Electric vehicle

Abstract

To provide an electric vehicle capable of properly inhibiting the superposition of higher harmonic waves during sudden increases in motor speed while suppressing narrowing the allowable rotational speed range for superimposition of higher harmonic waves.SOLUTION: When the rotation speed of the motor is less than the specified rotation speed and the rate of change of the rotation speed, which is the amount of change per unit time of the motor, is less than the specified rate of change, the voltage commands for the d-axis and q-axis are set without superimposing a higher harmonic wave. When the motor's rotation speed is greater than or equal to a specified value and when the rate of change of the motor's rotation speed is greater than or equal to a specified rate of change, a higher harmonic wave is superimposed to set the d-axis and q-axis voltage commands.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to electric vehicles. [Background technology]

[0002] A conventional electric vehicle of this type includes a motor connected to drive wheels, an inverter that drives the motor by switching a number of switching elements, and a control device that sets d-axis and q-axis voltage commands based on a torque command of the motor and controls the inverter based on the set d-axis and q-axis voltage commands (see, for example, Patent Document 1). In this electric vehicle, feedforward terms are set including a dead-time corresponding term for canceling out voltage fluctuations in the motor during dead time in the switching of a number of switching elements, a flux reluctance term that depends on the flux reluctance of the motor, and a resistance term that depends on the resistance value of the motor, and the set feedforward terms are used to set voltage commands for the d-axis and q-axis. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6760197 Summary of the Invention [Problem to be solved by the invention]

[0004] When controlling an inverter by pulse width modulation control (PWM control), harmonics are superimposed and voltage commands for the d-axis and q-axis are set to control the inverter. In order to superimpose harmonics, it is necessary to increase the carrier frequency by PWM control, and when the motor rotation speed exceeds a predetermined rotation speed, it is necessary to prohibit the superimposition of harmonics in order to ensure controllability. In a scene where the motor rotation speed increases suddenly (for example, when the drive wheels slip), the determination that the motor rotation speed has exceeded the predetermined rotation speed may be delayed due to the discrepancy between the detected value and the actual value of the motor rotation speed, and the prohibition of the superimposition of harmonics may be delayed. If the predetermined rotation speed is lowered in light of this, the allowable rotation speed range for the superimposition of harmonics in a scene where the motor rotation speed does not increase suddenly will be narrowed.

[0005] The main objective of the electric vehicle disclosed herein is to more appropriately prohibit the superposition of harmonics when the motor rotation speed increases suddenly, while preventing the permissible rotation speed range for the superposition of harmonics from becoming narrower. [Means for solving the problem]

[0006] The electric vehicle of the present disclosure employs the following means to achieve the above-mentioned main object. The electric vehicle of the present disclosure is an electric vehicle including a motor connected to drive wheels, an inverter that drives the motor by switching a plurality of switching elements, and a control device that sets d-axis and q-axis voltage commands based on a torque command of the motor and controls the inverter based on the d-axis and q-axis voltage commands, wherein the control device sets the d-axis and q-axis voltage commands without superimposing harmonics when the rotation speed of the motor is less than a predetermined rotation speed and a rotation speed change rate that is a change amount per unit time of the motor's rotation speed is less than a predetermined change rate, and sets the d-axis and q-axis voltage commands by superimposing the harmonics when the rotation speed of the motor is equal to or greater than the predetermined rotation speed and the rotation speed change rate of the motor is equal to or greater than the predetermined change rate. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic configuration diagram of an electric vehicle 20 according to an embodiment of the present disclosure. [Diagram 2] 4 is a flowchart showing an example of an inverter control routine. [Diagram 3] 4 is a flowchart showing an example of an inverter control routine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] An embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a schematic configuration diagram of an electric vehicle 20 according to an embodiment of the present disclosure. As shown in the figure, the electric vehicle 20 according to the embodiment includes a motor 32, an inverter 34, a battery 36, and an electronic control unit (hereinafter referred to as "ECU") 50.

[0009] The motor 32 is configured as a three-phase AC motor, and includes a rotor in which a permanent magnet is embedded in a rotor core, and a stator in which a three-phase coil is wound around a stator core. The rotor of the motor 32 is connected to a drive shaft 26 that is connected to the drive wheels 22a, 22b via a differential gear 24. The inverter 34 is used to drive the motor 32, and is connected to a power line 38 together with a battery 36. The inverter 34 includes six transistors T11-T16 as switching elements, and six diodes D11-D16 that are connected in parallel to the six transistors T11-T16, respectively. The transistors T11-T16 are arranged in pairs, two at a time, so as to be on the source side and the sink side with respect to the positive and negative pole lines of the power line 38, respectively. Each of the connection points of the paired transistors of the transistors T11-T16 is connected to each of the three-phase (U-phase, V-phase, W-phase) coils of the motor 32. Therefore, when a voltage is applied to the inverter 34, the ECU 50 adjusts the ratio of the on-time of the paired transistors T11 to T16, thereby forming a rotating magnetic field in the three-phase coil and rotating the motor 32. A smoothing capacitor 39 is attached to the power line 38. The battery 36 is configured as, for example, a lithium ion secondary battery or a nickel-metal hydride secondary battery having a rated voltage of several hundred volts, and is connected to the power line 38 together with the inverter 34 as described above.

[0010] The ECU 50 includes a microcomputer, and the microcomputer has a CPU, a ROM, a RAM, a flash memory, an input / output port, and a communication port. The ECU 50 inputs signals from various sensors via the input ports. For example, the ECU 50 inputs a rotational position θm from a rotational position sensor (e.g., a resolver) 32a that detects the rotational position of the rotor of the motor 32, and phase currents Iv and Iw from current sensors 32v and 32w that detect the V-phase and W-phase currents of the motor 32. The ECU 50 also inputs a voltage Vb from a voltage sensor 36a attached between the terminals of the battery 36, a current Ib from a current sensor 36b attached to the output terminal of the battery 36, and a voltage VH of the capacitor 39 (the voltage of the power line 38) from a voltage sensor 39a attached between the terminals of the capacitor 39. Also input to the ECU 50 are a start signal from a start switch 60, a shift position SP from a shift sensor 62 that detects the operation position of a shift lever 61, an accelerator opening Acc from an accelerator pedal position sensor 64 that detects the depression amount of an accelerator pedal 63, a brake pedal position BP from a brake pedal position sensor 66 that detects the depression amount of a brake pedal 65, and a vehicle speed V from a vehicle speed sensor 67. The ECU 50 outputs various control signals, such as control signals to the transistors T11 to T16 of the inverter 34, via an output port. The ECU 50 calculates the electrical angle θe and the rotation speed Nm of the motor 32 based on the rotation position θm of the rotor of the motor 32 from the rotation position sensor 32a, and calculates a rotation speed change rate ΔNm, which is the amount of change in the rotation speed Nm per unit time, based on the rotation speed Nm.

[0011] In the electric vehicle 20 of the embodiment thus configured, the ECU 50 sets a required torque Td* required for the drive shaft 26 based on the accelerator opening Acc and the vehicle speed V, sets the set required torque Td* as a torque command Tm* for the motor 32, and performs switching control of the transistors T11-T16 of the inverter 34 so that the motor 32 is driven by the torque command Tm*. The inverter 34 is basically controlled by pulse width modulation control.

[0012] Next, the operation of the electric vehicle 20 of the embodiment, particularly the control of the inverter 34, will be described. Fig. 2 is a flowchart showing an example of an inverter control routine repeatedly executed by the ECU 50. When this routine is executed, the ECU 50 inputs the electrical angle θe of the motor 32, the V-phase and W-phase phase currents Iv, Iw, the rotation speed Nm, the rotation speed change rate ΔNm, and the torque command Tm* (step S100), and performs coordinate conversion (three-phase to two-phase conversion) of the V-phase and W-phase phase currents Iv, Iw to d-axis and q-axis currents Id, Iq using the electrical angle θe assuming that the sum of the phase currents of the respective phases of the motor 32 is zero (step S110).

