This study proposes a novel asymmetric rotor structure with tuning-fork flux barriers for a permanent magnet (PM)-assisted synchronous reluctance machine (PMA-SynRM) to improve the torque characteristics. The proposed asymmetrical rotor structure can effectively decrease the flux leakage inside the rotor, as well as ensure the maximum values of the magnetic torque and the reluctance torque are near the same current phase angle as each other to achieve better utility. To realise this, the frozen permeability method is implemented to separate the total torque into the reluctance torque and the magnetic torque via a two-dimensional finite-element method – JMAG-Designer. To achieve the optimal torque characteristics in the proposed model, the Kriging method and a genetic algorithm are used for getting the optimised model. The contribution of this investigation into motor performance is validated by comparing the proposed model with a conventional PMA-SynRM with a symmetric rotor structure. Beyond that, all machine models are the same size, have the same number of magnets and are operated under the same conditions. A prototype of the proposed model is experimentally verified, i.e. the simulation results agree with the experimental results.

In this study, a new robust sensorless control of doubly-fed induction generator (DFIG) in the complex domain has been investigated. The proposed sensorless control is based on the extended complex Kalman filter (ECKF) and proportional–integral complex controller. The design of this sensorless control in the complex domain allowed a threefold objective: a decrease in the system's dimension by half, an optimisation in the implementation of the control strategy and a decrease of the CPU computational time. In fact, to obtain the latter, the dimension of the DFIG model involved in this control has been halved, which leads to a reduction in the control's schema. Moreover, all the matrices involved in the ECKF have smaller dimensions than those of the real extended Kalman filter and no matrix inversion is needed because the output of the system is a scalar variable. The proposed sensorless control has been tested experimentally for several operating points, namely: nominal operation, operation under asymmetrical voltage dip and parameter variations. Moreover, the observability of the complex state model has been analysed and the required conditions for the local weak observability have been defined. The experimental results confirm the theoretical study and show a good reliability and a high rotor speed estimation accuracy.

This study explores the upper limits in power-to-weight and torque-to-weight ratios of coreless axial-flux machines with permanent magnets. Moreover, it provides a comprehensive multifunctional optimisation procedure that is utilised for obtaining these limits. The procedure encompasses analytical analysis of electro-magnetic, thermal and structural (mechanical) aspects of axial-flux machines. Obtaining global minima is ensured by considering the whole machine design space, and mapping it into the performance space, where a Pareto front can be easily identified. From it, an optimal motor/generator for airborne wind turbines is identified. The design has a power-to-weight ratio of 6.4 kW/kg (19 Nm/kg at 3200 rpm) including structural (purely mechanical) parts, at an efficiency of 95%. This is a significantly higher ratio than the one in modern commercial machines or designs reported in the literature. Therefore, the resulting machine is manufactured and experimentally tested in order to verify the claimed limits and the optimisation methodology.

The no-load radial magnetic field and no-load back electromotive force (EMF) of external rotor permanent magnet brushless DC motor (PMBLDCM) are calculated by applying the correction coefficient of magnetic conductance here, taking into account the stator slotting and static eccentricity effects. An external rotor PMBLDCM with 51-slot/46-pole, used as in-wheel motor, is taken as an example, the analytical calculation results of the no-load back EMF are validated by the finite-element method and experiment. The influences of static eccentricity ratio on the no-load radial magnetic field and no-load back EMF are investigated based on the analytical model. The investigation shows that static eccentricity does not change the harmonic contents of no-load radial magnetic field, so it does not change the harmonic contents of three-phase no-load back EMFs. However, static eccentricity changes the space order of no-load radial magnetic field, resulting in the different total harmonic distortions of three-phase no-load back EMFs; in other words, the asymmetric distortions of three-phase no-load back EMFs are generated. The asymmetric distortions of three-phase no-load back EMFs are intensified with the increase in static eccentricity ratio.

