Multi-objective optimal control strategy of thyristor controlled transformer for power quality improvement

Thyristor controlled transformer (TCT) is a kind of static VAR compensator (SVC). It is mainly used to solve the power quality (PQ) problems of low power factor (PF) and three-phase unbalance. However, it pollutes the power system by producing harmonic currents during normal operation. This paper proposed a multi-objective optimal control strategy to improve the comprehensive PQ. Firstly, the total harmonic distortions (THD) of the three-phase currents are pre-estimated. Then the relations between the trigger angles and the PQ indices are deduced. The objective function is established based on the scoring function and the weights of the PQ indices. Finally, quasi-newton method is used to find the optimal trigger angles. This method improves the PQ without additional equipments. Simulation results of case studies show that the proposed control method is effective and feasible.