The impact of magnetic nonlinearities and cross-coupling effects on the properties of the discussed radial active magnetic bearings (AMBs) is evaluated in the entire operating range. The ...characteristics of flux linkages and radial force are all determined by finite element computation, while the current and position dependent partial derivatives of the flux linkages are calculated by analytical derivations of the continuous approximation functions. Calculated current and position-dependent partial derivatives, as well as the radial force characteristics are incorporated into the proposed dynamic AMB model. The results presented show that the magnetic nonlinearities and cross-coupling effects can change the electromotive forces and the radial force considerably. These disturbing effects have been determined and can be incorporated into the real-time realization of nonlinear control in order to achieve cross-coupling compensations.
The magnetically nonlinear and anisotropic iron core model of a synchronous reluctance motor (SRM) is presented. The iron core model is given by the current-dependent flux linkages and their partial ...derivatives. It is included in a dynamic SRM model and confirmed through the comparison of measured and calculated results in the case of current-controlled linear synchronous reluctance servomotor.
We studied 32 hips (in 27 patients) treated by intertrochanteric osteotomy for osteonecrosis of the femoral head. Average follow-up was 17 (range 9-26) years. There were 22 men and 5 women with an ...average age of 39 (range 25-55) years. Eleven hips were classified as Ficat stage II, 19 as stage III and two as early stage IV. Nine hips showed collapse of the femoral head within 3 years after operation and in six hips collapse occurred after 3-8 years. In 13 hips slow progression with incipient signs of arthrosis was noted 8 years after surgery. Four hips with a moderate degree of necrosis at the time of surgery showed no radiological progression 9-26 years after operation. We recommend intertrochanteric osteotomy for patients with Ficat stage II and early stage III, provided that they still have a good range of motion in the hip.
The paper deals with the Finite Element Method (FEM) based procedure for determination of operating point dependent inductances of a Linear Synchronous Reluctance Motor (LSRM). Special attention is ...paid to the effects of cross magnetization and saturation on the inductances of LSRM under load conditions. To achieve a deeper insight into the cross magnetization and the saturation phenomena a standard two-axis LSRM dynamic model is modified. The modified dynamic LSRM model contains explicit terms for the direct and the quadrature axis self-inductances and explicit terms for the cross coupling inductances. The last ones appear as a consequence of the cross coupling between the direct and the quadrature axis. All inductances of the modified LSRM model are current dependent.
Advanced Control of a Resistance Spot Welding System Klopcic, Beno; Dolinar, Drago; Stumberger, Gorazd
IEEE transactions on power electronics,
2008-Jan., 2008, 2008-1-00, 20080101, Letnik:
23, Številka:
1
Journal Article
Recenzirano
This paper deals with a middle-frequency resistance spot welding system. It consists of an input converter, welding transformer, and a full-wave rectifier mounted at the transformer secondary. The ...welding current at the full-wave rectifier output is normally controlled by the pulse width modulated primary voltage of the transformer supplied by the input converter. The unequal ohmic resistances of the two transformer's secondary circuits and the different characteristics of the diodes of output rectifier certainly lead to the magnetic saturation which, consequently, causes the unwanted spikes in the transformer's primary current and over-current protection switch-off. This disadvantage of classical spot welding systems is completely eliminated by the proposed advanced hysteresis controller (AHC), which keeps transformer iron core saturation within prescribed bounds regardless of how unequal the ohmic resistances and diodes' characteristics in the transformer's secondary circuits are. This is achieved by a combined closed-loop control of the welding current and closed-loop control of the iron core saturation level. The proposed AHC assures a very short rise time of the welding current and the best possible utilization of the transformer iron core.
The paper presents the use of the finite element method for determining the parameters of a two-axis model of a three-phase cage induction machine. The model parameters are obtained from the finite ...element field solutions. The saturation of the motor is taken into account in calculation of the flux distribution by using a static nonlinear vector potential solution. The linear time harmonic vector potential field solution is used for the inductances determination. All the inductances are determined as functions of the magnetizing current. Rotor skew is also taken into account. The accuracy of the described identification procedure is verified through laboratory measurements of the parameters.
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