http://www.ifac-papersonline.net/ en Copyright 11:24 PM Wednesday 10, 2010 IFAC-PapersOnline http://www.ifacpapersonline.com 11:24 PM Wednesday 10, 2010 11:24 PM Wednesday 10, 2010 ET webmaster@ifac-papersonline.net webmaster@ifac-papersonline.net http://www.ifac-papersonline.net/Detailed/38935.html 04:00 PM Wednesday 31, 1969 Operating a power station is much more than understanding the functional relationship between its many parts. In today's market driven economy it requires a multi-disciplined approach to balance the technical, economic, environmental and often times political forces, that influence the decision making process. This paper presents a method for quantifying the economic impact of condenser maintenance based on plant thermodynamics, condenser modelling and market forces in the form of power purchase agreements. An operating cost function is formulated which is able to estimate operating costs based on current plant data and operating parameters from the power purchase contracts. The results highlight the financial implications of any future maintenance decisions. Due to the complex, multi-modal and discontinuous nature of the cost function, conventional optimisation techniques struggle with his scheduling problem. However, using genetic algorithms, it is possible to search and identify a range of feasible least cost maintenance schedules. As a result, key schedules and their associated costs are quickly highlighted, allowing the user to make a more informed decision regarding future maintenance. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38932.html 04:00 PM Wednesday 31, 1969 The paper considers distributed model predictive control (MPC) strategies that are appropriate for controlling large-scale systems such as power systems. The overall system is decomposed into subsystems, each with its own MPC controller. To achieve performance equivalent to centralized MPC, these distributed regulators must work iteratively and cooperatively towards satisfying a common, systemwide control objective. Automatic generator control (AGC) provides a practical example for contrasting the performance of centralized and decentralized controllers. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38928.html 04:00 PM Wednesday 31, 1969 This paper formulates the power equations of power systems into the Hermitian power equations in terms of active/reactive power indices, based on which we complete two tasks: (i) constructing novel Newton-Raphson iterative algorithms for computing power flows of the power systems that include adjustable weighting coefficients; (ii) deriving possible eigenvalue/singular-value inequalities for nodal voltage evaluation with or without power flow computations. The results are significant in evaluating voltage stability of the power systems. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38930.html 04:00 PM Wednesday 31, 1969 The control of reactive power aims at both increasing the limit of power transfer between areas and monitoring the bus voltage magnitude. In order to increase the amount of energy transfer, suppliers must produce reactive power close to the place where it is needed. Additionally, extra reactive power capacity must be kept to protect the integrity of the system against unforeseeable contingencies and sudden changes of power load levels. The present work is addressed to the determination of operational solutions (that is, those satisfying all operational limits) of maximum loadability considering the reactive power reserve. A constraint related to the quadratic deviation of a pre-specified level of reactive power generation is included in the static optimization problem that models the computation of the maximum loadability solution. This modified problem is solved through the nonlinear version of the Interior Point method. It is shown how the critical loadability and the reactive power margins are modified as the priority of reactive power reserve changes. Numerical results obtained with a 57-buses system illustrate the application of the proposed approach. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38931.html 04:00 PM Wednesday 31, 1969 This paper investigates the ability of tabu search (TS) and simulated annealing (SA) optimization methods to deal with optimal placement of Static Var Compensators (SVC) in a large power system based on its primary function, where the optimization is made on two parameters: its location and size. The primary function of an SVC is improving transmission system voltage, thereby enhancing the maximum power transfer limit. Modal analysis is used to place several SVCs in the power system and the results obtained are compared with the results of applied TS and SA techniques. The results show that SA can give a good suboptimal placement while TS gives an optimal solution. Since by using the modal analysis alone SVCs may not be placed optimally in the power system, the study is carried out in two steps. In the first step, by using the modal analysis, the critical area of the power system is identified in view of the voltage instability. In the second step, once the weak area is identified, the SA technique is applied to get the level of compensation by the SVCs. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38927.html 04:00 PM Wednesday 31, 1969 Power systems involve both continuous and discrete acting components and subsystems. In this work a logical specification is used to define the transition dynamics of the discrete subsystem. A computational tool that reduces the logical specification to a set of inequalities and the use of the transformed model in a dynamic programming approach to the design of optimal feedback controls are described. An example of optimal load shedding for a power system with aggregate induction motor and constant admittance loads is given. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38893.html 04:00 PM Wednesday 31, 1969 Hybrid converter HVDC transmission is a new hybrid transmission system for connecting two AC systems. Because it uses different converters, this new configuration offers several advantages over conventional HVDC systems. This paper demonstrates the superior performance of hybrid converter based HVDC transmission systems with respect to increased stability and terminal ac voltage control. A control system is developed for the hybrid system and its dynamic performance is investigated. The hybrid system performance with emphasis on commutation failure during severe disturbances and its results is also compared with a conventional HVDC scheme. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38864.html 04:00 PM Wednesday 31, 1969 http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38896.html 04:00 PM Wednesday 31, 1969 The objective of this work is to study the primary control system of a hydropower plant operating isolated. The plant is modeled by differential equations and the results are compared with field data from an actual hydropower plant, with deviations lower than 1.0%. The study of the primary control system is conducted in order to define optimal parameters for the controllers. Four controllers are studied: traditional, PI, PID and PI-PD. The controllers' performances are evaluated by stability criteria and a performance index. For the hydropower plant studied, the PI controller has the best performance. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38886.html 04:00 PM Wednesday 31, 1969 This paper deals with the problem to regulate the nodal voltage amplitude in electrical power systems. A discrete-time linear model that embeds an unknown bias representing the no-load voltage is adopted to describe the power system dynamics. Due to the unpredictable and unknown variations of the power system normal operating points the model parameters are unknown and time-varying. To ensure that the controller exhibits the required performance even in presence of a such variations, the controller parameters are varied according to adaptive laws. These laws are developed on the basis of a gradient approach to minimize the squared augmented error. The properties of the designed adaptive laws are studied employing Lyapunov analysis. The results of numerical simulation are reported to validate the proposed design. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38904.html 04:00 PM Wednesday 31, 1969 Dispersed Generation (DG) affects the operation of distribution systems; the related modeling and analyzing techniques are affected too. A novel approach to the distribution load flow problem has been recently proposed, based on the Object Oriented (OO) paradigm and including DG. In this paper, the OO modeling and algorithm are extended to account for the inclusion of ULTC transformer's voltage regulation. To validate the proposed steady-state model and to verify its assumption of stability, a detailed dynamic model is developed in Matlab/Simulink environment for a simple case study. The numerical results give evidence of the effectiveness of the proposed steady-state model which accounts for the interaction between DG and ULTC voltage regulation. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38869.html 04:00 PM Wednesday 31, 1969 This paper presents a novel concept for stabilization of AC/DC network with Unified Power Flow Controller (UPFC). The system considered has the structure of two areas connected by HVDC link. The investigation for perturbation in ac bus voltages has been carried out and the effect on the stability deterioration has been analyzed. The new concept of control has been proposed by embedding UPFC and then generating the control decisions adequately which stabilizes the earlier one. The concept of including the Unified Power Flow Controller (UPFC) in AC/DC network especially where a DC link is embedded to connect the two AC Systems is proposed. The proposed control design has been done utilizing a Novel Discrete-Time model of AC/DC system. The complete system stability has been studied in which the individual controller such as HVDC-SVC and HVDC-SVC-UPFC performance under varying perturbation of ac system voltage has been widely analyzed. The results show that in situations the HVDC-SVC alone is unable to reject the perturbation, the UPFC along with the HVDC-SVC damps the oscillations, thus matching the real and reactive power demands adequately. This novel combination can effectively be utilized in situations when the ac system bus voltage undergoes the fluctuations due to changing P and Q requirements. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38913.html 04:00 PM Wednesday 31, 1969 The paper considers dual input Power System Stabiliser (PSS) and Automatic Voltage Controller (AVR) for a generating unit equipped with synchronous generator and static excitation system. The control system uses analytically derived, quasi-optimal values of parameters (time constants) that cause the PSS to produce damping torque component only. Good dynamic properties of the plant equipped with the proposed dual input PSS and AVR are confirmed by simulation using a non-linear, multimachine model of a power system (part of UCTE power system). http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38875.html 04:00 PM Wednesday 31, 1969 This paper uses a novel simplified version of GAs called Population-Based Incremental Learning (PBIL) to optimally tune the parameters of the power system stabilizers (PSSs) for a multi-machine system. The technique combines aspects of GAs and competitive learning-based artificial neural network. The issue of optimally tuning the parameters of the PSS is converted into an optimization problem that is solved via the PBIL algorithm. Simulation results are presented to show the effectiveness of the proposed approach. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38884.html 04:00 PM Wednesday 31, 1969 The use of fuel cell and supercaps as energy elements in transport application is now a reality. Having two power sources on board allows a certain energy management strategy. In order to reduce computation time consumption, a simplified physical fuel cell model is proposed. An accurate model is studied in simulation to derive a simpler model. The simplified model is used with parameters identification made on an actual fuel cell. Results obtained on current and voltage, with an actual power demand, are sufficient to use the proposed model in iterative optimization algorithms. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38920.html 04:00 PM Wednesday 31, 1969 In this paper we focus on an investigation of a mathematical approach to extrapolation, using a combination of a modified neural network architecture and the semigroup theory. Semigroup theory provides a unified and powerful tool for the study of differential equations, partial differential equations and combinations thereof. The target of this investigation will be the prediction (by way of extrapolation) of the mass unbalance of the rotating component in a power plant. Simple mass unbalance system is considered for the simulation purpose. A new technique is proposed for measurement of vibration directly from rotating component using extrapolation. