Efficient dynamic synchronous machine simulation with harmonics

Within this paper, an efficient procedure for the dynamic simulation of faulted synchronous machines operating in the presence of harmonics is presented. The algorithm employs steady-state frequency domain techniques for simulation of the transmission system sequence networks and time domain methods for synchronous machines represented in the odq frame of reference. The procedure affords greater accuracy than conventional fault analysis techniques based strictly on steady-state methods, yet requires far less computational time than full system dynamic simulations such as those using the EMTP     

A frequency-domain maximum likelihood estimation of synchronousmachine high-order models using SSFR test data

The authors propose a numerical scheme for processing noisy signals originating from standstill frequency response (SSFR) tests on synchronous machines. Instead of using a univariate nonlinear least-squares procedure to fit only the weighted sum of magnitude responses, they minimize a multivariate prediction error criterion based on the determinant of the residuals covariance matrix. The algorithm pertains to a large class of prediction error methods and results in a multiresponse nonlinear regression procedure related to the maximum likelihood viewpoint when the residuals distribution is Gaussian. To demonstrate the efficiency of the proposed scheme, the implementation was tested using noisy simulated data, based on the Rockport model 3.3. It is shown, using actual data from the Nanticoke turbogenerator, dating back to the EPRI-project RP-9997-2 (1980), that the frequency-domain maximum likelihood approach can be effective for direct estimation of generalized circuits with up to five equivalent windings per axis, providing satisfactory predictions of both magnitude and phase as far as the 16th harmonic     

Determination of synchronous machine parameters using networksynthesis techniques

This paper deals with the problem of the determination of synchronous machine parameters starting from two-port information. Network synthesis techniques are used to show that no unique solution can be found for models containing more than one damper winding. Only a limited number of parameters can be determined in a unique way from two-port information     

Identification of synchronous machine parameters using loadrejection test data

This work shows a computational methodology for the determination of synchronous machines parameters using load rejection test data. By machine modeling one can obtain the quadrature parameters through a load rejection under an arbitrary reference, reducing the present difficulties. The proposed method is applied to a real machine     

Test and simulation of a solar-powered absorption cooling machine

At the Institut fuer Thermodynamik und Waermetechnik (ITW) a solar cooling machine has been built for demonstration purposes. The main part of the device is an absorber/desorber unit which is mounted inside a concentrating solar collector. The working pair consists of NH₃ used as the refrigerant and SrCl₂ used as the absorbing medium. Performance of the solar refrigeration unit was measured in a field test. The working principle of a periodically working, dry absorption cooling machine will be explained using the demonstration machine as an example. Results obtained from a field test performed in 1995 are presented and discussed. Further, a simulation program for the numerical simulation of a solar-powered dry absorption cooling machine has been developed and tested.     

Harmonic compensation using a synchronous machine with resonantfield circuits

This paper deals with a harmonic compensation method using a synchronous machine with resonant field circuits. Harmonics have become one of the major problems in power systems and a lot of methods of harmonic suppression have been studied. The authors have proposed a new method of harmonic suppression using a synchronous machine excited with the 6th harmonic current. This paper shows that armature inductances for the 5th or 7th harmonics decrease when the field circuits are connected to capacitors resonating at the 6th harmonic. The variations of armature impedances are explained theoretically by Park's equations. The optimal capacitances are selected so as to resonate with field inductances for the short-circuited armature. The experiments to suppress the 5th and 7th harmonics using the synchronous machine are successful     

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     

IPM synchronous machine drive response to symmetrical and asymmetrical short circuit faults

A closed-form solution is presented for the steady-state response of interior permanent magnet (IPM) synchronous machines to symmetrical short circuits including the effects of q-axis magnetic saturation. Machine response to single-phase asymmetrical short circuits is also investigated. Experimental data are presented to verify predicted behavior for both types of short circuits. It is shown that single-phase asymmetrical short circuit faults produce more severe fault responses with high pulsating torque and a significant threat of rotor demagnetization. A control strategy that purposely transitions such faults into symmetrical three-phase short circuits can minimize the fault severity and associated demagnetization risks. Implications for the design of IPM machines with improved fault tolerance are discussed.     

The DC decay test for determining synchronous machine parameters:measurement and simulation

The DC flux decay test has been proposed as an attractive method of extracting synchronous machine parameters. This test is an attractive alternative to the variable-frequency static impedance test. It is quicker and easier to perform and with carefully chosen short-circuit resistance can give good values for transient and subtransient parameters (although ideally a test is required for each). With the machine stationary, direct current is passed through two phases and the decay of current is observed following the short-circuiting of the supply. Tests on two large turbine-generators performed and simulated by finite-element electromagnetic calculations are reported. The combination of tests, calculations, and analysis has enabled the cause of various difficulties associated with the test to be isolated. Recommendations are made to improve the accuracy of measurements     

Analysis of self-dual excited synchronous machine. II. Smallperturbation model and dynamic behaviour

