Control device for electric motor

Abstract

The purpose of the present disclosure is to provide a control device for an electric motor capable of protecting the winding of the electric motor without excessive limitation when the electric motor is driven by a power conversion device that does not include a boost converter.　The present disclosure provides a control device for an electric motor when the electric motor is driven using a power conversion device that does not include a boost converter, the control device comprising: a withstand voltage calculation unit that calculates the withstand voltage of the electric motor; an allowable surge voltage calculation unit that calculates the allowable surge voltage of the electric motor on the basis of the withstand voltage, a voltage sharing ratio, and an input voltage to the power conversion device; a phase current limit value calculation unit that calculates a phase current limit value on the basis of the allowable surge voltage; a power limit value calculation unit that calculates a power limit value on the basis of the input voltage to the power conversion device, the allowable surge voltage, and the phase current limit value; a current calculation unit that calculates an output current to the electric motor on the basis of a torque command value of the electric motor; and a torque limit value calculation unit that calculates a torque limit value of the electric motor on the basis of the power limit value, a rotational speed of the electric motor, and a loss of the electric motor.

Description

Control device for an electric motor

[0001] The present disclosure relates to a control device for an electric motor.

[0002] Patent Document 1 below discloses a vehicle drive motor control device aimed at controlling according to the state of a vehicle drive motor and the environment in which the vehicle drive motor is disposed. This vehicle drive motor control device includes a vehicle drive motor and a control unit that controls the vehicle drive motor, and the control unit controls the vehicle drive motor based on the temperature of the vehicle drive motor and the atmospheric pressure in the space where the vehicle drive motor is disposed.

[0003] Japanese Patent Application Laid-Open No. 2010-063207

[0004] By the way, in the control of an electric motor mounted on a vehicle, dealing with film thinning of the winding coating of the electric motor has become an important issue. When the winding coating thins, the dielectric breakdown voltage against the surge voltage decreases, so it is necessary to lower the surge voltage by limiting the output of the power conversion device that drives the electric motor. Also, since the dielectric breakdown voltage of the motor winding varies depending on the atmospheric pressure, winding temperature, etc., it is necessary to perform winding protection considering the atmospheric pressure, winding temperature, etc.

[0005] However, when the output is limited too much, there is a problem that the power performance of the electric motor is sacrificed and sufficient power performance cannot be ensured. Also, in conventional models for hybrid vehicles, a boost converter is mounted to boost the battery voltage to an efficient voltage for a plurality of electric motors such as for driving and power generation. When the dielectric breakdown voltage decreases, it is possible to lower the output voltage by adjusting the boost ratio to lower the inverter input voltage. However, for battery electric vehicles, a battery with an output corresponding to the rated voltage of the electric motor is mounted, and since there is no boost converter that is a cause of loss, the inverter input voltage cannot be changed, and it is necessary to suppress the surge voltage by limiting the current when the dielectric breakdown voltage decreases. Furthermore, in the control device for an electric motor for battery electric vehicles, it is necessary to perform winding protection corresponding to the inverter input voltage that varies depending on the SOC (State Of Charge: charge rate) in addition to the atmospheric pressure and winding temperature.

[0006] This disclosure is made in view of the circumstances described above, and aims to provide a motor control device that can protect the motor windings without imposing excessive restrictions when driving a motor with a power conversion device that does not have a boost converter.

[0007] A motor control device according to a first aspect of the present disclosure is a motor control device for driving a motor using a power converter that does not have a boost converter, and comprises: an insulation withstand voltage calculation unit for calculating the insulation withstand voltage of the motor; an allowable surge voltage calculation unit for calculating the allowable surge voltage of the motor based on the insulation withstand voltage, the voltage sharing ratio and the input voltage of the power converter; a phase current limit value calculation unit for calculating a phase current limit value based on the allowable surge voltage; a power limit value calculation unit for calculating a power limit value based on the input voltage of the power converter, the allowable surge voltage and the phase current limit value; a current calculation unit for calculating the output current to the motor based on the torque command value of the motor; and a torque limit value calculation unit for calculating a torque limit value of the motor based on the power limit value, the rotational speed of the motor and the losses of the motor.

[0008] In the first embodiment, the control device for an electric motor according to a second aspect of the present disclosure, the current output unit calculates an output current based on the torque limit value when the torque command value exceeds the torque limit value.

