Simulation of D-STATCOM for Power Quality Improvement under Unbalanced Load Condition

The mathematical model of Distribution Static Synchronous Compensator (D-STATCOM) in each sequence equivalent circuit and the problems encountered when conventional control strategies compensating for unbalanced load are analyzed. The input-output feedback linearization method combined with sliding mode control theory was put forward and applied to both the positive and negative sequence mathematical model. Since D-STATCOM is a multi-variable, strong coupling and nonlinear system in the synchronous rotating coordinate, the input-output feedback linearization method was used to linearize and decouple the original system to a pseudo linear system. A sliding mode control strategy was designed for the pseudo linear system. The positive sequence control compensates the reactive current required by the load to improve the power factor, while the negative sequence control compensates the negative sequence current due to load unbalance to balance the grid side current. A 10Mvar/10kV D-STATCOM simulation system was built in PSCAD, and the results proved that the control strategy can compensate the load unbalance and generate reactive current required by the load at the same time. Furthermore, when internal and external interferences occurred, the control strategy can also keep a good performance to improve the power quality.