Fixed-Frequency Sliding Mode Control in Synchronous Reference Frame for Three-Phase LCL Filtered Active Front-End Converter

In this study, a two-level voltage source converter based active front end (AFE) is designed. An LCL filter is used to suppress input current harmonics. A fixed switching frequency sliding mode controller is designed in synchronous reference frame to control the grid currents. In addition to the grid current, a capacitor voltage loop is used to suppress the LCL filter resonance. A PI controller is employed to regulate the output DC voltage. In addition, another PI controller is employed to generate the capacitor voltage reference, thus, requirement of the filter components is eliminated, and robust control structure is achieved. The performance of the proposed controller is validated with MATLAB/Simulink simulations and also compared with conventional PI control in synchronous reference frame which employs a passive damping for LCL filter. The simulation results show that the proposed method draws sinusoidal currents with low harmonic content from the grid while it regulates the output voltage. Besides, it provides fast response and robust structure.