A Switching Control Strategy Based on Switching System Model of Three-Phase VSR Under Unbalanced Grid Conditions

Abstract

The power electronic converters are typical nonlinear systems. The conventional linearized modeling methods cannot accurately describe the working process of the converter. The control strategies based on the linearized model can only achieve good performance near the working point. By considering the switching nonlinear system nature of the converters, the main contributions of this article are as follows: a current error switching model is developed for the three-phase voltage source rectifiers (VSRs) under unbalanced grid for the first time; and an improved stability analysis theorem is proved for the switching control of the three-phase VSRs under unbalanced grid condition. These contributions are used to design a simple current switching controller for VSRs. The main advantages of the proposed modeling and control strategy are as follows. The switching model of the converter is built without any approximation. It accurately describes the physical working principle of the three-phase VSR under unbalanced grid condition. The proposed current switching controller has a very simple control structure. The switching states of the converter are directly produced according to the switching rule. There are no control parameters, no complicated rotation transformation, and no voltage vector modulation in the proposed switching controller. The proposed switching controller is not sensitive to the circuit parameters. The robustness of the control system is improved without any extra compensators or observers. Simulation and experiment verifies the correctness, the effectiveness, and the superiority of the proposed theory and methodology.