Transient Response Improvement at Startup of a Three-Phase AC/DC Converter for a DC Distribution System in Commercial Facilities

In this paper, a soft-start method for improvement of the transient response during the initial startup of power converters in building applications is proposed. Most dc loads have sensitive electrical characteristics regarding the input voltage. In such systems, the power converter is operated after connecting with dc loads to minimize the overshoot of the control voltage that may occur during connection to the loads. But whenever the power converter is started, the parameters in the circuit can differ, since the power converter is connected with various load types at each startup. This is disadvantageous for PI controller design for power converters. In order to solve this problem, a novel voltage control method using sliding-mode control theory is proposed. The advantage of the proposed voltage controller is that it is able to minimize an overshoot of the control voltage at the startup of the converter in terms of the types of loads or the magnitude variation of loads because a sliding mode controller has the robust characteristic of a variation in the parameters and load. The characteristics of three types of voltage controllers were compared through simulations and experiments. Despite the variations of the system parameters, the proposed voltage controller has fast response in the steady-state and robustness characteristics in the transient state. In addition, the proposed controller fundamentally minimizes the overshoot of the control voltage. The proposed controller was applied to a three-phase ac/dc converter, and the controller performance was verified.