Disruptive innovations in electrical machine design optimization are observed in this paper, motivated by emerging trends. Improvements in mathematics and computer science enable more detailed optimization scenarios that cover evermore aspects of physics. In the past, electrical machine design was equivalent to investigating the electromagnetic performance. Nowadays, thermal, rotor dynamics, power electronics, and control aspects are included. The material and engineering science have introduced new dimensions on the optimization process and impact of manufacturing, and unavoidable tolerances should be considered. Consequently, multifaceted scenarios are analyzed and improvements in numerous fields take effect. This paper is a reference for both academics and practicing engineers regarding recent developments and future trends. It comprises the definition of optimization scenarios regarding geometry specification and goal setting. Moreover, a materials-based perspective and techniques for solving optimization problems are included. Finally, a collection of examples from the literature is presented and two particular scenarios are illustrated in detail.

Modern Electrical Machine Design Optimization: Techniques, Trends, and Best Practices

This paper analyzes the effects of the rotor position error in the performance of field-oriented-controlled permanent-magnet synchronous machine (PMSM) drives intended for electric vehicle (EV) traction applications. A special focus is given to the torque ripple generated along the characteristic trajectories in the different operating regions of the PMSM. An extended and generalized model of the torque ripple produced by the PMSM as a function of the rotor position error is analytically deduced. An infinite-speed interior-(I)PMSM drive and a finite-speed surface-mounted (SM)-PMSM drive are considered for the simulations carried out in MATLAB-SimPowerSystems. The experimental results have been validated with a TM4 EV drive controlling an 80-kW SM-PMSM. The torque ripple has been evaluated for both motoring and regenerative braking operation modes under maximum torque conditions going from 100 N · m at 1000 r/min up to 55 N · m at 9000 r/min. The obtained simulation and experimental results demonstrate the good accuracy of the proposed model for evaluating the torque ripple produced in PMSMs due to the error from the rotor position sensor.

Effects of Rotor Position Error in the Performance of Field-Oriented-Controlled PMSM Drives for Electric Vehicle Traction Applications

Permanent magnet synchronous machines (PMSM) have been widely used in a variety of applications. A strong electromagnetic force exists between the rotor magnets and the stator core in a PMSM. The force directly causes mechanical deformation and vibration of the stator. In small PM motors, mechanical vibration comes mainly from the electromagnetic force of the stator. This paper gives the general expression of the frequency and corresponding mode number of radial force harmonics for a PMSM with a three-phase symmetrical double-layer winding. The paper shows that the lowest mode number of radial force harmonics is the greatest common divisor of pole number and slot number. The force harmonics with a low mode number can induce a high mechanical vibration, especially for PMSMs with a fractional slot combination. This is simulated using a weak-coupling electromagnetic-mechanical finite element model. To illustrate the influence of radial force harmonics with a low mode number on vibration, a method to eliminate the lowest mode number force harmonics for the fractional slot combination motor is proposed. A test rig for the 12-slot 8-pole prototype motor is set up. The experimental and simulated results confirm that force harmonics with low mode number have a major impact on vibration.

Influence of Radial Force Harmonics With Low Mode Number on Electromagnetic Vibration of PMSM

In this paper, radial forces and torque ripple characteristics are investigated in permanent magnet (PM) machines having different pole and slot combinations. Using the PM machines with concentrated windings could be beneficial in direct-drive wind generators since it is possible to reduce the size and weight of the generator. The PM machines with concentrated windings having a large number of poles are compared to investigate the effect of pole and slot combinations on force and vibration characteristics in low-speed generators. Cogging torque waveforms and torque ripple are investigated using time-stepping finite-element analysis. Analysis of radial forces is presented, including investigation on radial force density distribution, total forces on teeth, and time-dependent force waveforms on a tooth. Structural analysis and experimental modal analysis are performed on the prototype generator. The main mode of vibration in the prototype machine is observed experimentally and the results are in good agreement with the simulations.

Influence of Pole and Slot Combinations on Magnetic Forces and Vibration in Low-Speed PM Wind Generators

Permanent-magnet synchronous motors (PMSMs) have been widely used as the driving core in electric vehicles due to the high power/torque density and high efficiency. Recent years have witnessed a great effort on the vibration and noise of PMSMs in order to ensure the driving comfort. In this paper, the state of the art and recent progress of the electromagnetic vibration and noise of PMSMs for electric vehicles are presented, with emphasis on the induced mechanism, prediction method, suppression method, and sound quality. The future trends faced are also described.

