JP2024167951A - Motor control device and motor drive system - Google Patents

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

This application relates to an electric motor control device and an electric motor drive system.

Motor control devices and motor drive systems that convert the form of power output typically include AC/DC converters (Alternate Current/Direct Current Converters) that convert AC power to DC power, and inverters that convert DC power to AC power. These motor control devices and motor drive systems are known to be configured with semiconductor switching elements.

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

The inverter circuit converts the DC power of the DC power source into AC power by turning on and off multiple semiconductor switches at a predetermined switching frequency, and adjusts the torque and rotation speed of the AC motor, which is the load. Depending on the operating conditions, the AC motor can also function as a generator, charging the DC power source with regenerative power generated by the power generation. Note that efficient permanent magnet three-phase synchronous motors are often used as AC motors for electric vehicles.

In a drive system using a three-phase synchronous motor, the inverter circuit is configured by connecting three series circuits in parallel with a DC power source, with the upper-stage switching element and the lower-stage switching element connected in series, and the midpoint of each of the three series circuits is connected to the input of the u-phase, v-phase, and w-phase of the three-phase synchronous motor.

Also, by sequentially turning on and off the switching elements provided for each phase of the inverter circuit, AC power with phases differing by 120 degrees from each other is supplied to each phase of the three-phase synchronous motor to drive the three-phase synchronous motor. Unless otherwise specified, the motor below refers to a three-phase synchronous motor. Note that the operating principle of the inverter circuit is widely known, so a description of it will be omitted here.

JP 2022-104708 A

As mentioned above, the motor control device drives the motor by supplying a power supply voltage from an external source. However, if the operation of the power supply voltage is unstable, the supplied voltage also becomes unstable. In this case, the inverter output current suddenly decreases, causing the torque of the motor to fluctuate and suddenly decrease.

As a suppression element for suppressing such torque fluctuations, a smoothing capacitor for voltage smoothing may be connected between the input power supply device and the drive system, and the capacitance of the smoothing capacitor may be increased to suppress fluctuations in the power supply voltage. However, there is an issue that increasing the capacitance of the smoothing capacitor increases the size, weight, and cost of the drive system.

To address this issue, a method is known in which sudden fluctuations in the power supply voltage of the drive system are detected, and when the power supply voltage in a certain period exceeds a predetermined threshold, a correction range is calculated from the power supply voltage fluctuation range/reference voltage correction range, and the current limit reference voltage is corrected to be lower than the normal value so as to limit the output current of the inverter (see, for example, Patent Document 1).

However, limiting the output current may result in a decrease in the torque of the electric motor. In other words, in Patent Document 1, when the power supply voltage in a certain period exceeds a predetermined threshold, a correction width is calculated and the current limit reference voltage is corrected to be lower than the normal value. At this time, by lowering the current limit reference voltage below 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 becomes lower than the normal value. As a result, the torque of the electric motor becomes lower than the normal value.

This application was made to solve the problems mentioned above, and makes it possible to reduce fluctuations in the torque of an electric motor, thereby realizing stable operation of the electric motor.

The motor control device disclosed in the present application is connected between a DC power source and an AC motor, and converts the DC power of the DC power source into AC power to drive and control the AC motor. The motor control device includes a power conversion circuit having a switching element for converting the DC power into AC power, and a switching control means for controlling the on/off 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 voltage of the DC power source, and an output command correction means for calculating a correction amount for suppressing torque fluctuations of the AC motor according to the slope of the voltage calculated by the voltage slope calculation means, and correcting the output command value with the correction amount.

The motor control device disclosed in this application can reduce motor torque fluctuations and achieve stable motor operation by correcting the output command value with a correction amount that suppresses torque fluctuations of the AC motor according to the gradient of the power supply voltage.

1 is a block diagram showing a configuration of an electric motor drive system equipped with an electric motor control device according to a first embodiment; 2 is a diagram illustrating an example of hardware of a switching control means of the electric motor control device according to the first embodiment. FIG. FIG. 2 is a block diagram illustrating a function of a voltage gradient calculation means of the motor control device according to the first embodiment. 3 is a block diagram illustrating a function of an output command calculation means of the electric motor control device according to the first embodiment. FIG. 3 is a block diagram illustrating a function of an output command correction means of the electric motor control device according to the first embodiment. FIG. 5 is a flowchart illustrating the operation of an output command correction unit of the electric motor control device according to the first embodiment. 4 is a timing chart illustrating time series changes in a power supply voltage, each phase current, and each phase voltage command correction amount of the electric motor control device according to the first embodiment. 5A to 5C are diagrams illustrating the effects of the motor control device according to the first embodiment. 10 is a flowchart illustrating the operation of an output command correction unit of the electrically-driven control device according to the second embodiment. 10 is a timing chart illustrating time series changes in a power supply voltage, each phase current, and each phase voltage command correction amount of the electric motor control device according to the second embodiment. 13A and 13B are diagrams illustrating the effects of the electric motor control device according to the second embodiment. FIG. 11 is a block diagram illustrating a function of an output command correction means of an electric motor control device according to a third embodiment. 13 is a flowchart illustrating the operation of an output command correcting means of the electric motor control device according to the third embodiment. 13 is a timing chart illustrating time series changes in a power supply voltage, each phase voltage command value, and each phase voltage command correction amount of the electric motor control device according to the third embodiment. 13A to 13C are diagrams illustrating the effects of the electric motor control device according to the third embodiment. 10 is a flowchart illustrating the operation of an output command correcting means of the electric motor control device according to the fourth embodiment. 13 is a timing chart illustrating time series changes in a power supply voltage, each phase voltage command value, and each phase voltage command correction amount of the electric motor control device according to the fourth embodiment. 13A and 13B are diagrams illustrating the effects of the motor control device according to the fourth embodiment. 13 is a diagram illustrating the relationship between the gradient of the power supply voltage and the amount of correction according to the fifth embodiment. FIG. 13 is a diagram illustrating the relationship between the gradient of the power supply voltage and the amount of correction according to the fifth embodiment. FIG.

