Definition of incremental PI function observer in broad sense and its mathematical analysis

Boiler super-heater steam temperature control object is generally with characteristic of parameters slow time variable, big inertia and larger time lag. Using the IFO-KDeltax and PI state observer for reference, the concept of "Incremental PI Function Observer in Broad Sense" (IFO-PI/BS) is presented. Theorem on stable conditions of control system based on the IFO-PI/BS is proved by mathematical analysis. And deduction shows that the theorem can be extended to control system with character of slow time variable. Taking the new concept applying in boiler super-heater steam temperature control system of a 300 MW power unit, even when the unit quickly change load of 50 MW with rate of 8 MW/min, it has good control result that biggest errors of the super-heater steam temperatures are within 4degC. This is very successful engineering application. It provides an actual example for solving those temperature control systems with character of great inertia and larger time lag and slow time variable.