A Robust Repetitive Control Strategy for CVCF Inverters with Very Low Harmonic Distortion

Combined an output voltage differential inner loop, an improved direct repetitive control strategy for CVCF inverters is proposed. The output voltage differential feedback effectively eliminates the inherent high-resonant peak of the open-loop inverter. Since the stability and the transient characteristics of the inverter plant are greatly improved, the repetitive controller is easier to be designed. A novel compensator, which combines a zero-phase-shift FIR filter and a conventional second-order filter, leads the repetitive control system good harmonic rejection and large tolerance to parameter variations. The proposed control strategy achieves low THD% (about 1.5%) with nonlinear loads and fast dynamic response by a 3.3kVA single phase EPS prototype developed in lab. It proves to be a simple and cost-effective solution for CVCF inverters.