Control System Of Negative Pressure Cabin

The negative pressure cabin maintains the negative pressure,keeps fresh air supplement and discharges the air inside after disinfecting,which is the key equipment for preventing the air infectious diseases from spreading or biochemical warfare.The mobile negative pressure cabin is used to transfer infected patients or the wounded infected with biochemical warfare agents.Therefore,the mobile negative pressure cabin has to deal with more complex working environment,such as the changes of air pressure,temperature and humidity,equipment friction and other factors,the negative pressure cabin control system is required to deal with the complicated environment.There is two challenges in the negative pressure cabin control system:on the one hand,there is no report on the negative pressure control system model based on which a suitable controller can be designed in theory;on the other hand,it is very hard to achieve the desired performance by using conventional Proportional Integral and Differential（PID）controller.To deal with the above difficulties,the mathematical model of negative pressure cabin control system is established based on the basic physical principle in this paper.The tracking differentiator is introduced to combine with PI controller to achieve the desired control performance.The improved third generation Nondominated Sorting Genetic Algorithm（NSGA-Ⅲ）is used to optimize the controller parameters.The prototype of the negative pressure cabin control system is built,then tested experimentally.The detail work of this paper is given as follows:First,the negative pressure cabin control system hardware platform is designed,and the elements selection and software programming are conducted.The experimental results show that the designed control system is capable of monitoring the pressure difference between inside and outside the cabin,the temperature and humidity in the cabin,the battery status,the motor operation;the system response curve and other information can be displayed on the control panel in a real time manner.The basic function of negative pressure cabin control system is performed well as shown by the test results.Second,according to the physical principles,the gas flow equation across the valve is obtained,and the mathematical model of negative pressure cabin system is established.Then the state space equation of the system is obtained by the linearization operation.The step response method is used for the model order identification.The inverse M sequence is used as the excitation signal and the least square algorithm is used for model parameters identification.The transfer function of the control system is obtained according to the system identification result.The step response of the model matches with the system response,which shows the correctness of the model identification.Thirdly,for the pressure difference control problem of the negative pressure cabin control system,the conventional PID control algorithm is designed by using the identified model and Matlab toolbox.The experimental results show that the PID parameters derived using the toolbox cannot get the desired performance.In order to solve the problem of parameter tuning,the improved NSGA-Ⅲ algorithm is adopted to experimentally optimize the PID parameters,which improves the control performance of the system.Fourth,the PID parameters optimized by the experimental optimization cannot balance dynamic and steady-state performance well.To solve this problem,a tracking differentiator is introduced to improve the dynamic performance of the control system.Meanwhile,PI control is adopted to guarantee the steady-state performance of the system.The optimization algorithm is also used to optimize the controller parameters as well,by this way,the performance is improved.The contributions of this paper include:1)Based on the basic physical laws,the mathematical model of pressure difference control in negative pressure cabin is established,which has not been reported from the best knowledge of the author;2)The experiment results of this paper show that,even if the PID parameters with optimized parameters are adopted,the balance between dynamic and steady-state performance cannot be achievedand no such report has been given before for this special equipment from the best knowledge of the author;3)The tracking differentiator combined with traditional PI controller is proposed to guarantee the dynamic performance and steady-state performance simultaneously.The experimental result shows the satisfactory performance of the proposed method.