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, but the same or corresponding parts in each drawing will be given the same reference numerals and detailed description thereof will be omitted. Similarly, in the following embodiments, duplicated descriptions of configurations given the same reference numerals will be omitted.
He explains.

Generally, electric motors convert electric power into driving force and operate as power generators, but they can also convert driving force back into electric power and operate as regenerative power with the same structure. Also, generators, which are also called electric power generators, convert driving force into electric power and operate as regenerative power, but they can also convert electric power back into driving force and operate as power generators with the same structure. In other words, electric motors and generators have basically the same structure, and both are capable of powering and regenerative powering. Therefore, in this specification, a rotating electric machine that has the functions of both an electric motor and a generator will simply be referred to as an electric motor.

Embodiment 1.
The configuration and operation of a motor control device 1 according to the first embodiment will be described with reference to Fig. 1. In the motor control device 1, DC buses 21a and 21b are connected to a DC power source 90 via a power switch 70, and driving power or regenerative power is exchanged with the DC power source 90. In addition, the motor control device 1 is connected to a motor 10 by an AC bus 2, and driving power or regenerative power is exchanged with the motor 10.

In addition, the electric motor 10 is equipped with a temperature detection unit 50 (hereinafter referred to as the temperature sensor 50) that detects the temperature of the permanent magnet of the electric motor 10, and a rotational speed detection unit 60 (hereinafter referred to as the rotational angle sensor 60) that detects the rotational speed from the rotational angle of the rotor of the electric motor 10.
The electric motor 10 is capable of rotating a load and regenerating the rotational energy of the load as electrical energy, and may be a three-phase brushless motor such as a permanent magnet three-phase AC synchronous motor.

The motor control device 1 is composed of an inverter circuit 20 and a switching control means 40. The inverter circuit 20 is equipped with a capacitor 22 connected between the DC busbars 21a and 21b on the power supply input side, a voltage detection means 23 that detects the voltage between the DC busbars 21a and 21b of the inverter circuit 20, a power conversion circuit 30 that is composed of switching elements 31 to 36 connected in a full bridge configuration and performs power conversion from DC to AC or AC to DC, and a current detection unit 24 that detects the current flowing through the AC busbar 2 of the motor 10.

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

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

As shown in FIG. 1, the power conversion circuit 30 includes switching elements 31 and 32, switching elements 33 and 34, and switching elements 35 and 36, which are connected in series to form arms and are connected in parallel to the DC power supply 90. The midpoints of the switching elements 31 and 32 are connected to the u-phase input of the motor 10, the midpoints of the switching elements 33 and 34 are connected to the v-phase input of the motor 10, and the midpoints of the switching elements 35 and 36 are 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 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 lower-stage switching elements.

The switching elements 31 to 36 are turned on and off by on and off control signals from the switching control signal generating means 41 described later, converting DC power to AC power and supplying it to the electric motor 10, and charging the DC power source 90 with regenerative power generated when the electric motor 10 is in a regenerative state.

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

The current detection unit 24 detects the motor current flowing through the AC bus 2, converts the current to a voltage, and outputs motor current information to the switching control means 40. In FIG. 1, as an example, a configuration is shown 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.

The rotation angle sensor 60 is a device such as a resolver or an encoder that detects the rotation angle of the rotor of the electric motor 10. The rotation angle of the rotor detected by the rotation angle sensor 60 is output to the switching control means 40, and is used as the rotation speed in the switching control means 40.

The temperature sensor 50 is, for example, 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. Note that 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.

The switching control means 40 is responsible for the overall control of the motor control device 1, and is composed of a driving circuit including a microcontroller, and has a switching control signal generating means 41, a voltage gradient calculating means 42, an output command calculating means 44, an output command correcting means 45, and a current detecting means 43. Each of these means may be realized partially by dedicated hardware and partially by software or firmware. An example of the hardware of the microcomputer in the switching control means 40 is shown in FIG. 2. It is composed of a processor 150 and a storage device 200, and although not shown, the storage device includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. In addition, an auxiliary storage device such as a hard disk may be included instead of the flash memory. The processor 150 performs each function of the switching control signal generating means 41, the voltage gradient calculating means 42, the current detecting means 43, the output command calculating means 44, and the output command correcting means 45 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. In addition, the processor 150 may output data such as the results of calculations to a volatile storage device of the storage device 200, or may store the data in an auxiliary storage device via the volatile storage device.