[0009] According to this disclosure, it is possible to provide a motor control device that can protect the motor windings without imposing excessive restrictions when driving a motor with a power conversion device that does not have a boost converter.

[0010] This is a block diagram showing the configuration of a control device for an electric motor according to one embodiment of the present disclosure. This is a characteristic diagram showing the insulation breakdown voltage map in one embodiment of the present disclosure. This is a characteristic diagram showing the phase current-surge voltage characteristics in one embodiment of the present disclosure. This is a flowchart showing the operation of a control device for an electric motor according to one embodiment of the present disclosure. This is an explanatory diagram showing the acquisition of the allowable surge voltage in one embodiment of the present disclosure.

[0011] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In Figure 1, reference numeral A denotes a control device for an electric motor according to this embodiment. This control device A is an in-vehicle device mounted on an electric vehicle and is a functional component that controls the electric motor M via an inverter D.

[0012] Here, we will first explain the functional components other than the control device A. The inverter D is equipped with a pair (two) of primary terminals, three secondary terminals, and three control terminals. In the inverter D, the pair of primary terminals are connected to the positive and negative electrodes of the battery B, respectively. The three secondary terminals are connected to the U-phase terminal, V-phase terminal, and W-phase terminal provided on the electric motor M, respectively. Furthermore, the three control terminals are connected to the three output terminals of the control device A, respectively.

[0013] Under the control of control device A, inverter D converts battery power (DC power) supplied from battery B into three-phase AC power and outputs it to motor M. Specifically, inverter D generates three-phase AC power consisting of U-phase, V-phase, and W-phase based on three control signals (U-phase control signal, V-phase control signal, and W-phase control signal) input from control device A and outputs it to motor M. In addition, inverter D converts regenerative power (AC power) input from motor M into DC regenerative power and outputs it to battery B.

[0014] As shown in the figure, the inverter D is equipped with a voltage sensor 1. This voltage sensor 1 detects the voltage of the DC power input from the battery B to the inverter D as the inverter input voltage. This voltage sensor 1 outputs a detection signal (input voltage detection signal) indicating the inverter input voltage to the control device A. The inverter input voltage is one of the control pieces of information necessary for the control device A to control the electric motor M.

[0015] Such an inverter D is a drive device that directly converts battery power (DC power) into three-phase AC power. In other words, inverter D is a power conversion device that does not have a boost converter to increase the voltage of the battery power (DC power). Since such an inverter D cannot change the input voltage (inverter input voltage) by adjusting the boost rate of the boost converter, it is difficult to reduce the surge voltage that is inevitably output to the motor M.

[0016] Battery B is a battery pack, such as a lithium-ion battery, and is a rechargeable secondary battery. The positive and negative electrodes of battery B are connected to a pair of primary terminals provided on inverter D. That is, the positive electrode of battery B is connected to one of the pair of primary terminals, and the negative electrode of battery B is connected to the other of the pair of primary terminals.

[0017] Battery B outputs battery power (DC power) at a predetermined voltage (battery voltage) to the primary terminals of inverter D from its positive and negative electrodes. In other words, when inverter D is operating in a powered state, battery B is in a discharge state and outputs battery power (DC power) to the primary terminals of inverter D. Also, when inverter D is operating in a regenerative state, battery B is in a charging state and charges with the regenerative power (DC power) input from the primary terminals of inverter D.

[0018] The motor M is equipped with three motor terminals (U-phase terminal, V-phase terminal, and W-phase terminal) connected to the three secondary terminals of the inverter D. Although not shown, the motor M also includes a rotor and motor windings for the U-phase, V-phase, and W-phase that constitute the stator. Each phase motor winding has an insulating winding coating formed on the surface of a conductive wire.

[0019] The electric motor M rotates when the inverter D supplies U-phase, V-phase, and W-phase drive currents to the motor windings of the U-phase, V-phase, and W-phase motors. In other words, this electric motor M is a power generating device that generates rotational torque corresponding to the U-phase, V-phase, and W-phase drive currents.

[0020] Such an electric motor M is, for example, the power source for an electric vehicle. That is, the electric motor M drives the electric vehicle by generating rotational torque corresponding to the U-phase drive current, V-phase drive current, and W-phase drive current. The rotational torque of the electric motor M is a physical quantity that determines the driving speed of the electric vehicle.

