Digital Implementation of Current-Mode Control for Power Factor Correction

Abstract

Presented in this dissertation is the implementation of power factor correction (PFC) preregulators controlled by a single microcontroller. Two microcontroller-based PFC preregulator systems, with input voltage sensing and without input voltage sensing, have been constructed and tested experimentally.

By using the on-board peripherals of the microcontroller, hybrid control method is proposed to implement the PFC preregulators, where the analog control loops and digital control loops were integrated into a complete PFC controller. The current loop was constructed by analog peripherals in responding to its fast dynamics, while pure digital control was implemented in the voltage loop. Hardware multiplication was achieved by using an on-board multiplying DAC approach. A ramp signal was generated by a module inside the microcontroller. The amplitude of the ramp signal used to control the switch was modulated and then scaled using the output voltage error. The scaled ramp signal was compared to the inductor current signal to produce the signal which controlled the switch. When implementing PFC preregulator without input voltage sensing, the information related to the input voltage is obtained by sensing the inductor current.

By using the hybrid control method, no complex algorithm or external multiplier was required to perform the PFC function correctly, and thus a one-chip solution has been achieved. Implementation issues for microcontroller-based PFC preregulators were discussed. These issues include system modeling, required functionalities of a microcontroller, main design procedures, and A/D conversion and time delay, as well as some considerations in hardware and software implementation. The proposed PFC preregulators have been tested successfully in the laboratory, and the measured power factor was above 0.99 at nominal operating conditions, and the output voltage was precisely controlled. Because of the simplicity of the circuit, the proposed PFC preregulator has low cost and high reliability.