 17, the motor control unit 18, the resistance discharge control unit 19, the position detection unit 21, the voltage detection unit 22, and other processing units may be implemented as semiconductor integrated circuits on which programs that realize the functions of each unit are written.

[0097] Furthermore, the motor drive unit 1 is provided with at least one memory, which is a storage device (recording device). The memory also includes the energy calculation unit 16, the abnormality determination unit 17, the motor control unit 18, the resistance discharge control unit 19, the position detection unit 21, the voltage detection unit 22, 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 programs for operating the energy calculation unit 16, the abnormality determination unit 17, the motor control unit 18, the resistance discharge control unit 19, the position detection unit 21, the voltage detection unit 22, and the other processing units. Furthermore, the memory stores the rotational angular velocities of motors 3, 3-1, and 3-2 detected by the position detection unit 21, and the voltage values ​​of the DC link unit 40 detected by the voltage detection unit 22. The memory also stores the first energies E1 and E estimated by the energy calculation unit 16. i1 , the first total energy E sum1 The second energy E2 and the third energy E3 are stored in the memory. The memory stores the determination result by the abnormality determination unit 17. The memory stores a "predetermined range" used for abnormality determination processing by the abnormality determination unit 17. The memory stores the discharge start level V ths and discharge termination level V the The following are stored in memory: the rotor inertia moment J of motor 3 and the rotor inertia moment J of motor 3-i. iThe memory stores the resistance value R of the discharge resistor 14 and the capacitance C of the capacitor 13. The memory also stores various programs and data related to the converter control unit that controls the PWM control type or 120-degree energization type converter 11. The memory also stores various programs and data related to the converter 11. The memory also stores various programs and data related to the motor control unit 18. The memory also stores various programs and data related to the inverter 12. The memory also stores various programs and data related to the motor drive unit 1.

[0098] <Advantages of Embodiments and Modifications of the Disclosure> According to embodiments and modifications of the disclosure, a space-saving and low-cost motor drive device can be realized that can detect abnormalities in the discharge circuit for suppressing voltage rise in the DC link section during regenerative operation. Conventionally, a hardware discharge circuit monitoring device was provided to monitor whether or not there was an abnormality in the discharge circuit. In contrast, according to embodiments and modifications of the disclosure, detectors commonly provided in motor drive devices can be used for the position detection unit and voltage detection unit, and the energy calculation unit and abnormality determination unit can be built in software within the arithmetic processing unit commonly provided in motor drive devices. As a result, the state of resistive discharge during regeneration can be determined at low cost, and the motor drive device can be made larger. Furthermore, according to embodiments and modifications of the disclosure, if the abnormality determination unit determines that the discharge circuit is abnormal, control is executed to stop the motor, so damage to components in the motor drive device can be prevented, resulting in high safety.

[0099] Although the present disclosure has been described in detail above, this disclosure 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 this disclosure or from the spirit of this 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.

[0100] <Note> The following additional information is disclosed regarding the above embodiments and modifications.

[0101] (Note 1) A converter that converts AC power supplied from an AC power source into DC power and outputs the DC power to a DC link section; an inverter that performs a powering operation that converts the DC power in the DC link section into AC power for driving the motor and supplies it to the motor, and a regenerative operation that converts the AC power regenerated by the motor into DC power and returns it to the DC link section; a capacitor provided in the DC link section; a discharge circuit having a discharge resistor and a discharge switch that, when closed, makes the discharge resistor and the DC link section conductive, and when opened, disconnects the discharge resistor and the DC link section; an energy calculation unit that, when the discharge switch is commanded to close during the regenerative operation of the inverter, estimates a first energy that returns from the motor to the DC link section via the inverter during a predetermined time, a second energy that is consumed by the discharge resistor during a predetermined time, and a third energy that is the increase or decrease in the stored energy of the capacitor during a predetermined time. A motor drive device comprising: an abnormality determination unit that determines the discharge circuit is normal if the difference between the sum of the second energy and the third energy and the first energy is within a predetermined range, and determines the discharge circuit is abnormal if it is outside the predetermined range. (Note 2) The motor drive device according to Note 1, wherein the energy calculation unit estimates the first energy based on the rotational angular velocity of the motor measured at the start and end of a predetermined time, estimates the second energy based on the voltage of the DC link section measured at the start and end of a predetermined time, and estimates the third energy based on the voltage of the DC link section measured at the start and end of a predetermined time. (Note 3) The motor drive device according to Note 2, wherein the energy calculation unit estimates the first energy including the kinetic energy of the motor based on the rotational angular velocity of the motor measured at the start and end of a predetermined time, and the potential energy of the actuator driven by the motor. (Note 4) The motor drive device as described in Note 2, wherein the energy calculation unit estimates a first energy that includes the kinetic energy of the motor based on the rotational angular velocity of the motor measured at the start and end of a predetermined time, and the frictional energy possessed by the motor.(Note 5) The motor drive device according to Note 2, wherein the energy calculation unit estimates a first energy that includes the kinetic energy of the motor based on the rotational angular velocity of the motor measured at the start and end of a predetermined time, the potential energy of the actuator driven by the motor, and the frictional energy of the motor. (Note 6) The motor drive device according to Note 1, further comprising a motor control unit that controls the rotational operation of the motor, wherein the motor control unit executes control to stop the motor when the abnormality determination unit determines that the discharge circuit is abnormal. (Note 7) The motor drive device according to Note 1, further comprising a resistance discharge control unit that issues a command to close the discharge switch in order to make the discharge resistor and the DC link conduct when the voltage of the DC link section becomes above the discharge start level during the regenerative operation of the inverter. (Note 8) A motor drive device as described in any one of Notes 1 to 7, wherein the converter is connected to an inverter corresponding to each of the multiple motors via a DC link section, the energy calculation section estimates the first energy that returns from the motor to the DC link section for each motor during a predetermined time, and the abnormality determination section determines that the discharge circuit is normal if the difference between the sum of the second energy and the third energy and the total sum of the first energy for each motor is within a predetermined range, and determines that the discharge circuit is abnormal if it is outside the predetermined range.

