The oceanic wave energy generation has been drawn significant attention in the field of power engineering recently. These generation systems are basically direct drive electrical power generators connected to the wave energy devices with the variable frequency drives (VFDs). This study proposes an application of high-frequency transformers at the output stages of VFDs for the galvanic isolation purpose among multiple output ports of VFDs in a wave farm. The design process of a high-frequency magnetic link involves multiphysics problems that entail complex tradeoffs between electrical and magnetic properties including efficiency. Moreover, the performance of the magnetic link depends on the switching characteristics of the power switching devices and various excitation signals. Therefore, extensive multiphysics research in the field of design and optimisation of magnetic links is needed to develop next-generation technologies. In this study, a finite-element method-based systematic process is presented for the design of amorphous alloy-based core of the high-frequency magnetic link. Two cores are developed and characterised in the laboratory. The characterised data obtained from the experiment can be used in the future design optimisation of other high-frequency magnetic links.

The linear permanent-magnet synchronous generator (LPMSG) for direct-drive wave energy conversion (WEC) suffers from many drawbacks that have not yet been overcome, such as a low power density and a bulky system volume. Therefore, a magnetic field-modulated linear permanent-magnet generator (FMLPMG) with a simple structure has been designed and manufactured. First, the operating principle of the FMLPMG is demonstrated by the equivalent magnetic circuit method, which explains the high power density of the FMLPMG. Second, at a constant speed and a sinusoidal speed, the electromagnetic characteristics of the FMLPMG under the no-load and load conditions are analysed by the finite-element method. Finally, a direct-drive WEC test platform is built to simulate the process of wave action on the FMLPMG. No-load and load experiments of the FMLPMG are conducted on the test platform, and the results are compared with those of an LPMSG with the same volume and operating conditions. The results show that the FMLPMG with a high power density converts wave energy effectively and solves the problem of low power density faced by the LPMSG in direct-drive WEC.

This study presents a novel technique for modelling of linear primary permanent-magnet (PM) vernier machine wave converter based on an improved magnetic-equivalent-circuit (MEC) method. Saturation effect is considered by a new method, where the B–H curve fitting is performed using a novel non-linear function. The machine properties such as the number of PMs, number of slots, magnets size, and all other machine parameters can be selected arbitrarily in the proposed model. The machine structure is considered by 12 individual zones. Each of the flux tubes in core and air gaps is modelled by a non-linear reluctance, and the machine performances in both transient and steady-state conditions are studied. Various machine properties such as magnets size and winding configuration are analysed and the dynamic behaviour is compared in various cases. Comparison to finite-element method (FEM) shows the effectiveness and accuracy of the proposed MEC method and its much shorter processing time compared with FEM.

Most of the conventional linear generator is constructed with either Alnico (specially AlNiCo-9) or Neodymium iron boron (NdFeB) permanent magnets (PMs) for harvesting oceanic wave energy. Alnico is a composition of aluminium (Al), nickel (Ni), and cobalt (Co) added to iron, which is its major volumetric component. Alnico has a poor magnetic energy product, and NdFeB contains a rare earth element. To overcome this issue, a recently developed rare-earth free iron nitride (Fe₁₆N₂) compound-based PM linear generator (PMLG) is proposed in this study as an alternative solution for avoiding rare earth material while obtaining high output power. To the best of authors’ knowledge, newly invented Fe₁₆N₂ is not proposed, analysed, and investigated in any electrical generator. In this context, Fe₁₆N₂ is proposed in a linear generator as PM for producing adequate magnetic flux. For analysis and testing the performance of the proposed material, a PMLG is designed. The performances are compared for using Fe₁₆N₂ and AlNiCo PMs in the same PMLG design for a fair comparison. It is considered that the proposed PMLG is connected to a direct drive power take-off system. Simulation results show that the proposed PMLG having Fe₁₆N₂ generates 55% more electrical power than that of using AlNiCo. The voltage, current, magnetic flux linkage, power, and magnetic flux density of the proposed PMLG are investigated extensively and compared with those of AlNiCo. The finite element method is applied in the ANSYS/Maxwell software environment for testing the PMLG with the conventional and the proposed PMs as well as results are presented. The proposed design is also validated with a small laboratory prototype.

