JP7287339B2 - motor drive system - Google Patents

Description

The present disclosure relates to motor drive systems.

International Publication No. 2013/001634 (Patent Document 1) discloses a motor drive device that selectively switches between a PWM control mode and a rectangular wave voltage control mode to control a motor generator. This motor drive device has a functional expression approximating the power loss characteristics of the inverter and the motor generator with a primary expression and a secondary expression for the system voltage for each operating point of the motor generator. is calculated (see Patent Document 1).

WO2013/001634

For example, it is conceivable to operate the motor drive system by calculating an ideal voltage command so as to minimize the power loss of the inverter and the motor generator according to the above-described functional expression. However, the voltage command may fluctuate continuously according to the function formula. When the output voltage of the buck-boost converter, which supplies the system voltage to the inverter, fluctuates in accordance with the continuously fluctuating voltage command, the output power of the motor generator and the output current of the battery fluctuate. stability (system stability) and increased power loss.

Therefore, it is desirable to appropriately set the voltage resolution of the voltage command so as to be discrete to some extent, and to follow the minimum power loss and stabilize the system. However, depending on the control mode of voltage conversion in the inverter (PWM control mode or rectangular wave voltage control mode), the voltage range of the system voltage in which the power loss of the inverter and motor generator can be minimized differs. Therefore, for example, if the voltage resolution is uniquely determined, it may not be possible to follow the minimum power loss depending on the control mode. It is conceivable to increase the voltage resolution over the entire voltage range that the system voltage can take, but this may increase the computational processing load and lead to a decrease in computational efficiency.

The present disclosure has been made to solve the above problems, and its purpose is to appropriately set the voltage resolution of a voltage command to suppress power loss in a motor drive system.

A motor drive system according to this disclosure is a motor drive system that drives a motor generator, and is provided between a DC power supply, an inverter, and the DC power supply and the inverter. It includes a converter that boosts the voltage to a voltage or higher, and a control device that controls the inverter and the converter. The inverter selectively switches a control mode between a PWM control mode in which a pulse width modulated voltage is applied to the motor generator and a rectangular wave voltage control mode in which a phase-controlled rectangular wave voltage is applied to the motor generator. to drive. This motor drive system is mounted on a vehicle. The controller determines the voltage resolution pattern of the system voltage as a function of vehicle speed. Then, for the system voltage, the control device sets, in the voltage command, the voltage value that minimizes the power loss of the inverter and the motor generator among a plurality of voltage values based on the voltage resolution pattern determined according to the speed of the vehicle. . The control device controls the converter to output the voltage of the set voltage command.

According to the above configuration, the control device determines the voltage resolution pattern according to the vehicle speed. The inventors focused on the relationship between the vehicle speed of a vehicle equipped with a motor drive system and the control mode. If the vehicle speed is low, there is a high possibility that the PWM control mode will be selected as the control mode, and if the vehicle speed is medium speed, there is a possibility that the control mode will be switched between the PWM control mode and the rectangular wave voltage control mode. is high and the vehicle speed is high, there is a high possibility that the rectangular wave voltage control mode will be selected as the control mode.

After determining the voltage resolution pattern according to the vehicle speed, the control device provides a voltage command for the system voltage that minimizes the power loss of the inverter and the motor generator, among a plurality of voltage values based on the determined voltage resolution pattern. set to Power loss in the motor drive system can be suppressed by operating the motor drive system based on the voltage command set in this way.

According to the present disclosure, it is possible to appropriately set the voltage resolution of the voltage command and suppress an increase in power loss in the motor drive system.

1 is an overall configuration diagram of a vehicle provided with a motor drive system according to an embodiment; FIG. FIG. 2 is a diagram for explaining control modes of a motor generator; FIG. FIG. 4 is a diagram showing system loss characteristics at operating points of a motor generator to which PWM control is applied; FIG. 4 is a diagram showing system loss characteristics at operating points of a motor generator to which rectangular wave voltage control is applied; FIG. 4 is a diagram showing characteristics of system loss at operating points where control modes are switched due to changes in system voltage; FIG. 10 is a diagram showing a first resolution pattern selected at low speed and the appearance frequency of the lowest point voltage at low speed; FIG. 10 is a diagram showing a second resolution pattern selected at medium speed and the appearance frequency of the lowest point voltage at medium speed; FIG. 10 is a diagram showing a third resolution pattern selected at high speed and the appearance frequency of the lowest point voltage at high speed; It is a functional block diagram of a control device. FIG. 10 is a diagram showing results of system loss calculated for each voltage value of the system voltage based on the voltage resolution pattern; 4 is a flow chart showing a procedure of processing executed by a control device; 4 is a flow chart showing a procedure of processing for determining a voltage resolution pattern; 4 is a flowchart showing a procedure of processing for calculating system loss; FIG. 4 is a diagram for explaining system loss in a motor drive system according to an embodiment and a motor drive system according to a comparative example;

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated.

<Overall composition>
FIG. 1 is an overall configuration diagram of a vehicle 1 provided with a motor drive system 100 according to this embodiment. Vehicle 1 is an electric vehicle. Note that the vehicle 1 may be any vehicle to which the motor drive system 100 is applied, and is not limited to being an electric vehicle. Vehicle 1 may be, for example, a hybrid vehicle or a fuel cell vehicle.

