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Vernier reluctance machine with DC field coils in stator is a competitive rare-earth-free design for variable-speed industrial applications due to its robust structure and controllable excitation, while its torque density is relatively disadvantageous. To address this issue, this paper proposes a new armature winding design method for VRM with DC field coils across two stator teeth. The key is to break the traditional winding design principle based on the flux modulation effect of fundamental DC field harmonic, and instead, reconstruct a novel harmonic winding to enhance the utilization factor of the modulated high-order DC field harmonics. By this means, the torque density can be improved by 75.6% compared to the existing poor counterpart. In this paper, the machine structure and operation principle are introduced, with emphasis on the high-order DC field harmonics distribution rule and its influence on the armature winding design. By finite element design and optimization, a comparative study is performed to evaluate the machine performance using two different winding configurations with variable slot pole combinations. A prototype is fabricated and tested, and the results agree well with finite element analysis, which verifies the feasibility and advantages of the proposed winding design method.

This paper investigates the eddy current loss mechanism of a dual permanent-magnet-excited machines (DPMM). Based on the flux modulation effect, abundant harmonics are induced in the air gap of DPMM. The harmonics of air-gap flux density due to rotor PMs, stator PMs, and armature reaction are investigated qualitatively and separately. Then, the orders, frequency, and rotation speed of the harmonics are deduced theoretically. The harmonics that contribute to the eddy current losses are deduced accordingly. Finally, the loss distribution of the proposed DPMM is estimated through simulation and the thermal field of the proposed motor is analyzed. A prototype is fabricated to validate the analysis. Temperature rise of both stator and rotor PMs under rated load condition is measured through experiment.

In this paper, a novel winding switching control strategy is proposed to extend the speed range of a consequent-pole ferrite-PM hybrid-excited machine (CPFPM-HEM) for electric vehicle application. The key is that in low-speed range, the AC armature winding and DC field winding are connected in series to achieve large starting torque, while in high-speed range, DC field winding are injected with adjustable DC currents to realize variable speed constant voltage of AC armature winding. Furthermore, consequent-pole rotor is used to reduce the usage of the permanent magnet (PM). In the meantime, ferrite PMs are used to replace rare-earth PMs to reduce the cost with the shortage of rare earth resources. In this paper, the machine configuration, operation principle with dual excitation sources, flux modulation principle and winding switching strategy are illustrated in detail. Then, the electromagnetic performance of the CPFPM-HEM in different speed ranges is investigated. Finally, the speed range extension with winding switching strategy is verified by the Maxwell/Simplorer co-simulation.

In this article, a novel pre-processing method is proposed for magnetic field approximation based on neural networks. The process of calculating magnetic fields based on neural networks is presented first. In order to save the training time and reduce the estimation error, an excitation distance function, which is inspired by an analytical formula of magnetic potential, is proposed to integrate the input data, such as the geometry, excitations, and boundaries. This pre-processing or roughly reduces the dimension of the input layer by three quarters, while the training process is accelerated by a more integrated input layer. Preliminary experiments show that the predicted results by the proposed pre-processing method are close to the ground truth, with a significant reduction of computation time compared with the traditional finite element method (FEM).

Turn fault detection technique is of key importance for system safety, which can protect the machine and enable the appropriate mitigation strategies. In this article, an advanced turn fault detection method is investigated for an interior permanent magnet machine (IPM) using the ripple current induced by the inherent pulse width modulation (PWM) voltage harmonics. The resultant current harmonics under high-frequency voltage harmonics are analyzed for both healthy and turn fault conditions. The feasibility of the detection method is validated by both simulation studies and prototype tests. It is confirmed that the PWM ripple current-based diagnosis technique can be employed to detect the turn fault in IPM without introducing undesirable noises and vibrations, and it is capable to detect early turn fault.

