Additional Core Losses Research Articles

Modeling Core Losses Under Exciting Waveforms With Zero Voltage Period in Power Converters

When the exciting waveform contains the interval of zero voltage, additional core losses have been observed, but lack of a clear physical explains. These additional losses may come from two aspects. The first one is the released energy caused by the interfacial dielectric loss between the isolation layers and grains. A function with two extracted relaxation coefficients is used to model the interfacial dielectric loss. The less important one is the released energy from the parasitic inductance of core materials. Based on the microscale material structure, an equivalent eddy current loss circuit model is proposed in this article, to include these two aspects. Based on the proposed model, core losses in N87 and 3C90 materials have been predicted successfully. The experimental results are in agreement with both theoretical analyses and simulation results.

Improvement of critical gradient model and establishment of an energetic particle module for integrated simulation

Based on the critical gradient model , the combination of the TGLFEP code and EPtran code is employed to predict energetic particle (EP) transport induced by Alfvén eigenmodes (AEs). To be consistent with the experimental results, the model was improved recently by taking into consideration the threshold evolution and orbit loss mechanism. The threshold is modified to be the normalized critical gradient ((d<i>n</i>/d<i>r</i>)/(<i>n</i>/<i>a</i>)) instead of the critical gradient (d<i>n</i>/d<i>r</i>), and the new threshold is defined as a function inversely proportional to the EP density as obtained by the TGLFEP code. Additionally, the EP loss cone calculated by ORBIT is added into the EPtran code, which provides an important additional core loss channel for EPs due to finite orbits. With these two improvements, the EP redistribution profiles are found to very well reproduce the experimental profiles of two DIII-D validation cases (#142111 and #153071) with multiple unstable AEs and large-scale EP transport. In addition, a neural network is established to replace TGLFEP for critical gradient calculation, and EPtran code is rewritten with parallel computing. Based on this, a module of EP is established and it is added into the integrated simulation of OMFIT framework. The integrated simulation of HL-3 with AE transported neutral beam EP profile indicates that EP transport reduces the total pressure and current as expected, but under some condition it could also raise the safety factor in the core.

Core Loss Analysis and Modeling of a Magnetic Coupling System in WPT for EVs

The magnetic core is an important part of the magnetic coupling system in wireless power transmission (WPT) for EVs. It helps to increase the coupling coefficient and reduce magnetic field leakage. However, it also brings additional core loss. While the traditional core loss model cannot be used directly due to the uneven distribution of the magnetic flux density, this paper focuses on the flux density distribution in the disk core of a WPT system. Based on a finite element analysis (FEA) simulation and a theoretical magnetic flux density distribution analysis, a mathematical model of magnetic flux density distribution is built, which is regarded as a quadratic function. Through this model, the flux density distribution can be calculated by the electrical and mechanical specifications of the magnetic coupling system. Combining the model of flux density distribution, the disk core loss model of the WPT system is proposed—the idea of which is dividing the disk core into several circle sheets firstly, and then summing the core loss of all circle sheets. Finally, the FEA simulation results verify the proposed model as being correct and flexible.

Magnetic Properties of Silicon Steel after Plastic Deformation.

The energy efficiency of electric machines can be improved by optimizing their manufacturing process. During the manufacturing of ferromagnetic cores, silicon steel sheets are cut and stacked. This process introduces large stresses near cutting edges. The steel near cutting edges is in a plastically deformed stress state without external mechanical load. The magnetic properties of the steel in this stress state are investigated using a custom magnetomechanical measurement setup, stress strain measurements, electrical resistance measurements, and transmission electron microscopic (TEM) measurements. Analysis of the core energy losses is done by means of the loss separation technique. The silicon steel used in this paper is non-grain oriented (NGO) steel grade M270-35A. Three differently cut sets of M270-35A are investigated, which differ in the direction they are cut with respect to the rolling direction. The effect of sample deformation was measured—both before and after mechanical load release—on the magnetization curve and total core energy losses. It is known that the magnetic properties dramatically degrade with increasing sample deformation under mechanical load. In this paper, it was found that when the mechanical load is released, the magnetic properties degrade even further. Loss separation analysis has shown that the hysteresis loss is the main contributor to the additional core losses due to sample deformation. Releasing the mechanical load increased the hysteresis loss up to 270% at 10.4% pre-release strain. At this level of strain, the relative magnetic permeability decreased up to 45% after mechanical load release. Manufacturing processes that introduce plastic deformation are detrimental to the local magnetic material properties.

