A Double Vector Sliding Mode Control Method for Improved Third Harmonic Distortion

The paper introduces a “Double-Vector Sliding Mode Control (DVSMC)” technique aimed at enhancing the performance of the current tracking with minimized Total Harmonic Distortion (THD) and average switching frequency in a grid connected neutral-point-clamped (NPC) inverter while fed to the utility grid as compared to traditional Sliding Mode Control (SMC) system. This method employs a fixed switching cycle and utilizes two symmetrically arranged voltage vectors with optimized time durations to minimize the sliding cost function, in contrast to the fixed hysteresis band typically used in conventional sliding mode control (CSMC). By utilizing double vectors, the current exhibits improved steady-state and dynamic performance, with a reduction in total harmonic distortion (THD). Additionally, for a THD of 1.41%, average switching frequency is reduced by approximately 70% to 2.5 kHz, compared to 8.3 kHz with 1.43% THD in the CSMC method. Simulation results obtained from MATLAB/Simulink effectively illustrate the advantages of the DVSMC approach, particularly the symmetric time division variant, in achieving a notable reduction in total harmonic distortion (THD) alongside a lower average switching frequency.