Motor drive system, control method, and computer program

Abstract

The present invention provides a motor drive system, control method, and computer program that can suppress increases in manufacturing costs and determine whether or not a malfunction has occurred. [Solution] The motor drive system comprises two DC buses connected to the output side of a converter, an inverter connected to the two DC buses that converts DC power to AC power and supplies AC power to a motor, a smoothing capacitor with a known capacitance connected between the two DC buses, a regenerative resistor connected between the two DC buses that has a known resistance value and absorbs regenerative power, a switching element connected in series with the regenerative resistor that controls the energization and de-energization of the regenerative resistor, a voltage detection unit that detects the voltage between the two DC buses, a voltage calculation unit that calculates the voltage between the two DC buses when the switching element is conducted for a predetermined time, and a determination unit that determines whether or not there is an abnormality based on the voltage calculated by the voltage calculation unit and the voltage detected by the voltage detection unit.

Description

Technical Field

[0001] The present technology relates to a motor drive system for driving a motor, a control method, and a computer program.

Background Art

[0002] There is an inverter regenerative resistor protection device including a regenerative resistor, a current detector that detects a current flowing through the regenerative resistor, and an inverter that converts DC power into AC power and supplies the AC power to a motor. The inverter regenerative resistor protection device determines whether a failure has occurred based on a current value from the current detector (see Patent Document 1).

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] Installation of the current detector increases the manufacturing cost of the circuit.

[0005] The present disclosure has been made in view of such circumstances, and an object of the present disclosure is to provide a motor drive system, a control method, and a computer program that can suppress an increase in manufacturing cost and determine whether a failure has occurred.

Means for Solving the Problem

[0006] A motor drive system according to one embodiment of the present disclosure comprises: a converter that converts power from an AC power source to DC power; a reactor connected between the AC power source and the converter; two DC buses connected to the output side of the converter; an inverter connected to the two DC buses that converts DC power to AC power and supplies AC power to a motor; a smoothing capacitor having a known capacitance connected between the two DC buses; and a regenerative resistor connected between the two DC buses that has a known resistance value and absorbs regenerative power. The motor drive system further comprises: a switching element connected in series with the regenerative resistor to control the energization and de-energization of the regenerative resistor; a voltage detection unit that detects the voltage between the two DC buses; a voltage calculation unit that calculates the voltage between the two DC buses when the switching element is conducted for a predetermined time; and a determination unit that determines whether or not there is an abnormality in the motor drive system based on the voltage calculated by the voltage calculation unit and the voltage detected by the voltage detection unit.

[0007] In one embodiment of this disclosure, the presence or absence of an abnormality is determined based on the voltage detected by an existing voltage detection unit and the voltage calculated by a calculation.

[0008] In one embodiment of the motor drive system of this disclosure, the voltage calculation unit calculates the voltage based on the resistance value of the regenerative resistor, the capacitance of the smoothing capacitor, and the predetermined time.

[0009] In one embodiment of this disclosure, the voltage is calculated based on the resistance value of the regenerative resistor, the capacitance of the smoothing capacitor, and the time for which the switching element is made to conduct.

[0010] In a motor drive system according to one embodiment of the present disclosure, the determination unit determines that there is an abnormality if the voltage detected by the voltage detection unit is equal to or greater than a first threshold value based on the voltage calculated by the voltage calculation unit.

[0011] In one embodiment of this disclosure, if the detected voltage is above a first threshold, it is determined that there is an abnormality.

[0012] In one embodiment of the motor drive system of this disclosure, if there is an open fault in the regenerative resistor, the voltage detected by the voltage detection unit is equal to or greater than the first threshold.

[0013] In one embodiment of this disclosure, an open fault in the regenerative resistor is detected.

[0014] In a motor drive system according to one embodiment of the present disclosure, the determination unit determines that there is an abnormality if the voltage detected by the voltage detection unit is less than or equal to a second threshold value based on the voltage calculated by the voltage calculation unit.

