A modular photovoltaic PCS with high-frequency isolation is proposed. The proposed system consists of a SEPIC converter and a full-bridge inverter Using the power slope versus voltage of the PV array, the MPPT controller is proposed that produces a smooth transition to the maximum power point. The dc current of the PV array is estimated without using a dc current sensor The disturbance of the line voltage is detected using a fast sensing technique. Experimental results obtained on a 500W prototype show high performance such as almost unity power factor, $90\%$ power efficiency, $3.6\%$ THD.