This study performs a design and parametric study of interior permanent-magnet (IPM) machines equipped with novel semi-overlapping windings (NSWs). The influence of the key design parameters including; number of turns per phase, stack length, distance and angle between V-shaped magnets, rotor yoke thickness, magnetic bridge width and thickness and number of magnet segments on the flux-weakening (FW) performance characteristics are evaluated in detail. The influence of material of segmentation (material of bridge namely, air or iron) is also considered. A combination of analytical calculation-based program and a time-stepping 2D finite-element analysis based program are employed to evaluate the FW characteristics. The accuracy of the FW calculations, particularly the performance at high-speed regions, is verified over changes in torque components; namely reluctance and permanent magnet (PM), inductance components, PM flux coefficient and inverse saliency ratio due to the change in considered design parameter. The electromagnetic torque, torque ripple, output power and FW capability are investigated by parametric analyses. Moreover, the power losses and efficiency maps together FW curves are calculated for the optimal NSW IPM machine. The experimental measurements, taken from manufactured prototype, verify that the performed analyses and methods described in this study are accurate and reliable.

The design of permanent magnet synchronous motor (PMSM) is a constrained multi-objective problem, and there are often conflicts between the goals. Aiming at the complexity of PMSM optimisation and a large number of variables, multi-objective optimisation design of PMSM using a multi-objective comprehensive teaching algorithm (MCTA) is proposed. This algorithm is improved based on the teaching–learning-based optimisation algorithm and can better adapt to large-scale sample space and multivariate optimisation. Also, based on a magnetic equivalent circuit, a static electromagnetic model of the radial magnetic field PMSM is derived, and the design requirements and goals of the PMSM are analysed. In the two PMSM multi-objective optimisation calculation processes, the optimal solution was calculated based on the composite fitness function and Pareto front, respectively. The results of the MCTA were compared with other natural optimisation algorithms. Finally, according to the optimisation results of two sets of experiments, the correctness of the optimal solution of the algorithm was verified by finite element analysis and actual measurement of the prototype. The analysis of results shows the effectiveness, simplicity, and inspiration of MCTA in the PMSM multi-objective structure optimisation design.

Although axial-flux permanent magnet machines have high torque densities, challenges regarding mass production of stators make them a less appealing choice. Printed circuit board (PCB) axial-flux machine is a type of machine with a stator that is made of layers of PCB. Given the precise, fast, and cheap mass production capabilities of PCB manufacturers, PCB axial-flux machines stand as a viable alternative for conventional round-wire winding machines. In this study, five different winding topologies are compared. Their induced phase voltages and torque are calculated using the developed magnetic scalar potential method and finite element analysis (FEA). Proposed windings are tested on a 16-pole, 2000-RPM, double rotor-single stator axial-flux permanent magnet synchronous machine. Results showed that the parallel winding had the smallest resistance and loss. Moreover, radial and concentric winding had the highest induced voltage and torque while the radial winding had 20% less phase resistance than concentric. Also, the induced voltage of radial winding had the smallest total harmonic distortion in comparison with other winding types. A novel unequal width parallel winding is proposed and it is compared with parallel winding separately. It is found that by simply increasing the cross-section area of wave windings, it is possible to decrease copper loss by 17%.

One of the main challenges in motor design is the winding layout, including winding distributions and magnetomotive force (MMF) harmonic analysis. Considering some shortcomings in the existing theories for winding distributions and difficulties in dealing with unconventional fractional-slot windings, a unified theory of symmetric winding distributions is proposed. First, this study gives the sufficient and necessary conditions for a m-phase symmetric winding and the novel winding distribution formula. Subsequently, a general method for MMF harmonic analysis including the amplitude of MMF harmonics and harmonic orders are proposed. Finally, the analysis results show that this unified theory is an efficient and compact method to deal with the winding layout to analyse all kinds of winding MMF harmonics.

This study represents an effective approach for detection and classification of bearing faults in brushless DC (BLDC) motors based on hall-sensor signal analysis. The envelope analysis and Hilbert–Huang transform are used to extract features from the time and frequency domains of each signal. A new feature selection technique is proposed based on the combination of the genetic algorithm strength and the advantage of the binary state transition algorithm. The genetic algorithm explores search space through cross-over operator while the binary state transition algorithm is based on four special transformation operators in the local exploitation capabilities. The artificial neural network and support vector machine are used as the classifier. Each model is separately analysed and compared, leading to a high possibility to distinguish the bearing faults.

Computation of iron losses in transformers requires significant numerical efforts, particularly under magnetic saturation when the magnetic non-linearity needs to be considered. This study proposes a Fourier method to calculate the magnetic flux density used for the iron loss evaluation in transformers under saturation. It includes pre-processing of the non-linear material. A permeability frequency spectrum is obtained from Fourier analysis, where the fundamental part is used as a magnetisation definition and the harmonic components are used for core loss calculation. The proposed method offers a time-efficient tool to calculate core loss under various saturation levels and non-sinusoidal excitation currents. The influence of the definition of the core material on the leakage field and the stray loss calculation is studied and compared with existing methods. The proposed methods have been implemented and validated in two- and three-dimensional finite-element models with isotropic and anisotropic cores. The results yield accuracy comparable to that of a time-domain calculation. Furthermore, the influences of various effective permeability methods on the leakage field and the associated stray loss are compared and discussed.

