UBC Theses and Dissertations
Digital control techniques for power quality improvements in power factor correction applications Clark, Colin William
The prevalence of standards and recommended practices to meet harmonic current limits has gained, and continues to gain, momentum over recent years. To meet these requirements, power electronic rectification devices are necessitated along with their specialized control techniques. A popular power electronic circuit to obtain low-harmonic input current is the boost power factor correction (PFC) converter, and with the advent of digital control, powerful control techniques to meet these harmonic current limits are possible. The first contribution is a detailed guide to the conversion of an analog IC-controlled boost PFC converter to a digitally controlled equivalent. Design of the voltage and current sensing networks, compensator, overview of the critical interrupt service routines, and the control implementation in a digital signal processor (DSP) is presented. The existing boost PFC converter modified for digital control is successful, and provides a flexible prototyping test bench for further use. The second contribution is a novel DSP-based discontinuous conduction mode (DCM) detection method for application to the boost PFC converter. The proposed detection method is computationally simple, and requires little or no modification to existing digitally controlled boost PFC converters using DSPs with on-board comparators. An experimental boost PFC converter verifies the effectiveness of the proposed detection method over traditional zero current detection and DCM detection techniques, enabling advanced control techniques for power quality improvements. The final contribution is a new adaptive mixed conduction mode (MCM) control technique for the boost PFC converter. This MCM control technique applies the proposed DSP-based DCM detection method to realize higher power factor and decreased total harmonic distortion (THD) over a commercially available analog controller and a conventional digital controller. Using a boost PFC converter operating in MCM with the proposed adaptive control method, THD improvements of up to 4.55% at light loads and power factor improvements of up to 17.4% are provided over the analog and conventional digital controller.
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