This study proposes an optimal control scheme for a permanent-magnet linear synchronous generator (PMLSG) using the state feedback control (SFC) method plus the grey wolf optimisation (GWO) algorithm. First, A novel state-space model of linear PMLSG is established in order to obtain desired dynamics and enough power when used for the smooth wave energy. Second, the GWO algorithm is adopted to acquire weighting matrices Q and R in the process of optimising linear quadratic regulator (LQR). What is more, a penalty term is brought into the fitness index to reduce the overstrike of output voltage and keep the rate of work more stable. Finally, optimal LQR-based SFC with and without penalty term and proportional-integral (PI) controllers are compared both in simulations and in experiments. Results clearly prove that the proposed optimal control strategy performs a better response when compared to other strategies.

The nature of wave resources usually requires wave energy converter (WEC) components to handle peak loads (i.e., torques, forces, and powers) that are many times greater than their average loads, accelerating equipment degradation. Moreover, due to their isolated nature and harsh operating environment, WEC systems are projected to possess high operations and maintenance (O&M) cost, i.e., around 27% of their leveled cost of energy. As such, developing techniques to mitigate these costs through the application of condition monitoring and fault tolerant control will significantly impact the economic feasibility of grid connected WEC power. Toward this goal, models of faulty components are developed in the open source modeling platform, WEC-Sim, to estimate the performance and measurable states of a WEC operating with likely device and sensor failures. Two types of faulty component models are then applied to a point absorber WEC model with basic controller damping and spring forces. Resulting changes in device behavior are recorded as a benchmark, and a graph-theoretic approach is proposed for fault detection and identification utilizing multivariate time series. Simulation results demonstrate that these faults can greatly affect the WEC performance, and that the proposed method can effectively detect and classify different types of faults.

Flux switching machines (FSMs) encompass unique features of conventional direct current machine, permanent magnet (PM) synchronous machine and switch reluctance machine. Permanent magnet FSM (PMFSM) is capable of high torque density and applicable for high-speed application, however conventional PMFSM exhibits demerits of high PM volume, high torque ripples and significant stator flux leakage. In this paper, a novel consequent pole E-core stator PMFSM is proposed and compared with conventional topology utilising 2D finite-element analysis (2D-FEA). Finite-element analysis revealed that proposed design enhanced flux modulation effects by introducing flux bridges and flux barriers as a result reduced cogging torque by reducing 46.53% of the total PM volume, reduce torque ripples by reducing PM slot effects and reduce flux leakage utilising flux bridges in the stator. Furthermore, analytical model for flux linkages, cogging torque, mechanical torque, no load and on-load magnetic flux density (MFD) is developed for initial design of conventional and proposed model. 2D analytical methodologies resolve equivalent magnetic circuits for open-circuit flux linkages, Fourier analysis for cogging torque, Laplace equations for MFD and Maxwell stress tensor for mechanical torque. Finally, results obtained from 2D-FEA and analytical methodologies are validated and compared.

This study proposes an induction motor drive system based on the LC filter integrated quasi-Z source indirect matrix converter (QZS-IMC). The proposed drive system shows the following features: (i) variable voltage control of inductor motor is achieved by the rectifier stage and variable frequency control is achieved by the inverter stage; (ii) automatic low voltage ride through ability enhances capability of the proposed drive against grid voltage sag; (iii) wide voltage gain range ensures the drive system with high performance in wide speed range; (iv) there is no additional input filter. The voltage control implementation in the rectifier stage is proposed to benefit low voltage stress and low converter loss. The control method combines motor vector control, minimum shoot-through duty cycle and maximum modulation indexes. As a result, the input power supply voltage and dc-link voltage are maximally utilised and the power loss is reduced. Simulation and experimental results verify the proposed QZS-IMC motor drive system.

