NEW MODELING AND ENHANCED CONTROL STRATEGY FOR GRID-CONNECTED FOUR-LEG INVERTER WITHOUT PHASE-LOCKED LOOP AND PARK’S TRANSFORMATION

Abstract

This paper proposes an enhanced voltage-oriented control strategy (EVOC) based on super twisting sliding mode control (STSMC) for a grid-connected four-leg source voltage inverter (GC-FLVSI) in the synchronous rotating frame (dq0–frame) without using a phase-locked loop (PLL) and Park's transformation. The proposed strategy is used not only to control the dq0–axes FLVSI inject currents but also to derive the mathematical model of the GC-FLVSI in the dq0–frame based on the direct instantaneous power control theory (DPC) and to eliminate the impact of PLL and Park's transformation. The principle of the proposed EVOC strategy is analyzed in detail. The STSMC is used for accurate dq0–axes FLVSI inject current control, and it can result in sinusoidal currents with high quality, high robustness against parametric variations, and low chattering with easy implementation. Finally, the superiority of the proposed EVOC-STSMC strategy in terms of complexity, response, steady-state errors, robustness, total harmonic distortion (THDs) mitigation, neutral current reduction, and robustness against parameter variations is verified through comparative analysis with the EVOC strategy based on the PI controller (EVOC-PIC).