Second order sliding mode control of three-level four-leg DSTATCOM based on instantaneous symmetrical components theory

In this paper, a second order sliding mode controller (SOSMC) is proposed to control a three-level four-leg DSTATCOM connected to three-phase four-wire distribution system. The controller is designed in synchronous reference frame using super twisting algorithm based on symmetrical components theory. The proposed DSTATCOM control is aimed for the power factor correction in both capacitive and inductive operation modes. It has also purpose the regulation of excessive neutral current in the fourth wire of the distribution utility system under unbalanced loads or asymmetrical fault in the grid cases. This paper also presents a simplified three-level three-dimensional space vector modulation (3DSVM) with DC-bus capacitor voltages balancing strategy based on the effective use of the redundant switching states of the inverter voltage vectors. The effectiveness and validity of the proposed SOSMC system and 3DSVM are maintained by computer simulation. From simulation results, the comparison between the SOSMC, first order integral SMC, and conventional PI controller shows superiority of the SOSMC with high performance under both dynamic and steady state operations even in worst cases such as fault and unbalancing loads.