STUDIES AND APPLICATIONS OF PFC-PID CASCADE CONTROL STRAGETY IN MAIN STEAM TEMPERATURE CONTROL SYSTEM

Main steam temperature control system in thermal power plant is a system with large time constant, long time-delay, slow time-varying and various of disturbance factors, traditional PID control generally can't satisfy the performance requirement. This paper introduces and analyses the basic theory and properties of Predictive Functional Control(PFC). The algorithm of first-order plus dead-time system is provided particularly. PFC-PID cascade control strategy is given out by combining PFC with PID control, and applied to main steam temperature control system in thermal power plant. Internal loop of the system adopts PID control strategy, and internal loop and the super-heater high temperature plant constitute generalized control plant of PFC. The control algorithm is simple because predictive model of PFC is first-order plus dead-time model which is gained by matching generalized control plant. Furthermore, the system with unmatched model still has favourable quality. Therefore the strategy is easy to be realized in computer or distributed control system(DCS), so it has hopeful application prospect. Many computer simulation results show that the advanced control strategy has more favorable dynamic characteristics than PID cascade control strategy in main steam temperature system, disturbance rejection and robustness.