Showing papers in "IEEE Transactions on Energy Conversion in 1996"
TL;DR: In this paper, a methodology for calculation of the optimum size of a battery bank and the PV array for a standalone hybrid wind/PV power system is developed, where long term data of wind speed and irradiance recorded for every hour of the day for 30 years were used.
Abstract: In this paper, a methodology for calculation of the optimum size of a battery bank and the PV array for a standalone hybrid wind/PV power system is developed. Long term data of wind speed and irradiance recorded for every hour of the day for 30 years were used. These data were used to calculate the average power generated by a wind turbine and a PV module for every hour of a typical day in a month. A load of a typical house in Massachusetts, USA, was used as a load demand of the hybrid system. For a given load and a desired loss of power supply probability, an optimum number of batteries and PV modules was calculated based on the minimum cost of the power system.
923 citations
TL;DR: An advanced model, based on recurrent high order neural networks, is developed for the prediction of the power output profile of a wind park, which outperforms simple methods like persistence, as well as classical methods in the literature.
Abstract: In this paper, an advanced model, based on recurrent high order neural networks, is developed for the prediction of the power output profile of a wind park. This model outperforms simple methods like persistence, as well as classical methods in the literature. The architecture of a forecasting model is optimised automatically by a new algorithm, that substitutes the usually applied trial-and-error method. Finally, the online implementation of the developed model into an advanced control system for the optimal operation and management of a real autonomous wind-diesel power system, is presented.
387 citations
TL;DR: In this article, a sequential Monte Carlo simulation technique is proposed for adequacy evaluation of a generating system including WECS, taking into account the auto-correlation and fluctuating characteristics of wind speeds, the random failure of generating units and other recognized dependencies.
Abstract: A wind energy conversion system (WECS) has a different impact on the reliability performance of a generating system than does a conventional energy conversion system. This is due to the variation of wind speeds and the dependencies associated with the power output of each wind turbine generator (WTG) in a wind farm. In this paper, a sequential Monte Carlo simulation technique is proposed for adequacy evaluation of a generating system including WECS. The method is based on an hourly random simulation to mimic the operation of a generating system, taking into account the auto-correlation and fluctuating characteristics of wind speeds, the random failure of generating units and other recognized dependencies. The hourly wind speeds are simulated utilizing autoregressive and moving average time series models that are established based on the F-criterion. A small reliability test system designated as the RBTS is used to illustrate the proposed method.
269 citations
TL;DR: In this article, a unified approach to the modeling and field-oriented control of dual three phase induction machines with one phase open is presented using the concept of vector space decomposition.
Abstract: The multiphase winding structure provides an induction machine with capabilities of starting and running even with one or more of its stator phases open-circuited. However, when operated with such a structurally unbalanced condition, the dynamic properties of the machine will change drastically from its balanced operation condition. For example, field-oriented control strategies developed for a balanced winding structure will no longer function properly and could lead to catastrophic consequences. In this paper, a unified approach to the modeling and field-oriented control of dual three phase induction machine with one phase open is presented. Using the concept of vector space decomposition, the proposed technique is established on the basis of the asymmetrical winding structure directly, and thus provides a precise, physically insightful tool to the modeling and control of induction machines with structural unbalance.
242 citations
TL;DR: The world's largest adjustable speed pumped storage unit for Ohkawachi Power Station, the Kansai Electric Power Co., Inc., Japan, was commissioned on Dec. 3, 1993.
Abstract: At 400 MW, the world's largest adjustable speed pumped storage unit for Ohkawachi Power Station, the Kansai Electric Power Co., Inc., Japan, was commissioned on Dec. 3, 1993. It can change power in steps of at least 32 MW in the generate mode and at least 80 MW in the pump mode, within 0.2 s. This paper describes principal design considerations for the control systems of the machine and presents actual performance of the machine with reference to some typical oscillograph charts.