[0021] As shown in the figure, the electric motor M is incidentally equipped with a resolver 2, a winding temperature sensor 3, and a pressure sensor 4. The resolver 2 is a rotation sensor that detects the rotation angle of the electric motor M. The resolver 2 outputs a detection signal (rotation angle detection signal) indicating the detected value of the rotation angle to the control device A. The rotation angle detection value, like the battery voltage mentioned above, is one of the control pieces of information necessary for the control device A to control the electric motor M.

[0022] The winding temperature sensor 3 is a temperature sensor that detects the temperature (winding temperature) of the U-phase, V-phase, and W-phase motor windings in the motor M. The winding temperature sensor 3 outputs a detection signal (winding temperature detection signal) indicating the winding temperature to the control device A. The winding temperature, like the battery voltage and rotation angle mentioned above, is one of the control pieces of information necessary for the control device A to control the motor M.

[0023] The pressure sensor 4 is a pressure sensor that detects the atmospheric pressure in the space where the electric motor M is located. The pressure sensor 4 outputs a detection signal (pressure detection signal) indicating atmospheric pressure to the control device A. The atmospheric pressure, like the battery voltage, rotation angle, and winding temperature mentioned above, is one of the control pieces of information necessary for the control device A to control the electric motor M.

[0024] Furthermore, the electric vehicle equipped with the control device A is provided with a driving control unit 5. The driving control unit 5 is an electromechanical component that receives operating instructions from the driver of the electric vehicle. This driving control unit 5 is electrically connected to the control device A and outputs operating signals indicating the driver's operating instructions to the control device A.

[0025] The operation instructions include a torque command value, which is the target value for controlling the electric motor M. This torque command value is an operation instruction supplied from the driving control unit 5 to the control device A based on the amount of accelerator pedal operation (depression amount) by the driver of the electric vehicle.

[0026] As shown in Figure 1, the control device A comprises an isolation voltage map storage unit a1, a surge-current characteristic storage unit a2, a motor loss map storage unit a3, and a control unit a4. These isolation voltage map storage unit a1, surge-current characteristic storage unit a2, motor loss map storage unit a3, and control unit a4 are functional components for controlling the electric motor M, and they work together as a whole to control the electric motor M.

[0027] The dielectric strength map storage unit a1 is electrically connected to the control unit a4 and stores dielectric strength maps in advance. The dielectric strength map storage unit a1 outputs the dielectric strength map to the control unit a4 in response to a read request input from the control unit a4.

[0028] The above insulation breakdown voltage map, as shown in Figure 2, is a data set that shows the relationship (characteristics) between the atmospheric pressure in the space where the motor M is located and the insulation breakdown voltage of the U-phase, V-phase, and W-phase motor windings of the motor M. More specifically, the insulation breakdown voltage map shows the relationship (characteristics) between the atmospheric pressure of the motor M and the insulation breakdown voltage of the motor windings, with the winding temperature of the U-phase, V-phase, and W-phase motor windings as a parameter. As shown in the figure, the relationship (characteristics) between the atmospheric pressure of the motor M and the insulation breakdown voltage of the motor windings is generally proportional.

[0029] The surge-current characteristic storage unit a2 is electrically connected to the control unit a4 and stores the phase current-surge voltage characteristics in advance. The surge-current characteristic storage unit a2 outputs the surge-current characteristics to the control unit a4 in response to a read request input from the control unit a4.

[0030] The above phase current-surge voltage characteristics, as shown in Figure 3, are a set of data showing the relationship (characteristics) between the phase current limit values ​​of the motor M, i.e., the limit values ​​of the U-phase drive current, V-phase drive current, and W-phase drive current (phase current limit values), and the surge voltage. Note that the surge voltage and the phase current limit values ​​are proportional, as shown in the figure.

[0031] The motor loss map storage unit a3 is electrically connected to the control unit a4 and stores the motor loss map in advance. The motor loss map storage unit a3 outputs the motor loss map to the control unit a4 in response to a read request input from the control unit a4.

[0032] The motor loss map shown above, although not illustrated, is a data set that illustrates the losses (copper loss and iron loss) of the motor M in relation to the motor M's torque, rotational speed, and the input voltage of the inverter D. Note that the losses of the motor M generally exhibit nonlinear characteristics.

