Lester Chong

Design and Experimental Verification of an 18-Slot/14-pole Fractional-Slot Concentrated Winding Interior Permanent Magnet Machine

This paper presents the design and the experimental verification of an 18-slot/14-pole fractional-slot concentrated winding interior permanent magnet machine. The prototype machine was optimized for wide constant power speed range (7:1) and very low cogging torque, two of the most important requirements for traction machines. Measured performance of the constructed prototype machine has confirmed the finite-element modeling results. Experience gained from this study has led to develop a set of design rules for the concentrated winding (CW)- interior permanent magnet (IPM) machine. Scaling up of the prototype design based on these rules is also discussed in this paper.

Winding Inductances of an Interior Permanent Magnet (IPM) Machine With Fractional Slot Concentrated Winding

This paper investigates inductance characteristics of a novel 14 pole/18 slot, fractional-slot concentrated-winding (FSCW) IPM machine. The variations of the self and mutual inductances were calculated analytically and also obtained from the finite element model. These results were compared with experimentally measured values of the self and mutual inductances of the prototype machine. Study of the inductance characteristics reveals that both self and mutual inductances vary with rotor positions nonsinusoidally. Presence of harmonics in the magnetomotive force (MMF) is responsible for this nonsinusoidal variation of inductances. The conventional distributed winding machine does not have these harmonics. This paper analyses the contribution of these harmonics in the Ld and Lq parameters in a dq-model of the prototype FSCW machine constructed. The self and mutual inductances were represented by a Fourier series in the inductance matrix of the machine for dq-transformation. It was seen that the difference between d- and q-axis inductance is mainly contributed by the harmonic terms of the mutual inductance.

Application of concentrated windings in interior permanent magnet machine

The use of concentrated windings in the interior permanent magnet (IPM) machine reduces its axial length and increases high-speed performance by enhancing flux- weakening capability although at the expense of higher cogging torque, decrease in winding factor and saliency ratio. In order to take full advantage of the concentrated winding in the IPM machine, optimization is required to minimize cogging torque and to maximize winding factor and saliency ratio. This paper is part of a detail investigation in which authors will attempt to optimize the concentrated winding structure for a high performance IPM machine. The full review of the existing optimization technologies for the concentrated winding applied to the permanent magnet machine is the first step toward developing new methods for the IPM machine. The paper presents the study of the various optimization techniques of the concentrated winding and their suitability in context with the IPM machine.

Field weakening performance of a concentrated wound PM machine with rotor and magnet geometry variation

Concentrated non-overlapping windings (CNW) have recently gained popularity due to key attributes of reduced machine axial length and simplified manufacturing. These attributes make it relatively more suitable for traction applications where reduced size and cost plays a vital role. In traction applications, good field weakening performance is desired. In this paper, the field weakening performance of the SPM rotor is compared to two different IPM rotor designs. Magnet eddy current loss with sintered, segmented and bonded magnets in SPM and IPM machines are also compared. Finite element analysis with Flux2D is used for this comparison due to its ability to handle complex calculations with non-linear material properties and precise geometry variations.

ANALYSIS AND EXPERIMENTAL VERIFICATION OF LOSSES IN A CONCENTRATED WOUND INTERIOR PERMANENT MAGNET MACHINE

It is well known that additional space harmonics in the air-gap magnetomotive force (MMF) distribution of the concentrated non-overlapping windings (CW) cause additional losses in the machine. This is especially so for machines used for traction applications where the machine requires to operate over its rated speed and frequency. In this paper, the authors investigates losses present in an interior permanent magnet (IPM) machine with CW designed to achieve a very wide fleld weakening range. Losses were quantifled analytically and also using flnite element methods. Loss estimations were experimentally verifled in a constructed prototype machine. Based on the analysis, key losses were identifled. The optimization process to minimize these losses and of improving e-ciency were discussed in details. The segregation of the losses in the studied machine indicates that the losses in the magnet are much smaller compared to the rotor and stator core losses caused by the slot harmonics. Therefore, core loss minimization techniques for this type of machine will involve reduction of slot harmonics. Also, copper loss is found to be the most dominating component of the total loss. Hence, copper loss minimization should be part of the design optimization process.

Design of a highly efficient 1kW concentric wound IPM machine with a very wide constant power speed range

This paper presents a design process of a 1kW interior permanent magnet machine with concentrated non-overlapping windings. The main focus of this design is to achieve a very wide constant power speed range and optimal efficiency throughout the entire speed range. The authors will explain how the increase in airgap harmonic components caused by concentrated windings affects core and magnet losses; how the speed range is optimized and how losses are minimized by machine geometrical variations, construction strategies and appropriate selection of materials. Finite element analysis with transient and steady-state AC magnets in FLUX2D is used for predicting machine loss and field weakening performance due to its ability to handle complex calculations with non-linear material properties and precise geometry variations.

Experimental verification of core and magnet losses in a concentrated wound IPM machine with V-shaped magnets used in field weakening applications

It is well known that concentrated windings results in an increase of airgap flux harmonics, which leads to additional losses. In the wider field weakening regions, the machine yields a non-linear increase in losses due to the frequency-squared dependence of eddy current loss. This paper compares the higher frequency losses in the stator core, rotor core and magnets with different rotor magnet configurations and lamination thicknesses. Known loss reduction techniques are investigated and implemented. Losses are predicted by 2D and 3D finite element analysis. A 1kW concentrated wound IPM machine prototype with V-shaped sintered neodymium magnets has been built and the experiment results are used to validate modeled losses.

Experimental verification of open circuit parameters of an IPM machine with concentrated windings

The application of concentrated windings (CW) in interior permanent magnet (IPM) machines has been claimed to enhance high-speed performance by increasing flux-weakening capabilities of the machine. However this is at the expense of a high cogging torque, decreased winding factor as well as saliency ratio. This paper illustrates the effects of implementing well known methods to improve open circuit characteristics of the CW-IPM machine. Theoretical results are proven by the use of finite element (FE) methods and models are verified with experimental results with a prototype machine.

Performance comparison between concentrated and distributed wound IPM machines used for field weakening applications

Distributed windings have been the winding of choice in IPM machines over the past decades. However recent studies have shown the benefits of applying concentrated windings in terms of increasing the power density of the machine as well as the field weakening performance. This paper states and addresses issues with the application of concentrated windings and compares its field weakening performance to equally sized IPM machines distributed windings. In this paper the authors show the extent of torque density increase, field weakening range increase as well as a comparison of machine characteristics such as cogging torque and efficiency.

Analysis of CPSR in motoring and generating modes of an IPM motor

This paper studied the variation seen in the constant power speed range (CPSR) of a prototype IPM machine in its generating and motoring modes. The influence of the stator resistive drop, saturation, cross-coupling, variation of the magnet flux-linkage and DC bus voltage over the current and voltage limits and trajectories on CPSR for motoring and generating were investigated as probable causes. Study revealed that the difference in the base speeds of motoring and generating is largely caused by the stator resistive drop whereas the reduced DC bus voltage influences the starting of the pseudo-constant power speed range. The saturation and cross-coupling affects the motoring and generating similar way by distorting the voltage limit ellipses and trajectories. Thus, they influence the CPSR of the motoring and generating mode in the same fashion and do not contribute to the difference in the CPSR.