Novel Empirical Model for Calculation of Core Losses in Permanent Magnet Machines

This article presents a simple model for the calculation of core losses in permanent magnet machines based on the total flux linkage of the stator winding. In reality, the total core losses will vary as a function of permanent magnet field and the combination of $d-q$ current components even in the case when different $d-q$ currents produce the same amount of stator winding flux linkage at a given speed. The classical model with constant equivalent core loss resistance predicts constant core losses for constant flux linkage which leads to incorrect results. The model presented in this paper expands the classical core loss resistance based model with a novel additional term which corrects the classical model and calculates an additional core loss component as a function of $d$ axis current, total flux linkage of the stator winding, and two constant parameters. The accuracy of the model is confirmed by finite element simulations and core loss measurements for the cases of an interior permanent magnet traction motor and an industrial surface permanent magnet motor (only simulations).

Control Method for Avoiding Transformer Saturation in High-Power Three-Phase Dual-Active Bridge DC–DC Converters

The classic top to down structure of electrical infrastructure is changing due to the extensive spread of renewable energy sources which are connected to medium-voltage and low-voltage grids. Especially for medium-voltage direct-current grids, the three-phase dual-active bridge (DAB) dc–dc converter is one of the most promising converter topologies, as it features bidirectional power flow and galvanic isolation at highest efficiency. Unwanted saturation of the transformer of this converter can occur, particularly for multimegawatt converters with highly efficient, low-loss transformers. The saturation leads to additional core losses, elevated voltage stress at the windings, and increased magnetostriction of the transformer core, which can result in undesired acoustic emissions. The following article presents a feedback control and modulation method that controls the DAB converter such that saturation of the transformer is avoided. The chosen approach evaluates the star-point voltage of the transformer to determine the dc component of the magnetizing current, thereby avoiding the need for expensive high-precision current sensors. The control method is analytically derived and verified by simulation. Experiments carried out using a 5 MW medium-voltage three-phase DAB converter prototype verify the presented modulation method.

The Influence of Electrical Sheet on the Core Losses at No-Load and Full-Load of Small Power Induction Motors

This paper presents the core losses and performance characteristics of a small power induction motor with the core made from different electrical sheets, supplied from mains or PWM frequency inverter at 50, 100, and 200 Hz. Field-circuit and analytical methods are used for loss calculations, taking into account the nonlinear phenomena and additional core losses. In the calculations, the characteristics of mechanical losses measured against the speed for the motors and different electrical sheets magnetization, for frequencies up to 2000 Hz, as well as losses density characteristics against the flux density were used. The results show a significant increase in core losses concomitant with the motor load increase. In addition, analytical methods were used to calculate the performance characteristics versus load power. Calculated results were verified by measurements.

Analysis on Harmonic Loss of IPMSM for the Variable DC-link Voltage through the FEM-Control Coupled Analysis

This paper describes the loss analysis based on load conditions of the air conditioning compressor motors using variable dc-link voltage. The losses of PMSM (Permanent Magnet Synchronous Motor) should be analyzed by the PWM (Pulse Width Modulation) output of inverter. The harmonic loss by the PWM cannot consider that using the current source analysis of the inverter. In addition, when the voltage of dc-link is variable with the condition of variable speed and load conditions in motor, the losses of motor are also changeable, however it is hard to analyze those losses by only electromagnetic finite element method (FEM). Therefore, this paper proposes the analysis method considering the carrier frequency of the inverter and the varying state of the dc-link voltage through the FEM-control coupled analysis. Using proposed analysis method, additional core loss and eddy current loss of permanent magnet caused by PWM could be analyzed. Finally, the validity of the proposed analysis method is verified through the comparison the result of coupled analysis with experiment.

Analytic Modeling of Inverter-Fed Induction Machines—A Practical Approach for Matching Measurement and Simulation Data

Electrical engineers rely on analytical models to design industrial induction motors for different customer-driven applications. These models are fundamental and do not normally consider additional core losses due to stamping or welding or the impact of being inverter fed. To overcome the resulting gap between analytical results and measured data, these equivalent circuit models are traditionally adapted by correction factors. This paper presents a methodology allowing the parameterization of such an analytical model based on inverter-fed load and no-load measurements carried out for several frequencies. The results show a fair agreement over a wide range of operating points, which is acceptable for daily regular industrial applications.

