Method and system for controlling motor

1. A method for controlling a motor, the method comprising:

obtaining electrical signals of the motor with a signal unit, the electrical signals comprising a motor torque and an angular velocity;

calculating a voltage phase angle of a voltage vector with a calculating component, wherein a command torque, the motor torque, the angular velocity and a voltage amplitude of the voltage vector are inputs of the calculating component, and wherein the voltage phase angle is a variable and the voltage amplitude is a constant;

modulating, with a modulator, the voltage phase angle and the voltage amplitude to form a switching signal for controlling an inverter;

converting, with the inverter, a direct current voltage to the voltage vector according to the switching signal; and

applying the voltage vector to the motor;

wherein the motor torque generated from the motor changes linearly with respect to the voltage phase angle at a certain value of the angular velocity of the motor and a certain monotonous range of the voltage phase angle.

2. The method of claim 1 , wherein the voltage vector outputted from the inverter is a rectangular-wave voltage, and wherein the voltage amplitude is fixed at a maximum value of a fundamental wave voltage of the rectangular-ware voltage.

3. The method of claim 1 , wherein the certain monotonous range of the voltage phase angle varies with respect to the angular velocity.

4. The method of claim 3 , wherein the certain monotonous range of the voltage phase angle is obtained from a derivative of the motor torque with respect to the voltage phase angle, wherein the derivative of the motor torque is equal to or larger than zero.

5. The method of claim 1 , wherein the voltage phase angle is adjusted based on a torque deviation of the motor torque from the command torque with a gain function.

6. The method of claim 5 , wherein the gain function is larger than zero.

7. The method of claim 1 , wherein the calculating a voltage phase angle of a voltage vector with a calculating component comprises limiting the command torque by an available maximum torque of the motor.

8. The method of claim 1 , wherein the calculating a voltage phase angle of a voltage vector with a calculating component further comprises inputting the command torque into a feed-forward system.

9. A method for controlling a motor torque generated from a motor, the method comprising:

fixing a voltage amplitude of a voltage vector outputted from an inverter; and

changing a voltage phase angle of the voltage vector to control the motor torque, wherein the motor torque changes linearly with respect to the voltage phase angle at a certain value of an angular velocity of die motor and a certain monotonous range of the voltage phase angle, wherein the certain monotonous range of the voltage phase angle varies with respect to the angular velocity, wherein the certain monotonous range of the voltage phase angle is obtained from a derivative of the motor torque with respect to the voltage phase angle, wherein the derivative of the motor torque is equal to or larger than zero.

10. The method of claim 9 , wherein the voltage vector outputted from the inverter is a rectangular-wave voltage, and wherein the voltage amplitude is fixed at a maximum value of a fundamental wave voltage of the rectangular-ware voltage.

11. A control system for controlling a motor, the control system comprising:

a signal unit far outputting electrical signals of the motor, the electrical signals comprising a motor torque and an angular velocity; and

a controller coupled to the signal unit and comprising a calculating component configured to calculate a voltage phase angle of a voltage vector, wherein inputs of the calculating component comprise a command torque, the motor torque, the angular velocity, wherein a voltage amplitude of the voltage vector is a constant and wherein an output of the calculating component is the voltage phase angle;

wherein the motor torque changes linearly with respect to the voltage phase angle at a certain value of the angular velocity of the motor and a certain monotonous range of the voltage phase angle, wherein the certain monotonous range of the voltage phase angle varies with respect to the angular velocity, wherein the certain monotonous range of the voltage phase angle is obtained from a derivative of the motor torque with respect to the voltage phase angle, wherein the derivative of the motor torque is equal to or larger than zero.

12. The control system of claim 11 , further comprising:

a modulator coupled to the controller, the modulator configured to modulate the voltage phase angle and the voltage amplitude to form a switching signal; and

an inverter coupled to the modulator and controlled by the switching signal, wherein the inverter is configured to convert, a direct current voltage to the voltage vector applied to the motor.

13. The control system of claim 12 , wherein the voltage vector outputted from the inverter is a rectangular-wave voltage, and wherein the voltage amplitude is fixed at a maximum value of a fundamental wave voltage of the rectangular-ware voltage.

14. The control system of claim 11 , wherein the calculating component comprises:

an adder configured to calculate a torque deviation between the command torque and the motor torque;

a function module configured to receive the angular velocity, the voltage amplitude and the voltage phase angle as inputs and to calculate a value of a gain function;

a multiplier coupled to the adder and the function module and configured to multiply the torque deviation and the value of the gain function to obtain a derivative of the voltage phase angle with respect to time; and

an integrator coupled to the multiplier and configured to integrate the derivative of the voltage phase angle to obtain the voltage phase angle.

15. The control system of claim 14 , wherein the calculating component further comprises a proportional-integral compensator coupled to the integrator and configured to accelerate integral convergence.

16. The control system of claim 15 , wherein the calculating component further comprises a feed-forward system parallel to the adder, the multiplier, the integrator and the proportional-integral compensator.