The Research On A Digital Control Method Of Power Factor Correction

Power factor correction (PFC) regulators improve the converting efficiency of energy from the power grid to the power electronic equipment and reduce harmonic pollution brought by the power electronic equipment. And digital control methods have been proved to equip digital power management products with advantages of simpler design process, smaller sizes and better performance than products controlled by conventional analog methods. However, the current digital PFC control methods are converted directly from analog ones, resulting in some design defects due to delay and complex computation.This dissertation proposes a duty cycle digital control method for BOOST PFC regulators. The proposed method is derived from a digital design perspective and replaces the PID compensation of inner current loop in the conventional average current control, hence reduces the computation complexity. Since the input of PFC regulators is sinusoidal line voltage, this dissertation also develops a small signal model of the outer voltage loop for the compensation design. When designing the outer voltage loop compensation in the DC-DC converters, the discrete-time transfer function is achieved by means of converting from the continuous-time transfer function. However, in PFC regulators application, the way becomes less efficient. In this dissertation the reason is analyzed and, based on power balance, a simpler discrete-time transfer function is provided. The simulation results verify the feasibility of the proposed digital control method and show near unity power factor in steady state and transient response.