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This article systematically compares two axial flux permanent magnet machines designed for a university student racing car application: a double-rotor single-stator yokeless and segmented armature (YASA) structure, and a single-stator single-rotor configuration. Both machines are optimized for minimum loss and active weight using three-dimensional finite element analysis and the highest performing candidate designs are compared in more detail. The studies indicate that the benefits offered by the YASA configuration over the single-stator single-rotor machine are achieved only for specific designs that are heavier. For the design space with lower mass, albeit with increased losses, the Pareto front designs overlap. In this envelope, the YASA configuration demonstrates higher efficiencies at higher speeds, whilst the single-stator single-rotor is more efficient in high torque duty cycles. This shows the performance of the two machines is very similar and the choice is application specific. To validate the finite element analysis used in the optimization, a prototype was built and tested. Results showed good alignment between simulation and experimental data. [ABSTRACT FROM AUTHOR]

Outer-rotor switched reluctance machines (SRMs) have drawn much attention as promising candidates for in-wheel direct-drive motors of future electric vehicles. This article presents a systematic performance comparison of three outer-rotor SRM topologies for in-wheel traction applications in terms of the specific torque, electromagnetic efficiency, torque ripple, radial force, and mechanical aspects. A generalized design optimization framework for SRMs is proposed to enable the fast evaluation of large numbers of designs generated from the differential evolution by incorporating an analytical current profile estimation into the transient finite element analysis. The relationship between the saliency ratio and converter volt-ampere rating is also discussed. The calculations are then benchmarked with the experimental results from an existing prototype. The effectiveness of the performance prediction method and the proposed optimization approach is validated. [ABSTRACT FROM AUTHOR]

Axial-flux permanent-magnet machines are used particularly in applications requiring a compact structure. Their disc-shaped topology and axial airgap have led to a variety of configurations including two popular ones: the yokeless and segmented armature (YASA), and the single-stator single-rotor or single-sided machine. In this study, a comprehensive comparative analysis of these configurations is conducted at different magnetic and electric loadings. It is found that at lower loadings, typically employed for air-cooled machines, the torque/ampere characteristics of the YASA machine are almost identical to those of a single-sided machine constructed with half the magnet volume. On the other hand, the single-sided machine outperforms the YASA machine when the magnet volumes in both machines are maintained equal. However, for higher electric loadings, the torque/ampere characteristics of the YASA machine droop significantly less than those of the single-sided machine. This article includes analytical estimations, which are verified with experimentally validated finite element analysis (FEA) simulations. In addition, the impacts of the armature reaction on saturation and the magnetic flux linkage, the magnet losses, and eddy current losses in both machines are also explored. [ABSTRACT FROM AUTHOR]

Optimizing the design of electric machines is a vital step in ensuring the economical use of active materials. The three-dimensional (3-D) flux paths in axial flux permanent magnet (AFPM) machines necessitate the use of computationally expensive 3-D electromagnetic analysis. Furthermore, a large number of design evaluations is required to find the optimum, causing the total computation time to be excessively long. In view of this, a two-level surrogate assisted algorithm capable of handling such expensive optimization problems is introduced, which substantially reduces the number of finite element analysis (FEA) evaluations to less than 200 while conventional algorithms require thousands of designs to be analyzed. The proposed algorithm is employed to optimally design an AFPM machine within a specified envelope, and to identify the limits of cost and efficiency. In order to obtain these limits, the variables' ranges are assigned to be as wide as possible, resulting in a vast design space, the study of which was enabled by the developed special algorithm. Additionally, optimized designs with different rotor polarities are systematically compared in order to form the basis for a set of generalized design rules. [ABSTRACT FROM AUTHOR]

Equivalent circuit parameters serve as the basis for performance estimation and implementation of power electronic drives controls and therefore their accurate evaluation is very important. Specified in the newly approved IEEE Std 1812, a short-circuit test can be employed, in combination with an open-circuit measurement, in order to determine the back emf and the synchronous inductance. In the case of interior permanent magnet (IPM) machines, this approach can be used only to determine the d-axis inductance and additional and separate measurements are required for the q-axis inductance. In this respect, various methods, inclusive of dc step response tests, on-load tests, and a widely used test in industry, which involves locked-rotor measurements at variable voltage and constant frequency supply, are studied in detail, based on two-dimensional finite element analysis. Locked-rotor methods based on dc current supply and static torque versus rotor position measurements are introduced for determining the q-axis inductance in combination with the standardized open-circuit and short-circuit tests. A critical study of the inductances determined from different tests is conducted, and experimental results on an IPM motor design with non-sinusoidal back emf, relatively high torque ripple, and low leakage are presented. [ABSTRACT FROM AUTHOR]

