The induction motor is the most popular motor in energy conversion and industrial drive systems. This popularity is due to its robustness, low cost, and easy maintenance. Electrical, mechanical, thermal, magnetic and environmental stresses cause faults in the induction motor during the operation process. One of the challenging topics for many researchers is the development of a reliable efficient induction motor fault diagnostic techniques. The broken rotor bar fault is one of the critical faults that need to be early detected due to its sudden severe damages. The objective of this study is to present a survey of existing broken rotor bar fault detection techniques with new classification based on fault signature. Various monitoring conditions and signal processing techniques are considered for the detection process. A comprehensive list of references is reported for each fault signature and classified based on (i) loading level, (ii) the number of broken bars, (iii) validation and (vi) signal processing.

A decoupled two-degree of freedom switched reluctance motor is investigated for a special application in concentrated photovoltaic (CPV) power generation system. Firstly, a new method to adjust the gesture of solar cells by the motor is proposed. Second, the motor is introduced elaborately, including its structure, design and control. Importantly, this motor has been manufactured and initially used by the CPV power generation system. Thirdly, experimental measurements involving force outputs and torque outputs are given. The tracking accuracies in linear and rotary directions can achieve high accuracy in both degree of freedom of 0.3° and 100 μm, respectively, that is utterly needed by CPV. As the results of the tracking upgraded, the power generation output of the new CPV system has been enhanced, validating the effectiveness of the motor and the solar tracking system proposed. This power generation approach can be used in solar energy harvesting in future.

Magnetic-equivalent-circuit model for surface mounted permanent-magnet synchronous machines in both healthy and faulty cases is presented in this study, where both saturation effect and space harmonics are considered. Pole numbers, magnets and slot numbers can be chosen arbitrarily in the proposed model, and the behavior of the machine can be studied under various kinds of faults by a single model. Demagnetization, as well as inter-turn short short-circuit faults of the stator windings, are modelled, and a fault detection method is proposed. It is shown that the demagnetization fault is not detectible by stator current analysis, therefore an additional pole specific coil is considered in this study as a search coil. For modelling, the differential equations representing the electrical part of the PMSM model are converted into an algebraic type using the well-known trapezoidal technique and are solved simultaneously together with the non-linear magnetic equations using the Newton-Raphson method. It is shown that the presented model in this study is capable of effective modelling of the healthy and faulty machine under mentioned faults by a single model, thus reducing the computational complexity of the model. The effectiveness of the proposed MEC model is verified using finite-element method via Maxwell software.

Compared with the single-phase excitation mode of the switched reluctance motor (SRM), the static torque curves of the SRM with two-phase excitation mode are more flexuous and wide flat regions are absent from the curves. To improve the static torque performance of the SRM with two-phase mode, geometrical multi-objective optimisation strategy is developed in this paper. Considering the requirements of the electric vehicles, four indicators are presented and defined to evaluate the development of the SRM. Six main independent variables are determined and a novel multi-objective optimisation function was proposed to simultaneously improve static performance of the SRM. Furthermore, to simplify the optimisation, a sensitivity index that reflects the relative importance of each variable is developed to eliminate insignificant variables. The four-phase 8/6 SRM with two-phase mode is optimised by means of the proposed multi-objective optimisation method based on effects and sensitivity analysis of the design variables on indicators. The static and dynamic torque performance of the optimised SRM is evaluated and compared with those of the initial motor. The comparison results show that the multi-objective simultaneous optimisation strategy can improve the static average torque, static average torque per mass, and global index by 18.09, 12.08, and 6.57%, respectively.

V-shape interior permanent-magnet machines (IPMs) have been widely utilised in the industry due to their high-power density, high efficiency, and low manufacturing cost. There has been growing interest in applying multi-objective optimisation to the design of electric machines. In the context of V-shape IPM designs, it is important to include stress analysis in the optimisation design analysis as the steel bridges in the IPM rotor are structural weak points, where high stresses develop. However, traditional finite element analysis (FEA) that is normally used to compute bridge stresses becomes cumbersome due to its high computational cost. In this study, a computationally efficient analytical method is proposed to compute the mechanical stresses developed within the steel bridges in a V-shape IPM. The proposed method is shown to yield accurate predictions compared with FEA while reducing computational cost. A design study is conducted that demonstrates that the machine performance can be improved by incorporating the proposed structural analysis in a multi-objective optimisation-based-design environment.

