A Robust Approach to the Load Frequency Control Problem with Speed Regulation Uncertainty

The load frequency control problem of power systems has attracted a lot of attention from engineers and researchers over the years. Increasing and quickly changing load demand, coupled with the inclusion of more generators with high variability (solar and wind power generators) on the network are making power systems more difficult to regulate. Frequency changes are unavoidable but regulatory authorities require that these changes remain within a certain bound. Engineers are required to perform the tricky task of adjusting the control system to maintain the frequency within tolerated bounds. It is well known that to minimize frequency variations, a large proportional feedback gain (speed regulation constant) is desirable. However, this improvement in performance using proportional feedback comes about at the expense of a reduced stability margin and also allows some steady-state error. A conventional PI controller is then included as a secondary control loop to drive the steadystate error to zero. In this paper, we propose a robust controller to replace the conventional PI controller which guarantees performance and stability of the power system over the range of variation of the speed regulation constant. Simulation results are shown to validate the superiority of the proposed approach on a simple single-area power system model.

• S. Z. Sayed Hassen

• Robust control
• power system
• integral action
• minimax LQG control.

[1] O. I. Elgerd, "Control of electric power systems," IEEE Control Syst.
Mag., vol. 1, no. 2, pp. 4-16, 1981.
[2] H. Bevrani, Robust Power System Frequency Control. Springer, 2009.
[3] R. K. Boel, M. R. James, and I. R. Petersen, "Robustness and risk
sensitive filtering," IEEE Trans. Autom. Control, vol. 47, no. 3, pp. 451-
461, 2002.
[4] P. Dupuis, M. R. James, and I. R. Petersen, "Robust properties of risksensitive
control," Mathematics of Control, Signals, and Systems, vol. 13,
no. 4, pp. 318-332, 2000.
[5] I. R. Petersen, M. R. James, and P. Dupuis, "Minimax optimal control
of stochastic uncertain systems with relative entropy constraints," IEEE
Trans. Autom. Control, vol. 45, no. 3, pp. 398-412, 2000.
[6] I. R. Petersen, V. A. Ugrinovskii, and A. V. Savkin, Robust Control Design
using H∞ methods. Springer-Verlag, London, 2000.
[7] A. V. Savkin and I. R. Petersen, "Minimax optimal control of uncertain
systems with structured uncertainty," Int. J. Robust and Nonlinear
Control, vol. 5, no. 2, pp. 119-137, 1995.
[8] V. A. Ugrinovskii and I. R. Petersen, "Time-averaged robust control of
stochastic partially observed uncertain systems," in Proc. IEEE Conf. on
Decision and Control, Tampa, Florida, 1998, pp. 784-789.
[9] ÔÇöÔÇö, "Finite horizon minimax optimal control of stochastic partially observed
time varying uncertain systems," Mathematics of Control, Signals
and Systems, vol. 12, no. 1, pp. 1-23, 1999.