This study investigates the underlying mechanism of low-power factor issue of variable flux reluctance machines (VFRMs) from the perspective of magneto-motive force (MMF)-permeance model. On the basis of a simplified analytical model, the relationship between the design parameters and the power factor is identified and systematically summarised into three predictable ratios: the rotor permeance ratio, stator/rotor-pole ratio and DC/AC winding ampere turns ratio. Specifically, the smaller the rotor-pole arc, the air-gap length, the rotor-pole number and the AC/DC winding ampere turns ratio are, the higher the power factor will be. In addition, the weak coupling between the field and armature windings caused by the modulation effect of the salient rotor is responsible for the low-power factor issue of VFRMs, regardless of the control scheme, winding configuration or saturation effect. A 6-stator-pole/4-rotor-pole VFRM is prototyped and tested for verification.

A tubular flux-switching permanent-magnet linear machine (PMLM), which features unified magnetic field between the mover and two stators, is investigated for free-piston energy converter. The topology evolution, topology, operating principle and design considerations of the machine are thoroughly analysed. With the sinusoidal speed characteristic of free-piston Stirling engine considered, a tubular unified magnetic-field flux-switching PMLM is designed by finite-element analysis. Several main structural parameters, which include the outer and inner radius of the mover, the mover tooth width, the magnet thickness, the tooth widths of both the outer and inner stators and the widths of both the outer and inner stator yokes are studied to achieve high-force and mass-power density. Finally, the proposed machine is compared with two typical flux-switching PMLMs. The comparison results show that the unified magnetic-field flux-switching PMLM is suitable for applications which require high-power density, light mover structure and fast dynamic.

The stator Can and rotor Can are unique structures in double canned induction motors, and Can losses include Can eddy current losses and Can circulating current losses between the Can and other end structures. However, the current research of Can losses is mainly focused on Can eddy current losses, and operation conditions are limited to the no-load condition, rated-load condition and start condition. Aiming at this problem, two kinds of Can losses are calculated and analysed in details. The influence factors are researched. Based on this, a reduction method of Can losses is proposed, and the efficiency curve is provided. Calculation results are compared with test values to validate the accuracy of the solving model. The reliable basis is provided for reducing Can losses in double canned induction motors.

A new series of linear flux-switching permanent magnet (LFSPM) motors has elicited considerable attention. This series incorporates the merits of the high efficiency of permanent magnet linear motors and the low cost of linear switched reluctance motors for a long-distance drive system. However, the vector control of the LFSPM motor requires an expensive and unreliable linear encoder, which must be as long as the entire railway (or at least the whole linear motor). Such a large encoder will lead to extra costs and will even weaken the benefit of the motor performance. Thus, developing its sensorless control for engineering applications is necessary. Sliding-mode sensorless control has the advantage of strong robustness to parameter variations and external disturbances, as well as high dynamic performance, which is important for long-distance drive systems. The proposed algorithms can extend the minimum operating speed, thereby enabling the motor to work at a lower speed. Both simulation and experimental results are provided for verification.

The Vernier permanent-magnet (VPM) machines are recently attracting more attention for utilisation in low-speed, high-torque applications including renewable energy conversion systems, electric vehicles and elevators. Although, the VPM machines present interesting advantages, they suffer from lower power factor (PF) in comparison to the conventional permanent-magnet (PM) drives. In this study, a novel structure of the VPM machine with dual-stator and consequent-pole (CP) rotor topology is proposed with enhanced PF. The objectives in this new structure are achieving higher torque density per PM volume, higher efficiency, simpler and more robust installation of PM pieces, lower cogging torque and simpler rotor core laminations compared to the previously proposed VPM structures with reasonably improved PF. The low PF issue of VPM machines is analysed in details and the novel CP-VPM geometry is designed to diminish this drawback. Then analytical relations are derived based on the magnetic-equivalent-circuit for evaluating the flux density distribution, induced back electromotive force, magnetising reactance and PF. The effectiveness of the novel structure in enhancing the operating features is validated using analytical and 2D-FE simulation results. Finally, it is concluded that the performance of the optimally designed structure can be enhanced reasonably so that to consider it as a good choice for direct-drive applications.