In the magnetic levitation planar motor which can achieve six degrees-of-freedom motion, decoupling control is realised by coil array commutation algorithm, due to the limitation of the sampling period of the real-time system, a high-dynamic coil array commutation algorithm is needed to achieve higher computational efficiency, but this will lead to the coil array not accurately providing the force/torque required for the trajectory movement, and generate a certain torque ripple error. In this study, the cause of this torque ripple error is analysed, and a feedforward compensation method is proposed. The results of simulation and experiment show that the proposed feedforward compensation method of high-dynamic coil array commutation algorithm can reduce torque ripple error by 88%, and achieve higher trajectory tracking accuracy while satisfying high computational efficiency.

For diagnosing deformation fault and latent loosing status of winding, this study proposed a state diagnosis method of transformer winding deformation based on fusing vibration and reactance parameters. The wavelet energy – matrix norm transformation method and reactance identification method were proposed to extract vibration and reactance parameters. The multi-information collection system of transformer winding deformation state was designed. Aiming at the S-11-M-500/35 transformer, short circuit current impact experiment was made and three deformation fault windings were designed. Status database of multi-information for normal, loosing, deformation and specific fault types of winding were established. State diagnosis experiment on normal winding, loosing winding after short circuit current impact and deformation fault winding was made. Per unit value-space vector transformation method was proposed to fuse vibration and reactance parameters, fusing eigenvector was established, and the winding deformation state was diagnosed by extracting fusing feature. On the basis of the above research, regarding deformation fault state winding, fault types were diagnosed based on the relevance vector machine. Results indicated that latent loosing, deformation fault and three deformation fault types of winding can be diagnosed accurately. Fusing diagnosis method proposed in this study was superior to the single vibration or reactance parameter diagnosis method.

In this study, an unsymmetrical bistable multi-magnetic circuit permanent magnetic actuator is proposed. The operating principle and mathematical model of the high-voltage circuit breaker with the proposed machine are analysed. Additionally, the static and dynamic characteristics of the high-voltage circuit breaker with the presented machine are investigated and evaluated using numerical finite element analysis methods. Furthermore, the influence of the length of the middle gap and the additional coil in the proposed machine are studied. The advantages of the presented machine, such as less magnet volume, low cost, high force density, and short starting time, are discussed. Finally, a prototype is created and tested, followed by the retrieval of the characteristic curves of the holding force to confirm the proposed design.

In the case of designing linear voice coil motors (LVCMs), the aluminium tube is usually used to support and fix the windings. Due to the high-speed linear reciprocating motion, the eddy-current damping force in aluminium tube has a large effect on the dynamic characteristic of LVCMs and weakens the resultant force. In this study, an LVCM with forward winding is studied. The cause of eddy current damping force in the original structure of the aluminium tube is analysed, and the corresponding mathematic model is established which is verified by finite element method. To restrain the damping effect, three restraining measurements have been discussed. Then a novel structure of aluminium tube with axial slits and ribbed stiffeners is proposed according to the simulation analysis. During the experimentation process, the mover resultant force is replaced with its acceleration. Results show that the mover acceleration of LVCM with stiffened aluminium tube is bigger than that of the initial one. Hence the resultant force of the proposed structure is improved effectively and the new structure has a good inhibition effect on eddy-current damping effect.

In this study, the identification and control scheme of the motor-drive servo turntable are researched to achieve accurate tracking. Firstly, the input–output identification experiments are designed and realised for the global model of motor-drive servo turntable. The order of the global controlled auto-regressive model is determined by the Akaike information criterion, and the parameters are estimated by a particle swarm optimisation-cuckoo search algorithm. Secondly, the switched friction model is built combining the LuGre structure and the Stribeck curve. The switching conditions and the parameters of the switched friction model are determined though the input–output and the friction experiments. A constrained multi-objective optimisation problem is constructed for the parameter identification of the switched friction model. It is solved via a fuzzy comprehensive evaluation. Finally, the composite control strategy, in which the proportional–integral–derivative controller and model-based friction observer are combined, is proposed in the azimuth angle system of the motor-drive servo turntable. The trajectory tracking results in simulation and experiment illustrate the effectiveness of the proposed switched model, identification method, and composite control strategy.