The coupling between the rotary and linear magnetic fields is a special feature of two-degrees-of-freedom (2DoF) motors. The magnetic-coupling effect on the performances of 2DoF direct-drive induction motors (2DoF-DDIMs) is exposed and investigated based on 3D finite-element analysis and experiments on a prototyped motor. The performances of the 2DoF-DDIM are analysed under the conditions of with and without coupling. Further, the speed coupling coefficient is introduced and calculated to consider the effect of the magnetic-coupling effect on speed. The magnetic-coupling effect of 2DoF-DDIM, which leads to induced voltages and currents under rotary or linear motion and lower speed and higher fluctuations under helical motion, enhances with an increase in the source frequency and rotary speed. This research on the magnetic-coupling effect of 2DoF-DDIM will provide a significant reference for characteristic research and precise control of 2DoF-DDIM.

This study proposes an offset concentrated wound air-core linear synchronous machine for launch applications where reduced supply volt-amp per newton (VA/N) and attraction force is essential. A winding factor model based on the conductor distribution is derived and used to analyse the winding factor of possible topologies. Two configurations, 3-coil/4-pole and 12-coil/14-pole, have high fundamental winding factors and are selected for the design comparisons. Machines using single- and double-sided offset windings are compared. The results obtained for these selected designs show that the 3-coil/4-pole design with offset winding provides the highest thrust due to its higher winding factor, but the 12-coil/14-pole design has lower supply VA/N. The implementation of the offset windings reduces VA/N. A significant reduction can be seen when the long stator short rotor arrangement is considered. A half-segment prototype is built and tested. The experimental results obtained validate both the algebraic and three-dimensional finite element analysis.

This research study presents the fuzzy space vector pulse width modulation (FSVPWM) method of current control for three-phase voltage source inverter. The hybrid fuzzy particle swarm optimisation-based maximum power point (MPP) tracking algorithm has been employed to obtain high tracking efficiency as well as optimal MPP under adverse operating states. The FSVPWM technique provides less current harmonic content, fixed switching pattern, protection from over current, low switching losses and able to handle the non-linearities and uncertainties of the photovoltaic-wind grid integrated system. Grid synchronisation with sinusoidal current injection is achieved using the inverter controller. Fuzzy logic controller-based SVPWM controller compensates current error and provides DC-link utilisation with high efficiency. The experimental responses have been validated using MATLAB/Simulink interfaced real-time dSPACE DS 1104 controller. Irrespective of solar irradiance and wind velocity, the proposed hybrid system obeys MPP accurately with high performance.

In engineering terms, it is always desirable to maximise the efficiency of the motor and to look the problem in economic viewpoint, minimisation of the weight and cost of the motor is required. As these two aspects are like two sides of a coin, it is usually aimed to acquire the best efficiency per weight and cost. As a result, the performance improvement of permanent-magnet synchronous motor (PMSM) has two sides: technical and economic. This study proposes a new approach for design optimisation of an interior PMSM (IPMSM) taking into account both technical performances and economic considerations. The selected rotor configuration is a good candidate for general purpose industrial applications. A multi-objective optimisation technique based on a new and efficient magnetic equivalent circuit of the motor is applied to obtain optimal motor parameters. A Pareto front composed of possible optimal solutions is provided. The best optimal solution is then selected using a k-means clustering algorithm. To verify the efficacy of the design optimisation, the performance characteristics of the optimal PMSM are compared by both the finite element simulations and the experiments. In the test setup, an 8-pole, 200-Watt, four-phase IPMSM with an optimised structure is prototyped where the results give agreeable accuracy.

