Effects of DC-Field Excitation on the Incremental Inductance of a Variable Flux Reluctance Machine

This paper presents a method for the computation of the incremental inductances in a 12/10 variable flux reluctance machine using the hybrid analytical modeling coupled with a fixed-point nonlinear solver. The variation of incremental and apparent inductance with respect to the dc-field excitation is investigated for both zero and non-zero ac-field excitations. The results show that the difference between both inductance values is not negligible after 25 A/mm2 dc-current density for the investigated benchmark without the ac field. Moreover, when a non-zero ac field is introduced in addition to the dc-field, the apparent inductance becomes misleading not only under magnetic saturation but also under low excitation in the linear region of the saturation curve. The results obtained with the proposed nonlinear hybrid model are compared with the finite element method in terms of magnetic flux density distribution and incremental inductance value. The root-mean-square discrepancy of magnetic flux density distribution is found to be 37.6 mT. Furthermore, the discrepancy between incremental inductance results of the proposed method and the finite element model is calculated as 1.43%, while the proposed approach requires less post-processing and necessitates ten times less number of degrees-of-freedom

Convergence analysis of the fixed-point method with the hybrid analytical modeling for 2-D nonlinear magnetostatic problems

This paper presents the convergence analysis of the fixed-point method (FPM) to model the nonlinear magnetic characteristics of a 2-D magnetostatic problem. In this study, FPM is used as the iterative nonlinear solver of the hybrid analytical modeling (HAM) technique for the accurate computation of the magnetic field distribution. The benchmark consists of a stator with excitation windings, an airgap, and a slotless mover. The relative errors between two successive iterations are calculated using different error estimators: the attraction force on the mover, the Fourier coefficients defined in the airgap, the magnetic flux density, and the magnetic scalar potential distributions. The effect of the number of mesh elements and harmonics on the accuracy and computational cost of the model is investigated for different levels of magnetic saturation. It is observed that the maximum rate of change in the relative difference of attraction force during the iterations is found to be 0.52 under the magnetic saturation. In addition, the absolute error of the attraction force between the developed hybrid model with FPM and the finite element method (FEM) is achieved to be 0.18%, while HAM has approximately three times less number of degrees-of-freedom compared to FEM

Candidates of motor drives for 48V automotive applications

Abstract-In automotive systems, reliability and cost are paramount for the success of electrical drive systems. Considering the interior permanent magnet motor, the cost of the rareearth permanent magnet is becoming a big concern. In this paper, the switched reluctance motor, variable flux reluctance motor and synchronous reluctance motor are analyzed and compared as candidates for the 48V automotive applications. A recommendation is given for the selection of the motor drives

Multi-objective optimization of a variable flux reluctance machine for high-torque operations

This paper proposes a new multi-objective optimization approach to investigate the feasibility of 12/10 variable flux reluctance machines for heavy-duty applications requiring a high-torque generation. Eight parameters describing the geometry of the variable flux reluctance machine are optimized by the tournament selection-based genetic algorithm aiming at the minimum torque ripple, maximum torque density, and efficiency. A 2-D magnetostatic finite element method model is coupled with the nonlinear single-valued magnetization curve of the soft-magnetic material to calculate the objective function. Boundaries of the optimization variables are determined by scaling an existing design. Two constraints are introduced for the winding temperature and developed torque to reduce the number of optimization variables. The torque constraint, 500 Nm, is achieved by selecting a suitable stack length while the constraint of 100 °C maximum winding temperature is satisfied by the applied current density, which a 3-D analytical steady-state thermal model calculates. The magnetic vector hysteresis property of the soft-magnetic material is investigated at the end of the optimization to improve the estimation of torque and efficiency. The optimal variable flux reluctance machine exhibits 20.4 Nm/L torque density, 5.2% torque ripple, and 92.8% efficiency at the base speed of 1200 rpm

A novel modeling technique via coupled magnetic equivalent circuit with vector hysteresis characteristics of laminated steels