Variation of additional losses at no-load and full-load for a wide range of rated power induction motors

This paper presents a comparison of losses at no load and full load of six different induction motors which rated powers are between 3kW to 280kW. The results show that additional core losses are strongly dependent on the load of the motor. The reason is the saturation of rotor tips which leads to an increase of the effective slot openings and the strengthening of harmonic by the induced currents in rotor cage. That leads to significant increase in additional core losses concomitant with motor load increases. For loss calculations, field-circuit and analytical methods are used. Using the FEM is presented an in-depth analysis of the phenomena at no-load and load indicating the reasons for increasing losses at the load conditions. Additionally, improved analytical method was employed to calculate the curves of stray losses versus load power. The results for no-load losses, stray losses and efficiency are compared with the measurements and good agreement was obtained for both field-circuit and analytical method. The change of stray losses versus output power was compared with formula proposed by IEC 60034-2-1 standard. The assigned values of stray load loss were found to be generally lower than average test result for motor with rated power below 18.5kW and generally higher for motors with bigger rated power. In situations where a fixed value of stray load losses may be required the obtained curves can be used.

Calculation of core loss and copper loss in amorphous/nanocrystalline core-based high-frequency transformer

Amorphous and nanocrystalline alloys are now widely used for the cores of high-frequency transformers, and Litz-wire is commonly used as the windings, while it is difficult to calculate the resistance accurately. In order to design a high-frequency transformer, it is important to accurately calculate the core loss and copper loss. To calculate the core loss accurately, the additional core loss by the effect of end stripe should be considered. It is difficult to simulate the whole stripes in the core due to the limit of computation, so a scale down model with 5 stripes of amorphous alloy is simulated by the 2D finite element method (FEM). An analytical model is presented to calculate the copper loss in the Litz-wire, and the results are compared with the calculations by FEM.

Impact of Input Voltage Sag and Unbalance on DC-Link Inductor and Capacitor Stress in Adjustable-Speed Drives

This paper investigates the impact of input voltage unbalance and sags on stresses in the dc-bus choke inductor and dc-bus electrolytic capacitors of adjustable-speed drives (ASDs). These stresses are primarily attributable to the rectifier's transition into single-phase operation, giving rise to low-order harmonic voltages (120 Hz, 240 Hz, etc.) that are applied to the dc-link filter components. These harmonics elevate the ac-flux densities in the dc choke core material significantly above values experienced during normal balanced-excitation conditions, causing additional core losses and potential magnetic saturation of the core. It is shown that the effects of voltage unbalances and sags on the dc-link capacitor lifetime will be the same when either line inductors or a dc-link choke inductor are used if the dc choke-inductance value is twice the value of the line inductance. Simulations and experimental tests are used to verify the accuracy of predictions provided by closed-form analysis and simulation for a 5-hp or 3730-W ASD system.

Additional core losses in induction machines with pwm inverter

AbstractInduction machine drives with squirrel‐cage rotor will more and more replace the DC motor for its various advantages. The additional motor losses are essentially copper and iron losses in stator and rotor. Iron losses are significantly influenced by machine construction, magnetic materials used and supply type. Different formulae and estimations are given in the literature for these losses. In this contribution a method is presented for the calculation of additional iron losses in induction machines with PWM inverter. Two limits are deduced for the calculation of eddy‐current losses, within which the losses lie, and which agree with the theoretical basis and most empirical formulae given in the previous works. Similarly a new method is proposed for the additional hysteresis losses. The proposed methods give good results compared with the other known methods.

Performance evaluation of a dc motor fed from an asymmetrical single-phase bridge

Lack of simple methods for predicting some of the losses in a machine in service has limited the theoretical work on additional losses in DC motors with armature current ripple to the prediction of additional copper losses. The additional core losses of a machine fed from the asymmetrical single-phase bridge are predicted from equivalent circuits which contain elements for the core. A method is developed for predicting the additional ‘skin effect’ losses in armature conductors. It is proposed that, by the use of generalised charts developed, the derating of a ‘standard’ bridge-fed DC motor at a specified operating condition can be estimated from look-up tables of additional losses measured on a standard machine.