Method and Apparatus for Controlling Motor for Skid Mode of Electric Vehicle

FIELD OF TECHNOLOGY

This invention relates to motor control field of an electric vehicle, that is, relates to a method and apparatus for controlling motor for skid mode of an electric vehicle.

BACKGROUND

In the Chinese patent application CN1861443A titled "Method of Motor Control", it disclosed a method for controlling motor in background, which adopts the velocity ring control to fulfill the PI control for the rotary speed of motor rotor, then control the torque of motor through the quadrature current and d-axis current adjustment for motor. This invention provides a motor control method for electric vehicle, which predetermined the quadrature target current according to the angular velocity of motor and predetermined the d-axis target current according to the torque of motor; detect and collect the 3 -phase current of motor, meanwhile, the rotary transformer may detect the rotor position of motor and the revolving decoding unit may measure the angle of rotor; convert the 3 -phase current of motor into the actual d-axis current and quadrature current according to the Park conversion and Clark conversion of rotor position angle; take the difference between the target current and actual current as the input of current ring for PI adjustment to output the required d-axis current and required quadrature current; output the required d-axis current and required quadrature current according to PI adjustment and calculate the 3 -phase voltage value according to the motor rotor angle; and obtain the pulse width modulation control waveform from the 3 -phase voltage, convert the DC into relevant AC to drive the motor.

The above mentioned velocity ring feedback control or current ring feedback control are only the basis of motor control. During practices, for complex and varying road surface cases and modes, thus, the decision making must be combined

with various parameters of vehicle, and the current service conditions of electric vehicle, with the special control mode, calculate the target d-axis current and quadrature current, and finally given through PI adjustment to prevent the motor out-of-control.

One of the modes of electric vehicle is the skid mode. For example, when the vehicle travels from a normal surface of road into a smooth surface, such as an icy surface with very low friction, the situation equals to the load of motor suddenly reduced, due to sudden unload, the rotor of motor accelerates, the generated surge current and voltage may cause the protection of intelligent power module (IPM), directly cause the motor out-of-control, which is unallowable during the normal travel. On the contrary, when the vehicle is on the smooth surface of road, the motor may only output very low torque to ensure the normal travel of vehicle, but when the vehicle travels from the smooth surface to a section with normal friction of road surface, i.e., the situation equals to suddenly apply a load on the motor, the sudden growth of load may cause the torque of motor suddenly reduced at very low output, and even stall. This case may cause the protection of motor controller, moreover, during extreme case, i.e. blocked rotor, all the electric power may be converted into the heat of motor winding, which may cause the winding overheated. Both cases mentioned above are generally called "skid mode". Under these cases, due to sudden increasing or decreasing of motor rotary speed, the out-of-control of motor may be caused.

There is no method or apparatus in the existing motor control strategys for controlling motor for electric vehicle aimed at the skid mode.

SUMMARY OF THE INVENTION

In order to avoid both cases of skid mentioned above, the present invention provides a control strategy for the skid mode, that is, provides a method and apparatus for controlling motor for electric vehicle, to ensure the safety and comfort of electric vehicle under skid modes.

In order to realize the purpose mentioned above, the present invention provides a

method for controlling a motor for an electric vehicle, comprising the following steps:

51) detecting rotor positions of the motor in a sampling period;

52) calculating a current acceleration a of the motor according to the detected rotor position values within a specified statistical duration;

53) comparing the calculated current acceleration a with a predetermined forward acceleration aO and a predetermined backward acceleration al respectively, and going to step S4 if the current acceleration a is greater than the predetermined forward acceleration aO or is less than the predetermined backward acceleration α/, otherwise controlling output torque of the motor according to normal travel control strategy; and

S4) decreasing output torque of the motor if the current acceleration a is greater than the predetermined forward acceleration aO, or increasing output torque of the motor if the current acceleration a is less than the predetermined backward acceleration al, and then returning to step Sl.

