Coordinated active and reactive power management implementation based on dual-stage PLL method for grid-connected PV system with battery

This paper presents a single phase grid-connected PV system integrating energy storage system (ESS) using cascaded multilevel inverter. A Discrete Fourier Transform (DFT) Phase Locked Loop (PLL) method is proposed to improve system dynamic performance. A coordinated active and reactive power management (ARPM) strategy is developed based on the dual-stage DFT PLL method. The point of common coupling (PCC) overvoltage caused by reverse power flow can be mitigated by properly storing extra solar energy in the local ESS. In particular, the proposed system can provide wide range reactive power compensation to improve power quality and system stability. Furthermore, a control system, including dual-current-loop control, energy storage voltage balance control and ARPM control, is developed in grid-connected mode. Finally, a 3.5 kW single phase grid-connected PV system with batteries is implemented in the laboratory. Both simulation and experimental results are presented to verify the validity of the proposed power management strategy.