A standstill frequency response method for large salient pole synchronous machines

In this article, a Standstill Frequency Response Test (SSFR) is proposed, with the aim of determining the direct and quadrature axis operational impedances for salient pole synchronous machines. The method is applied with the rotor at standstill in a given arbitrary position, thus avoiding the difficulties in rotor mechanical alignment and rendering it suitable for large salient pole synchronous machines of hydroelectric power plants.     

Off-line testing of reluctance machines

Experimental techniques for determining the machine parameters and results demonstrating their performance on an axially-laminated synchronous reluctance motor are presented. A new software implementation of the control algorithm for conducting an instantaneous flux-linkage test is developed. A low frequency AC test allowing better estimation accuracy compared to a standard 50-Hz test is proposed. Effects of stator slotting on the quality of DC torque test estimates are examined     

Standstill frequency-response methods and salient-pole synchronousmachines

Standstill frequency-response (SSFR) literature to date has primarily focused on turbo-alternators, which have a double-cylindrical topology. Synchronous machines driven by hydraulic turbines or internal combustion engines are salient-pole machines whose electrical constants are somewhat different due to construction differences: (1) the salient-pole topology produces a ratio of L_q/L_d of approximately 0.5 as opposed to unity for cylindrical-rotor machines; (2) the salient poles are constructed of steel-sheet stampings rather than forged steel; (3) salient-pole field windings are concentric whereas those of cylindrical rotor machines are distributed; (4) salient-pole generators often have amortisseur windings embedded in the pole faces; and (5) fractional slot/pole/phase (SPPP) stator windings are commonly employed in salient-pole machines whereas turbo-alternators are more apt to be limited to integral SPPP windings. These differences alter time constants, inductances, and transfer functions. This paper provides needed information for the modeling of salient-pole machines for use in simulation studies using a theoretical approach     

Constraints on saturation modeling in AC machines

The author presents constraints which must be satisfied by saturation models of lossless fields. Nonlinear terms are added to linear models to represent the saturation phenomenon. The major point is to emphasize that these nonlinear terms cannot be arbitrarily specified when lossless fields are assumed. This is done by returning to the fundamental laws which make up a typical dynamic model and showing that the traditional assumptions impose well defined constraints on the nonlinear terms. The constraints are derived from energy balance principles and must be satisfied by the flux linkage/current relationships in order to ensure consistency with the assumptions of a lossless field. The constraints are used to design a consistent saturation model for a synchronous machine     

On equivalent circuit modeling for synchronous machines

This paper presents alternative equivalent circuits for modeling the steady state frequency response (SSFR) data measured for turboalternator synchronous machines. These models provide direct representation of the frequency-dependent skin-effect properties of the dampers and rotor iron. The parameters are determined by matching the measured data to the model frequency response using standard optimization methods. The accuracy of matching is comparable to that of conventional third-order d-q models but the required number of parameters is reduced     

A systematic method for the determination of the parameters ofsynchronous machines from the results of frequency response tests

This paper deals with the analysis of the frequency responses of the d and q axis impedances of synchronous machines. Numerical curve-fitting techniques have normally been used to find the best set of time constants to fit the frequency response data, but limitations or constraints are introduced with these techniques. The process to be described here is based on characteristic features of the equivalent circuits which overcome the need to make the assumptions inherent in a numerical approach. The extraction process is demonstrated using an equivalent circuit chosen to produce a frequency response similar to that for the direct axis of a production machine. This enables the intrinsic advantages of the proposed process for extraction of the time constants to be demonstrated which then leads directly to a unique set of equivalent circuit parameters     

Simulation of the impulse response of electrical machines

This paper presents three different methods for modeling the transient response of electrical machines. The state-space approach, the Laplace transformation technique and the realization of a new, wide-frequency range equivalent circuit of the machine terminal impedance are applied to obtain the transient response to any waveform. The introduced methods are based on the frequency response of the machine which is often seen as a black box. Both laboratory- and large-scale machines are used to investigate the effect of a variety of impulse waveforms on the transient response of the other phases and to obtain the voltage distribution along the winding of each phase. A frequency response test for the machine is applied to obtain the resonance frequencies and the rational forms for both the voltage gains and terminal impedance. Excellent agreement (error is within 3%) is found between the three methods and the experimental results for different types and ratings of electrical machines under different impulse waveforms     

Diagnostic testing in modeling energy demand

In recent years, a number of formal diagnostic tests for identifying misspecification of models and criteria for comparing alternative models have been proposed. Not many of them, however, have found common use among energy analysis. This paper provides a comprehensive listing of these techniques and describes them in a manner easily accessible to modelers of energy demand. The methods suggested are illustrated with an application to the modeling of peak electricity demand in a utility service area in the upper midwest.     

