A Direct Power Control Strategy for AC/DC Converter Based on Best Switching State Approach

In this paper, we propose a direct power control (DPC) method for the ac/dc converter based on the designed dynamic nonlinear model and an approach on selecting the best possible switching state, aiming at guaranteeing the ac current quality, and improving the transient performance, especially under the unbalanced power-source voltage conditions. The proposed DPC mainly consists of three parts, sector selection, outer dc voltage control loop, and inner power control loop. Certain logical expressions are proposed in the sector selection to determine the position of the positive sequence power-source voltage vector. In the outer dc voltage loop, a control law is constructed based on a Lyapunov function. Moreover, a controller based on the best switching state is designed in the inner power loop to eliminate the negative sequence current. The proposed scheme is tested on an experimental platform, and the results show that, compared with the conventional DPC method, the total harmonic distortion of ac currents is reduced by more than 40%, and the transient settling time is almost reduced by 57% under the balanced power-source voltage condition. When the power-source voltage is unbalanced, the ac current quality can still be guaranteed with the proposed control method.