On the Input Resistance of a Reconfigurable Switched Capacitor DC-DC Converter-Based Maximum Power Point Tracker of a Photovoltaic Source

The use of a switched capacitor (SC) dc-dc converter for tracking the maximum power point (MPP) of a photovoltaic (PV) array with the possibility of partial shading is described. The SC converter topology can be reconfigured to maximize conversion efficiency depending on the solar radiation and load. A new control scheme for MPP tracking based on tuning the input resistance (RIN) of the SC converter MPP tracker with a battery tied load to match the output resistance of the array at MPP is proposed. RIN of the SC converter MPP tracker is studied extensively. The limits of RIN and its sensitivity to Pulse-width modulation (PWM), frequency modulation (FM), and circuit parameters of the SC converter are analyzed. Based on the sensitivity analysis, the proposed control scheme consists of an inner FM loop for fine control, an outer PWM loop for coarse control, and a provision to increase the dynamic range of RIN with adjustments of certain converter circuit parameters. A hardware prototype of a 10-W SC converter-based MPP tracker is built. Experimental measurements on the hardware model confirm the theoretical analysis. An algorithm to implement the MPP tracking control scheme is also tested.