Dynamic temperature modeling of an SOFC using least squares support vector machines

Cell temperature control plays a crucial role in SOFC operation. In order to design effective temperature control strategies by model-based control methods, a dynamic temperature model of an SOFC is presented in this paper using least squares support vector machines (LS-SVMs). The nonlinear temperature dynamics of the SOFC is represented by a nonlinear autoregressive with exogenous inputs (NARXs) model that is implemented using an LS-SVM regression model. Issues concerning the development of the LS-SVM temperature model are discussed in detail, including variable selection, training set construction and tuning of the LS-SVM parameters (usually referred to as hyperparameters). Comprehensive validation tests demonstrate that the developed LS-SVM model is sufficiently accurate to be used independently from the SOFC process, emulating its temperature response from the only process input information over a relatively wide operating range. The powerful ability of the LS-SVM temperature model benefits from the approaches of constructing the training set and tuning hyperparameters automatically by the genetic algorithm (GA), besides the modeling method itself. The proposed LS-SVM temperature model can be conveniently employed to design temperature control strategies of the SOFC.     

Practical considerations concerning impulse voltage testing ofform-wound coils for rotating machines

The authors review the response of the windings of high-voltage AC rotating machines to system-generated transient voltages and also impulse test techniques and withstand levels of form-wound stator coils. Design tests on coils with a vacuum pressure impregnation (VPI) insulation system have confirmed very high turn-to-turn insulation strength well above actual system transient voltages. Because of this and since the amplitude of line-to-ground overvoltages to which windings are exposed in service can be controlled to some extent, there appears to be no need for impulse testing of complete machines. Also, the line-to-ground withstand capability of a winding would be adequately verified by the standard AC applied potential test. If, under special conditions, the actual turn-to-turn insulation strength must be demonstrated experimentally, such tests should be performed on additionally fabricated sacrificial coils which are manufactured with and identical to those in the winding     

Modelling and identification of synchronous machines, a newapproach with an extended frequency range

Correct modeling of turbogenerators is difficult, as currents are flowing during transients not only in the field and damper winding but also in the solid rotor iron. To model this effect, especially at high frequencies, new model structures called ladder networks are introduced. Their parameters are identified by combining the standstill frequency response measurements with the results of the standardized three-phase no-load short-circuit test. By means of this combination the errors in the standstill frequency responses, caused by the iron nonlinearity and the contact uncertainty of the slot wedges at standstill, are expected to be reduced. Both the new ladder networks and the standard models are used to simulate disturbances for comparison. In some cases (three-phase terminal fault out-of-phase synchronization) both models yield equivalent results, but in other cases (operation after a close-up fault) the results of the two models can differ considerably     

Closure to discussion of a systematic method for the determination of the parameters of synchronous machines from the results of frequency response tests

A. Mariscotti comments on the original paper by A. Walton (see ibid., vol.15, no.2, p.218-23, 2000). The author points out other literature that may be of use to the survey conducted in relation to whether the algorithm presented has been tested using measurement data. The original author replies to the comments     

Comparison of single-cell testing,short-stack testing and mathematical modeling methods for a direct methanol fuel cell

In this paper, a comparison between direct methanol fuel cell (DMFC) measurements performed on a single cell and a short-stack, and the results of a mathematical model for a DMFC, is presented. The testing of a short-stack, which consists of 5 cells with an active area of 315 cm², was performed at various current densities, permeation current densities, and cathode flow rates (CFR) in order to determine the voltage outputs of each cell. Methanol concentration and stack temperature results obtained from short-stack testing were then integrated into the single cell test and single cell mathematical model as the input parameters. For the mathematical modelling, transport equations originating from methanol, water, and oxygen were coupled with the electrochemical relations. Therefore, a comparison between these three methods is made in order to gain a deeper understanding of the effects of the operating parameters on DMFC performance. This study showed that the model could describe experimental results well when lower methanol concentrations (under 1.2 M) and temperature (under 60 °C) values are used as input parameters. The results also show very good agreement at lower methanol permeation rates and therefore lower temperatures. It is found that the voltage output for a given current density is higher for the theoretical model than that of the experimental studies; and the differences in the results can be up to 0.04 V for a cell.     

