Kostas G. Arvanitis

A nonlinear feedback technique for greenhouse environmental control

Abstract Climate control for protected crops brings the added dimension of a biological system into a physical system control situation. The plants in a greenhouse impose their own needs, significantly affect their ambient conditions in a nonlinear way, and add long-time constants to the system response. Moreover, the thermally dynamic nature of a greenhouse suggests that disturbance attenuation (load control of external temperature, humidity, and sunlight) is far more important than is the case for controlling other types of buildings. This paper presents a feedback–feedforward approach to system linearization and decoupling for climate control of greenhouses and more specifically for the operation of ventilation/cooling and moisturizing. The proposed method consists of three parts: (a) a model-based feedback–feedforward compensation of external disturbances (loads) on the basis of input–output linearization and decoupling; (b) the transformation of user-defined desired settings for temperature and humidity into feasible controller setpoints, taking into account the constraints imposed by the capacities of the actuators and the psychrometric laws; and (c) additional PI outer loops to compensate for model uncertainties and deviations from expected disturbances (weather). Moreover, some tuning tests lump together several physical system parameters to be easily identified, and the method guarantees accuracy in setpoint tracking while simplifying stability issues. The proposed method is applicable to any air-conditioning system and is expected to gain wide acceptance in modern climate control systems.

DASH7 Mode 2: A Promising Perspective for Wireless Agriculture

Abstract In search of robust wireless standardized solutions for the harsh agricultural environment, the 433 MHz based DASH7 Mode 2 technology is proposed as the enabler for a new perspective of the wireless sensor networks in Agriculture. In particular, DASH7 foundation background and its technical characteristics are reported. A comparison between DASH7 and its main competitive technologies such as the ZigBee, the Low Energy Bluetooth, and the WiFi is quoted as well. DASH7 advantages for the wireless Agriculture are classified according to environment, systems development, systems deployment, cost, integration and reliability. Subsequently, the development tools ecosystem as well as the typical architecture of a DASH7-based wireless sensor node has been presented. A systems architecture focusing on DASH7 inherent ability for different wireless systems domains unification in Agriculture is proposed. Finally, as a proof of concept, a DASH7-based WSN node implemented to host applications such as IEEE 1457 smart transducers interface and radio frequency identification is presented.

Solution Properties of Linear Descriptor (Singular) Matrix Differential Systems of Higher Order with (Non-) Consistent Initial Conditions

In some interesting applications in control and system theory, linear descriptor (singular) matrix differential equations of higher order with time-invariant coefficients and (non-) consistent initial conditions have been used. In this paper, we provide a study for the solution properties of a more general class of the Apostol-Kolodner-type equations with consistent and nonconsistent initial conditions.

Decentralized Predictive Control ofthe Heat Dynamics of a Greenhouse

Abstract This paper proposes a decentralized model - based predictive controller approach for the design of discrete-time control systems for the regulation of the air temperature and heat supply in greenhouses. A state space model is used at the greenhouse to predict the corresponding indoor temperature over a long-range time period. The sun radiation and outdoor temperature are treated as external disturbances tliat affect the overall system dynamics. A series of energy fluxes consist the heating system and the predictive controllers have proved to be powerful in controlling the supply temperature.

On-line PID controller tuning for open-loop unstable processes

Abstract New methods for tuning PID controllers for unstable first-order plus dead-time processes are reported. The proposed methods ensure smooth closed-loop response to set-point changes, fast regulatory control and robustness against parametric uncertainty while retaining the classical PID control structure. Their application to an unstable transfer function model describing a biological reactor is also presented. The simulation results prove the effectiveness of the proposed PID tuning methods.