Referring to FIG. 1 , vehicle 1 includes motor drive system 100 , driving wheels 310 and vehicle speed sensor 320 . The motor drive system 100 includes a motor generator 10, a power control unit (PCU) 20, a battery 30, a monitoring unit 35, system main relays SR1 and SR2, a control device 40, and a current sensor 60. , a rotation angle sensor (resolver) 65 and a temperature sensor 67 .

Motor generator 10 is, for example, a driving electric motor that generates torque for driving drive wheels 310 of vehicle 1 . Motor generator 10 is an AC rotary electric machine, and is configured, for example, as a permanent magnet type synchronous motor having a rotor in which permanent magnets are embedded. Motor generator 10 may further have a function of a generator, or may be configured to have both functions of a motor and a generator.

The battery 30 is composed of a secondary battery such as a nickel-metal hydride battery or a lithium-ion battery. The secondary battery may be a secondary battery having a liquid electrolyte between the positive electrode and the negative electrode, or may be a secondary battery having a solid electrolyte (all-solid battery). Moreover, the battery 30 may be configured by an electric double layer capacitor or the like.

The monitoring unit 35 detects the voltage of the battery 30 (battery voltage) VB, the input/output current of the battery 30 (battery current) IB, and the temperature of the battery 30 (battery temperature) TB, and controls signals indicating these detection results. Output to device 40 .

System main relay SR1 is connected between the positive terminal of battery 30 and power line PL1. System main relay SR2 is connected between the negative terminal of battery 30 and power line NL. System main relays SR<b>1 and SR<b>2 are switched between open and closed states by a control signal from control device 40 .

PCU 20 boosts the DC power supplied from battery 30 , converts it into AC power, and supplies it to motor generator 10 . PCU 20 also converts AC power generated by motor generator 10 into DC power and supplies the DC power to battery 30 . That is, battery 30 can transfer electric power to and from motor generator 10 via PCU 20 .

PCU 20 includes a capacitor C 1 , a step-up/down converter 21 , a capacitor C 2 , an inverter 22 and a voltage sensor 23 .

Capacitor C1 is connected between power line PL1 and power line NL. The capacitor C<b>1 smoothes the battery voltage VB and supplies it to the step-up/step-down converter 21 . A voltage sensor may be provided to detect the voltage across capacitor C1, and the value detected by the voltage sensor may be used as battery voltage VB.

Buck-boost converter 21 boosts battery voltage VB according to control signals S1 and S2 from control device 40, and supplies the boosted voltage to power lines PL2 and NL. Buck-boost converter 21 steps down the DC voltage between power lines PL2 and NL supplied from inverter 22 to charge battery 30 in accordance with control signals S1 and S2 from control device 40 .

Specifically, buck-boost converter 21 includes a reactor L, switching elements Q1 and Q2, and diodes D1 and D2. Reactor L is connected between a connection node of switching elements Q1 and Q2 and power line PL1. Each of switching elements Q1, Q2 and switching elements Q3 to Q8, which will be described later, can be, for example, an IGBT (Insulated Gate Bipolar Transistor), a MOS (Metal Oxide Semiconductor) transistor, a bipolar transistor, or the like. Diodes D1 and D2 are connected in anti-parallel between the collectors and emitters of switching elements Q1 and Q2, respectively.

Capacitor C2 is connected between power line PL2 and power line NL. Capacitor C<b>2 smoothes the DC voltage supplied from step-up/step-down converter 21 and supplies it to inverter 22 . Voltage sensor 23 detects the voltage across capacitor C2, that is, the voltage VH between power lines PL2 and NL connecting buck-boost converter 21 and inverter 22 (hereinafter also referred to as “system voltage”), and a signal indicating the detection result. is output to the control device 40 .

Inverter 22 includes a U-phase arm 221 , a V-phase arm 222 and a W-phase arm 223 . Each phase arm is connected in parallel between power line PL2 and power line NL. The U-phase arm has switching elements Q3 and Q4 connected in series. V-phase arm 222 has switching elements Q5 and Q6 connected in series. W-phase arm 223 has switching elements Q7 and Q8 connected in series. Diodes D3 to D8 are connected in anti-parallel between the collectors and emitters of the switching elements Q3 to Q8, respectively.

The midpoint of each phase arm is connected to each phase end of each phase coil of motor generator 10 . An intermediate point of switching elements Q3 and Q4 is connected to one end of a U-phase coil of motor generator 10 . An intermediate point of switching elements Q5 and Q6 is connected to one end of the V-phase coil of motor generator 10 . An intermediate point of switching elements Q7 and Q8 is connected to one end of a W-phase coil of motor generator 10. FIG. The other ends of the three U-phase, V-phase and W-phase coils of motor generator 10 are commonly connected to a neutral point.

When system voltage VH is supplied, inverter 22 converts a DC voltage into an AC voltage to drive motor generator 10 in accordance with control signals S3-S8 from control device . Thus, motor generator 10 is controlled by inverter 22 to generate torque according to torque command value Trqcom.