[0015] In one embodiment of this disclosure, if the detected voltage is below a second threshold, it is determined that there is an abnormality.

[0016] In a motor drive system according to one embodiment of the present disclosure, the determination unit determines that there is an abnormality if the voltage detected by the voltage detection unit is equal to or greater than a first threshold value based on the voltage calculated by the voltage calculation unit, or if it is equal to or less than a second threshold value which is smaller than the first threshold value based on the voltage calculated by the voltage calculation unit.

[0017] In one embodiment of this disclosure, an abnormality is determined if the detected voltage is above a first threshold or below a second threshold.

[0018] In a motor drive system according to one embodiment of the present disclosure, if the determination unit determines that there is an abnormality, the switching element becomes non-conductive.

[0019] In one embodiment of this disclosure, if the detected voltage is below a second threshold, the switching element is set to a non-conductive state.

[0020] In one embodiment of the motor drive system of this disclosure, when the regenerative resistor is short-circuited, the voltage detected by the voltage detection unit is less than or equal to the second threshold.

[0021] In one embodiment of this disclosure, a short circuit in the regenerative resistor is detected.

[0022] In the motor drive system according to an embodiment of the present disclosure, turning on and off the switching element is repeated a plurality of times such that the total conduction time of the switching element falls within the predetermined time.

[0023] In an embodiment of the present disclosure, turning on and off the switching element is repeated a plurality of times to shorten the conduction time.

[0024] A control method according to an embodiment of the present disclosure is for a motor drive system including: a converter configured to convert alternating-current power to direct-current power; a reactor connected between an alternating-current power source and the converter; two DC buses connected to an output side of the converter; an inverter connected to the two DC buses, configured to convert DC power to AC power and supply the AC power to a motor; a smoothing capacitor with a known capacitance connected between the two DC buses; a regeneration resistor connected between the two DC buses, having a known resistance value and configured to absorb regenerative power; a switching element connected in series with the regeneration resistor and configured to control conduction and non-conduction to the regeneration resistor; and a voltage detector configured to detect a voltage between the two DC buses, the control method comprising: calculating a voltage between the two DC buses obtained when the switching element is kept conducting for a predetermined predetermined time, and determining whether there is an abnormality based on the calculated voltage and the voltage detected by the voltage detector.

[0025] In an embodiment of the present disclosure, the presence or absence of an abnormality is determined based on the voltage detected by an existing voltage detector and the voltage obtained by calculation.

[0026] A computer program according to an embodiment of the present disclosure is a computer program for controlling a motor drive system including: a converter that converts AC power into DC power; a reactor connected between the AC power supply and the converter; two DC buses connected to an output side of the converter; an inverter connected to the two DC buses, which converts DC power into AC power and supplies the AC power to a motor; a smoothing capacitor having a known capacitance connected between the two DC buses; a regenerative resistor connected between the two DC buses, having a known resistance value and absorbing regenerative power; a switching element connected in series with the regenerative resistor and controlling energization and de-energization to the regenerative resistor; and a voltage detection unit that detects a voltage between the two DC buses, wherein the computer program executes a process of calculating a voltage between the two DC buses when the switching element is turned on for a predetermined set period of time, and determining whether there is an abnormality based on the calculated voltage and the voltage detected by the voltage detection unit.

[0027] In an embodiment of the present disclosure, the presence or absence of an abnormality is determined based on the voltage detected by an existing voltage detection unit and the voltage obtained by calculation.

Effect of the Invention

[0028] In the motor drive system, control method, and computer program according to an embodiment of the present disclosure, the presence or absence of an abnormality can be determined while suppressing an increase in manufacturing cost.

