Identification of armature, field, and saturated parameters of alarge steam turbine-generator from operating data

This paper presents a step by step identification procedure of armature, field and saturated parameters of a large steam turbine-generator from real time operating data. First, data from a small excitation disturbance is utilized to estimate armature circuit parameters of the machine. Subsequently, for each set of steady state operating data, saturable mutual inductances L_ads and L_aqs are estimated. The recursive maximum likelihood estimation technique is employed for identification in these first two stages. An artificial neural network (ANN) based estimator is used to model these saturated inductances based on the generator operating conditions. Finally, using the estimates of the armature circuit parameters, the field winding and some damper winding parameters are estimated using an output error method (OEM) of estimation. The developed models are validated with measurements not used in the training of ANN and with large disturbance responses     

Coupled finite-element/state-space modeling of turbogenerators inthe abc frame of reference-the short-circuit and load cases includingsaturated parameters

In this paper, a coupled finite-element/state space modeling technique is applied in the determination of the steady-state parameters of a 733 MVA turbogenerator in the abc frame of reference. In this modeling environment, the forward rotor stepping-finite element procedure described in a companion paper is used to obtain the various machine self and mutual inductances under short-circuit and load conditions. A fourth-order state-space model of the armature and field winding flux linkages in the abc frame of reference is then used to obtain the next set of flux linkages and forcing function currents for the finite-element model. In this process, one iterates between the finite-element and state-space techniques until the terminal conditions converge to specified values. This method is applied to the determination of the short-circuit, and reduced- and rated-voltage load characteristics, and the corresponding machine inductances. The spatial harmonics of these inductances are analyzed via Fourier analysis to reveal the impact of machine geometry and stator-to-rotor relative motion, winding layout, magnetic saturation, and other effects. In the full-load infinite-bus case, it is found that, while the three-phase terminal voltages are pure sinusoidal waveforms, the steady-state armature phase currents are nonsinusoidal and contain a substantial amount of odd harmonics which cannot be obtained using the traditional two-axis analysis     

Synchronous generator model identification and parameter estimation from operating data

A novel technique to estimate and model parameters of a 460-MVA large steam turbine generator from operating data is presented. First, data from small excitation disturbances are used to estimate linear model armature circuit and field winding parameters of the machine. Subsequently, for each set of steady state operating data, saturable inductances L/sub ds/ and L/sub qs/ are identified and modeled using nonlinear mapping functions-based estimators. Using the estimates of the armature circuit parameters, for each set of disturbance data collected at different operating conditions, the rotor body parameters of the generator are estimated using an output error method (OEM). The developed nonlinear models are validated with measurements not used in the estimation procedure.     

Coupled finite-element/state-space modeling of turbogenerators inthe abc frame of reference-the no-load case

This first of two companion papers centers on applying a coupled finite-element/state-space technique to the determination of self and mutual winding inductances of a 733 MVA turbogenerator and computing its open-circuit characteristic, in the natural abc frame of reference. In this method, the apparent self and mutual inductance profiles of the armature and field windings, expressed as functions of rotor position angle, are computed from a series of magnetic field solutions performed at uniformly-distributed samples of rotor positions covering the entire 360° electrical cycle, using the energy perturbation method. These inductances, which are obtained at no-load for three different excitation levels, include the full effect of space harmonics introduced by the magnetic circuit geometry, winding layouts and magnetic circuit saturation. The abc-frame/finite-element computed open-circuit characteristic is in excellent agreement with the test results. This computed no-load set of parameters forms the initial data for simulation of the full-load performance given in the companion paper, including the full impact of space harmonics and saturation on the flux linkage, current and voltage waveforms, and other performance parameters     

Computation of load performance and other parameters of extra highspeed modified Lundell alternators from 3D-FE magnetic field solutions

A combined magnetic vector potential, magnetic scalar potential method of computation of 3-D magnetic fields by finite elements, in combination with state modeling in the abc frame of reference, is used for global 3-D magnetic field analysis and machine performance computation under rated load and overload condition in an example 14.3 kVA modified Lundell alternator. The results vividly demonstrate the 3-D nature of the magnetic field in such machines and show how this model can be used as an excellent tool for computation of flux density distributions, armature current and voltage waveform profiles, and harmonic contents, as well as for computation of torque profiles and ripples. Use of the model in gaining insight into locations of regions in the magnetic circuit with heavy degrees of saturation is demonstrated. Experimental results which correlate well with the simulations of the load case are given     

The effects of noise on frequency-domain parameter estimation ofsynchronous machine models

The authors present results of a study conducted to evaluate the effects of measurement noise on the estimation of machine parameters from standstill frequency response test data. Results obtained indicate that, because the test data are inherently noise-corrupted, multiple solution sets can be obtained. Moreover, some of the estimated machine parameters could be unrealistic. It is shown that the results are very sensitive to the value of armature resistance used in the data analysis. Even a 0.5% error in the value of armature resistance could result in unrealistic estimation of the machine parameters     

