Low-Cost High-Efficiency Discrete Current Sensing Method Using Bypass Switch for PV Systems

Abstract

This paper proposes a simplified current sensing technique for the successful tracking of maximum power point with boost converter for photovoltaic (PV) power systems. To achieve the optimum solutions, the simplest sensing strategy is proposed with high resolution, maximum efficiency, and low cost. In general, PV current of a solar power system is obtained not in continuous time domain but in discrete one due to the digital signal processor-based controller. Instead of continuous resistive sensors, the improved method uses a bypass circuit to bypass the measuring current when the controller halts the sampling of the voltage across resistive sensor. To make this approach more efficient, current sensing process is set to flow through the resistor during some sporadically selected sampling period for responding the slow dynamic of the maximum power point transition. The bypassing approach can be further improved by removing the resistive sensor replaced to the bypass MOSFET. The proposed method contributes to the sensing loss reduction (the ultimate loss reduction is 97% of conventional resistive sensor) as well as to minimization of the thermal stresses on the sensor (23.2 degrees C), which enables the proposed methods applied to middle range power conversion systems. Finally, the maximum power point tracking ability of the PV system is evaluated under a rapidly changing cloudy day condition and the superior performance of the proposed technique is demonstrated by comparing the results obtained using conventional current sensing method and proposed current sensing method.