Weak Distribution Grid Interfaced PV-Battery System With Modified Second Order Sequence Filter Based Control Strategy and Grid Supportive Features

This article presents a battery integrated photovoltaic (PV) system, which maintains grid interconnection at adverse grid conditions. Additionally, sinusoidal and balanced grid currents are achieved under grid voltage distortions, unbalanced grid voltages, and unbalanced load currents, using the presented modified second order sequence filter (MSOSF). The MSOSF eliminates DC offset in the sensed control signals. The DC-DC boost converter ensures the optimum PV array power utilization. A bi-directional DC-DC converter (BDC) is suitably controlled for the BESS (battery energy storage system) charging and discharging. The developed control strategy draws several operational benefits from the BESS. The intermittencies in the grid power at the variations in PV array power and local loads are eliminated. The grid disconnection encountered in conventional systems at large voltage drops is mitigated and the system provides continued support to the utility. At overvoltage situations, the utility is assisted by ceasing power export while permitting power inflow from the utility. In contrast to conventional systems, no PV array de-rating is necessitated. The injected grid power is a function of the prevailing feed-in tariffs, thereby ensuring greater economic benefits and helps to flatten the demand side power curve. The BESS health is conserved by transition to a recovery operation, on detection of over-charge or over-discharge conditions. Performance of the system at various operating situations is evaluated in detail using test results derived from a prototype developed in the laboratory.