This study proposes a permanent-magnet (PM)-free magnetic-modulated motor where the magnetic flux variation in a differential frequency between the armature fundamental rotating magnetic field frequency and the rotor rotation speed frequency is effectively utilised for the field magnetisation instead of PMs. The operation principle of the self-excitation with a diode rectifier circuit on the rotor is discussed. Magnetic circuit design and structural design of downsized prototype machine are performed for the purpose of experimental verifications of self-excitation. In addition, the preliminary experimental test results are demonstrated with prototype machine. Consequently, it is confirmed that the proposed PM-free magnetic-modulated motor can automatically obtain the field magnetisation power by utilising differential frequency which is inevitably generated by magnetic-modulation technique.

This study presents analytical and numerical modelling and experimental demonstration of a litz wire-based induction heating system suitable for high-temperature application such as melting. The use of litz wire in induction heating coil minimises the skin effect and proximity effect and in turn improves the system efficiency. This makes it superior compared with a solid wire and copper tube induction coil. However, the limitation of litz wire is temperature withstanding capacity of the strand insulation material as a result of which it is rarely used in high-temperature applications (>700°C). Numerical modelling of induction heating process was done by using magnetic vector potential formulation and Fourier equations. Temperature-dependent material properties were taken account to precisely model the induction heating process. Analytically estimated and measured equivalent impedances of litz coil were compared at different frequency (1–20 kHz) for initial validation of simulation. The number of turns and frequency were selected as per required litz coil efficiency and induced power in crucible. Finally during the experimental demonstration, crucible and litz coil temperatures were measured by ‘K’ type thermocouples and were compared with simulation results. The maximum temperature of ∼750°C could be attained in the design while limiting the litz coil temperature within 85°C.

Multiphase machines and drives are attractive to researchers due to the capability of fault tolerance. Finite-control-set model predictive control (FCS-MPC) has been introduced to the post-fault operation of multiphase drives and is superior with rapid dynamic response. However, conventional FCS-MPC is always troubled with low switching frequency and the consequent current ripples. This study proposes a fault-tolerant two-vector predictive control (FT-TVPC) that utilises a zero voltage vector to modulate with the active vector in each sampling period. The post-fault model of the machine and the drive is obtained in original phase frame with the purpose of achieving various control modes with different reference currents. A group of experiments are carried out and proves the effectiveness of the proposed control technique on improving the current quality. The average switching frequency of the inverter increases in exchange. The results also demonstrate that different control modes have little influence but working conditions have a great impact on the improvement of performance.

Here, different feasible configurations of passive permanent magnet bearings (PMBs) are presented and compared with each other. In these configurations, stiffness is improved by adding iron cores and air intervals between magnets. Bearings with opposite magnetisation stacking (standard) and rotating magnetisation stacking (Halbach) are studied here. A two-dimensional planner model is used to calculate the magnetic field and stiffness. The optimisation will be performed for obtaining maximum stiffness per magnet volume ratio. The results show that standard stacking with radially magnetised PMs and having back iron and air intervals between magnets is the most optimum structure. For larger dimensions of magnets, other structures will be useful too.

This study researches the multi-objective design optimisation of permanent magnet linear synchronous motors (PMSLMs) which are applied in high-precision laser cutting machines. The innovative fuzzy inference Taguchi method (FITM) coupled with finite element analysis (FEA) is proposed to solve the multi-objective optimisation problems as well as the maximum motor thrust with minimum thrust ripple. On the basis of the orthogonal array established by Taguchi method, the fuzzy inference system was introduced to translate the multiple optimisation targets to a single target. After the optimal selection analysis, the best combination of motor structure factors is obtained with a small FEA computation. Experimental results from the PMSLM prototype can confirm the validity and superiority of FITM.

Three-dimensional (3D) finite element (FE) modelling of axial flux permanent magnet (AFPM) motors is one of the time-consuming tasks which must be completed before manufacturing the prototype motor. A simple, fast, accurate, and effective numerical modelling approach for such 3D problems would be particularly useful for researchers. This study presents simple and effective 2D FE modelling approaches for AFPM motors with good accuracy with less computational effort. The modelling approaches are based on a number of 2D models or planes with inner rotor, outer rotor, or linear motor topologies. All the 2D planes with either topology are superposed together to represent the real AFPM machine. These approaches are examined in detail with various types of experimentally verified AFPM motors. Results obtained from the proposed modelling approaches are verified with 3D FE analyses and experimental data. The results indicate that the proposed 2D modelling approaches can significantly reduce the computation time with good accuracy as opposed to conventional 3D FE modelling of AFPM motors.

