Method for controlling rotation rate of electric motor

1. A method for controlling a rotation rate of an electric motor, comprising:

determining if an absolute value of a difference between an objective rotation rate of the electric motor and an actual rotation rate of the electric motor is greater than or equal to a predetermined value; and

if yes, compensating a q axis current of the electric motor to adjust the rotation rate,

wherein compensating a q axis current of the electric motor to adjust the rotation rate comprises:

compensating a q axis current of the electric motor according to the equation I q ′=I q −K*Δn,

where K is a coefficient, I q ′ is an actual value of the q axis current, I q is a given value of the q axis current, and Δn is a difference between an average of an actual rotation rate during current N cycles and an average of an actual rotation rate during N cycles before the current N cycles, and N≧1; and

compensating a torque by compensating the q axis current of the electric motor to adjust the rotation rate.

2. The method according to claim 1 , wherein the predetermined value ranges from about 100 RPM to about 300 RPM.

3. The method according to claim 1 , wherein if yes, compensating a q axis current of the electric motor to adjust the rotation rate comprises:

determining if Δn<0 if the difference between the objective rotation rate and the actual rotation rate is greater than or equal to the predetermined value;

if yes, setting I q ′=I q −K*Δn and otherwise setting I q ′=I q ; and compensating a torque by compensating the q axis current of the electric motor to adjust the rotation rate; and;

where K is a coefficient, I q ′ is an actual output of the q axis current, I q is a given output of the q axis current, and Δn is a difference between an average of an actual rotation rate during current N cycles and an average of an actual rotation rate during N cycles before the current N cycles, and N≧1.

4. The method according to claim 1 , wherein if yes, compensating a q axis current of the electric motor to adjust the rotation rate comprises:

determining if Δn>0 if the difference between the actual rotation rate and the objective rotation rate is greater than or equal to the predetermined value;

if yes, setting I q ′=I q −K*Δn and otherwise setting I q ′=I q and compensating a torque by compensating the q axis current of the electric motor to adjust the rotation rate; and

where K is a coefficient, I q ′ is an actual output of the q axis current, I q is a given output of the q axis current, and Δn is a difference between an average of an actual rotation rate during current N cycles and an average of an actual rotation rate during N cycles before the current N cycles, and N≧1.

5. The method according to claim 1 , wherein N ranges from about 32 to about 128.

6. The method according to claim 1 , wherein K ranges from about 0.05 to about 0.2.

7. A method for controlling a rotation rate of an electric motor, comprising:

determining if an absolute value of a difference between an objective rotation rate of the electric motor and an actual rotation rate of the electric motor is greater than or equal to a predetermined value;

if yes, compensating a q axis current of the electric motor to adjust the rotation rate; and

using a proportional integral method to adjust the rotation rate if the absolute value of the difference between the objective rotation rate and the actual rotation rate is less than the predetermined value.

8. The method according to claim 7 , wherein the proportional integral method comprises:

calculating a difference err(k) between the objective rotation rate and the actual rotation rate at a current time; and

adjusting the rotation rate according to the equation Out(k)=Out(k−1) +(Kp+Ki)*err(k),

where Kp is a proportional coefficient, Ki is an integral coefficient, Out(k) is an actual rotation rate at the current time, and Out(k−1) is an actual rotation rate at a previous time.

9. A method for controlling a rotation rate of an electric motor, comprising:

determining if an absolute value of a difference between an objective rotation rate of the electric motor and an actual rotation rate of the electric motor is greater than a predetermined value, and if the absolute difference is greater than the predetermined value, compensating a q axis current of the electric motor to adjust the rotation rate of the electric motor,

wherein compensating a q axis current of the electric motor to adjust the rotation rate comprises:

compensating a q axis current of the electric motor according to the equation I q ′=I q −K*Δn,

where K is a coefficient, I q ′ is an actual value of the q axis current, I q is a given value of the q axis current, and Δn is a difference between an average of an actual rotation rate during current N cycles and an average of an actual rotation rate during N cycles before the current N cycles, and N≧1; and

compensating a torque by compensating the q axis current of the electric motor to adjust the rotation rate.

10. The method according to claim 9 , wherein the predetermined value ranges from about 100 RPM to about 300 RPM.

11. The method according to claim 9 , wherein if yes, compensating a q axis current of the electric motor to adjust the rotation rate comprises:

determining if Δn<0 if the difference between the objective rotation rate and the actual rotation rate is greater than or equal to the predetermined value;

if yes, setting I q ′=I q −K*Δn and otherwise setting I q ′=I q and compensating a torque by compensating the q axis current of the electric motor to adjust the rotation rate; and;

where K is a coefficient, I q ′ is an actual output of the q axis current, I q is a given output of the q axis current, and Δn is a difference between an average of an actual rotation rate during current N cycles and an average of an actual rotation rate during N cycles before the current N cycles, and N≧1.

12. The method according to claim 9 , wherein if yes, compensating a q axis current of the electric motor to adjust the rotation rate comprises:

determining if Δn>0 if the difference between the actual rotation rate and the objective rotation rate is greater than or equal to the predetermined value;

if yes, setting I q ′=I q −K*Δn and otherwise setting I q ′=I q and compensating a torque by compensating the q axis current of the electric motor to adjust the rotation rate; and

where K is a coefficient, I q ′ is an actual output of the q axis current, I q is a given output of the q axis current, and Δn is a difference between an average of an actual rotation rate during current N cycles and an average of an actual rotation rate during N cycles before the current N cycles, and N≧1.

13. The method according to claim 9 , wherein N ranges from about 32 to about 128.

14. The method according to claim 9 , wherein K ranges from about 0.05 to about 0.2.