When the torque command value of motor generator 10 is positive (Trqcom>0), inverter 22 converts DC voltage to AC voltage by switching elements Q3-Q8 according to control signals S3-S8 from control device 40. The motor generator 10 is driven so as to convert and output a positive torque. Thereby, motor generator 10 is driven to generate positive torque.

When the torque command value of motor generator 10 is zero (Trqcom=0), inverter 22 converts DC voltage into AC voltage by switching elements Q3-Q8 according to control signals S3-S8 from control device 40. The motor generator 10 is driven so that the torque is converted to zero. Thereby, the motor generator 10 is driven to generate zero torque.

When the torque command value of motor generator 10 is negative (Trqcom<0), inverter 22 converts DC voltage into AC voltage by switching elements Q3-Q8 according to control signals S3-S8 from control device 40. The motor generator 10 is driven so as to convert and output a negative torque. Thereby, motor generator 10 is driven to generate negative torque.

Current sensor 60 detects three-phase currents (motor currents) iu, iv, and iw flowing through motor generator 10 and outputs signals indicating the detection results to control device 40 .

Rotation angle sensor (resolver) 65 detects a rotation angle θ of motor generator 10 and outputs a signal indicating the detection result to control device 40 . Control device 40 can detect the rotation speed (rotation speed) Nm of motor generator 10 from the rate of change of rotation angle θ detected by rotation angle sensor 65 .

Temperature sensor 67 detects temperature TM of motor generator 10 and outputs a signal indicating the detection result to control device 40 .

Vehicle speed sensor 320 detects the speed (vehicle speed) V of vehicle 1 and outputs a signal indicating the detection result to control device 40 .

The control device 40 receives a torque command value Trqcom input from an externally provided electronic control unit (higher-level ECU: not shown), a battery voltage VB detected by the monitoring unit 35, a system voltage detected by the voltage sensor 23, Based on VH, motor currents iu, iv, and iw from current sensor 60 and rotation angle θ from rotation angle sensor 65, step-up/step-down converter 21 is adjusted so that motor generator 10 outputs torque according to torque command value Trqcom. and the operation of the inverter 22 . That is, control device 40 generates control signals S 1 to S 8 for controlling buck-boost converter 21 and inverter 22 and outputs them to buck-boost converter 21 and inverter 22 .

During the boosting operation of buck-boost converter 21, control device 40 feedback-controls output voltage VH of capacitor C2 and generates control signals S1 and S2 so that output voltage VH becomes voltage command VHr.

Further, when control device 40 receives a signal RGE indicating that vehicle 1 has entered the regenerative braking mode from the host ECU, control device 40 receives control signals S3 to S8 to convert AC voltage generated by motor generator 10 into DC voltage. is generated and output to the inverter 22 . As a result, inverter 22 converts the AC voltage generated by motor generator 10 into a DC voltage and supplies the DC voltage to step-up/down converter 21 . Control device 40 generates control signals S<b>1 and S<b>2 to step down the DC voltage supplied from inverter 22 , and outputs the signals to step-up/step-down converter 21 . As a result, the AC voltage generated by the motor generator 10 is converted into a DC voltage, stepped down, and supplied to the battery 30 .

Further, control device 40 generates a control signal for switching the open/close state of system main relays SR1 and SR2, and outputs the control signal to system main relays SR1 and SR2.

<Motor generator control mode>
FIG. 2 is a diagram for explaining the control mode of motor generator 10. As shown in FIG. Motor drive system 100 according to the present embodiment switches between a PWM (Pulse Width Modulation) control mode and a rectangular wave voltage control mode for control of motor generator 10 , that is, power conversion in inverter 22 .

PWM control modes include sinusoidal PWM control and overmodulation PWM control. In the sinusoidal PWM control, the upper and lower arms of each phase of the inverter 22 are on/off controlled in accordance with a pulse width modulated signal generated based on the magnitude comparison between a sinusoidal voltage command and a carrier wave (typically a triangular wave). be done. As a result, for a set of high-level periods corresponding to the ON period of the upper arm and low-level periods corresponding to the ON period of the lower arm, the fundamental wave component of the upper and lower arms becomes a sine wave within a certain period. Duty is controlled. In this sinusoidal PWM control in which the amplitude of the sinusoidal voltage command is limited to the carrier wave amplitude or less, as is well known, the voltage applied to the motor generator 10 (hereinafter simply referred to as "motor voltage") is The fundamental wave component can only be increased to approximately 0.61 times the input voltage. The ratio of the fundamental wave component (rms value) of the motor voltage (line voltage) to the input voltage (that is, system voltage VH) of inverter 22 is hereinafter referred to as "modulation factor".

Overmodulation PWM control performs PWM control similar to the above sine wave PWM control within a range in which the amplitude of the voltage command (sine wave component) is greater than the amplitude of the carrier wave. In particular, by distorting the voltage command from the original sine wave waveform (amplitude correction), the fundamental wave component can be increased, and the modulation rate can be increased from the maximum modulation rate in sine wave PWM control to a range of 0.78. can. In overmodulation PWM control, since the amplitude of the voltage command (sine wave component) is greater than the amplitude of the carrier wave, the line voltage applied to motor generator 10 is not a sine wave but a distorted voltage.