Synchronous machine parameter estimation using the Hartley series

This paper presents a novel alternative to estimate armature circuit parameters of large utility generators using real time operating data. The proposed approach uses the Hartley series for fitting operating data (voltage and currents measurements). The essence of the method is the use of linear state estimation to identify the coefficients of the Hartley series. The approach is tested for noise corruption likely to be found in measurements. The method is found to be suitable for the processing of digital fault recorder data to identify synchronous machine parameters     

Impact of load on winding inductances of permanent magnetgenerators with multiple damping circuits using energy perturbation

A computer-aided method for determining the impact of load on winding inductances and other machine parameters of permanent magnet generators with multiple damping circuits is presented. The method is general in nature so that it can be applied to detailed computer-aided design processes of permanent magnet generator systems. The method is based on use of the abc frame of reference for development of the necessary state equations     

Transient Analysis of Partial Armature Short Circuit in an Electronically Commutated Permanent Magnet Motor System using an Integrated Nonlinear Magnetic Field-Network Model

The simulation of the dynamic performance characteristics of an electronically commutated brushless dc machine system with radially oriented permanent magnets, which is experiencing a partial short in one of its phases, is reported in this paper. The newly introduced integrated field network (IFN) method was used throughout this work. The IFN method, which is detailed in a companion paper, is based on simultaneously solving the dynamic equations of the machine system network, using machine winding parameters (inductances and emfs) which are determined from numerical solutions of the nonlinear magnetic field prevailing in the machine cores for the corresponding winding currents. These field solutions and corresponding machine parameters are updated at every time step of the solution of the dynamic equations. The results presented here document effects of the shorting of a portion of an armature phase winding on the dynamic performance of a 15 hp (11.2 kw), 120 volts samarium-cobalt permanent magnet brushless dc motor. A comparison of the current, inductance, enf, torque and power time profiles of the motor system with and without partial armature winding failure (short) is given here. These studies are of importance in motor system security and redundancy considerations. The dramatic change of the values of machine parameters upon occurrence of the partial short circuits demonstrate that conventional solution methods would have left much to be desired.     

Equivalent circuit for the performance analysis of universal motors

An equivalent circuit of universal motors is developed, based on the design data. After representing the magnetomotive force distribution in the air gap, an analytical expression of the flux linkage of the armature winding coils is derived; this allows for the determination of the expressions of the speed and transformer EMFs induced in the armature winding and their representation by means of circuit parameters, as a function of the magnetic core saturation. The motor performances are computed, using the circuit parameters determined both analytically (by the design data) and by measurements. Some quantities are also compared with the ones obtained by finite-element analyses. Finally, the model is validated by experimental tests.     

Integrated Nonlinear Magnetic Field-Network Simulation of an Electronically Commutated Permanent Magnet Motor System under Normal Operation

An integrated magnetic field-network computer-aided method is presented, and is verified here by applying it in the determination of the performance of an electronically commutated permanent magnet motor system, and comparing the results with test results at rated operating conditions. Test results were found to be in very good agreement with numerical simulation data. At the core of this method are the instantaneous calculation of the magnetic field distribution within the machine, using the finite element method, and the determination of the winding inductances from these field solutions with the aid of an energy perturbation technique. The armature induced emfs are also obtained from these field solutions. These winding parameters, which are load dependent, are used in a nonlinear time domain network model of first order differential equations governing the dynamic performance of the motor to solve for the instantaneous phase currents. These new currents are then used at every time instant to determine the corresponding machine winding parameters, and the above process is repeated at successive time instants until the complete analysis period is covered. Though the validity of this method of analysis is verified in this paper by applying it to a 15 hp (11.2kw), 120 volt electronically commutated brushless dc motor system operating under normal and balanced conditions, the real utility of the method lies in its ability to analyze these motor systems under unbalanced partial or total component failure (fault) in the windings and associated conditioners. This type of application is given in a companion paper.     

Analysis and Detection of Short Circuits in Fractional Horsepower Commutator Machines

An improved mathematical model for transient simulations of commutator machines is presented in this paper. This model can simulate and predict the line current harmonics during healthy and faulty operation conditions. A lumped parameter model that considers every single coil in the stator and rotor as a separate electrical and magnetic circuit is proposed. Self and mutual inductances of the coils are estimated by means of the winding function approach (WFA), accounting for the most relevant space harmonics in the machine air gap. The commutation is modeled by using the real brush width and assuming that the brush-commutator contact resistance is a function uniquely of their contact area, which depends on the armature position. Short circuits between adjacent commutator bars are investigated. It is shown that the model achieves good accuracy, reproducing fairly well the armature current ripple for healthy and faulty operation of the machine.     

