Energy storage quasi-Z source photovoltaic grid-connected virtual impedance VSG control strategy considering secondary frequency regulation

To ensure frequency stability across a wide range of load conditions, reduce the impacts of the intermittency and randomness inherent in photovoltaic power generation on systems, and enhance the reliability of microgrid power supplies, it is crucial to address significant load variations. When a load changes substantially, the frequency may exceed permissible limits. In addition, command power or load disturbances can lead to power oscillations and overshoot. The grid-connected inverters of power electronic devices are characterized by low inertia and under-damping, which exacerbates these issues. To resolve the problems of frequency deviation and power oscillation in photovoltaic power generation systems, a control strategy is proposed in this paper for virtual synchronous generators (VSGs) with virtual impedance that considers secondary frequency regulation, based on an analysis of equivalent impedance principles and secondary frequency control. Simulation and experimental results demonstrate that the proposed control strategy enhances both the speed and stability of the VSG frequency recovery process and effectively suppresses power oscillations.