Power Boundary Controlled Single-Stage LLC Power Factor Correction Converter and Its Optimal Parameter Design

Abstract

The time-domain analysis on single-stage LLC power factor correction (PFC) converter is performed in this paper, which reveals that PON mode may occur around the peak point of instantaneous input power and cause instability issue. In order avoid PON mode, the power boundary between PO and PON mode is calculated. For the common design methods of LLC PFC converter with average mode control strategy, the power boundary requires to be higher than the instantaneous input power at its worst point. However, higher power boundary brings higher RMS value of resonant current, and causes higher reactive power loss. Therefore, it is a wasteful designing methodology, as the other points of instantaneous input power don't need such high power boundary. In order to improve the efficiency, a power boundary control strategy is proposed in this paper. By controlling the input current to make the instantaneous input power follow the power boundary, PON mode is eliminated. Consequently, the required power boundary is overall reduced, and the minimal RMS current of resonant tank can be achieved. Furthermore, the optimal parameter design is also presented. A 90∼240VAC input and 250W/48V output experimental prototype has been built to verify the analysis results.