This paper deals with the detection of saturation in the magnetic core of a welding transformer which is a part of a middle-frequency direct current (MFDC) resistance spot welding system (RSWS). It ...consists of an input rectifier, which produces dc bus voltage, an inverter, a welding transformer, and a full-wave rectifier that is mounted on the output of a transformer. During normal RSWS operation welding transformer's magnetic core can become saturated due to the unbalanced resistances of both transformer secondary windings and different characteristics of output rectifier diodes, which causes current spikes and over-current protection switch-off of the entire system. In order to prevent saturation of the transformer magnetic core, the RSWS control must detect that the magnetic core is approaching the saturated region. The aim of this paper is to present a reliable method for detection of magnetic core saturation that does not require an additional sensor. It is based on the artificial neural network (ANN). Its input is the measured primary current of the welding transformer. The applied ANN is trained to recognize the waveform of the current spikes in the primary current caused by the magnetic core saturation, which is used for magnetization level detection.
The paper deals with the detailed analysis of the flux linkages, motor thrust and friction force of the linear synchronous reluctance motor (LSRM). The flux linkages, the motor thrust and the ...friction force are determined experimentally. Their characteristics, given as functions of the position and the direct and the quadrature axis currents, are used to introduce the nonlinear dynamic LSRM model. The agreement between measured and calculated results in the case of the test at blocked primary and in the ease of kinematic control is very good. The presented results show that the motor thrust calculated by using flux linkages should be used with caution especially if an accurate position dependent motor thrust is required.
Abstract In a single-surgeon series of 119 patients with unilateral primary uncemented total hip arthroplasty, four leg-length discrepancy measurement methods (absolute, relative, trochanteric, ...standardized-trochanteric) were analyzed for their impact on WOMAC score, Oxford Hip Score and self-perceived leg-length discrepancy. After adjustment for age, gender and BMI, postoperative WOMAC scores correlated only with clinical absolute measurements of leg elongation ( P = 0.05). Self-perceived leg-length discrepancy corresponded best to the clinically measured relative leg-length discrepancy (11 mm perceived vs. 7 mm unperceived; P = 0.04) while there was no significant correspondence with radiographic measurements or leg elongation magnitudes. Within the < 10 mm range of mean postoperative leg length discrepancy in the studied series, its impact on the overall clinical satisfaction was detectable but not considerable.
Identification of linear synchronous reluctance motor parameters Stumberger, G.; Stumberger, B.; Dolinar, D.
Conference Record of the 2000 IEEE Industry Applications Conference. Thirty-Fifth IAS Annual Meeting and World Conference on Industrial Applications of Electrical Energy (Cat. No.00CH37129),
2000, Letnik:
1
Conference Proceeding
The paper deals with the identification of parameters of a two-axis linear synchronous reluctance motor (LSRM) dynamic model. The model parameters are identified by experiments performed on an LSRM ...using a controlled voltage source inverter. The current dependent direct- and quadrature axis inductances are identified by experiments and calculated by the finite element method. The calculated inductances are compared with the inductances identified by experiments. As the translation range of the tested LSRM is limited, the proposed parameter identification procedure has been verified indirectly through the comparison of simulation and experimental results in the case of kinematic control. Compared are the reference and the actual position, speed, current and voltage trajectories obtained by experiment and by simulation. The agreement of the results is good.
The paper presents the evaluation of saturation and cross-magnetization effects in interior permanent magnet synchronous motor (IPMSM) over the entire range of direct and quadrature axis excitation. ...The conventional two-axis machine model is modified in order to include the influence of saturation and cross-coupling effects on the variation of self and cross-coupling inductances in the direct and the quadrature axis. The two-axis machine model parameters are evaluated by experiments performed on a IPMSM using a controlled voltage source inverter and are compared with parameters values evaluated by the finite element method. The evaluation of two-axis machine model parameters reveals significant saturation and cross-magnetization effects in both axes, especially in the flux-weakening regime.
The paper reflects an analysis of thermal behaviour of a half-bridge IGBT power module. The main objective of this research is achieved by proposing analytical, numerical and experimental methods for ...boundary conditions determination and temperature calculation. The analytical approach is carried out from basic heat equation and corresponding boundary conditions. The modelling of boundary conditions offers an entirely new definition for temperature calculation for this particular case. The finite element method (FEM) investigates the influence of different boundary conditions on the transient thermal analysis. The experiment confirms the obtained results.
Pillars in underground limestone mines are required to support the overburden and provide a safe, stable working environment for mining personnel and equipment. Pillar stability was assessed by the ...National Institute for Occupational Safety and Health in underground limestone mines in the Eastern and Midwestern United States. It was found that current mine layouts have been successful in providing support to the overburden, while a small number of isolated pillar failures were observed. The stable pillar layouts and failed pillars were plotted on a chart that demonstrates the relationship between pillar width-to-height ratio and pillar stress. The results show that pillar failures occurred at the lower range of width-to-height ratios and can occur at relatively low stress levels. Zones indicating the potential risk of pillar instability are shown on the chart, based on hazards associated with the onset of rib spalling, large angular discontinuities and unconfined pillars. The chart can assist limestone mine planners to evaluate potential instability in current or new pillar layouts that are similar to those included on the stability chart.
This paper deals with a middle frequency resistance spot welding system. It consists of a semiconductor input converter, a single phase welding transformer with one primary coil and two secondary ...coils, and a full-wave output rectifier connected to the transformer's secondary coils. The unwanted current spikes often appear in the transformer's primary coil current during steady state operation, which was proven by measurements. The numerical analysis, based on a nonlinear model of the discussed system, has shown that these current spikes are caused by the interaction among asymmetrical design of the transformer, its magnetically nonlinear behavior, and unequal characteristics of the diodes in the output rectifier. This undesirable phenomenon can be efficiently avoided by the passive or active approach proposed in this work. The passive approach is based on the correct positioning of carefully chosen diodes in the output rectifier, while the active one includes the closed loop welding current control and the closed loop control of flux density in the transformer's iron core. The consequent employment of the active approach makes possible reduction of the transformer's iron core size at the same power of the spot welding system.
PDF