The reluctance machine with dc field coils in stator is an emerging brushless candidate for the in-wheel direct drive for its wide speed range and robust mechanical structure, while it suffers from relatively low torque density and efficiency, due to the poor excitation ability of dc field coils and worse extra dc saturation effect in the stator core. To address this issue, a new hybrid reluctance machine is proposed in this article, in which an integrated dual-layer PM source is introduced into stator slots, aiming to relieve dc saturation and, meanwhile, evoke flux modulation effect. In this way, the stator core utilization factor can be boosted due to dc saturation elimination by inner-layer slot permanent magnets (PM). On the other side, extra PM torque is generated by the flux modulation effect of outer-layer slot PMs. Hence, with synthetic assistance from dual-layer slot PMs, the torque density is improved distinctly especially under relatively high current density. Besides, slot PMs share a parallel magnetic circuit with dc field coils, which enables a bidirectional dc magnetization control for speed range extension. In this article, the proposed new topology is fully evaluated by both finite element (FE) analysis and prototype experiments.

This article proposes a novel compact dual-permanent magnet (PM) dual-stator generator for hybrid ac/dc generation system. Two sets of windings are installed in the inner and outer stator separately. It has two electric ports, in which one is used to generate ac voltage and the other electric port that also generates ac voltage is rectified to obtain the dc voltage. The key of the generator is that two stators share one rotor with consequent PM structure, and the output power of the machine is much higher than that of the machine with only one stator. Besides, with two separated stator core and armature windings, the reliability of the proposed generator is improved. The advantage of the proposed dual-stator dual-PM generator is illustrated theoretically, and its slot/pole selection guideline is given. Comprehensive sensitivity analysis of the proposed generator is performed and multilevel design optimization method is adopted. The efficiency, torque ripple, and total harmonic distortion of the inner and outer armature windings of the generator after optimization are calculated to verify the effectiveness of the proposed machine design.

Due to the flux leakage and large detent force, the thrust force ripple of transverse-flux linear motor is relatively large, which restricts its further application. Also, the field of most existing transverse-flux machines is hard to be altered and regulated considering the permanent magnet (PM) excitation. Therefore, to suppress the force ripple and strengthen the flux regulation capability of transverse-flux machines, a novel hybrid excitation transverse-flux tubular motor with complementary structure is proposed in this article. The key is that a complementary and parallel structure is constructed in this motor, and hybrid excitation of both dc windings and small auxiliary PMs installed at opening of the slot is adopted in this motor as well. In addition, unequal teeth design of dc winding and ac winding is also employed to increase the thrust force density. Finite element calculation results verify the effectiveness of the proposed machine.

Vernier permanent-magnet (VPM) machines which have high torque density and high efficiency have been extensively used in direct drive. This article attempts to propose a new winding form and compare it with a traditional winding form as a part of fractional slot winding in the VPM machines to provide a design guideline in the aspect. Different winding forms are compared with the same copper loss and the same design. The design guideline of winding forms is provided by multiobjective generation algorithm (GA) optimization. Maximum torque value and minimum torque ripple are the optimization objectives in the GA optimization process. In addition, several models of the modularized motor with the new winding form based on the fractional-slot windings are compared, and the suitable application range of these models are discussed.

This study proposes a novel power supply system that utilises wind power to produce AC and DC power. A special designed generator based on bidirectional flux modulation effect is the key part of the proposed power supply system. The novel power system has a compact structure since the proposed generator has two electric port. There are three essential points that make the proposed system outstanding. One is the contra‐rotating rotors, which will cluster wind power even under low wind speed. Second one is the dual armature winding structure, which will provide AC and DC power simultaneously. There are two electric port in the proposed generator. One port can produce AC power to the non‐sensitive resistive load. The other can provide AC power with different frequency to the rectifier to obtain DC power. The induced voltage due to flux modulation effect can be used to offer AC power, and the induced voltage due to the outer rotor can be used to offer DC power. The voltage frequency of two sets windings is different. The last one is the air gap flux rotation speed amplification due to flux modulation effect. Time stepping finite element method is used to analyse the dynamic performance of the proposed machine.

