This paper deals with experimental methods for the identification of linear synchronous reluctance motor (LSRM) parameters. A magnetically nonlinear two-axis dynamic LSRM model is derived. This model ...accounts for the effects of slotting, saturation, cross-saturation, and the end effects. The parameters of the obtained model are not constant. They are given by the characteristics of the flux linkages, thrust, and friction force depending on the mover position and the direct (d) and quadrature (q) axis currents. These characteristics are determined experimentally by a controlled voltage-source inverter employing closed-loop current control in the d-q reference frame. The proposed model, experimental methods, and determined characteristics are confirmed through a comparison between the measured and calculated results. Two tests are performed: a test at the locked mover, and kinematic control at low speed. The effects of cross saturation under dynamic operating conditions and the effects of slotting can be clearly seen in the measured and calculated results.
The behavior of a power transformer (PT) depends considerably on the properties of the magnetically nonlinear iron core. This paper deals with the modeling of a three-phase, three-limb power ...transformer laminated iron core. The proposed iron core model is given by the corresponding partial derivatives of measured flux linkage characteristics. The magnetically nonlinear characteristics of flux linkages are determined by the controlled simultaneous magnetic excitation of all three limbs. This enables determination of magnetic cross couplings between different limbs, due to the saturation. The obtained iron core model integrated in the circuit model of PT is compared to the classical saturated iron core model without cross couplings, by analyzing the transient behavior of an unsymmetrically excited transformer. The numerical results obtained by the proposed iron core model agree with the measured results much better than those obtained by the existing nonlinear iron core model known from literature
The properties of magnetic material are normally described by the permeability tensor, while the magnetically nonlinear properties of electromagnetic devices (EMDs) can be described by the ...current-dependent characteristics of flux linkages. This paper presents and evaluates different experimental methods appropriate for determining the magnetically nonlinear characteristics of EMDs. The tested device is supplied by a controlled voltage source. Sinusoidal voltages, sinusoidal voltages with offset, and stepwise changing voltages are applied. Current-dependent characteristics of flux linkages are determined from the measured voltages and currents, either by numerical integration or by Fourier analysis and calculation of impedances.
In order to increase the lifetime of the total hip endoprosthesis, it is necessary to understand mechanisms leading to its failure. In this work, we address volumetric wear of the artificial cup, in ...particular the effect of its inclination with respect to the vertical. Volumetric wear was calculated by using mathematical models for resultant hip force, contact stress and penetration of the prosthesis head into the cup. Relevance of the dependence of volumetric wear on inclination of the cup (its abduction angle ϑ
A
) was assessed by the results of 95 hips with implanted endoprosthesis. Geometrical parameters obtained from standard antero-posterior radiographs were taken as input data. Volumetric wear decreases with increasing cup abduction angle ϑ
A
. The correlation within the population of 95 hips was statistically significant (P = 0.006). Large cup abduction angle minimises predicted volumetric wear but may increase the risk for dislocation of the artificial head from the cup in the one-legged stance. Cup abduction angle and direction of the resultant hip force may compensate each other to achieve optimal position of the cup with respect to wear and dislocation in the one-legged stance for a particular patient.
Different methods for voltage sag source detection are discussed. They are based either on disturbance energy, voltage-current characteristic or active (real) current component. It is shown that, in ...the cases of asymmetrical voltage sags, both current-based methods known from literature do not work well. These two methods are therefore generalised using a vector-space approach. Furthermore, three new methods are introduced using an orthogonal Clarke's transformation, which can be used to detect the sources of those voltage sags provoked by earth faults. All the discussed methods for voltage sag source detection have been tested by applying extensive simulations, laboratory tests and field testing. The results obtained show the very high effectiveness of the proposed methods, which are superior to the methods known from literature, especially for detecting sources of asymmetrical voltage sags.
This paper suggests the possibility of improving digital power transformer protection. The establishment of inrush in power transformers is becoming unreliable in existing numerical protection. An ...artificial neural network (ANN) was applied to inrush detection. The saturation of protective current transformers (CT) cannot be totally eliminated despite proper dimensioning. ANN was used for the reconstruction of distorted secondary CT currents due to saturation. In both cases, an ANN was included in the protection algorithm as an extension of the existing methods, which improved the reliability of the protection operation. The paper presents the digital protection algorithm completed in this way and the laboratory equipment by means of which experimental results were obtained. The results confirm faster and more reliable recognition of transformer inrush, as well as satisfactory reconstruction of the distorted secondary CT currents.
This paper deals with the differential evolution (DE)-based method for determining the magnetically nonlinear iron core characteristics of transformers and iron core inductors. The unknown iron core ...characteristic, approximated by the sum of exponential functions, is included in a dynamic model of the tested device. The approximation function parameters are determined by DE. The optimization objective is the best possible agreement between the measured and the dynamic model calculated currents in the time and frequency domains. Using the measured inrush currents and corresponding voltages, the magnetically nonlinear characteristic can be determined over a broad operational range. The inclusion of iron core characteristic, as determined by the proposed method, in the transformer dynamic model gives very good agreement between the measured and calculated currents in both transient and steady states.
This work presents an experimental method appropriate for determining magnetically nonlinear characteristics of electric machines which contain magnetically nonlinear and anisotropic iron core, ...damping windings, and permanent magnets. The method is based on the two-axis dynamic model of a three-phase machine with wye-connected three-phase stator winding. The d-axis is defined with the magnetic axis of permanent magnets (ldquoflux linkage vectorrdquo due to the permanent magnets), while the q-axis is displaced by electrical pi/2. The tested machine is supplied by a controlled voltage source inverter. Voltage in one axis is changed in the stepwise manner, while current in the orthogonal axis is closed loop controlled. The characteristic flux linkage versus current in the form of a hysteresis loop is determined numerically using the time behavior of measured applied voltage and responding current in the same axis. Unfortunately, the currents induced in the machine's damping windings or squirrel cage disturb the flux linkage characteristic determined in this way. Therefore, only the final points of each hysteresis loop, where the currents induced in the damping windings already died-out, can be used as correct points of the machine's magnetically nonlinear iron core characteristic. The proposed method is confirmed by the tests performed with a single three-phase stator and four different rotors: the reluctance rotor, the reluctance rotor with squirrel cage, the reluctance rotor with inserted permanent magnets, and the reluctance rotor with inserted permanent magnets and squirrel cage.
An optimization of radial active magnetic bearings is presented in the paper. The radial bearing is numerically optimized, using differential evolution-a stochastic direct search algorithm. The ...nonlinear solution of the magnetic vector potential is determined, using the 2D finite element method. The force is calculated by Maxwell's stress tensor method. The parameters of the optimized and nonoptimized bearing are compared. The force, the current gain, and the position stiffness are given as functions of the control current and rotor displacement.
A linearized model of active magnetic bearings (AMBs) is normally used for determining the settings of decentralized PID controllers, which are used in industrial applications. Parameters of the ...linearized model, i.e., current gain and position stiffness, are defined for the nominal operating point and, thus, vary according to the operating point. These variations are analyzed by the finite element (FE) computation. The obtained results show considerable variations for the discussed parameters. Therefore, AMB geometry is numerically optimized, using differential evolution in combination with FE computation. The optimization objective is a minimal variation of the current gain, and position stiffness. The optimized AMBs shows good properties according to the linearized model over the entire operating range. In this way, the robustness of the closed-loop controlled AMB system is increased.
