DEVELOPMENT OF MICRO-CIRCUITRY FOR THIN-FILM SOLAR-TO-BATTERY CHARGER

Abstract

Over the years, perovskite solar cells have continued to improve, and now the Internet of Things (IoT) devices can be powered by these emerging photovoltaic (PV) cells for indoor applications. This work develops a PV-powered charger that constantly supplies an IoT device and has a stand-by battery. The battery serves to assist the PV during Fractional Open-Circuit Voltage (FOCV) Maximum Power Point Tracking (MPPT) probing, low PV generation, and night times. Battery charging and discharging simulations are included as well. Simulations were conducted using LTspice software. The perovskite solar cell simulation model is designed using on-site behavioral conditions. The battery model is designed according to the common Li-ion battery behavior. Voltage matching between the PV and battery is performed using a boost converter. The charger uses a FOCV MPPT approach. Sample and Hold (S&H) circuit technique is included to enhance MPPT performance. FOCV applies a scaling constant to calculate maximum power point voltage using open-circuit voltage; however, the scaling constant is different for each irradiance level. Therefore, a light-dependent resistor (LDR) is added to the voltage divider part of the FOCV for maximum power point adjustments during light level variations. Case studies of PV-powered charger were conducted for irradiance levels of 0.03 and 1 sun, and different battery charge states. According to simulations of different scenarios demonstrated in case studies, the charger circuit operates as designed initially.