The decoupling control scheme can modulate power flow rapidly and stably in UPFC

but the feedback value is set at a constant point in the power loop. This control scheme has unsatisfactory robustness performances. This paper improves the decoupling control scheme with the impedance tracking. In this method

the feedback value would change from constant value to the tracking value of impedance in the line. So the decoupling control scheme can modulate the power flow of different impedance parameter

and it can modulate the power flow rapidly and stably as usual. The impedance tracking does not increase any sampling signals

and it is easily achieved. Simulation results show that the decoupling control scheme has good robustness.