Research And Application On Temperature Control Method For Tankless Gas Water Heater

Under the background of "peak carbon dioxide emissions" and "carbon neutralization",natural gas will continue to serve as bridge in the transformation of energy from fossil energy to solar energy,wind energy,water energy,nuclear energy and other new energy.Gas water heater using natural gas as fuel will usher in a new stage of rapid development after west-toeast natural gas transmission and coal to gas project.At present,there are many problems while using gas water heater,such as slow heating time and unstable water temperature.Comfort is the core competitiveness of gas water heater products.Temperature control is the key to the comfort of gas water heater.And how to reduce the settling time and overshoot and improve the anti-disturbance ability of the system is the important research topic in this thesis.Firstly,this thesis introduces the basic structure and working principle of gas water heater,then the mathematical model of the gas water heater system is established to know that the system is first order plus dead time model.What's more,the model parameters is identified by the least square method.According to the results of the identification,the parameters of the system are fitted by water flow,which lays a foundation for subsequent controller design.Secondly,based on the established model of gas water heater,aiming at the problem that the stability margin of the system is reduced and oscillation is easy to occur due to the time delay caused by ignition,heat exchange,pipeline and sensor measurement,a PI+Smith compound control scheme is designed to improve the system stability and reduce the settling time and overshoot.Then,the internal model control principle is used to tune the parameters to achieve the expected system dynamic characteristics.In addition,for the external disturbance and system uncertainty caused by the change of inlet temperature,environment temperature and water flow,a disturbance observer considering the time delay and model mismatch is designed to suppress lumped disturbance.On this basis,the control scheme based on the disturbance observer P+Smith+DOB is designed to improve the anti-disturbance performance of the system.Finally,in order to verify the performance of the control scheme,the experiment tests the dynamic characteristics,steady-state characteristics and anti-interference performance of the system.The experimental results show that the control algorithm improves the comfort of gas water heater effectively and satisfies the design standard.