AC-AC converter with high frequency link

1. A single-phase AC-AC converter for an AC source, comprising:

a first rectifier section rectifying the AC source into a first pulsed DC link voltage signal;

a high frequency modulating section coupled to said first pulsed DC link voltage signal and producing a high frequency AC voltage signal, wherein said high frequency AC voltage signal is a modulated waveform having substantially similar amplitude to said first pulsed DC link voltage signal and having a varying switching frequency to maintain a relatively constant flux;

a high frequency transformer coupled to said high frequency AC voltage signal producing a transformed high frequency AC voltage signal;

a second rectifier section coupled to said transformed high frequency AC signal and producing a second pulsed DC voltage signal; and

an unfolder section coupled to said second pulsed DC voltage signal and producing an output AC signal.

2. The AC-AC converter of claim 1 further comprising a reactive converter section supplying a reactive current to said output AC signal.

3. The AC-AC converter of claim 2 wherein said reactive converter section is coupled to said output AC signal by one of a parallel and series connection.

4. The AC-AC converter of claim 1 wherein said first and second rectifier section comprises antiparallel switches providing bidirectional and reactive power flow.

5. The AC-AC converter of claim 1 further comprising at least one additional series coupled electronic transformer forming a stacked electronic transformer.

6. The AC-AC converter of claim 1 further comprising at least one additional parallel coupled electronic transformer forming a stacked electronic transformer.

7. The AC-AC converter of claim 1 further comprising at least one capacitor coupled between said first rectifier section and said high frequency modulating section for filtering high frequency components.

8. The AC-AC converter of claim 1 further comprising at least one capacitor coupled between said second rectifier section and said unfolder section for removing high frequency components.

9. The AC-AC converter of claim 1 wherein said high frequency modulating section comprises an inverter with at least two series coupled transistors to each switch position of said high frequency transformer.

10. The AC-AC converter of claim 9 wherein at least one of said series coupled transistors has a different voltage rating.

11. The AC-AC converter of claim 9 wherein said series coupled transistors are controlled such that at least one of said transistors is not toggled for at least some period of time.

12. The AC-AC converter of claim 11 wherein said series coupled transistors are switched according to a threshold level selected from the group consisting of: only one of said transistors is toggled during a lower voltage region, only one of said transistors is toggled during a middle voltage range, and all of said transistors are toggled during peak voltages.

13. The AC-AC converter of claim 12 wherein said one of said transistors toggled during said lower voltage region is a lower voltage-rated transistor with respect to said transistor toggled during said middle voltage region.

14. The AC-AC converter of claim 12 wherein said switching is based upon at least one of a measured voltage range or a calculated voltage range.

15. The AC-AC converter of claim 1 wherein said high frequency transformer is one of a step-up transformer, a step-down transformer or a unity transformer.

16. A single-phase AC-AC converter comprising:

a first rectifier section rectifying an AC source into a first pulsed DC link voltage signal;

an inverter section coupled to said first pulsed DC link voltage signal and producing a high frequency AC signal, wherein said inverter section is comprised of at least two transistor banks;

a high frequency transformer coupled to said high frequency AC signal producing a transformed high frequency AC signal, wherein the high frequency AC signal ( 235 ) has substantially similar amplitude to said first pulsed DC link voltage signal and is formed by applying the DC link voltage in alternating forward and reverse directions at a varying switching frequency to maintain a relatively constant flux;

a second rectifier section coupled to said transformed high frequency AC signal and producing a second pulsed DC voltage signal; and

an unfolder section coupled to said second pulsed DC voltage signal and producing an AC signal output at approximately a same frequency as the AC source.

17. The AC-AC converter of claim 16 wherein each transistor bank comprises at least two transistors coupled in series.

18. The AC-AC converter of claim 17 wherein at least one of said transistors has a different voltage rating.

19. The AC-AC converter of claim 17 wherein said transistors in each said transistor bank are switched such that at least one of said transistors is not toggled for at least some period of time.

20. The AC-AC converter of claim 16 further comprising at least one additional series coupled electronic transformer forming a stacked electronic transformer.

21. A three phase AC-AC converter, comprising:

three single-phase electronic transformers coupled together to convert a three phase AC signal input to a three phase AC signal output, each of said electronic transformers comprising:

a first rectifier section rectifying said AC signal into a first pulsed DC link signal;

an inverter section coupled to said first pulsed DC link signal and producing a high frequency AC signal;

a high frequency transformer coupled to said high frequency AC signal producing a transformed high frequency AC voltage signal, wherein said high frequency AC signal is a modulated waveform having substantially similar amplitude to said first pulsed DC link signal and having a varying switching frequency to maintain a relatively constant flux;

a second rectifier section coupled to said transformed high frequency AC signal and producing a second pulsed DC link signal; and

an unfolder section coupled to said second pulsed DC link signal;

wherein said three electronic transformers produce said three phase AC signal output having a frequency and shape similar to said three phase AC signal input.

22. The converter of claim 21 wherein each said electronic transformer produces a phase current that is used to generate a line current, wherein each said phase current combines a harmonic component altering said phase current, and wherein said line current remains the same.

23. The converter of claim 21 wherein said electronic transformers are coupled to form one of a delta and wye connection on at least one of a primary or a secondary.

24. A method for converting AC power using a single phase AC-AC converter section, comprising:

receiving an input AC signal;

rectifying said input AC signal into a first pulsed DC link voltage signal;

modulating the first pulsed DC link voltage signal into a high frequency AC signal, wherein the high frequency AC signal ( 235 ) has substantially similar amplitude to said first pulsed DC link voltage and is formed by applying the DC link voltage in alternating forward and reverse directions at a varying switching frequency to maintain a relatively constant flux;

transforming said high frequency link to a transformed voltage link;

rectifying the transformed voltage link into a second pulsed DC link voltage signal; and

unfolding the second pulsed DC link voltage signal into an output AC voltage signal.

25. The method of claim 24 further comprising introducing reactive currents into said output AC signal.

26. The method of claim 24 further comprising providing bidirectional and reactive power flow.

27. The method of claim 24 further comprising at least two of said AC-AC converter sections coupled together to accommodate a higher voltage AC source.

28. The method of claim 24 wherein modulating said rectified AC signal comprises switching among at least two transistors coupled in series in each switch position.

29. The method of claim 28 wherein said switching uses a lower voltage-rated transistor for lower voltages.