Dan M. Ionel

On the variation with flux and frequency of the core loss coefficients in electrical machines

A model of core losses, in which the hysteresis coefficients are variable with the frequency and induction (flux density) and the eddy-current and excess loss coefficients are variable only with the induction, is proposed. A procedure for identifying the model coefficients from multifrequency Epstein tests is described, and examples are provided for three typical grades of non-grain-oriented laminated steel suitable for electric motor manufacturing. Over a wide range of frequencies between 20-400 Hz and inductions from 0.05 to 2 T, the new model yielded much lower errors for the specific core losses than conventional models. The applicability of the model for electric machine analysis is also discussed, and examples from an interior permanent-magnet and an induction motor are included.

Computation of Core Losses in Electrical Machines Using Improved Models for Laminated Steel

Two new models for specific power losses in cold-rolled motor lamination steel are described together with procedures for coefficient identification from standard multifrequency Epstein or single sheet tests. The eddy-current and hysteresis loss coefficients of the improved models are dependent on induction (flux density) and/or frequency, and the errors are substantially lower than those of conventional models over a very wide range of sinusoidal excitation, from 20 Hz to 2 kHz and from 0.05 up to 2 T. The model that considers the coefficients to be variable, with the exception of the hysteresis loss power coefficient that has a constant value of 2, is superior in terms of applicability and phenomenological support. Also included are a comparative study of the material models on three samples of typical steel, mathematical formulations for the extension from the frequency to the time domain, and examples of validation from electrical machine studies.

Assessment of torque components in brushless permanent magnet machines through numerical analysis of the electromagnetic field

For the calculation of torque in brushless (BL) AC motors a local method is proposed, based on the Maxwell stress theory and the filtered contributions due to the harmonics of the magnetic vector potential in the motor air-gap. By considering the space fundamental field only, the method can efficiently estimate the average synchronous torque for a variety or motor topologies, including concentrated winding designs. For BLDC motor analysis a global method is introduced, based on the virtual work principle expressed in terms of energy components in various motor regions. The method leads to simplifications in the average torque calculation and enables the direct identification of the cogging and ripple components. The mathematical procedures have been validated against experiments and other numerical techniques.

Finite-Element Surrogate Model for Electric Machines With Revolving Field—Application to IPM Motors

The model allows the ultra-fast simulation of the steady-state performance of synchronous machines and is particularly suitable for brushless motors with non-overlapping windings having coils concentrated around the teeth. Finite element analysis (FEA) is employed only for calculating the magnetic vector potential in the coils. For the example IPM motors presented, as little as one magnetostatic FE solution was used for fundamental flux linkage and average torque computation. Two FE solutions were employed for core flux density waveforms and power loss estimation. A minimum of three solutions is recommended for torque ripple, back emf and induced voltage. A substantial reduction of one to two orders of magnitude was achieved for the solving time as compared with detailed time-stepping FEA. The surrogate FE model can also be tuned for increased speed, comparable with that of magnetic equivalent circuit solvers. The general applicability of the model is discussed and recommendations are provided. Successful validation was performed against detailed FEA and experiments.

Ultrafast Finite-Element Analysis of Brushless PM Machines Based on Space–Time Transformations

A computationally efficient method is proposed for the steady-state performance simulation of brushless permanent-magnet (PM) motors. Only a minimum number of magnetostatic finite-element (FE) analysis (FEA) solutions are used in conjunction with space-time transformations, which are based on the periodicity specific to synchronous machines. For an example electronically controlled interior PM (IPM) motor with six teeth per pole and a distributed winding, a single nonlinear magnetostatic FE solution was employed to estimate the flux density time waveforms in the stator teeth and yoke. Other results include core losses, back electromotive force, and torque. The extension of the method to fractional-slot topologies with reduced number of teeth and concentrated (non-overlapping) coils is discussed with reference to a nine-slot six-pole IPM motor example. The computational time is reduced by one to two orders of magnitude as compared with more laborious time-stepping FEA. Successful validation was performed against experimental data and detailed FEA results.

