Frequency-domain analysis of resonant current controllers for active power conditioners

This paper performs a frequency-domain analysis of three different resonant current controllers for active power conditioners. The analysis is focused on the closed loop frequency response and Nyquist plots for all current controllers of interest. The system stability when the active power conditioner attempts compensating high order harmonics is investigated. To perform this analysis, the time delay introduced by the inverter and the sampling is taken into account in the current controller closed loop transfer function. This procedure demonstrates the importance and effectiveness of the delay compensation to maintain the whole system stability. Experimental results obtained for a 25 kVA shunt active power conditioner prototype are presented to confirm the theoretical analysis.