Switched reluctance (SR) machines are attractive because they present relatively high efficiency and torque density in spite of lacking permanent magnets. This paper focuses on a two-objective optimization of an external rotor SR motor with a stator that has concentrated coils and a rotor with magnetically isolated modules. The objectives are minimum loss and mass, and 11 independent dimensionless geometric variables are considered as inputs that affect them. A combined design of experiments (DOE) and differential evolution (DE) approach is proposed. The DOE methodology is used to reduce the search space by eliminating from consideration input variable values, leading to poor-performing designs. Following this initial DOE study, an optimization study based on DE is run over the reduced search space, which leads to significant savings in computation time. Furthermore, a directed graph-based method for comparing different designs on the Pareto front to rank the best compromise designs is proposed. [ABSTRACT FROM AUTHOR]

Performance trade offs for achieving high torque density and high drive-cycle efficiency in spoke-type permanent magnet (PM) motors are investigated. Unlike the traditional method, which relies on analytical equations, this trade-off study is conducted through a statistical analysis of the Pareto-optimal design candidates resulting from a large-scale design optimization of an example traction machine over a Le Mans-based drive cycle. In the design optimization process, both low-speed and extended-speed/field-weakening operating regions are evaluated using high-fidelity electromagnetic finite element (FE) simulations with an objective to simultaneously increase the torque density and decrease the power losses over the high energy-throughput-zones of the machine torque–speed plane. The resultant 3400 design candidates are utilized to investigate the impact of increasing power density on other important performance metrics such as power losses, PM demagnetization, and torque ripple. This analysis is supplemented by multiphysics simulation of three counterpart optimized designs and successful experimental verification of a prototype of one of those three designs which represents a record high power density motor in traction applications. [ABSTRACT FROM AUTHOR]

Coreless axial flux machines are of interest because of the absence of stator core losses and cogging torque. These machines generally employ concentrated windings. One of the challenges with such a winding is that the torque producing MMF component that corresponds to the fundamental of the magnet excitation is accompanied by substantial asynchronous components. These harmonics cause losses in the rotor core and magnets, which can become significant at high speeds. This paper proposes a new multilayer winding arrangement to eliminate the non-torque producing MMF components. This winding is applied to a 12-coil 16-pole coreless axial flux machine. The efficacy of the winding is established by 3-D finite-element analysis. [ABSTRACT FROM AUTHOR]

Coreless axial flux permanent magnet (AFPM) machines are attracting increasing attention due to their compact structure and high torque density. The torque to weight ratio can be further enhanced by the use of alternate conductor materials, such as carbon nanotube (CNT), or aluminum windings in place of the copper material coils. This paper proposes a coreless AFPM synchronous motor with CNT windings. Analytical equations are developed to allow a systematic comparison of machine designs with different conductor materials. The performance of machine designs with different coil materials, namely, copper, aluminum, and CNT, is evaluated and compared. The calculations are also backed by 3-D finite-element analysis. [ABSTRACT FROM AUTHOR]

This paper uses formal mathematical optimization techniques based on parametric finite-element-based computationally efficient models and differential evolution algorithms. For constant-power applications, in the novel approach described, three concurrent objective functions are minimized: material cost, losses, in order to ensure high efficiency, and the difference between the rated and the characteristic current, aiming to achieve very high constant-power flux-weakening range. Only the first two objectives are considered for constant-torque applications. Two types of interior permanent magnet rotors in a single- and double-layer V-shaped configuration are considered, respectively. The stator has the typical two slots per pole and phase distributed winding configuration. The results for the constant-torque design show that, in line with expectations, high efficiency and high power factor machines are more costly, and that the low-cost machines have poorer efficiency and power factor and most importantly, and despite a common misconception, the saliency ratio may also be lower in this case. For constant-power designs, the saliency ratio can be beneficial. Nevertheless, despite a common misconception, when cost is considered alongside performance as an objective, a higher saliency ratio does not necessarily improve the power factors of motors suitable for ideal infinite flux weakening. [ABSTRACT FROM AUTHOR]

