IIR filter-based compensator with modified feedback repetitive control scheme of voltage source inverter for nonlinear load applications

Inverters are the most common power electronic circuits used in systems like uninterruptible power supplies, electric motor drives, and distributed power generation. It is essential to keep the total harmonic distortion (THD) at the output of most inverters under certain limits, such as 5% or below as defined by different international standards. Nonlinear and high crest factor loads at the inverter output are the major external factors for the output voltage distortion. A linear controller such as a PID controller is not able to curtail the harmonic distortions generated by nonlinear loads as per industry standards. In these conditions, a repetitive controller (RC) is a more effective solution. A new design approach of RC proposed without requiring any additional hardware, and that can be implemented easily via digital tools. Typically, a standard RC solution has always few limitations in compensating harmonics near and above resonant frequency that causes the system to lead to unstable zone. To resolve these issues, this manuscript focuses on a suitable compensator design for the RC which can mitigate the harmonics below 2.5% variations as per the standard operating procedures. The authors proposed an IIR notch filter as a compensator along with a modified RC scheme. The proposed RC scheme experimentally verified using a hardware test bench. Experimentation shows the robustness and efficiency of the closed-loop controlled inverter with THD below 2.5% by suppressing the dominant lower-order harmonics. Further, the manuscript also compares the difference between the efficacy of the FIR filter and IIR filter as a compensator with the proposed RC scheme. The proposed compensator has also recorded improved throughput in terms of faster computational time.