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.

Determining the state of health of fuel cell systems is essential to improving its performance and life expectancy. This paper presents the development of a new rapid online condition monitoring system using optimized broadband impedance spectroscopy (OBIS). The hardware was specifically designed to be low cost and scalable to meet the needs of single cell and stack level testing. It is shown how classic electrochemical impedance spectroscopy (EIS) is limited when testing under extreme nonlinear conditions. The design process of the broadband signal is tailored for polymer electrolyte membrane fuel cell diagnostics in order to minimize measurement time and system disturbance while maximizing accuracy. The long measurement time of standard EIS makes it impractical to use for rapid fault diagnosis, and it is shown how the OBIS system is able to deliver impedance measurements under conditions where EIS cannot be applied. The proposed system is tested for an array of possible operational phenomena and faults and the results compared with that obtained from a commercial frequency response analyzer to demonstrate performance.

Presently, many condition monitoring techniques that are based on steady-state analysis are being applied to wind generators. However, the operation of wind generators is predominantly transient, therefore prompting the development of non-stationary techniques for fault detection. In this paper we apply steady-state techniques, e.g. motor current signatures analysis (MCSA) and the extended Park's vector approach (EPVA), as well as a new transient technique that is a combination of the EPVA, the discrete wavelet transform and statistics, to the detection of turn faults in a doubly-fed induction generators (DFIG). It is shown that steady-state techniques are not effective when applied to DFIG's operating under transient conditions. The new technique shows that stator turn faults can be unambiguously detected under transient conditions.

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.