Repetitive control of grid-connected inverter using a high resonance frequency LCL filter

This paper presents a high performance repetitive current controller for grid-connected inverters based on a high-resonance-frequency LCL filter. Conventional grid-connected inverters with LCL filter use either passive or active damping techniques to achieve system stability. In this paper, the resonance frequency of the LCL filter is deliberately selected higher than 40% of the inverter switching frequency. By properly selecting the current sensor position and introducing an extra delay with a low pass filter on the feedback path, the system stability is obtained without the adoption of any extra damping techniques. Resultantly, minimal LCL filter size and cost are obtained and the controller cost is reduced. Moreover, a high performance plug-in repetitive controller is adopted to regulate the grid current. High power factor (>0.99) and very low total harmonic distortions (1.72%~3.72%) are guaranteed under both heavy and light load conditions. Dynamic stiffness is also achieved under step-changed current command. Experimental results are provided to verify the validity and performance of the repetitive current controller based on the high-resonance-frequency LCL filter.