SSR alleviation via analog and digital PID controller

Abstract

Power plants are generally far away from the distributing center. Transmission line is employed to transfer energy to a city. Transmission line is a complex system, so the transmission line's overload is always a challenging problem for utilities protection engineers. As a result, a series compensating capacitor (SCC) is placed along the transmission line to make the power factor correction, and increase the load capability. However, adding the SCC to the transmission line increases the potential risk of subsynchronous resonance (SSR) at a low frequency oscillation, which may lead to a possible torsional interaction and damages the turbine generator shaft when the mechanical frequency falls below the electrical frequency of the grid. To studies the SSR phenomenon, the mathematical model of the IEEE second benchmark (SBM) is utilized and computed at the system operating point, and then compensated with an analog proportional integral and derivative (PID) controller to the linearized and controllable transformed model of the system. The extended discrete PID controller is developed from an analog PID controller via bilinear transformation, which yields similar result. This extended discrete PID controller is a preferred method in preventing the SSR in the power system for its flexibility updating parameters of the nonlinear system to tolerate variation in different operational conditions.