Robust H∞ load-frequency control for interconnected power systems with D-stability constraints via LMI approach

The aim of this paper is to investigate the problem of robust H_∞ load-frequency control for interconnected power systems with circular pole constraints. The problem we address is to design both state feedback and output feedback controllers such that, for all admissible parameter uncertainties, the closed-loop system satisfies not only the prespecified H_∞ norm constraint on the transfer function from the disturbance input to the system output, but also the prespecified circular pole constraint or D-stability constraint on the closed-loop system matrix. The necessary and sufficient conditions for the existence of desired controllers are derived in terms of a linear matrix inequality (LMI). The performance of the proposed robust controller is not only validated through simulation with the two-area power systems model, but also compared with the recent works of Wang et al. (1993), Ray et al. (1999), and the traditional LQR control method. The simulation results show that the system responses with the proposed state feedback controller are the best transient responses, compared with the three methods mentioned. Besides, it is also shown that the transient responses of the proposed output feedback controller with circular pole constraints is improved.