In this article, an adaptive degrees-of-freedom (DoFs) finite-element method (FEM) is presented to solve the 3-D transient magnetic problems. For time-dependent problems, the error distribution changes over time, and hence mesh coarsening is needed in some regions to keep the number of DoFs small. In this novel h-type adaptive FEM, real mesh coarsening is replaced by an implicit elimination of DoFs, which avoids the following operations after mesh coarsening and the interpolation errors from fine mesh to coarse mesh. The DoFs to be eliminated are constrained by interpolation functions, which are formulated by the master DoFs. To adapt to the 3-D field, a constraint with a variable number of master DoFs and rational coefficients is adopted. The constraints are then integrated into the finite-element (FE) equation in the element level using the slave–master technique, which is followed by a global assembly process. After solving the global FE equation, the solution of constrained DoFs can be recovered from the solution of master DoFs. Several transient problems are computed to showcase the effectiveness of this proposed method.

This article proposes a novel model predictive control for a three-phase permanent-magnet synchronous motor (PMSM) with enhanced robustness against parameter variation and higher current control precision. First, the extended set of voltage vectors are adopted to increase the current control precision. Then, the parameter sensitivity problem is avoided in the first stage using an indirect reference vector strategy for the sake of computation time reduction. Subsequently, the inductance disturbance observer is adopted in the current prediction process to enhance the robustness against machine parameter mismatch. The intrinsic connection between the discrete control sets precision and disturbance observer is analyzed. The proposed method improves the robustness against parameter mismatch and current control precision simultaneously. Experimentations are conducted to verify the effectiveness of the proposed method.

This article investigates and compares the electromagnetic performance of two novel hybrid-magnetic-circuit variable flux memory machines (HMC-VFMMs) with different hybrid permanent magnet (PM) configurations. The investigated HMC-VFMMs are both geometrically characterized by a combination of series and parallel magnetic circuit topologies, but with different positions of series and parallel PM branches. The developed HMC design can combine the merits of wide flux adjustment range in parallel structure and excellent unintentional demagnetization withstand capability in series structure. The topologies, features, and working principles of the studied HMC-VFMMs with different hybrid magnet configurations are described, respectively. The magnetic circuit model is utilized to analytically reveal the performance metrics of the two machines. The electromagnetic characteristics of the radially magnetized (RM) and circumferentially magnetized LCF types of HMC-VFMMs are evaluated and compared by the finite-element method. Furthermore, the performance comparison of the proposed RM-type HMC-VFMM with a benchmark interior PM machine is conducted. The experiments on RM-type HMC-VFMM prototype with RM-structure are carried out to validate the FE analyses.

Metamaterial is an artificial material with unique material properties that cannot be found in a naturally existing one, and hence it is able to perform functions that a conventional material cannot do. Consequently, it has shown great potential in various engineering applications such as resonance coupled mid-range wireless power transmission (R-WPT) systems. However, the analysis and design of an application-oriented metamaterial include both the unit cells and their combinations, and thus are very complex. Moreover, the performance of a metamaterial is very sensitive to uncertainties in both manufacturing and operating conditions. In this regard, a two-phase methodology for robust design optimizations of metamaterial slabs in R-WPT applications is proposed and applied to the design optimization of a prototype R-WPT system with promising results.

This paper proposes a novel direct-drive dual-PM motor for electric automatic guided vehicles (AGV). The proposed motor has split teeth on stator and dual PMs in stator and rotor sides, which contributes to reduced torque ripple, and enhanced torque. The airgap field of the proposed motor is analyzed theoretically, and the slot/pole selection guide line is concluded. The simulation results of the airgap flux density are shown and Fourier Transformation (FFT) analysis results agree well with the theoretically analyses results. Besides, the effects of design parameters of the proposed motor to the performances of the proposed motor are investigated. And it is found that reduced slot open could produce improved efficiency and decreased torque ripple. The efficiency of the proposed motor is relatively high within the operation range. A corresponding prototype is fabricated and the experiment validates the design.