This paper proposes a method to include the anisotropic hysteresis characteristics of soft-magnetic laminated steels in the magnetic equivalent circuit (MEC) modeling. The loop-based MEC formulation is improved to handle the nonlinearity of the anisotropic magnetic hysteresis, including the dynamic classical eddy-current and excess fields. The developed MEC model is coupled with both the single-valued B-H curve (SVC) in magnetostatic and the dynamic vector hysteresis model (VHM) in transient analysis. Results with a single elementary MEC element show that an alternating magnetic field in a single direction with a peak value smaller than 300 A/m causes a discrepancy of more than 10% between the magnetic flux densities calculated by the VHM and SVC at 50 and 200 Hz excitation frequencies. Moreover, the proposed modeling technique is verified experimentally using the laminated transformer core of TEAM problem 32. The induced voltage calculated by the MEC model with the VHM demonstrates a good agreement with the measurements, while the MEC model with the SVC calculates inaccurate voltage waveforms. Lastly, the total iron loss dissipated in the transformer's iron core is investigated to verify the proposed technique under different excitation levels and frequencies up to 500 Hz. It is observed that the proposed MEC model with the vector hysteresis characteristics of laminated steels is able to calculate the iron loss accurately, while the conventional single-valued curve method fails to estimate the iron loss

High-speed slotless permanent magnet machines:modelling and design frameworks

\u3cp\u3eThis paper presents a design framework for high-speed slotless permanent magnet machines based on extended harmonic modeling (HM) technique to predict various electromagnetic properties and torque distribution. The developed models for generic design framework are able to evaluate slotless PM machines' topologies with a wide range of 3D slotless windings, (including those with skewing), and can be also used for future design optimization routines.\u3c/p\u3

Effects of DC-Field Excitation on the Incremental Inductance of a Variable Flux Reluctance Machine

This paper presents a method for the computation of the incremental inductances in a 12/10 variable flux reluctance machine using the hybrid analytical modeling coupled with a fixed-point nonlinear solver. The variation of incremental and apparent inductance with respect to the dc-field excitation is investigated for both zero and non-zero ac-field excitations. The results show that the difference between both inductance values is not negligible after 25 A/mm2 dc-current density for the investigated benchmark without the ac field. Moreover, when a non-zero ac field is introduced in addition to the dc-field, the apparent inductance becomes misleading not only under magnetic saturation but also under low excitation in the linear region of the saturation curve. The results obtained with the proposed nonlinear hybrid model are compared with the finite element method in terms of magnetic flux density distribution and incremental inductance value. The root-mean-square discrepancy of magnetic flux density distribution is found to be 37.6 mT. Furthermore, the discrepancy between incremental inductance results of the proposed method and the finite element model is calculated as 1.43%, while the proposed approach requires less post-processing and necessitates ten times less number of degrees-of-freedom

Surge control of the electrically driven centrifugal compressor

This paper presents a method of the energy efficiency and the operational performance improvement of the electrically driven air compression system. The key innovation of the proposed method-the active surge suppression of the centrifugal compressor by means of the speed control of the electrical drive has been experimentally validated. This method allows the load following operation of the compression system keeping the fast response on the application demands. The described control approach is considered to be applied to the Balance-of-Plant of a fuel-cell power syste

Convergence analysis of the fixed-point method with the hybrid analytical modeling for 2-D nonlinear magnetostatic problems

This paper presents the convergence analysis of the fixed-point method (FPM) to model the nonlinear magnetic characteristics of a 2-D magnetostatic problem. In this study, FPM is used as the iterative nonlinear solver of the hybrid analytical modeling (HAM) technique for the accurate computation of the magnetic field distribution. The benchmark consists of a stator with excitation windings, an airgap, and a slotless mover. The relative errors between two successive iterations are calculated using different error estimators: the attraction force on the mover, the Fourier coefficients defined in the airgap, the magnetic flux density, and the magnetic scalar potential distributions. The effect of the number of mesh elements and harmonics on the accuracy and computational cost of the model is investigated for different levels of magnetic saturation. It is observed that the maximum rate of change in the relative difference of attraction force during the iterations is found to be 0.52 under the magnetic saturation. In addition, the absolute error of the attraction force between the developed hybrid model with FPM and the finite element method (FEM) is achieved to be 0.18%, while HAM has approximately three times less number of degrees-of-freedom compared to FEM