Modeling of a four-leg inverter based DSTATCOM for load compensation

This paper derives a generalized mathematical model of a three-phase, four-wire, four-leg voltage source inverter topology for a DSTATCOM application. The four-leg inverter is operated in a current controlled mode by a suitable control strategy, to inject compensator currents in order to achieve harmonic compensation, load balancing and power factor correction. The four-leg compensator topology is also capable of compensating the dc component of the zero sequence current in the neutral conductor. The reference currents extracted through the instantaneous symmetrical component theory are tracked through hysteresis current control technique. The conditions required for a stable switching control are obtained using the Lyapunov stability criterion. The derived model has been verified by carrying out simulation studies through MATLAB and PSCAD, along with relevant results and discussions. Compensation is found to be effective with the supply relieved of harmonics, reactive power and unbalanced currents, confirming the correctness of the model developed.