On modeling and control of MHD-steam system

This work deals with the development of an elementary model for a coal fired, open cycle, MHD steam plant and its use in the selection of a control strategy for responding to changing load demands.

Assuming the system variables are perturbed a small amount from their steady-state values when such a load demand is received, a linear incremental model of the plant is constructed. The model makes use of a fuel dependent linear load-line for the MHD channel and takes into account the voltage current characteristics of the inverter when operated between the MHD channel and a constant voltage source of AC. The incremental power flow in the combined plant is described by these models when combined with the usual characteristics of a steam turbine driven alternator.

Using Megawatt-Frequency Control ideas from power systems theory, methods for dealing with step load demands are studied by both classical and modern control theory techniques. It is found that the fuel input to the combustor, as well as an auxiliary boiler, are necessary to control the combined plant. The auxiliary boiler supplies the throttling capacity usually controlled by the governor in a conventional steam plant.

For a representative plant a specific state feedback scheme is determined and is found to be acceptable with regard to frequency deviation and control effort.