Robust terminal sliding mode power flow controller using unified power flow controller with adaptive observer and local measurement

Unified power flow controller (UPFC) is one of the multipurpose flexible AC transmission system devices which controls the transmission line parameters independently and simultaneously. This study presents a novel power flow controlling method based on terminal sliding mode control (TSMC) method using UPFC. The proposed controller has the advantages of finite-time convergence and chattering-free properties. A chattering-free state variable controller is designed and employed to address the problems of reference tracking, robustness against uncertainties and disturbances performance of the proposed controller is compared with an existing sliding mode controller (SMC) and a PI controller. Chattering phenomena and discontinuity of the sliding mode controller are also eliminated. Another objective of the proposed control scheme is to use only locally-measurable states, and to avoid remote long distance measurements. An adaptive observer is used to estimate the receiving end bus voltage, to avoid the data transfer problems over long distances, and to fulfil advantages such as fault detection and isolation. The presented observer could also be used to estimate the measurable states of the system. Simulation results demonstrate the efficiency of the proposed controllers. It is shown that the convergence time of the proposed TSMC is lower than those of the SMC and PID controllers'. Stability of the proposed controllers is mathematically proved. The performance of the presented adaptive observer, in the noisy environment, is also evaluated by simulation. Finally, simulation results of the suggested controllers under transient states and faulty conditions are presented.