Modeling of Washing Circuits in Mining - A Networked System Approach

The models of two process system networks in an alumina refinery are developed in this paper. These models have been used in the numerical simulations in previous work. They are the washing circuits widely used in the mineral processing plants. The process modeling here is to derive a state space model for the multi-variable feedback control design purpose. The complex process system is modelled as an interconnected system having a mixed connection configuration. The interactions between equipment and sub-processes via the material flows within an unit operation are modelled as interactive variables of subsystems under the auspices of interconnected system formulation

Modeling and experimental validation of a solar-assisted direct expansion air conditioning system

Continuous increase in global electricity consumption, environmental hazards of pollution and depletion of fossil fuel resources have brought about a paradigm shift in the development of eco-friendly and energy-efficient technologies. This paper reports on an experimental study to investigate the inherent operational characteristics of a new direct-expansion air conditioning system combined with a vacuum solar collector. Mathematical models of the system components are firstly derived and then validated against experimental results. To investigate the potential of energy savings, the hybrid solar-assisted air-conditioner is installed and extensively equipped with a number of sensors and instrumentation devices, for experimentation and data collection. The influence on the system energy usage of the average water temperature, storage tank size and room set-point temperature are then analyzed. Once the air-conditioned room has achieved its desired temperature, the compressor turns off while the cooling process still continues until the refrigerant pressure no longer maintains the desired temperature. The advantages of the proposed hybrid system rest with the fact that the compressor can remain off in a longer period by heat impartation into the refrigerant via the water storage tank. Results show an average monthly energy saving of about between 25% and 42%. © 2013 Elsevier B.V. All rights reserved

Laboratory demonstration for model predictive multivariable control with a coupled drive system

Teaching multivariable control usually involves a certain level of mathematical sophistication and hence requires some labaratorial exemplification of the material given in formal lectures. This paper reports on a hands-on approach to multivariable control education via the implementation of a model predictive controller on a two-input, two output coupled drive apparatus. This scaled-down system represents many industrial processes while provides an excellent set-up for demonstrating the cross-coupled effects in multi-input multi-output systems. Here, a model predictive controller (MPC) is developed and implemented on the basis of a constrained optimization problem to show control performance via the belt tension and velocity outputs, demonstrate the decoupling capability, and also illustrate such issues as control input saturation, the selection of operating point, reference inputs, and system robustness to external disturbance and varying parameters. The implementation is based on Labview and MATLAB Model Predictive Control Toolbox. ©2010 IEEE. Model predictive Control

Integral controller design for nonlinear systems using inverse optimal control

This paper proposes an integral controller design scheme for nonlinear systems based on optimal control and the passivity theorem in order to suppress the effect of external disturbances. The main strategy is to augment an optimal controller with a PI type controller. To guarantee the proposed controller has a desired stability margin, the passivity-based design method is introduced. Here, the inverse optimal control technique is employed to avoid the need of solving a Hamilton-Jacobi equation. An illustrative example is given to show the design procedure and the controller effectiveness. © 2008 IEEE

Modelling and optimization of direct expansion air conditioning system for commercial building energy saving

This paper presents a comprehensive refinement of system modeling and optimization study of air-cooled direct expansion (DX) refrigeration systems for commercial buildings to address the energy saving problem. An actual DX rooftop package of a commercial building in the hot and dry climate condition is used for experimentation and data collection. Both inputs and outputs are known and measured from the field monitoring. The optimal supply air temperature and refrigerant flow rate are calculated based on the cooling load and ambient dry-bulb temperature profiles in one typical week in the summer. Optimization is performed by using empirically-based models of the refrigeration system components for energy savings. The results are promising as approximately 9% saving of the average power consumption can be achieved subject to a predetermined comfort constraint on the ambient temperature. The proposed approach will make an attractive contribution to residential and commercial building HVAC applications in moving towards green automation

Energy-efficient HVAC systems: Simulation-empirical modelling and gradient optimization

This paper addresses the energy saving problem of air-cooled central cooling plant systems using the model-based gradient projection optimization method. Theoretical-empirical system models including mechanistic relations between components are developed for operating variables of the system. Experimental data are collected to model an actual air-cooled mini chiller equipped with a ducted fan-coil unit of an office building located in hot and dry climate conditions. Both inputs and outputs are known and measured from field monitoring in one summer month. The development and algorithm resulting from the gradient projection, implemented on a transient simulation software package, are incorporated to solve the minimization problem of energy consumption and predict the system's optimal set-points under transient conditions. The chilled water temperature, supply air temperature and refrigerant mass flow rate are calculated based on the cooling load and ambient dry-bulb temperature profiles by using the proposed approach. The integrated simulation tool is validated by using a wide range of experimentally collected data from the chiller in operation. Simulation results are provided to show possibility of significant energy savings and comfort enhancement using the proposed strategy. © 2012 Elsevier B.V

Second-order sliding mode control for offshore container cranes

Open-sea stevedores of containers provide an alternative way to avoid port congestion. This process involves a mobile harbour equipped with a crane which loads/unloads containers from a large cargo ship. However, the presence of ocean waves and gusty winds can produce an excessive sway to the hoisting ropes of the crane system. This paper presents a second-order sliding mode controller for trajectory tracking and sway suppression of an offshore container crane. From the proposed control law, the asymptotic stability of the closed-loop system is guaranteed in the Lyapunov sense. Simulation results indicate that the developed control system can achieve high performance in trajectory tracking and swing angle suppression despite the presence of parameter variations and external disturbances as in the case of offshore cranes

Modeling and optimal control of an energy-efficient hybrid solar air conditioning system

© 2014 Elsevier B.V. All rights reserved. The paper addresses the modeling and optimal control problem of a new hybrid solar-assisted air conditioning system developed for performance enhancement and energy efficiency improvement. To regulate the mass flow rate of the refrigerant vapor passing through a water storage tank for increasing the refrigerant's sub-cooling process at partial loads, we propose a new discharge bypass line together with an inline solenoid valve, installed after the compressor. In addition, to control the air flow rate, a variable speed drive is coupled with the condenser fan. For the control purpose, a lumped parameter model is first developed to describe the system dynamics in an explicit input-output relationship; then, a linear optimal control scheme is applied for the system's multivariable control. The system has been fully-instrumented to examine its performance under different operation conditions. The system model is then validated by extensive experimental tests. Based on the obtained dynamic model, an optimal controller is designed to minimize a quadratic cost function. Numerical algorithms, implemented in a simulation tool, are then employed to predict the energy performance of the system under transient loads. The experimental results obtained from implementation with PLC demonstrate that the newly-developed system can deliver higher system efficiency owing to amelioration of the refrigeration effect in the direct expansion evaporator and adjustment of its air flow rate. The development is thus promising for improvement of energy efficiency, enhancement of the system performance while fulfilling the cooling demand

Design of a Variable Reactor for Load Balancing and Harmonics Elimination

This paper presents the design of a variable inductor with a rotational magnetic core whose position is controlled in a closed-loop system. This magnetic structure facilitates the impedance changes which may be used for load balancing, harmonics elimination, transient response improvement, and as a controlled reactor in static VAr compensation (SVC). The design of the inductor and analysis of its impedance change caused by positioning a movable element are carried out by using the finite element method. As a result, the variation range of the impedance is determined. The proposed variable inductor is compared with a typical SVC reactor. The results show good performances in static var compensation with higher reliability and no harmonics generated. For closed-loop control, a secondorder sliding mode controller is designed for position control of the rotating core via a DC motor. Simulation results of the proposed system present highly robust and accurate responses without control chattering in face of nonlinearities and disturbances