UDE-Based Current Control Strategy for LCCL-Type Grid-Tied Inverters

LCL filter is usually used as an interface between inverters and the grid. However, due to the characteristics of LCL filter and system uncertainties, it is complex to design a controller with proper parameters. In this paper, with LCCL filter, the order of the inverter control system can be reduced from third order to first order, and an uncertainty and disturbance estimator based control strategy for grid-tied inverters with LCCL filter is proposed. Specifically, the proposed control strategy consists of differential feedforward, proportional-integral controller, and grid voltage feedforward. Moreover, with one-sampling computation plus half-sampling pulse width modulation delays considered, a simple and clear tuning algorithm for the proposed control strategy is presented. Finally, the inverter system with the proposed control strategy is investigated, and the effectiveness is supported by the tuning and comparative experiments with a 2-kW inverter.