Bidirectional converters and flux-balancing control methods thereof
A flux-balancing method for an isolated bidirectional converter uses a flux-balancing control loop and a current-balancing control loop to control the DC components in the primary and secondary currents. The flux-balancing control loop keeps the average magnetizing current substantially zero and the current-balancing control loop keeps the average primary current or the average secondary current substantially zero. The flux-balancing loop adjusts the duty ratio of a set of switches in a corresponding bridge. The adjusted duty ratio is designed to substantially eliminate the DC component in the magnetizing current. The current-balancing loop keeps the average primary current and the average secondary current substantially zero, and adjusts the duty ratio of the switches in a corresponding bridge to eliminate the corresponding DC component.
1. An isolated bidirectional converter, comprising:
an inductor;
a transformer in series with the inductor;
a first bridge circuit having first and second pairs of complementary switches operating alternately to provide a first current flowing to and from the inductor;
a second bridge circuit having first and second pairs of complementary switches operating alternately to provide a second current flowing to and from the transformer;
a first current-control feedback loop regulating the first current; and
a second current-control feedback loop regulating the magnetizing current of the transformer.
2. The isolated bidirectional converter of claim 1 , wherein the second current-control feedback loop maintains an average of the magnetizing current substantially zero.
3. The isolated bidirectional converter of claim 1 , wherein the second current-control feedback loop regulates the magnetizing current using a difference between the first current and a scaled second current, the scaled second current being proportional to the turns ratio between two windings of the transformer.
4. The isolated bidirectional converter of claim 3 , wherein the second current-control feedback loop maintains an average of the difference substantially zero.
5. The isolated bidirectional converter of claim 2 , wherein the average is obtained from samples of the magnetizing current.
6. The isolated bidirectional converter of claim 2 , wherein the average is obtained from a single sample of the magnetizing current.
7. The isolated bidirectional converter of claim 2 , wherein the average is obtained by summing two or more samples of the magnetizing current taken one-half of a switching period apart.
8. The isolated bidirectional converter of claim 1 , wherein the second current-control feedback loop comprises a proportional compensator with either a constant gain or an adaptive gain.
9. The isolated bidirectional converter of claim 1 , wherein the second current-control feedback loop has a higher bandwidth than the first current-control feedback loop.
10. The isolated bidirectional converter of claim 1 , wherein the first current-control feedback loop maintains an average current of the first current substantially zero.
11. The isolated bidirectional converter of claim 10 , wherein the average current is obtained using a low-pass filter.
12. The isolated bidirectional converter of claim 10 , wherein the first current-control feedback loop further comprises an integral compensator, an integral and proportional, or a proportional-only compensator.
13. The isolated bidirectional converter of claim 1 , wherein the second current-control feedback loop maintains an average current of the second current substantially zero.
14. The isolated bidirectional converter of claim 1 , wherein the first and second current-control feedback loops each adjust a duty ratio in one of the first and second pairs of complementary switches during one half of a switching period of the corresponding bridge circuit.
15. The isolated bidirectional converter of claim 1 , wherein the first and second current-control feedback loops each adjust duty ratios of both the first and second pairs of complementary switches in opposite directions.
16. The isolated bidirectional converter of claim 1 , wherein the second current-control feedback loop has substantially the same bandwidth as the first current-control feedback loop.
17. The isolated bidirectional converter of claim 1 , further comprising first and second power sources, coupled respectively to the first and second bridges.
18. The isolated bidirectional converter of claim 17 , further comprising first and second feedback control loops for regulating the first and second power sources.
19. A method for regulating an isolated bidirectional converter that comprises an inductor, a transformer in series with the inductor, a first bridge circuit having first and second pairs of complementary switches operating alternately to provide a first current flowing to and from the inductor and a second bridge circuit having first and second pairs of complementary switches operating alternately to provide a second current flowing to and from the transformer, the method comprising:
operating a first current-control feedback loop to regulate the first current; and
operating a second current-control feedback loop to regulate the magnetizing current.
20. The method of claim 19 , wherein the second current-control feedback loop maintains an average of the magnetizing current substantially zero.
21. The method of claim 19 , wherein the second current-control feedback loop regulates the magnetizing current using a difference between the first current and a scaled second current, the scaled second current being proportional to the turns ratio between two windings of the transformer.
22. The method of claim 21 , wherein the second current-control feedback loop maintains an average of the difference substantially zero.
23. The method of claim 20 , wherein the average is obtained from samples of the magnetizing current.
24. The method of claim 20 , wherein the average is obtained from a single sample of the magnetizing current.
25. The method of claim 20 , wherein the average is obtained by summing two or more samples of the magnetizing current taken one-half of a switching period apart.
26. The method of claim 19 , wherein the second current-control feedback loop comprises a proportional compensator with either a constant gain or an adaptive gain.
27. The method of claim 19 , wherein the second current-control feedback loop has a higher bandwidth than the first current-control feedback loop.
28. The method of claim 19 , wherein the first current-control feedback loop maintains an average current of the first current substantially zero.
29. The method of claim 28 , wherein the average current is obtained using a low-pass filter.
30. The method of claim 28 , wherein the first current-control feedback loop further comprises an integral compensator, an integral and proportional, or a proportional-only compensator.
31. The method of claim 19 , wherein the second current-control feedback loop maintains an average current of the second current substantially zero.
32. The method of claim 19 , wherein the first and second current-control feedback loops each adjust a duty ratio in one of the first and second pairs of complementary switches during one half of a switching period of the corresponding bridge circuit.
33. The method of claim 19 , wherein the first and second current-control feedback loops each adjust duty ratios of both the first and second pairs of complementary switches in opposite directions.
34. The method of claim 19 , wherein the second current-control feedback loop has substantially the same bandwidth as the first current-control feedback loop.
35. The method of claim 19 , further comprising first and second power sources, coupled respectively to the first and second bridges.
36. The method of claim 35 , further comprising first and second feedback control loops for regulating the first and second power sources.