Multilevel inverter control schemes

1. A method of controlling a multilevel inverter comprising:

determining at least a peak amplitude of a target waveform;

determining a number of discrete steps to achieve the peak amplitude of the target waveform;

calculating a plurality of switching angles to substantially minimize an area difference between the target waveform and a step signal of the multilevel inverter, in response to the number of discrete steps; and

activating a plurality of voltage sources in response to the plurality of switching angles.

2. The method of claim 1 wherein the determining at least a peak amplitude of a target waveform comprises:

accepting the peak amplitude with a hysteretic controller.

3. The method of claim 1 wherein the determining a number of discrete steps to achieve the peak amplitude of the target waveform comprises:

filtering an output of the multilevel inverter to extract a fundamental frequency component waveform from the output of the multilevel inverter;

determining a peak amplitude of the fundamental frequency component waveform;

comparing the peak amplitude of the fundamental frequency component waveform against the peak amplitude of the target waveform; and

adjusting the number of discrete steps in response to the comparison.

4. The method of claim 1 wherein the calculating a plurality of switching angles to substantially minimize an area difference between the target waveform and a step signal of the multilevel inverter, in response to the number of discrete steps comprises:

calculating each of the plurality of switching angles as

α

i

′

=

sin

-

1

⁡

(

(

i

-

1

2

)

⁢

V

m

V

p

)

where V m is a discrete voltage step magnitude, V p is the peak amplitude of the target waveform, and i is an indice ranging from 1 to m, where m is the number of discrete steps.

5. The method of claim 1 wherein the calculating a plurality of switching angles to substantially minimize an area difference between the target waveform and a step-signal of the multilevel inverter in response to the number of discrete steps comprises:

calculating each of the plurality of switching angles as

α 1 ′=sin −1 ((V i-l +V 1 )/2V p )

where V i are V i-l are discrete voltage step magnitudes indexed against i, V p is the peak amplitude of the target waveform, and i is an indice ranging from 1 to m, where m is the number of discrete steps.

6. The method of claim 1 wherein the activating a plurality of voltage sources in response to the plurality of switching angles comprises:

energizing a plurality of transformers.

7. The method of claim 1 wherein the calculating a plurality of switching angles to substantially minimize an area difference between the target waveform and a step signal of the multilevel inverter, in response to the number of discrete steps comprises:

calculating a peak amplitude of a fundamental frequency component waveform;

comparing the calculated peak amplitude of the fundamental frequency component waveform against the peak amplitude of the target waveform to obtain an error signal;

generating a correction factor in response to the error signal; and

multiplying at least one of the plurality of switching angles by the correction factor.

8. The method of claim 7 wherein the generating a correction factor in response to the error signal comprises:

accepting the error signal into an input of a proportional integral controller; and

summing an output of the proportional integral controller with a constant.

9. A multilevel inverter control system, the control system comprising:

means for determining at least a peak amplitude of a target waveform;

means for determining a number of discrete steps to achieve the peak amplitude of the target waveform;

means, responsive to the number of discrete steps, for calculating a plurality of switching angles to substantially minimize an area difference between the target waveform and a step signal of a multilevel inverter; and

means for activating a plurality of voltage sources in response to the plurality of switching angles.

10. The control system of claim 9 wherein the means for determining at least a peak amplitude of a target waveform comprises:

means for accepting the peak amplitude.

11. The control system of claim 9 wherein the means for determining a number of discrete steps to achieve the peak amplitude of the target waveform comprises:

means for filtering an output of the multilevel inverter to extract a fundamental frequency component waveform from the output of the multilevel inverter;

means for determining a peak amplitude of the fundamental frequency component waveform;

means for comparing the peak amplitude of the fundamental frequency component waveform against the peak amplitude of the target waveform; and

means for adjusting the number of discrete steps in response to the comparison.

12. The control system of claim 9 wherein the means, responsive to the number of discrete steps, for calculating a plurality of switching angles to substantially minimize an area difference between the target waveform and a step signal of the multilevel inverter comprises:

means for calculating each of the plurality of switching angles as

α

i

′

=

sin

-

1

⁡

(

(

i

-

1

2

)

⁢

V

m

V

p

)

where V m is a discrete voltage step magnitude, V p is the peak amplitude of the target waveform, and i is an indice ranging from 1 to m, where m is the number of discrete steps.

