Gennadi Y. Sizov

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

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.

Analysis and Diagnostics of Adjacent and Nonadjacent Broken-Rotor-Bar Faults in Squirrel-Cage Induction Machines

In this paper, faults associated with the rotor of an induction machine are considered. More specifically, effects of adjacent and nonadjacent bar breakages on rotor fault diagnostics in squirrel-cage induction machines are studied. It is shown that some nonadjacent bar breakages may result in the masking of the commonly used fault indices and, hence, may lead to a possible misdiagnosis of the machine. A discussion of the possible scenarios of these breakages as well as some conclusions regarding the types of squirrel-cage induction machines (number of poles, number of squirrel-cage bars, etc.) that may be more prone to these nonadjacent types of failures are presented. This discussion is supported through both simulation and experimental results. It is also shown that secondary fault effects can be used to diagnose such nonadjacent bar breakages.

Calculation of Magnet Losses in Concentrated-Winding Permanent-Magnet Synchronous Machines Using a Computationally Efficient Finite-Element Method

The proposed hybrid method combines computationally efficient finite-element analysis (CE-FEA) with a new analytical formulation for eddy-current losses in the permanent magnets (PMs) of sine-wave current-regulated brushless synchronous motors. The CE-FEA only employs a reduced set of magnetostatic solutions yielding substantial reductions in the computational time, as compared with the conventional FEA. The 3-D end effects and the effect of pulsewidth-modulation switching harmonics are incorporated in the analytical calculations. The algorithms are applied to two fractional-slot concentrated-winding interior PM motors with different circumferential and axial PM block segmentation arrangements. The method is validated against 2-D and 3-D time-stepping FEA.

Automated Multi-Objective Design Optimization of PM AC Machines Using Computationally Efficient FEA and Differential Evolution

The design optimization methods described in this paper are employing an ultrafast computationally efficient finite element analysis technique. A minimum number of magnetostatic solutions are used for the analysis, which makes possible the study of thousands of candidate motor designs with typical PC-workstation computational resources. A multi-objective differential evolution algorithm that considers a large number of independent stator and rotor geometric variables and performance criteria, such as average and ripple torque, losses, and efficiency, is used. The optimization method is demonstrated on different permanent magnet (PM) ac synchronous motors in the kilowatt and megawatt power ranges. For the low-power PM ac machine study, a nine-slot six-pole topology is considered. For the high-power PM ac machines, four case studies were carried out with the following: fractional-slot embedded surface PM (SPM), fractional-slot interior PM (IPM), integer-slot SPM, and integer-slot IPM, respectively. Four motor topologies are systematically compared based on optimal Pareto sets. The design optimization of IPM motors includes an additional search for an optimum operating torque angle corresponding to the maximum-torque-per-ampere condition.

Multi-objective optimization of PM AC machines using computationally efficient - FEA and differential evolution

A total of eleven independent stator and rotor variables are simultaneously employed for the optimization of a generic example IPM motor design. The multi-objective criterion maximizes efficiency, while minimizing torque ripple at the rated output condition. A Pareto-based differential evolution (DE) algorithm with 100 generations, each with a population of 100 individuals, is presented. Computationally efficient FEA (CE-FEA), which is based on a reduced number of magnetostatic solutions for a motor model in the abc reference frame, is employed. As a result, a total of 10,000 candidate motor designs, which are included in the comprehensive study, are evaluated in a record short time on a typical PC-based workstation. The paper includes an engineering trade-off discussion based on a typical-reference motor, two optimum designs in terms of average torque and torque ripple, and a best-compromise solution. For the case-study, an order of magnitude reduction of the rated-load torque ripple and open-circuit cogging torque has been achieved. This is while, at the same time, the specific torque output has been increased by as much thirty seven percent.

