Multi-objective Optimal The Pressure Set Point Of Large Coal-fired Unit Control System

In order to reduce the loss of turbine throttle valve regulator and guarantee a high unit efficiency, the sliding pressure operation mode is widely used when unit load is changing. But the sliding pressure operation curve is often obtained by people practical experience. So the control effect is difficult to guarantee. Therefore it is very meaningful to presents a method of getting coordinated control system pressure set-point with multi-objective optimization.In this paper, a general mathematics model has been established in view of the multiple objective optimization pressure set point. The inputs of dynamic model are the fuel mass flow rate, the position of turbine throttle valve actuator and the feedwater mass flow rate. And the outputs of dynamic model are the electrical power, drum steam pressure and the main steam pressure. The power-pressure operating region and the feasibility regions of control variable could be determined by inverse static model. Furthermore, to achieve optimal load-tracking and throttling loss in the main steam, the load-tracking error, fuel usage and the position of turbine valve actuator should be taken into account. Then the optimal control variables are got by particle swarm optimization techniques. Finally every vector of optimal control variables is generated a main pressure set-point through the direct steady state model of the coal-fired unit.This method is applicable to300-600MW, drum boiler and condensing steam turbine unit plant. The main pressure set point of multi-objective optimization can not only ensure fast load-tracking, and can reduce the throttling loss of the main steam. In addition, it can provide reference to the determination of sliding pressure operation curve.