Unbalanced magnetic pull (UMP) occurred due to the uneven distribution of magnetic flux around the airgap, which can be caused by the existence of rotor eccentricity in the machines. Here, a UMP damping coefficient is introduced to explain the UMP damping effect from the counteracting flux produced by a parallel-connected cage rotor. An empirical method is proposed to calculate the UMP using the damping coefficient and an analytical model. Using the proposed method, a four-pole and eight-pole squirrel cage induction machine with static eccentricity are investigated, which uses inputs from both finite element analysis and experimental work. Then, the UMP calculation for a dynamic eccentricity with the extracted parameters is done to verify the empirical method. A slip control method is described which uses a UMP/torque ratio to find the operating slip with the lowest UMP. Comparisons between results with and without slip control are made on both induction machines. It shows that great reduction in UMP can be achieved when the machine is lightly loaded.

A starter generator is a core technology of the more-electric aircraft and all-electric aircraft. The traditional switched reluctance machine (SRM) requires a high accuracy position sensor and high-speed processor while generating power. Therefore, the cost of the controller is high and the maximum speed of the machine is limited. A dual-mode doubly salient starter/generator is proposed in the study. In the process of starting and generating power, the machine operates based on the SRM principle and the doubly salient electromagnetic machine principle, respectively. In order to realise the transformation of the operating principle, the machine uses a winding switching device, and half of the windings are replaced as field winding that provide DC excitation in the generator mode. A suitable power converter is proposed based on introducing the structure and working principle of the machine. A winding switching device is designed, and the conversion process is explained in detail. A finite-element method is simultaneously used to analyse the motor-driven performance and the power-generation performance of the machine. A 12/8-pole prototype machine is developed. Additionally, the effectiveness of the starting, generating, and dual-mode conversion is verified by experiments.

This study investigates the origin of resonance in switched reluctance motor (SRM). It has been found that the second-order harmonic component of phase current is one of the major origins, which may cause resonance when its frequency multiplied by three caused by three phases coincides with natural frequency. It has also been demonstrated that there is a natural-frequency-centred band, saying that as long as the excitation frequency or its harmonics locates in the band, resonance will be excited. Accordingly, influence of critical parameters such as turn-on and turn-off angles on second-order current harmonic and corresponding vibration caused by resonance have been fully studied. Based on the study, optimal switch angles can be used to reduce second-order current harmonic, and thus to reduce vibration and noise caused by resonance. Both simulation and experimental results show that resonance can be effectively reduced by selection of optimal switch angles.

This study proposes a new high-temperature superconductor (HTS) modular flux-switching linear machine for rail transit, in which the armature windings and HTS field windings are placed on the short mover, while the long stator is only made of segmented low-cost iron. The key is to adopt a modular mover consisting of three separate phase modules whose positions are mutually 120° electrical degrees apart to greatly offset the cogging force for suppressing the thrust force ripple, accompanied with the features of high-fault tolerance. Also, the HTS excitation can produce stronger magnetic field than permanent magnet excitation to obtain a high force density; meanwhile, it easily regulates the air-gap flux density for achieving flexible high-speed constant-power operation. The operation principle and general design method of the proposed machine with concerning the HTS-excitation pattern are described in details. By using the finite element analysis, the machine performances are comparatively analysed with its counterpart without using modular mover to verify its validity. The results show that the proposed machine can offer more sinusoidal back electromotive force, better fault tolerance, higher thrust force and smaller force ripple.

This study presents an approach to build a reduced-order model (ROM) for the governor control systems of diesel-engine generators in an island power system. The hybrid particle swarm optimisation (PSO) is used in the parameter identification of the ROM. The reduced-order governor system model could be a useful and feasible model in the stability analysis of the island power system by using power system simulator for engineering. The results of the ROM and a sixth-order model have been compared. It is found that the ROM with the parameter values identified using the hybrid PSO is robust. Moreover, real-case validation of the ROM shows that it is usable to analyse stability and contingency in the power system.