13. The control system of claim 9 wherein the means, responsive to the number of discrete steps, for calculating a plurality of switching angles to substantially minimize an area difference between the target waveform and a step signal of the multilevel inverter comprises:

means for calculating each of the plurality of switching angles as

α i ′=sin −1 ((V i-l =V i )2V p )

where V i are V i-l are discrete voltage step magnitudes indexed against i, V P is the peak amplitude of the target waveform, and i is an indice ranging from 1 to m, where m is the number of discrete steps.

14. The control system of claim 9 wherein the means for activating a plurality of voltage sources in response to the plurality of switching angles comprises:

means for energizing a plurality of transformers.

15. The control system of claim 9 wherein the means, responsive to the number of discrete steps, for calculating a plurality of switching angles to substantially minimize an area difference between the target waveform and a step signal of the multilevel inverter comprises:

means for calculating a peak amplitude of a fundamental frequency component waveform;

means for comparing the calculated peak amplitude of the fundamental frequency component waveform against the peak amplitude of the target waveform to obtain an error signal;

means for generating a correction factor in response to the error signal; and

means for multiplying at least one of the plurality of switching angles by the correction factor.

16. The control system of claim 15 wherein the means for generating a correction factor in response to the error signal comprises:

means for accepting the error signal; and

means for summing an output of a proportional integral controller with a constant.

17. The control system of claim 9 , further comprising:

a power-related device including the control system.

18. A power-related device comprising:

means for determining at least a peak amplitude of a target waveform;

means for determining a number of discrete steps to achieve the peak amplitude of the target waveform;

means for calculating a plurality of switching angles based on at least one of a frequency and the number of discrete steps to achieve the peak amplitude of the target waveform; and

means for activating a plurality of voltage sources in response to the plurality of switching angles.

19. A multilevel inverter control system the control system comprising:

a step number determination module; and

a switch angle determination module comprising logic configured to substantially minimize an area difference between a target Waveform and a step signal of a multilevel inverters; wherein the switch angle determination module comprises:

a switch angle calculation module; and

a switch angle correction factor module.

20. The control system of claim 19 wherein the step number determination module comprises a hysteretic controller.

21. The control system of claim 19 wherein the switch angle calculation module comprises logic configured to calculate each of a plurality of switching angles as

α

i

′

=

sin

-

1

⁡

(

(

i

-

1

2

)

⁢

V

m

V

p

)

where V m is a discrete voltage step magnitude, V p is a peak amplitude of the target waveform, and i is an indice ranging from 1 to m, where m is a number of discrete steps.

22. The control system of claim 19 wherein the switch angle calculation module comprises logic configured to calculate each of a plurality of switching angles as

α i ′=sin −1 ((V i-l =V i )/2V p )

where V i are V i-l are discrete voltage step magnitudes indexed against i, V p is a peak amplitude of the target waveform, and i is an indice ranging from 1 to m, where m is a number of discrete steps.

23. The control system of claim 19 wherein the switch angle determination module further comprises:

a proportional integral voltage regulator.

24. The control system of claim 19 wherein the switch angle determination module further comprises:

a fundamental peak value determination unit comprising logic configured to calculate a peak amplitude of the fundamental frequency component waveform as

b

1

=

4

⁢

V

m

π

⁢

∑

i

=

1

m

⁢

⁢

cos

⁢

⁢

α

i

where V m is a discrete voltage step magnitude, and i is an indice ranging from 1 to m, where m is a number of discrete steps.

25. The control system of claim 19 , further comprising:

a power-related device wherein the control system is integrated with the power-related device.

26. A multilevel inverter control system, the control system comprising:

a switch angle determination module comprising logic configured to substantially minimize an area difference between a target waveform and a step signal of a multilevel inverter wherein the switch angle determination module comprises:

a switch angle calculation module; and

a switch angle correction factor module.

27. The control system of claim 26 wherein the switch angle calculation module comprises logic configured to calculate each of a plurality of switching angles as

α

i

′

=

sin

-

1

⁡

(

(

i

-

1

2

)

⁢

V

m

V

p

)

where V m is a discrete voltage step magnitude, V P is a peak amplitude of the target waveform, and i is an indice ranging from 1 to m, where m is a number of discrete steps.

28. The control system of claim 26 wherein the switch angle calculation module comprises logic configured to calculate each of a plurality of switching angles as

α i ′=sin −1 ((V i-l =V i )/2V p )

where V i are V i-l are discrete voltage step magnitudes indexed against i, V p is a peak amplitude of the target waveform, and i is an indice ranging from 1 to m, where m is a number of discrete steps.

29. The control system of claim 26 , farther comprising:

a power-related device wherein the control system is integrated with the power-related device.