214 citations
TL;DR: In this paper, the average efficiency of three 500 kW wind energy converters is compared, and it is shown that a variable-speed generator system can be almost as efficient as one for constant speed, although it has much higher losses at rated load.
Abstract: This paper presents a method to calculate the average efficiency from the turbine shaft to the grid in wind energy converters. The average efficiency of three 500 kW systems are compared. The systems are: a conventional grid-connected four-pole induction generator equipped with a gear, a variable-speed synchronous generator equipped with a gear and a frequency converter, and a directly driven variable-speed generator equipped with a frequency converter. In this paper it is shown that a variable-speed generator system can be almost as efficient as one for constant speed, although it has much higher losses at rated load. The increased turbine efficiency that variable speed leads to has not been included in this paper. It is also found that a directly driven generator can be more efficient than a conventional four-pole generator equipped with a gear.
185 citations
TL;DR: In this paper, the finite element analysis method is used directly in optimisation algorithms to optimise in multidimensions the design of the cageless reluctance synchronous machine.
Abstract: The finite element analysis method is used directly in optimisation algorithms to optimise in multidimensions the design of the cageless reluctance synchronous machine. Two optimisation methods are evaluated to minimise or maximise the function value. These are the direction set method of Powell and the quasi-Newton algorithm. Both methods proved to be successful, with some advantages and disadvantages. Using these methods at a power level below 10 kW, results are given of structures of the reluctance synchronous machine which have been optimised according to specific criteria. Calculated and measured results show that the maximum torque optimum designed reluctance synchronous machine has the advantages of high power density and high efficiency.
140 citations
TL;DR: In this article, a new average-value model of a synchronous machine fed load-commutated converter is presented in which the stator dynamics are combined with the DC link dynamics.
Abstract: A new average-value model of a synchronous machine fed load-commutated converter is set forth in which the stator dynamics are combined with the DC link dynamics. This model is shown to he extremely accurate in predicting system transients and in predicting frequency-domain characteristics such as the impedance looking into the synchronous machine fed load-commutated converter. The model is verified against a detailed computer simulation and against a hardware test system, thus providing a three-way comparison. The proposed model is shown to be much more accurate than models in which the stator dynamics are neglected.
130 citations
TL;DR: A systematic approach to fuzzy logic control design is proposed, directed at developing robust stabilizer design and analysis methods appropriate when fuzzy logic is applied.
Abstract: Power system stabilizers (PSS) must be capable of providing appropriate stabilization signals over a broad range of operating conditions and disturbances. Traditional PSS rely on robust linear design methods. In an attempt to cover a wider range of operating conditions, expert or rule-based controllers have also been proposed. Fuzzy logic as a novel robust control design method has shown promising results. The emphasis in fuzzy control design centers around uncertainties in system parameters and operating conditions. Such an emphasis is of particular relevance as the difficulty of accurately modelling the connected generation is expected to increase under power industry deregulation. Fuzzy logic controllers are based on empirical control rules. In this paper, a systematic approach to fuzzy logic control design is proposed. Implementation for a specific machine requires specification of performance criteria. This performance criteria translates into three controller parameters which can be calculated off-line or computed in real-time in response to system changes. The robustness of the controller is emphasized. Small signal and transient analysis methods are discussed. This work is directed at developing robust stabilizer design and analysis methods appropriate when fuzzy logic is applied.
126 citations
TL;DR: In this paper, the power quality of a lowvoltage grid with two wind turbines is investigated and the spectrum of the power is determined so that the presence of periodic power components can be investigated.
Abstract: The power quality of a low-voltage grid with two wind turbines is investigated. Slow voltage variations as well as transients and harmonics are measured and analysed. Furthermore, the spectrum of the power is determined so that the presence of periodic power components can be investigated. Although periodic power fluctuations reaching 10% of the rated power are registered, voltage variations are lower than the prescribed IEC flicker limit at steady-state operation. As the turbines are put on-line, the voltage level is lowered by 3%, which exceeds the flicker limit. The risk for flicker increases if the X/R ratio of the grid is low and if turbines which have a tendency to produce large periodic power fluctuations are used.