This study deals with inter-turn short-circuit assessment of DC traction motors used in railway locomotives. This has been done by analysing input current spectra of rectifier unit feeding the traction motor. The analysis includes multi-resolution analysis and discrete wavelet transform (DWT) of current spectra to calculate approximate and detailed coefficients and then to evaluate the skewness, kurtosis and root mean square values. Variation of those values with respect to percentage of inter-turn short circuit at different DWT decomposition levels has been observed. A number of curves have been chosen for fault assessment based on the observations. Deviations from normal condition have also been observed by logic matrix. Depending on the features obtained, normal and different percentages of short in the traction motor windings have been classified and an algorithm has been proposed accordingly. Case study has been carried out on Indian WAP4 locomotive, wherein the input current to the rectifiers has been analysed and efficacy of the proposed algorithm has been validated. If for the locomotives, these parameters are monitored, percentage of inter-turn short circuit in the winding may be assessed far before massive system degradation occurs.

This study proposes a model-based control strategy for flux weakening operation of a synchronous reluctance machine, with a methodology that is extendible to any synchronous machine. The strategy leverages in the presence of digital non-linear models that describe the relation between currents and flux linkages in the machine. Such models are usually needed for conventional maximum-torque-per-ampere control and sensorless control, but here they are exploited to achieve flux-weakening operation without the need of flux weakening regulators, ensuring a seamless transition between the operating regions of the machine. The external voltage regulation loop for flux weakening is thus eliminated and substituted by a combination of look-up tables and binary searches, which are executed within one digital control period and which generate the required current and voltage references that fulfil the drive limitations. The method can also be coupled with mechanisms to compensate for magnetic parameter inaccuracies, to achieve an accurate tracking of the reference torque. The proposed solution is simulated and validated in a laboratory test bench on an 11 kW synchronous reluctance machine.

It is usually difficult to obtain the radial levitation force of the radial-type superconducting magnetic bearing (SMB) due to the massive numerical calculations and the sophisticated experimental measurements. This study presents a method for fast calculating the radial levitation force of radial-type SMB, which is based on the infinitesimal method and the 2D finite-element method. During the modelling, the radial-type SMB is assumed to be composed circumferentially of infinite superconductor-permanent magnet (SC-PM) infinitesimals with shape of rectangular thin slice. The dependence of levitation force for the SC-PM infinitesimal on the air-gap length between the SC stator and the PM rotor can be obtained using the 2D finite-element model established in Cartesian coordinate system. Moreover, a simplified analytical model of calculating radial levitation force is developed based on the infinitesimal method and the circumferential distribution formula of non-uniform air-gap when the PM rotor exhibits radial eccentricity. The results of theoretical calculation and experimental measurement of radial levitation force show a good agreement, which verifies the feasibility of the proposed method. It has the advantages of fastness and easiness, and can be used as a theoretical tool for the design, optimisation and performance prediction of the radial-type SMB.

A new optimum structural design is presented here in order to shift the natural frequencies of the stator structure in brushless DC motor to the highest values at different mode shapes and increase the stator stiffness. Shifting the stator natural frequencies to higher values reduces or eliminates the severe effects of the structural resonances as the coincidence of the natural frequencies and the components of the motor electromagnetic excitation forces occur at higher frequencies at which the forces have lower amplitudes. In the proposed structural design, some parameters relating to stator slot are optimised to shift the stator's natural frequencies to the highest values without changing the slot areas and the stator outer diameter as the problem constraints. The optimisation is done by the response surface methodology combined with the modal analysis by the finite element method (FEM). The validity of the optimisation method is confirmed by FEM simulations and experimental tests at different speed regions. Moreover, the performances of the prototype and optimum motors are analysed by FEM and experimental tests to show that the stator parameters optimisation process does not cause any negative influences on the quality of the motor performance.