The hardware-in-the-loop (HIL) real-time simulation for high-speed train electrical traction system aims to reduce the design cost and speed up control verification process of algorithms in the developmental stage of the traction control unit. In this study, based on the dSPACE real-time simulator, the multiple-simulator, multiple-simulation step of HIL real-time simulation system is first built. Second, for the associated discrete circuit modelling method, an optimisation method is proposed to minimise the switching loss and improve the simulation accuracy by selecting the optimal discrete-time switch admittance parameter, G _S . To decrease the computational burden for field-programmable gate array (FPGA), a decoupling method without simulation latency is presented to reduce the matrix dimension of the system model. Finally, the real-time simulation models of electrical traction system are realised by CPU + FPGA-based simulator, in which the power electronics converter models are computed in FPGA with a fixed 100 ns time-step. The validity and reliability of the real-time simulation system is verified by the HIL simulation and experimental results, which indicate that the real-time HIL simulation at the nanosecond level improves the accuracy essentially.

This study proposes a modified structure of the E-core permanent magnet (PM) assist switched reluctance motor by relocating the PM blades inside the stator core. For this purpose, the PMs are removed from the stator poles and placed slantwise inside the yoke. The proposed yoke-PM assist structure is characterised with higher average torque and a lower torque ripple with respect to the conventional pole-PM assist structure. An analytical approach based on the magnetic equivalent circuit is applied at the preliminary design stage to predict the performance of the motor. Based on the presented analytical modelling, the physical dimensions of the motor are optimised via a genetic algorithm to maximise the motor torque and the overall steady state performance. For further verifications, the finite-element analysis simulation results are verified by the experimental tests on the motor prototype.

Electrical machines are widely used as a driving source for various applications because of their wide speed range, high efficiency, and torque density. Similar to any other machine, manufacturing tolerances occur when mass producing the motors. In particular, the tolerances of the shape of the motor or the residual flux density in the permanent magnet significantly affect the back-electromotive force (EMF), inductance etc. When the magnitude of the back-EMF is changed, the armature current must be changed to obtain the same torque. This consequently affects the loss of the motor, and hence leads to changes in efficiency. In particular, the loss changes cause thermal problems such as irreversible demagnetisation of the magnets and dielectric breakdown due to the increase in the temperature of the coils. Therefore, to reduce the inevitable manufacturing tolerance, a robust methodology should be assured. Here, the Taguchi's robust design is applied to an integrated starter-generator motor by using the signal-to-noise ratio to consider the coil temperature.

A doubly-salient relative permeance method is presented herein to predict the magnetic field of bearingless flux-switching permanent-magnet machines (BFSPMMs). Firstly, the subdomain model method is used to compute the magnetic field of slotless BFSPMMs. Then, the slotting effect of the stator and rotor is obtained by the doubly-salient relative permeance method. By combining the two above, the air-gap magnetic field of slotted BFSPMMs can be obtained. The doubly-salient relative permeance method is based on the theory of the subdomain model method. The whole doubly-salient structure is divided into several subdomains, and the Laplace equations for subdomains are established. Then, according to the boundary conditions between subdomains and the core, and the continuity conditions between adjacent subdomains, the equations are solved to calculate the slotting effect. Based on the proposed analytical model, the flux density and electromagnetic performances including back-electromotive force (EMF), torque, and suspension force are predicted and compared with the finite element method results. Furthermore, the back-EMF of the prototype motor is measured and the suspension experiments are carried out based on the analytical method. The comparison results and experiment results verify the validity of the analytical method.

