Nikolaos D. Kouvakas

Two-stage robust control of substrate concentration for an activated sludge process

A two-stage robust control scheme improving the performance of an Activated Sludge Process is proposed. In the first stage, asymptotic command following the substrate concentration with simultaneous attenuation of the fluctuations of the dissolved oxygen concentration is assured. The first stage is a pure dynamic controller. The second stage is a PID controller. Good performance of the proposed control scheme on the corresponding nonlinear ASP model is illustrated through extensive simulation experiments. The contribution of the paper can be summarized to the derivation of the following two results: An accurate to a wide range of inputs and disturbances, linearized generic model of the ASP and, most important, a linear robust controller that controls accurately the effluent substrate concentration without using measurements of it.

Indirect adaptive neural control for precalcination in cement plants

Control of the precalcination degree in the precalciner of cement plants is a problem of great importance due to its effect to the quality of the clinker, the consumed energy and the byproducts of the whole cement pyroprocess. Divergence of the desired precalcination degree of the raw mix may cause increased carbon monoxide production which is a significant pollution factor that under certain circumstances may lead to explosive gas mixtures. The basic inputs of the precalciner are the temperature and pressure of the tertiary air, temperature and mass flow rate of the raw mix, and the mass flow rate of the fuel, namely pulverized coal. From these inputs, the coal mass flow rate is the only actuatable one. The outputs of the precalciner are the calcinated raw mix, characterized by its mass flow rate, temperature and degree of precalcination, and the abgasses consisting of oxygen, carbon monoxide, carbon dioxide, water and nitrogen, characterized by their temperature and the concentrations of the above elements. Some of the variables of the process, namely the raw mix and coal mass flow rates, the raw mix temperature, the temperature and pressure of the tertiary air and abgasses, and the oxygen concentration in them, can be measured by appropriate sensors. The rest variables can be computed from the measurable variables after appropriate approximations. In this paper, the precalcination degree is controlled via a dynamic controller that regulates the abgasses temperature. The parameters of the controller are computed on the basis of a polynomial neural network that identifies off-line the variations (around nominal values) of the real industrial measurements of the variables of the process. The results are illustrated via simulations of the closed loop system where it is shown that the abgasses temperature is set to a desired level while a desirable precalcination degree is derived.

A Simulated Annealing Controller for Sloshing Suppression in Liquid Transfer with Delayed Resonators

A simulated annealing controller for sloshing suppression during the transfer of a liquid using a vehicle with active and passive vibration absorption is proposed. The proposed design technique aims to suppress sloshing induced by vehicle vibrations due to force disturbances applied on the liquid carrying vehicle due to road surface unevenness, while dealing with practical problems like the lack of measurements of the liquids motion within the tank. Active vibration absorption is achieved with the use of a couple of Delayed Resonators. Despite the high complexity of the systems model, the proposed technique results in an easy to implement linear static measurement output feedback controller with satisfactory performance with respect to sloshing suppression

Metaheuristic control of substrate concentration for an activated sludge process

In this paper, a two-stage linear dynamic control scheme, using a metaheuristic approach, will be developed to control the effluent substrate concentration of an ASP. In the first stage, a static output feedback controller will be designed, using only measurements of the oxygen concentration. In the second stage, an asymptotic non-linear estimator of the substrate concentration will be used and the estimate will be fed back through a PI controller. In particular, the model of the ASP will be presented both in its non-linear and linearised form. Based on the linearised approximation, a static inner loop controller will be designed using a metaheuristic search algorithm for the computation of the controller parameters. Following, an outer PI controller will be designed based on the linearised model, again using a metaheuristic search algorithm in order to compensate the influence of the non-linearities when the static controller is applied to the non-linear model. The performance of the overall closed loop system will be illustrated through simulation experiments.

I/O Decoupling with simultaneous Disturbance Rejection of general neutral time delay systems via a measurement output feedback dynamic controller

The problem of Input - Output (I/O) Decoupling with simultaneous Disturbance Rejection (DDR) is studied for the class general linear neutral multi-delay differential systems with measurable disturbances. The problem is solved using a dynamic multi-delay controller with proper and realizable feedback of the measurement outputs, a realizable precompensator and a realizable dynamic controller matrix mapping the measurable disturbances to the system inputs. For this system case and controller type the necessary and sufficient conditions for the problem to have a solution are established and the general analytical expression of the controller matrices solving the problem is derived.

Delayless dynamic controllers for Disturbance Rejection of general neutral time delay systems

The problem of Disturbance Rejection (DR) for MIMO general neutral multi-delay systems, is studied for the case of left invertible systems with measurable disturbances. The controller used is of the delayless dynamic type feeding back the measurable disturbances and the plant measurement outputs. The necessary and sufficient conditions for the problem to have a solution are established and the general analytical expression of the delayless dynamic controller matrices is derived. The present results cover the solution of the Robust DR problem with uncertain delays.

Towards dynamic controller design for Disturbance Rejection of MIMO neutral time delay systems

The problem of Disturbance Rejection (DR) for MIMO general neutral multi-delay systems, is studied for the case of left invertible systems with measurable disturbances. The controller used is of the dynamic type involving delays and feeding back the measurable disturbances and the plant measurement outputs. The controller is assumed to be realizable. For this system case and controller type the necessary and sufficient conditions for the problem to have a solution are established and the general analytical expression of the controller matrices solving the problem is derived.

A three term controller for ride comfort improvement

For a quarter car model, a PID controller that provides ride comfort is developed. The PID controller parameters are derived using a metaheuristic algorithm. The performance of the proposed control scheme and its robustness with respect to uncertainties of the model parameters are examined through computational experiments. The proposed control scheme has satisfactory performance and feeds back only one measurable variable thus providing a simple and cheap solution.

Mobile robots in singular time-delay form – Modeling and control

Abstract Modeling and control of a mobile robotic manipulator having a wheeled platform, with passive and active suspension, and a manipulator carrying an inertia load, is studied. The overall model is developed in a nonlinear singular neutral time delay system form. The special case of flat road and single joint manipulator is studied and the linear approximant of its model is derived. Using a dynamic controller involving delays, I/O decoupling between the vertical position of the load and the velocity of the wheeled platform under the constraint of norm bounded load contact forces, is derived.

Independent motion control of a tower crane through wireless sensor and actuator networks

The problem of independent control of the performance variables of a tower crane through a wireless sensor and actuator network is investigated. The complete nonlinear mathematical model of the tower crane is developed. Based on appropriate data driven norms an accurate linear approximant of the system, including an upper bound of the communication delays, is derived. Using this linear approximant, a dynamic measurable output multi delay controller for independent control of the performance outputs of the system is proposed. The controller performs satisfactory despite the nonlinearities of the model and the communication delays of the wireless network.