[0033] The control unit a4 is electrically connected to the aforementioned insulation withstand voltage map storage unit a1, surge-current characteristic storage unit a2, and motor loss map storage unit a3. The control unit a4 is also electrically connected to the voltage sensor 1, resolver 2, winding temperature sensor 3, pressure sensor 4, operation unit 5, and inverter D.

[0034] The control unit a4 generates three control signals (U-phase control signal, V-phase control signal, and W-phase control signal) to be supplied to the inverter D by executing a pre-stored control program. When generating the U-phase control signal, V-phase control signal, and W-phase control signal, the control unit a4 refers to the isolation voltage map obtained from the isolation voltage map storage unit a1, the phase current-surge voltage characteristics obtained from the surge-current characteristics storage unit a2, and the motor loss map obtained from the motor loss map storage unit a3.

[0035] Furthermore, when generating the U-phase control signal, V-phase control signal, and W-phase control signal, the control unit a4 refers to the rotation angle detection signal input from the voltage sensor 1, the winding temperature detection signal input from the resolver 2, the winding temperature detection signal input from the winding temperature sensor 3, the pressure detection signal input from the pressure sensor 4, and the operation signal input from the operation unit 5.

[0036] Specifically, the control unit a4 generates three control signals (U-phase control signal, V-phase control signal, and W-phase control signal) based on the insulation breakdown voltage map, phase current-surge voltage characteristics, motor loss map, rotation angle detection value, winding temperature detection value, atmospheric pressure detection value, and torque command value (operation instruction). The control unit a4 controls the motor M via the inverter D by outputting the three control signals to the inverter D.

[0037] Here, although details will be described later, the control unit a4 functions as an insulation withstand voltage calculation unit, an allowable surge voltage calculation unit, a phase current effective value calculation unit, a power limit value calculation unit, a current output unit, and a torque limit value calculation unit in the present invention. Specifically, the control unit a4 calculates the insulation withstand voltage of the motor M and calculates the allowable surge voltage of the motor M based on the insulation withstand voltage and the inverter input voltage of the inverter D (power converter).

[0038] Furthermore, control unit a4 calculates a limit value for the RMS value of the phase current based on the allowable surge voltage, and calculates a power limit value based on the inverter input voltage of inverter D (power converter), the allowable surge voltage, and the RMS value of the phase current.

[0039] Furthermore, the control unit a4 calculates the output current to the motor M based on the torque command value of the motor M, and calculates the torque limit value of the motor M based on the power limit value, the rotational speed of the motor M, and the losses of the motor M. Based on the torque limit value of the motor M calculated in this way, the control unit a4 generates three control signals (U-phase control signal, V-phase control signal, and W-phase control signal).

[0040] Next, the operation of the drive unit A of the electric motor M according to this embodiment will be explained in accordance with the flowchart shown in Figure 4. This flowchart shows the processing procedure based on the control program of the control unit a4.

[0041] First, the control unit a4 obtains the dielectric strength based on the dielectric strength map (step S1). Specifically, in step S1, the control unit a4 obtains the atmospheric pressure in the space where the motor M is located based on the atmospheric pressure detection signal input from the pressure sensor 4, and obtains the winding temperatures of the U-phase, V-phase, and W-phase motor windings based on the winding temperature detection signal input from the winding temperature sensor 3. Then, the control unit a4 retrieves the dielectric strength of the U-phase, V-phase, and W-phase motor windings corresponding to the atmospheric pressure and winding temperatures by searching the dielectric strength map using the atmospheric pressure and winding temperatures.

[0042] Next, as shown in Figure 5, the control unit a4 obtains the allowable surge voltage by subtracting the inverter input voltage from the value obtained by dividing the dielectric strength by the voltage distribution ratio (step S2). That is, in step S2, the control unit a4 considers that the voltage applied to the motor winding is distributed within the winding and converts the dielectric strength to the dielectric strength at the input terminal by dividing the dielectric strength by the voltage distribution ratio (ratio of input voltage to maximum voltage between windings). It also obtains the inverter input voltage based on the input voltage detection signal input from the voltage sensor 1. Then, the control unit a4 obtains the allowable surge voltage of the motor M by subtracting the inverter input voltage from the value obtained in step S1 by dividing the dielectric strength of the motor winding by the voltage distribution ratio.

