Burst Mode Control of Active-Power-Decoupling Integrated Active Clamp Flyback PFC Rectifiers

Abstract

To mitigate the bulky and heavy twice-line frequency power buffer in single-phase power-factor-correction (PFC) rectifiers while maintaining a lower cost, active-power-decoupling integrated active clamp flyback (iACF) PFC rectifier is recently proposed in the literature. The solution inherits all the benefits of conventional ACF converters such as low component count, leakage energy recycling, and soft-switching while being able to reduce the size of the power buffer in the system without hardware modifications. However, existing modulation and control strategies, based on Continuous-Conduction-Mode (CCM), can only achieve a high efficiency at heavy load but not at light load. This paper proposes a new modulation to improve the light-load efficiency of iACF PFC rectifiers. By combining CCM and burst mode of operation, this new modulation method can maintain all good features of CCM while effectively reducing the operating frequency, thus reducing the switching losses of the system at light load. This paper firstly reviews the existing light-load modulation methods for ACF converters and limitations of applying these methods to iACF are highlighted. The detailed operating principles of the proposed modulation method are explained, and controller implementation that supports simultaneous full-load, medium load and ultra-light load operation is developed. A 100-W laboratory iACF prototype is developed to verify the feasibility of the proposal, showcasing a 4-point average efficiency 91.9%, superior to the conventional two-stage solutions.