Motor control device and motor drive system

Abstract

To achieve stabilization of output of an electric motor driving system by suppressing fluctuations in an output current of an inverter circuit and a torque of an electric motor due to fluctuations in a power supply voltage of the inverter circuit.SOLUTION: On the basis of a gradient of a power supply voltage, an output command for each phase is corrected so that fluctuations in a torque of an electric motor becomes less. Specifically, means for controlling switching of an inverter circuit comprises: output command calculation means for calculating an output command value for driving an AC electric motor; voltage gradient calculation means for calculating a gradient of the power supply voltage; and output command correction means for correcting the output command value by an amount of correction that suppresses the fluctuations in the torque of the AC electric motor according to the gradient of the voltage calculated by the voltage gradient calculation means.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application relates to a motor control device and a motor drive system.

Background Art

[0002] As motor control devices and motor drive systems for converting the output form of electric power, an AC / DC converter (Alternate Current / Direct Current Converter) that converts alternating current power into direct current power, an inverter that converts direct current power into alternating current power, etc. are common. These motor control devices and motor drive systems are known to have a configuration including semiconductor switching elements.

[0003] Here, the motor control device and the motor drive system are composed of a DC power supply, a capacitor, and a plurality of semiconductor switches, and include an inverter circuit connected to the DC power supply and an AC motor connected to the inverter circuit as a load. In particular, as the power supply of the drive system of an electric vehicle, it often consists of a lithium-ion battery and a system with a boost converter via lithium ions.

[0004] The inverter circuit converts the DC power of the DC power supply into AC power by turning on and off a plurality of semiconductor switches at a predetermined switching frequency, and adjusts the torque and rotational speed of the AC motor as the load. Further, the AC motor operates as a generator depending on the operating conditions, and charges the regenerative power generated by power generation into the DC power supply. Note that, as the AC motor applied to an electric vehicle, an efficient permanent magnet three-phase synchronous motor is often used.

[0005] In a drive system using a three-phase synchronous motor, the inverter circuit is configured such that three sets of series circuits in which an upper-stage switching element and a lower-stage switching element are connected in series are each connected in parallel to the DC power supply, and the midpoint of each of the three sets of series circuits and the input of each of the u-phase, v-phase, and w-phase of the three-phase synchronous motor are connected.

[0006] Furthermore, by sequentially switching on and off the switching elements provided in each phase of the inverter circuit, AC power with a phase difference of 120 degrees is supplied to each phase of the three-phase synchronous motor, thereby driving the three-phase synchronous motor. Hereafter, unless otherwise specified, "motor" refers to a three-phase synchronous motor. The operating principle of the inverter circuit is generally well known, so an explanation will be omitted here. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-104708 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] As mentioned above, the motor control device drives the motor by supplying power voltage from an external source. However, if the operation of the power supply voltage is unstable, the supplied voltage will also become unstable. In this case, the output current of the inverter will decrease sharply, causing the motor's torque to fluctuate and decrease sharply as well.

[0009] One way to suppress such torque fluctuations is to connect a smoothing capacitor between the input power supply and the drive system, and increase the capacitance of the smoothing capacitor to suppress fluctuations in the power supply voltage. However, increasing the capacitance of the smoothing capacitor presents challenges in terms of increasing the size, weight, and cost of the drive system.

[0010] To address these issues, a method is known in which the power supply voltage of the drive system fluctuates rapidly, and when the power supply voltage exceeds a predetermined threshold over a certain period, a correction range is calculated from the power supply voltage fluctuation range / reference voltage correction range, and the current limiting reference voltage is corrected to be lower than the normal value in order to limit the output current of the inverter (see, for example, Patent Document 1).

[0011] However, limiting the output current may reduce the torque of the motor. Specifically, in Patent Document 1, when the power supply voltage exceeds a predetermined threshold at a certain period, a correction range is calculated and the current limiting reference voltage is corrected to be lower than the normal value. At this time, by lowering the current limiting reference voltage to be lower than the normal value, the output current of the inverter is limited so that the voltage command is reduced, and the output current of the inverter falls below the normal value. As a result, the problem arises that the torque of the motor falls below the normal value.

[0012] This invention was made to solve the problems described above, and it is possible to reduce fluctuations in the torque of the electric motor and achieve stable operation of the electric motor. [Means for solving the problem]

[0013] The motor control device disclosed herein is connected between a DC power supply and an AC motor, and drives and controls the AC motor by converting the DC power of the DC power supply into AC power, and comprises a power conversion circuit having a switching element for converting DC power into AC power, and a switching control means for controlling the on and off of the switching element, wherein the switching control means comprises an output command calculation means for calculating an output command value for driving the AC motor, a voltage slope calculation means for calculating the slope of the voltage of the DC power supply, and an output command correction means for calculating a correction amount to suppress torque fluctuations of the AC motor according to the voltage slope calculated by the voltage slope calculation means, and correcting the output command value with this correction amount. Furthermore, the AC motor is a three-phase AC motor, and is further equipped with a current detection unit that detects the current flowing through each phase of the three-phase AC motor from the power conversion circuit, and when the voltage of the DC power supply increases, the output command value of the phase with the highest current amplitude among the currents flowing through each phase is corrected by a first correction amount, and the output command values ​​of the other phases are corrected by a second correction amount which is half of the first correction amount. It is characterized by the following: [Effects of the Invention]

[0014] According to the motor control device disclosed herein, the torque fluctuation of the motor can be reduced and stable motor operation can be achieved by correcting the output command value with a correction amount that suppresses torque fluctuations of the AC motor in accordance with the slope of the power supply voltage. [Brief explanation of the drawing]

