Modified PID load-frequency control with the consideration of valve position limits

This paper proposes a new load frequency control (LFC) scheme with a modified PID controller which guarantees the stability of the LFC loop for the wide control ranges of PID feedback gains. By observing the fact that the ratios between PID gains have more information than the individual gains, we proposed a modified PID controller by implementing feedback circuits by differentiating and integrating the output of the flyball speed governor. The proposed control scheme guarantees wide-range stability boundary of the PID gain controls, which can be easily checked by observing the root locus diagram. This paper shows that the valve position limits can be modeled in several ways, and that the control performance significantly depends on steam valve modeling in the case of large disturbances. The proposed LFC scheme has been tested for a sample 4-machine 10-bus system.