Differential Power Processing Converter Design for a Photovoltaic-Powered Charging Bag

Abstract

Traditional photovoltaic (PV) systems are stationary PV systems mounted in one location and, generally, receive consistent and even illumination across the PV panels. However, solar photovoltaic (PV) power is also getting widely used in lower-power emerging applications, like wearables or internet of things (IoT) devices. One fundamental challenge of using PV power in wearable applications is that individual PV cells may be pointing in different angles, receiving different light intensities. Under these uneven illumination, resulting system efficiency depends on the configurations of the PV cells and converters. Through this thesis, the system efficiencies of five configurations are compared with nine realistic test cases. The five configurations are: PV in series with central converter, PV in parallel with central converter, PV with cascaded converters, PV in series with differential power processing (DPP) converters, and PV in parallel with DPP converters. The nine test cases are composed of an ideal case (all PV cells at 1,000 W/m2) and eight realistic illumination cases based on the weather (sunny or cloudy) and realistic usage scenarios. Based on these cases the system efficiency is calculated for each configuration considering a range of converter efficiencies (70% to 100%). Results show that the parallel DPP configuration shows the highest system efficiency in all cases. Parallel DPP converters can achieve individual PV control and maximizing output power by processing small fraction of the PV power. There are two types of parallel DPP architectures which are with and without a front-end converter. Two parallel DPP architectures are analyzed and compared for a target 5-W wearable application. Between the two architectures, the DPP system without a front-end converter shows consistently high performance and operates properly over a wider range of lighting conditions. Therefore, the proper operation, such as maximum power point tracking (MPPT) of PV cells, using parallel DPP converters without the front-end converter is validated through simulation and hardware experiments. The PV-powered wearable prototype is able to charge a portable battery under low-light and partial shading conditions.