N.A. Demerdash

A combined finite element-state space modeling environment for induction motors in the ABC frame of reference: the no-load condition

This paper centers on the development of a modeling environment to predict performance and operating characteristics of squirrel cage induction motors. The model basically consists of two sections, a Finite Element computation algorithm coupled to a State-Space algorithm, hence the term Combined Finite Element- State Space (CFE-SS) modeling environment. The output of the FE section is the entire set of winding inductances which represents the key input data to the SS portion

Computation of winding inductances of permanent magnet brushless DC motors with damper windings by energy perturbation

A method for the calculation of motor winding inductances is presented in which damping effects due to metallic retainment sleeves and intentionally introduced damper bar (amortisseur) windings are included. The inductance computation method makes use of the combined energy perturbation concept and finite-element field solutions. These parameters are necessary for the prediction of the dynamic performance of such motors with rotor damping. This modeling approach accounts for all saliency effects, and is entirely carried out in the natural abc frame of reference. Thus, it facilitates the process of integration of the modeling of the motor and its associated power electronics. The approach is most effective in the design of damper bar systems for enhancement of the performance of such motors, as demonstrated in the application of this approach to a 15 hp, 120 V, 6-pole, samarium-cobalt, permanent-magnet brushless DC motor. >

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, 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. >

A coupled finite-element state-space approach for synchronous generators. I. model development

Presented here is the development of a time stepping coupled finite-element state-space (CFE-SS) modeling environment, totally within the natural time domain ABC flux-linkage frame of reference, to predict the steady-state machine parameters and performance characteristics, including laminated iron core losses, of salient-pole synchronous machines. The time stepping CFE-SS model allows one to rigorously account for the full synergistic impact of space harmonics and time harmonics on the machine parameters and performance characteristics.

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

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. >

Extra high speed modified Lundell alternator parameters and open/short-circuit characteristics from global 3-D-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. >

Computer-aided modeling and experimental verification of the performance of power conditioner operated permanent magnet brushless DC motors including rotor damping effects

A model is presented for computer-aided prediction of performance of permanent-magnet brushless DC motors, including effects of rotor damping due to metallic retainment sleeves. The computer-generated parameters given by N.A. Demerdash et al. (ibid., vol.3, see p.705-13, 1988) are used in a model formulated entirely in the natural abc frame of reference. This avoids the complication of transformation from one frame of reference to another, and hence this approach enables one to incorporate all insignificant harmonic effects due to any saliency and slotting. The development of the model in the natural abc frame of reference also facilitates the integration of the machine and the electronic power conditioner into one all-encompassing equivalent network model for the entire business DC motor system. The validity of the model was verified by applying it to the prediction of the performance of a 15 hp, 120 V, 6-pole, samarium-cobalt permanent-magnet brushless DC motor and comparing the digital simulation results with the corresponding test data for this motor system. >

A combined finite element-state space modeling environment for induction motors in the ABC frame of reference: the blocked-rotor and sinusoidally energized load conditions

The combined finite element-state space (CFE-SS) modeling environment was used to predict the performance of a 1.2 hp, three-phase case-study squirrel cage induction motor under blocked rotor and typical load operating conditions. The nature of this CFE-SS environment allows one to rigorously account for the impact of space harmonics generated by the magnetic circuit, winding, and cage geometric, as well as layout peculiarities and magnetic saturation, on the current and torque profiles, and ohmic losses in the stator armature and cage. This includes the ability to predict the profiles of connector and bar currents. The results of the CFE-SS simulations compare favorably with blocked rotor and load experimental test data. Potential capabilities of this CFE-SS modeling environment, and its use in impacting motor design decisions, are discussed in the light of reported findings. >

Modeling of effects of skewing of rotor mounted permanent magnets on the performance of brushless DC motors

A method for computation of the parameters and performance of permanent-magnet brushless DC motor drives is developed in which the concept of skewing is implemented through the geometries of permanent magnet mounting on the rotor and not through the usual skewing of the armature slots. This technique of permanent-magnet mounting eliminates the 2-D axial symmetry in the resulting magnetic fields. This difficulty is overcome by the use of multiple cross-sectional 2-D finite-element field computations, coupled with a concept of an artificial mutual-coupling inductance between the armature phase windings and the rotor-mounted permanent magnets for induced EMF and torque computations. The computed induced EMF waveforms, motor phase winding current waveforms, and other performance characteristics are found to be in excellent agreement with test data obtained using a 1.2 hp, 120 V brushless DC motor drive system. >

Harmonics and core losses of permanent magnet DC motors controlled by chopper circuits

The impact of chopper control on armature current harmonics and core losses of permanent-magnet DC motors is analyzed. A computer-aided two-dimensional finite-element method is used to analyze the magnetic field and obtain the nonlinear parameters of the machine. The armature current waveforms are predicted from the machine system network analysis at different chopping frequencies and decomposed into their AC and DC components. These currents with their ripple contents are further used in the field analysis to compute the core losses of a 1.2 hp permanent-magnet DC motor at different operating conditions. In addition to the numerical analysis, supporting experimental work was carried out for verification of some of the results. It is found that armature current harmonics can lead to significant increases in core losses. >