[0015] [Figure 1] It is a block diagram showing the configuration of an electric motor drive system equipped with the electric motor control device according to Embodiment 1. [Figure 2] It is a diagram for explaining an example of the hardware of the switching control means of the electric motor control device according to Embodiment 1. [Figure 3] It is a block diagram for explaining the function of the voltage gradient calculation means of the electric motor control device according to Embodiment 1. [Figure 4] It is a block diagram for explaining the function of the output command calculation means of the electric motor control device according to Embodiment 1. [Figure 5] It is a block diagram for explaining the function of the output command correction means of the electric motor control device according to Embodiment 1. [Figure 6] It is a flowchart for explaining the operation of the output command correction means of the electric motor control device according to Embodiment 1. [Figure 7] It is a timing chart for explaining the time-series changes of the power supply voltage, each-phase current, and each-phase voltage command correction amount of the electric motor control device according to Embodiment 1. [Figure 8] It is a diagram for explaining the effect of the electric motor control device according to Embodiment 1. [Figure 9] It is a flowchart for explaining the operation of the output command correction means of the electric control device according to Embodiment 2. [Figure 10] It is a timing chart for explaining the time-series changes of the power supply voltage, each-phase current, and each-phase voltage command correction amount of the electric motor control device according to Embodiment 2. [Figure 11] It is a diagram for explaining the effect of the electric motor control device according to Embodiment 2. [Figure 12] It is a block diagram for explaining the function of the output command correction means of the electric motor control device according to Embodiment 3. [Figure 13] It is a flowchart for explaining the operation of the output command correction means of the electric motor control device according to Embodiment 3. [Figure 14]It is a timing chart for explaining the time-series changes in the power supply voltage, each-phase voltage command value, and each-phase voltage command correction amount of the motor control device according to Embodiment 3. [Figure 15] It is a diagram for explaining the effect of the motor control device according to Embodiment 3. [Figure 16] It is a flowchart for explaining the operation of the output command correction means of the motor control device according to Embodiment 4. [Figure 17] It is a timing chart for explaining the time-series changes in the power supply voltage, each-phase voltage command value, and each-phase voltage command correction amount of the motor control device according to Embodiment 4. [Figure 18] It is a diagram for explaining the effect of the motor control device according to Embodiment 4. [Figure 19] It is a diagram for explaining the relationship between the slope of the power supply voltage and the correction amount according to Embodiment 5. [Figure 20] It is a diagram for explaining the relationship between the slope of the power supply voltage and the correction amount according to Embodiment 5.

Embodiments for Carrying out the Invention

[0016] Hereinafter, preferred embodiments of the motor control device and the motor drive system according to the present application will be described with reference to the drawings. For the same or corresponding parts in each figure, the same reference numerals are given, and detailed descriptions thereof are omitted. Similarly, in the following embodiments, duplicate descriptions for the configurations with the same reference numerals are omitted. will be described.

[0017] Generally, a motor converts electric power into driving force and performs power running operation. However, it is also possible to reverse-convert the driving force into electric power and perform regeneration operation with the same structure. Further, a generator, also called a dynamo, converts driving force into electric power and performs regeneration operation. However, it is also possible to reverse-convert electric power into driving force and perform power running operation with the same structure. That is, a motor and a generator basically have the same structure, and both can perform power running operation and regeneration operation. Therefore, in this specification, a rotating electrical machine having both functions of a motor and a generator is simply referred to as a motor.

[0018] Embodiment 1. The configuration and operation of the motor control device 1 according to Embodiment 1 will be explained using Figure 1. The motor control device 1 is connected to a DC power supply 90 via a power switch 70, with DC buses 21a and 21b connected to the DC power supply 90, and driving power or regenerative power is exchanged with the DC power supply 90. The motor control device 1 is also connected to the motor 10 via an AC bus 2, and driving power or regenerative power is exchanged with the motor 10.

[0019] Furthermore, the electric motor 10 is equipped with a temperature detection unit 50 (hereinafter referred to as the temperature sensor 50) for detecting the temperature of the permanent magnets of the electric motor 10, and a rotational speed detection unit 60 (hereinafter referred to as the rotational angle sensor 60) for detecting the rotational speed from the rotational angle of the rotor of the electric motor 10. The electric motor 10 is capable of rotating the load and regenerating the rotational energy of the load as electrical energy. Three-phase brushless motors, including permanent magnet three-phase AC synchronous motors, are used.

[0020] The motor control device 1 consists of an inverter circuit 20 and a switching control means 40. The inverter circuit 20 includes a capacitor 22 connected between the DC buses 21a and 21b on the power input side, a voltage detection means 23 for detecting the voltage between the DC buses 21a and 21b of the inverter circuit 20, a power conversion circuit 30 configured by full-bridge connection of switching elements 31 to 36 to perform power conversion from DC to AC or AC to DC, and a current detection unit 24 for detecting the current flowing through the AC bus 2 of the motor 10.

[0021] Capacitor 22 has the function of suppressing ripple in the DC bus voltage, the function of lowering the power supply impedance of the inverter circuit 20 to improve the AC current driving capability of the inverter circuit 20, or the function of absorbing surge voltage.

[0022] Furthermore, the voltage detection means 23 divides the voltage between DC buses 21a and 21b, for example, using a voltage divider resistor to obtain voltages that can be read by the switching control means 40, and outputs DC bus voltage information to the switching control means 40.

[0023] As shown in Figure 1, the power conversion circuit 30 has switching elements 31 and 32, switching elements 33 and 34, and switching elements 35 and 36 connected in series to each other to form an arm, which is connected in parallel to the DC power supply 90. The midpoint of switching element 31 and switching element 32 is connected to the u-phase input of the motor 10, the midpoint of switching element 33 and switching element 34 is connected to the v-phase input of the motor 10, and the midpoint of switching element 35 and switching element 36 is connected to the w-phase input of the motor 10. Here, the switching elements 31, 33, and 35 connected to the positive side of the DC power supply 90, i.e., the DC bus 21a, are referred to as the upper-stage switching elements, and the switching elements 32, 34, and 36 connected to the negative side of the DC power supply 90, i.e., the DC bus 21b, are referred to as the lower-stage switching elements.

[0024] Switching elements 31 to 36 are turned on and off by on and off control signals from a switching control signal generation means 41 (described later), converting DC power to AC power and supplying it to the motor 10, and charging the DC power supply 90 with regenerative power generated when the motor 10 is in a regenerative state.

[0025] As the switching element, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) as shown in Figure 2 may be used, or an IGBT (Insulated Gate Bipolar Transistor) may be used. In addition, a free-wheeling diode (FWD) is provided in parallel with each of the MOSFETs from switching elements 31 to 36, with the forward direction being from the negative terminal side to the positive terminal side of the DC power supply 90, that is, from the lower stage side to the upper stage side.

[0026] The current detection unit 24 detects the motor current flowing through the AC bus 2, converts the current into a voltage, and outputs the motor current information to the switching control means 40. Figure 1 shows, as an example, a configuration in which the current is detected by a shunt resistor. The current detection unit 24 may also be a current sensor using a Hall element.

[0027] The rotation angle sensor 60 detects the rotation angle of the rotor of the electric motor 10, such as a resolver or encoder. The rotation angle of the rotor detected by the rotation angle sensor 60 is output to the switching control means 40, where it is used as the rotation speed.

