Super Twisting Sliding-Mode Control Strategy for Three-Level Dynamic Voltage Restorers

A super twisting sliding mode control (STSMC) method is introduced for single-phase three-level T-type inverter based dynamic voltage restorers. This method is capable of alleviating chattering by producing a continuous-time modulation signal. The continuous-time modulation signal does not involve the discontinuities in the sliding surface function. Hence, the occurrence of chattering is prevented. The use of STSMC strategy suppresses the chattering to its minimum while preserving the other important features of the sliding mode control method like zero steady-state error, robustness and fast response. The effectiveness of the proposed method has been tested by Matlab simulations under voltage sags, voltage swells, and distorted grid voltage conditions for resistive and resistive-inductive loads. It is shown that the modulation signal from which PWM signals are produced is continuous. Also, the use of three-level T-type inverter results in improvement in the total harmonic distortion (THD) of the load voltage.