| In a steam boiler system,the steam drum is the core device that absorbs the latent heat of vaporization of water,stores energy,and converts it into steam.It is crucial to maintain the steam drum liquid level within the required range to ensure efficient operation and safe production of the boiler system.Based on the principles of material balance and energy conservation,this thesis analyzes and derives the dynamic mathematical model of the steam drum liquid level,verifies the conventional control scheme of the steam drum liquid level through simulation,proposes the use of a triple-step nonlinear control law for steam drum liquid level control,develops and implements the triple-step nonlinear control law program based on the Siemens S7-300 PLC platform.The simulation process achieved good control results.The specific work contents mainly include the following aspects:(1)Based on the working principle of the boiler water-steam cycle,a mathematical model of the steam drum water level object was established using the mechanism analysis method.An open-loop simulation program for the steam drum water level was designed using Matlab/Simulink,and the applicability of the model was verified.(2)The principles of the current conventional single,double,and triple impulse steam drum liquid level control schemes were studied,and the closed-loop control effects of each scheme were analyzed and verified through a simulation control experiment program built using Simulink software.The results showed that the conventional control scheme for the steam drum liquid level has issues with long adjustment time and large overshoot for changes in steam flow rate and feedwater flow rate,leading to unsatisfactory control effects.(3)In response to address the issue of liquid level fluctuations caused by disturbances,the improved control scheme was developed based on the conventional three-pulse control.The triple-step nonlinear control system for the steam drum level was designed using the triple-step nonlinear control method.The triple-step nonlinear control law was derived,and the design of the program for the triple-step nonlinear control law for the steam drum level was implemented using structured programming methods on the Siemens S7-300 PLC platform.The research results indicate that the improved steam drum liquid level triple-step nonlinear control scheme,compared to the conventional triple-impulse control scheme,mitigates the impact of false liquid level on the system and improves the system’s tracking control ability.It has optimized and improved various performance indicators such as response speed,overshoot,and adjustment time.The excellent operation and control effects of the simulation control program lay a theoretical foundation for the practical engineering application of subsequent control schemes. |
