Nonlinear Time-stepping Finite Element Method Research Articles

Characteristics Improvement of Claw-Pole Alternators for Automobile Applications by Analyzing 3-D Flux Paths in Rotors

In this article, we investigate rotor design of claw-pole alternators for automobile applications to increase output and decrease core loss. First, the electromagnetic field distribution is calculated by the three-dimensional (3-D) nonlinear time-stepping finite-element method, which considers eddy currents generated at a solid rotor core and a laminated stator core. From the results, a novel rotor design is proposed. Experimental verification is carried out to confirm the advantage of the proposed design. The mechanism of output increase and loss reduction by the proposed alternator is revealed by analyzing detailed 3-D flux paths in the rotors.

Adaptive finite element meshing at each iterative calculation for electromagnetic field analysis of rotating machines

AbstractIn this paper, we propose a novel algorithm of the nonlinear time‐stepping finite element method for analyses of rotating machines. In the method, the adaptive finite element meshing is applied at each nonlinear and time‐stepping iterative calculation with the interpolate calculations of the potentials from the previous step. The primary finite element mesh at each time step is obtained from the final mesh of the previous time step with minor modification due to the movement of the rotor. The proposed method is applied to the characteristics calculations of a permanent magnet motor and an induction motor to verify the method's validity and its usefulness. It is clarified that the proposed method gives almost identical results to the conventional adaptive meshing method whereas the calculation time is reduced to less than 1/10 in most cases. As a result, the proposed method can reduce not only the time of making mesh manually but also the calculation time compared with the usual finite element method without adaptive meshing. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(3): 78–91, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20308

Effect of Armature Reaction of a Permanent-Magnet Claw Pole SMC Motor

The finite-element method enables an accurate analysis for the study on effects of armature reaction in electromagnetic devices, particularly those with complex structures and three-dimensional (3-D) magnetic flux paths. This paper investigates the effects of armature reaction on the parameters and performance of a permanent-magnet (PM) claw pole motor with soft magnetic composite (SMC) core, based on the magnetic field analysis using the 3-D nonlinear time-stepping finite-element method. The current in the stator winding produces a magnetic field, which interacts with the air gap field generated by the rotor magnets. Consequently, the air gap flux density profile against the rotor position produced by the rotor magnets deviates, and so does the back electromotive force. Since the stator field also changes the local saturation level of the magnetic core, the winding inductance varies with both the rotor position and stator currents. The inclusion of these effects in terms of parameter variations in the motor model is important for accurate performance analysis. On the other hand, the pattern of inductance against the rotor position and stator currents can be employed to effectively predict the rotor position at standstill and low speeds for robust sensorless control. The parameter computations are verified by experimental results on the PM claw pole SMC motor prototype

Adaptive Finite Element Meshing at Each Iterative Calculation for Electromagnetic Field Analysis of Rotating Machines

In this paper, we propose a novel algorithm of the nonlinear time-stepping finite element method for analyses of rotating machines. In the method, the adaptive finite element meshing is applied at each nonlinear and time-stepping iterative calculation with the interpolate calculations of the potentials from the previous step. The primary finite element mesh at each time step is obtained from the final mesh of the previous time step with minor modification due to the movement of the rotor. The proposed method is applied to the characteristics calculations of a permanent magnet motor and an induction motor to verify the method's validity and its usefulness. It is clarified that the proposed method gives almost identical results to the conventional adaptive meshing method whereas the calculation time is reduced to less than 1/10 in most cases. As a result, the proposed method can reduce not only the time of making mesh manually but also the calculation time compared with the usual finite element method without adaptive meshing. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(3): 78–91, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20308

Finite-Element Analysis of Electromechanical Field of a HDB Spindle Motor at Elevated Temperature

This research presents a finite element method to analyze the electromechanical field of a hydrodynamic-bearing (HDB) spindle motor of computer hard disk drives at elevated temperature. Magnetic field is analyzed by the nonlinear time-stepping finite element method considering the switching action of PWM inverter, and magnetic force and torque are calculated by the Maxwell stress tensor. Mechanical motion of a rotor is determined by Newton's equation of motion, in which the hydrodynamic bearing force and friction torque are calculated by solving the Reynolds equation. Both the analyses of magnetic and mechanical field are combined in a closed loop to control the speed using PWM. Simulation results are verified by the experiments. This research also investigates the electromechanical performance of a HDB spindle motor at elevated operating temperature.

Harmonic Torque Calculation of Induction Motors Using Electromagnetic Field Analysis

In this paper, we investigate effects of harmonic electromagnetic field to torque characteristics of induction motors from both side of experiment and electromagnetic field analysis. The characteristics of two kinds of the aluminum cage three-phase induction motors are measured and calculated. One is with the closed rotor slots. The other is semi-closed. In the experiment, the negative torque at synchronous speed is measured by driving the induction motor by the synchronous permanent magnet motor. The total torque at load condition is also measured by the torque detector. In the analysis, the harmonic magnetic fields, the harmonic losses and the harmonic torques at each time and space harmonic order are calculated using the nonlinear time-stepping finite element method to clarify the mechanism of the harmonic torque generation. The measured and the calculated results agree well. It is clarified that the negative torque caused by the slot harmonics at the rated load condition is not negligible and that the negative torque is mainly generated by the harmonic core losses.

Finite-element analysis of an electromechanical field of a BLDC motor considering speed control and mechanical flexibility

This research presents a finite-element analysis of the electromechanical field of a BLDC motor considering speed control and mechanical flexibility. The magnetic field is analyzed by the nonlinear time-stepping finite-element method considering the switching action of the pulse width modulation (PWM) inverter. Magnetic force and torque are calculated by the Maxwell stress tensor. Mechanical motion of a rotor is determined by a time-stepping finite-element method considering the flexibility of shaft, rotor, and bearing. Both magnetic and mechanical finite-element equations are combined in the closed loop to control the speed using PWM. Simulation results are verified by the experiments, and they are in good agreement with the experimental results.