[0102] 1 Motor drive unit 2 AC power supply 3, 3-1, 3-2, 3-i Motor 11 Converter 12, 12-1, 12-2, 12-i Inverter 13 Capacitor 14 Discharge resistor 15 Discharge switch 16 Energy calculation unit 17 Anomaly detection unit 18 Motor control unit 19 Resistive discharge control unit 20, 20-1, 20-2 Encoder 21 Position detection unit 22 Voltage detection unit 30 Discharge circuit 40 DC link unit

Claims

1. A converter that converts AC power supplied from an AC power source into DC power and outputs the DC power to a DC link section; an inverter that performs a powering operation that converts the DC power in the DC link section into AC power for driving a motor and supplies it to the motor, and a regenerative operation that converts the AC power regenerated by the motor into DC power and returns it to the DC link section; a capacitor provided in the DC link section; a discharge circuit having a discharge resistor and a discharge switch that, when closed, makes the discharge resistor and the DC link section conductive, and when opened, disconnects the discharge resistor and the DC link section; and an energy calculation unit that, when the discharge switch is commanded to close during the regenerative operation of the inverter, estimates a first energy that returns from the motor to the DC link section via the inverter during a predetermined time, a second energy that is consumed by the discharge resistor during the predetermined time, and a third energy that is the increase or decrease in the stored energy of the capacitor during the predetermined time. A motor drive device comprising: an abnormality determination unit that determines the discharge circuit is normal if the difference between the sum of the second energy and the third energy and the first energy is within a predetermined range, and determines the discharge circuit is abnormal if it is outside the predetermined range.

2. The motor drive device according to claim 1, wherein the energy calculation unit estimates the first energy based on the rotational angular velocity of the motor measured at the start and end of the predetermined time, estimates the second energy based on the voltage of the DC link section measured at the start and end of the predetermined time, and estimates the third energy based on the voltage of the DC link section measured at the start and end of the predetermined time.

3. The motor drive device according to claim 2, wherein the energy calculation unit estimates the first energy, which includes the kinetic energy of the motor based on the rotational angular velocity of the motor measured at the start and end of the predetermined time, and the potential energy of the actuator driven by the motor.

4. The motor drive device according to claim 2, wherein the energy calculation unit estimates the first energy, which includes the kinetic energy of the motor based on the rotational angular velocity of the motor measured at the start and end of the predetermined time, and the frictional energy of the motor.

5. The motor drive device according to claim 2, wherein the energy calculation unit estimates the first energy, which includes the kinetic energy of the motor based on the rotational angular velocity of the motor measured at the start and end of the predetermined time, the potential energy of the actuator driven by the motor, and the frictional energy of the motor.

6. The motor drive device according to claim 1, further comprising a motor control unit for controlling the rotational operation of the motor, wherein the motor control unit executes control to stop the motor when the abnormality determination unit determines that the discharge circuit is abnormal.

7. The motor drive device according to claim 1, further comprising a resistance discharge control unit that issues a command to close the discharge switch in order to make the discharge resistor and the DC link unit conduct when the voltage of the DC link unit rises to or above the discharge start level during the regenerative operation of the inverter.

8. The motor drive device according to any one of claims 1 to 7, wherein the inverter, which is connected to each of the plurality of motors, is connected to the converter via the DC link section, the energy calculation unit estimates the first energy that returns from the motor to the DC link section for each motor during the predetermined time, and the abnormality determination unit determines that the discharge circuit is normal if the difference between the sum of the second energy and the third energy and the total sum of the first energy for each motor is within a predetermined range, and determines that the discharge circuit is abnormal if it is outside the predetermined range.

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