[0013] Next, it is determined whether the rotation speed Nm is equal to or lower than a threshold value Nmref (step S120), and whether the rotation speed change rate ΔNm is equal to or lower than a threshold value ΔNmref (step S130). Here, the threshold value Nmref is a threshold value used to determine whether the rotation speed of the motor 32 has become relatively large. The threshold value ΔNmref is a threshold value used to determine whether the rotation speed of the motor 32 has suddenly increased (for example, the drive wheels 22a, 22b have slipped). The processes of steps S120 and S130 are processes for determining whether harmonic superposition control is permitted.

[0014] When it is determined in step S120 that the rotation speed Nm is equal to or lower than the threshold value Nmref and when it is determined in step S130 that the rotation speed change rate ΔNm is equal to or lower than the threshold value ΔNmref, the harmonic superposition control is permitted (step S140). In this case, the torque command Tm* is applied to a basic current command map that is determined in advance by experiment, analysis, machine learning, etc. as the relationship between the torque command Tm* and the basic current commands Idbs and Iqbs of the d and q axes, to set the basic current commands Idbs and Iqbs of the d and q axes (step S150). Next, the torque command Tm*, the electrical angle θe, and the rotation speed Nm are applied to a harmonic superposition current command map that is determined in advance by experiment, analysis, machine learning, etc. as the relationship between the torque command Tm*, the electrical angle θe, the rotation speed Nm, and the harmonic superposition current commands Idh and iqh of the d and q axes, to set the harmonic superposition current commands Idh and iqh of the d and q axes (step S152). The d-axis and q-axis harmonic superimposed current commands Idh, iqh include harmonics. The sum of the d-axis and q-axis basic current commands Idbs, Iqbs and the d-axis and q-axis harmonic superimposed current commands Idh, iqh is calculated as the d-axis and q-axis current commands Id*, Iq* (step S154). The d-axis and q-axis current commands Id*, Iq* include harmonics.

[0015] When the d-axis and q-axis current commands Id* and Iq* are calculated in this way, the d-axis and q-axis voltage command FB (feedback) terms Vdfb and Vqfb are calculated by current feedback control based on the differences ΔId and ΔIq between the d-axis and q-axis current commands Id* and Iq* and the d-axis and q-axis currents id and Iq (step S160). Next, the torque command Tm*, the electrical angle θe, and the rotation speed Nm are applied to a harmonic superimposed voltage command FF term map that is determined in advance by experiment, analysis, machine learning, etc. as the relationship between the torque command Tm*, the electrical angle θe, the rotation speed Nm, and the d-axis and q-axis voltage command FF (feedforward) terms Vdff and Vqff to set the d-axis and q-axis voltage command FF terms Vdff and Vqff (step S162). The d-axis and q-axis voltage command FF terms Vdff and Vqff include harmonics. Then, the sum of the d-axis and q-axis voltage command FB terms Vdfb, Vqfb and the d-axis and q-axis voltage command FF terms Vdff, Vqff is calculated as the d-axis and q-axis voltage commands Vd*, Vq* (step S164). The d-axis and q-axis voltage commands Vd*, Vq* include harmonics.

[0016] When the d-axis and q-axis voltage commands Vd* and Vq* are calculated in this way, the d-axis and q-axis voltage commands Vd* and Vq* are converted to U-phase, V-phase and W-phase voltage commands Vu*, Vv* and Vw* by coordinate conversion (2-phase to 3-phase conversion) using the electrical angle θe (step S230), and the switching control of the transistors T11 to T16 of the inverter 34 is performed using the voltage commands Vu*, Vv* and Vw (step S210), and this routine ends. In the process of step S210, the PWM signals of the transistors T11 to T16 are generated by comparing the voltage commands Vu*, Vv* and Vw with the carrier wave (triangular wave) of the carrier frequency fc, and the switching control of the transistors T11 to T16 is performed using the generated PWM signals of the transistors T11 to T16. The carrier frequency fc is set appropriately. Since the d-axis and q-axis voltage commands Vd* and Vq* contain harmonics, the torque of the motor 32 also contains harmonics.

