Study On Control Methods For Temperature And Humidity Of The Climate Chamber For Determining Formaldehyde

As the main factors affecting indoor air quality,formaldehyde and volatile organic compounds released from building materials threaten human health seriously.Therefore,in order to ensure the quality of indoor environment,an accurate and efficient method for detecting formaldehyde and volatile organic compounds emissions is urgently needed.Compared with other methods,the climate chamber method can better simulate the formaldehyde emission process of building materials,and it is also the only method used in arbitration.During the process for determining formaldehyde,the temperature and relative humidity of the climate chamber are required to remain at set values so that high detection accuracy,which largely depends on the stabilization of the controlled variables,can be guaranteed.Consequently,high-precision control of the temperature and relative humidity of the climate chamber plays an significant role in the field of formaldehyde detection.In this thesis,aiming at the 1m~3climate chamber for formaldehyde detection,Backstepping method is employed to design controllers,which realize the temperature and humidity in the climate chamber converge to given values with high accuracy and efficiency.In this way,a favourable experimental environment for formaldehyde emission detection of building decoration materials can be guaranteed.Firstly,the control problem of the temperature and humidity for the climate chamber system with known parameters is studied.Considering the pure-feedback nonlinear system with coupled temperature and humidity,the implicit function theorem and Backstepping method are employed and the coupled temperature and humidity variables are transformed into a vector.In this way,the complex decoupling procedure can be avoided.Without using fuzzy logic and neural network,the complicated nonlinear terms are eliminated by exact feedback so that the huge amount of computation caused by the increase of fuzzy rules can be avoided.Besides,the decrease of control accuracy caused by system linearization can also be avoided.The controller is designed by Backstepping technique and can drive the temperature and humidity of the climate chamber to set values steadily with high control accuracy and efficiency,which are verified by simulation results.Then,the control problem of the unknown climate chamber system is addressed,which takes more practical experiences into account.Considering the unknown control coefficients of the system caused by the failure of refrigeration and heating equipment,the Nussbaum gain technique is introduced to deal with the unknown control coefficients caused by above matters.Additionally,due to the evaporation of water and the water cycle,the water quality in temperature control tank and dew-point humidity generator is fluctuating so that some parameters in the system are changing during actual operation.In order to overcome the obstacle caused by unknown parameters,an parameter adaptive law is designed to estimate unknown parameters.The presented control law can control the temperature and humidity of the climate chamber to desired values accurately,which is verified by simulation results.Additionally,in order to verify the superiority of the proposed controllers,simulation results are given compared with PID controller and sliding mode controller.