[0028] The temperature sensor 50 is configured, for example, by a thermistor and detects the temperature of the permanent magnet of the electric motor 10. The detected temperature of the permanent magnet is output to the switching control means 40. Alternatively, the temperature sensor may be configured by a device that detects or estimates the winding temperature instead of detecting the temperature of the permanent magnet.

[0029] The switching control means 40 is responsible for the overall control of the motor control device 1 and is composed of a drive circuit including a microcontroller, and includes a switching control signal generation means 41, a voltage slope calculation means 42, an output command calculation means 44, an output command correction means 45, and a current detection means 43. Each of these means may be partially implemented by dedicated hardware and partially by software or firmware. An example of the microcontroller hardware within the switching control means 40 is shown in Figure 2. It consists of a processor 150 and a storage device 200. Although not shown, the storage device includes a volatile storage device such as random access memory and a non-volatile auxiliary storage device such as flash memory. Alternatively, an auxiliary storage device such as a hard disk may be provided instead of flash memory. The processor 150 performs the functions of the switching control signal generation means 41, voltage slope calculation means 42, current detection means 43, output command calculation means 44, and output command correction means 45, which are described below, by executing a program input from the storage device 200. In this case, the program is input from the auxiliary storage device to the processor 150 via the volatile storage device. Furthermore, the processor 150 may output data such as calculation results to the volatile memory of the storage device 200, or it may save the data to the auxiliary storage device via the volatile memory.

[0030] The switching control signal generation means 41 generates on and off control signals to control the on and off states of the multiple switching elements 31 to 36 that constitute the power conversion circuit 30. As shown in Figure 1, the switching control signal generation means 41 generates on / off control signals for each switching element 31 to 36 of the power conversion circuit 30 according to the following information (1) to (4) from the voltage detection means 23 (DC bus voltage information), (2) the rotation angle information (rotation speed) of the motor 10 from the rotation angle sensor 60 (motor current information), (3) the current detection unit 24 (motor current information), and (4) the output from the output command correction means 45, and outputs on / off control signals to the power conversion circuit 30.

[0031] The voltage slope calculation means 42 calculates the slope of the power supply voltage detected by the voltage detection means 23. For example, as shown in Figure 3, the detected power supply voltage value is stored in the detection value holding unit 421, and the voltage slope calculation unit 422 calculates the slope of the power supply voltage using the previously stored detection value and the current detection value.

[0032] The slope of the power supply voltage can be calculated using the following method, as an example. • Power supply voltage slope = (Currently detected power supply voltage - Previously detected power supply voltage) / Detection time • Power supply voltage slope = (Currently detected power supply voltage - Previously detected power supply voltage) / Currently detected power supply voltage • Power supply voltage slope = (Currently detected power supply voltage - Previously detected power supply voltage) / Previously detected power supply voltage • Power supply voltage slope = (Currently detected power supply voltage - Previously detected power supply voltage) / Nominal voltage

[0033] The current detection means 43 performs a 3-phase / dq conversion from the output result of the current detection unit 24, using the detected current values ​​iu, iv, and iw flowing through the motor 10 and the motor angle θ detected by the rotation angle sensor 60, and outputs the d-axis current detection value id and the q-axis current detection value iq.

[0034] As shown in Figure 4, the output command calculation means 44 compares the d-axis current command value id* provided by the higher-level control device with the d-axis current detection value id detected by the current detection means 43 in the d-axis current control unit 441 to calculate the d-axis voltage command value vd*. Similarly, the q-axis current command value iq* with the q-axis current detection value iq calculated by the current detection means 43 in the q-axis current control unit 442 to calculate the q-axis voltage command value vq*. The calculated d-axis voltage command value vd*, q-axis voltage command value vq*, and rotational position information of the motor 10 are input to the 2-phase 3-phase conversion unit 443, and the voltage command values ​​Vuc*, Vvc*, and Vwc* of the u-phase, v-phase, and w-phase windings constituting the motor 10 are output.

[0035] As shown in Figure 5, the output command correction means 45 takes as input the power supply voltage slope calculated by the voltage slope calculation means 42, the voltage command values ​​Vuc*, Vvc*, and Vwc* for the u-phase, v-phase, and w-phase respectively, and the detected current values ​​iu, iv, and iw for the u-phase, v-phase, and w-phase respectively detected by the current detection unit 24, and outputs a corrected voltage command value for each of the three phases.

[0036] The operation of the output command correction means 45 will be explained based on Figures 6 and 7. Figure 6 is a flowchart illustrating the operation of the output command correction means 45, and Figure 7 is a timing chart illustrating the time-series changes in the power supply voltage, each phase current, and each phase voltage command correction amount.

[0037] The voltage detection means 23 is equipped with a filter such as a low-pass filter to remove noise generated by the operation of the inverter circuit 20. However, due to the effect of the low-pass filter, a detection delay occurs, and when the power supply voltage increases, the reflection of the power supply voltage information used to generate the output voltage command value of the inverter circuit 20 is delayed, resulting in the output of a voltage larger than the commanded voltage value (step S1 in Figure 6), which can cause the output current to become larger than normal and the output torque to fluctuate in an upward direction.

[0038] In response to such an increase in power supply voltage, the slope of the power supply voltage is detected. Based on the detected slope of the power supply voltage, if the power supply voltage is increasing (Step S1 in Figure 6), the inverter circuit 20 that controls the three phases utilizes the proportional relationship where, when the current of one of the three phases is at its peak, the magnitude of the current of the other phases becomes -1 / 2 times. This allows the phase with the highest current amplitude to be identified (Steps S2-S3, P, Q, R in Figure 7), a correction amount ΔAdd is calculated (Step S7), and the voltage command value of the identified phase (Steps S4-S6 in Figure 6) is corrected by the correction amount ΔAdd (Step S8 in Figure 6, ΔAdd in Figure 7). Then, the voltage command values ​​of the other phases, excluding the phase with the highest current amplitude, are corrected by -1 / 2 × ΔAdd (Step S9 in Figure 6, ΔAdd × 0.5 in Figure 7). This suppresses the increase in the current amplitude of each phase, thereby suppressing the torque fluctuation of the motor 10. Therefore, a motor drive system can be obtained that operates stably without fluctuations in the torque of the motor 10. Note that if the power supply voltage does not increase, the voltage command value is not corrected (step S10).

