Stability Improvement of Electromechanical Oscillations by Control Co-ordination of PSSs and FACTS Devices in Multi-Machine Systems

This paper develops an optimal procedure for optimal control co-ordination of controllers of power system stabilizers (PSSs) and FACTS devices for improving small- disturbance stability, particularly the stability of inter-area modes, in multi-machine power systems. The control coordination problem is formulated as a constrained optimization by which the objective function formed from selected eigenvalues of the power systems state matrix is minimized. By representing the eigenvalue-eigenvector equations as equality constraints in the optimization, the procedure does not require any special eigenvalue calculation software or eigenvalue calculations at each iteration. Inequality constraints include those for imposing bounds on the controller parameters. The constraints which guarantee that the modes are distinct ones are derived and incorporated in the control co-ordination formulation. Simulation results of a multi-machine power system confirm that the procedure is effective in designing controllers that guarantee and enhance the stability of electromechanical modes.