An Improved ω-φ Droop Control for Cascaded PV-ES System in Islanded Mode

The cascaded H-bridge structure has raised more and more attention in the field of photovoltaic (PV) power generation. This paper presents an improved omega-phi droop control method for the islanded cascaded photovoltaic-energy storage (PVES) system. The PV units mainly focus on outputting active power with unity power factor characteristic while the ES unit is responsible for the total output voltage regulation, frequency restoration, and power fluctuation suppression. With the proposed method, the string voltage can be regulated by the ES unit. Further, both the frequency synchronization with no steady state error and the cooperation between ES and PVs are realized automatically with only ES control requires PCC information. Therefore, the communication dependence is reduced which improves the system reliability. In addition, stability analysis and simulation results are provided to verify the effectiveness of the proposed controller.