Integrated control of a nonlinear turboalternator model under fault conditions

Abstract

The integrated control of a nonlinear turboalternator model interconnected with a grid system and supplying a local asynchronous-type load is studied. The alternator equations incorporate the effects of transient saliency, positive-sequence damping, field-flux-linkage variation, machine saturation and excitation control. Turbine input power is controlled by a conventional governor representation with facilities for speed resetting. Transient performance of the system operating under external-load-change and short-circuit-fault conditions with line switching is studied by digital simulation, using conventional and linear-model control of the nonlinear system. Integrated control of governor-valve and alternator-field excitation is related to the optimisation of a sequence of piecewise-linearised models associated with quadratic cost functions. Improved machine-voltage and speed performance is obtained with extended stability limits using a limited set of linear models, compared with the use of independent conventional controllers. The transient control of a quadrature-axis rotor field winding in the synchronous machine is investigated and is found to be effective in improving overall performance and in extending the synchronous-machine and induction-motor stability limits.