[0039] The correction amount ΔAdd described above is for suppressing torque fluctuations and is calculated by the output command correction means 45 by taking into account the slope of the power supply voltage, the ratio of the current value to the nominal current value of the phase with the largest absolute value of the phase current, the ratio of the voltage command value to the nominal voltage value of the phase with the largest absolute value of the phase current, and a correction coefficient, or a combination thereof. When the slope of the power supply voltage is large, and when the difference between the detected current values ​​iu, iv, iw and the command current is large, the amount of fluctuation in output current and the amount of torque fluctuation of the motor 10 are large, so the correction amount ΔAdd of the voltage command value is increased. The correction coefficient corrects the error between the output voltage command value and the voltage actually applied to the motor 10 due to detection delay, control delay, and parameter errors present in the inverter circuit 20. By using the calculation method performed by this output command correction means 45, it is possible to suppress the torque fluctuation of the motor 10 due to fluctuations in the power supply voltage according to the slope of the power supply voltage, and a motor drive system with stable operation in which the output torque does not fluctuate can be obtained.

[0040] To illustrate with a specific example, the correction amount ΔAdd is calculated based on the slope vmove of the power supply voltage, the ratio of the current value iphase and the nominal current value imax* of the phase with the largest absolute current, the ratio of the voltage command value vphase* and the nominal voltage value vmax* of the phase with the largest absolute current, the actual device correction coefficient K_c for more accurate operation, and the previous voltage detection value vdet(z-1) and the current voltage detection value vdet(z). For example, it is calculated as shown in equation (1) below. However, equation (1) is just one example and is not the only way to calculate it.

[0041] ΔAdd = vmove × iphase / imax* × vphase* / vmax* × K_c··(1) ΔAdd: Voltage command correction amount vmove: Power supply voltage slope iphase: The current value of the phase with the largest absolute value of phase current. imax*: Nominal current value (rated maximum value) vphase*: Voltage command value of the phase with the largest absolute value of phase current. vmax*:: Nominal voltage value (rated maximum value) K_c: Coefficient for adjusting on actual machine (1 if no adjustment is needed) Here, we use the formula vmove = vdet(z) - vdet(z-1) / vdet(z), but as mentioned above, other methods for calculating the slope of the power supply voltage may also be used.

[0042] The aforementioned power supply voltage increase detection may also involve setting a power supply voltage slope threshold. During normal operation, the operation of the inverter circuit 20 may cause voltage ripple at the power supply voltage terminal, potentially leading to a false detection by the voltage detection means 23 that the slope has fluctuated. To eliminate such false detections and prevent excessive suppression of the motor 10's torque, a power supply voltage slope threshold is set to distinguish between slope fluctuations due to an increase in power supply voltage during normal operation and slope fluctuations due to false detection when voltage ripple occurs. For example, the voltage ripple at the power supply voltage terminal can be measured in advance, and this value can be used as the power supply voltage slope threshold. This makes it possible to obtain a motor drive system that can operate stably without falsely detecting voltage ripple that occurs during normal operation.

[0043] Furthermore, the correction amount ΔAdd of the voltage command value may be adjusted based on the temperature information from the temperature sensor 50. When the temperature of the motor 10 is high, the electrical resistance component on the load side of the motor drive system 100 is large, so the current and torque fluctuations of the motor 10 due to fluctuations in the power supply voltage become smaller. Therefore, when the temperature of the motor 10 is high, the correction amount ΔAdd of the voltage command value is set low, and when the temperature of the motor is low, the correction amount ΔAdd of the voltage command value is set high. By using this method, a more appropriate correction amount can be calculated according to the state of the motor drive system 100, and a motor drive system 100 that can operate stably by suppressing torque fluctuations more appropriately can be obtained.

[0044] As a result, the target motor torque or target current of the motor 10 is input to the switching control means 40 via CAN (Controller Area Network) from other control devices, including a vehicle ECU (not shown). Using the voltage information of the DC buses 21a and 21b input from the voltage detection means 23, the rotation angle information of the motor 10 input from the rotation angle sensor 60, and the motor current information input from the current detection unit 24, current feedback control is performed to calculate on / off control signals for each switching element 31 to 36 of the power conversion circuit 30 so that an appropriate target motor torque or target current of the motor 10 can be obtained, and on / off control signals are output to the power conversion circuit 30. Note that current feedback control is well known, so a detailed explanation is omitted here.

[0045] The type of semiconductor used for the switching elements 31 to 36 applied to the power conversion circuit 30 is not particularly limited, but for example, a wide-bandgap semiconductor can be used. As a wide-bandgap semiconductor element, for example, one made of silicon carbide (SiC), gallium nitride (GaN)-based material, or diamond (C) can be used.

[0046] An inverter circuit 20 composed of switching elements formed from such wide-bandgap semiconductors has the characteristics of high voltage resistance, low loss, and high-frequency driving compared to an inverter circuit composed of switching elements formed from conventional silicon (Si). Hereinafter, an inverter circuit composed of switching elements formed from wide-bandgap semiconductors will be referred to as a wide-bandgap inverter circuit, and an inverter circuit composed of switching elements formed from silicon (Si) will be referred to as a silicon inverter circuit.

[0047] Therefore, in an electric motor control device using a wide-bandgap inverter circuit, the switching speed of the switching elements is higher compared to an electric motor control device using a silicon inverter circuit. This allows for a higher switching speed and enables the fast and accurate execution of output commands. The above-mentioned effects can also be obtained in embodiments 2 to 4 described below by using wide-bandgap semiconductors.

[0048] <Effects when applying Embodiment 1> Figures 8(a) and 8(b) illustrate the effects of applying Embodiment 1. Figure 8(a) shows a comparative example without using the control of Embodiment 1, while Figure 8(b) shows the case with the control of Embodiment 1. In Figure 8(a), the voltage command correction amount for each phase is zero, but as shown in Figure 8(b), an increase in the power supply voltage is detected, and the voltage command value of the phase with the highest current amplitude is corrected by a correction amount ΔAdd to reduce the current amplitude, and the voltage command values ​​of the other phases are corrected by a correction amount of -1 / 2 × ΔAdd. This utilizes the fact that in the 3-phase inverter circuit 20, when the current of one phase peaks, the magnitude of the other phases becomes -1 / 2, thereby suppressing the current amplitude of each phase. Furthermore, by increasing the correction amount ΔAdd of the voltage command value when the slope of the power supply voltage is large, the effect of suppressing the increase in output current caused by the increase in power supply voltage can be obtained, and the increase in motor torque can be suppressed. As a result, a motor drive system that performs stably can be obtained.

