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Energy Conversion, IEEE Transactions on

Issue 4 • Date Dec 1991

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Displaying Results 1 - 21 of 21
  • Effect of excitation capacitors on transient performance of reluctance generators

    Page(s): 714 - 720
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    The transient responses of a reluctance generator connected to an infinite power system excited by a bank of terminal capacitances are compared to those when load excitation is used. A mathematical model is developed to simulate the machine with its terminal capacitor. With the aid of a least-square-error method, this model is used to optimize the machine parameters. The capacitance excitation requirements for different load conditions are then computed using a steady-state model. The comparison of the transient responses shows that the terminal-capacitor excitation method has several advantages over the load excitation method. It reduces the first rotor swing and gives more damping to the subsequent rotor oscillations. It also increases the critical fault-clearing time and hence the transient stability limits. In addition, it suppresses all power frequency torque oscillations, which are quite pronounced when load excitation is used View full abstract»

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  • Modeling of effects of skewing of rotor mounted permanent magnets on the performance of brushless DC motors

    Page(s): 721 - 729
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    A method for computation of the parameters and performance of permanent-magnet brushless DC motor drives is developed in which the concept of skewing is implemented through the geometries of permanent magnet mounting on the rotor and not through the usual skewing of the armature slots. This technique of permanent-magnet mounting eliminates the 2-D axial symmetry in the resulting magnetic fields. This difficulty is overcome by the use of multiple cross-sectional 2-D finite-element field computations, coupled with a concept of an artificial mutual-coupling inductance between the armature phase windings and the rotor-mounted permanent magnets for induced EMF and torque computations. The computed induced EMF waveforms, motor phase winding current waveforms, and other performance characteristics are found to be in excellent agreement with test data obtained using a 1.2 hp, 120 V brushless DC motor drive system View full abstract»

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  • Experience with turn insulation failures in large 13.2 kV synchronous motors

    Page(s): 670 - 678
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    Experience of dealing with a very high rate of failures in a population of 21000 HP motors is recounted. Special testing done to identify the failure mechanism and the conclusions that were drawn are described. Various recommendations to prevent premature winding failures proved ineffective. It is shown how an engineering analysis indicated that the accepted view of the failure mechanism was untenable. A theory of partial discharge in the end turn of the stator winding that is compatible with all known facts is proposed View full abstract»

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  • Application of superconducting magnetic energy storage unit to improve the damping of synchronous generator

    Page(s): 573 - 578
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    A systematic approach to the design of a controller for superconducting magnetic energy storage (SMES) units to improve the dynamic stability of a power system is presented. The scheme employs a proportional-integral (PI) controller to enhance the damping of the electromechanical mode oscillation of synchronous generators. The parameters of the PI controller are determined by the pole assignment method based on modal control theory. Eigenvalue analysis and nonlinear computer simulations show that SMES with the PI controller can greatly improve the damping of the system under various operating conditions. Although the PI controller is designed for a special load condition, it can also provide good damping under other load conditions View full abstract»

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  • Analysis of a concentrated winding induction machine for adjustable speed drive applications. I. Motor analysis

    Page(s): 679 - 683
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    The performance of multiphase machines designed for operation with static power converters is investigated. The winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters. Equations which define the transient as well as steady-state behavior, including the computation of all machine inductances, are derived. In deriving these equations the space harmonics are specifically included. Equations for calculation of terminal voltages and electromagnetic torque are modified to account for nonsinusoidal air-gap-flux distributions. A conventional three-phase induction motor including the effect of space harmonics is simulated View full abstract»

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  • Accelerating power versus electrical power as input signals to power system stabilizers

    Page(s): 620 - 626
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    Power system stabilizers (PSSs) using electrical and accelerating power as supplementary signals are compared. The effect on terminal voltage and volt-ampere reactive, offset and damping of a simulated single-machine-infinite-bus system is investigated. The results show that the damping offered by a PSS using accelerating power and electrical power feedback is very similar even in the presence of large mechanical power disturbances. The benefits of accelerating power over electrical power as the supplementary signal to the PSS are not evident in the simulation studies considered. Considering the relative ease of measuring the electrical power signal compared to accelerating power signal, it is concluded that a PSS using electrical power as a supplementary signal is sufficient for damping rotor oscillations. Frequency response data are shown to support this point of view View full abstract»

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  • Control synthesis for an impulse turbine: The Bradley Lake project

    Page(s): 639 - 648
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    The synthesis of a viable control strategy for the multiple-jet impulse turbines utilized in the Bradley Lake hydroelectric project in Alaska is discussed. Digital simulation is used to assess modifications to various control schemes. Control is locally stable, but unstable to large perturbations. A strategy is developed which achieves global stability of the system. The new control is primarily based on enhancing deflector contributions to control View full abstract»

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  • Performance analysis of a PV powered health clinic with single-stage dual priority regulator

