A forced switching technique for current controlled three-level NPC ac-dc converter

In this paper forced switching control of three-level Neutral Point Clamped (NPC) ac-dc converter having rectification and regeneration capability is presented. This converter is utility friendly and maintains the dc-link voltage constant. Hysteresis current controller (HCC) is used for current control because of its simplicity, easy implementation and good dynamic performance. The comparison of a high frequency carrier signal at the input to the nonlinear element serves as an effective method of sustaining or quenching the limit cycles present in the system. This method ensures the advantages of HCC and guarantees constant switching frequency operation. This switching technique is called forced switching algorithm. Magnitude conditions of carrier signals are developed for proper switching of the converter. The closed-loop control scheme with hysteresis current control is implemented using Lab VIEW based data acquisition system. The performance of the proposed three-level ac-dc converter has been studied using MATLAB/Simulink and experimental results are presented to validate the proposed control scheme.