Search

The present paper deals with the issue of measurement delays which constitute a very prominent problem faced by most control systems. The system considered is that of a bioreactor used for the biological treatment of wastewater. The recording of the output substrate concentration of such systems usually involves a delay which results from the dependency of the flow of the liquid on its consistency. A PI observer-based control is applied and its performance is analysed in terms of the maximum delay for which the system is stable and converges as well as in terms of the convergence times. Based on these parameters, the results are compared to those obtained by a feedback linearising observer-based system. This comparative analysis showed that the PI controller performed better than the feedback controller, hence confirming its efficiency in biomass regulation in the presence of delayed measurements.

This paper proposes the application of a Proportional-Integral (PI) controller for the observer-based regulation of biomass concentration for a continuous-discrete system. An observer is essential to estimate the values of biomass concentration since the controller depends on these measurements. The analysis focuses on the continuous-discrete nature of the system which is represented by a continuous bioreactor system with discrete output measurements. The maximum allowable sampling partition diameter is determined along with the corresponding convergence time. These results are then compared to another work that used a feedback linearising control to achieve biomass regulation. The results obtained with the PI controller proved to be far more superior both in terms of maximum possible sampling time and convergence time. These findings confirmed the satisfactory and improved performance of the proposed observer-based controller.

Wastewater treatment is a biological process which involves the streaming of solid waste products in tubes and makes use of sensors which provide outputs at distinct instants of time. These issues lead to problems in the control of the output, which is the substrate concentration. In this work, we present an observer and a controller which is used to control the biomass concentration of such bioreactors in the presence of delayed and discrete measurements. The aim of this paper is to make a realistic analysis of the proposed observer-based control system and conclude on the effects of delayed measurements on the maximum possible sampling partition diameter as well as to study the effect of the sampling rate on the maximum possible delay. The results obtained confirmed the satisfactory performance of the system.

This work provides the observation and control of biomass concentration in Waste Water Treatment Plants. To achieve this, a PI controller was designed together with an observer to form an observer-based control system. The optimal values of the proportional gain and integral gain were determined to obtain the convergence of the observer in the least amount of time without compromising on the time taken by the response to reach steady state. Encouraging results which shall provide a basis for further and more in-depth research on the system were obtained.

This paper illustrates a control technique for single-input linear systems with delay in the state. We first proceed by introducing a novel definition of stability called Ω-stability which translate the fact that a system is stable in the Krasovskii sense over a set Ω derived from the negative real side of the complex plane. In other words, all the eigenvalues of the system lies inside the set Ω with a given stability margin. Then, for the control design, the system’s model is transformed into an extended Jordan controllable canonical form (JCCF). Based on the JCCF, we proposed a systematic construction of the controller gain such that the system under consideration becomes Ω-stable. The effectiveness of the controller is shown, via simulation, by using a typical academic example.

This paper proposes an observer-based control system to estimate and control biomass concentration in a simple microbial system under known output delays. More precisely, these delays are represented by time lags in the measurement of substrate concentration. We employ a feedback linearising controller that has previously been developed for a system without measurement delay. In the present work, the delay is applied to the controller and the maximum allowable delay that maintains stability is computed. Next, a nonlinear observer is proposed to predict the biomass concentration. The stability of the overall closed-loop feedback system incorporating the observer and the controller is analysed. Simulation study has revealed that the combination of the observer and controller provided a satisfactory response and was successful in regulating the biomass concentration. Finally some conclusions are drawn.

In this paper, an observer-based control system is presented for the regulation of biomass concentration in bioreactors. The importance of the observer is highlighted by the dependency of the feedback linearising controller on the measurements of biomass concentration. Further, the discrete nature of output substrate concentration is considered and the performance of the system proposed is analysed through a simulation study using Matlab/Simulink. This study is also used to determine the limit on the sampling partition diameter for which the observer and controller designed give satisfactory performance. The implemented observer-based control system showed satisfactory performance both in terms of stability and convergence for given values of sampling partition diameters.

It is now well established that rate of leakage of water is directly related to the distribution pressure in a network. In this context, pumps can consume up to 60% of the overall energy requirement in the case of pressure driven demand whereby they are solicited for direct supply. In this paper, we investigate the energy efficiency of distribution in an experimental network which is embedded with two levels of leakage (low and high) using three different methods. They are analysed and compared in terms of specific energy consumption and rate of leakage. A novel concept known as the Harmonic Oscillator Tank has been developed whereby the conventional hydropneumatic tank is pressure modulated so as to produce a constant output flowrate within the presence of leaks. Experimental results show that the throughput of the Harmonic Oscillator Tank for a heavy leaking network is highest (86.45%) with the lowest percentage leakage of 13.5% at a specific energy consumption of only 0.354 kWh/m3/day when compared to the other two schemes namely direct pumping and pumping through a variable speed drive in a loop. This Harmonic Oscillator Tank opens up new avenues for reducing energy and leakage in old damaged networks whereby a short or medium-term solution is often required since infrastructure renewal requires time and a massive investment.

In this paper, we investigate the behaviour of scalar controlled AC Variable Frequency Drives for induction motors when coupled with different types of loads. It is well known that slip is more pronounced at high speeds rather than low speeds in loads such as in pumps and fans operation because the torque load varies as the square or cube of the speed. Slip compensation in Voltage/Frequency controlled Variable Frequency Drives may work only up to a certain limit since the problem can be exacerbated by overcompensation causing low magnetisation flux of the stator and the Variable Frequency Drive becomes uncontrollable. In this research work, we investigate the behaviour of the motor and Variable Frequency Drive assembly with regards to slowly changing loads from low to high speeds. Results show that at reduced speeds for the Variable Frequency Drive and motor assembly, the efficiency is lowest for square and cubic torques loads compared to linear and constant torque loads. Highest efficiency and torque are achieved only in a restricted interval of speed. This problem therefore compels us to avoid using the Variable Frequency Drives in the Voltage/Frequency mode at low speeds for pumps and fans.

A power distribution system includes sectionalizing switches and tie switches. Sectionalizing switches are normally closed switches while tie switches are normally open switches. By changing the status of the switches, an optimal configuration can be obtained such that the real power loss in the system is minimum. In this paper, a music based metaheuristic algorithm was applied to the Distribution Network Reconfiguration Problem to minimize real power losses. The Harmony Search Algorithm is presented in the paper and its application to the Distribution Network Reconfiguration problem is described. Simulation results are presented for 4 test systems: 16-bus, 33-bus, 70-bus system and a local Mauritian system. Optimal configurations were obtained in all cases. (6 pages)

Modelling real distribution networks can be particularly difficult if they are so leaky that the types of leak and their nature can hardly be determined from scarce field measurements. In this context, a new approach to model development of such WDNs is proposed. The method is based on leakage estimation from MNF and the burst frequency of AZPs. After applying it to a real DMA in Mauritius, the resulting calibrated model from EPANET is found to approach the actual status of the network very closely in terms of overall real losses, coefficients of discharge, nodal flow and pressure.