Electric vehicle (EV) technology proposed itself as a great solution for the predictable shortage in traditional energy sources. Using wireless power transfer (WPT) technology for charging the battery can be considered as a good solution to overcome the battery charging time problem. The considered WPT technique in this research is an inductive magnetic resonance (IMR). The problem now is to design a smart controller system that enables the EVs to obtain the optimum value of WPT by using the machine vision and the technology of Internet of Things (IOT). The utilisation technique of the maximum WPT in this research based on the simulation study of the magnetic flux density between the sending and receiving coils of the WPT system. Maximum efficiency of IMR method depends directly on the ideality of coils alignment. To achieve this alignment, a smart controller has been introduced with four integrated controlling layers. Coordinating an image processing technique with smart embedded sensing elements is considered the main solution key to better positioning. National instrument packages NI LabVIEW and NI vision are considered to fully control the system. NI Data Dashboard enables creating a wireless link using the concept of IOT to a smartphone running simple graphical user interface.

It is commonly acknowledged that a direct-drive linear wave energy converter (DDLWEC) will achieve maximum power extraction in the resonance state, which can be realised through impedance matching under the assumption that the wave is regular. While the real ocean waves are hardly regular. Considering swell, a relatively regular type of real ocean wave, by approximating it with a sum of multiple frequency components, the DDLWEC can be forced resonance to the swell through velocity control, the optimal velocity is derived based on the dynamical model of the DDLWEC through frequency domain analysis. The stability of velocity control is proven and the float equilibrium position deviation due to the velocity control is analysed and countered through compensation control. In real-time control, the excitation force is approximated by the sum of four sinusoids, simulation and experiment results demonstrate that the proposed method is valid, stable, capable of achieving a high-power extraction efficiency, and superior to some existing methods.

An efficient online flux-based diagnostic approach is proposed to detect turn-to-turn faults in the stator and rotor windings of wound rotor induction machines, at an early stage of development, which can be applied in the online mode. Some flux sensors are installed in the stator slots to detect the rotational magnetic field at various positions along the air-gap circumference. These sensors measure the flux linked to all winding coil groups, in the three phases. Any fault occurring either in the stator or rotor windings will disturb the air-gap flux and create an asymmetry in the rotational magnetic field, which is detectable through the difference of the induced voltages in the corresponding flux sensors. The proposed diagnostic technique is evaluated by finite element analysis as well as by multiple experimental tests. The obtained results show that such invasive technique is able to detect and discriminate various faults in the stator and rotor windings with high accuracy, low calculation burden, proper sensitivity and appropriate robustness in the face of machine load level variations.

Due to the voltage limitation of the inverter DC-link of railway traction systems, six-step operations are widely used in the high-speed region to improve the voltage utilization and increase the maximum fundamental frequency. The magnitude of the output voltage fundamental harmonic reaches the maximum for six-step operations, while only the phase angle can be adjusted. This limitation makes it challenging to control the instantaneous current of permanent magnet synchronous motors (PMSM). This paper proposes a single d-axis current regulator flux-weakening control scheme to improve the current control over six-step operations of PMSM without changing the inverter output voltage modulation ratio by controlling only one degree of freedom. The voltage in six-step operations is generated by synchronous space vector pulse width modulation based on basic bus clamping strategy with an effective limitation of the switching frequency in the full-speed region. A simplified model of the current regulator is developed for the analysis and design of the controller parameters. This paper presents clear rules for entering and quitting six-step operations effectively to achieve a smooth transition between double current regulators and the single current regulator control. The numerical results are verified by experimental measurements on a 7.5 kW PMSM drive.

This study proposes a crossed flat solenoid coupler (CFSC) for electric vehicle wireless charging. The impact of four size parameters of CFSCs on coupling coefficient and misalignment tolerance is studied using finite-element analysis. The optimisation methodology of CFSCs considering size constraints is given. The CFSC is compared with the planar square coupler (PSC) and double D coupler (DDC) from three aspects: coupling coefficient, misalignment tolerance, and copper usage. The CFSC performs the best in the three aspects, and the DDC performs the worst. Two wireless power transfer prototypes, one employing CFSCs and the other utilising PSCs, were built to demonstrate the superiority of the proposed coupler. Primary inductor-capacitor-capacitor secondary series compensation topologies were employed in the two prototypes. Experiments agree well with theoretical analysis and simulations. The power transfer efficiency of the CFSC-based prototype was 1.6% higher than the PSC-based prototype when the Z-axis displacement is 45 mm.