The switching control signal generating means 41 generates an on/off control signal for controlling the on/off of the multiple switching elements 31 to 36 that constitute the power conversion circuit 30 .
As shown in FIG. 1 , the switching control signal generating means 41 generates on/off control signals for each of the switching elements 31 to 36 of the power conversion circuit 30 in accordance with (1) DC bus voltage information from the voltage detection means 23, (2) rotation angle information (rotation speed) of the motor 10 from the rotation angle sensor 60, (3) motor current information from the current detection unit 24, and (4) output from the output command correction means 45, as well as the motor torque command value and current command value of the motor 10 input from the outside, and outputs on/off control signals to the power conversion circuit 30.

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 FIG. 3, the detected power supply voltage detection value is stored in the detection value storage unit 421, and the voltage slope calculation unit 422 calculates the slope of the power supply voltage based on the stored previous detection value and current detection value.

The slope of the power supply voltage can be calculated, for example, as follows.
・Power supply voltage slope = (currently detected power supply voltage value - previously detected power supply voltage value) / detection time ・Power supply voltage slope = (currently detected power supply voltage value - previously detected power supply voltage value) / current detected power supply voltage value ・Power supply voltage slope = (currently detected power supply voltage value - previously detected power supply voltage value) / previously detected power supply voltage value ・Power supply voltage slope = (currently detected power supply voltage value - previously detected power supply voltage value) / nominal voltage value

The current detection means 43 performs a three-phase/dq transformation based on 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, based on the output result of the current detection unit 24, and outputs the d-axis current detection value id and the q-axis current detection value iq.

As shown in FIG. 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*. Also, the q-axis current command value iq* is compared 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 to 3-phase conversion unit 443, which outputs the voltage command values Vuc*, Vvc*, and Vwc* of the windings of the u-phase, v-phase, and w-phase that constitute the motor 10.

As shown in FIG. 5, the output command correction means 45 uses as input the power supply voltage gradient calculated by the voltage gradient calculation means 42, the voltage command values Vuc*, Vvc*, 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 the corrected voltage command values obtained by correcting the voltage command values for each of the three phases.

The operation of the output command correction means 45 will be described with reference to Figures 6 and 7. Figure 6 is a flowchart explaining the operation of the output command correction means 45, and Figure 7 is a timing chart explaining the time series changes in the power supply voltage, each phase current, and each phase voltage command correction amount.

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. 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 greater than the commanded voltage value (step S1 in FIG. 6), which causes the output current to become larger than normal and the output torque to fluctuate in an increasing direction.

In response to such an increase in the power supply voltage, the slope of the power supply voltage is detected. If the power supply voltage is increasing due to the slope of the detected power supply voltage (step S1 in FIG. 6), the inverter circuit 20 controls three phases, and when the current of one of the three phases peaks, the current of the other phases is proportional to -1/2 times the current of the other phases. This is used to determine the phase with the highest current amplitude (steps S2 to S3, P, Q, and R in FIG. 7), calculate the correction amount ΔAdd (step S7), and correct the voltage command value of the determined phase (steps S4 to S6 in FIG. 6) with the correction amount ΔAdd (step S8 in FIG. 6, ΔAdd in FIG. 7). Then, the voltage command values of the phases other than the phase with the highest current amplitude are corrected by -1/2×ΔAdd (step S9 in FIG. 6, ΔAdd×0.5 in FIG. 7), thereby suppressing the increase in the current amplitude of each phase and suppressing the torque fluctuation of the electric motor 10. This allows for a stable motor drive system that operates without fluctuating torque of the motor 10. If the power supply voltage is not increasing, the voltage command value is not corrected (step S10).

The above-mentioned correction amount ΔAdd is for suppressing torque fluctuations, and is calculated by the output command correction means 45 taking into account any one or a combination of the following: the gradient of the power supply voltage, the ratio of the current value of the phase with the largest absolute value of the phase current to the nominal current value, the ratio of the voltage command value of the phase with the largest absolute value of the phase current to the nominal voltage value, and the correction coefficient. When the gradient of the power supply voltage is large, or when the difference between the detected current values iu, iv, and iw and the command current is large, the fluctuation amount of the output current and the torque fluctuation amount 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 such a calculation method performed by the output command correction means 45, it is possible to suppress the torque fluctuation of the motor 10 due to the fluctuation of the power supply voltage according to the gradient of the power supply voltage, and it is possible to obtain a motor drive system that operates stably without output torque fluctuations.

To explain using a specific example, the correction amount ΔAdd is calculated based on the power supply voltage gradient vmove, the ratio of the current value iphase of the phase having the largest absolute value of the phase current to the nominal current value imax*, the ratio of the voltage command value vphase* of the phase having the largest absolute value of the phase current to the nominal voltage value vmax*, an actual machine 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 according to the following formula (1). However, this formula (1) is an example and is not limited to this.

