ROBUST CONTINUOUS SPEED GOVERNOR CONTROL FOR SMALL-SIGNAL AND TRANSIENT STABILITY

A robust continuous governor control for small-signal and transient st ability is proposed. The turbine under consideration is a steam turbin e with two sections and is of retreat type. The controller call be vie wed as including the speed droop governor and the fast-valving; the la tter is not standard, in that it generates a continuous control. Hence , the disadvantages of the (usual) bang-bang fast-valving are avoided. The control signal is generated by two controllers, with the first on e for small disturbances and the second one for large disturbances. Ou r approach is innovative in that both controllers have the same struct ure and only differ in the tuning of their parameters. They generate a continuous control and are switched with a bumpless transition to ens ure the continuity of the overall control. The most important non-line arity of the turbine is taken into account, and a feedback linearizati on is made-but in a somewhat unusual manner to obtain a robust control ler. A linear quadratic control is also used to ensure that the steady -state objectives are met and that good transients are obtained. Simul ations with the EUROSTAG software show improved efficiency with the pr oposed controller compared with the current one, especially in the cas e of a short-circuit, an islanding or a temporary loss of synchronism of the machine considered; the current controller has a standard struc ture, including a bang-bang fast-valving.