Optimal control of UPFC for load flow control and voltage flicker elimination and current harmonics elimination

Recent advances in the power system handling capabilities of static switches have made the use of the voltage source inverter (VSI) feasible at both transmission and distribution levels. Most of the control schemes introduced were designed either for eliminating current harmonics or eliminating voltage flickers or for load flow control. They are mostly based on the PI controller. None of these control schemes were based on a systematic optimal control law that can control the converters to achieve all purposes at the same time, load flow control, voltage flicker elimination and also current harmonics elimination. This paper presents three novel control strategies: optimal control with tracking according to desired steady-state behaviour, optimal control with linear quadratic tracker design, and optimal control with tracking with PI controllers. The strategies were tested using a power system distribution model. The presented results show that all three control strategies improve the performance of the load flow and eliminate the current harmonics and voltage flicker. The controller design based on the desired steady-state behaviour is superior compared to other way of designs as the low value of the weighting matrix Q is satisfactory to obtain the desired tracking.