Primary and secondary frequency regulation in a longitudinal hydrothermal system by Liapunov method

The problem of primary and secondary frequency regulation of a multi-machine power system is analysed with a Liapunov function method based on a quadratic performance index. The main purpose is to determine the best set of parameters of primary and secondary regulation according to an optimisation criterion. The objective consists of achieving a settling time as short as possible which is relevant in a longitudinal system, whose structure includes long transmission lines with a reduced number of loops.Frequency and turbine valve positions are used as state variables, and optimal control parameters for primary and secondary regulation are used as control variables. Performance index behaviour under different frequency control schemes is then used to determine the optimal values to set the droops and gains of primary and secondary regulation. Tests for different disturbance locations and selection of regulating units are simulated on a model of the Chilean Central Interconnected System (CIS). It is shown that significant improvements can be achieved with the proposed method.