In the rectangular wave voltage control, one pulse of a rectangular wave having a high-level period and a low-level period at a ratio of 1:1 is applied to the motor generator 10 within the predetermined period. This increases the modulation factor to 0.78 in square wave voltage control.

In motor generator 10, the induced voltage increases as the number of rotations and/or the output torque increases, so the required drive voltage (required motor voltage) increases. The voltage boosted by the buck-boost converter 21, that is, the system voltage VH must be set higher than the motor required voltage. On the other hand, system voltage VH has a limit value (VH maximum voltage). Therefore, a PWM control mode based on sine wave PWM control or overmodulation PWM control, and a rectangular wave voltage control mode as a kind of field weakening control are selectively applied according to the operating state of motor generator 10 . In rectangular wave voltage control, since the amplitude of the voltage applied to the motor is fixed, phase control of the rectangular wave voltage pulse based on the torque deviation from the torque command value (the difference between the actual torque value (estimated value) and the torque command value) Torque control is executed by

Controller 40 determines which of the control modes shown in FIG. 2 to use based on the modulation factor. Specifically, the control device 40 uses sine wave PWM control in a low rotation region where the motor voltage is low and the modulation rate is low. Control device 40 uses overmodulation PWM control and rectangular wave voltage control, respectively, in the middle speed range and high speed range where the modulation factor increases as the motor voltage increases.

Here, in motor drive system 100, it is desirable to reduce the power loss of inverter 22 and motor generator 10 (hereinafter also referred to as "system loss"). Power loss in inverter 22 is also referred to as "inverter loss", and power loss in motor generator 10 is also referred to as "motor loss".

In order to reduce the system loss, for example, a functional expression that defines the relationship between the system loss and the system voltage is derived, and the ideal voltage command is calculated so that the system loss is minimized according to the functional expression, and the motor drive system 100 can be considered to operate. However, in such a case, the voltage command may continuously fluctuate according to the functional formula. When the output voltage of step-up/step-down converter 21 fluctuates in accordance with the continuously fluctuating voltage command, the output power of motor generator 10 and the output current of battery 30 fluctuate, resulting in stability of the output of motor generator 10. (system stability) and increased system loss.

Therefore, it is desirable to appropriately set the voltage resolution of the voltage command so as to be discrete to some extent, and to follow the minimum power loss and stabilize the system. However, as will be described later with reference to FIGS. 3 to 5, the voltage range of system voltage VH in which system loss can be minimized differs depending on the control mode of motor generator 10 (the control mode of voltage conversion in inverter 22). Therefore, for example, if the voltage resolution is uniquely determined, it may not be possible to track the minimum system loss depending on the control mode. It is conceivable to increase the voltage resolution over the entire voltage range that system voltage VH can take, but this may increase the computational processing load and lead to a decrease in computational efficiency.

Therefore, in motor drive system 100 according to the present embodiment, a plurality of voltage resolution patterns (in the present embodiment, first to third resolution patterns to be described later) for a voltage command are stored, and control mode of motor generator 10 is stored. determines the voltage resolution pattern. In the voltage resolution pattern, a high-resolution voltage region (high-resolution region) and a low-resolution voltage region (low-resolution region) are set in the voltage range that system voltage VH can take. Each resolution in the high-resolution region and the low-resolution region is set, for example, based on experiments and simulations, so as to appropriately balance the calculation of the minimum system loss and the reduction in computational efficiency due to an increase in computational load. be. As a result, even in the high resolution area, the voltage is set to be discrete to some extent. Although the details will be described later, the voltage bands set in the high resolution area and the low resolution area differ depending on the voltage resolution pattern. A detailed description will be given below in order.

3 to 5 are diagrams for explaining trends in loss characteristics showing the relationship between system voltage VH and system loss.

FIG. 3 is a diagram showing characteristics of system loss at operating points of motor generator 10 to which PWM control is applied. Referring to FIG. 3, in the PWM control mode, the system loss characteristic is substantially proportional to system voltage VH. That is, in the PWM control mode, the current is determined when the operating point (torque and rotation speed) of motor generator 10 is determined, and the current is constant regardless of system voltage VH. Therefore, even if system voltage VH changes, the copper loss of motor generator 10 and the ON loss of inverter 22 do not change. On the other hand, the switching loss of inverter 22 depends on system voltage VH and is proportional to system voltage VH. Therefore, the system loss characteristics when the control mode is the PWM control mode can be approximated by a linear expression of the system voltage VH. As can be recognized from FIG. 3, the system voltage VH at which the system loss is minimized (hereinafter also referred to as "lowest point voltage") exists in a region where the system voltage VH is low.

FIG. 4 is a diagram showing characteristics of system loss at operating points of motor generator 10 to which rectangular wave voltage control is applied. Referring to FIG. 4, in the rectangular wave voltage control mode, the system loss characteristic is indicated by a curve in which the loss monotonously decreases as system voltage VH rises and no inflection point exists. In the rectangular wave voltage control mode, the motor voltage is constant (constant amplitude), and the copper loss of motor generator 10 is dominant. The current changes when the system voltage VH changes, and the current increases when the system voltage VH decreases. Since the copper loss is proportional to the square of the current, the characteristics of the system loss when the control mode is the rectangular wave voltage control mode can be approximated by the quadratic expression of the system voltage VH. As can be recognized from FIG. 4, the nadir voltage exists in the region where the system voltage VH is high.