For Part I, see ibid., vol.3, no.2, June 1988, pp.305-314. Having developed the general mathematical model of an isolated self-dual excited synchronous machine in part I, the author derives the small displacement equations for the two alternative excitation systems. A novel analytical method is developed for the small displacement model of the self-dual excited synchronous machine that requires less CPU time than previously. This method is general and take into account the variation of the firing angle and the automatic feedback control circuit during small disturbances. The coefficients of the characteristic equation and the eigenvalues are calculated to study the dynamic stability of the system. The effects of the ratio of the two field currents, the inertia constant, the power factor, and the gain and time constant of the feedback control circuit on the dynamic stability of the system are investigated. The results obtained show that the self-dual excited synchronous machine with the two field windings having MMF ratios between 0.75 and 1.5 presume better dynamic stability bounds than the conventional self-excited synchronous machine. In the range where the other proposed excitation system can be compared with the conventional machine, it has been found that the developed system has the same dynamic stability response with the advantage that the effect of automatic voltage regulator is implicitly included with a smaller time constant. Including the change of the firing angle during the small disturbance, a pronounced effect on the dynamic stability of the system results     

Influence of saturation on estimated synchronous machine parametersin standstill frequency response tests

In this paper the measurement results of a series of standstill frequency response tests, performed at different magnetization levels, are discussed. For each data set an individual model is estimated, which allows the variation of the different parameters to be seen as a function of the saturation. Further, an estimator is presented which uses the different data sets to estimate one global model, including the field to armature turns ratio. Finally the expected error level of a more traditional saturated synchronous machine model is studied     

Impact of dynamic cross-saturation on accuracy of saturatedsynchronous machine models

Cross-saturation effect in synchronous machines has been a subject of considerable attention. Inclusion of the cross-saturation in the machine model has two consequences. The first one, called here “steady-state cross-saturation”, consists of dependence of the steady-state d-q axis magnetizing inductances on the currents in both axes. The second one, termed here “dynamic cross-saturation”, is the existence of nonzero elements in the system matrix, that describe cross coupling between d- and q-axis. Dynamic cross-saturation appears in all the saturated machine models, regardless of the selected set of state-space variables, with the exception of the winding flux linkage state-space model. The aim of this paper is to compare behavior of various models when dynamic cross-saturation is neglected. It is shown that the impact of dynamic cross-saturation on accuracy depends on the selected set of state-space variables. In the majority of cases omission of dynamic cross-saturation leads to very inaccurate results. However, it is found that for one particular class of models, omission of dynamic cross-saturation has practically no impact on accuracy. These models therefore fully describe the complete saturation effect by means of only continuous variation of the d-q axis magnetizing inductances     

Identification of synchronous machine parameters using a multipleinput multiple output approach

This paper presents an alternative method for the identification of the d-axis parameters of a synchronous machine. The first part of the paper describes a multiple input multiple output (MIMO) broadband excitation and measurement method which is more time efficient than the standard standstill frequency response (SSFR) method. The second part describes a MIMO frequency domain identification procedure which estimates the d-axis parameters in 3 steps. The proposed identification procedure is self starting. It does not require starting values or other prior information. The measurement method and the identification procedure are tested on a 20 kVA salient pole synchronous machine     

Estimation of a global synchronous machine model using a multiple-input multiple-output estimator

In this paper, the measurement results of a series of standstill frequency-response (SSFR) tests, performed at different magnetization levels, are discussed. For each data set, an individual d-axis model is estimated, which allows seeing the variation of the different parameters as a function of saturation. A global estimator is presented which uses the different data sets to estimate one global model, including the field-to-armature turns ratio. The global estimator is based on an impedance matrix representation of the synchronous machine. This global estimator assumes that only the d-axis main inductance is saturation dependent. The individual estimated models justify this assumption. Finally, the relative additional error of the global estimated d-axis equivalent circuit with the individual estimated ones is studied. The measurement results discussed in this paper are obtained on a four-pole 130-kVA synchronous machine.     

Analysis of leakage flux distributions in a salient-pole synchronous machine using finite elements

It is important to understand the relationship between iron core configurations and leakage flux distributions to get a better design of synchronous machines. This paper presents a method for calculating the steadyand transient-state leakage flux distributions in salient-pole synchronous machines. The method provides information on leakage flux distributions that cannot be obtained by terminal quantities. The method analyzes the leakage inductances that properly represent the corresponding leakage fluxes. They are calculated using the gap flux distributions by finite elements with magnetic saturation. The calculated leakage inductances of a synchronous machine under various loads are also shown and the relationship between the inductances and magnetic saturation is discussed.     

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     

Rotor design optimization of synchronous reluctance machine

It is demonstrated that the rotor design of synchronous reluctance machines can be optimized in terms of a key geometric parameter, i.e., the ratio of the rotor insulation width to the rotor iron width so as to obtain maximum torque production. The equation which gives the maximum motor power factor in terms of the saliency ratio has been derived and it is shown that the power factor of 0.8 is a realizable value with the optimal rotor design. An experimental motor has been fabricated and the results of measurements of the motor parameters prove the validity of the rotor design optimization     

Synchronous machine steady-state stability analysis using anartificial neural network

In the developed artificial neural network, those system variables which play an important role in steady-state stability, such as generator outputs and power system stabilizer parameters, are used as the inputs. The output of the neural net provides the information on steady-state stability. Once the connection weights of the neural network have been learned using a set of training data derived offline, the neural net can be applied to analyze the steady-state stability of the system in real-time situations where the operating conditions change with time. To demonstrate the effectiveness of the proposed neural net, steady-state stability analysis is performed on a synchronous generator connected to a large power system. It is found that the proposed neural net requires much less training time than the multilayer feedforward network with back-propagation-momentum learning algorithm. It is also concluded from test results that correct stability assessment can be achieved by the neural network