ABSTRACT
This chapter presents the development of battery energy storage system (BESS) with photovoltaic (PV) emulated output characteristics for direct PV string DC coupling. The proposed method using direct PV string DC coupling only required a bidirectional DC-DC converter. However, BESS output during discharging causes PV string output mismatch and shifted the maximum power operating point of the PV string. A PV characteristic emulated output BESS can discharge power that is identical to PV string and prevent PV string output mismatch. The proposed BESS using half-bridge bidirectional DC-DC converter topology with PV emulating function operating in boost mode for discharging and constant current control operating in buck mode for battery charging. The PV string emulating function is used as current and voltage feedback control loop operating in boost mode. Pulse-width modulation switching control of half-bridge bidirectional DC-DC converter is achieved using PI controller in the feedback control loop. The operation and performance of the BESS in direct PV string DC coupling is evaluated and shows promising results for practical applications. The proposed method provides easy retrofit and direct PV string integration of BESS for existing solar PV system without the need of additional DC-DC converter for the PV string.