Brief Description of Drawings

[0029] [Figure 1] It is a circuit diagram schematically illustrating the motor drive system according to the first embodiment. [Figure 2] It is a graph showing on / off of the switching element and the voltage between the positive bus and the negative bus when no abnormality occurs. [Figure 3] It is a graph showing on / off of the switching element and the voltage between the positive bus and the negative bus when an abnormality caused by an open fault occurs. [Figure 4]This graph shows the on / off state of the switching element and the voltage between the positive and negative busbars when a short-circuit malfunction occurs. [Figure 5] This is a flowchart illustrating the abnormality detection process performed by the control unit. [Figure 6] This is a graph showing the on / off state of the switching element and the voltage between the positive and negative busbars when no abnormality occurs, according to Embodiment 2. [Modes for carrying out the invention]

[0030] (Embodiment 1) The present invention will be described below based on the drawings showing a motor drive system 1 according to Embodiment 1. Figure 1 is a schematic circuit diagram of the motor drive system 1. The motor drive system 1 is connected to the motor 100 and controls the drive of the motor 100. The motor 100 is a three-phase AC motor. The motor 100 has a star-connected U-phase winding, a V-phase winding, and a W-phase winding. When the motor 100 is driven, for example, current flows through each winding with a phase difference of 120° in electrical angle.

[0031] The motor drive system 1 includes a converter 14 that rectifies the current from a three-phase AC power supply 2. The converter 14 converts AC power to DC power. The three-phase AC power supply 2 and the converter 14 are connected via an AC reactor 3. The AC reactor 3 is connected in parallel between the three-phase AC power supply 2 and the converter 14. One end of two DC buses, namely positive bus 5a and negative bus 5b, is connected to the output side of the converter 14. The positive bus 5a and negative bus 5b constitute two DC buses. An inverter 40 is connected to the other ends of the positive bus 5a and negative bus 5b. The inverter 40 converts DC power to AC power and supplies the AC power to the motor 100. A single-phase AC power supply may be used instead of the three-phase AC power supply 2.

[0032] A smoothing capacitor 6 with a known capacitance is connected between the positive busbar 5a and the negative busbar 5b. A voltage detection unit 7 is also connected between the positive busbar 5a and the negative busbar 5b. The voltage detection unit 7 detects the voltage between the positive busbar 5a and the negative busbar 5b. A regenerative resistor 8 with a known resistance value that absorbs regenerative power and a switching element 9 are connected between the positive busbar 5a and the negative busbar 5b. The regenerative resistor 8 and the switching element 9 are connected in series. The regenerative resistor 8 is located on the positive busbar 5a side, and the switching element 9 is located on the negative busbar 5b side. The switching element 9 is, for example, a transistor. The switching element 9 may also be a MOSFET or IGBT or other switching element. Furthermore, a mechanical contact may be used instead of the switching element 9. Note that if the regenerative resistor 8 and the switching element 9 are connected in series, the regenerative resistor 8 may be located on the negative busbar side.

[0033] The motor drive system 1 includes a control unit 10. The control unit 10 includes a control circuit, main memory, auxiliary memory, etc. (none of which are shown). The control circuit includes, for example, a processor or logic circuit. The processor includes, for example, a CPU, MPU, or GPU. The logic circuit includes, for example, an FPGA or ASIC. The main memory includes, for example, RAM. The auxiliary memory includes a rewritable memory, such as an EEPROM, flash ROM, or hard disk. The control circuit may include, for example, multiple processors or logic circuits. The control circuit performs multiple processes, such as various arithmetic and control processes. Multiple processes may be performed by one processor or logic circuit in the control unit circuit, or by multiple processors or logic circuits in the control circuit in a distributed manner. A processor or logic circuit that performs one process and a processor or logic circuit that performs other processes may exist separately.

[0034] The auxiliary storage device stores a control program for controlling the motor 100. The control circuit reads the control program from the auxiliary storage device into the main memory and executes it. The control program may be stored in a storage medium 11, such as an optical disc, flash memory, or hard disk, and downloaded from the storage medium 11 to the auxiliary storage device. Alternatively, it may be downloaded from an external server to the auxiliary storage device via a network (not shown). The processing by the control program may be implemented by a server or terminal connected to the motor drive system 1, or by distributed processing between a server and other devices (e.g., terminals).