This study presents the parasitic effects on different carrier signal injection methods with alternative sensing signals for the sensorless control of permanent magnet synchronous machines (PMSMs). The different carrier injection methods are the rotating injection in the stationary reference frame with carrier current sensing and with zero-sequence carrier voltage sensing, the pulsating injection in the estimated synchronous reference frame with carrier current sensing, and pulsating injection in the anti-rotating reference frame with zero-sequence carrier voltage sensing, respectively. The parasitic effects, e.g. the magnetic saturation, inverter non-linearity, iron and PM losses, torque ripple etc. will be fully analysed and compared for these different injection methods. All the theoretical analyses are validated by either finite-element analyses or experiments on a laboratory PM machine.

A dq model representation of segmented secondary linear flux switching motors (SSLFSMs) is investigated. In these motors, the armature and field windings are both mounted in the primary slots and the secondary is only composed of simple laminated segments. This type of motors inherits both merits of high force density from linear synchronous motors and simple secondary structure from linear induction motors. Due to its simple and consequently low-cost secondary structure, it is applicable to transportation systems like Maglev. Position and speed control of this motor is essential for rail transportation applications. Therefore, derivation of an appropriate analytical model for control purposes is needed. An analytical method to represent the dq model of SSLFSMs is presented. Employing this method, the d- and q-axis inductances and the developed electromagnetic thrust and normal force are calculated. To verify the proposed model, three different finite-element method-based models are studied and one is chosen as the basis for comparison. All results obtained by the analytical model are verified by this finite-element method-based model. Moreover, a prototype of SSLFSMs is built to validate the study.

Hysteresis motors are widely employed for a variety of high speed applications, thanks to their unique features. Usual design methods could not be used for these motors since the operation mechanism of hysteresis motors is also unique. However, an appropriately developed design method has not been provided by the few relevant published works. This study presents a new iterative design method, which is capable of being used for almost all hysteresis motor structures. Also, it is almost independent of the approach of obtaining the design equations. Multi-stack disc-type slotless structure has been selected as the case study, because of its interesting capabilities. Its design equations are derived by combining the fundamental laws of electromagnetism with the elliptical model of hysteresis loops. Some new techniques are introduced to increase the accuracy of these equations. A sample motor has been designed by applying the direct search optimisation to the proposed design method. The prototyped sample motor has been subjected to various tests. The measured operating characteristics show a great agreement with the design requirements.

This study presents the analysis and experimental verification of a coaxial magnetic gear (CMG) for speed-change transmission. The key design of this CMG is to adopt a stationary permanent-magnet (PM) ring between the inner and outer rotors, aiming at removing the PMs and only retaining the salient-pole-iron on the outer rotor to improve its mechanical reliability. Meanwhile, due to a large equivalent magnetic clearance promoting low torque ripples, the proposed CMG can offer the advantages of achieving a consistent speed ratio and stable transmission within the entire pull-out torque range. By using the two-dimensional finite element method, the detailed parametric analysis and static characteristics of the proposed CMG are performed to set up its design criteria. Moreover, a quantitative comparison with a conventional CMG is conducted, and a prototype is also fabricated for experimentation to verify the validity of the proposed CMG.