Here, the new expressions for the mutual inductance and the magnetic force between two Bitter coils (thick coil and pancake) with the inverse radial current densities are presented. These types of coils are used for producing the high magnetic fields. For producing strong magnetic fields, the coils are extremely heated, so that they could be cooled to avoid this problem. During a water-cooled magnet trip, the induced current in coil changes as a function of decay time constant which is determined by the self-inductance and the resistance of the water-cooled magnet. Moreover, such high fields develop the strong magnetic forces which can cause the mechanical stress upon the supporting structure. This way the precise evaluation of these electrical quantities between coils must be calculated to optimise the support structure of Bitter coils. With the newly presented approach, these quantities are obtained in an analytical and semi-analytical form expressed over elliptical integrals and simple integrals. For validating this method, the comparative improved filament method is used.

This study presents a comprehensive design procedure of a permanent magnet assisted synchronous reluctance machine (PMaSynRM) for replacing a permanent magnet synchronous motor (PMSM) in a commercial washer. The motors used in these applications have to perform efficiently on a wide speed range with constant-torque region for washing, and field-weakening region for spinning. A design methodology is determined consisting of electromagnetic design, thermal/mechanical stress analysis, optimisation and prototyping. There are limitations and decisions on the initial design steps, considering the volume allocated for the machine, magnetic material and permanent magnet (PM) selection and the electromagnetic parameters for constant-torque and field-weakening regions. Design process is carried out following the initial parameter selection then the motor is produced and tested. Test results show that the PMaSynRM is 8.26% higher in volume and lower in power density than those of PMSM with a better field-weakening characteristic and fault tolerance. As a result, the authors proposed a methodology to design a PMaSynRM which becomes a good alternative for the mass produced home appliance motors since the materials’ amount are decreased in 20% for silicon steel and 50% for PMs consequently decreasing the total cost and offering nearly the same efficiency and power density for the application.

Nowadays, inductive power transfer is of great interest to the system working with electric power by virtue of its safety, reliability, and convenient characteristics. In fact, efficiency and compactness are the two parameters which play an important role in recharging electric vehicles. Double-D quadrature pad (DDQP) is a suitable magnetic structure that due to the use of an additional coil, can enhance the X-axis tolerance. Although there are several compensation methods to boost the efficiency, series and inductor–capacitor–capacitor (LCC) compensation types seem to be more practical and optimal. In this study, the LCC and series compensations are used together in the DDQP as the receiver side and calculated the value of the primary capacitor for enhancing the efficiency. Moreover, it is shown that, in the misaligned position which compensation has a better performance when utilising in the quadrature coil. Also, it is demonstrated that for making a system more compact, the quadrature and compensated coils integrated with the main coil in the secondary side do not have any significant effect on each other, neither on the other coils. Finally, the double-D pad transmitter and DDQP receiver with the integrated LCC compensation method is prototyped to verify the results.

A new direct adaptive fuzzy speed control method for a linear switched reluctance motor with unknown control gain sign is presented. The proposed control system consists of two parts: a fuzzy system and an adaptive law. Fuzzy system approximates an unknown ideal control law with unknown adjustable parameters. After determination of the control law, an appropriate adaptation law is designed to update the adjustable parameters to achieve control objectives. The adaptation law is designed using the error between the unknown ideal control law and fuzzy control law. Unlike previous works, in this study, the unknown control gain sign is taken as an unknown constant parameter and is determined online by an appropriate adaptation law. Proposed control method along with a fuzzy sliding mode speed control and a proportional integral speed control strategies are experimentally studied and the performance index is used to evaluate each strategy. The robustness of the proposed method to the parameters and external load force change has been verified via simulation and experiments. The results indicate that the proposed control method has an acceptable performance.

A wind turbine transformer resonance can occur due to high frequency transients at its terminal i.e.; under its energization through a length of cable. Occurrence of resonance can be addressed by a sophisticated transformer design procedure. The goal is to obtain an optimum design capable of controlling the frequency response of the winding in such a way to avoid occurrence of any resonance under transient conditions. Three insulation clearances parameters which are employed for the wind turbine transformer winding design have been investigated in design of a (800 kVA, 690/20,000 V) wind turbine transformer to determine effect of their variation on its frequency response. It is shown that the best way to control the frequency response is to adjust the distance between LV and HV windings while maintaining other clearances as short as possible; realizing limitations enforced by other insulation constraints. Multiple-design algorithm is also investigated and found to be effective in control of the amplification factor under resonance frequency condition. Finally a 20 kV/690 V–400 kVA dry type wind turbine transformer is employed to verify the promising features of this design methodology, through comparison of the frequency responses of the real transformer against the model.

