A Study on Wide-Area Controller Design and Effect of Delays in Power Systems

One of the major issues in an interconnected power system is the damping of the inter-area oscillations which significantly reduces the power transfer capability. Though conventional controllers have been used such as power system stabilizer (PSS) to stabilize the local oscillations, these are not efficient to provide adequate damping to the inter-area modes. Advances in Wide-Area Measurement System (WAMS) makes it possible to use the information from geographical distant location to improve power system performances. A speed based Wide-area Damping Controller (WDC) provides supplementary control signal through the exciter of selected machine. The controller takes local and remote speed deviation signal as feedback. Here, geometrical measures for controllability and observability is performed to select the feedback signals and controller location. However, obtaining the remote signal may introduce a time-delay which may degrade the system performances or may even lead to instability. Here, depending upon feedback, two type of configurations are illustrated i.e. synchronous and non-synchronous. The effect of time-delay is studied for both the configurations. To consider the time-delay in the design stage, it is modeled with 2 order Pade approximation. The controllers are synthesized with an objective of H∞ control with regional pole placement. Performances for both the type of feedback configurations are evaluated. To show the effectiveness of the designed controllers, two case studies have been taken up a 4 machine system and another 10 machine system. It has been found that with WDC the oscillations died out quickly. Also, study illustrated that a non-synchronous feedback performs better compare to synchronous feedback WDC.