ارزیابی یکپارچه قابلیت اطمینان و پایداری سیستم های قدرت Integrated Evaluation of Reliability and Stability of Power Systems

I. INTRODUCTION MODERN power systems are increasingly being operated close to their stability limits due to the increase in the penetration level of renewable energy sources, market forces, and recent advances in computation and communication technologies. In composite system reliability evaluation, following a contingency, faulted components are assumed to be disconnected from the grid immediately and the system is assumed to return to a stable state with suitable generation rescheduling for minimum load curtailments. Although the generation rescheduling optimization problem may converge to a feasible solution representing a steady-state operating point, a stable transition to a post-fault Stable Equilibrium Points (SEP) is not guaranteed. Therefore, transient stability assessment is an important factor that should be considered in evaluating the reliability of a given system. However, transient stability assessment is computationally expensive and for this reason system dynamics are often ignored in reliability evaluation. Power systems may evolve along any of numerous possible trajectories after occurrence of potentially destabilizing contingencies. The computational challenge of performing time-domain simulation of every or even a selected set of probable trajectories has prohibited the inclusion of transient stability analysis in the applications that require repetitive computations such as reliability assessment. More recently, however, there have been theoretical developments that potentially enables determination of system stability with low computation burden. These methods are predominantly based on direct methods, such as Lyapunov and energy function methods. Direct methods recursively filter a set of possible contingencies into stable, potentially unstable, and undetermined sets. In other words, direct methods screening tools selectively exclude stable contingencies and perform detailed analyses on the undertermined and potentially unstable contingencies [1]–[6]. For instance, three levels of filtering each of which has inertial and post-inertial time frames has been proposed in [1], [2]. The filtering process is applied along the solution sequence toward controlling unstable equilibrium points (controlling UEPs). Transient stability screening for online applications using the Boundary of stability region based Controlling Unstable equilibrium point method (BCU method) has been proposed in [3]. Six classifiers are used to omit stable and mild contingencies and pass undertermined contingencies for further detailed analyses. Subsequently, the authors of [3] introduced improvements to the classifiers in [4]. One of the improvements is adding an islanding mode classifier. A screening tool based on direct methods that utilizes a homotopy-based approach has been proposed in [7], [8].