Dynamic Pulse-Positioning for a Single-Stage Isolated AC-DC Converter

The control of a grid connected single-stage isolated ac-dc converter is presented where the transformer power flow occurs at high frequency where the transformer primary has both low and high frequency current components. The converter primary, used to control the low frequency grid current, creates a high frequency transformer switch mode voltage pattern whose pulse widths are determined by the instantaneous modulation index used by the primary side converter to control the grid current. The secondary side converter matches the primary side transformer voltage switching patterns and introduces a custom cycle-by-cycle phase shift to control the high frequency power flow between the transformer primary and secondary windings. This coordination of pwm pulses is done in such a way as to lower the flow of high frequency reactive currents when compared to using a standard phase shift control approach. Hence, the rms of the high frequency currents are lowered together with their associated conduction losses. The operation of the transformer isolating converter is verified with simulations and experimental results using a 2.2kW prototype converter.