Robust continuous speed governor control for small-signal and transient stability

A robust continuous governor control for small-signal and transient stability is proposed. The turbine under consideration is a steam turbine with two sections and is of the reheat type. The controller can be viewed as including the speed droop governor and the fast-valving; the latter 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 one for small disturbances and the second one for large disturbances. Our approach is innovative in that both controllers have the same structure and only differ in the tuning of their parameters. They generate a continuous control and are switched with a bumpless transition to ensure the continuity of the overall control. The most important nonlinearity of the turbine is taken into account, and a feedback linearization is made-but in a somewhat unusual manner to obtain a robust controller. A linear quadratic control is also used to ensure that the steady-state objectives are met and that good transients are obtained. Simulations with the EUROSTAG software show improved efficiency with the proposed controller compared with the current one, especially in the case of a short-circuit, an islanding or a temporary loss of synchronism of the machine considered; the current controller has a standard structure, including a bang-bang fast-valving.