Development of a new control method for the dynamic liquid desiccant dehumidification process

Abstract

Liquid desiccant dehumidification technology as an efficient way of handling moisture load has attracted much attention, while the performance of liquid desiccant dehumidifiers has characteristics of uncertainty and time-varying in actual runtime, limiting its application fields. Thus, it is necessary to develop dynamic control methods to achieve stable and efficient operation. As the liquid desiccant dehumidification process is a multi-parameter, time-varying and large delay nonlinear dynamic process, therefore it is difficult to achieve the dynamic control. In this paper, dynamic control methods of the liquid desiccant dehumidification process were studied experimentally for the first time and main difficulties in the dynamic control of the liquid desiccant dehumidification process were presented clearly, helping to learn more knowledge on dynamic control process and facilitate the development of control methods. PID control as a classic control method was applied to control the liquid desiccant dehumidification process firstly, the result showed that it requires long adjusting time to follow the command and is not suitable to control nonlinear dynamic process with large delay. Novel fuzzy logic control (FLC) as an advanced control method was implemented as well, the result demonstrated that it follows command quickly while is unable to maintain the new set point accurately. Then reasons for shortcomings of each control method were analyzed. Along with the above analysis, a new control method, combining the PID control and novel FLC was developed. The command following experiment and disturbance rejection experiment for the newly developed control method were conducted. Control performances are great and validate the feasibility of the new control method. Besides, the newly developed control method also provides a good reference for achieving the dynamic control of a multi-parameter, time-varying, nonlinear dynamic process with large delay.