Multi-Objective Tradeoffs in the Design Optimization of a Brushless Permanent-Magnet Machine With Fractional-Slot Concentrated Windings

In this paper, a robust parametric model of a brushless permanent magnet machine with fractional-slot concentrated windings, which was developed for automated design optimization is presented. A computationally efficient finite-element analysis method was employed to estimate the dq-axes inductances, the induced voltage and torque ripple waveforms, and losses of the machine. A method for minimum effort calculation of the torque angle corresponding to the maximum torque per ampere load condition was developed. A differential evolution algorithm was implemented for the global design optimization with two concurrent objectives of minimum losses and minimum material cost. An engineering decision process based on the Pareto-optimal front for 3,500 candidate designs is presented together with discussions on the tradeoffs between cost and performance. One optimal design was finally selected, prototyped and successfully tested.

Design optimization of spoke-type ferrite magnet machines by combined design of experiments and differential evolution algorithms

In this paper, a combined design optimization method utilizing Design of Experiments (DOE) and Differential Evolution (DE) algorithms was implemented to provide practical insights in the multi-objective design optimization of a 12-slot, 8-pole, spoke-type, ferrite magnet machine, with fractional-slot concentrated windings. A robust parametric model of this type of machine is provided here. In this combined design optimization approach, the Central Composite Design (CCD) method, as one of the DOE approaches, was used to perform the variables sensitivity study, from which the significant design variables were selected and the corresponding variables ranges were defined, for the DE design optimization procedure. A Computationally Efficient-Finite Element Analysis (CE-FEA) approach was utilized to estimate the performance and characteristics of 3000 candidate designs. From the study of design objectives utilizing the pareto-set and color maps, three candidate designs with minimized losses, material cost and torque ripple were compared.

A Reconfigurable Motor for Experimental Emulation of Stator Winding Interturn and Broken Bar Faults in Polyphase Induction Machines

The benefits and drawbacks of a 5-hp reconfigurable induction motor, which was designed for experimental emulation of stator winding interturn and broken rotor bar faults, are presented in this paper. It was perceived that this motor had the potential of quick and easy reconfiguration to produce the desired stator and rotor faults in a variety of different fault combinations. Hence, this motor was anticipated to make a useful test bed for evaluation of the efficacy of existing and new motor fault diagnostics techniques and not the study of insulation failure mechanisms. Accordingly, it was anticipated that this reconfigurable motor would eliminate the need to permanently destroy machine components such as stator windings or rotor bars when acquiring data from a faulty machine for fault diagnostic purposes. Experimental results under healthy and various faulty conditions are presented in this paper, including issues associated with rotor bar-end ring contact resistances that showed the drawbacks of this motor in so far as emulation of rotor bar breakages. However, emulation of stator-turn fault scenarios was successfully accomplished.

Establishing the Relative Merits of Interior and Spoke-Type Permanent-Magnet Machines With Ferrite or NdFeB Through Systematic Design Optimization

In this paper, a multiobjective design optimization method combining design-of-experiments techniques and differential-evolution algorithms is presented. The method was implemented and utilized in order to provide practical engineering insights for the optimal design of interior and spoke-type permanent-magnet machines. Two combinations with 12 slots and 8 poles and 12 slots and 10 poles, respectively, have been studied in conjunction with rare-earth neodymium-iron-boron (NdFeB) and ferrites. As part of the optimization process, a computationally efficient finite-element electromagnetic analysis was employed for estimating the performance of thousands of candidate designs. Three optimization objectives were concurrently considered for minimum total material cost, power losses, and torque ripple, respectively. Independent variables were considered for both the stator and rotor geometries. A discussion based on a systematic comparison is included, showing, among other things and despite common misconception, that comparable cost versus loss Paretos can be achieved with any of the rotor topologies studied.

Magnetic equivalent circuit modeling of induction machines under stator and rotor fault conditions

In this paper, stator and rotor failures in squirrel-cage induction machines are modeled using the magnetic equivalent circuit (MEC) approach. Failures associated with stator winding and rotor cage are considered. More specifically, stator inter-turn short circuit and broken rotor bar failures are modeled. When compared to conventional modeling techniques, the MEC modeling approach offers two main advantages: 1) relatively high speed of execution, and 2) high accuracy. The developed MEC model is validated here with respect to the experimental tests and time-stepping finite-element simulations for healthy and various faulty conditions.