Active power control for minimum switching of three-phase electrolytic capacitor-less PWM converter

This paper presents active power control method for three-phase electrolytic capacitor-less PWM converter which is operated by minimum switching. In the proposed method, motor side inverter regulates DC-link voltage as the level optimized in the efficiency and then grid side converter always works in the boundary of the limit hexagon in the voltage vector space. By this operation, the switching number of grid side converter is minimized and the system efficiency is improved. Here, when this system operates for motoring mode, undesirable resonance occurs between small DC-link capacitor and filter inductor, and it makes the system unstable. This paper analyzes the resonance and proposes active power control method for DC-link voltage regulation and resonance suppression. This proposed method directly manipulates output voltage references and stably operates the system in both generating and motoring modes. The feasibility of proposed method is verified by simulation and experimental results.