[0035] The control unit 10 acquires the voltage detected by the voltage detection unit 7 (hereinafter referred to as the detected value) and stores it in an auxiliary storage device, for example. The detected value indicates the voltage applied to the smoothing capacitor 6, or the voltage applied to the regenerative resistor 8 when the switching element 9 conducts. The control unit 10 outputs a conduction signal or a non-conduction signal to the switching element 9. When the control unit 10 outputs a conduction signal, the switching element 9 conducts, and current can flow through the regenerative resistor 8. When the control unit 10 outputs a non-conduction signal, the switching element 9 does not conduct, and current cannot flow through the regenerative resistor 8. In other words, the switching element 9 controls the energization and de-energization of the regenerative resistor 8. When the detected value exceeds a predetermined threshold, for example a threshold stored in the auxiliary storage device, i.e., when excessive charge has accumulated in the smoothing capacitor 6, the control unit 10 causes the switching element 9 to conduct, releasing the charge from the smoothing capacitor 6. The voltage detection unit 7 is usually provided to determine whether or not excessive charge has accumulated in the smoothing capacitor 6.

[0036] The control unit 10 determines whether or not there is an abnormality in the regenerative resistor 8 based on the detected value. The control unit 10 calculates the voltage between the positive busbar 5a and the negative busbar 5b, i.e., the voltage applied to the regenerative resistor 8, when the switching element 9 is kept conductive for a predetermined time. Hereinafter, the calculated voltage will be referred to as the calculated value. The control unit 10 determines that an abnormality has occurred in the regenerative resistor 8 if the detected value is greater than or equal to a first threshold based on the calculated value, or if it is less than or equal to a second threshold based on the calculated value.

[0037] Figure 2 is a graph showing the on / off state of the switching element 9 and the voltage between the positive busbar 5a and the negative busbar 5b when no abnormality occurs. The upper part of Figure 2 shows the voltage between the positive busbar 5a and the negative busbar 5b, and the lower part of Figure 2 shows the on / off state of the switching element 9. When the control unit 10 outputs a conduction signal, the switching element 9 turns on and conducts. When the control unit 10 outputs a non-conduction signal, the switching element 9 turns off and does not conduct. As shown in the lower part of Figure 2, the switching element 9 is on between time t0 and time t1, and is off before time t0 and after time t1. The time between time t0 and time t1 is a predetermined time Δt. That is, the switching element 9 is on for the predetermined time Δt. The predetermined time Δt is a very small time, during which no current is supplied from the AC power supply 2, or can be considered as not being supplied from the AC power supply 2.

[0038] In the upper part of Figure 2, V0 and V1 are detected values. V0 is the voltage detected immediately before turning on the switching element 9, i.e., the voltage detected at time t0. V1 is the voltage detected at time t1. Time t1 is the time when the switching element 9 is turned off after being turned on. Vp is a calculated value, and is calculated based on, for example, the following equation (1). Vp=V0·exp(-Δt / RC)···(Formula 1) Here, R is the resistance value of the regenerative resistor 8, and C is the capacitance of the smoothing capacitor 6. Vp + α is the first threshold, and Vp - β is the second threshold. The magnitude of the first threshold is greater than the magnitude of Vp, and the magnitude of the second threshold is less than the magnitude of Vp. α and β are pre-stored in auxiliary memory.

[0039] Equation 1 is an equation that shows the voltage across the capacitor, i.e., the smoothing capacitor 6, during discharge in a simple RC series circuit. Equation 1 holds because of the presence of the reactor 3. The reason is as follows: If the reactor 3 is not present, when the switching element 9 is turned on for a small amount of time, i.e., for a predetermined time Δt, current is supplied from the AC power supply 2 to the smoothing capacitor 6 and the regenerative resistor 8 without delay, making it difficult to estimate the bus voltage value. On the other hand, as in this embodiment, when the reactor 3 is present, the change in current is inhibited by the reactor 3, and for a predetermined time Δt, no current is supplied from the AC power supply 2, or if it is supplied, it is only a small current, so it can be considered that no current is supplied from the AC power supply 2. Therefore, the circuit of this embodiment can be approximated as a simple RC series circuit, and equation 1 holds.

[0040] As shown in Figure 2, the detected value V1 at the end of the predetermined time Δt, i.e., at time t1, is smaller than the first threshold and larger than the second threshold. In this case, the control unit 10 determines that no abnormality has occurred in the regenerative resistor 8.

[0041] Figure 3 is a graph showing the on / off state of the switching element 9 and the voltage between the positive busbar 5a and the negative busbar 5b when an abnormality occurs due to an open fault. As shown in the upper part of Figure 3, the detected value V0 at time t0 and the detected value V1 at time t1 are approximately the same. The detected value V1 is greater than or equal to the first threshold Vp + α. In this case, the control unit 10 determines that there is an abnormality in the regenerative resistor 8, more specifically, an abnormality due to an open fault. An open fault refers to a state in which the regenerative resistor 8 is opened, for example, by melting.

[0042] Figure 4 is a graph showing the on / off state of the switching element 9 and the voltage between the positive busbar 5a and the negative busbar 5b when an abnormality occurs due to a short circuit. As shown in the upper part of Figure 4, the detected value V1 at time t1 is less than or equal to the second threshold Vp-β. In this case, the control unit 10 determines that there is an abnormality in the regenerative resistor 8, more specifically, an abnormality due to a short circuit. A short circuit refers to a state in which the regenerative resistor 8 is in contact with, for example, another component in the motor drive system, causing a short circuit.

[0043] Figure 5 is a flowchart illustrating the abnormality detection process by the control unit 10. The control unit 10 acquires the detected value V0 at time t0 (S1) and turns on the switching element 9 for a predetermined time Δt (S2). The control unit 10 acquires the detected value V1 at time t1 (S3). The control unit 10 calculates the voltage Vp (S4). The control unit 10 that executes the process in step S4 constitutes a voltage calculation unit. The control unit 10 determines whether the detected value V1 is greater than or equal to the first threshold Vp + α (S5). If it is determined that the detected value V1 is greater than or equal to the first threshold Vp + α (S5: YES), that is, if it is determined that an abnormality has occurred in the regenerative resistor 8 due to an open fault, the control unit 10 outputs a signal to notify the first error (S7) and terminates the process. In step S7, the control unit 10 outputs a signal to a display unit (not shown) to display information indicating that an open fault has occurred, for example. It may also output a signal to drive a buzzer or a lamp (neither of which are shown).

[0044] If the control unit 10 determines that the detected value V1 is not equal to or greater than the first threshold Vp+α (S5:NO), it determines whether the detected value V1 is equal to or less than the second threshold Vp-β (S6). If the control unit 10 determines that the detected value V1 is equal to or less than the second threshold Vp-β (S6:YES), that is, if it determines that an abnormality has occurred in the regenerative resistor 8 due to a short circuit fault, it outputs a signal to notify the second error (S8). In step S8, the control unit 10 outputs a signal to the display unit to display information indicating that a short circuit fault has occurred, for example. It may also output a signal to drive a buzzer or lamp. The control unit 10 continuously outputs a non-conductive signal, keeping the switching element 9 continuously off (S9), and terminates the process. The control unit 10 that executes the processes in steps S5 and S6 constitutes a determination unit.