Demands for various products, higher qualities, reduction of costs and competitiveness, have resulted in the use of intelligent fault detection systems. Bearing fault diagnosis as a major component of the electric motors has had an essential role in the operation of production units’ reliability. In addition, vibration analysis is one of the most powerful tools in diagnostics. Advances in signal processing technology and electrical equipment have developed a machinery condition monitoring for defect detection. This study has used the extracted features of vibration signals and the adaptive neuro-fuzzy interface system (ANFIS) network proposing a structure for fault detection and diagnosis of rolling bearings. Time-domain and frequency-domain statistical characteristics have been extracted fault information from vibration signals. Besides, the test data sets are presented to the ANFIS network. Simulation results indicated that the performance of the ANFIS network is acceptable. The results reveal that this method has more accuracy and better classification performance in comparison with other methods proposed in the literature.

In order to improve the operation performance and decrease the torque ripple of switched reluctance motor (SRM), a new current control method for SRM based on voltage space vector was proposed. In which the stator windings are excited by sinusoidal current with a DC offset to realise the unipolar current excitation. In this control system, zero vectors were used to control zero-sequence current alone and non-zero voltage space vector was selected to control d–q-axis current considering coupling. The reluctance torque component was offset by injecting third harmonic current into the DC bias current, and copper loss was minimised by selecting appropriate current ratio. Experiences verified that the new method can effectively control SRM current. The torque ripple can be reduced with third times harmonic current injection, but the efficiency is also decreased. Compared with the traditional control method, the proposed method is simple, easy to implement, and can effectively suppress torque ripple.

Here, a novel flywheel structure is proposed with passive permanent magnet (PM) bearings in the radial and axial directions and an active magnetic bearing (AMB) in the axial direction. In the proposed structure, passive magnetic bearings do not provide a stable magnetic levitation in all directions, but it is possible to maintain the dynamic stability of the flywheel by using AMB in the axial direction. In the proposed bearing structure, radial repulsive magnetic bearings (RMBs) reduce the power consumption with less complexity in the bearing structure but impose disturbance forces that deteriorate the stability of the actively controlled flywheel system. A complete model of the flywheel system is derived and transformed for a control design. A Lyapunov-based composite adaptive feedback control is designed for maintaining the stability under disturbances and a close convergence to the desired trajectory with fast parameter estimation. The performance of the composite adaptive control was experimentally verified for different cases using the RMB flywheel system. Additionally, a PID control was experimentally verified to demonstrate the usefulness of parameter estimation.

Combined radial–axial magnetic bearings (MBs) use a common bias magnetic circuit to provide radial and axial bias magnetic flux. Different from separate MBs, there is a constraint relation between the radial and axial bias flux. Meanwhile, there is also a constraint relationship between the radial and axial maximum bearing capacity. Therefore, the design method for separated MB is not suitable for a combined radial-axial MB (CRAMB). In this study, a design method of the CRAMB based on an asymmetric factor was proposed. The definition of the asymmetric factor was proposed. In order to avoid the radial and axial magnetic flux into the weak magnetic field and saturation region, the optimum range of the asymmetric factor is analysed. The influence of the asymmetry factor on stiffness is analysed; the prototype designed by this method can run stably. The validity and accuracy of the design method are verified by experimental results.

Axial-flux permanent magnet synchronous machines (AF-PMSM) using printed circuit board (PCB) windings are attracting interest because of an increased demand for machines with thinner geometries. A critical element in designing these machines is the choice of its PCB winding which should ensure high-performance characteristics with an efficient use of the PCB surface. However, there is a gap in the knowledge regarding the performance of different PCB topologies. The research reported here is motivated by the need to compare common wave-type PCB windings stator topologies. Accordingly, overlapping parallel wave, non-overlapping radial wave and overlapping radial wave PCB winding topologies are assessed, using finite-element analysis, and compared based on their key performance characteristics such as the generated back-electromotive forces, inductances and electromagnetic torque. The PCB winding that provides the best torque production is then chosen and manufactured. Experimental tests on the prototyped PCB AF-PMSM provide validation.