Stabilization of a PV Fed Current Mode Controlled SEPIC with MPPT Using Piecewise Quadratic Slope Compensation

Instabilities in the form of subharmonic oscillations are addressed in this paper for a Single-Ended Primary Inductor Converter (SEPIC) used for Maximum Power Point Tracking (MPPT) in a Photovoltaic (PV) system under current mode control. It is widely known that this kind of system may exhibit undesired subharmonic oscillations when the duty ratio is larger than 50%. Piecewise quadratic (PWQ) slope compensation technique has been proven to be an efficient technique for eliminating this kind of undesired behavior in DC-DC switching converters. With this technique, the stability of the converter is guaranteed for all values of the duty ratio. In this work, the technique is applied on a SEPIC supplied from a photovoltaic energy source and linked at its output to a DC load. Under varying environmental conditions, the system is used for MPPT. A peak current mode controller is used for the current loop whose reference is provided by a Perturb and Observe (P&O) MPPT algorithm. The obtained results show that the system exhibits a fast MPPT of the PV generator under (a) sudden changes in the environmental conditions while the guaranteeing fast-timescale stability (b) change of inductance. The mathematical modeling, design procedures are validated by numerical simulations. The comparison with the conventional slope compensation technique is also given to show the suitability of the PWQ.