High-efficiency variable-speed electric motor drive technologies for energy savings in the US residential sector

Electric motors account for a substantial proportion of the electricity consumed in American homes. In order to maximize energy efficiency, the US appliance industry has increasingly adopted, over the last decade, variable speed motor technology. State of the art solutions employing high-efficiency brushless (BL) permanent magnet (PM) motors and power-electronics drives are described. These include a variety of types, such as scalar voltage-regulated BLDC and vector controlled current-regulated BLAC. The motors comprise surface PM or interior PM (IPM) rotors and 3-phase stators with distributed or concentrated windings. Single-phase low power applications are also discussed. The review covers a wide range of power between 0.002hp and 5hp at relatively low speeds suitable for fans and blowers and higher speeds specific to pumps and compressors. A discussion of the trends and anticipated developments is also included.

Finite element surrogate model for electric machines with revolving field — application to IPM motors

The model allows the ultra-fast simulation of the steady-state performance of synchronous machines and is particularly suitable for brushless motors with non-overlapping windings having coils concentrated around the teeth. Finite element analysis (FEA) is employed only for calculating the magnetic vector potential in the coils. For the example IPM motors presented, as little as one magnetostatic FE solution was used for fundamental flux linkage and average torque computation. Two FE solutions were employed for core flux density waveforms and power loss estimation. A minimum of three solutions is recommended for torque ripple, back emf and induced voltage. A substantial reduction of one to two orders of magnitude was achieved for the solving time as compared with detailed time-stepping FEA. The surrogate FE model can also be tuned for increased speed, comparable with that of magnetic equivalent circuit solvers. The general applicability of the model is discussed and recommendations are provided. Successful validation was performed against detailed FEA and experiments.

Factors Affecting the Accurate Prediction of Iron Losses in Electrical Machines

A model of core losses, in which the hysteresis coefficients are variable with the frequency and induction (flux density) and the eddy-current and excess loss coefficients are variable only with the induction, is proposed. A procedure for identifying the model coefficients from multi-frequency Epstein tests is described and examples are provided for three typical grades of non grain-oriented laminated steel suitable for electric motor manufacturing. Over a wide range of frequencies between 20 Hz and 400 Hz and inductions from 0.05 T up to 2 T the new model yielded much lower errors for the specific core losses than conventional models. The applicability of the model for electric machine analysis is also discussed and examples from an interior permanent and an induction motor are included

A Study of the Engineering Calculations for Iron Losses in 3-phase AC Motor Models

This paper presents a study of the practical issues that need to be addressed by the engineering approaches to the incorporation of iron loss calculations into analytical and numerical models of AC motors. The total iron loss is estimated by summing up different loss components according to the analysed engineering approach. Illustrative examples are used and these are a 3-phase interior permanent magnet (IPM) motor and a 3-phase induction motor. All the models presented are compared with the no-load and loaded conditions test data.

Modeling and design optimization of PM AC machines using computationally efficient - finite element analysis

Computationally Efficient - Finite Element Analysis (CE-FEA) is detailed and demonstrated on a design optimization study for a sine-wave current regulated Interior Permanent Magnet (IPM) machine. In CE-FEA symmetries of electric and magnetic circuits of AC machines are fully exploited to minimize the number of required magnetostatic solutions. CE-FEA employs Fourier analysis and is capable of accurately estimating major steady-state performance parameters (average torque, profiles of cogging torque and torque ripples, back emf waveforms, and core losses), while preserving the main benefits of detailed finite element analysis. Significant reduction of simulation times is achieved (approx. two orders of magnitude) permitting a comprehensive search of large design spaces for optimization purposes. In a case-study IPM machine, three design variables, namely, stator tooth width, pole arc, and slot opening are used to optimize three performance parameters, namely, average torque, efficiency, and full-load torque ripple.