FIG. 5 is a diagram showing system loss characteristics at an operating point at which the control mode is switched due to changes in system voltage VH. Referring to FIG. 5, at this operating point, the system loss is characterized by a curve with one local minimum and no inflection points. More specifically, at this operating point, the PWM control mode is applied when system voltage VH is high, and the square wave voltage control mode is applied when system voltage VH is low. Therefore, in the region where the system voltage VH is low, the curve is close to the quadratic equation of the system voltage VH as described with reference to FIG. 4, and in the region where the system voltage VH is high, the linear equation becomes a straight line close to As can be recognized from FIG. 5, at the operating point at which the control mode is switched, the lowest point voltage is the local minimum system voltage.

As described with reference to FIGS. 3 to 5, the voltage range in which the lowest point voltage can exist differs depending on the control mode of motor generator 10. FIG. Here, the inventors paid attention to the relationship between the vehicle speed V and the control mode. When the vehicle speed is "low speed" lower than the first threshold speed Vth1, there is a high possibility that the operating point of the motor generator 10 will be the operating point at which the PWM control mode is selected as the control mode. When the vehicle speed is equal to or higher than the first threshold speed Vth1 and is lower than the second threshold speed Vth2 (>Vth1), the operating point of the motor generator 10 is the operating point near the switching of the control mode. Probability is high. When the vehicle speed is at or above the second threshold speed Vth2, i.e., at a "high speed", the operating point of motor generator 10 is likely to be the operating point at which the rectangular wave voltage control mode is selected as the control mode. That is, when the vehicle speed V is low, there is a high possibility that the PWM control mode will be selected. is likely to select the rectangular wave voltage control mode.

Therefore, in the present embodiment, control device 40 selects a voltage resolution pattern according to vehicle speed V. FIG. When the vehicle speed V is low, the control device 40 selects the first resolution pattern as the voltage resolution. When the vehicle speed V is medium speed, the control device 40 selects the second resolution pattern as the voltage resolution. When the vehicle speed V is high, the control device 40 selects the third resolution pattern as the voltage resolution.

FIG. 6 is a diagram showing the first resolution pattern selected at low speed and the appearance frequency of the lowest point voltage at low speed. FIG. 7 is a diagram showing the second resolution pattern selected at medium speed and the appearance frequency of the lowest point voltage at medium speed. FIG. 8 is a diagram showing the third resolution pattern selected at high speed and the appearance frequency of the lowest point voltage at high speed.

Referring to the left diagram of FIG. 6, the first resolution pattern has a high voltage resolution in a low voltage region (for example, V1 or more and less than Vx) in the voltage range (V1 to Vmax) that system voltage VH can take. Also, it is a voltage resolution pattern in which the voltage resolution in a high voltage region (for example, Vx or more and less than Vmax) is set to low resolution.

The right diagram of FIG. 6 is a diagram showing experimental data obtained for the appearance frequency of the lowest point voltage at low speed. As can be recognized from the right diagram of FIG. 6, when the vehicle speed is low, many lowest point voltages appear in the high resolution region (for example, V1 or more and less than Vx). Therefore, it can be appreciated that at low speeds it is desirable to select the first resolution pattern. As a result, system voltage VH can be selected accurately, and system loss can be reduced.

Referring to the left diagram of FIG. 7, the second resolution pattern reduces voltage resolution in a low voltage region (for example, V1 or more and less than Vy) in the voltage range (V1 to Vmax) that system voltage VH can take. And, the voltage resolution is set to high voltage resolution in a region near the middle of the voltage (for example, Vy or more and less than Vz), and the voltage resolution is set to low resolution in a high voltage region (for example, Vz or more and less than Vmax). It's a pattern.

The right diagram of FIG. 7 is a diagram showing experimental data obtained for the appearance frequency of the lowest point voltage at medium speed. As can be recognized from the right diagram of FIG. 7, when the vehicle speed is medium speed, many lowest point voltages appear in the high resolution region (for example, Vy or more and less than Vz). Therefore, it is understood that it is desirable to select the second resolution pattern at medium speeds. As a result, system voltage VH can be selected accurately, and system loss can be reduced.

Referring to the left diagram of FIG. 8, the third resolution pattern reduces voltage resolution in a low voltage region (for example, V1 or more and less than Vw) in the voltage range (V1 to Vmax) that system voltage VH can take. Moreover, it is a voltage resolution pattern that makes the voltage resolution in a high voltage region (for example, Vw or more and less than Vmax) high resolution.

The right diagram of FIG. 8 is a diagram showing experimental data obtained by obtaining the appearance frequency of the lowest point voltage at high speed. As can be recognized from the right diagram of FIG. 8, when the vehicle speed is high, many lowest point voltages appear in the high resolution region (for example, Vw or more and less than Vmax). Therefore, it can be appreciated that at high speeds it is desirable to select the third resolution pattern. As a result, system voltage VH can be selected accurately, and system loss can be reduced.

<Functional block of control device>
FIG. 9 is a functional block diagram of the control device 40. As shown in FIG. Control device 40 includes a system state determination unit 41 , a power loss calculation unit 42 , a voltage command selection unit 43 and a voltage command generation unit 44 .