[0043] Next, the control unit a4 acquires current limit values ​​based on the phase current-surge voltage characteristics (step S3). That is, the control unit a4 retrieves the phase current-surge voltage characteristics of the surge-current characteristic storage unit a2 using the allowable surge voltage acquired in step S2, thereby acquiring the limit values ​​(phase current limit values) for the phase currents of the motor M, namely the U-phase drive current, V-phase drive current, and W-phase drive current.

[0044] Next, the control unit a4 calculates an inverter output power limit value based on the phase current limit value (step S4). That is, the control unit a4 calculates the inverter output power limit value P based on the following formula (1), where the effective value of the line voltage is "V", the phase current limit value is "I", and the power factor of the motor M is "cosθ". P = √3 × V × I × cosθ (1)

[0045] Next, the control unit a4 calculates a torque limit value of the motor M based on the inverter output power limit value P (step S5). That is, in step S5, the control unit a4 obtains the loss L of the motor M by searching the motor loss map in the motor loss map storage unit a3 using the torque, rotational speed N, and input voltage of the inverter D of the motor M.

[0046] Further, the control unit a4 calculates the torque limit value T of the motor M by substituting the rotational speed N, loss L, and inverter output power limit value P of the motor M into the following formula (2). T = (P - L) × 60 / 2πN (2)

[0047] Then, the control unit a4 generates three control signals (U-phase control signal, V-phase control signal, and W-phase control signal) by limiting the torque command value (target value) input from the operation control unit 5 based on the torque limit value T. The inverter D generates three-phase AC power composed of the U-phase, V-phase, and W-phase based on the three control signals thus generated in the drive device A and outputs it to the motor M.

[0048] The drive device A for the motor M according to this embodiment is used when driving the motor M using an inverter D (power conversion device) that does not include a boost converter, and includes an insulation breakdown voltage calculation unit that calculates the insulation breakdown voltage of the motor, an allowable surge voltage calculation unit that calculates the allowable surge voltage of the motor based on the insulation breakdown voltage and the input voltage of the power conversion device, a phase current limit value calculation unit that calculates a phase current limit value based on the allowable surge voltage, a power limit value calculation unit that calculates a power limit value based on the input voltage of the power conversion device, the allowable surge voltage, and the phase current limit value, a current calculation unit that calculates an output current to the motor based on the torque command value of the motor, and a torque limit value calculation unit that calculates a torque limit value of the motor based on the power limit value, the rotational speed of the motor, and the loss of the motor as a control unit a4.

[0049] According to such this embodiment, when driving the motor M with an inverter D (power conversion device) that does not include a boost converter, when the torque command value exceeds the torque limit value, it is possible to protect the windings of the motor M without excessive restriction.

[0050] Further, in the drive device A for the motor M according to this embodiment, when the torque command value exceeds the torque limit value, an output current is calculated based on the torque limit value. According to such this embodiment, since the output current of the inverter D (power conversion device) is limited by the torque command value (target value) being limited by the torque limit value, it is possible to accurately protect the windings of the motor M.

[0051] This disclosure can be used for a control device for a motor when driving the motor with a power conversion device that does not include a boost converter.

[0052] A Control device a1 Insulation breakdown voltage map storage unit a2 Surge-current characteristic storage unit a3 Motor loss map storage unit a4 Control unit B Battery D Inverter M Motor 1 Voltage sensor 2 Resolver 3 Winding temperature sensor 4 Air pressure sensor 5 Operation operation unit

Claims

1. A motor control device for driving an electric motor using a power conversion device that does not have a boost converter, comprising: an insulation withstand voltage calculation unit for calculating the insulation withstand voltage of the electric motor; an allowable surge voltage calculation unit for calculating the allowable surge voltage of the electric motor based on the insulation withstand voltage, the voltage sharing ratio, and the input voltage of the power conversion device; a phase current limit value calculation unit for calculating a phase current limit value based on the allowable surge voltage; a power limit value calculation unit for calculating a power limit value based on the input voltage of the power conversion device, the allowable surge voltage, and the phase current limit value; a current calculation unit for calculating the output current to the electric motor based on the torque command value of the electric motor; and a torque limit value calculation unit for calculating a torque limit value of the electric motor based on the power limit value, the rotational speed of the electric motor, and the losses of the electric motor.

2. A motor control device according to claim 1, wherein if the torque command value exceeds the torque limit value, the motor control device calculates the output current based on the torque limit value.

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