Active Disturbance Rejection Control of Photovoltaic Three-Phase Grid Following Inverters under Uncertainty and Grid Voltage Variations

A PV three-phase grid following inverter (GFI) with LCL filters can reduce current harmonics and deliver active power to the grid. Controlling such higher-order systems is challenging due to system uncertainties, grid voltage variations, and filter resonance. Active disturbance rejection control (ADRC) provides resilience to these uncertainties and a prompt response to disturbances. A linear extended state observer and a phase-locked loop observer are integrated into the ADRC structure to optimize tracking performance. The proposed controller uses a structured inner and outer closed-loop ADRC that takes into account process delays and extended state observer dynamics. The GFI can operate under variable grid voltage frequencies or even deviations in frequency caused by grid failure, and is able to meet these challenges as part of the design process and the synchronization approach. Both simulation and experimental results are given to validate the dual ADRC-based methods for an 8 kW laboratory prototype PV-GFI system.