[0017] When it is determined in step S120 that the rotation speed Nm is greater than the threshold value Nmref, or when it is determined in step S130 that the rotation speed change rate ΔNm is greater than the threshold value ΔNmref, the harmonic superposition control is prohibited (step S170). In this case, the d-axis and q-axis basic current commands Idbs and Iqbs are set (step S180) in the same manner as in the process of step S150 described above, and the set d-axis and q-axis basic current commands Idbs and Iqbs are set as the d-axis and q-axis current commands Id and Iq* (step S184). In this case, the d-axis and q-axis current commands Id* and Iq* do not include harmonics. When the d-axis and q-axis current commands Id* and Iq* are set in this manner, the d-axis and q-axis voltage command FB terms Vdfb and Vqfb are set (step S190) in the same manner as in the process of step S160. Next, the torque command Tm* is applied to a normal voltage command FF term map that is determined in advance as the relationship between the torque command Tm* and the d-axis and q-axis voltage command FF terms Vdff and Vqff by experiment, analysis, machine learning, etc., to set the d-axis and q-axis voltage command FF terms Vdff and Vqff (step S192). Then, the sum of the d-axis and q-axis voltage command FB terms Vdfb and Vqfb and the d-axis and q-axis voltage command FF terms Vdff and Vqff is calculated as the d-axis and q-axis voltage commands Vd* and Vq* (step S194). In this case, the d-axis and q-axis voltage commands Vd* and Vq* do not include harmonics. Next, the processes of steps S200 and S210 are executed, and this routine is terminated.

[0018] In this embodiment, by comparing the rotation speed change rate ΔNm with the threshold value ΔNmref, it is possible to more appropriately prohibit the superimposition of harmonics when the rotation speed of the motor 32 increases suddenly (for example, when the drive wheels 22a, 22b slip). This allows the threshold value Nmref used for comparison with the rotation speed Nm to be somewhat large, so that it is possible to prevent the permissible rotation speed range for the superimposition of harmonics from narrowing when the rotation speed of the motor is not increasing suddenly. As a result, it is possible to more appropriately prohibit the superimposition of harmonics when the rotation speed of the motor 32 increases suddenly, while preventing the permissible rotation speed range for the superimposition of harmonics from narrowing.

[0019] In the electric vehicle 20 of the embodiment described above, when the rotation speed Nm of the motor 32 is equal to or lower than the threshold value Nmref and the rotation speed change rate ΔNm of the motor 32 is equal to or lower than the threshold value ΔNmref, the inverter 34 is controlled by setting the d-axis and q-axis voltage commands Vd* and Vq* without superimposing harmonics, and when the rotation speed Nm of the motor 32 is greater than the threshold value Nmref or the rotation speed change rate ΔNm of the motor 32 is greater than the threshold value ΔNmref, the inverter 34 is controlled by setting the d-axis and q-axis voltage commands Vd* and Vq* with superimposition of harmonics. This makes it possible to more appropriately prohibit superimposition of harmonics when the rotation speed of the motor 32 increases suddenly (for example, when the drive wheels 22a, 22b slip) while suppressing narrowing of the permissible rotation speed region for superimposition of harmonics.

[0020] In the above-described embodiment, the ECU 50 executes the inverter control routine of Fig. 2, but may execute the inverter control routine of Fig. 3. The routine of Fig. 3 differs from the routine of Fig. 2 in that the processes of steps S100, S120, and S130 are replaced with processes of steps S300 to S330. Therefore, the same step numbers are used for the processes of the routine of Fig. 3 that are the same as those of the routine of Fig. 2, and detailed descriptions thereof will be omitted.

