Due to such characteristics as nonlinearity

large time-varying and large delay of the superheated steam temperature

the conventional PID cascade control can no obtain satisfactory effect.In this regard

by combining the internal model control with the fuzzy control and introducing the concept of multi-model

the two-mode control scheme was proposed

on the basis of the internal model principle and fuzzy control.Moreover

the superheated steam temperature cascade control system in once-through boiler of an ultra-supercritical 660 MW unit was optimized

and the improved control strategy was applied in EDPF-NT DCS.The results show that

compared with the conventional PID cascade control system

the improved control system has stronger adaptability and robustness of the load

and it still has good control quality when the unit load greatly changes.