ΔAdd = vmove × iphase / imax* × vphase* / vmax* × K_c... (1)
ΔAdd: Voltage command correction amount vmove: Power supply voltage gradient iphase: Current value of the phase with the largest absolute value of the phase current imax*: Nominal current value (rated maximum value)
vphase*: Voltage command value of the phase with the largest absolute value of the phase current vmax*: Nominal voltage value (rated maximum value)
K_c: Coefficient for adjusting the actual machine (1 if no adjustment is required)
Note that here, vmove=vdet(z)-vdet(z-1)/vdet(z), but as described above, other methods of calculating the gradient of the power supply voltage may be used.

The increase in the power supply voltage may be determined by setting a power supply voltage slope threshold. During normal operation, a voltage ripple occurs at the power supply voltage terminal due to the operation of the inverter circuit 20, which may cause the voltage detection means 23 to erroneously detect that the slope has changed. In order to eliminate such erroneous detection, a power supply voltage slope threshold is set so as not to excessively suppress the torque of the electric motor 10, thereby distinguishing between a change in slope due to an increase in the power supply voltage under normal operating conditions and a change in slope due to erroneous detection when a voltage ripple occurs. For example, the voltage ripple at the power supply voltage terminal is measured in advance, and this value is set as the power supply voltage slope threshold. This makes it possible to obtain an electric motor drive system that can operate stably without erroneously detecting voltage ripples that occur during normal operation.

The correction amount ΔAdd of the voltage command value may also be adjusted based on 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 fluctuation amount of the motor 10 associated with fluctuations in the power supply voltage are small. 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 more appropriately suppressing torque fluctuations can be obtained.

As a result, the target motor torque or target current of the motor 10 is input to the switching control means 40 via the CAN (Controller Area Network) from other control devices, including the vehicle ECU (not shown), and current feedback control is performed 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, and the on/off control signals to each switching element 31 to 36 of the power conversion circuit 30 are calculated so that an appropriate target motor torque or target current of the motor 10 is obtained, and the on/off control signals are output to the power conversion circuit 30. Note that the current feedback control is well known, so a detailed description is omitted here.

The type of semiconductor used for the switching elements 31 to 36 in the power conversion circuit 30 is not particularly limited, but may be, for example, a wide band gap semiconductor. Wide band gap semiconductor elements that may be used include those made of, for example, silicon carbide (SiC), gallium nitride (GaN)-based materials, or diamond (C).

Inverter circuit 20 configured with switching elements formed from such wide bandgap semiconductors has the characteristics of high voltage resistance, low loss, and high frequency operation compared to conventional inverter circuits configured with switching elements formed from silicon (Si). Hereinafter, an inverter circuit configured with switching elements formed from wide bandgap semiconductors will be referred to as a wide bandgap inverter circuit, and an inverter circuit configured with switching elements formed from silicon (Si) will be referred to as a silicon inverter circuit.

Therefore, in a motor control device using a wide band gap inverter circuit, the switching speed of the switching elements is higher than in a motor control device using a silicon inverter circuit, so the switching speed can be increased and output commands can be realized quickly and accurately. In the second to fourth embodiments described below, the above-mentioned effects can be obtained by using wide band gap semiconductors in the same way.

<Effects when the first embodiment is applied>
Based on FIG. 8(a) and FIG. 8(b), the effect of applying the first embodiment is shown. FIG. 8(a) shows a comparative example in which the control of the first embodiment is not used, and FIG. 8(b) shows a case in which the control of the first embodiment is used. In FIG. 8(a), the voltage command correction amount of each phase is zero, but as shown in FIG. 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 the correction amount ΔAdd so that the current amplitude is reduced, and the voltage command values of the other phases are corrected by the correction amount of -1/2 x ΔAdd, respectively, so that the current amplitude is reduced. As a result, in the three-phase inverter circuit 20, when the current of one phase peaks, the current amplitude of each phase can be suppressed to be reduced by utilizing the proportional relationship in which the magnitude of the current of the other phases is -1/2. Furthermore, if the slope of the power supply voltage is large, the correction amount ΔAdd of the voltage command value is increased, and the effect of suppressing the increase in output current caused by the increase in the power supply voltage can be obtained, and the torque increase of the motor can be suppressed. As a result, it is possible to obtain an electric motor drive system that operates stably.

Embodiment 2.
9 to 11, the configuration and operation of the rotary electric machine control device according to the second embodiment will be described, focusing on the differences between the first and second embodiments. Note that parts that are the same as or equivalent to those in the first embodiment are given the same reference numerals.

The operation of the second embodiment will be described with reference to Figures 9 and 10. Figure 9 is a flow chart explaining the operation of the output command correction means 45, and Figure 10 is a timing chart explaining 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 the second embodiment compares the current information of each phase with a predetermined current threshold (steps S11, S12, S13 in Figure 9, 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 with the correction amount ΔAdd (step S8 in Figure 9, 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 x ΔAdd (step S9 in FIG. 9, ΔAdd x 0.5 in FIG. 10), thereby suppressing the increase in the current amplitude of each phase and suppressing the torque fluctuation of the electric motor 10. This suppresses the increase in the current amplitude of each phase and suppresses the torque fluctuation of the electric motor 10. Therefore, it is possible to obtain an electric motor drive system that operates stably without fluctuating the torque of the electric motor 10. Note that if the power supply voltage is not increasing, the voltage command value is not corrected (step S10).