125 citations
TL;DR: A novel maximum power point (MPP) search algorithm for photovoltaic (PV) array power systems is introduced that requires neither the measurement of temperature and solar irradiation level nor a PV array model that is mostly used in look-up table based algorithms.
Abstract: A novel maximum power point (MPP) search algorithm for photovoltaic (PV) array power systems is introduced. The proposed algorithm determines the maximum power point of a PV array for any temperature and solar irradiation level using an online procedure. The method needs only the online values of the PV array output voltage and current, which can be obtained easily by using just current and voltage transducers. The algorithm requires neither the measurement of temperature and solar irradiation level nor a PV array model that is mostly used in look-up table based algorithms. Satisfactory results were obtained with the proposed algorithm in a laboratory prototype implementation scheme consisting of a PV array computer emulation model, a chopper controlled permanent magnet DC motor, and a DT2827 data acquisition board with the ATLAB software drivers for interfacing.
TL;DR: In this article, the benefits and costs of applying energy storage to three situations on the Niagara Mohawk Power Corporation system were investigated, including thermal overload on a transmission line to a growing load in an environmentally sensitive location.
Abstract: The values of benefits and costs have been estimated for applying energy storage to three situations on the Niagara Mohawk Power Corporation system, One situation is a valuable industrial customer requiring high quality, reliable power. The second situation is the need for reliable power at the end of a radial distribution feeder. The third situation is a case of thermal overload on a transmission line to a growing load in an environmentally sensitive location. The first case requires a small storage system (30 MJ); the second and third require relatively large systems (250 and 550 MWh, respectively). A variety of energy storage technologies was considered for each case (superconducting magnet energy storage (SMES), batteries, flywheels, capacitors, compressed air energy storage (CAES), compressed air in vessels, pumped hydro). This paper presents the benefit/cost results for the technologies considered for each case.
Journal Article•
TL;DR: An unbalanced stationary to synchronous reference frame transformation for stator current was developed in this article to deal with the asymmetrical structure and thus make the field-oriented control techniques developed from balanced machine winding structure become applicable Experimental tests were conducted on a dual three phase induction machine with a open phase to verify the proposed analytical modeling and control techniques
Abstract: Field-oriented control techniques for a multi-phase induction machine with an unbalanced stator winding structure is presented in this paper An unbalanced stationary to synchronous reference frame transformation for stator current was developed in this paper to deal with the asymmetrical structure and thus make the field-oriented control techniques developed from balanced machine winding structure become applicable Experimental tests were conducted on a dual three phase induction machine with a open phase to verify the proposed analytical modeling and control techniques
TL;DR: Studies show that the proposed adaptive network-based fuzzy logic PSS (ANF PSS) can provide good damping of power systems over a wide range of operating conditions and improve the dynamic performance of the power system.
Abstract: A fuzzy logic-based power system stabilizer (PSS) with learning ability is proposed in this paper. The proposed PSS employs a multilayer adaptive network. The network is trained directly from the input and the output of the generating unit. The algorithm combines the advantages of artificial neural networks (ANNs) and fuzzy logic control (FLC) schemes. Studies show that the proposed adaptive network-based fuzzy logic PSS (ANF PSS) can provide good damping of power systems over a wide range of operating conditions and improve the dynamic performance of the power system.
TL;DR: In this paper, a Monte Carlo based method for predicting the economic performance and reliability of autonomous energy systems consisting of diesel generators and wind energy converters (WECs), is proposed.
