Presently, the main ST generator units of the Chinese power grid are 1 ST and 1 boiler units with reheaters. So the modeling work of prime-mover is based on this unit type [
7]. The ST prime-mover consists of stage group model of through-flow parts and middle cubage model of reheaters. The first model describes the dynamic flow characteristics of the cascade path, and the last model describes the dynamic pressure and flow characters of middle cubage. The whole transfer function model of ST unit prime-mover can be obtained based on these two models, whose input signal is servo-valve opening value and output signal is ST mechanical power, shown as Fig. 5. The model can be simplified by ignoring the affection of exhaust steam pressure to stage group flow. The simplified model includes 6 parameters: power proportions of HP, IP, and LP cylinder (
FHP ,
FIP and
FLP), time constant of steam cubage, reheater and cross tube (
TCH,
TRH, and
TCO).