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38909.html 04:00 PM Wednesday 31, 1969 With increasing ease of access to plant-wide process signals in many power stations, operators face a growing challenge, particularly under alarm conditions, to monitor plant operations. However, recognizing that many of the signals are both highly correlated and collinear naturally lends itself to the adoption of data mining techniques. Typically, plant models are identified under normal conditions from historical data records. Subsequently, deviations from trained behaviour are used as indicators of poor plant performance and / or process faults. Both principal component analysis (PCA) and sub-space PCA have been applied to monitoring of a combined cycle gas turbine (CCGT). The capabilities of both approaches are demonstrated following a multi-block implementation, and the influence of external ambient conditions on CCGT performance are also examined. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38874.html 04:00 PM Wednesday 31, 1969 The proposed algorithm of extended predictive control (EPC) represents an exact method for removing the ill-conditioning in the system matrix by developing a unique weighting structure for any control horizon. The main feature of EPC algorithm is that it uses the condition number (CN) of the system matrix to evaluate a single tuning parameter that provides a specified closed loop response. Tuning of EPC is effective and simple since there is a direct relationship between closed loop performance and its tuning parameter. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38919.html 04:00 PM Wednesday 31, 1969 A dynamic simulation model of a once-through boiler in low to medium load is developed. When the system is in low load, water from the evaporator is recirculated through a bottle. This recirculation system is included in the model, which is then shown to fit closed-loop data from a real plant nicely. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38923.html 04:00 PM Wednesday 31, 1969 The improvements and developments of power plant automation systems make operation easier. This comes along with an increased tendency for the operator of losing knowledge about his plant. The consequential need for effective training possibilities led to the development of a new well-priced simulation tool "Operator Guidance Simulator" which combines early availability with high plant similarity. It is based on Siemens' longtime experience in simulation of power plant processes, which ranges from steady state performance simulations, dynamic plant and automation simulations to Operator Training Simulators. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38897.html 04:00 PM Wednesday 31, 1969 This paper proposes a novel approach to coal flow estimation in pulverized coal mills, which utilizes measurements of oxygen content in the flue gas. Pulverized coal mills are typically not equipped with sensors that detect the amount of coal injected into the furnace. This makes control of the coal flow difficult, causing stability problems and limits the plant's load following capabilities. To alleviate this problem without having to rely on expensive flow measurement equipment, a novel observer-based approach is investigated. A Kalman filter based on measurements of combustion air flow led into the furnace and oxygen concentration in the flue gas is designed to estimate the actual coal flow injected into the furnace. With this estimate, it becomes possible to close an inner loop around the coal mill itself, thus giving a better disturbance rejection capability. The approach is validated against a fairly detailed, nonlinear differential equation model of the furnace and the steam circuit using data measured at a Danish power plant. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38892.html 04:00 PM Wednesday 31, 1969 A performance test of digital protective relay is divided into three parts ; a static test, a dynamic test, a EMC test. Among these, a dynamic test is increasingly important, but it is not easy to diffuse a technique for dynamic test because of the intricate approach to real time digital simulator. In order to solve these problems, KEPRI(Korea Electric Power Research Institute) has established environments for performance test, which consist of a system model and a performance test procedure for the dynamic test. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38889.html 04:00 PM Wednesday 31, 1969 Artificial neural network based technology, which is inspired by biological neural networks, has developed rapidly in the previous decade and has been applied in power system protection applications. Protection of transmission and sub transmission lines is most frequently done using distance relays. This paper discusses the design, implementation and testing of an artificial neural network (ANN) based distance relay that implements characteristics of a mho (admittance) relay. The Artificial Neural Network based designs of distance relays proposed so far work well for faults well within the boundary characteristics of a relay, but are not able to maintain the integrity of the boundaries of the relay characteristics of generic designs. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38882.html 04:00 PM Wednesday 31, 1969 A novel technique to estimate the electric parameters of a synchronous generator from on-line measurement is presented in this paper. The proposed algorithm has two steps. In the first step, replacing the damper currents by higher derivatives of field and armature d-q currents, the electric parameters of the armature are estimated. In the second step, a current estimator is designed to estimate the damper winding currents, from which the parameters of field and damper windings are estimated. Simulation results show very good estimate of the electric parameters of a seventh order synchronous generator. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/38895.html 04:00 PM Wednesday 31, 1969 The authors investigate the stability of an islanded generator. They examine the effect of a predominantly resistive load on small-signal (frequency) stability of an islanded generator. The authors derive a new linear generator model for the islanded power station, and perform small-signal analyses using this model. The analyses are also performed using two industrial -grade software packages, and the results are compared. The authors show that predominantly resistive loads lead to poor damping of the speed response, and that an increase in the L/R ratio further decreases the damping. The use of a power system stabilizer is proposed to increase the damping of the speed response by varying the generator terminal voltage in response to speed changes. In this sense the PSS is also contributing to frequency control. Finally, the authors study the effect of the turbine and its control system on stability. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif