Critical modulation method based on PWAM in back-to-back three-phase system

This paper proposes an efficient operating strategy for grid-connected back-to-back (B2B) system based on pulse-width amplitude modulation (PWAM). In the proposed method, grid side converter and motor side inverter alternately conduct PWAM in accordance with operating conditions. The conditions are decided by magnitude-comparison between grid voltage and back electro-motive force (EMF) of motor, and this is related with DC-link voltage shaping for PWAM. This paper introduces the specific control sequence for the proposed method and analyzes its influence on gird and motor circuit. In comparison with conventional constant DC-link voltage boosting system, the system with the proposed method can reduce its switching loss in overall torque-speed curve. Also this method is normally applied in electrolytic capacitor-less system due to reasonable DC-link power compensating, so compact and efficient system can be realized by adopting proposed method. The feasibility of proposed strategy is verified by simulation and experimental results.