A simple repetitive controller embedded in PI-based UPS for reducing Total Harmonic Distortion with nonlinear loads

This paper presents a simple plug-in repetitive control scheme for the PI-based UPS control to reduce periodic distortions caused by nonlinear loads. The drawback of the conventional PI-controlled UPS is presented under the rectifier-type nonlinear load conditions. A plug-in repetitive controller is adopted to address this problem. The analysis of the proposed control scheme reveals the repetitive controller could be very simple since the control plant is remodeled by multi-loop PI/P controllers. The effectiveness of the proposed scheme is verified in a 2 KW (50 Hz) prototype using a single chip digital signal processor (DSP) TMS320F2812. Experimental results show that the control scheme can both lower a THD below 3.4% under nonlinear loads and preserve good dynamic response