Abstract: A Monte Carlo based method for predicting the economic performance and reliability of autonomous energy systems consisting of diesel generators and wind energy converters (WECs), is proposed. Several technical constraints are applied, among them the most significant are the limitation of wind power penetration due to both the load demand and a minimum permissible power of the diesel generators. Start up-shutdown costs, two-fuel diesel units and reliability are considered. The proposed method divides the total simulation period into time intervals and for every time interval uses dynamic programming techniques to determine the diesel unit commitment. Results are presented for two Greek islands. It is shown that proper central control of WECs in a system increases significantly the wind energy penetration, which is strongly affected by the way commitment is made.
TL;DR: In this article, a detailed wind park model has been developed and is briefly presented, where singular perturbations theory has been applied to reduce the order of the detailed model, and therefore create the conditions for the development of a dynamic equivalent which is able to retain the relevant dynamics with respect to the existing AC power system.
Abstract: Due to the increasing penetration of wind energy, it is necessary to possess design tools that are able to simulate the impact of these installations on electric utility grids. In order to provide a net contribution to this issue, a detailed wind park model has been developed and is briefly presented. However, the computational costs associated with the performance of such a detailed model in describing the behavior of a wind park composed by a considerable number of units may render its practical application very difficult. To overcome this problem, singular perturbations theory has been applied to reduce the order of the detailed wind park model, and therefore create the conditions for the development of a dynamic equivalent which is able to retain the relevant dynamics with respect to the existing AC power system. Validation results proving the ability of singular perturbations reduced order model to match the results provided by the detailed model are shown and commented upon.
Journal Article•
TL;DR: Computer Models suitable for representation of newer digital-based excitation systems in transient stability programs are presented and it is the intent of the subcommittee to include these models in standard 421.5 at the time of its next revision.
Abstract: Computer Models suitable for representation of newer digital-based excitation systems in transient stability programs are presented in this paper. These models are an addendum to the most recent issued IEEE standard 421.5 (1992) for recommended excitation system models. It is the intent of the subcommittee to include these models in standard 421.5 at the time of its next revision.
TL;DR: In this paper, a simple analytical model was proposed to account for the damping effects of a cage rotor on the unbalanced magnetic pull (UMP) when the rotor is dynamically eccentric.
Abstract: This paper sets out a simple analytical model which is able to account for the damping effects of a cage rotor on the unbalanced magnetic pull (UMP) when the rotor is dynamically eccentric. The algorithm is implemented for a 4-pole cage induction motor with a variety of rotors with different rotor eccentricity and skew. The model is verified by the assessment of the UMP vibration when the different rotors are fitted in the stator. The characteristics are compared and it is found that the predicted and measured UMP characteristics compare well. It is observed that skewing the rotor cage increases the UMP when the motor is loaded.
TL;DR: In this paper, the influence of three capacitor excitation topologies (shunt, short-shunt and longshunt) on the steady-state and dynamic performance of a single-phase, self-excited induction generator is explored.
Abstract: The influence of three capacitor excitation topologies (shunt, short-shunt and long-shunt) on the steady-state and dynamic performance of a single-phase, self-excited induction generator is explored in this paper. Attention is focused on the influence of the different capacitor connections on the generator overloaded and output power capabilities. The generator voltage with shunt excitation connection collapses when overloaded, while with either the long or short-shunt excitation connection the generator is able to sustain the load at a lower operating voltage and larger load current.
TL;DR: In this article, the steady-state analysis and performance of self-excited induction generators (SEIG) driven by regulated and unregulated turbines is discussed, based on the nodal admittance method as applied to the equivalent circuit model.
Abstract: This paper discusses the steady-state analysis and performance of self-excited induction generators (SEIG) driven by regulated and unregulated turbines. The basis of the analysis is the nodal admittance method as applied to the equivalent circuit model. For constant-speed operation, a simple iterative technique is used for the determination of the electrical frequency. When the turbine speed is regulated to give constant-frequency operation, a direct solution is possible by solving a quadratic equation in the per-unit speed. In the case of an SEIG driven by an unregulated turbine, a two-level iterative procedure is required for determining the operating speed and torque. The Secant method is found suitable for the additional level of iteration and convergence is fast. Experimental investigations on a 2 kW three-phase induction machine confirm the accuracy of the proposed methods of analysis.