[0049] Embodiment 2. The configuration and operation of the rotating electric machine control device according to Embodiment 2 will be described below, focusing on the differences between Embodiment 1 and Embodiment 2, based on Figures 9 to 11. Parts identical or corresponding to those in Embodiment 1 are denoted by the same reference numerals.

[0050] The operation of Embodiment 2 will be explained based on Figures 9 and 10. Figure 9 is a flowchart illustrating the operation of the output command correction means 45, and Figure 10 is a timing chart illustrating the time-series changes in the power supply voltage, each phase current, and each phase voltage command correction amount. The output command correction means of Embodiment 2 compares the current information of each phase with a predetermined current threshold (steps S11, S12, S13 in Figure 9, and S, T, U in Figure 10), determines the voltage command value of the phase that exceeds the current threshold (steps S14, S15, S16 in Figure 9), calculates the correction amount ΔAdd (step S7), and corrects the voltage command value of the determined phase by the correction amount ΔAdd (step S8 in Figure 9, and ΔAdd in Figure 10). Then, the voltage command values ​​of the other phases that do not exceed the current threshold are corrected by -1 / 2 × ΔAdd (step S9 in Figure 9, and ΔAdd × 0.5 in Figure 10), thereby suppressing the increase in the current amplitude of each phase and achieving the effect of suppressing torque fluctuations of the motor 10. This suppresses the increase in the current amplitude of each phase, thereby suppressing torque fluctuations of the motor 10. As a result, a motor drive system can be obtained that operates stably without fluctuations in the torque of the motor 10. Note that if the power supply voltage does not increase, the voltage command value is not corrected (step S10).

[0051] The current threshold may be set to be greater than or equal to the sum of the rated current of the inverter circuit 20 and the current ripple generated during the operation of the inverter circuit 20, and less than or equal to the overcurrent (OC) threshold. By using this current threshold for control, when the power supply voltage is fluctuating, the current remains within the normal operating current range, and there is no need to suppress the current. Therefore, the output current is not excessively suppressed, and a stable motor drive system can be obtained.

[0052] Furthermore, the current threshold can be made variable. For example, by using the command current as the threshold current, the limiting operation is performed only when it exceeds the command value. This allows for a stable motor drive system that does not misdetect the normal operating state where the motor is operating according to the command value.

[0053] <Effects when applying Embodiment 2> Figures 11(a) and 11(b) illustrate the effects of applying Embodiment 2. Figure 11(a) shows a comparative example without using the control of Embodiment 2, while Figure 11(b) shows the case with the control of Embodiment 2. In Figure 11(a), the voltage command correction amount for each phase is zero, but as shown in Figure 11(b), an increase in the power supply voltage is detected and corrected by a correction amount ΔAdd to reduce the current amplitude, and the voltage command values ​​of the other phases are corrected by a correction amount of -1 / 2 × ΔAdd. As a result, not only is there no fluctuation in the output current of the inverter circuit 20 even when the power supply voltage fluctuates, but if there is no fluctuation in the motor torque, a motor drive system can be obtained that can operate stably without excessively limiting the output torque of the motor.

[0054] Embodiment 3. The configuration and operation of the rotating electric machine control device according to Embodiment 3 will be described below, focusing on the differences between Embodiment 1 and Embodiment 3, based on Figures 12 to 15. Parts identical or corresponding to those in Embodiment 1 are denoted by the same reference numerals.

[0055] Based on Figure 12, the input and output elements of the output command correction means 45 of Embodiment 3 will be described. Embodiment 3, like Embodiment 1, uses the slope of the power supply voltage and the voltage command values ​​Vuc*, Vvc*, and Vwc* for the u-phase, v-phase, and w-phase, respectively, as inputs. However, it differs in that the detected current values ​​iu, iv, and iw for the u-phase, v-phase, and w-phase, respectively, detected by the motor current detection unit 24, are not required, and voltage commands are used for the phases used to calculate the correction amount.

[0056] The operation of Embodiment 3 will be explained based on Figures 13 and 14. Figure 13 is a flowchart illustrating the operation of the output command correction means 45, and Figure 14 is a timing chart illustrating the time-series changes in the power supply voltage, each phase voltage command value, and each phase voltage command correction amount. The output command correction means of Embodiment 3 pre-sets a determination range for the voltage command value from the respective voltage command values ​​Vuc*, Vvc*, and Vwc* of the u-phase, v-phase, and w-phase (see "Voltage Command Determination Range" in Figure 14), and determines whether the magnitude of the voltage command value is within the determination range of the voltage command value (steps S17, S18, and S19 in Figure 13). It extracts the phases whose voltage command value is within the determination range of the voltage command value (steps S20, S21, and S22 in Figure 13), calculates the correction amount ΔAdd (step S7), and corrects the voltage command value of the determined phase with the correction amount ΔAdd (step S8 in Figure 13, and ΔAdd in Figure 14). Then, by correcting the phases outside the voltage command value's judgment range by -1 / 2 × ΔAdd (in Figure 13, step S9; in Figure 14, ΔAdd × 0.5), the increase in the current amplitude of each phase can be suppressed, thereby suppressing torque fluctuations of the motor 10. As a result, a motor drive system that operates stably without fluctuations in the torque of the motor 10 can be obtained. Furthermore, a motor drive system that is compact, low-cost, and operates stably can be obtained without using a current sensor. Note that if the power supply voltage is not increasing, the voltage command value is not corrected (step S10).

[0057] The voltage command value determination range is set so that the phase with the peak current can be extracted from the three phases based on the relationship between the power factor, phase voltage, and phase current. For example, when the power factor is 1, the command value of the phase voltage is considered as the phase voltage, and the current of the phase whose amplitude is between -1 / 2 and 1 / 2 times the peak value will be at its peak. The relationship between the power factor, phase voltage, and phase current is a well-known technique and will not be explained here. By using the above means, the current amplitudes of different phases can be corrected to be reduced, and current fluctuations and motor torque fluctuations accompanying increases in power supply voltage can be suppressed without excessively suppressing the motor torque, thereby obtaining a motor drive system that can operate stably.