System state determination unit 41 determines a voltage resolution pattern according to vehicle speed V. FIG. Specifically, the system state determination unit 41 acquires the vehicle speed V from the vehicle speed sensor 320 and determines whether the vehicle speed V is classified into low speed, medium speed, or high speed. When the system state determination unit 41 determines that the vehicle speed V is low, it selects the first resolution pattern as the voltage resolution pattern. When the system state determination unit 41 determines that the vehicle speed V is medium speed, it selects the second resolution pattern as the voltage resolution pattern. When the system state determination unit 41 determines that the vehicle speed V is high, it selects the third resolution pattern as the voltage resolution pattern. System state determination unit 41 outputs the selected voltage resolution pattern to power loss calculation unit 42 .

Since the copper loss and iron loss of motor generator 10 are affected by the temperature of motor generator 10, the characteristics of system voltage VH and system loss shown in FIGS. . For example, the temperature of motor generator 10 may change the operating point of motor generator 10 at which the control mode is switched. Therefore, system state determination unit 41 may determine the voltage resolution pattern in consideration of temperature TM of motor generator 10 or battery temperature TB in addition to vehicle speed V. FIG.

Power loss calculation unit 42 calculates system loss Wsys (Wsys1, Wsys2, . . . , Wsysmax). Torque command value Trqcom, rotation angle θ of motor generator 10 and voltage resolution pattern are input to power loss calculation unit 42 . Torque command value Trqcom is received, for example, from a host ECU, and rotation angle θ of motor generator 10 is received from rotation angle sensor 65 . Power loss calculation unit 42 calculates the number of rotations (rotational speed) Nm of motor generator 10 based on rotation angle θ. Note that the torque command value Trqcom is calculated by the higher-level ECU, for example, based on the vehicle output demand according to the degree of opening of the accelerator.

Power loss calculation unit 42 calculates a motor required voltage (induced voltage) from torque command value Trqcom and rotation speed Nm based on a preset map or the like. The power loss calculator 42 calculates the modulation rate from the motor required voltage and the system voltage, and determines the control mode based on the calculated modulation rate.

When it is determined that the control mode is PWM control, power loss calculation unit 42 calculates d-axis current command Idcom and q-axis current command Iqcom according to torque command value Trqcom. Then, the power loss calculator 42 calculates the current value (current amplitude) I according to the following equation (1) and the current phase θi according to the following equation (2), for example.

I=√{(Idcom) ² +(Iqcom) ² }/√3 (1)
θi=tan ⁻¹ (Iqcom/Idcom)×360/2π+90 (2)
When it is determined that the control mode is rectangular wave voltage control, power loss calculation unit 42 calculates the rectangular wave voltage phase according to torque command value Trqcom. For example, power loss calculation unit 42 calculates estimated torque value Trq according to the following equation (3), and calculates the rectangular wave voltage phase from the relationship between torque command value Trqcom and estimated torque value Trq.

Trq=A+{B×(V/ω)×sin(2πθv/360)}+{C×(V/ω) ² ×sin(2πθv/360)} (3)
A, B, and C are motor dependent constants depending on the motor generator, θv is the rectangular wave voltage phase, and ω is the motor angular velocity. ω is represented by Nm×2π×P (number of pole pairs)/60.

Power loss calculation unit 42 calculates the rectangular wave voltage phase using torque command value Trqcom and torque estimated value Trq as arguments, for example, using a map that defines the relationship between torque command value Trqcom, torque estimated value Trq, and rectangular wave voltage phase. Calculate

Then, the power loss calculation unit 42, for example, stores a map defining the relationship between the rectangular wave voltage phase, the K value (=system voltage VH/angular velocity ω), and the d-axis current command Idcom, and the rectangular wave voltage phase and the K value. and the q-axis current command Iqcom, the d-axis current command Idcom and the q-axis current command Iqcom are calculated. Then, the power loss calculator 42 calculates the current value (current amplitude) I according to the above equation (1) and the current phase θi according to the above equation (2).

After calculating the current value I and the current phase θi according to the control mode as described above, the power loss calculator 42 calculates the inverter loss Winv and the motor loss Wm. First, the power loss calculator 42 uses the current value I and the current phase θi to calculate the d-axis inductance Ld, the q-axis inductance Lq, and the magnetic flux φ due to the permanent magnet of the rotor. For calculation of the d-axis inductance Ld, the q-axis inductance Lq and the magnetic flux φ, a map defining the relationship between the current value I, the current phase θi and the d-axis inductance Ld, the current value I, the current phase θi and the q-axis inductance Lq and a map that defines the relationship between the current value I and the magnetic flux φ are used.

Power loss calculator 42 calculates inverter loss Winv according to the following equation (4).

Winv=A1×I×VHr+A2×I (4)
A1 and A2 are inverter loss coefficients and inverter dependent constants dependent on the inverter 22 . VHr is a voltage command.

Motor loss Wm includes “motor copper loss Wc” indicating the copper loss of motor generator 10 and “motor iron loss Wiron” indicating the iron loss of motor generator 10 . Power loss calculator 42 calculates motor copper loss Wc and motor iron loss Wiron according to the following equations (5) and (6), respectively.

