Thermal Control of a Greenhouse by Variation in Ventilation Rate using a Fuzzy Parallel Distributed Compensation Controller with an RST Regulator in Each Rule

Problem statement: The greenhouse has uncontrollable inputs that affect its climate, which arises the difficulty to regulate its inside temperature. The solution can be found using a multi-system approach like the Takagi-Sugeno System from which a design of a Parallel Distributed Compensation (PDC) controller is performed. However, a stability problem arises and was negotiatesd in general based on a Lyapunov criterion. The latter isn’t appropriate in our case because of the great number of rules describing the greenhouse. Approach: An alternative solution is proposed using a PDC controller with a local RST regulator in each rule. The synthesis of each one is determined using pole placement avoiding the cross-coupling (that may cause instability) between the local regulators and the sub-models related to differents rules. Results: The proposed fuzzy controller was applied to an experimental greenhouse and was able to lead the inside temperature to the desired value despite the externals perturbations. Conclusion: The presented study offer a simple solution to the stability problem when using PDC controller and so can be mush more implementable than the others stabilization methods presented in the literature. In the agriculture field, it can replace the on-off control action that is widely used in the greenhouses because of the processus complexity.