The current threshold may be set to a value equal to or greater than the sum of the rated current of the inverter circuit 20 and the current ripple that occurs when the inverter circuit 20 is operating, and equal to or less than the overcurrent (OC) threshold. By using this current threshold for control, when the power supply voltage is fluctuating, the current is within the normal operating current range, making it unnecessary to suppress the current, and it is possible to obtain a motor drive system that operates stably without excessively suppressing the output current.

The current threshold may be variable. For example, by using a command current as the threshold current, limiting operation is performed only when the command value is exceeded, so that a motor drive system that can operate stably can be obtained without falsely detecting the normal operating state in which the motor operates according to the command value.

<Effects when the second embodiment is applied>
The effect of applying the second embodiment is shown based on FIG. 11(a) and FIG. 11(b). FIG. 11(a) shows a comparative example in which the control of the second embodiment is not used, and FIG. 11(b) shows a case in which the control of the second embodiment is used. In FIG. 11(a), the voltage command correction amount of each phase is zero, but as shown in FIG. 11(b), an increase in the power supply voltage is detected and corrected by the correction amount ΔAdd so that the current amplitude is reduced, 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 if the power supply voltage fluctuates, but if there is no fluctuation in the torque of the motor, it is possible to obtain an electric motor drive system that can operate stably without excessively limiting the output torque of the motor.

Embodiment 3.
The configuration and operation of the rotary electric machine control device according to the third embodiment will be described below with reference to Figures 12 to 15, focusing on the differences between the first and third embodiments. Note that parts that are the same as or equivalent to those in the first embodiment are given the same reference numerals.

The input/output elements of the output command correction means 45 of the third embodiment will be described with reference to FIG. 12. As in the first embodiment, the third embodiment uses as inputs the gradient of the power supply voltage and the voltage command values Vuc*, Vvc*, and Vwc* of the u-phase, v-phase, and w-phase, respectively. However, it differs in that the detected current values iu, iv, and iw of the u-phase, v-phase, and w-phase, respectively, detected by the motor current detection unit 24, are not required, and a voltage command is used for the phase to calculate the correction amount.

The operation of the third embodiment will be described with reference to Figs. 13 and 14. Fig. 13 is a flow chart for explaining the operation of the output command correction means 45, and Fig. 14 is a timing chart for explaining the time series changes of the power supply voltage, each phase voltage command value, and each phase voltage command correction amount. The output command correction means of the third embodiment predefines a voltage command value judgment range based on the voltage command values Vuc*, Vvc*, and Vwc* of the u-phase, v-phase, and w-phase (see "Voltage command judgment range" in Fig. 14), and determines whether the magnitude of the voltage command value is within the voltage command value judgment range (steps S17, S18, and S19 in Fig. 13). Phases whose magnitude of the voltage command value is within the voltage command value judgment range are extracted (steps S20, S21, and S22 in Fig. 13), the correction amount ΔAdd is calculated (step S7), and the voltage command value of the determined phase is corrected with the correction amount ΔAdd (step S8 in Fig. 13, ΔAdd in Fig. 14). Then, by correcting the phases outside the judgment range of the voltage command value by -1/2 x ΔAdd (step S9 in FIG. 13, ΔAdd x 0.5 in FIG. 14), the increase in the current amplitude of each phase can be suppressed, and the effect of suppressing the torque fluctuation of the electric motor 10 can be obtained. Therefore, it is possible to obtain an electric motor drive system that operates stably without the torque of the electric motor 10 fluctuating. Furthermore, it is possible to obtain an electric motor drive system that is small, low-cost, and capable of stable operation without using a current sensor. Note that if the power supply voltage is not increasing, the voltage command value is not corrected (step S10).

The voltage command value judgment range is set so that the phase in which the current is at its peak 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 phase voltage command value is regarded 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 a description thereof will be omitted here. By using the above means, it is possible to obtain a motor drive system capable of stable operation by correcting to reduce the current amplitude of different phases and suppressing the current fluctuation and motor torque fluctuation that accompany an increase in the power supply voltage without excessively suppressing the motor torque.

<Effects when the third embodiment is applied>
Based on Fig. 15(a) and Fig. 15(b), the effect of applying the third embodiment is shown. Fig. 15(a) shows a comparative example in which the control of the third embodiment is not used, and Fig. 15(b) shows a case in which the control of the third embodiment is used. In Fig. 15(a), the voltage command correction amount of each phase is zero, but as shown in Fig. 15(b), the phase voltage command value is regarded as a phase voltage by utilizing the relationship between the phase voltage, the phase current, and the power factor, and the judgment range of the voltage command value is set so that the phase in which the phase current is at a peak can be extracted. The phase within the judgment range of the voltage command value is corrected by the correction amount ΔAdd of the voltage command value, and the voltage command value of the other phases is corrected by the correction amount of -1/2 × ΔAdd. This makes it possible to obtain a small-sized, low-cost electric motor drive system that can operate stably without using a current sensor.