This article aims to propose a new hybrid reluctance machine equipped with relieving-dc-saturation (RDCS) ability for electric vehicle in-wheel drive. The proposed machine uses integrated ac and dc current excitation to eliminate extra dc field coils for the efficient torque generation. Besides, considering the inherent dc saturation in stator core caused by dc current excitation, slot PMs are artificially introduced to provide RDCS effect and thus boost torque density. Moreover, with a modular magnetic field configuration, the proposed topology exhibits excellent fault-tolerant potential at both open-circuit and short-circuit condition, making it suitable for safety-critical in-wheel vehicle propulsion. In this article, the machine configuration and operation principle are introduced, with emphasis on its RDCS effect and corresponding design consideration. Further, performance of this new topology is evaluated by both finite element analysis and prototype experiments. It is revealed that, with this RDCS ability, torque density of the proposed machine can be enhanced by about 25% under relatively high current density.

Benefiting from flexible flux control and short-circuit withstand ability, the hybrid excitation machine is an emerging starter generator solution for hybrid electric vehicle propulsion. However, to realize a brushless hybrid design in conventional permanent magnet machines, a three-dimensional magnetic circuit is usually adopted, leading to complicated mechanical structure and torque density sacrifice. To address this issue, a new relieving-dc-saturation hybrid excitation Vernier machine is proposed in this article, which integrates good torque density and bidirectional flux control within a simple and brushless structure. The key is to artificially construct reluctance effect in a consequent-pole Vernier permanent magnet machine (CP-VPMM) by introducing extra dc field excitation equipped with the relieving-dc-saturation ability. In this way, the advantages of bidirectional flux control in stator-dc-excited reluctance machine and good torque density in CP-VPMM are well combined in this topology, making it especially suitable for multimode starter generator application. In this article, the machine structure and its design mechanism are introduced, with its electromagnetic performance evaluated by the finite-element simulation. A prototype is manufactured and tested. Experiment results verify the feasibility of this new topology.

In this article, the optimal configuration of the stator for the dual-permanent-magnet vernier machine (DPMVM) is investigated. A novel numerical model used to perform the optimization and compare the performances between different permanent magnet (PM) arrangements on the stator part is first presented in this article. According to the proposed numerical model, the effects of the location of PMs at different positions of the stator are studied in terms of output torque, torque ripple, efficiency, and power factor (PF). It is found that the PMs at stator slots contribute more to the output torque than PMs on stator teeth. Moreover, it is found that the stator PMs will add extra cogging torque to the machine compared with the rotor-PM machine. The PF of the dual-PM machine with the combination of the selected stator slots and rotor poles can be higher than 0.9, which is relatively higher compared with both the rotor-PM machine and stator-PM machine.

This article proposes a new hybrid-excited dual-permanent-magnet generator with the relieving-dc-saturation (RDCS) structure for stand-alone wind power generation. The proposed generator integrates the stator dc source and rotor permanent-magnet (PM) source in a single brushless structure, which enables coordinated power generation and flexible power adjustment. Moreover, considering the parasitic saturation effect in the stator core caused by the dc field source, a constant PM bias is introduced at the stator side to construct an RDCS structure, so that the core utilization ratio is improved as well as the generator power density. In this article, the generator structure and the operation principle are introduced. Some leading design parameters are determined based on the sensitivity analysis. A finite element and genetic algorithm combined method is further adopted to realize a multi-objective design optimization, and the optimal design of the proposed topology is verified to be a potential generator candidate for stand-alone wind power generation.

