Switching-function-based modeling and control of a SEPIC power factor correction circuit operating in continuous and discontinuous current modes

In this paper, a new switching-function-based model is proposed for a DC-to-DC single ended primary inductance converter (SEPIC). Compared to conventional buck or boost converters, this topology allows a low current ripple at the input for a relatively low level of the DC-bus voltage. Consequently, the high frequency filter needed at the AC-side of a buck converter is avoided, and the high voltage stresses applied on the switches are significantly reduced with respect to the boost converter. The converter is integrated as a power factor correction circuit at the DC-end of a single-phase diode bridge. Based on the averaged model of the converter, a pulse-width-modulated (PWM) control algorithm is developed in order to ensure a unity power factor at the AC-source side and a regulated voltage at the DC-load side. In order to verify the performance of the proposed control scheme, simulation experiments are carried out on a numerical version of the converter with its control circuit. The implemented model of the converter is obtained by using the switching function technique under the assumption of the most general case of a discontinuous current mode (DCM). The control system is tested under both rated and disturbed operating conditions. The system performance is evaluated in terms of source current total harmonic distortion (THD), voltage regulation, robustness and dynamic time response to a set point offset.