A Discrete Duty Ratio Control for CCM Boost PFC Converter: Principle, Modeling, and Analysis

In this article, a discrete duty ratio (DDR) control strategy is proposed to improve both power factor (PF) and transient response performance for boost power factor correction (PFC) converters operating in continuous conduction mode. By directly generating discrete duty cycles to fit a target duty ratio with unity PF and reference output voltage, the proposed control can achieve fast, accurate, and low computation control. The control principle and discrete parameter design of the proposed control are presented. Due to the inherent characteristic of discrete control pulses, the linear control theory-based modeling and analysis methods are not suitable for the PFC converter system with DDR control. Therefore, another contribution of this article lies in establishing a discrete-time iteration model to assess the stability and explain the discrete control process of the DDR control system under steady-state and transient conditions. Experimental results on a 110 Vrms-400 Vdc-320 W prototype are presented to demonstrate the high PF and fast transient response of the DDR control strategy and verify the theoretical predictions. With a simple control loop design and low computational effort, the proposed DDR control is ideally positioned for high PF and fast transient response PFC applications that require tight cost control and high reliability.