A Coordinated Control Framework for PV-Energy Storage Systems Integrating Improved VSG with Diurnal Active and Nocturnal Reactive Power Support

As the penetration of renewable energy continues to increase, the application of Photovoltaic-Energy Storage (PV-storage) systems has become more widespread. However, these systems face challenges, including low coordination ability during the day, insufficient utilization of nighttime power and reactive power capacity, which limit the system's flexibility and its potential for frequency and voltage support. To address these issues, this paper builds upon traditional Virtual Synchronous Generator (VSG) control, establishing a coupling relationship between the PV-storage system's Direct Current (DC) capacitor voltage and power. An improved VSG control strategy is proposed that integrates flexible daytime power delivery and nighttime reactive power compensation. A coordinated power distribution mechanism for daytime power, based on PV active power reserve and hybrid energy storage frequency division control, is designed. Furthermore, a voltage over-limit regulation scheme is introduced, optimizing the utilization of the system's remaining capacity by enhancing the reactive power support during nighttime operation. Finally, simulations and analysis in MATLAB/Simulink demonstrate that the proposed control strategy can significantly improve the system's ability to dynamically regulate power across all periods, thereby enhancing its frequency and voltage support capabilities.