Wireless power transmission (WPT) technique has advanced rapidly in the past two decades. For wireless power transmission distances from 40 to 200 mm, the resonance coupling WPT (R-WPT) technique has surpassed its original inductive coupling counterpart in terms of transmission efficiency. Nevertheless, the power transfer efficiency of a R-WPT system is still lower than that of a wired power transfer system. To increase the power transfer efficiency of a R-WPT system, metamaterial (MM) slabs are inserted between the transmitter and receiver. Moreover, it has recently been validated that a hybrid MM (HMM) slab with different resonance frequency unit cells behaves better than a homogeneous MM slab with identical resonance frequency unit cells in a R-WPT application. However, in the existing HMM slab designs for WPT applications, a trial and error approach, is commonly used to decide the physical and circuit parameters of the HMM slab due to the overwhelmingly high computational cost of numerical simulations using three-dimensional (3-D) finite element method. To overcome the deficiencies of the existing designing methodology and to fully automate the design process, a design-of-experiment (DOE) assisted sequential refinement methodology is proposed by introducing an adaptive surrogate model with tabu search method, for design optimizations of HMM slabs in R-WPT applications. Compared with the existing refinement searching procedures, the salient feature of the proposed one is its bi-directional characteristics, which can refine the searches in the promising sub spaces by intensifying sampling points; and use coarse searches or even discarding the exploitations in the worst sub spaces using some adaptive upper and lower limits of the decision parameters. To validate the feasibility and show the advantages of the proposed methodology, detailed numerical and experimental studies on a case study of a four-coil WPT system working at 13.88 MHz are conducted, and the results have shown that the HMM slab optimized by using the proposed methodology does have better performance in WPT applications when compared to its homogenous counterparts.

To alleviate the adverse impact due to the deterioration of electrical insulation, this paper presents an electromagnetic-thermal-fluid analysis for the prediction of temperature distribution in transformers with oil-based nanofluids or pure oil. The core loss and copper loss are taken as the heat sources for the temperature analysis using computational fluid dynamics. To strive for computing the temperature distribution accurately in the nano-oil, an effective numerical method using finite volume method and improved physical parameter model are employed. Numerical simulation of the thermal performance of the nanofluid with different volumetric fractions with Al2O3 nanoparticles is compared with those using pure transformer oil in a 500 VA single-phase transformer. From the comparisons of the simulation results, it is found that the volumetric fraction 0.01% is an optimum concentration in reducing the transformer size for the same power rating. The observation is served as useful guidelines and detailed process for the design of oil-based power transformers.

Thrust ripple and density greatly impact the performance of the linear machine and other linear actuators, causing positioning control precision, dynamic performance, and efficiency issues. Generalized pole-pair combinations are difficult to satisfy both the thrust and ripple for double salient reluctance linear machines. In this paper, a DC-Biased vernier reluctance linear machine (DCB-VRLM) is proposed to solve the abovementioned issues. The key to the proposed design is to reduce the ripple and enhance the thrust density with non-uniform teeth by utilizing and optimizing the modulated flux in the air gap. To effectively verify the proposed design, the DCB-VRLMs with different winding pole pairs and secondary poles are compared. The 12-slot/10-pole combination is chosen to adopt a non-uniform air gap structure. Moreover, the energy distribution of AC/DC winding is studied and optimized to further enhance the performance of the proposed DCB-VRLM. The results indicate that the DCB-VRLM with the non-uniform air gap has a lower thrust ripple, better overload capability, and higher thrust density, which confirms its superiority in long-stroke linear rail transit and vertical elevator applications.

