Patent Number: 047708417
Section: claims

1. A method of controlling water level in nuclear power plant steam supply systems of the type having steam flow and water flow as inputs to the system and water level as an output of the system, said method comprising: (a) estimating the state variables of said system by applying observer theory to the inputs and the outputs of said system;  (b) generating a compensated water level from said estimated state variables, said compensated water level being dynamically related to said steam flow and feed water flow by a compensated transfer function which comprises the integration modes and unstable modes of behavior included in the overall transfer function relating the transforms of said inputs to the transforms of said outputs, said compensated transfer function having no right half plane zeros;  (c) displaying said compensated water level and said water level; and  (d) controlling said water level by comparing the compensated water level and the water level. 2. The method of claim 1 wherein said compensated water level is dynamically related to said feed water flow and said steam flow such that no time lag exists for said dynamic relation. 3. The method of claim 1 or 2 wherein said dynamic relation is such that the estimate of said state variables has a constant multiplier c.sub.i, said multiplier being the unique set of constants which satisfy the following identity: ##EQU22## where H.sub.c (s) is a compensated transfer function comprising at least the integration modes and the unstable modes of the overall transfer function of the system, where G.sub.i (s) is the observer based transfer function relating the transform of said estimated state variables to the transforms of said system inputs, and where n is the order of the system. 4. The method of claim 1 wherein said controlling step includes comparing said compensated water level to a set point. 5. The method of claim 1 wherein said controlling step further comprises the step of adjusting at least said feed water flow or said steam flow based upon said comparison. 6. The method of claim 1 further comprising the step of generating a bounded water level from said estimated state variables, said bounded water level being an estimate of minimum and/or maximum excursion of said water level over time. 7. The method of claim 6 wherein said controlling step includes comparing said bounded water level to predetermined limits for said water level. 8. The method of claim 7 further comprising the step of displaying said bounded water level. 9. The method of claim 7 or 8 wherein said controlling step further includes comparing said bounded water level to said water level.