Control Strategy for Photovoltaic-Storage Hybrid System Based on Cascaded Linear-Nonlinear Extended State Observer

In response to issues such as the strong output power fluctuations of photovoltaic units caused by external environmental factors like solar irradiance, and the susceptibility of traditional control methods to grid disconnection incidents under significant system disturbances, a control strategy based on cascaded linear-nonlinear Extended State Observer (ESO) Active Disturbance Rejection Control (ADRC) is proposed for photovoltaic-storage hybrid systems. A model of the photovoltaic-storage hybrid system is constructed to achieve high- and low-frequency power distribution among energy storage units. The cascaded linear-nonlinear ESO-based ADRC is employed to estimate and compensate for system disturbances in real-time. Simulation results verify the effectiveness of the proposed control strategy, demonstrating a reduction in frequency deviation by 0.08 Hz under normal frequency dips. More critically, during severe AC bus voltage sags, the proposed strategy prevents the system frequency from falling below 49.0 Hz, thereby avoiding the under-frequency load shedding (UFLS) that occurs with conventional PI control. Additionally, the DC bus voltage fluctuation is limited to within 8 V under grid disturbances, and unlike the severe oscillations exhibited by PI control during system recovery, the proposed cascade strategy ensures an immediate and smooth transient response.