The demand for fast magnetic field approximation for the optimal design of electromagnetic devices is urgent nowadays. However, due to the lack of a publicly available dataset and the unclear definition of each parameter in the magnetic field dataset, the expansion of data-driven magnetic field approximation is severely limited. This study presents a physics-informed generative adversarial network (PIGAN), as well as a permanent magnet linear synchronous motor (PMLSM)-based magnetic field dataset, for fast magnetic field approximation. It includes the current density, material distribution, electromagnetic material properties, and other parameters of the electric machine. Physics-informed loss functions are utilized in the training process, making the output governed by Maxwell’s equation. Different slot-pole combinations of the PMLSM are involved in the dataset to extend the generalization of PIGAN. Some indicators for the further evaluation of magnetic approximation performance, including image-based metrics and calculation methods for the performance of electric motors, are presented in this study. Some challenges of magnetic field approximation using PIGAN are also discussed. The effectiveness of the physics-informed method is verified by comparing the magnetic field approximation results and the performance analysis results of the PMLSM with FEM, and the speed of PIGAN is approximately 40 times faster than that of FEM, while the accuracy is similar.

This paper proposes a novel modular relieving-dc-saturation Vernier reluctance machine for electric vehicle application, which integrates the merits of a robust structure, controllable excitation field, strong fault-tolerant capacity, and enhanced torque density, benefiting from its special relieving-dc-saturation design. In the proposed machine, zero-sequence current establishes a modular magnetic path and functions as the dominant excitation source for the torque generation. Especially, slot permanent magnets are introduced into each module, which mitigates the saturation effect in stator core caused by dc-biased flux with the zero-sequence current source. Therefore, the proposed machine can achieve enhanced torque density with relatively high current density. In this paper, the machine structure and operation principle are illustrated in detail, with its electromagnetic performance evaluated by time-stepping finite-element analysis. It is revealed that, due to its relieving-dc-saturation ability, torque density of the proposed machine is enhanced by about 20% with high current density.

A novel adjustable degrees-of-freedom numerical method for computing the temperature distribution of electrical devices is presented. The proposed method provides a convenient, accurate and efficient approach to increase/reduce variables and couple/decouple variables. In traditional finite element method (FEM), the electromagnetic field and thermal field need different FEM meshes, which reduce the efficiency and accuracy of the field coupling. Also, the traditional method introduces the inevitable error when the power loss is plotted from Maxwell to Fluent as the different meshes are employed. In this paper, the greatest advantage is that the electromagnetic field and thermal field can be computed using a single mesh with the proposed technology of exploiting different constrained degrees-of-freedom, which decreases the computation time and system complexity. The global domain divided into several sub-domains were utilizing various corresponding functions and also employed to reduce the computational burden when calculating the core loss, copper loss, stray loss and temperature distribution. Numerical examples are reported to showcase the accuracy and effectiveness of the proposed method.

A quantitative analysis and design guideline for dual-permanent-magnet Vernier machine (DPMVM) are presented in this paper. First, by winding factor analysis for dominant air-gap harmonics, torque components excited by stator PMs and rotor PMs are quantified, which reveals that, in DPMVM, the rotor PMs essentially have higher torque generation ability than stator PMs, due to the effective utilization of fundamental PM harmonic without flux modulation. Furthermore, mutual influence between dual PM sources is analyzed. It is revealed torque contribution of stator PMs is unilaterally affected by design parameters of rotor PMs. Finally, a design guideline is provided for DPMVM, considering the design priorities of dual-PM sources. Finite element simulation and prototype experiments prove the validity of the theoretical analysis.

To enhance both the solution speed and quality of a topology optimization (TO), a multiscale TO methodology by combining the sequential element rejection–admission (SERA) and boundary element evolvement is presented. In the proposed SERA approach, only the sensitivities of the boundary elements need to be computed and used, and an adaptive parameter updating strategy is introduced to balance the requirements on both convergence and quality performances. To eliminate the dependence of the final solution on the initial topology, a new hole generating mechanism is proposed. In addition, a sensitivity filter is designed to remove the checkerboard patterns as well as to further eliminate the mesh-dependent problem. Numerical results are reported to showcase the merits of the proposed methodology.