    Page(s): 586 - 592
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    The performance of a photovoltaic-powered health clinic system which uses two separate batteries, one to power a vaccine refrigerator and the other to power auxiliary loads is investigated. The two batteries were sized according to the demand of their loads. The power control system utilizes a single-stage dual-priority controller to charge the two separate batteries from a single photovoltaic array. The main refrigerator battery always has priority over the auxiliary battery, and therefore the use of auxiliary loads will never jeopardize the reliability of the critical load. This system provides power for auxiliary loads while utilizing the same number of photovoltaic modules as systems which power only a vaccine refrigerator. The performance of this system is evaluated using a data-acquisition system, and the experimental results are compared with their theoretical values View full abstract»

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  • Tuning of power system stabilizers using an artificial neural network

    Page(s): 612 - 619
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    A new approach using an artificial neural network is proposed to adapt power system stabilizer (PSS) parameters in real time. A pair of online measurements i.e., generator real-power output and power factor which are representative of the generator's operating condition, are chosen as the input signals to the neural net. The outputs of the neural net are the desired PSS parameters. The neural net, once trained by a set of input-output patterns in the training set, can yield proper PSS parameters under any generator loading condition. Digital simulations of a synchronous machine subject to a major disturbance of a three-phase fault under different operating conditions are performed to demonstrate the effectiveness of the proposed neural network View full abstract»

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  • Analysis of steady-state operation of a multistack variable-reluctance stepper motor using qd0 variables

    Page(s): 693 - 699
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    An approximate method of calculating the steady-state characteristics of a multistack, variable-reluctance stepper motor operating in the continuous speed mode is developed. The mathematical model of the motor is set forth, and the unipolar inverter drive of interest is discussed. The differential equation which governs the flux linkage is then solved explicitly using numerical integration to evaluate the flux linkage waveform. As an alternative to the direct solution, the Floquet transformation is used to obtain a time-invariant differential equation. The qd0-variables are used with the reference frame fixed in the rotor. This approach provides a means of accurately accounting for the harmonic components of the current. The method is shown to be more accurate than existing approximate methods, with a marked computational advantage over exact methods View full abstract»

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  • A thermal cycling type test for generator stator winding insulation

    Page(s): 707 - 713
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    A test has been designed and implemented which cycles the temperature between 40°C and 150°C in about 80 min by the use of circulating currents and cooling air. The test has been successfully used to evaluate the relative performance of similar stator bars made by three different manufacturers. The thermal cycling test was able to duplicate the insulation delamination process and presumably those insulation systems which performed well in the thermal cycling test could last longer in service. In addition to being used for pumped-storage generators, the thermal cycling test may be useful to evaluate the insulation system in combustion turbine generators View full abstract»

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  • Global warming and electric power generation: What is the connection?

    Page(s): 599 - 604
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    The greenhouse effect is explained, followed by a discussion of the US fossil fuel use and its contribution of greenhouse gases. US electric utilities' share of CO2 and other emissions is quantified, including the effects of using various fuels. The possible recovery and disposal of CO2 from power-plant flue gases is also discussed. The information presented should help prepare electric utilities to address future public concerns and the related regulatory pressures regarding the utility's role in carbon-dioxide proliferation and global warming View full abstract»

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  • Dynamics and stability of wind and diesel turbine generators with superconducting magnetic energy storage unit on an isolated power system

    Page(s): 579 - 585
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    Dynamic system analysis is carried out on an isolated electric power system consisting of a diesel generator and a wind-turbine generator. The 150 kW wind turbine is operated in parallel with a diesel generator to serve an average load of 350 kW. A comprehensive digital computer model of the interconnected power system including the diesel and wind-power dynamics with a superconducting magnetic energy storage (SMES) unit is developed. Time-domain solutions are used to study the performance of the power system and control logic. Based on a linear model of the system, it is shown that changes in control-system settings could be made to improve damping and optimization of gain parameters and stability studies are done using the Lyapunov technique and eigenvalue analysis. The effect of introducing the SMES unit for improvement of stability and system dynamic response is studied View full abstract»

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  • Considerations for improving the reliability of the off-site power supply for nuclear generating stations

    Page(s): 649 - 655
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    It is argued that improvements in plant distribution system analysis, maintenance procedures, work control, definition of ownership, provision of detailed operational procedures and improved training can reduce loss of offsite power events. These improvements are not simple to implement in many cases, but as maximum grid loads grow and control and protective relaying become more complicated, it is essential that the processes to ensure adequate analysis, training, maintenance, and work control be in place View full abstract»

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  • A new sensor for detecting partial discharges in operating turbine generators

    Page(s): 700 - 706
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    A partial discharge (PD) sensor has been developed which is able to unequivocally differentiate between PD in the winding and all types of electrical interference. Thus, the sensor will permit an online test for turbine generators, similar to the test now used for hyrogenerators. The sensor requires no high-voltage connection to the winding, and is easily installed in the stator slot, underneath the wedges. Noise is differentiated from PD by the shapes of the electrical pulses from the sensor. The sensor, called the Stator Slot Coupler (SSC), is essentially a directional electromagnetic coupler. Calculations as well as laboratory tests indicate that the couplers can easily survive the electrical, thermal, magnetic, and mechanical stresses in the generator View full abstract»

