A simple and effective time delay compensation method for grid-connected inverter with an LCL filter: Application to active damping method

A grid-connected inverter is equipped with an LCL filter after its output. This filter has a resonant characteristic and many active damping methods have been researched to suppress the resonant effects. The inverter is often controlled digitally and there is a control time delay which is inevitable due to A/D conversion, computation times, and so on. This delay degrades stabilities and damping effects of the inverter because frequency characteristics are different from its designed one especially around the resonant frequency. This paper proposes a simple and effective compensation of the control time delay to improve the damping effects. It is based on an estimation method of future state values advanced by the delay time. The proposed method is applied to the grid-connected inverter control and its effectiveness is investigated and validated through transfer functions of the regulated current errors by experiment.