TL;DR: In this paper, a fuzzy-logic based supervisor monitors the overall plant operation and carries out the tasks of coordination, fault diagnosis, fault isolation, and fault accommodation, with minimum or no human assistance.
Abstract: Achieving a more autonomous power plant operation is an important part of power plant control. To be autonomous, a control system needs to provide adequate control actions in the presence of significant uncertainties and/or disturbances, such as actuator or component failures, with minimum or no human assistance. However, a reasonable degree of autonomy is difficult to obtain without incorporating intelligence in the control system. This paper presents a coordinated intelligent control scheme with a high degree of autonomy. In this scheme, a fuzzy-logic based supervisor monitors the overall plant operation and carries out the tasks of coordination, fault diagnosis, fault isolation, and fault accommodation.
TL;DR: In this paper, a neural network-based power system stabilizer (neuro-PSS) is designed for a generator connected to a multi-machine power system utilizing the nonlinear power flow dynamics.
Abstract: A neural network-based power system stabilizer (neuro-PSS) is designed for a generator connected to a multi-machine power system utilizing the nonlinear power flow dynamics. The use of power flow dynamics provides a PSS for a wide range of operation with reduced size neural networks. The neuro-PSS consists of two neural networks: neuro-identifier and neuro-controller. The low-frequency oscillation is modeled by the neuro-identifier using the power flow dynamics, then a generalized backpropagation-through-time (GBTT) algorithm is developed to train the neuro-controller. The simulation results show that the neuro-PSS designed in this paper performs well with good damping in a wide operation range compared with the conventional PSS.
TL;DR: In this article, the steady-state performance of a stand-alone permanent magnet synchronous generator driven by a diesel engine is analyzed using d-q circuits and the phasor diagram of such a generator under steady state conditions.
Abstract: A method to analyze the steady-state performance of a stand-alone permanent magnet synchronous generator driven by a diesel engine is presented. The proposed method is based on equivalent d-q circuits and the phasor diagram of such a generator under steady-state conditions. A fixed capacitor-thyristor controlled reactor scheme is used to regulate the generator terminal voltage by controlling the thyristor ignition angle. Furthermore the overall system dynamics are modelled in terms of state variables and control inputs. Based on a reduced order linearized model, digital optimal state and output feedback controllers are designed by minimising a quadratic performance index using the dynamic programming technique. The objective of the controller is to maintain the load voltage and frequency constant under varying load conditions. The controller's effectiveness is assessed by examining the closed-loop system response to sudden load changes.
TL;DR: In this paper, a straightforward hybrid observer is set forth which enables rotor position to be estimated on a continuous basis using information available from the Hall-effect sensors, and the proposed observer is experimentally shown to perform just as well as an optical encoder for steady-state conditions.
Abstract: Brushless DC motor drive systems are used in a wide variety of applications These drives may be classified as being one of two types: sinusoidal drives in which there are no low-frequency harmonics in the current waveforms and no low-frequency torque ripple; and nonsinusoidal drives in which there is considerable low-frequency harmonic content, both in the current and torque waveforms Although sinusoidal drives feature superior performance, they are generally more expensive since rotor position must be sensed on a continuous basis, thus requiring an optical encoder or a resolver, whereas relatively inexpensive Hall-effect sensors may be used for nonsinusoidal drives In this paper, a straightforward hybrid observer is set forth which enables rotor position to be estimated on a continuous basis using information available from the Hall-effect sensors The proposed observer is experimentally shown to perform just as well as an optical encoder for steady-state conditions and nearly as well as the optical encoder during transient conditions The proposed scheme provides designers with a new option for rotor position sensing, one which offers an excellent compromise between accuracy and expense
TL;DR: In this article, a method for detecting shorted windings in turbine-generators is described, which is based on the traveling wave method described by El-Sharkawi et al. (1971) and extended to operational rotors by the application of a neural network feature extraction and novelty detection.
