Active voltage controller for an electric motor

1. An apparatus comprising:

a controller configured

to identify a desired speed for an electric motor during operation of the electric motor;

to identify a duty cycle for the desired speed;

to identify a voltage to cause the electric motor to turn at the desired speed based on the duty cycle identified for the desired speed;

to generate the duty cycle as a duty cycle command for the electric motor;

to generate a voltage command based on the duty cycle command;

to generate the voltage as a regulator voltage for a voltage regulator circuit based on the voltage command; and

to apply the voltage to the electric motor during operation of the electric motor.

2. The apparatus of claim 1 ,

wherein the controller is further configured

to identify the desired speed for the electric motor during operation of the electric motor;

to identify the voltage to cause the electric motor to turn at the desired speed; and

to apply the voltage to the electric motor during operation of the electric motor repeatedly in response to changes in loading on the electric motor.

3. The apparatus of claim 1 , wherein in being configured to identify the desired speed for the electric motor during operation of the electric motor, the controller is configured to receive the desired speed for the electric motor from one of a user input and a device.

4. The apparatus of claim 1 , wherein the controller is configured to identify the voltage to cause the electric motor to turn at the desired speed using a group of control laws.

5. The apparatus of claim 4 , wherein the group of control laws comprises a current identifier, a duty cycle selector, a voltage identifier, and a regulator controller.

6. The apparatus of claim 4 , wherein a control law in the group of control laws includes a proportional-integral-derivative controller.

7. The apparatus of claim 1 , wherein the controller is configured to control operation of the electric motor in four quadrants.

8. The apparatus of claim 1 , wherein the voltage to cause the electric motor to turn at the desired speed is identified while maintaining a duty cycle at substantially 100 percent.

9. The apparatus of claim 1 ,

wherein the controller comprises a voltage identifier configured to adjust the voltage across the electric motor to maintain a speed of the electric motor at the desired speed when the duty cycle is at about 100 percent; and

wherein the electric motor is a brushless electric motor.

10. The apparatus of claim 1 ,

wherein the controller is further configured

to generate a current command based on a speed command for the electric motor and a measured speed of the electric motor;

to generate the duty cycle as the duty cycle command for the electric motor and an indicator, the duty cycle command and the indicator based on a measured current of the electric motor subtracted from the current command;

to generate the voltage command based on the duty cycle command subtracted from the indicator; and

to generate the voltage as the regulator voltage for the voltage regulator circuit, the regulator voltage based on a measured regulator voltage from the voltage regulator circuit subtracted from the voltage command that is limited by a first rate limiter;

wherein the electric motor receives the duty cycle command from the controller and receives the voltage from the voltage regulator circuit;

wherein the first rate limiter limits the voltage command to prevent the voltage across a three-phase H bridge of the electric motor from increasing more quickly than desired; and

wherein a second rate limiter limits a value of the regulator voltage.

11. An electric motor system comprising:

an electric motor; and

a controller configured

to identify a desired speed for the electric motor during operation of the electric motor;

to identify a duty cycle for the desired speed;

to identify a voltage to cause the electric motor to turn at the desired speed with the duty cycle being about 100 percent using a group of control laws based on the duty cycle identified for the desired speed;

to generate the duty cycle as a duty cycle command for the electric motor;

to generate a voltage command based on the duty cycle command;

to generate the voltage as a regulator voltage for a voltage regulator circuit based on the voltage command; and

to apply the voltage to the electric motor during operation of the electric motor with the duty cycle through the voltage regulator circuit.

12. The electric motor of claim 11 , wherein the group of control laws comprises a current identifier, a duty cycle selector, a voltage identifier, and a regulator controller.

13. A method for controlling an electric motor, the method comprising:

identifying a desired speed for the electric motor during operation of the electric motor;

identifying a duty cycle for the desired speed;

identifying a voltage to cause the electric motor to turn at the desired speed based on the duty cycle identified for the desired speed;

generating the duty cycle as a duty cycle command for the electric motor;

generating a voltage command based on the duty cycle command;

generating the voltage as a regulator voltage for a voltage regulator circuit based on the voltage command; and

applying the voltage to the electric motor during operation of the electric motor.

14. The method of claim 13 further comprising:

repeating the identifying steps and the applying step to maintain a current speed of the electric motor at the desired speed in response to changes in loading on the electric motor.

15. The method of claim 13 , wherein identifying the desired speed for the electric motor during operation of the electric motor comprises:

receiving the desired speed for the electric motor from one of a user input and a device.

16. The method of claim 13 , wherein identifying the voltage to cause the electric motor to turn at the desired speed comprises:

identifying the voltage to cause the electric motor to turn at the desired speed using a group of control laws.

17. The method of claim 16 , wherein the group of control laws comprises a current identifier, a duty cycle selector, a voltage identifier, and a regulator controller.

18. The method of claim 17 , wherein a control law in the group of control laws includes a proportional-integral-derivative controller.

19. The method of claim 13 , wherein a controller is configured to control operation of the electric motor in four quadrants.

20. The method of claim 13 , wherein the voltage to cause the electric motor to turn at the desired speed is identified while maintaining a duty cycle at substantially 100 percent.