A novel automated design optimization procedure based on the application of an ultrafast computationally efficient finite-element analysis (CE-FEA) for current-regulated synchronous reluctance machines supplied from power electronic converters is proposed. The CE-FEA uses only a minimum number of magnetostatic solutions in order to comprehensively evaluate performance, including ripple torque and core losses. The optimization algorithm is based on differential evolution, and uses as independent variables the torque angle and ratios for a generic rotor topology with four flux barriers. Two problems, one with two and the other with three objectives, are studied and results are compared. Global performance indices and objectives incorporate the effect of average torque output, losses, torque ripple, and power factor at fixed cost. It is shown that through optimal studies with more than 5000 candidate designs, high output power, high efficiency, and low torque ripple can be achieved, while the relatively low power factor remains an inherent limitation of synchronous reluctance technology. Simulations are validated versus tests from a 10-hp 1800-r/min prototype. [ABSTRACT FROM AUTHOR]

A large-scale finite element model-based design optimization algorithm is developed for improving the drive-cycle efficiency of permanent magnet (PM) synchronous machines with wide operating ranges such as those used in traction propulsion motors. The load operating cycle is efficiently modeled by using a systematic k-means clustering method to identify the operating points representing the high-energy-throughput zones in the torque–speed plane. The machine performance is evaluated over these cyclic representative points using a recently introduced computationally efficient finite element analysis, which is upgraded to include both constant torque and field-weakening operations in the evaluation of the machine performance metrics. In contrast with the common practice, which aims at enhancing the rated performance, the entire range of operation is considered in the present design optimization method. Practical operational constraints imposed by the voltage and current limits of the motor-drive system, excessive PM demagnetization, and torque ripple are accounted for during the optimization process. The convergence to the optimal design solutions is expedited by utilizing a new stochastic optimizer. The developed design algorithm is applicable to any configuration of sinewave-drive PM and synchronous reluctance motors over any conceivable load profile. Its effectiveness is demonstrated by optimizing the well-established benchmark design represented by the Toyota Prius Gen. 2 interior PM motor configuration over a compound operating cycle consisting of common U.S. driving schedules. Multiphysics electromagnetic, thermal, and mechanical performance of the optimized design solutions is discussed in a postdesign optimization stage. [ABSTRACT FROM PUBLISHER]

Performance improvement of permanent magnet (PM) motors through optimization techniques has been widely investigated in the literature. Oftentimes the practice of design optimization leads to derivation/interpretation of optimal scaling rules of PM motors for a particular loading condition. This paper demonstrates how these derivations vary with respect to the machine ampere loading and ferrous core saturation level. A parallel sensitivity analysis using a second-order response surface methodology followed by a large-scale design optimization based on evolutionary algorithms are pursued in order to establish the variation of the relationships between the main design parameters and the performance characteristics with respect to the ampere loading and magnetic core saturation levels prevalent in the naturally cooled, fan-cooled, and liquid-cooled machines. For this purpose, a finite-element-based platform with a full account of complex geometry, magnetic core nonlinearities, and stator and rotor losses is used. Four main performance metrics including active material cost, power losses, torque ripple, and rotor PM demagnetization are investigated for two generic industrial PM motors with distributed and concentrated windings with subsequent conclusions drawn based on the results. [ABSTRACT FROM PUBLISHER]

This paper describes a systematic method for optimally designing with multiple objectives and differential evolution (DE) algorithms, current regulated electronically controlled synchronous reluctance (SynRel) machines. A large-scale study with thousands of designs calculated with a ultrafast computationally efficient electromagnetic finite-element analysis (CE-FEA) establishes the performance limitations of conventional radially laminated technology with multiple flux barriers. The potential advantages of employing permanent-magnet (PM)-assisted technology with additional ferrites in the rotor are quantified in terms of substantially improved power factor, specific power, and efficiency. Numerical and experimental results for a 10-hp, 1800-r/min typical rating are included. [ABSTRACT FROM PUBLISHER]

A new technique for coupling the electromagnetic, thermal, and airflow analysis is proposed particularly for electric machines that exhibit reduced dependence of core losses with temperature and load and have low rotor losses. Within the overall iterative loop, another inner loop that cycles only the thermal calculations and employs a simplified model to estimate losses is introduced. The thermal and airflow analysis models the conduction, radiation, and convection heat transfer and is based on equivalent circuit networks. A computationally efficient finite-element (FE) technique is employed for the electromagnetic field analysis. The combination of algorithms results in ultrafast processing as the number of outer loop iterations, which include electromagnetic FE analysis, is minimized. The overall computational time is significantly reduced in comparison with the conventional method, such that the new technique is highly suitable for large-scale optimization studies. Example simulation studies and measurements from an integral horsepower interior permanent-magnet motor are included to support validation. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]