An optimal Lyapunov-based control strategy for digitally controlled single-phase power factor correction AC/DC converters

AC-DC converters are widely used for conversion of utility ac input to a dc voltage suitable for telecom and other dc loads. There is dedicated analog control ICs available for controlling such converters and to accomplish their input power factor correction. Presently with decreasing cost of DSPs they are being applied more and more for controlling power electronic converters by taking advantage of the ease of implementation of different control laws with DSPs and also the immunity of digital systems towards noise and component ageing. This paper presents a simple and novel digital control scheme for a power factor correction (PFC) AC/DC boost converter based on Control-Lyapunov Function (CLF) theory. It is shown in this paper that the dynamics of the boost converter can be significantly improved by implementing the proposed controller, which introduces a Lyapunov function to the system and determines the optimal converter duty-ratio needed to minimize the Lyapunov function. The performance of the proposed controller is confirmed on a digitally controlled 3 kW boost PFC converter operating at 100 kHz switching frequency. Experimental results show that the proposed controller causes the boost converter to operate with low input current harmonics and very fast output voltage transient responses that are much less than a single input line cycle, compared to responses of several input line cycle transient periods seen in conventional control schemes.