Electromagnetic Vibration and Noise of the Permanent-Magnet Synchronous Motors for Electric Vehicles: An Overview

This paper investigates the effect of pole and slot combination on the vibration and noise in permanent magnet synchronous motor (PMSM). Two PMSMs that have the same performances but different pole and slot combinations are studied. A numerical analysis process for the vibration is introduced. First, by using the electromagnetic field finite element analysis (FEA) and Maxwell stress tensor method, the radial forces of these two motors are analyzed. In order to evaluate the effect of the radial force on the vibration, then the equivalent magnetizing current method is used to calculate the local force which then is employed in the mechanical FEA analysis. Finally, an experiment is processed to test the vibration and noise of these two motors, and verify the proposed analysis process. The effect of the pole and slot combination on the noise and vibration are revealed.

Effect of pole and slot combination on noise and vibration in permanent magnet synchronous motor

This paper presents a design methodology and analysis for a 4-kW 150-krpm ultra-high-speed surface-mounted permanent-magnet synchronous motor (SPMSM) to electrically assist a turbocharger. The proposed design methodology is aimed at achieving a required torque and speed. In addition, this study seeks a fast-speed response as a design objective to eliminate turbo lag more effectively. First, an existing prototype that does not meet the target performance is presented. The loss for the prototype, which is difficult to obtain theoretically, is obtained experimentally and reflected in the design. The speed response characteristic of the machine is analyzed through the electromechanical undamped natural frequency and damping ratio. Design parameters such as the permanent-magnet (PM) grade, the turn number of coils, and the axial length of the motor are designed. The resulting improved motor achieves higher power density as well as faster speed response than the prototype. Experiments verified the effectiveness of the motor in the electrically assisted turbocharger. In system experiments with the turbocharger, the rising speed of the boost pressure is improved by 44.9% due to the designed motor.

Design of an Ultra-High-Speed Permanent-Magnet Motor for an Electric Turbocharger Considering Speed Response Characteristics

Consideration of the saturation in the core is essential in designing motors for automotive application, because of the stringent size limitations in automotive electric motors, such as those equipped with electrical power steering. In the design of squirrel-cage induction motors, equivalent circuit analysis using lumped parameters is often used to investigate the motor performance. However, estimation of the motor characteristics has been limited because the standard equivalent circuit that considers space harmonics does not consider the core loss. To improve the reliability of the characteristic analysis, a new method that can solve these problems is required. Thus, study of a new equivalent circuit that considers the saturation in the core and the core loss harmonics is needed. Therefore, to obtain the reliable characteristics of induction motors, this paper presents a modified space harmonic equivalent circuit that considers the harmonics of core loss resistance. The modified equivalent circuit is verified by comparing the analysis results of the suggested method and the experimental results of the test model.

Equivalent circuit considering the harmonics of core loss in the squirrel-cage induction motor for electrical power steering application

Electric machines are widely used across a variety of applications. In particular, the cogging torque of a permanent magnet (PM) synchronous motor is a significantly important characteristic in the application of electric power steering (EPS) systems. Accordingly, various optimal design methods are adopted to reduce the cogging torque for an EPS motor. However, in most cases, the measured cogging torque of the EPS motor is much greater than finite element method result, because the additional cogging torque harmonic components are generated by manufacturing tolerances. Especially, the specific harmonic components are produced due to magnetic unbalance by the asymmetry of motor shape which is caused by the tolerances in motor cores or PMs. These components are not eliminated by applying a skew. Thus, in order to reduce the effect of the tolerances, a robust design is needed. In this study, the effect of PM tolerances is studied, and Taguchi robust design is performed to enhance the motor quality regardless of the tolerances.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-epa.2015.0638

Taguchi robust optimum design for reducing the cogging torque of EPS motors considering magnetic unbalance caused by manufacturing tolerances of PM

The reduction of cogging torque is the most important design objective for electric power steering (EPS) motors, because the rotation characteristics of the motor are directly transmitted to a driver. Therefore, a variety of optimal design methods are applied to reduce the cogging torque for EPS motors. However, the measured cogging torques of fabricated models are significantly greater than the finite-element analysis (FEA) results, because the additional harmonic components (AHCs) of the cogging torque are generated by manufacturing tolerances. The cogging torque generated by manufacturing tolerances can be divided into two components, which are generated by stator and rotor tolerances. In this study, AHCs, which cause cogging torque, are analysed by FEA by applying various tolerances to the analysis model, and harmonic analysis is also conducted. The relation of AHC generated from the stator and rotor is analysed by a rotor swapping test. Consequently, this study can be helpful to analyse the components of the cogging torque generated by manufacturing processes.

Ji-Min Kim

Papers

Effect of pole and slot combination on noise and vibration in permanent magnet synchronous motor

Design of an Ultra-High-Speed Permanent-Magnet Motor for an Electric Turbocharger Considering Speed Response Characteristics

Equivalent circuit considering the harmonics of core loss in the squirrel-cage induction motor for electrical power steering application

Taguchi robust optimum design for reducing the cogging torque of EPS motors considering magnetic unbalance caused by manufacturing tolerances of PM

Analysis of cogging torque caused by manufacturing tolerances of surface-mounted permanent magnet synchronous motor for electric power steering