This study presents a design method to obtain an innovative structural design of a magnetising fixture that can achieve a target magnetisation orientation for a ring-type magnet of a surface-mounted permanent magnet (SPM) motor. The optimisation problem is formulated to minimise the integrated value of the difference between the magnetic flux distribution, produced by the input current of the magnetising fixture, and the target orientation that improves the torque performance of SPM motor. Two level set functions are employed to express both the structural boundaries and the material properties of the ferromagnetic material and coil comprising the magnetising fixture. The optimal shape of the fixture is obtained by using an adjoint design sensitivity and a time evolution equation for each level set function. To confirm the effectiveness of the proposed method, it is applied to a magnetisation problem for an 8-pole 12-slot SPM motor designed for a battery cooling system in a hybrid electric vehicle.

A novel rotor structure with a set of compensation winding for line-start permanent magnet synchronous motors for high capacity and low speed, which can meet the requirements of a ball mill with a high moment of inertia, is proposed to improve the motor-starting performance. A control strategy for the compensation winding current is implemented to increase the synchronisation ability with a high-inertia load. The compensation current and its control method are analysed using a mathematical model and verified using a time-step finite-element analysis. The simulation shows that the permanent magnet motor proposed in this study can successfully start at a load of 15 times rotor inertia.

This study analysed the characteristics of electromagnetic force and noise of claw pole alternators with different pole and slot combinations and different phase number. The magnetic flux density in the airgap was first derived based on the magnetomotive force and permeance. Then the electromagnetic force was obtained using Maxwell stress tensor method. According to the analytical model, the spatial order and frequency of electromagnetic force can be expressed as the function of pole-pairs number p, slot number s and phase number m. Afterwards, the electromagnetic noise of three different alternators was tested in a semi-anechoic chamber. Combined with the 2D fast Fourier transform of electromagnetic force, the main force harmonics that caused the electromagnetic noise were distinguished. Finally, the relationship between the frequencies of electromagnetic force and noise and the number of pole-pairs and phase were established. Analysis result shows that for m-phase 2p-pole/s-slot integer slot claw pole alternators, the spatial order of electromagnetic force is kp (k = 0, 1, 2, 3,…) and the corresponding frequency of these force harmonic is [±2mpk′ + (±kp)]f _r (k′ = 0, 1, 2, 3 …). The main order (frequency domain) of electromagnetic noise is 2mp which is independent of the slot number.

In this study, a combined ON/OFF and conformal mapping method is applied to the permanent magnet shape optimisation of the surface-mounted permanent magnet synchronous motor (SPMSM). The magnet shape has a profound impact on the cogging torque and torque profile of the SPMSM. The proposed method is based on the combination of the conformal mapping and ON/OFF methods, which can reduce computation time significantly as compared with methods that are based on the finite-element method (FEM). For the optimisation process, genetic algorithms are used and applied to three cases. Finally, the FEM is used to verify the magnetic model and characteristics of the optimised machine.

With its simple construction, excellent mechanical and thermal capabilities to withstand stress, solid rotor induction motors (SRIMs) have become widely used in the areas of high-speed and high-pressure application fields. In this study, a novel solid rotor structure with slits in axial directions, of which the top of the rotor iron teeth is coated with copper, is presented. The design of the novel construction is discussed in detail and all rotor geometrical design parameters are optimised. The performance of the novel rotor design is compared with that of equivalent axial-slit and copper-coated solid rotors. To determine the performances, the systems were simulated by two-dimensional time stepping finite-element analysis. In the novel structure, the fundamental flux can penetrate much deeper than that of a smooth-type induction motor because of the presence of slits. In addition, because of the existence of coating on the top of the teeth, the rotor creates decreased torque ripple resulting in less vibration. The novel rotor design provides a better efficiency with less rotor loss together with a disadvantage of decreased power factor.

