Complementary electronic power converter

Abstract

Minimal energy storage is required in complementary converters, a family of zero-voltage switching circuits which achieve non-pulsating input and output currents by employing a ripple-cancelling technique instead of conventional filtering. The input voltage in these circuits is divided between a primary winding of a main transformer and a primary winding of a second transformer referred to as a complement transformer. The turns ratios of the two transformers are adjusted so that the secondary voltage of the complement transformer cancels the ripple in the rectified output of the main transformer. The symmetry of these circuits allows an AC voltage waveshape to be impressed upon the main transformer, independent of the load current passing through it. If desired, a sinusoidal voltage can be produced across the main transformer with only a small resonant current, which can be achieved with minimal energy storage. The complement transformer also requires minimal energy storage because the flux produced by the DC primary currents is cancelled by the DC secondary currents. The symmetry of these circuits allows them to have bidirectional power flow if synchronous rectification is used. Further, if bidirectional switches are used, reversing the input voltage will reverse the output voltage. Thus, complementary converters can be made to emulate an ideal transformer, passing both AC and DC if the input frequency is well below the switching frequency.