Axial Field Permanent Magnet DC Motor With Powder Iron Armature

The paper describes a double-gap axial field permanent magnet (PM) dc motor whose double-layer armature wave winding is constructed of copper strips. It investigates the performance of two machines using powder iron and lamination steel materials as armature teeth. Tests are conducted to evaluate the motor torque and speed curves as well as their efficiency under different loads. Finite element analysis (FEA) and equivalent circuit models are used to determine the levels of the magnetic saturation in the motors; calculate torque, inductance, and electromotive force (EMF); and determine the distribution of losses in the machine. The results show that the powder iron armature machine has lower back EMF and torque constants, and is less efficient than the steel laminations machine, which is due to the lower permeability and saturation flux density of the powder iron material.     

Comprehensive salient-pole synchronous machine parametric designanalysis using time-step finite element-state space modeling techniques

This paper details the application of a time-stepping coupled finite element-state space (CFE-SS) model to predict a salient-pole synchronous generator's parameters and performance, including damper bar current profiles and bar losses as well as iron core (including pole face) losses, under various operating conditions. The CFE-SS modeling environment is based on the natural ABC flux linkage frame of reference, which is coupled to a time/rotor stepping FE magnetic field and machine winding inductance profile computation model. This allows one to rigorously include the synergism between the space harmonics generated by magnetic saturation and machine magnetic circuit as well as winding layout topologies, and the time harmonics generated by the nonsinusoidal phase currents, ripple rich field excitation and damper bar currents. The impact of such synergism between these space and time harmonics on damper bar current profiles and losses, iron core losses, various machine winding current, voltage and torque profiles/waveforms is studied here for a 10-pole, 44.9 kVA, 17,143 RPM, 1428.6 Hz, 82 V (L-N), wound-pole aircraft generator     

Dynamic study of an electronically brushless DC machine viacomputer simulations

The authors analyze a machine with a conventional DC armature winding on the stator which does not have a field winding connected with slip rings. At positions where the winding would have been attached to a commutator segment, a transistor switch is attached instead. The rotor contains a permanent magnet field. The lap wound stator winding is sequentially commutated by a system consisting of a position sensor and logic circuitry. Analytical expressions for a full pitch lap wound machine are given. A computer simulation of the machine was implemented. The results serve to illustrate the considerations which must be made in the design of this type of machine, in particular the effects of the winding design on commutation and cost efficiency     

Analysis of generically configured PSC induction machines

A multiple reference frame based model of a generically configured permanent split capacitor (PSC) induction machine is set forth. The model provides for the possibilities of asymmetrical winding arbitrary tapping of the main winding, and shifting of the auxiliary winding from the quadrature position. The model is valid for both steady-state and transient analysis, and features state variables which are constant in the steady-state. This feature makes the model readily linearizable for derivation of transfer functions. In addition, a procedure for estimation of the machine parameters based on standstill measurements is set forth. Finally, both the model and the parameter measurement scheme are verified experimentally     

Two-Step Method for Identification of Nonlinear Model of Induction Machine

A two-step method is applied for parameter identification of a saturated electromechanical model of an induction machine (IM). The k-factor cross saturation technique is used to account for iron saturation. Balanced and unbalanced short-circuits armature current waveforms of this machine are less sensitive to variations in the mechanical parameters. Conversely, any change in these parameters has a strong impact on the start-up test. Accordingly, in the proposed estimation method, the online double-line-to-neutral short-circuit test is performed to estimate the electrical parameters of the machine and the results obtained are then used to compute the mechanical parameters from the starting test. The good agreement of the estimated results with actual data attests to the effectiveness and suitability of the proposed algorithm in computing the electromechanical parameters of these machines.     

Modeling of effects of skewing of rotor mounted permanent magnetson the performance of brushless DC motors

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     

Maximum likelihood estimation of synchronous machine parametersfrom standstill time response data

This paper presents a systematic approach for identification of a three-phase salient-pole synchronous machine rated at 5 kVA from standstill time-domain data. Machine time constant models and the equivalent circuit models are identified and their parameters are estimated. The initialization of the estimated parameters is achieved by the Laplace transformation of the recorded standstill time-response data and the derivation of the well-known operational inductances. The estimation is performed using the Maximum Likelihood algorithm. Based on the best estimated equivalent circuit models, simulation studies using the measured on-line dynamic responses are performed to validate the identified machine models     

Effects of toothless stator design on dynamic model parameters ofpermanent magnet generators

The effects of toothless stator design on the dynamic model parameters of permanent magnet (PM) generators are presented. These parameters, which include inductances and induced back EMFs, are determined for a 75 kVA, 208 V, 400 Hz, two-pole, permanent magnet generator. Two particular stator designs, a toothless stator, and a conventional type stator (with iron teeth), are considered. The method which is used to determine these parameters is general in nature and is based on the use of a series of magnetic field solutions. A validation of the computed EMF and inductance values based on experimentally obtained data is given. The results of using these parameters in a state space model in the abc frame of reference to study the effects of a toothless stator design on the PM generator synchronous inductances are presented. Based on that, it is demonstrated that the effects of rotor saliency and armature loading on the machine parameters are minimized in the case of the toothless design