On Sliding Mode Control for Three-phase Voltage Source Converters

For three-phase voltage source converters (VSC), current control in d-q reference frame (RF) and direct power control (DPC) under balanced voltage conditions (BVC) are regulation problems, and current control in the alpha-beta RF (CCAB) is a tracking problem. Conventional sliding mode control-based proportional controllers are sometimes adopted for current and power regulation, proportional plus resonant controllers are often used for CCAB. However, these controllers cannot ensure accurate current and power control due to time delays in the control loops. In this paper, practical SMC-based regulation and tracking controllers for VSC are designed. For current and power regulation, an integral SMC controller of which integral actions are included in both the control law and the sliding manifold is proposed. For CCAB, a current tracking controller, including proportional, resonant and derivative control laws is presented. System stability in Lyapunov sense is guaranteed and convergence of the state errors to zero is strictly proved based on Barbalat' Lemma. Finally, simulation studies on DPC under BVC and on CCAB are conducted to verify the effectiveness and to demonstrate superiority of the proposed controllers.