Moreover, the present invention further provides a systerm for controlling a motor for an electric vehicle, comprising a rotor position detection unit and a motor controller, the rotor position detection unit is connected with the motor controller, the rotor position detection unit is for detecting rotor positions in a sampling period and outputting the detected rotor position values to the motor controller; wherein, the motor controller comprises a mode dertermination module and a skid control module

The mode dertermination module is configured to calculate a current acceleration a of the motor according to the received rotor position values within a specified statistical duration; compare the calculated current acceleration a with a predetermined forward acceleration aO and a predetermined backward acceleration al respectively, and active the skid control module if the current acceleration a is greater than the predetermined forward acceleration aO or is less than the predetermined backward acceleration al.

The skid control module is configured to output a motor control signal for decreasing output torque if the current acceleration a is greater than the predetermined forward acceleration aO, or output a motor control signal for increasing output torque

if the current acceleration a is less than the predetermined backward acceleration al in the situation of activation.

In the present invention, the control strategy for skid mode is provided. When the vehicle travels from the normal surface of road into a smooth road surface or on the contrary, the speed of drive wheel may be jumped, i.e., the rotary speed of motor shall be greatly increased or decreased beyond the threshold value, just then the motor shall operate under the skid control mode, according to the method specified in the present invention, decreasing or increasing output torques may suppress the abrupt varying of vehicle speed, and according to that specified in the preferred embodiment, firstly reducing output torque during early period may suppress the current abrupt varying, protect the power device, in order to avoid the vehicle out-of-control caused by blocked rotor or skid of motor, thus improve the vehicle's safety and comfort.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a structural view of an electrical drive system for electric vehicle applied to the apparatus for controlling motor according to the present invention;

Fig. 2 is a working flow chart of the mode dertermination module according to the present invention;

Fig. 3 is a working flow chart of the skid control module according to the present invention;

Fig. 4 is a flow chart of the method for controlling motor according to the present invention;

Fig. 5 is a flow chart of the method for controlling motor according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is further described as below through the detailed embodiment and combined with the attached figures.

The systerm for controlling a motor provided in the present invention comprises

a rotor position detection unit and a motor controller 4, the rotor position detection unit is connected with the motor controller 4, the rotor position detection unit is for detecting rotor positions with a sampling period and outputting the detected rotor position values to the motor controller 4; wherein the motor controller 4 may output a motor control signal corresponding to the rotor position value.

Referred to Fig. 1, said motor control system is described as below. Fig. 1 is a structural view of electrical drive system for the electric vehicle, this system comprises: a battery set 1, a set of capacitor 2, an inverter 3, the motor controller 4, a photo-coupler isolating unit 5, the motor 6, a rotary transformer 7, a revolving decoding unit 8 and a brake signal detection unit 9.

Wherein the battery set 1 is the energy source for the whole electric drive system; both the positive and negative poles of the set of capacitor 2 are respectively connected with the positive and negative poles of the battery set 1 for absorbing the high frequency impact voltage and smoothing the voltage waveform; the inverter 3 comprises three intelligent power modules (IPM) (the power devices such as IGBT, transistor etc may be also used), each IPM is divided into a upper bridge arm and a lower bridge arm, the input terminals of upper bridge arms for three IPMs are connected with the positive bus of the battery set 1, the lower bridge arms are connected with the negative bus of the battery set 1, all contact points among IPMs are respectively connected with 3 -phase coils (U phase, V phase, and W phase) of the motor 6.

The motor controller 4 outputs motor control signals, i.e. PWM signals, to the inverter 3 through the photo-coupler isolating unit 5, and the inverter 3 may adjust ON/OFF of the upper and lower bridge arms of each IPM according to the motor control signals to control the rotary speed of motor 6, i.e., the output torques of control motor 6.

