Structural stability analysis of a rate limited automatic generation control system

This paper deals with the the stability analysis of a controller structure used for automatic generation control (AGC). The AGC structure is derived from the literature and augmented to handle generation rate constraints. The derived structure is then compared to the structure of the AGC used within DONG Energy, which removes deviations between reference and production. The analysis is conducted on a linear approximation of the closed loop system, with focus on the structure of the controller. We show that with the chosen structure, the closed loop system will be internally unstable independently of the controller parameters. The analysis shows that the different units in the portfolio might drift in opposite directions, a behavior also observed in the real system. The drifting ruins the economical optimisation. The instability issue can, however, be alleviated by introducing so-called parallel run.