[0058] <Effects when applying Embodiment 3> Figures 15(a) and 15(b) illustrate the effects of applying Embodiment 3. Figure 15(a) shows a comparative example without using the control of Embodiment 3, while Figure 15(b) shows the case with the control of Embodiment 3. In Figure 15(a), the voltage command correction amount for each phase is zero, but as shown in Figure 15(b), the relationship between phase voltage, phase current, and power factor is used to consider the phase voltage command value as the phase voltage, and the determination range of the voltage command value is set so that the phase where the phase current is at its peak can be extracted. Phases within the determination range of the voltage command value are corrected by a correction amount ΔAdd of the voltage command value, and the voltage command values ​​of the other phases are corrected by a correction amount of -1 / 2 × ΔAdd. As a result, a compact, low-cost, and stable motor drive system can be obtained without using a current sensor.

[0059] Embodiment 4 The configuration and operation of the rotating electric machine control device according to Embodiment 4 will be described below, focusing on the differences between Embodiment 1 and Embodiment 4, based on Figures 16 to 18. Parts identical or corresponding to those in Embodiment 1 are denoted by the same reference numerals.

[0060] The operation of Embodiment 4 will be explained based on Figures 16 and 17. The difference from Embodiment 1 is that when the power supply voltage decreases, a correction is made to increase the current amplitude. Figure 16 is a flowchart explaining the operation of the output command correction means 45, and Figure 17 is a timing chart explaining the time-series changes in the power supply voltage, each phase voltage command value, and each phase voltage command correction amount. In Embodiment 3, when the power supply voltage decreases, the output command correction means corrects the voltage command value of the phase with the largest voltage command value by a correction amount ΔAdd, and corrects the voltage command values ​​of the other phases by -1 / 2 × ΔAdd, thereby suppressing fluctuations in the output current of the inverter circuit 20 and the torque of the motor that occur with a decrease in power supply voltage, and a motor drive system that can operate stably can be obtained.

[0061] The voltage detection means 23 is equipped with a filter, such as a low-pass filter, to remove noise generated by the operation of the inverter circuit 20. However, due to the effect of the low-pass filter, a detection delay occurs, and when the power supply voltage decreases, the power supply voltage information used to generate the output voltage command value of the inverter circuit 20 is not reflected. As a result, the actual output voltage becomes smaller than the command voltage value, and the output current becomes smaller than normal, which can cause the output torque to fluctuate in a downward direction.

[0062] In response to such power supply voltage reduction events, the slope of the power supply voltage is detected. Based on the detected slope of the power supply voltage, if the power supply voltage is decreasing (step S23 in Figure 16), the voltage command value of the phase with the highest voltage command value is determined (steps S24, 25, A, B, C in Figure 17) by utilizing the proportional relationship where the magnitude of the current in the other phases becomes -1 / 2 when the current in one of the three phases reaches its peak (steps S24, 25, A, B, C in Figure 17), and a correction amount ΔAdd is calculated (step S7). The determined highest-current phase (steps S26, S27, S28) is then corrected by the correction amount ΔAdd (step S8 in Figure 16, ΔAdd in Figure 17). Then, the voltage command values ​​of the other phases, except for the phase with the highest current amplitude, are corrected by -1 / 2 × ΔAdd (step S9 in Figure 6, ΔAdd × 0.5 in Figure 7). This suppresses fluctuations in the direction of decreasing current amplitude in each phase, thus suppressing fluctuations in motor torque. Therefore, a motor drive system 100 can be obtained that can operate stably without fluctuations in the motor's torque. Note that if the power supply voltage has not increased, the voltage command value is not corrected (step S10).

[0063] The correction amount ΔAdd described above is calculated by the output command correction means 45 using one or a combination thereof of the slope of the power supply voltage, the magnitude of the detected current detected by the current detection unit 24, the correction coefficient, and the command current assigned by the higher-level control device. When the slope of the power supply voltage is large, or when the difference between the detected current values ​​iu, iv, iw and the command current value is large, the amount of fluctuation in the output current and the amount of fluctuation in the torque of the motor 10 are large, so the correction amount ΔAdd of the voltage command value is increased. The correction coefficient corrects the error between the output voltage command value and the voltage actually applied to the motor 10 due to the detection delay, control delay, and parameter error present in the inverter circuit 20. By using this calculation method performed by the output command correction means 45, it is possible to suppress fluctuations in the motor torque in accordance with the slope of the power supply voltage, the fluctuations in the power supply voltage due to the decrease in power supply voltage and the fluctuations in the output current, and to obtain a motor drive system that can operate stably.

[0064] <Effects when applying Embodiment 4> Figures 18(a) and 18(b) illustrate the effects of applying Embodiment 4. Figure 18(a) shows a comparative example without using the control of Embodiment 4, while Figure 18(b) shows the case with the control of Embodiment 4. In Figure 18(a), the voltage command correction amount for each phase is zero, but as shown in Figure 18(b), a decrease in the power supply voltage is detected, and the voltage command value of the phase with the highest voltage command value is corrected by ΔAdd so that the current amplitude increases, and the voltage command values ​​of the other phases are corrected by a correction amount of -1 / 2 × ΔAdd. This prevents a decrease in the current amplitude of each phase. As a result, a compact, low-cost, and stable motor drive system can be obtained without using a current sensor.

[0065] Embodiment 5. <Other methods> The embodiments 1 to 4 described above may be used in combination with other current control methods. Other current control methods include, for example, current control using PID control (Proportional-Integral-Differential Controller) in current feedback control, and a method of combining PID control with embodiments 1 to 4 will be described.

[0066] Unlike PID control, which requires a certain amount of time to respond to increases and decreases in power supply voltage, embodiments 1 to 4 can respond from the moment the slope of the power supply voltage is detected. Therefore, control is started instantaneously during the transient period required for PID control response, and the output current is suppressed, thereby suppressing fluctuations in the torque of the motor 10. Subsequently, the correction amount is gradually reduced by PID control, and the output command voltage of the current control can be gradually increased, thereby achieving stable control. As a result, current fluctuations and motor torque fluctuations associated with power supply voltage fluctuations can be suppressed, and a motor drive system that can operate stably can be obtained.

[0067] For example, as shown in Figure 19, after calculating the slope of the power supply voltage, the correction amount ΔAdd of the voltage command value is decreased in proportion to the elapsed time during the period shown in t1. Also, as shown in Figure 20, the correction amount ΔAdd is decreased in proportion to the elapsed time from the point in time when the slope of the power supply voltage becomes zero during the period shown in t2.

