Methods, systems and apparatus for optimization of third harmonic current injection in a multi-phase machine

1. A method for improving voltage utilization in a five-phase vector controlled machine drive system that employs third harmonic current injection to increase torque and power output by a five-phase machine having a rotor that rotates at a variable angular speed, the method comprising:

receiving a combination of inputs comprising a torque command, angular speed of the rotor, and a DC input voltage; and

generating, based on the combination of inputs, an optimized fundamental current angle of a fundamental current vector.

2. A method according to claim 1 , wherein the step of generating, based on the combination of inputs, an optimized fundamental current angle of a fundamental current vector, further comprises:

generating, based on the combination of inputs:

a first value for a total root mean square (RMS) current corresponding to the combination of inputs;

a second value for a third harmonic current injection factor;

a third value for a third harmonic current angle; and

a fourth value of the fundamental current angle, wherein the second value and the third value are designed to optimize the fourth value of the fundamental current angle.

3. A method according to claim 2 , wherein the first value for the total RMS current corresponds to a particular torque/speed and DC input voltage operating point that is defined based on the combination of inputs.

4. A method according to claim 3 , wherein the second value and the third value are designed to optimize the fourth value to increase a value of a ratio of torque-to-total RMS phase current.

5. A method according to claim 3 , wherein the second value, the third value and the fourth value are designed to increase the value of the ratio of output torque-to-total RMS phase current at the first value of the total RMS current to improve phase voltage utilization by the five-phase machine.

6. A method according to claim 2 , wherein the step of generating further comprises:

generating a third harmonic RMS current signal and a fundamental RMS current signal based on the total RMS current and the third harmonic current injection factor; and

based on the fundamental RMS current signal, the third harmonic RMS current signal, the fundamental current angle, and the third harmonic current angle, generating a plurality of synchronous reference frame current command signals comprising: fundamental synchronous reference frame current command signals and third harmonic synchronous reference frame current command signals.

7. A five-phase system, comprising:

a five-phase machine having a rotor that rotates at a variable angular speed; and

a torque-to-current mapping module designed to:

receive a combination of inputs comprising a torque command, angular speed of the rotor, and a DC input voltage;

generate, based on the combination of inputs, an optimized fundamental current angle of a fundamental current vector; and

generate, based on the optimized fundamental current angle, a plurality of synchronous reference frame current command signals comprising: fundamental synchronous reference frame current command signals.

8. A five-phase system according to claim 7 , wherein the torque-to-current mapping module comprises:

a torque-to-current command table designed to generate in response to the combination of inputs:

a first value for a total root mean square (RMS) current corresponding to the combination of inputs;

a second value for a third harmonic current injection factor;

a third value for a third harmonic current angle; and

a fourth value of the fundamental current angle, wherein the second value and the third value are designed to optimize the fourth value of the fundamental current angle.

9. A five-phase system according to claim 8 , wherein the first value for the total RMS current corresponds to a particular torque/speed and DC input voltage operating point that is defined based on the combination of inputs.

10. A five-phase system according to claim 9 , wherein the second value and the third value are designed to optimize the fourth value to increase a value of a ratio of torque-to-total RMS phase current.

11. A five-phase system according to claim 9 , wherein the second value, the third value and the fourth value are designed to increase the value of the ratio of output torque-to-total RMS phase current at the first value of the total RMS current to maximize phase voltage utilization by the five-phase machine.

12. A five-phase system according to claim 8 , wherein the torque-to-current mapping module further comprises:

a first current conversion module designed to generate a third harmonic RMS current signal and a fundamental RMS current signal based on the total RMS current and the third harmonic current injection factor.

13. A five-phase system according to claim 12 , wherein the torque-to-current mapping module further comprises:

a second current conversion module designed to generate the synchronous reference frame current command signals based on the fundamental RMS current signal, the third harmonic RMS current signal, the fundamental current angle, and the third harmonic current angle.

14. A five-phase system according to claim 7 , wherein the plurality of synchronous reference frame current command signals further comprise third harmonic synchronous reference frame current command signals, and further comprising:

a stationary-to-synchronous transformation module designed to generate synchronous reference frame current signals comprising: fundamental synchronous reference frame current signals and third harmonic synchronous reference frame current signals; and

a synchronous frame current regulator module designed to generate a plurality of synchronous reference frame voltage command signals based on corresponding ones of the synchronous reference frame current command signals and corresponding ones of the synchronous reference frame current signals.

15. A five-phase system that employs third harmonic current injection, the system comprising:

a five-phase machine; and

a control loop that controls the five-phase machine, the control loop being designed to:

generate an optimized fundamental current angle of a fundamental current vector that is optimized to reduce total RMS phase current and to increase a ratio of output torque-to-total RMS phase current for a particular torque command, angular rotor speed and DC input voltage; and

generate a plurality of synchronous reference frame current command signals based on the total RMS phase current and the optimized fundamental current angle.

16. A five-phase system according to claim 15 , wherein the five-phase machine has a rotor that rotates at an angular speed, and wherein the control loop is designed to:

receive a combination of inputs comprising a torque command, angular speed of the rotor, and a DC input voltage;

generate, based on the combination of inputs, an optimized fundamental current angle of a fundamental current vector; and

generate, based on the optimized fundamental current angle, the plurality of synchronous reference frame current command signals comprising: fundamental synchronous reference frame current command signals and third harmonic synchronous reference frame current command signals.

17. A five-phase system according to claim 16 , wherein the control loop comprises:

a torque-to-current command table designed to generate in response to the combination of inputs:

a first value for a total root mean square (RMS) current corresponding to the combination of inputs;

a second value for a third harmonic current injection factor;

a third value for a third harmonic current angle; and

a fourth value of the fundamental current angle, wherein the second value and the third value are designed to optimize the fourth value of the fundamental current angle.

18. A five-phase system according to claim 17 , wherein the first value for the total RMS current corresponds to a particular torque/speed and DC input voltage operating point that is defined based on the combination of inputs, and wherein the second value and the third value are designed to optimize the fourth value to increase a value of a ratio of torque-to-total RMS phase current at the first value of the total RMS current to maximize phase voltage utilization by the five-phase machine.

19. A five-phase system according to claim 18 , wherein the control loop further comprises:

a first current conversion module designed to generate a third harmonic RMS current signal and a fundamental RMS current signal based on the total RMS current and the third harmonic current injection factor; and

a second current conversion module designed to generate the synchronous reference frame current command signals based on the fundamental RMS current signal, the third harmonic RMS current signal, the fundamental current angle, and the third harmonic current angle.

20. A five-phase system according to claim 19 , further comprising:

a stationary-to-synchronous transformation module designed to generate the synchronous reference frame current signals comprising: fundamental synchronous reference frame current signals and third harmonic synchronous reference frame current signals; and

a synchronous frame current regulator module designed to generate a plurality of synchronous reference frame voltage command signals based on corresponding ones of the synchronous reference frame current command signals and corresponding ones of the synchronous reference frame current signals.