Steam turbine governor modeling and parameters testing for power system simulation

The theoretical modeling, parameters test and model correction for a steam turbine (ST) governor are discussed. A set of ST Governor system model for power system simulation is created based on this research. A power system simulation for an actual power grid accident is conducted using this new model and the comparison between the simulation and actual data show that the results are satisfactory.     

Fabrication,modeling and testing of a thin film Au/Ti microheater

A thin film gold/titanium (Au/Ti) microheater is developed for microthruster ignition, micro explosive boiling, and micro sensor applications. The microheater was fabricated onto a Pyrex bulk substrate using a micro-fabrication technology. A finite-element based electro-thermal modeling was employed to predict the microheater performance. The variations of the microheater temperature with time, space, and power supply are determined from the modeling. A method is presented to determine the thin film Au/Ti electrical resistivity and thermal conductivity. It was found that significant differences exist between heat transfer in microheater and conventional heater. Experimental testing of the microheater temperature was performed using a customized circuitry. The finite-element model is validated by the experimental measurements.     

Energy-cost allocation based on the theory of frequency response

Energy-cost allocation systems apportion heating and/or cooling costs among the individual apartments in centrally-metered buildings based on various measures of relative energy use or thermal comfort. The most commonly used systems measure one or more parameters related to the thermal output of the terminal elements. In this paper, a new method for energy-cost allocation purposes was developed and studied. Taking advantage of the theory of frequency response, the individual apartments' energy consumption for cooling in summer may be calculated using several parameters that include indoor and outdoor temperatures and the values of solar radiant-intensity. Experiments were done in this study, which indicates that the method of frequency response is fairly good in calculating the energy use of cooling.     

大型水轮发电机组主轴系统动力特性研究现状及建模方法

水轮发电机组动态特性研究的关键,在于建立正确的数学模型、确定重要零部件边界条件以及采用稳定、高精度的求解方法.本文论述了机组主轴系统动态响应的求解现状及建模方法,分析了几个重要相关零部件的边界条件确定,即支承部件的动力学建模问题.     

A novel method for modeling dynamic air-gap eccentricity insynchronous machines based on modified winding function theory

This paper presents the modeling of synchronous machines under eccentric rotors. The winding function theory accounting for all space harmonics and presented by earlier researchers has been modified to adopt a nonsymmetric air-gap for the calculation of machine winding inductances. The effect of dynamic air-gap eccentricity on the inductances of a salient-pole synchronous machine using the modified winding function approach (MWFA) has been discussed. The coupled magnetic circuits approach has been used for simulating the machine behavior under healthy and eccentric rotor conditions. The simulation results are in close agreement with the experimental results     

Flexible demand response programs modeling in competitive electricity markets

In recent years, extensive researches have been conducted on implementation of demand response programs (DRPs), aimed to electricity price reduction, transmission lines congestion resolving, security enhancement and improvement of market liquidity. Basically, DRPs are divided into two main categories namely, incentive-based programs (IBPs) and time-based rate programs (TBRPs). Mathematical modeling of these programs helps regulators and market policy makers to evaluate the impact of price responsive loads on the market and system operational conditions. In this paper, an economic model of price/incentive responsive loads is derived based on the concept of flexible price elasticity of demand and customer benefit function. The mathematical model for flexible price elasticity of demand is presented to calculate each of the demand response (DR) program’s elasticity based on the electricity price before and after implementing DRPs. In the proposed model, a demand ratio parameter has been introduced to determine the appropriate values of incentive and penalty in IBPs according to the level of demand. Furthermore, the importance of determining optimum participation level of customers in different DRPs has been investigated. The proposed model together with the strategy success index (SSI) has been applied to provide an opportunity for major players of the market, i.e. independent system operator (ISO), utilities and customers to select their favorite programs that satisfy their desires. In order to evaluate the performance of the proposed model, numerical studies are conducted on the Iranian interconnected network load profile on the annual peak day of the year 2007.