[0068] Furthermore, while embodiments 1 to 4 describe detecting the power supply voltage and calculating the slope of the power supply voltage, the means of detecting the slope of the power supply voltage may also be estimated using the input current, output current, output voltage of the inverter circuit 20, or a combination thereof. For example, one method is to calculate the power supply voltage as power supply voltage = output voltage × output current / input current. By estimating the power supply voltage in this way, a motor drive system that can operate stably can be obtained even when (1) it is used in a drive system where it is difficult to detect the power supply voltage or the slope of the power supply voltage, (2) power supply voltage detection is not performed in order to reduce costs, or (3) feedforward control such as VVVF (Variable Voltage Variable Frequency) control is used.

[0069] Furthermore, when driving the three-phase inverter circuit 20, the relationship between the voltage command correction amounts for each phase does not have to be fixed as ΔAdd and -1 / 2×ΔAdd, but can be calculated based on the phase relationship. For example, in the case of the three-phase inverter circuit 20, let the u-phase current be iu, the v-phase current be iv = -2 / 3×iu, and the w-phase current be iw = -1 / 3×iu. When the power supply voltage fluctuates, the relationship in which the sum of the three phase currents becomes zero can be used to correct the u-phase voltage command value by ΔAdd, the v-phase voltage command value by -2 / 3×ΔAdd, and the w-phase voltage command value by -1 / 3×ΔAdd. By doing so, the amplitude of the output current of the inverter circuit 20 can be reduced, the torque fluctuation of the motor 10 can be reduced, and a motor drive system capable of stable operation can be obtained.

[0070] It should be noted that the above embodiments are merely examples, and the present invention is not limited in any way to embodiments 1 to 4 described above, as long as it is applicable to the present invention. For example, while embodiments 1 and 2 described the case in which the DC power supply 90 and the motor control device 1 are directly connected, a configuration in which a DC / DC converter that performs voltage boosting or stepping down is placed between the DC power supply 90 and the motor control device 1 may also be used, or a configuration in which the AC power supply is connected via a rectifier or AC / DC converter that converts the AC power of the AC power supply into DC power may also be used.

[0071] Furthermore, although embodiments 1 to 4 described above have explained the features and operation of an electric motor control device, it may also be applied to an electric motor drive system 100 including the electric motor control device 1 and the electric motor 10, in which case the advantages of miniaturization of both the electric motor control device 1 and the electric motor 10 can be enjoyed simultaneously.

[0072] Furthermore, although embodiments 1 to 4 described above were explained using an electric motor control device as an example, they may also be applied to electric vehicles or hybrid vehicles that use both an engine and an electric motor, and are not limited to vehicles.

[0073] Although this application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but can be applied individually or in various combinations to the embodiments. Accordingly, countless variations not illustrated are conceivable within the scope of the art disclosed herein. These include, for example, modifications, additions, or omissions of at least one component, as well as the extraction of at least one component and its combination with components of other embodiments.

[0074] The various aspects of this disclosure are summarized below as an appendix.

[0075] (Note 1) A motor control device connected between a DC power supply and an AC motor, which converts the DC power of the DC power supply into AC power to drive and control the AC motor, A power conversion circuit having a switching element for converting the DC power into AC power, The system includes a switching control means for controlling the on / off state of the switching element, The motor control device is characterized in that the switching control means includes an output command calculation means for calculating an output command value for driving the AC motor, a voltage slope calculation means for calculating the slope of the DC power supply voltage, and an output command correction means for calculating a correction amount to suppress torque fluctuations of the AC motor according to the voltage slope calculated by the voltage slope calculation means, and correcting the output command value with this correction amount. (Note 2) The motor control device according to Appendix 1, wherein the AC motor is a three-phase AC motor, and further comprises a current detection unit that detects the current flowing from the power conversion circuit to each phase of the three-phase AC motor, and when the voltage of the DC power supply increases, the motor control device corrects the output command value of the phase with the highest current amplitude among the currents flowing to each phase by a first correction amount, and corrects the output command values ​​of the other phases by a second correction amount which is half of the first correction amount. (Note 3) The motor control device according to Appendix 1, wherein the AC motor is a three-phase AC motor, and further comprises a current detection unit that detects the current flowing from the power conversion circuit to each phase of the three-phase AC motor, and corrects the output command value of the phase whose current exceeds a predetermined current threshold among the currents of each phase detected by the current detection unit with a first correction amount, and corrects the output command value of the other phases with a second correction amount which is half of the first correction amount. (Note 4) The motor control device described in Appendix 1 is a three-phase AC motor, characterized in that a determination range for the output command value at which the current amplitude of each phase is highest is set in advance, the output command value of the phase within the determination range is corrected by a first correction amount, and the output command value of the other phases is corrected by a second correction amount which is half of the first correction amount. (Note 5) The motor control device according to Appendix 1, wherein the AC motor is a three-phase AC motor, and further comprises a current detection unit that detects the current flowing from the power conversion circuit to each phase of the three-phase AC motor, and when the voltage of the DC power supply decreases, the motor control device corrects the highest output command value among the output command values ​​of each phase by a first correction amount, and corrects the output command values ​​of the other phases by a second correction amount which is half of the first correction amount. (Note 6) The motor control device according to any one of the appendices 1 to 5, characterized in that the correction amount is calculated by at least the slope of the voltage and the output current output from the power conversion circuit to the AC motor, or a combination thereof. (Note 7) The motor control device according to Appendix 6, characterized in that the correction amount increases as the slope of the voltage increases. (Note 8) The motor control device according to Appendix 6, characterized in that the correction amount increases as the output current increases. (Note 9) The motor control device according to any one of the appendices 1 to 8, characterized in that the correction amount is reduced as the temperature of the driven AC motor increases. (Note 10) The motor control device according to any one of the appendices 1 to 9, characterized in that the correction amount set according to the voltage slope calculated by the voltage slope calculation means is reduced in proportion to the elapsed time from the time the voltage slope was calculated. (Note 11) The motor control device according to any one of the appendices 1 to 9, characterized in that the correction amount is reduced in proportion to the elapsed time from the point in time when the slope calculated by the voltage slope calculation means becomes zero. (Note 12) The motor control device according to any one of the appendices 1 to 11, characterized in that when the voltage slope calculated by the voltage slope calculation means is greater than a predetermined voltage slope threshold, it is corrected by the correction amount. (Note 13) The motor control device according to any one of the appendices 1 to 12, characterized in that the voltage slope calculation means is calculated based on fluctuations in the detected voltage of the DC power supply. (Note 14) The motor control device according to any one of the appendices 1 to 12, characterized in that the voltage slope calculation means is calculated based on at least one of the input current to the power conversion circuit, the output current from the power conversion circuit, and the output voltage of the power conversion circuit. (Note 15) The motor control device according to any one of the appendices 1 to 14, characterized in that the semiconductor switching element is formed of a wide-bandgap semiconductor. (Note 16) An electric motor control device as described in any one of the appendices 1 to 15, and an electric motor drive system comprising an AC motor connected to the electric motor control device. [Explanation of symbols]