Wc=B1× ^I2 (5)
B1 is the motor copper loss coefficient and is a motor dependent constant.

Wiron=C1( ^Ld2 × ^ω2 × ^I2 ×(sinθi) ² )+C2(φ× ^ω2 )+C3(Lq× ^ω2 ×I×cosθi) (6)
C1, C2, and C3 are motor iron loss coefficients and motor dependent constants.

Power loss calculator 42 adds motor copper loss Wc and motor iron loss Wiron to calculate motor loss Wm (=Wc+Wiron). Power loss calculation unit 42 then adds inverter loss Winv and motor loss Wm to calculate system loss Wsys (=Winv+Wm). Power loss calculation unit 42 calculates system loss Wsys for each voltage value for a plurality of voltage values of system voltage VH based on the voltage resolution pattern, and outputs the calculated plurality of system losses Wsys to voltage command selection unit 43. do.

Upon receiving a plurality of system losses Wsys, voltage command selection unit 43 selects a voltage value that minimizes system loss Wsys, and sets the selected voltage value as voltage command VHr. Voltage command selection unit 43 then outputs voltage command VHr to voltage command generation unit 44 .

FIG. 10 is a diagram showing results of system loss Wsys calculated for each voltage value (V1, V2, . . . , Vmax) of the system voltage based on the voltage resolution pattern. For example, when the voltage value is V1, the system loss of Wsys1 is calculated, and when the voltage value is V2, the system loss of Wsys2 is calculated. The magnitude of the difference between adjacent voltage values (specifically, for example, the magnitude of the difference between V1 and V2 and the magnitude of the difference between V2 and V3) varies depending on the voltage resolution pattern. Voltage command selection unit 43 selects the minimum system loss Wsys, sets a voltage value corresponding to system loss Wsys to voltage command VHr, and outputs voltage command VHr to voltage command generation unit 44 .

Referring to FIG. 9 again, voltage command generator 44 receives battery voltage VB and voltage command VHr. Voltage command generation unit 44 generates control signals S1 and S2 so that system voltage VH becomes voltage command VHr, and outputs the generated control signals S1 and S2.

<Processing Executed by Control Device>
FIG. 11 is a flow chart showing a procedure of processing executed by the control device 40. As shown in FIG. The flowchart shown in FIG. 11 is repeatedly executed by the control device 40 at each predetermined control cycle. 11 and FIGS. 12 and 13 to be described later (steps are abbreviated as "S" below) will be described as being realized by software processing by the control device 40, but some or all of them may be implemented by hardware (electrical circuitry) fabricated within the control device 40 .

Control device 40 acquires torque command value Trqcom and rotation angle θ of motor generator 10 (S1). Control device 40 calculates rotation speed Nm of motor generator 10 using acquired rotation angle θ.

The control device 40 acquires the vehicle speed V (S3). Then, control device 40 determines a voltage resolution pattern based on vehicle speed V (S5). FIG. 12 is a flow chart showing a procedure of processing for determining a voltage resolution pattern.

The control device 40 determines whether or not the vehicle speed V is low (S51). Specifically, control device 40 determines whether or not vehicle speed V is within a predetermined low speed range.

If it is determined that vehicle speed V is low (YES in S51), control device 40 determines the first resolution pattern as the voltage resolution pattern (S53).

If it is determined that the vehicle speed is not low (NO in S51), control device 40 determines whether vehicle speed V is medium speed (S55). Specifically, control device 40 determines whether or not vehicle speed V is within a predetermined medium speed range.

If it is determined that the vehicle speed is medium speed (YES in S53), control device 40 determines the second resolution pattern as the voltage resolution pattern (S57).

If it is determined that the vehicle speed is not medium speed (NO in S53), control device 40 determines that the vehicle speed is high speed, and determines the voltage resolution pattern to be the third resolution pattern (S59).

Referring to FIG. 11 again, when the voltage resolution pattern is determined, control device 40 calculates the system loss for each voltage value (V1, V2, . . . , Vmax) of system voltage VH based on the determined voltage resolution pattern. Calculate (S7).

FIG. 13 is a flowchart showing a procedure of processing for calculating system loss. Control device 40 selects one voltage value based on the determined voltage resolution pattern (S71).

Control device 40 calculates motor required voltage (induced voltage) VM from torque command value Trqcom and rotational speed Nm based on a preset map or the like (S72).

Control device 40 calculates a modulation rate (VM/VH) from required motor voltage VM and system voltage VH (S73). The control device 40 determines the control mode based on the modulation rate (S74).

Then, control device 40 calculates current value I and current phase θi according to the determined control mode (S75).

Control device 40 uses current value I and current phase θi to calculate inverter loss Winv and motor loss Wm, respectively (S76, 77). Control device 40 calculates inverter loss Winv according to the above equation (4) (S76). Further, the control device 40 calculates the motor copper loss Wc according to the above equation (5), calculates the motor iron loss Wiron according to the above equation (6), and calculates the calculated motor copper loss Wc and the motor iron loss Wiron. Then, the motor loss Wm is calculated (S77).

Control device 40 adds the calculated inverter loss Winv and motor loss Wm to calculate system loss Wsys (S78). Control device 40 associates the calculated system loss Wsys with the voltage and stores it in a memory, for example.