The rotor position detection unit of the present invention may be a sensor unit suitable for detecting the rotor positions. Shown as Fig. 1, in the embodiment, the rotor position detection unit comprises a rotary transformer 7 and a revolving decoding unit 8, an output terminal of the rotary transformer 7 is connected with an

input terminal of the revolving decoding unit 8, an output terminal of the revolving decoding unit 8 is connected with an input terminal of the motor controller 4. The rotary transformer 7 locates nearby the rotor of the motor 6 for collecting the rotor angle position signals in a sampling period and outputting the rotor angle position signals to the revolving decoding unit 8, and the revolving decoding unit 8 may calculate rotor position values based on the received rotor angle position signals and output the rotor position values to the motor controller 4. The range of the sampling period is 10-100μs.

Wherein, apart from the skid control module for skid mode, the motor controller 4 further comprises a normal travel control module and a brake control module which are necessary for the vehicle. See Fig. 2, it shows the activation conditions of these modules, i.e., the working flow of the mode dertermination module.

Shown as Fig. 2, firstly, according to the received rotor position values within a specified statistical duration, the mode dertermination module may calculate the current acceleration a of the motor. The rotor position values are provided by the revolving decoding unit 8 mentioned above, the rotor speed may be calculated according to rotor position values, and the current acceleration a may be calculated according to rotor speed values. This acceleration may be positive or negative, the positive value indicates the acceleration, and negative value indicates the deceleration. In which, the range of the specified statistical duration is 3-10 sampling periods.

Then the mode dertermination module may compare the calculated current acceleration a with a predetermined forward acceleration a0 and a predetermined backward acceleration al respectively. Wherein the predetermined forward acceleration a0 and the predetermined backward acceleration al are the maximum forward acceleration and the maximum backward acceleration of the motor 6 specified according to the mass of the whole vehicle and the power of motor 6, its value depends on the vehicle models. When the motor 6 is a specified motor, the maximum forward acceleration and maximum backward acceleration are the maximum rotor forward rotary or backward rotary acceleration of rotor within a sampling period of revolving decoding unit 8 caused by this motor 6 under its

maximum output power. In which, the predetermined forward acceleration aO is a positive value, and the predetermined backward acceleration al is a negative value, the absolute values of the two values may be equal or unequal.

If the current acceleration a is greater than the predetermined forward acceleration aO or is less than the predetermined backward acceleration α/, the skid control module is actived; and if the current acceleration a is between the predetermined forward acceleration aO and the predetermined backward acceleration α/, the normal travel control module is actived.

Apart from the skid mode may cause the situation that the current acceleration a is less than the predetermined backward acceleration α/, the situation may be also caused by the initiative braking of driver, thus, under this case, the brake control strategy should be preferred, but not the activation of skid control strategy. Thus, shown as Fig. 1, the apparatus provided in the present invention further comprises the brake signal detection unit 9 for detecting a brake signal and outputting the detected brake signal to the motor controller 4, the brake signal detection unit 9 may be a brake signal sensor, for detecting the pedal position of brake.

Shown as Fig. 2, the mode dertermination module is further configured to determine whether or not the brake signal detection unit (9) detectes a brake signal if the calculated current acceleration a is less than predetermined backward acceleration α/, and active the skid control module when no brake signal is detected, otherwise active the brake control module when a brake signal is detected.

When the skid control module is actived, it shall be configured to execute the working flow shown as Fig. 3. In Fig. 3, if the current acceleration a is greater than the predetermined forward acceleration aO, outputting a motor control signal for decreasing output torque, if the current acceleration a is less than the predetermined backward acceleration α/, outputting a motor control signal for increasing output torque.

Wherein the increased and decreased range shall be controlled by the skid control module, it may be a specified value or a function value concerned with the current acceleration a, but its increased or decreased value can't be beyond the

toleranted value of the motor 6.

Thus, through the working flow shown as Fig. 3 executed by skid control module, the sudden increase or decrease of motor rotary speed may be controlled reversely to solve the skid modes with the load suddenly increase or suddenly decrease, thus avoid the rotor of the motor blocked or vehicle out-of-control caused by skid, and improve the vehicle's safety and comfort.