Nowadays, most brushless DC (BLDC) motors use Hall sensors or sensorless algorithms based on back-electromotive force (back-EMF) sensing to detect rotor position information. These methods detect the commutation moments but imply the use of rectangular stator currents which, according to recent literature, limits the energy efficiency. In this study, sinusoidal stator currents are used to increase the motor energy efficiency. As a consequence, standard control based on the feedback of the Hall sensors or based on sensorless techniques detecting the back-EMF zero-crossing cannot be used. Therefore, the authors propose a load angle control algorithm for BLDC motors without using position and speed sensors. The objective is to obtain energy-efficient sensorless control for the BLDC motor based on the measurement of only two current and one voltage signal. The energy saving potential of the proposed method is especially outspoken for fixed speed applications with varying loads, which are typical BLDC applications. Experimental results are presented to validate the proposed method. Energy efficiency measurements over the whole operating range of the BLDC motor are included and show an energy saving potential up to 9.5%.

The optimisation design of air-cored axial flux permanent magnet (PM) generator is a complex non-linear problem with constraints, multi-objective, multivariable and multi-peak value. The different variables will affect the same optimisation goal. In this paper, a multi-objective optimisation design of air-cored axial flux PM generator based on Taguchi–response surface method (RSM) is proposed. The main characteristics of generator efficiency, power quality, induction electromotive force and other main characteristics are taken as optimisation objectives. The parameter ranges that influence the optimisation objectives of the motor are selected as optimisation variables. First, the orthogonal matrix is established according to the number of selected parameters and the level factor of each parameter and the finite element method is used to solve the experimental matrix. Then, the mean and variance of the simulation results are analysed. The optimisation mathematical model was established between the target and the impact factor by using RSM for the conflicting factors, which can determine the optimal variable parameters. The effectiveness of the optimisation method is verified by finite element analysis and prototype experiments. The results show that the performance of optimised core less flux PM generator has been greatly improved.

The accuracy of flux linkage measurement is significantly important for a number of sensorless control methods for switched reluctance motor (SRM). This study proposes a novel flux linkage measurement circuit with the automated resistance correction, which comprises only circuit components. During the SRM sensorless operation, the dependence of resistance on temperature leads to the errors in flux linkage measurement and position estimation. The developed scheme is based on the zero-crossing property which asserts that the flux linkage and current pass through zero simultaneously. Hence, the flux linkage error captured at the time when the current falls to zero represents the resistance error and is used for resistance correction. The proposed circuit has been successfully implemented and tested on a sensorless SRM system. Experiment results indicate that the proposed system in sensorless control can be operated stably at different load torques and at the condition of given speed mutation and load mutation, and the speed range in steady state with rated load torque is 0–160 r/min. The overall estimated position error remains within an acceptable margin of 2%. Hence, it significantly improves the sensorless position estimation and thus SRM performance.

In this study, the authors aimed to analyse the influence of massive ferromagnetic shaft on the distribution of the electromagnetic field and to evaluate the magnetising current from the mains. To achieve this, they used motors powered by 50 and 200 Hz. They also used both numerical two-dimensional (2D) and 3D field-circuit methods as well as an analytical method based on the results of field analysis. This modified analytical method is based on the magnetisation characteristics of the shaft's material. According to the results, there was a significant impact of shaft's saturation on the machine with one pair of poles in the form of a significant increase in the amplitude of induction in the rotor yoke, which resulted in an increase in the magnetising component of the current drawn by the motor from the grid. This phenomenon was found to increase, in particular, when using non-magnetic shafts. In the case of machines with two pairs of poles, this effect was found to be much smaller than that of one pair of poles. They verified the results experimentally by comparing the calculated and measured magnetising currents.