This study is concerned with the unified analytical solution of rotor strength for the segmented permanent magnet (PM) rotor retained by the carbon-fibre sleeve and non-magnetic alloy sleeve in high-speed surface-mounted permanent magnet synchronous machine. Considering the influence of different densities and coefficients of thermal expansion of PMs and pole fillers on rotor stress, the analytical solution for rotor strength was proposed based on displacement method and stress potential method in polar coordinate. The proposed analytical solution was validated by the finite-element method (FEM) and experiment, respectively, and the influences of rotational speed, retaining sleeve thickness and interference fit between the retaining sleeve and PMs on rotor strength were further investigated based on the analytical solution proposed. It is shown that the results calculated by the proposed analytical solution and the FEM are in good agreement with each other, and the analytical solution can accurately predict the stress distributions of the segmented PM rotor retained by the carbon-fibre sleeve and non-magnetic alloy sleeve. The difference in density and coefficient of thermal expansion between PM and pole filler, rotational speed and operating temperature have great effects on rotor strength.

The authors present the study and control of a new concept of hybrid generator in order to improve the behaviour of a synchronous generator during transients. The solution adopted is to place an energy storage system in parallel with the synchronous generator. The storage system consists of an inverter with a supercapacitor on the DC bus. A control law with a best compromise between energy exchanged in the supercapacitor and group speed efficiency has been developed and presented. To achieve that, a feedback control with integration of the deviation using a linear matrix inequalities approach has been used for current loop synthesis of the regulators. A second control law was developed to regulate the variable voltage across the supercapacitor. All validations were made on an experimental test rig. Experimental tests highlighted the significant contribution of this hybridisation to the motor speed variations and to the terminal voltage of the generator during impact or load shedding.

This study proposes a two-phase single-air-gap axial flux permanent magnet (AFPM) motor that offers a trapezoidal back-electromotive force (EMF) waveform to improve the performance of the only-pull drive technique compared with the radial flux PM (RFPM) motor. The only-pull drive technique provides the benefit of allowing the use of thin magnets in the motor without suffering from irreversible demagnetisation. In the proposed motor, the design geometry is primarily considered to achieve the desired trapezoidal shape of back-EMF. The effects of the geometry are explained with the help of air-gap flux density, flux linkage, and the leakage flux. Both the radial flux and the proposed motor adopt the same design concept and hold equal electromagnetic loadings. The profile of back-EMF and the electromagnetic torque driven by the only-pull drive technique are compared with that of RFPM motor with non-trapezoidal back-EMF. Furthermore, the split configuration is proposed for the AFPM motor to reduce torque ripples. The demagnetisation analysis is performed to confirm the operating point of the magnets in a split-AFPM motor. The results reveal that the AF motor is a good candidate for the only-pull drive technique.

Vienna rectifier is a typical three-level rectifier with complicated operating constraints. Also, the constraints pose a challenge for designing controllers with good dynamic performance. As predictive control is good at dealing with constraints, an optimal switching sequence model predictive control (OSS-MPC) strategy for the three-phase Vienna rectifier is proposed. A proportional–integral controller is designed to regulate the dc-link voltage. Also, an improved OSS-MPC method is utilised to control the input currents. Compared to the conventional finite control set model predictive control, it has the extra advantages of improved steady-state performance, fixed switching frequency, and elimination of weight factors. Simulation and experimental results verify the correctness and effectiveness of the proposed control scheme.

Rounded rectangular coils are more common in wireless power applications. It is important in practical engineering to calculate the self- and mutual inductances of rounded rectangular coils. A new model of the self- and mutual inductances of rounded rectangular coils with rectangular cross-sections is derived in this study. The proposed formulae are applicable not only to the rounded rectangular coils, but also to the extreme cases such as circular, rectangular, and race-track coils. The coil layouts including coaxial alignment and lateral misalignments are also discussed. Comparison of calculated self- and mutual inductances with experimental observations is provided and an excellent agreement between the two proves the feasibility of the proposed formulae.

High-temperature gas cooled reactor cooling medium drive motor is a unique driving equipment for coolant circulation in a reactor. The reliability of the motor is becoming increasingly vital to the stable operation of the reactor. To study the influence of the ventilation structure on the temperature distribution of a drive motor, the ventilation network model of the motor was developed using the fluid network method, the results of the ventilation system calculations were applied to the physical model as boundary conditions, and the temperature distribution was determined using the finite volume method. Meanwhile, two improvement schemes were proposed for the ventilation structure, and the influence of the ventilation duct geometrical dimension on the temperature distribution was investigated. Results show that the use of the proposed improvement schemes improved the utilisation rate of the coolant and reduced the maximum temperature of the motor by 5.7°C compared with the original structure. Furthermore, the validity of the calculation results was verified by comparing its results with test data. The maximum calculation error between the calculated results and test data was ∼9%.