In this study, the radial displacement of the stators is proposed to improve sensor-less speed control for dual-stator brush-less DC motor drives. The mechanical offset between stators leads to the double number of edges in the zero-crossing signal (ZCS) and thus, a more accurate speed estimation. Moreover, updating the speed in the control process will become faster that can decrease speed control error. As stators’ axes are displaced 90° electrical, the distance between ZCS edges becomes symmetrical. Therefore, it would provide a uniform estimated speed updating, and can effectively decrease speed ripple. Also, asymmetrical stators displacement can decrease speed ripple compared to the aligned structure when the distance between adjacent zero-crossing points is appropriate. In addition, stators displacement is well known as an efficient technique to decrease torque ripple. This idea is verified via computer simulations and experimental results.

This study presents a general optimisation method for determining the dimensions of the magnetic levitation (maglev) actuator for rotary tables. Combined with an improved electromagnetic numerical model of the maglev rotary tables, the optimal thickness dimensions of coils and magnets are obtained by the evolutionary optimisation algorithm. Different from the existing magnetic force model built by the harmonic analysis method, the improved numerical model involves the clearances of the neighbouring magnets in the circular magnet array and applies the numerical integration method to solve the complex Lorentz integrals. According to the evaluation function based on the numerical force model, the optimal thickness dimensions are determined via an evolutionary optimisation algorithm. By this method, the size of coils and magnets in the rotary table with the circular Halbach magnet array can be determined accurately and directly, rather than obtaining a single structure dimension by an analytical approach. In this work, the method is applied to optimise the dimensions of a maglev rotary table, and a prototype is manufactured according to the obtained optimal parameters. The experimental and simulation results verify the accuracy and validity of the proposed optimisation design method.

In this study, design optimisation of an axial-flux reluctance magnetic coupling is presented. The optimal design procedure is based on a two-dimensional (2D) semi-analytical model defined at the mean radius combined with a multi-objective genetic algorithm (NSGA-II). In order to take into account the end-effects in the radial direction, a correction factor is defined to improve the torque and the axial-force determination. The obtained results are compared with those of 3D non-linear finite element simulations and experimental results. It is shown that the proposed semi-analytical model is very accurate and requires very little computing time.

In order to widen the flux-weakening range of motors, this study proposed a DC-link voltage control strategy for high-speed permanent magnet motor drive systems powered by Z-source inverter. In this strategy, the DC-link voltage, also known as the output voltage of the impedance network, varies with the inverter output voltage and remains optimal at all times, whether in steady state or transient state. As for the shoot-through duty ratio and the modulation index, the two main control variables in the Z-source inverter are under unified control to ensure the stability of the system, while achieving fast tracking and reducing the loss. In addition, a new sliding mode control system based on the indirect control of the capacitor voltage is used to control the DC-link voltage to suppress the system fluctuation caused by the change of the given value or the motor load. Besides, various conventional voltage Z-source inverter pulse width modulation strategies can be applied to this technology. Simulations and experiments verified the effectiveness of the proposed strategy.

Transformer winding hot-spot temperature (HST) is one of the important factors affecting transformer oil–paper insulation deterioration. This study presents a three-dimensional coupled electromagnetic-fluid-thermal analysis method for HST calculation in a 10 kV oil-immersed distribution transformer, the influence of the transformer internal metal structure parts on the HST of the winding is considered in the simulation. Combining electromagnetic-field calculation with no-load test and load test of the transformer provides a more accurate method to determine internal losses of the transformer. Taking those power losses as heat sources, the transformer fluid-thermal field analysis is conducted with the finite volume method. The variation of physical parameters of transformer oil with temperature is considered in the simulation. On the basis of the equivalent thermal resistance theory, the equivalent thermal conductivities of transformer windings are obtained. The simulation results deduced from the proposed method agree well with the experimental ones, which are obtained with fibre optic temperature sensors during the transformer temperature rise test, the maximum temperature difference is <3°C. The results validated the validity and accuracy of the proposed transformer HST calculation method.