Saturation-induced 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, interactions between the speed governor limits and the automatic voltage regulator (AVR) can lead to frequency instability that would not be evident from power-flow analysis or simulations of only the electromechanical dynamics. Analysis of the case study shows that when the generation limit is reached there is an unstable eigenvalue in the system matrix, but we show this observation alone cannot predict whether the instability will occur.We also show that stability can be achieved with the introduction of a power system stabilizer (PSS), which is normally used for transient (fast) stability. This work suggests several directions for further research.