Abstract: A method for detecting shorted windings in operational turbine-generators is described. The method is based on the traveling wave method described by El-Sharkawi, et. al. (1971). The method is extended in this paper to operational rotors by the application of a neural network feature extraction and novelty detection. The results of successful laboratory experiments are also reported.
TL;DR: In this paper, a design approach for a decentralized controller for a power plant is presented, where the interconnecting variables between the subsystems are treated as constant boundary conditions for the controller design and the local controllers are designed to be robust in order to accommodate fluctuations in the interaction variables once the overall system is considered.
Abstract: This paper presents a design approach for a decentralized controller for a power plant. An electric power plant nonlinear model is decomposed into three subsystems: boiler, turbine, and generator. The interconnecting variables between the subsystems are treated as constant boundary conditions for the controller design. The local controllers are designed to be robust in order to accommodate fluctuations in the interaction variables once the overall system is considered. The drum pressure set-point is automatically obtained from the power demand through a functional mapping.
TL;DR: In this paper, the authors present a number of models of saturated double-cage (deep-bar) induction machines where alternative sets of state-spate variables are selected.
Abstract: The available models of saturated double-cage and deep-bar induction machines are the current state-space model and the flux state-space model, where state-space variables are selected either as stator current and currents of both rotor cages, or stator flux linkage and flux linkages of both rotor cages. This paper presents a number of models of saturated double-cage (deep-bar) induction machines where alternative sets of state-spate variables are selected. The method of main flux saturation modelling relies on recently introduced concept of 'generalised flux space vector', which has originally been developed for modelling of saturated single-cage induction machines. The procedure and the novel models are verified by experimental study and simulation of self-excitation process in a double-cage induction generator.
TL;DR: In this paper, a fuzzy logic excitation system has been proposed to enhance the overall stability of power systems, which has two control loops: the voltage control loop and the damping control loop.
Abstract: A fuzzy logic excitation system has been proposed to enhance the overall stability of power systems. The proposed excitation system has two control loops. One is the voltage control loop which achieves the automatic voltage regulator (AVR) function, and the other is the damping control loop which gives the PSS function. Simple fuzzy logic control rules are applied to both loops. The input signal to the voltage control loop is the terminal voltage, and the input signal to the damping control loop is the real power output. Simulation studies show the advantages of the fuzzy logic excitation system.
TL;DR: In this article, a nonlinear adaptive generator control system using neural networks, called an adaptive neuro-control system (ANCS), was proposed to generate supplementary control signals to conventional controllers and works adaptively in response to changes in operating conditions and network configuration.
Abstract: This paper proposes a nonlinear adaptive generator control system using neural networks, called an adaptive neuro-control system (ANCS). This system generates supplementary control signals to conventional controllers and works adaptively in response to changes in operating conditions and network configuration. Through digital time simulations for a one-machine infinite bus test power system, the control performance of the ANCS and advanced controllers such as a linear optimal regulator and a self-tuning regulator is evaluated from the viewpoint of stability enhancement. As a result, the proposed ANCS using neural networks with nonlinear characteristics improves system damping more effectively and more adaptively than the other two controllers designed for the linearized model of the power system.
TL;DR: In this paper, the impact of photovoltaic (PV) generation when added to an existing rural utility's distribution system is examined in the light of voltage support, loss reduction, and reduction in peak demand.
Abstract: The impact of photovoltaic (PV) generations, when added to an existing rural utility's distribution system, is studied. The addition of PV is examined in the light of voltage support, loss reduction, and reduction in peak demand. Comparisons are made with the conventional and widely used methods for voltage control and loss minimization, such as the addition of series and shunt capacitors and voltage regulators. The economics of distributed PV systems in the context of conventional grid power purchases are also studied. Results of this study are meant to be used as general guidelines for evaluating the impact of significant PV penetration in any distribution system.