An optimal grid current control strategy with grid voltage observer (GVO) for LCL-filtered grid-connected inverters

An optimal grid current control strategy with grid voltage observer (GVO) for LCL-filtered grid-connected inverters is proposed in this paper. The quasi proportional resonant (QPR) controller is applied in this control strategy conducted in a stationary frame to suppress the transient fluctuations and the total harmonic distortion (THD) of the output grid current and achieve faster transient performance. Active damping is chosen as the damping method in this paper, which uses the capacitor current acting as the feedback of the inner current loop to replace the actual resistor in parallel with the filter capacitor digitally. The LCL-filtered resonance frequency can be changed by this virtual impendence, and the control system will be stabilized more effectively. In this proposed control strategy, a GVO is introduced to replace the actual sensors, the sampling precision of which can be influenced negatively in the actual experimental environment. The introduced GVO can provide clean and noise-free estimation of the grid voltage and also reduce the overall cost of the whole control system. The estimated grid voltage acts as the feedforward of the internal current loop, which accelerates the regulating rate of the internal current loop, improves the dynamic response of the system effectively, and restrains the influence caused by grid voltage variation. Finally, the validity of the proposed approach is verified through simulations and a three-phase prototype test system with a TMS320F28335 digital signal processor. (c) 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.