Fourth embodiment
The configuration and operation of the rotary electric machine control device according to the fourth embodiment will be described below with reference to Figures 16 to 18, focusing on the differences between the first and fourth embodiments. Note that parts that are the same as or equivalent to those in the first embodiment are given the same reference numerals.

The operation of the fourth embodiment will be described with reference to Figs. 16 and 17. The difference from the first embodiment is that when the power supply voltage decreases, a correction is made so that the current amplitude is increased. Fig. 16 is a flow chart explaining the operation of the output command correction means 45, and Fig. 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. When the power supply voltage decreases, the output command correction means of the third embodiment corrects the voltage command value of the phase with the largest voltage command value by the correction amount ΔAdd so that the current amplitude increases, and corrects the voltage command values of the other phases by -1/2 × ΔAdd, respectively, thereby suppressing the fluctuation of the output current of the inverter circuit 20 and the fluctuation of the torque of the electric motor due to the decrease in the power supply voltage, and obtaining an electric motor drive system that can operate stably.

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 influence of the low-pass filter, a detection delay occurs. When the power supply voltage decreases, the information on the power supply voltage used to generate the output voltage command value of the inverter circuit 20 is not reflected, and the actual output voltage becomes smaller than the command voltage value. As a result, the output current becomes smaller than normal, and the output torque fluctuates in the decreasing direction.

In the event of such a power supply voltage decrease, the slope of the power supply voltage is detected. If the power supply voltage is decreasing due to the detected slope of the power supply voltage (step S23 in FIG. 16), the voltage command value of the phase with the highest voltage command value is determined (steps S24, 25, A, B, C in FIG. 17) by utilizing the proportional relationship in which the current of one of the three phases peaks and the current of the other phases is -1/2 times greater, and the correction amount ΔAdd is calculated (step S7), and the determined highest phase (steps S26, S27, S28) is corrected with the correction amount ΔAdd (step S8 in FIG. 16, ΔAdd in FIG. 17). Then, the voltage command values of the phases other than the phase with the highest current amplitude are corrected with -1/2×ΔAdd (step S9 in FIG. 6, ΔAdd×0.5 in FIG. 7), so that the current amplitude of each phase can be suppressed from fluctuating in the decreasing direction, and the effect of suppressing the torque fluctuation of the electric motor is obtained. Therefore, it is possible to obtain an electric motor drive system 100 that can operate stably without fluctuating the torque of the electric motor. Note that if the power supply voltage is not increasing, the voltage command value is not corrected (step S10).

The above-mentioned correction amount ΔAdd is calculated by the output command correction means 45 using the gradient of the power supply voltage, the magnitude of the detected current detected by the current detection unit 24, the correction coefficient, the command current given by the upper control device, or a combination of them. When the gradient of the power supply voltage is large or the difference between the detected current values iu, iv, iw and the command current value is large, the fluctuation amount of the output current and the torque fluctuation amount of the electric 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 electric motor 10 due to the detection delay, control delay, and parameter error present in the inverter circuit 20. By using such a calculation method performed by the output command correction means 45, it is possible to obtain an electric motor drive system that can suppress the fluctuation of the torque of the electric motor according to the gradient of the power supply voltage, the fluctuation of the power supply voltage due to the decrease in the power supply voltage, and the fluctuation amount of the output current, and can operate stably.

<Effects of applying the fourth embodiment>
Based on FIG. 18(a) and FIG. 18(b), the effect of applying the fourth embodiment is shown. FIG. 18(a) shows a comparative example in which the control of the fourth embodiment is not used, and FIG. 18(b) shows a case in which the control of the fourth embodiment is used. In FIG. 18(a), the voltage command correction amount for each phase is zero, but as shown in FIG. 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 becomes large, and the voltage command values of the other phases are corrected by a correction amount of −1/2×ΔAdd. This makes it possible to suppress the current amplitude of each phase from decreasing. As a result, it is possible to obtain a small-sized, low-cost, and stable motor drive system without using a current sensor.

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

Unlike PID control, which requires a certain amount of time to respond to increases and decreases in the power supply voltage, the first to fourth embodiments are able to respond from the point in time when the slope of the power supply voltage is detected. Therefore, control is instantaneously started during the transition period required for the PID control response, and the output current is suppressed, thereby suppressing fluctuations in the torque of the electric motor 10. After that, the PID control gradually changes the correction amount to be smaller, and the output command voltage of the current control can be gradually increased, thereby achieving stable control. As a result, it is possible to obtain an electric motor drive system that can suppress current fluctuations and motor torque fluctuations that accompany fluctuations in the power supply voltage, and can operate stably.

For example, as shown in FIG. 19, after the slope of the power supply voltage is calculated, the correction amount ΔAdd of the voltage command value is decreased in proportion to the elapsed time during the period shown by t1. Also, as shown in FIG. 20, the correction amount ΔAdd is decreased in proportion to the elapsed time from the point at which the slope of the power supply voltage becomes zero during the period shown by t2.

