Boundary Control With Corrected Second-Order Switching Surface for Buck Converters Connected to Capacitive Loads

Boundary control (BC) with second-order switching surface is exploited for achieving faster response time and robust operation of switching power converters. However, the system performance of the boundary-controlled converters is significantly affected when it is connected to a second-stage converter with a large input capacitor. This article studies the shortcomings in second-order BC schemes of buck converter with capacitive loads and nonlinear switching loads. Second, this article proposes a BC scheme with corrected second-order switching surface to drive buck converters cascaded to boost converters. The switching criteria of the corrected control law account for the effect of unknown load capacitance as well as the variation in filter parameters. Therefore, an outer voltage ripple feedback loop is introduced to determine the corresponding switching criteria gain factor that adjusts the overall gain, while maintaining the output voltage ripple at a specified voltage band. The proposed method is verified by both simulation and hardware experiments. A 250-W buck converter prototype has been built to validate the control scheme under different load types, including a resistive-capacitive load, a boost converter, and a commercial dc electronic load. A comparison is drawn between conventional BC and the proposed method in both simulation and experimental environment, in order to highlight the advantages of the proposed method. With this approach, the converter operates at designed BC parameters independent of load capacitance and system parameter variations.