Control device 40 determines whether or not system loss Wsys has been calculated for all voltage values of system voltage VH based on the voltage resolution pattern (S79). If system loss Wsys has not been calculated for all voltage values (NO in S79), control device 40 returns the process to S71. When system loss Wsys has been calculated for all voltage values (YES in S79), control device 40 terminates the processing of this flowchart.

Returning to FIG. 11 again, control device 40 selects a voltage value that minimizes system loss Wsys, and sets this voltage value as voltage command VHr (S9).

Control device 40 generates control signals S<b>1 and S<b>2 and outputs them to buck-boost converter 21 so that the output voltage of buck-boost converter 21 becomes voltage command VHr.

As described above, in the present embodiment, control device 40 determines a voltage resolution pattern according to vehicle speed V. FIG. Then, for system voltage VH, system loss Wsys (Wsys1, Wsys2, . . . , Wsysmax) at each of a plurality of voltage values (V1, V2, . . Then, control device 40 selects the minimum system loss Wsys from among the calculated system losses Wsys (Wsys1, Wsys2, . do. By operating motor drive system 100 based on voltage command VHr set in this manner, system loss in motor drive system 100 can be suppressed.

Also, the voltage resolution pattern includes a high resolution region and a low resolution region. By providing the high-resolution region and the low-resolution region, compared to the case where the voltage resolution is increased over the entire voltage range that the system voltage VH can take, an increase in the computational processing load is suppressed, and a decrease in computational efficiency is suppressed. be able to.

In addition, since the voltage range in which the system loss can be minimized may differ depending on the control mode of the motor generator 10, focusing on the relationship between the vehicle speed V and the control mode, the control device 40 provides a voltage resolution pattern according to the vehicle speed V. to decide. As a result, the vicinity of the voltage value at which the system loss Wsys can be minimized can be set with high resolution. Therefore, even when the high-resolution region and the low-resolution region are set, the minimum system loss Wsys can be accurately calculated.

<Comparative example>
FIG. 14 is a diagram for explaining system losses in motor drive system 100 according to the present embodiment and a motor drive system according to a comparative example. The upper diagram in FIG. 14 shows the relationship between time and voltage command, and the lower diagram in FIG. 14 shows the relationship between time and system loss. The inventors obtained the results shown in FIG. 14 through experiments. A solid line L1 represents the time change of the voltage command in the comparative example. A solid line L2 represents the time change of the voltage command in the present embodiment. A solid line L3 is the time change of the system loss in the comparative example. A solid line L4 is the change over time of the system loss in this embodiment.

The motor drive system according to the comparative example controls the buck-boost converter so as to follow the voltage command calculated according to the functional expression of the system voltage and the system loss. That is, in the motor drive system according to the comparative example, the voltage command continuously fluctuates as indicated by the solid line L1. In this case, the output voltage of the buck-boost converter continuously fluctuates following the continuously fluctuating voltage command. Fluctuations in the output current can result in increased system losses.

Motor drive system 100 according to the present embodiment, as described above, operates with a voltage command that minimizes system loss among a plurality of voltage values based on the determined voltage resolution pattern. The voltage command in motor drive system 100 according to the present embodiment is determined by the resolution determined by the voltage resolution pattern, and takes discrete values as indicated by solid line L2. A solid line L4 indicates the time change of the voltage in the present embodiment. By making the voltage command discrete, fluctuations in the output voltage of the step-up/step-down converter 21 can be suppressed, and system loss can be reduced.

As can be recognized from the comparison between the solid lines L3 and L4, by discretely changing the voltage command, system loss can be suppressed compared to the case of continuously changing the voltage command.

The embodiments disclosed this time should be considered as examples and not restrictive in all respects. The scope of the present disclosure is indicated by the scope of claims rather than the description of the above-described embodiments, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

1 vehicle, 10 motor generator, 20 PCU, 21 buck-boost converter, 22 inverter, 23 voltage sensor, 30 battery, 35 monitoring unit, 40 control device, 41 system state determination unit, 42 power loss calculation unit, 43 voltage command selection unit , 44 voltage command generator, 60 current sensor, 65 rotation angle sensor, 67 temperature sensor, 100 motor drive system, 310 drive wheel, 320 vehicle speed sensor, C1 capacitor, C2 capacitor, SR1, SR2 system main relay, NL, PL1, PL2 power line.

Claims (1)

A motor drive system for driving a motor generator,
a DC power supply;
A control mode is selectively switched between a PWM control mode in which a pulse width modulated voltage is applied to the motor generator and a rectangular wave voltage control mode in which a phase-controlled rectangular wave voltage is applied to the motor generator. an inverter that drives the
a converter provided between the DC power supply and the inverter for stepping up a system voltage input to the inverter to a voltage of the DC power supply or higher;
A control device that controls the inverter and the converter,
The motor drive system is mounted on a vehicle,
The control device is
determining a voltage resolution pattern of the system voltage according to the speed of the vehicle;
for the system voltage, setting a voltage value that minimizes power loss of the inverter and the motor generator among a plurality of voltage values based on the voltage resolution pattern determined according to the speed, as a voltage command;
A motor drive system that controls the converter to output a voltage of a set voltage command.

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