Forward-feed decoupling based UPFC and converter system design

In this paper, an equivalent controlled source circuit for the unified power flow controller (UPFC) is established. In the circuit, a series connected voltage controlled source is employed to control the power flow on the lines and a parallel connected current controlled source is adopted to stabilize the node voltage. For these control systems with nonlinear coupling, a method by using small disturbance around the operating-point is adopted to linearize the control system, and a feedforward control scheme is employed to realize the decoupling control. In order to overcome the drawback of instability of the small disturbance linearizing method while the variables change greatly, a controller algorithm with fuzzy parameter adaptive regulation is designed. Taking into account the UPFC power system, a PWM AC/DC converter and a PWM DC/AC inverter are used in shunt branch and series branch configurations respectively, and the deadbeat algorithm is adopted. The MATLAB simulation results have proved the proposed scheme to be correct.