In addition, in the first to fourth embodiments, the power supply voltage is detected and the slope of the power supply voltage is calculated. However, the slope of the power supply voltage may be detected by estimating it from any one of the input current, output current, and output voltage of the inverter circuit 20, or a combination of these. For example, the calculation may be performed as follows: power supply voltage = output voltage x output current / input current. By estimating the power supply voltage in this way, it is possible to obtain an electric motor drive system that can operate stably even in the following cases: (1) when used in a drive system in which it is difficult to detect the power supply voltage or the slope of the power supply voltage, (2) when the power supply voltage is not detected in order to reduce costs, or (3) when feedforward control such as VVVF (Variable Voltage Variable Frequency) control is used.

When the three-phase inverter circuit 20 is driven, the relationship between the voltage command correction amounts for each phase may not be fixed to ΔAdd and -1/2 x ΔAdd, but may be calculated based on the phase relationship. For example, in the case of the three-phase inverter circuit 20, the u-phase current is iu, the v-phase current iv = -2/3 x iu, and the w-phase current iw = -1/3 x iu. By utilizing the relationship in which the sum of the three-phase currents becomes 0 when the power supply voltage fluctuates, the u-phase voltage command value is corrected by ΔAdd, the v-phase voltage command value is corrected by -2/3 x ΔAdd, and the w-phase voltage command value is corrected by -1/3 x ΔAdd, the amplitude of the output current of the inverter circuit 20 is reduced, the torque fluctuation of the motor 10 is reduced, and a motor drive system capable of stable operation can be obtained.

The above-mentioned embodiment is merely an example, and is not limited to the above-mentioned embodiments 1 to 4 as long as the present application is applicable. For example, in the above-mentioned embodiments 1 and 2, the DC power supply 90 and the motor control device 1 are directly connected, but a DC/DC converter that steps up or steps down the voltage may be disposed between the DC power supply 90 and the motor control device 1, or the AC power supply may be connected via a rectifier or an AC/DC converter that converts the AC power of the AC power supply into DC power.

In addition, while the above-mentioned embodiments 1 to 4 have been described with respect to the characteristics and operation of an electric motor control device, they 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 the compact electric motor control device 1 and the compact electric motor 10 can be enjoyed at the same time.

In addition, the above-mentioned first to fourth embodiments have been described using an electric motor control device as an example, but the invention may also be applied to an electric vehicle or a hybrid vehicle that uses both an engine and an electric motor, and is not limited to vehicles.

Although the present application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations.
Therefore, countless modifications not illustrated are assumed within the scope of the technology disclosed in the present specification, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment.

Various aspects of this disclosure are summarized below as appendices.

(Appendix 1)
1. A motor control device that is connected between a DC power source and an AC motor, and converts DC power of the DC power source into AC power to drive and control the AC motor,
a power conversion circuit having a switching element for converting the DC power into the AC power;
A switching control means for controlling the on/off of the switching element is provided,
a voltage gradient calculation means for calculating a gradient of a voltage of the DC power supply; and an output command correction means for calculating a correction amount for suppressing torque fluctuations of the AC motor in accordance with the gradient of the voltage calculated by the voltage gradient calculation means and correcting the output command value with the correction amount.
(Appendix 2)
2. The motor control device according to claim 1, wherein the AC motor is a three-phase AC motor, and further comprises a current detection unit that detects a 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, an output command value of a phase having the highest current amplitude among the currents flowing to each phase is corrected by a first correction amount, and output command values of the other phases are corrected by a second correction amount that is 1/2 of the first correction amount.
(Appendix 3)
2. The motor control device according to claim 1, wherein the AC motor is a three-phase AC motor, and further comprises a current detection unit that detects a current flowing from the power conversion circuit to each phase of the three-phase AC motor, and an output command value of a phase of the current of each phase detected by the current detection unit that exceeds a predetermined current threshold is corrected by a first correction amount, and an output command value of the other phases is corrected by a second correction amount that is 1/2 of the first correction amount.
(Appendix 4)
2. The motor control device according to claim 1, wherein the AC motor is a three-phase AC motor, and a determination range of an output command value at which a current amplitude of each phase is highest is set in advance, and the output command value of a phase within the determination range is corrected by a first correction amount, and the output command value of the other phase is corrected by a second correction amount that is 1/2 of the first correction amount.
(Appendix 5)
2. The motor control device according to claim 1, wherein the AC motor is a three-phase AC motor, and further comprises a current detection unit that detects a current flowing from the power conversion circuit to each phase of the three-phase AC motor, and when a voltage of the DC power supply decreases, the highest output command value among the output command values of the phases is corrected by a first correction amount, and the output command values of the other phases are corrected by a second correction amount that is 1/2 of the first correction amount.
(Appendix 6)
The motor control device according to any one of claims 1 to 5, wherein the correction amount is calculated based on at least one of the slope of the voltage and the output current output from the power conversion circuit to the AC motor, or a combination thereof.
(Appendix 7)
7. The motor control device according to claim 6, wherein the correction amount is increased as the voltage gradient increases.
(Appendix 8)
7. The motor control device according to claim 6, wherein the correction amount is increased as the output current increases.
(Appendix 9)
9. The motor control device according to claim 1, wherein the correction amount is made smaller as the temperature of the AC motor being driven increases.
(Appendix 10)
The motor control device according to any one of claims 1 to 9, characterized in that the correction amount, which is set in accordance with the voltage gradient calculated by the voltage gradient calculation means, is reduced in proportion to the elapsed time from the point in time when the voltage gradient is calculated.
(Appendix 11)
10. The motor control device according to claim 1, wherein 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.
(Appendix 12)
12. The motor control device according to claim 1, wherein when the voltage gradient calculated by the voltage gradient calculation means is greater than the predetermined voltage gradient threshold value, the voltage gradient is corrected by the correction amount.
(Appendix 13)
13. The motor control device according to claim 1, wherein the voltage gradient calculation means calculates the voltage gradient based on fluctuations in the detected voltage of the DC power supply.
(Appendix 14)
The motor control device according to any one of appendixes 1 to 12, characterized in that the voltage gradient calculation means calculates the voltage gradient based on at least one of an input current to the power conversion circuit, an output current from the power conversion circuit, and an output voltage of the power conversion circuit.
(Appendix 15)
15. The motor control device according to any one of claims 1 to 14, wherein the semiconductor switching element is formed of a wide band gap semiconductor.
(Appendix 16)
16. An electric motor drive system comprising: an electric motor control device according to any one of claims 1 to 15; and an AC motor connected to the electric motor control device.