[0045] If a short-circuit fault occurs in the regenerative resistor 8, turning on the switching element 9 may cause a large current to flow through it, potentially leading to a failure of the switching element 9. Therefore, in step S9, the switching element 9 is kept continuously off. If an open-circuit fault occurs in the regenerative resistor 8, turning on the switching element 9 will not cause a large current to flow through it, so the process of keeping the switching element 9 continuously off is not performed. However, if an open-circuit fault occurs in the regenerative resistor 8, the process of keeping the switching element 9 continuously off may be performed. If it is determined that the detected value V1 is not below the second threshold Vp-β (S6: NO), that is, if there is no abnormality in the regenerative resistor 8, the control unit 10 terminates the process.

[0046] In the motor drive system 1 according to Embodiment 1, the voltages V0 and V1 are detected using the existing voltage detection unit 7 that detects the voltage of the smoothing capacitor 6, and the presence or absence of an abnormality is determined using the detected voltages V0 and V1. Therefore, the motor drive system 1 can determine the presence or absence of an abnormality while suppressing an increase in manufacturing costs by utilizing the existing configuration.

[0047] Furthermore, the voltage is calculated based on the resistance value of the regenerative resistor 8, the capacitance of the smoothing capacitor 6, and the time for which the switching element 9 is conductive. If the detected voltage is greater than or equal to the first threshold Vp+α, or less than or equal to the second threshold Vp-β, it is determined that there is an abnormality in the regenerative resistor 8. If the detected voltage is less than or equal to the second threshold Vp-β, the switching element 9 is de-conducted.

[0048] (Embodiment 2) The present invention will be described below based on the drawings showing a motor drive system 1 according to Embodiment 2. In the configuration of Embodiment 2, components similar to those in Embodiment 1 are denoted by the same reference numerals, and their detailed descriptions are omitted.

[0049] Figure 6 is a graph showing the on / off state of the switching element 9 and the voltage between the positive busbar 5a and the negative busbar 5b when no abnormality occurs. In Embodiment 2, the switching element 9 is turned on multiple times. For example, as shown in the lower part of Figure 6, the switching element 9 is turned on between time point t0 and time point t2, i.e., for a period of Δt1, and then turned on between time point t3 and time point t1, i.e., for a period of Δt2. Time points t2 and t3 are between time points t0 and t1. Time point t2 is before time point t3. Both Δt1 and Δt2 are shorter than the predetermined time Δt, and the total time of Δt1 and Δt2 is equal to or shorter than the predetermined time Δt.

[0050] As shown in the upper part of Figure 6, V0 is the voltage detected at time t0. V1 is the voltage detected at time t1. V2 is the voltage detected at time t2. The control unit 10 compares the detected value V1 at the time when multiple ON cycles of the switching element 9 have been completed with the first threshold Vp+α and the second threshold Vp-β, and performs abnormality determination processing.

[0051] In the motor drive system 1 according to Embodiment 2, the conduction and deconduction of the switching element 9 are repeated multiple times to shorten the conduction time. Therefore, the load on the switching element 9 can be suppressed.

[0052] Furthermore, computer programs (program products) can be deployed to run on a single computer, located in one site, or distributed across multiple sites and interconnected by a communication network.

[0053] The embodiments disclosed herein should be considered illustrative and not restrictive in all respects. The scope of the present invention is intended to include all modifications within the claims and equivalents thereof. The matters described in each embodiment can be combined with one another. Furthermore, the independent and dependent claims described in the claims can be combined with one another in any combination, regardless of the form of reference. In addition, the claims use a multi-claim format in which claims refer to two or more other claims (multi-claim format), but are not limited thereto. They may also be described using a multi-claim format in which at least one multi-claim refers to another multi-claim (multi-multi-claim format). [Explanation of Symbols]

[0054] 1. Motor drive system 2 Three-phase AC power supply 3 AC reactor 5a Positive bus line 5b negative bus 6. Smoothing Capacitor 7 Voltage detection unit 8th year student resistance 9 Switching elements 10 Control Unit 11 Storage medium 14 Converters 40 Inverters 100 motor

