Saturation-induced frequency instability in electric power systems

This paper concerns the effects of generator controller limits on long-term power system stability. It is shown through an example that when the system operates near its limits, saturation in the turbine/governor controllers can lead to frequency instability that would not be evident from load-flow analysis. A linearized model with controller saturation nonlinearity is obtained that preserves the saturation-induced instability phenomenon. A linear matrix inequalities (LMI) technique is used to find a region of attraction for the saturated linear system that gives an estimate of the maximum load disturbance that can be tolerated when the saturation effect is taken into account. Simulation also shows a power system stabilizer (PSS) providing frequency feedback to the automatic voltage regulator (AVR) significantly enhances the system robustness to large disturbances, while reducing the AVR gain has little effect. This work suggests several directions for further research.