[0021] 3, the ECU 50 inputs the electrical angle θe of the motor 32, the V-phase and W-phase currents Iv, Iw, the rotation speed Nm, the rotation speed change rate ΔNm, and the torque command Tm* as in the process of step S100, and also inputs a predicted rotation speed Nmpr of the motor 32 (step S300). Here, the predicted rotation speed Nmpr is a rotation speed predicted based on the rotation speed Nm and the rotation speed change rate ΔNm a predetermined number of times before (for example, about 1 to 3 times before) of this routine.

[0022] After the process of step S110, it is determined whether the rotation speed change rate ΔNm is equal to or less than a threshold value ΔNmref2 (step S310). Here, the threshold value ΔNmref2 is a threshold value used to determine whether the actual rotation speed of the motor 32 has changed suddenly (there is a possibility that the deviation between the rotation speed Nm and the actual rotation speed has become large). When it is determined that the rotation speed change rate ΔNm is equal to or less than the threshold value ΔNmref2, it is determined that the actual rotation speed of the motor 32 has not changed suddenly, and it is determined whether the rotation speed Nm is equal to or less than the threshold value Nmref as in the process of step S120 (step S320). Then, when it is determined that the rotation speed Nm is equal to or less than the threshold value Nmref, the process of step S140 and subsequent steps is executed, and when it is determined that the rotation speed Nm is greater than the threshold value Nmref, the process of step S170 and subsequent steps is executed.

[0023] When it is determined in step S310 that the rate of change in rotation speed ΔNm is greater than the threshold value ΔNmref2, it is determined that the actual rotation speed of the motor 32 has changed suddenly, and it is determined whether the predicted rotation speed Nmpr is equal to or less than the threshold value Nmref (step S330). When it is determined that the predicted rotation speed Nmpr is equal to or less than the threshold value Nmref, the process from step S140 onwards is executed, and when it is determined that the predicted rotation speed Nmpr is greater than the threshold value Nmref, the process from step S170 onwards is executed. In this way, by using the predicted rotation speed Nmpr instead of the rotation speed Nm, it is possible to more appropriately determine whether or not to permit harmonic superposition control even when the actual rotation speed of the motor 32 has changed suddenly.

[0024] In the above-described embodiment, the electric vehicle 20 is provided with the motor 32 and the inverter 34. However, the electric vehicle 20 may be provided with a hybrid vehicle that includes an engine in addition to the motor 32 and the inverter 34, or a fuel cell vehicle that includes a fuel cell in addition to the motor 32 and the inverter 34.

[0025] The above describes embodiments for implementing the present disclosure, but the present disclosure is not limited to these embodiments, and it goes without saying that the present disclosure can be implemented in various forms without departing from the gist of the present disclosure. [Industrial Applicability]

[0026] The present disclosure can be used in the electric vehicle manufacturing industry and the like. [Explanation of symbols]

[0027] 20 electric vehicle, 22a, 22b drive wheels, 32 motor, 34 inverter, 50 ECU, T11~T16 transistors.

Claims

[Claim 1] An electric vehicle comprising: a motor connected to drive wheels; an inverter that drives the motor by switching a plurality of switching elements; and a control device that sets d-axis and q-axis voltage commands based on a torque command of the motor and controls the inverter based on the d-axis and q-axis voltage commands, the control device sets the d-axis and q-axis voltage commands without superimposing harmonics when the rotation speed of the motor is less than a predetermined rotation speed and a rotation speed change rate, which is a change amount per unit time of the rotation speed of the motor, is less than a predetermined change rate, and sets the d-axis and q-axis voltage commands by superimposing the harmonics when the rotation speed of the motor is equal to or greater than the predetermined rotation speed and the rotation speed change rate of the motor is equal to or greater than the predetermined change rate. Electric car.

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