The objective of this paper is to provide a comparison among permanent magnet (PM) wind generators of different topologies. Seven configurations are chosen for the comparison, consisting of both radial-flux and axial-flux machines. The comparison is done at seven power levels ranging from 1 to 200 kW. The basis for the comparison is discussed and implemented in detail in the design procedure. The criteria used for comparison are considered to be critical for the efficient deployment of PM wind generators. The design data are optimized and verified by finite-element analysis and commercial generator test results. For a given application, the results provide an indication of the best-suited machine.

The magnetic coupler is the heart of an inductive power transfer system, which facilitates wireless power transfer through its air gap. The couplers are designed to maximize efficiency, power density, power transfer distance, and misalignment tolerance while minimizing leakage flux, weight, cost, and volume. The coupler design process becomes complex due to the non-linear behavior of magnetics, sophisticated geometrical structures, and mandatory design limitations imposed by standards such as SAE J2954/1, IEC 61980-1:2015, and ISO 19363:2020. Initially, this paper reviews the advancements in coil design methodologies and their structures over the last few decades to identify the ongoing challenges and trends. The impact of the power electronics system, industrial standards, material selection, numerical and analytical modelling methods, and thermal modelling on the coil design process are identified to formalize the design procedure. A coil design example based on finite element analysis (FEA) tools is presented to identify the drawbacks of the existing design and optimization process. A sensitivity analysis, 3D-Pareto plots, and optimal design selection by considering misalignment variations are proposed to improve the multi-objective optimization process. A generalized guideline for coil design is proposed, which highlights essential design stages of an inductive power transfer (IPT) coupler. Current trends are identified, and future directions are proposed.

Slotted axial-flux machines have excellent power and torque densities. However, it is difficult to reduce their cogging torque due to the complexity associated with implementing classical techniques. In this paper, slot-opening widths and tooth profiles will be shown to be significant in mitigating cogging torque in these machines. In particular, varying the slot opening reduced it by 52%, whereas a parallel-tooth (rectangular) profile lowered it by 24%, when compared with a conventional trapezoidal-tooth profile. An analytical quasi-3-D analysis was formulated and used to analyze and determine cogging torque. It was validated numerically and experimentally. Its versatility is in its ability to analyze different shapes of poles and slot openings, which can be extended to model air-gap nonuniformity. This paper also presents cogging torque minimization techniques that maintain the ease of manufacture of the parallel-tooth stator. Experimental results showed 73% and 48% reduction in cogging torque, which are achieved by the use of alternating pole arcs and skewed poles.

Vibration analysis (VA) has been proposed for fault diagnosis in electric machines, but its efficacy is hinged on accurate determination of vibrating frequencies due to faults. Thus, this paper explores the applicability of VA in detecting static eccentricity (SE) in an axial-flux permanent-magnet (AFPM) machine with concentrated windings. The vibrations induced by the electromagnetic forces incited by the fault are tracked and detected in both frequency and time-frequency domains using standard signal processing techniques. The more dominant vibration harmonic component affected is that which is related to the lowest mode of magnetic force in the pole/slot combination investigated. It is revealed that the amplitude of the harmonic increased considerably with worsening eccentricities. Along with other harmonic components identified, it is proposed as an index for SE detection in AFPMs.

In this paper, the effect of static eccentricity on current harmonics and torque ripple in an axial-flux permanent-magnet machine with fractional-slot concentrated winding is investigated. Cogging torque minimization techniques are also explored in the presence of the anomaly to better understand their sensitivity to the condition. Also, the impact of single-sided and double-sided rotor topologies on both current harmonics and torque ripple is examined. It is found that static eccentricities incite significant increases in the amplitudes of space and subharmonics in the single-sided topology, which may be mitigated by the cogging torque minimization techniques. The double-sided topology is tolerant to the presence of static eccentricities unlike the single-sided topology; this is due to the opposing effect of the resulting asymmetrical properties of the air gap. Finally, this paper establishes a detection technique for static eccentricities in single-sided axial-flux permanent-magnet machine whereby the cogging torque minimization techniques do not impair on them.

Most non-intrusive Induction Motor (IM) efficiency estimation methods rely on the machine slip to compute the output power and the efficiency. To achieve the overall non-intrusive nature of the entire process, it is vital to utilize a reliable and non-intrusive rotor speed measurement technique in order to obtain the slip of an in-service motor. A number of rotor speed estimation techniques have been proposed in literature. This paper focusses on the review and analysis of different techniques in terms of intrusiveness, relative accuracy, sensitivity and computational overhead particularly when the IM is fed by an inverter supply. An experimental accuracy and sensitivity analysis of some motor current and vibration-based techniques is carried out to check the accuracy trends reported in literature and the robustness of these techniques. Potential techniques for non-intrusive rotor speed estimation of inverter-fed induction motors are recommended.