Moreover, the sudden load and unload of vehicle caused by skid cases may cause the current surge, thus, in the present invention, the apparatus further comprises the embodiment for suppressing the current surge, in this embodiment, after the skid control module is actived, if the current acceleration a is greater than the predetermined forward acceleration aO or is less than the predetermined backward acceleration α/, then firstly outputing a motor control signal for decreasing output torque before outputting the motor control signals for decreasing or increasing output torque, thus the current via the motor may be restricted, the instantaneous abrupt varying of current may be suppressed, which further protect the power devices from the aspect of hardware. After the abrupt varying of current is suppressed, then outputting said motor control signal for decreasing or increasing output torques according to the mentioned skid control strategy.

The control strategy for the mentioned normal travel control module and brake control module may adopt various control solutions for normal travel and brake, no influences to the skid control strategy of the present invention, thus no further description given.

Combined with Fig. 4 and Fig. 5, the motor control method in the present invention is described below.

Shown as Fig. 4, the method comprises the following steps: in step Sl, detecting rotor positions of the motor in a sampling period. In step S2, calculating a current acceleration a of motor according to the detected rotor position values within a specified statistical duration. In step S3, comparing the calculated current acceleration a with a predetermined forward acceleration aO and a predetermined backward acceleration al respectively, and going to step S4 if the current acceleration

a is greater than the predetermined forward acceleration aO or is less than the predetermined backward acceleration α/, otherwise controlling output torque of the motor according to normal travel control strategy. In step S4, if the current acceleration a is greater than the predetermined forward acceleration aO, then decreasing output torque of the motor, and if the current acceleration a is less than the predetermined backward acceleration α/, then increasing output torque of the motor, and then returning to step S 1.

The step Sl is executed by the rotor position detection unit, as comprising the described rotary transformer 7 and the revolving decoding unit 8, in which, the range of the sampling period is 10-100μs. The step S2 and S3 are executed by the mode dertermination module in the mentioned motor controller 4, and the step S4 is executed by the skid control module in the mentioned motor controller 4, both execution processes are described as above, no further description hereon. In which, the range of the specified statistical duration in step S2 is 3-10 sampling periods. And the increase and decrease range in step S4 may be controlled by the skid control module control, it may be a specified value or a function value concerned with the current acceleration α, its increase or decrease range shall be not beyond the toleranted value of the motor 6.

In which, considering the situation of the initiative braking of driver, the preferred step is also provided, that is, if the current acceleration a is less than predetermined backward acceleration a J in step S3, determination whether there is brake signal or not just then at first, if there is no brake signal, going to step S4, otherwise, controling output torque of the motor according to brake control strategy.

Moreover, the method in the present invention also provides an embodiment for suppressing the current surge, shown as Fig. 5, in this embodiment, if the current acceleration a is greater than the predetermined forward acceleration aO or is less than predetermined backward acceleration al in step S3, then firstly decreasing output torque of the motor in step S5 before executing step S4, thus the current of motor may be suppressed, and the instantaneous abrupt varying of current may be decreased to protect the power device. After the abrupt varying of current is suppressed, the

output torque of motor may be increased or decreased in step S4 according to the introduced skid control strategy.

The predetermined forward acceleration aO and predetermined backward acceleration al are the maximum forward acceleration and the maximum backward acceleration of the motor 6 specified according to the mass of the whole vehicle and the power of the motor 6, its value depends on the vehicle models. When the motor 6 is a specified motor, the maximum forward acceleration and maximum backward acceleration are the maximum rotor forward rotary or backward rotary acceleration of rotor within a sampling period of revolving decoding unit 8 caused by this motor 6 under its maximum output power. Wherein the predetermined forward acceleration aO is a positive value, the predetermined backward acceleration al is a negative value, and the absolute values of both may be equal or unequal.

The control strategy for the mentioned normal travel control module and brake control module may adopt various control solutions for normal travel and brake, no influences to the skid control strategy of the present invention, thus no further description given.