The SWASTIK type radial magnetic field (RMF) contact design is widely used in vacuum interrupters. The mutually perpendicular petal limbs are a unique feature of this contact design. The focus of this work is to relate the Lorentz force acting on the arc with petal dimensions through closed-form expressions. Considering the petal limbs as equivalent to finite current carrying conductors, analytical equations are derived to compute the magnetic flux density at any point in space. The results are verified by using finite-element method (FEM) simulations of rail electrodes. The expressions are then used to compute the Lorentz force on the arc in SWASTIK contacts. The analytical predictions are compared with three-dimensional FEM simulations of a CAD model of the contacts. Applicability of the analytical results is investigated in the context of parametric variation of the radius, length and position of the arc and temporal variation of the contact current. The present work can be used in the first iteration of contact petal design. It is also applicable for the design of rail gun geometries.

Dynamic states in the power grid – deep voltage sags and swells, voltage fluctuation – can cause faults and defects in sensitive loads and in consequence financial losses. This study presents a voltage conditioner based on a direct PWM AC/AC converter with matrix chopper cooperating with a distribution transformer, called a hybrid distribution transformer (HDT). In comparison with other solutions of hybrid and smart distribution transformers, the proposed HDT is characterised by having a simple construction and small number of power electronic switches, a wide range and continuously variable voltage control character, and good dynamic properties, in combination with a high reliability. The study contains a detailed operational description and the experimental test results of a 1 kVA rated power laboratory model. The experimental tests were conducted in a closed control-loop with a peak detector unit in a feedback path, as well as with various types of voltage perturbation with linear and non-linear loads. In addition, some of the properties of the proposed HDT have been compared with other similar hybrid and smart distribution transformers described in the literature.

In this study, an improvement method for double-fed asynchronous motor-generators (DFAMG) design with open slots is proposed to reduce the capacity demand of rotor converter for the first time. The proposed method is achieved by decreasing the air-gap length (AGL) and applying conductive and magnetic rotor slot wedges. The design method of magnetic slot wedges and AGL in large DFAMG is presented. The mechanical analysis of a large DFAMG prototype reveals the necessity of using metal rotor wedges. To precisely investigate the influence of magnetic wedges in DFAMG, a two-dimensional field-circuit coupled model is proposed to consider the effects of rotor converter. Several wedge configurations of commercially available products are designed and analysed. The relationships between the electromagnetic properties of rotor wedges and prototype performance are investigated. The feasibility and advantage of the proposed method in DFAMG design are verified. A guidance for applying the proposed method in design improvement of large DFAMG is developed.

To overcome the inherent demerit of low power factor existing in transverse-flux permanent-magnet (TFPM) machines, a tubular staggered-teeth TFPM linear machine is presented here. Linear alternator integrated with free-piston Stirling engines could offer a great potential in a wide variety of applications ranging from solar energy generation to space power supply. The thermal behaviour of the machine is studied using a three-terminal lumped-parameter thermal network (LPTN) to solve the problem of temperature overestimation of the traditional LPTN. The determination of thermal resistances and thermal parameters are introduced in detail. The temperatures of various components of the machine under different load conditions are calculated by both the three-terminal LPTN model and the numerical thermal model. Sensitivity analysis is carried out to study the influence of critical thermal parameters on the temperature rise of the machine. On this basis, the effectiveness of the forced air cooling is investigated. A prototype is fabricated and temperature experiment indicates that there is a good agreement between measurement and calculation.

This study discusses the design strategy and response analysis of the brushless doubly fed reluctance machine (BDFRM) with an aim of commercially feasible implementation with satisfactory performance. In this regard, basic operation theory is reviewed, and a control strategy is proposed to maximise the motor torque capability. A BDFRM design is proposed and simulated for investigation. Subsequently, a prototype machine is built and tested. Predicted simulation torque data is compared with the actual machine data to evaluate the design approach.