Claims

1. A converter that converts AC power to DC power, A reactor connected between the AC power supply and the converter, Two DC buses connected to the output side of the converter, An inverter connected to the two DC buses converts DC power to AC power and supplies AC power to the motor, A smoothing capacitor with a known capacitance is connected between the two DC buses, In a motor drive system comprising a regenerative resistor connected between the two DC buses, having a known resistance value, and absorbing regenerative power, A switching element connected in series with the regenerative resistor controls the energization and de-energization of the regenerative resistor, A voltage detection unit for detecting the voltage between the two DC buses, A voltage calculation unit that calculates the voltage between the two DC buses when the switching element is kept conductive for a predetermined time, A determination unit determines whether or not there is an abnormality in the motor drive system based on the voltage calculated by the voltage calculation unit and the voltage detected by the voltage detection unit. Equipped with Motor drive system.

2. The voltage calculation unit calculates the voltage based on the resistance value of the regenerative resistor, the capacitance of the smoothing capacitor, and the predetermined time. The motor drive system according to claim 1.

3. The determination unit determines that there is an abnormality if the voltage detected by the voltage detection unit is equal to or greater than a first threshold value based on the voltage calculated by the voltage calculation unit. A motor drive system according to claim 1 or 2.

4. If there is an open fault in the regenerative resistor, the voltage detected by the voltage detection unit is equal to or greater than the first threshold. The motor drive system according to claim 3.

5. The determination unit determines that there is an abnormality if the voltage detected by the voltage detection unit is less than or equal to the second threshold value based on the voltage calculated by the voltage calculation unit. A motor drive system according to claim 1 or 2.

6. The determination unit determines that there is an abnormality if the voltage detected by the voltage detection unit is equal to or greater than a first threshold based on the voltage calculated by the voltage calculation unit, or if it is equal to or less than a second threshold that is smaller than the first threshold based on the voltage calculated by the voltage calculation unit. A motor drive system according to claim 1 or 2.

7. If the determination unit determines that there is an abnormality, the switching element will enter a non-conductive state. The motor drive system according to claim 5.

8. If the regenerative resistor is short-circuited, the voltage detected by the voltage detection unit is less than or equal to the second threshold. The motor drive system according to claim 7.

9. The conduction and deconduction of the switching element are repeated multiple times such that the total conduction time of the switching element falls within the predetermined time. A motor drive system according to claim 1 or 2.

10. A converter that converts AC power to DC power, A reactor connected between the AC power supply and the converter, Two DC buses connected to the output side of the converter, An inverter connected to the two DC buses converts DC power to AC power and supplies AC power to the motor, A smoothing capacitor with a known capacitance is connected between the two DC buses, A regenerative resistor is connected between the two DC buses, has a known resistance value, and absorbs regenerative power. A switching element connected in series with the regenerative resistor controls the energization and de-energization of the regenerative resistor, A voltage detection unit that detects the voltage between the two DC buses. A control method for a motor drive system including, The voltage between the two DC buses is calculated when the switching element is kept conductive for a predetermined time. Based on the calculated voltage and the voltage detected by the voltage detection unit, the presence or absence of an abnormality is determined. Control method.

11. A converter that converts AC power to DC power, A reactor connected between the AC power supply and the converter, Two DC buses connected to the output side of the converter, An inverter connected to the two DC buses converts DC power to AC power and supplies AC power to the motor, A smoothing capacitor with a known capacitance is connected between the two DC buses, A regenerative resistor is connected between the two DC buses, has a known resistance value, and absorbs regenerative power. A switching element connected in series with the regenerative resistor controls the energization and de-energization of the regenerative resistor, A voltage detection unit that detects the voltage between the two DC buses. A computer program that controls a motor drive system, including The voltage between the two DC buses is calculated when the switching element is kept conductive for a predetermined time. Based on the calculated voltage and the voltage detected by the voltage detection unit, the presence or absence of an abnormality is determined. A computer program that performs a process.

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