Adaptive Iterative Control of Temperature in Greenhouse

Abstract

Introduction. Creation and development of efficient agricultural complexes providing high yields at minimal time, material, and energy costs is impossible without the use of automatic control systems (ACS), which allow for maintaining the microclimate of the greenhouse with high accuracy. Improvements of the microclimate by ASC are aimed at neutralizing the influence of parametric perturbations of processes inside and outside the greenhouse. Using the example of a temperature control channel in a greenhouse with a heating circuit based on hot piped water supply, an adaptive iterative (search) algorithm for adjusting the components of a proportional-integral-differential (PID) controller in the heating circuit is proposed to ensure the required quality of the control process. Materials and Methods. The management is based on a parametrically uncertain model of temperature in the greenhouse, the structure of which, based on the principle of superposition, is transformed into a form with control and disturbances concentrated on an output coordinate. The use of an adaptive PID controller is based on the real-time analysis of a database containing trends of the controlled process. Using operators of Database Managment System or SQL language, queries evaluate regulation quality in accord with quality assessment. Proportional and differential components of the PID controller are adjusted so that the control system works on the verge of switching to auto-oscillation mode. The resulting static error is compensated by a change in the driving force. Results. Simulation of the real structure of a single-circuit automatic control system with temperature in the greenhouse with built-in regulating, executive and measuring elements, with a delay of a coolant movement was carried out using the software MVTU (SimIn- Tech). The proposed adaptation algorithm, consisting of the additive adjustment of the PID controller coefficients and being conveniently implemented within the SCADA system, was shown to provide the minimum oscillatory temperature maintenance for arbitrary parametric perturbations in the presence of the delay. Discussion and Conclusion. The proposed adaptation algorithm provides for compensation for model uncertainty and disturbances, while achieving the required accuracy of maintaining the temperature in the greenhouse. Results of the study will serve as the basics for development of multi-contour ACS microclimate greenhouses with the examination of the impact and compensation of parametric and structural uncertainty, inertia and nonlinearities of real elements. Our results may be used in many sectors of the national economy to study the general and applied problems of digital adaptive process control.