An Efficient Energy Conversion in Standalone Photovoltaic Lithium-Ion Battery System With Modified Pulse-Ripple-Current Charging

The lithium-ion (Li-ion) battery in electric vehicles charged by photovoltaic (PV) is a feasible solution for reducing grid demand. The existing standalone PV system with pulse-ripple-current (PRC) charging uses one converter and battery; and the PV remains idle in the PRC rest period, making the system inefficient. In this paper, one more converter and battery connected in parallel with PV in the standalone PV battery system with PRC charging is proposed to improve the efficiency. A single converter and double converters with synchronous and asynchronous operations are analyzed. The double converter asynchronous operation demonstrates the highest efficiency. In asynchronous operation, to charge batteries with different initial state-of-charge (SOC) (50-50, 60-30, 40-80%), the PRC pulse width is modified to deliver more energy to the lower SOC battery. Battery performance is assessed under both excess and lack of PV powers. A simulation model of an 8 kW PV, 320 V Li-ion battery system and an experimental prototype of a 250 W PV, 48 V Li-ion battery system are developed to validate the aforementioned operations. The results obtained in both exhibit similar trends.