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  • Salem plant dynamic voltage study and validation of computer models by tests

    Page(s): 656 - 662
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    A voltage profile study was performed for the power distribution system of the Salem Nuclear Generating Station to determine the cause of an apparent misoperation of undervoltage relays. A dynamic model of the distribution system was developed for simulation of the bus transfer and from the generator's auxiliary transformer to the station power transformer. The work in validating the computer dynamic simulation model by a test is presented. It is shown that the PTI Salem Electric Model and PSS/E software package are able to predict the static voltages at the 460 V and 230 V buses within a difference of 1.6% of the measured values. In addition, the model-predicted transient condition comparison test and computer simulation results validate the ability of the model to predict static and transient voltage levels. An inquiry throughout the nuclear power industry indicated that the described validation program represents the most detailed and accurate method of validating the accuracy of the electrical power analysis software View full abstract»

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  • Analysis of a concentrated winding induction machine for adjustable speed drive applications. II. Motor design and performance

    Page(s): 684 - 692
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    For pt.I. see ibid, vol.6, no.4, p.679-83 (1991). The performance of multiphase machines designed for operation with static power converters is described. The winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters. Fourier analysis is used for investigation of the effects of different air-gap-field spatial distributions and time harmonics in the supply. The approach to analysis of such machines, derived in Part I, is implemented by means of a digital-computer simulation. Compound results indicate that when operating in conjunction with a converter supply, a specially wound five-phase machine is theoretically capable of a 10% improvement in torque per root-mean-square ampere assuming the same peak air-gap-flux density level in the air gap of the machine as in a conventionally designed induction motor of the same rating View full abstract»

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  • Optimal design parameters for a PV array coupled to a DC motor via a DC-DC transformer

    Page(s): 593 - 598
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    A study is presented of the optimal operating parameters of a system comprising a photovoltaic solar array and a DC electromechanical energy converter (motor) driving a mechanical load. The analysis and design procedure includes the addition of a variable DC-DC matching transformer placed between the array and the motor. It is responsible for adjusting the load curve seen by the array to coincide with its maximum power point. The model takes into consideration the effect of different temperature as well as isolation profiles along the year. The analysis procedure guides the design of DC motors as well as variable DC transformers especially suited to be operated in conjunction with PV arrays. The procedure determines optimal motor constants which lead to an improved overall design in terms of maximizing the total annual gross mechanical energy delivered to a load of a given torque-speed characteristic View full abstract»

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  • Identification and control of a DC motor using back-propagation neural networks

    Page(s): 663 - 669
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    An artificial-neural-network (ANN)-based high-performance speed-control system for a DC motor is introduced. The rotor speed of the DC motor can be made to follow an arbitrarily selected trajectory. The purpose is to achieve accurate trajectory control of the speed, especially when motor and load parameters are unknown. The unknown nonlinear dynamics of the motor and the load are captured by the ANN. The trained neural-network identifier is combined with a desired reference model to achieve trajectory control of speed. The performances of the identification and control algorithms are evaluated by simulating them on a typical DC motor model. It is shown that a DC motor can be successfully controlled using an ANN View full abstract»

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  • An approach to assess the performance of utility-interactive wind electric conversion systems

    Page(s): 627 - 638
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    A probabilistic approach based on the convolution technique is presented to assess the performance of utility-interactive wind electric conversion systems supplying tools. The wind regime is modeled using a Weibull distribution. Expressions are developed to obtain the duration curve for the power injected into the utility grid. The energy injected into the grid and drawn from it to supply the load during the study period can be calculated from this duration curve. The load model employed enables the study period to range from one year to one particular hour-of-day, thus allowing the inclusion of the time-value of energy as appropriate in economic assessments View full abstract»

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  • An adaptive control scheme for speed control of diesel driven power-plants

    Page(s): 605 - 611
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    The performance of an incremental Clarke-Gawthrop adaptive control scheme, suitable for a diesel-engine prime mover, is described. The controller uses a predictor that is derived from explicit estimates of the plant deadtime and time constants. Its performance under speed reference changes and load disturbances has been compared to that of a fixed, tuned proportional-integral (PI) controller. The algorithm is found to operate satisfactorily under different values of droop without any additional complexity of computation being incurred. However, the improvement in plant response due to the adaptive algorithm is somewhat reduced at high droops. The effective improvement due to adaptation is also seen to be reduced under `cold oil' conditions. However, even under such conditions, it is possible to obtain improved response as compared to the PI controller View full abstract»

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Aims & Scope

The IEEE Transactions on Energy Conversion includes in its venue the research, development, design, application, construction, installation, operation, analysis and control of electric power generating and energy storage equipment (along with conventional, cogeneration, nuclear, distributed or renewable sources, central station and grid connection). The scope also includes electromechanical energy conversion, electric machinery, devices, systems and facilities for the safe, reliable, and economic generation and utilization of electrical energy for general industrial, commercial, public, and domestic consumption of electrical energy.

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Meet Our Editors

Editor-in-Chief
Juri Jatskevich
University of British Columbia