Modeling and Stability Analysis of SMIB system incorporating a VSC based HVDC link

Abstract

In recent years, power demand has increased substantially while the expansion of power generation and transmission facilities have been severely limited due to limited resources and environmental restrictions. As a consequence, power systems are being operated under high stress level conditions. These operating conditions have negative impact on system stability, reliability, controllability and security margins. The instability problem causes fluctuation in different parameters of power system which may cause great damage or even cause complete shutdown of the system. FACTS devices and HVDC transmissions have emerged as solution to help power system to increase the stability margins. HVDC transmissions are of particular interest since its ability to independently control active and reactive power. This paper discusses the impact of HVDC on power system stability. Different disturbances are applied in order to analyze dynamic response of the system. HVDC tends to make the system unstable if the setting of a line is not changed during and after a disturbance. A control mechanism has been proposed to strengthen the system stability. The establishment of the linearized Phillips-Heffron model of a system equipped with VSC-HVDC link is presented in this paper. On the basis of linearized Phillips-Heffron model, open loop eigenvalues are calculated and state space equations are used to design damping controller. Finally an optimal lead lag controller is designed to enhance damping of low frequency oscillations. The effectiveness and performance of the proposed controller is demonstrated through eigenvalue analysis and non linear time domain simulations. Moreover, the performance of the controller with different control input signals is evaluated and most effective control input is determined. Simulation results carried by MATLAB show the effectiveness of proposed strategy for enhancing dynamic stability.