Two-speed elevator induction machines, because of their economic usage, are still widely used in residential applications of low- and medium-height buildings. In this study, a three-stage method is presented for achieving torque-speed characteristic with an improving low-speed braking curve. In designing a procedure, firstly, a rotor aluminium alloy is changed for reaching the maximum torque at start-up. Secondly, a skew angle of rotor slots is calculated for reducing pulsating torque and smooth high-speed performance and finally, an intermediate ring rotor is proposed in order to reduce the effects of skewing leakage at a low-speed braking curve. The proposed approach for this purpose has been investigated with a finite-element method, and several prototypes have been constructed for confirmation and validation of the presented approach. The accuracy of the proposed analysis is confirmed by experimental tests and laboratory measurements are applied on all prototypes

The electromagnetic repulsion mechanism (ERM) is highly consistent with the operation mechanisms of the high-speed switch (HSS) owing to its simple structure and fast response capability. To investigate the performance difference between the coil–disk ERM and the coil–coil ERM, the authors adopt the finite element models for simulations with the aid of ANSYS Maxwell software. Then, an HSS prototype based on the mechanism of permanent magnet closing and repulsion force opening is developed to verify the numerical simulations. Simulations and experiments demonstrate that under the same excitation conditions, the coil–disk ERM has shorter inherent open time, while the coil–coil ERM has shorter full stroke time. Moreover, it is shown that the difference between the full stroke times of the two mechanisms gradually decreases with the increasing discharging energy.

In this study, common mode voltage (CMV) reduction using space vector pulse-width modulation (SVPWM) technique is proposed for a three-phase induction motor drive fed by a three-to-three phase indirect matrix converter (MC). The proposed SVPWM effectively reduces the peak of the CMV without affecting the output voltage gain. By adopting the proposed SVPWM there is no change in the dv/dt of CMV at the terminal of the machine when compared to the existing method. The proposed control is possible by proper placement of zero vectors in the rectifier stage and discarding zero voltage vectors in the inverter stage of the indirect MC. The control technique is implemented in MATLAB/Simulink environment. Hardware setup is developed and control algorithm is implemented using dSPACE working in conjunction with the FPGA interface board. The results of the proposed SVPWM are compared with the existing method of CMV elimination and the improvement is established. The simulation results obtained are verified with the experimental results. The obtained results confirm a reduction of CMV by 48% (peak) and validate the viability of the proposed scheme in a three-phase induction motor drive system.

Voltage unbalance and distortion become one of the most common power quality problems in industrial utilities, which cause significant increase of the electromagnetic losses in induction motors. For energy saving of the induction motor system, there is a need for a detailed research of the loss characteristics of induction motor under unbalanced and distorted supply voltage. For accurate and fast prediction of the induction motor losses, this study proposes a method to identify rotor harmonics using the data from one supply cycle. The slip-frequency rotor harmonics are determined by using the space-time symmetrical characteristics of the induction motor. And based on a numerical method, the higher order harmonics of rotor flux density or current density are determined from data within one supply cycle. The electromagnetic losses are then calculated from those harmonics. With this method, the electromagnetic losses of a 5.5 kW induction motor under unbalanced and distorted supply voltage are calculated and analyzed. The proposed method and the analysis results are validated by comparing the predicted and measured motor losses of the 5.5 kW induction motor under different supply conditions.

This study presents a design method of a linear transverse-flux machine with mutually coupled windings aiming at the force ripple optimisation. Considering the three-dimensional (3D) magnetic flux in the proposed machine, a mathematic model based on Maxwell stress tensors is developed to facilitate the optimisation, so that the objectives depending on the selected design parameters can be analytically calculated. In order to reduce the optimisation time of the complex machine, mostly influential design parameters are evaluated by the Taguchi method first. Furthermore, the selected parameters are optimised with the human group optimisation algorithm. The main purpose of the algorithm is to attain the desired electromagnetic force with the minimum force ripple coefficient under the restriction of the overall volume. The proposed optimisation has been applied for a case study, and the final design is compared with that optimised by the genetic algorithm. The results show that the optimal machine design obtained by the proposed method has the lower force ripple coefficient, which is also verified by the 3D finite-element method and experiments.

This study proposes a power factor correction (PFC)-based half-bridge dual-output converter-fed switched reluctance motor (SRM) drive for home appliances. The proposed converter provides two equal output voltages to feed a mid-point converter of a four-phase SRM. An adjustable speed drive is proposed here such that the speed control is obtained by regulating converter output voltage. The converter is operated in discontinuous conduction mode to obtain inherent PFC at supply side. The sensors requirement is reduced by selecting a voltage follower approach. The performance of proposed drive is evaluated for steady-sate and dynamic conditions. The input current total harmonic distortion is reduced below 5% as per an IEC standard.