An improved sliding mode control scheme for voltage-controlled four-leg inverter in the natural reference frame

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Name of the Speaker: Lokesh N (EE17D006)
Name of the Guide: Prof. Mahesh Kumar
Date/Time: July 22, 2022, 3.30 pm

Due to the presence of neutral-point voltage of four-leg voltage source converter (VSC) in the natural reference frame, the voltage dynamics of VSC are coupled through control inputs of all phases. This coupling leads to difficulty in assigning appropriate values to the control input variables using SMC with a conventional sliding surface. To eliminate this coupling, a new sliding variable for each converter leg is proposed. The proposed sliding variable for each leg is a function of the respective filter-capacitor voltage and the fictitious voltage which is a function of converter neutral-point voltage (NPV). Thus, the control of converter NPV is possible in addition to the control of compensator voltages using the proposed scheme. Further, the optimum value of sliding co-efficient, to maximize the existence region of sliding mode, is found for a four-leg VSC-based dynamic voltage restorer (DVR). The performance of a DVR with the proposed control scheme under various operating conditions is validated through detailed experimental studies carried out on a laboratory prototype of a four-leg DVR.