[0076] 1: Motor control device, 10: Motor, 2: AC bus, 20: Inverter circuit, 21a, 21b: DC bus, 22: Capacitor, 23: Voltage detection means, 24: Current detection unit, 30: Power conversion circuit, 31-36: Switching elements, 40: Switching control means, 41: Switching control signal generation means, 42: Voltage slope calculation means, 43: Current detection means, 44: Output command calculation means, 45: Output command correction means, 50: Temperature sensor, 60: Rotation angle sensor, 70: Power switch, 90: DC power supply, 100: Motor drive system.

Claims

1. A motor control device connected between a DC power supply and an AC motor, which converts the DC power of the DC power supply into AC power to drive and control the AC motor, A power conversion circuit having a switching element for converting the DC power into AC power, The system includes a switching control means for controlling the on / off state of the switching element, The switching control means includes an output command calculation means for calculating an output command value for driving the AC motor, a voltage slope calculation means for calculating the slope of the DC power supply voltage, and an output command correction means for calculating a correction amount to suppress torque fluctuations of the AC motor according to the voltage slope calculated by the voltage slope calculation means, and correcting the output command value with this correction amount. The motor control device is a three-phase AC motor, further comprising a current detection unit that detects the current flowing from the power conversion circuit to each phase of the three-phase AC motor, and is characterized in that, when the voltage of the DC power supply increases, the output command value of the phase with the highest current amplitude among the currents flowing to each phase is corrected by a first correction amount, and the output command values ​​of the other phases are corrected by a second correction amount which is half of the first correction amount.

2. A motor control device connected between a DC power supply and an AC motor, which converts the DC power of the DC power supply into AC power to drive and control the AC motor, A power conversion circuit having a switching element for converting the DC power into AC power, The system includes a switching control means for controlling the on / off state of the switching element, The switching control means includes an output command calculation means for calculating an output command value for driving the AC motor, a voltage slope calculation means for calculating the slope of the DC power supply voltage, and an output command correction means for calculating a correction amount to suppress torque fluctuations of the AC motor according to the voltage slope calculated by the voltage slope calculation means, and correcting the output command value with this correction amount. The motor control device is a three-phase AC motor, further comprising a current detection unit that detects the current flowing from the power conversion circuit to each phase of the three-phase AC motor, and is characterized in that the output command value of the phase whose current exceeds a predetermined current threshold among the currents of each phase detected by the current detection unit is corrected by a first correction amount, and the output command value of the other phases is corrected by a second correction amount which is half of the first correction amount.

3. A motor control device connected between a DC power supply and an AC motor, which converts the DC power of the DC power supply into AC power to drive and control the AC motor, A power conversion circuit having a switching element for converting the DC power into AC power, The system includes a switching control means for controlling the on / off state of the switching element, The switching control means includes an output command calculation means for calculating an output command value for driving the AC motor, a voltage slope calculation means for calculating the slope of the DC power supply voltage, and an output command correction means for calculating a correction amount to suppress torque fluctuations of the AC motor according to the voltage slope calculated by the voltage slope calculation means, and correcting the output command value with this correction amount. The motor control device is a three-phase AC motor, characterized in that it sets a predetermined range for determining the output command value at which the current amplitude of each phase is highest, corrects the output command value of the phases within the determination range with a first correction amount, and corrects the output command value of the other phases with a second correction amount that is half of the first correction amount.

4. A motor control device connected between a DC power supply and an AC motor, which converts the DC power of the DC power supply into AC power to drive and control the AC motor, A power conversion circuit having a switching element for converting the DC power into AC power, The system includes a switching control means for controlling the on / off state of the switching element, The switching control means includes an output command calculation means for calculating an output command value for driving the AC motor, a voltage slope calculation means for calculating the slope of the DC power supply voltage, and an output command correction means for calculating a correction amount to suppress torque fluctuations of the AC motor according to the voltage slope calculated by the voltage slope calculation means, and correcting the output command value with this correction amount. The motor control device is characterized in that the AC motor is a three-phase AC motor, and further comprises a current detection unit that detects the current flowing from the power conversion circuit to each phase of the three-phase AC motor, and when the voltage of the DC power supply decreases, the motor control device corrects the highest output command value among the output command values ​​of each phase by a first correction amount, and corrects the output command values ​​of the other phases by a second correction amount which is half of the first correction amount.

5. The motor control device according to any one of claims 1 to 4, characterized in that the correction amount is calculated by at least the slope of the voltage and the output current output from the power conversion circuit to the AC motor, or a combination thereof.

6. The motor control device according to claim 5, characterized in that the correction amount increases as the slope of the voltage increases.

7. The motor control device according to claim 5, characterized in that the correction amount increases as the output current increases.

8. The motor control device according to any one of claims 1 to 4, characterized in that the correction amount is reduced as the temperature of the driven AC motor increases.

9. The motor control device according to any one of claims 1 to 4, characterized in that the correction amount set according to the voltage slope calculated by the voltage slope calculation means is reduced in proportion to the elapsed time from the time the voltage slope was calculated.

10. The motor control device according to any one of claims 1 to 4, characterized in that the correction amount is reduced in proportion to the elapsed time from the point in time when the slope calculated by the voltage slope calculation means becomes zero.

11. The motor control device according to any one of claims 1 to 4, characterized in that when the voltage slope calculated by the voltage slope calculation means is greater than a predetermined voltage slope threshold, it is corrected by the correction amount.

12. The motor control device according to any one of claims 1 to 4, characterized in that the voltage slope calculation means is calculated based on fluctuations in the detected voltage of the DC power supply.

13. The motor control device according to any one of claims 1 to 4, characterized in that the voltage slope calculation means is calculated based on at least one of the input current to the power conversion circuit, the output current from the power conversion circuit, and the output voltage of the power conversion circuit.

14. The motor control device according to any one of claims 1 to 4, characterized in that the switching element is formed of a wide-bandgap semiconductor.

15. An electric motor control device according to any one of claims 1 to 4, and an electric motor drive system comprising an AC motor connected to the electric motor control device.

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