This paper investigates the average torque separation in permanent magnet (PM) synchronous machines. In order to accurately separate the PM and armature fields, and, hence, the torque components accounting for the magnetic saturation and crosscoupling, the frozen permeability (FP) method is often employed, while the torque can be calculated by different methods, such as Maxwell stress tensor and virtual work principle. Although these two methods result in identical torques in normal finite element (FE) analyses when appropriate FE meshes are used, the average torques calculated by these two methods are found to be different when the FP method is employed due to the influence of equivalent rotational magnetic saliency in the stator, which causes a part of PM torque being improperly attributed to the reluctance torque when Maxwell stress tensor method is employed. However, by using the virtual work principle, this is eliminated, and, hence, the average torque components can still be appropriately separated and analyzed.

Average Torque Separation in Permanent Magnet Synchronous Machines Using Frozen Permeability

Computationally efficient finite-element analysis (FEA) (CE-FEA) fully exploits the symmetries of electric and magnetic circuits of sine-wave current-regulated synchronous machines and yields substantial savings of computational efforts. Motor performance is evaluated through Fourier analysis and a minimum number of magnetostatic solutions. The major steady-state performance indices (average torque, ripple and cogging torque, back-electromotive-force waveforms, and core losses) are satisfactorily estimated as compared with the results of detailed time-stepping (transient) FEA. In this paper, the CE-FEA method is presented and applied to a parametric design study for an interior-permanent-magnet machine. Significant reduction of simulation times is achieved (approximately two orders of magnitude), permitting a comprehensive search of large design spaces for optimization purposes. In this case study, the influence of three design variables, namely, stator tooth width, pole arc, and slot opening, on three performance indices, namely, average torque, efficiency, and full-load torque ripple, is examined, and design trends are derived. One hundred candidate designs are simulated in less than 20 minutes on a state-of-the-art workstation.

Modeling and Parametric Design of Permanent-Magnet AC Machines Using Computationally Efficient Finite-Element Analysis

In this paper, a comprehensive presentation of a time-stepping coupled finite element-state space modeling approach for diagnosis and characterization of effects of rotor (cage) broken bars and connectors in squirrel-cage induction motors is given. The model is used to compute/predict the characteristic frequency components which are indicative of rotor bar and connector breakages in the armature current waveforms and developed torque profiles, respectively. It was found that failures due to rotor connector breakages tend to degrade the developed torque of the machine considerably more than failures due to rotor bar breakages. Also, the effects and implications of rotor breakages on core loss distributions are quantified and described. Furthermore, this model has great potential in future applications to generate databases for use in overall noninvasive diagnostics of faults or troubleshooting in relation to quality assessments of the state of the motor and the overall drive.

Diagnosis and characterization of effects of broken bars and connectors in squirrel-cage induction motors by a time-stepping coupled finite element-state space modeling approach

A claw pole synchronous generator, or Lundell alternator, is the main source of electric energy in today's internal combustion engine automobile. Having in mind that as consumer power onboard a vehicle steadily increases, the importance of creating an accurate computational tool for Lundell alternator analysis and potential gains on output, efficiency and weight, such a tool is clearly needed. This article shows how a contemporary electric machine analysis tool, the magnetic equivalent circuit method (MEC) helps one predict performance of a Lundell alternator with a very high accuracy and a minimum of computational time.

A magnetic equivalent circuit based performance computation of a Lundell alternator

Statistics show that 80% of faults are due to eccentricity in induction motors, promoting many research efforts still devoted to the eccentricity in these motors. This paper classifies different common faults in the stator and rotor. It then presents analysis techniques for faulty induction motors. Four more applied methods in the diagnosis and detection of faults in induction motors are investigated and critiqued. The finite difference method is introduced, and its drawbacks are noted. An equivalent magnetic circuit method is then discussed as a fast but less accurate method. The reduced accuracy of the latter method is due to neglect of the spatial harmonics, the relationship between these harmonics, and time harmonics, and particularly non-linearity of the magnetic materials. An analytical method of winding functions is investigated for the analysis of faulty induction motors. This method also neglects the spatial harmonics and their relationship with time harmonics, which could considerably influence ...

Different Faults and Their Diagnosis Techniques in Three-Phase Squirrel-Cage Induction Motors—A Review

A combined magnetic vector potential, magnetic scalar potential method of computation of 3-D magnetic fields by finite elements, in combination with state modeling in the abc frame of reference, is used for global 3-D magnetic field analysis and machine performance computation under rated load and overload condition in an example 14.3 kVA modified Lundell alternator. The results vividly demonstrate the 3-D nature of the magnetic field in such machines and show how this model can be used as an excellent tool for computation of flux density distributions, armature current and voltage waveform profiles, and harmonic contents, as well as for computation of torque profiles and ripples. Use of the model in gaining insight into locations of regions in the magnetic circuit with heavy degrees of saturation is demonstrated. Experimental results which correlate well with the simulations of the load case are given. >

Computation of load performance and other parameters of extra high speed modified Lundell alternators from 3D-FE magnetic field solutions

A combined magnetic vector potential, magnetic scalar potential method of computation of 3-D magnetic fields by finite elements is used for global 3-D field analysis and machine performance computations under open-circuit and short-circuit conditions for an example 14.3 kVA modified Lundell alternator, whose magnetic field is of an intrinsic 3-D nature. The computed voltages and currents under these machine test conditions were verified and found to be in very good agreement with corresponding test data. Results of the use of this modeling and computation method in the study of a design alteration example, in which the stator stack length of the example alternator is stretched in order to increase voltage and volt-ampere rating, are given. These results demonstrate the inadequacy of conventional 2-D based design concepts and the need for this type of 3-D magnetic field modeling in the design and investigation of such machines. >

Extra high speed modified Lundell alternator parameters and open/short-circuit characteristics from global 3-D-FE magnetic field solutions

A three-dimensional (3-D) finite-element (FE) approach was developed and implemented for computation of global magnetic fields in a 14.3 kVA modified Lundell alternator. The essence of the method is the combined use of magnetic vector and scalar potential formulations in 3-D FEs. This approach makes it practical, using state-of-the-art supercomputer resources, to globally analyze magnetic fields and operating performances of rotating machines which have 3-D magnetic flux patterns. The 3-D FE computed fields and machine inductances as well as various machine performance simulations of the 14.3-kVA machine are presented. >

Three dimensional magnetic fields in extra high speed modified Lundell alternators computed by a combined vector-scalar magnetic potential finite element method

R. Wang

Papers

Computation of load performance and other parameters of extra high speed modified Lundell alternators from 3D-FE magnetic field solutions

Extra high speed modified Lundell alternator parameters and open/short-circuit characteristics from global 3-D-FE magnetic field solutions

Three dimensional magnetic fields in extra high speed modified Lundell alternators computed by a combined vector-scalar magnetic potential finite element method