OPTIMAL APPLICATION OF SMES FOR SMALL-SIGNAL STABILITY ENHANCEMENT IN POWER SYSTEMS

The problem of lightly damped or unstable modes of oscillation in power systems has been successfully alleviated by means of the application of Static Var Compensation (SVC). This involves the modulation of the output susceptance of the SVC in response to appropriate system signals in such a manner as to improve the small-signal or dynamic stability of the system. Superconducting Magnetic Energy Storage (SMES) involves the short- or long-term storage of energy in the magnetic field of a superconducting coil. Four quadrant control of SMES units has been achieved, allowing for positive and negative flows of both active and reactive power to the coil. Hence, SMES has potential applications for power system stability enhancement but, unlike SVC, simultaneous and independent active and reactive control is possible. In this paper, an appropriate active power-modulated SMES model for eigenvalue and frequency domain investigations is presented. This model is incorporated into a full system representation so that its effects on the system damping can be assessed. Essential aspects of the analysis of SMES to system stability applications are those of placement and controller tuning. The results of an investigation into the optimal application of a SMES unit in a small power system are presented. The possible controller input signals are also assessed with regard to their use for stability enhancement. The parameters of the SMES controller are tuned using the gradient method and the improvement in system stability in terms of eigenvalue shift is demonstrated. The performance of SMES is compared with SVC as a method of stability enhancement.