1: Motor control device, 10: Motor, 2: AC busbar, 20: Inverter circuit, 21a, 21b: DC busbar, 22: Capacitor, 23: Voltage detection means, 24: Current detection section, 30: Power conversion circuit, 31-36: Switching elements, 40: Switching control means, 41: Switching control signal generation means, 42: Voltage gradient 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 (16)

1. A motor control device that is connected between a DC power source and an AC motor, and converts DC power of the DC power source into AC power to drive and control the AC motor,
a power conversion circuit having a switching element for converting the DC power into the AC power;
A switching control means for controlling the on/off of the switching element is provided,
a voltage gradient calculation means for calculating a gradient of a voltage of the DC power supply; and an output command correction means for calculating a correction amount for suppressing torque fluctuations of the AC motor in accordance with the gradient of the voltage calculated by the voltage gradient calculation means and correcting the output command value with the correction amount. The motor control device according to claim 1, 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 corrects the output command value of the phase with the highest current amplitude among the currents flowing to each phase when the voltage of the DC power source increases, by a first correction amount, and corrects the output command values of the other phases by a second correction amount that is 1/2 of the first correction amount. The motor control device according to claim 1, characterized in that the AC motor is a three-phase AC motor, and further includes 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 a phase of the current of each phase detected by the current detection unit that exceeds a predetermined current threshold value with a first correction amount, and corrects the output command value of the other phases with a second correction amount that is 1/2 of the first correction amount. The motor control device according to claim 1, characterized in that the AC motor is a three-phase AC motor, a judgment range of the output command value in which the current amplitude of each phase is the highest is set in advance, the output command value of the phase within the judgment range is corrected by a first correction amount, and the output command value of the other phase is corrected by a second correction amount that is 1/2 of the first correction amount. The motor control device according to claim 1, characterized in that the AC motor is a three-phase AC motor, and further includes 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 source decreases, the highest output command value among the output command values of 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 that is 1/2 of the first correction amount. The motor control device according to any one of claims 1 to 5, characterized in that the correction amount is calculated based on at least one of the slope of the voltage and the output current output from the power conversion circuit to the AC motor, or a combination of these. The motor control device according to claim 6, characterized in that the larger the voltage gradient, the larger the correction amount is. The motor control device according to claim 6, characterized in that the correction amount is increased as the output current increases. The motor control device according to any one of claims 1 to 5, characterized in that the correction amount is reduced as the temperature of the driven AC motor increases. The motor control device according to any one of claims 1 to 5, characterized in that the correction amount set according to the voltage gradient calculated by the voltage gradient calculation means is reduced in proportion to the elapsed time from the time point when the voltage gradient was calculated. The motor control device according to any one of claims 1 to 5, characterized in that the correction amount is reduced in proportion to the time elapsed since the slope calculated by the voltage slope calculation means becomes zero. The motor control device according to any one of claims 1 to 5, characterized in that the voltage gradient calculated by the voltage gradient calculation means is corrected by the correction amount when it is greater than a predetermined voltage gradient threshold value. The motor control device according to any one of claims 1 to 5, characterized in that the voltage gradient calculation means calculates the voltage gradient based on fluctuations in the detected voltage of the DC power source. The motor control device according to any one of claims 1 to 5, characterized in that the voltage gradient calculation means calculates the voltage gradient 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. The motor control device according to any one of claims 1 to 5, characterized in that the switching element is formed from a wide band gap semiconductor. An electric motor drive system comprising an electric motor control device according to any one of claims 1 to 5 and an AC motor connected to the electric motor control device.

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