The six-phase direct-drive permanent magnet synchronous motor (DDPMSM) has a good prospect in electric vehicles, ship propulsion, aerospace and other fields due to the advantages of low voltage, high power, low speed and high torque. In this study, a six-phase DDPMSM is proposed with 60° phase-belt toroidal winding configuration (60°-TW). Different from traditional overlapping windings, each coil of 60°-TW is wound onto the stator yoke in the same direction. The topology of the proposed motor is introduced, and its operation principle is analysed by describing the variation of the magnetic field produced by the six-phase 60°-TW versus time. Meanwhile, based on the same power grade and effective volume, the six-phase PMSM and dual-three phase PMSM with different winding arrangements are designed. The magnetic field distribution, back-EMF, cogging torque, torque and loss characteristics are explored in detail. The results show that the proposed six-phase DDPMSM with 60°-TW has the characteristics of low speed and high torque in comparison to the traditional six-phase PMSM and dual-three phase PMSM, which is expected for direct-drive systems.

The eccentric magnetic harmonic gear (EMHG) utilises the change of the magnetic permeability caused by eccentric structure to achieve large torque transmission with high gear ratios. This study presents an exact EMHG analytical model based on the hyperbolic cotangent transformation method. The exact method has no truncation errors and thus it is appropriate for the analysis of magnetic fields in the EMHG with large eccentricity. Firstly, the eccentric air-gap magnetic field distributions are obtained by modulating the concentric magnetic field distributions with the relative permeance function. Then, the air-gap flux density of the EMHG is obtained according to the superposition of the flux density by the eccentric rotor and stator permanent magnets acting alone. Furthermore, the analytical results of the air-gap flux density and electromagnetic torque are compared with those of the finite-element method, which verifies the correctness and validity of the analytical model. Finally, the experimental measurements on the dual-stage EMHG confirm the validity of the analytical prediction.

A dual-rotor permanent magnet Vernier machine (DRPMVM) with permanent magnets (PMs) on both sides of the rotor and stator is proposed and studied here. The configuration and working principle are provided, then the expression of coil-side voltage is obtained based on the rotating harmonics of the air gap flux density. The effects of the rotor slot number on the amplitudes and phase differences of the voltage components are explored, and suitable combinations of the stator and rotor slot numbers are selected. The impact of the rotor and stator PMs on the voltage is also compared. Different coil connection methods are adopted for the DRPMVM with 12-stator slot and 10-rotor slot, and the back electromotive force, d- and q-axes inductances, and torque-speed characteristics are compared. Using the finite element method, the effect of the main parameters, including slot and yoke width on the average torque and torque ripple are then studied. Finally, a prototype machine is produced and tested to verify the conclusions.

Fractional pole-ratio winding is a new type of AC winding, consisting of coils with different pitches. The application of fractional pole-path ratio windings in synchronous generators will bring new problems to the modelling and simulation of internal faults. It is important to establish a mathematical model for the fractional pole-path ratio synchronous generators with internal faults and accurately calculate the fault currents. In this study, the multi-loop model of fractional pole-path ratio synchronous generators is first proposed. The method for calculating mutual inductances between stator coils with arbitrary pitch is given, and all the space harmonics, including the fractional ones, are considered in the inductance calculation. In order to improve the simulation accuracy of turn-to-turn faults, the effect of core localised saturation is modelled by modifying the air gap function of fault coils. A 300 MW fractional pole-path ratio synchronous generator is set as an example, and three types of internal faults are simulated. The comparisons of simulation results are made between the multi-loop model and the finite element model to verify the validity of the multi-loop model proposed in this study.

This study proposes a model predictive control (MPC) method with a fixed weighting factor for three-phase four-switch inverter-fed permanent magnet synchronous motor drives to suppress the capacitor voltage offset. The prediction model of the capacitor voltage difference is obtained based on the relationship between capacitor voltage and phase current. Then by analysing the relationship between basic voltage vector, electromagnetic torque and flux amplitude, the control of electromagnetic torque and flux in the model predictive torque control is transformed into the control of the voltage vector. The dimension of the capacitor voltage difference is the same as that of the voltage vector, hence the cost function with the fixed weighting factor is defined with the consideration of the capacitor voltage offset suppression. The effectiveness of the proposed MPC method is validated by the simulation and experiment.

Two-bladed wind turbines (WTs) are recently discussed as a potential alternative to reduce the cost of energy in offshore wind farms which have a higher cost compared to onshore wind farms. However, the dynamic response and performance of these WTs are different from the three-bladed WTs. In this study, new and comprehensive models for rigid and teetered rotor WTs are developed in FAST and emulated with a setup of the previous simulation-based works. Then, the power quality issues are discussed and compared for two-bladed WTs with rigid and teetered rotors as the main contribution of this study. The performance of a WT with different rotors is evaluated and compared in terms of power fluctuations, voltage fluctuations, flicker emission level. In addition, the structural loads of the turbine are studied and compared with both rotor types. This was done in emulation and simulation by varying linear horizontal and logarithmic vertical wind shear as well as utilising a turbulent wind time series without shear. The study presents results obtained by simulation and by emulation, using a scaled-down WT emulator. It presents conclusions as to which type of rotor offers better performance for various operating conditions.