Tuning the PID parameters for greenhouse control based on CFD simulation

Modern greenhouse is becoming more and more complex and big, traditional manual control has been incompetent for the greenhouse control. Automatic control could greatly improve the work efficiency. PID (Proportional Integral and Derivative) controller is the most effective way to control the greenhouse microclimate. Recently some advanced control methods have been investigated, but most of them are still based on PID control, such as neural control and fuzzy control. The PID parameters play the important role for these methods. However the PID parameters can not be determined by a certain principle; they are usually defined by try and error way or some heuristic self-tuning method. How to get the optimal PID parameters is discussed by a number of researchers. And in the end it is still necessary to check these theories on site. The correctness is still uncertain if the season changed or some other climate devices changed beyond the site work. This paper investigates a new method of tuning the PID controller parameters for the greenhouse climate control system using CFD simulation. CFD simulation can correctly predict the greenhouse microclimate status, and can provide 3D results of the simulation process for the complex and comprehensive microclimate situations. CFD software can simulate the main factors of real greenhouse such as temperature and air velocity, and the other factors such as solar radiation heat, buoyancy effect and gravity can also be considered. Another important superiority is that CFD can simulate any climate (winter or summer, etc) by purpose. A greenhouse CAD model with its main accessories is built by a real greenhouse dimensions in this paper. And the rough steps of CFD simulation are introduced first, and then the workflow of tuning the PID values based on greenhouse simulation process is introduced in details. Finally some CFD simulation results are showed and discussed.