A novel parallel-hybrid dual permanent magnet (PM) machine topology with both enhanced torque density and improved flux weakening capability is proposed for electric vehicle propulsion in this paper. The key is to artificially construct the harmonics diversity with a single-layer concentrated armature winding in the stator and thus simultaneously couple the armature field with the excitation field produced by slot PM, rotor PM, and stator dc source, respectively. Enhanced torque density is obtained in this new topology due to the symmetrical flux-modulation effect between dual PM sources. Moreover, benefiting from a parallel excitation characteristic of hybrid magnetic circuit, the demagnetization risk is significantly mitigated for slot PM source and thus an extended flux weakening range is obtained. In this paper, the proposed new topology and its design mechanism are investigated, along with its electromagnetic performance evaluated based on finite-element analysis. Further, some leading design parameters are analyzed and determined to provide a design guideline for the proposed new topology. Finally, a prototype is built and fully tested. Relevant experimental results agree well with the finite-element predication.

An adaptive degrees-of-freedom finite element method (FEM) for 3-dimensional nonlinear magneto-thermal fields is proposed in this article. Both magnetic field and thermal field are discretized usin...

This paper proposes the operation principle and a new flux estimation method for sensorless control strategy for the dual-fed flux modulated electric motor (DFFM). The DFFM is designed based on the flux modulation theory, it includes two stator windings and one rotor which simplify the mechanical structure. The rotor has only modulation iron and no permanent magnets on it, so there is no cogging torque problem in this motor. With adjustment of the outer and inner stator flux rotating frequency and amplitude, different rotation speed and torque of the sandwiched rotor can be gained for the DFFM. Furthermore, an improved flux estimation based sensorless control strategy is performed on the proposed machine to fit the two winding set control situation. The startup and performance of the proposed control strategy is verified by the simulation and experiments.

A novel bidirectional flux-modulation permanent magnet (BFMPM) machine for stand-alone dc wind power generation is proposed in this paper. The key is to control the inner rotor position with a small servo motor, and with the bidirectional flux-modulation effect, the resultant induced voltages in two sets of stator windings can be adjusted accordingly. Consequently, in a wide wind speed range, the various-speed constant-amplitude-voltage operation is realized. The novel structure has two major merits. First, it has high reliability without the maintenance problems caused by mechanical gearboxes, slip ring assembly, and brushes. Second, the proposed system requires a low-cost uncontrolled diode rectifier, which enhances the reliability and reduces the cost of the system. The analytical model and operation principle of the BFMPM machine are illustrated and the simulation results using a finite-element method is presented. A prototype is optimized and fabricated. The experimental results agree well with the simulation results and verify the correctness of the analytical model and the effectiveness of the proposed structure. Therefore, the novel structure offers a potential solution to provide a stable dc power for the standalone condition, such as remote area and offshore island.

Nanofluid is an innovative approach to improve the thermal conductivity of fluid by adding nanoparticles. Transformer oil-based nanofluids have been prepared and measured, which verifies the concept and demonstrates the potential in oil-immersed power transformer applications. In this paper, the effect that nanofluids (oil/SiC) have on the natural convective heat transfer in disc-type transformer windings is investigated numerically. The multi-phase mixture model is employed for the first time to analyze such a nanofluid flow field, and the single-phase model is also used for comparison and mutual authentication. After using the nanofluid, significant temperature drops inside the windings are observed, and in some cases, the heat transfer performance is further improved by the adjusted mass flow rate distribution. The impact of nanofluids is enhanced with the rising volume fraction of nanoparticles. Before performing the study, the numerical model is validated using the existing results of the referenced windings cooled by transformer oil.

In this paper, the response surface method (RSM) is exploited in the cooling system design optimization of oil-immersed transformers. To generate the training data for RSM, a 3-D computational fluid dynamic model for the transformer under study is constructed and solved, followed by verification on the solutions. Based on the simulation data, two types of RSMs, i.e., the second-order polynomial method and the Kriging method, are employed to evaluate their performance for this specific problem. The response surface with the best performance is used in the optimization process. The solution is compared with that found by the direct optimization method to showcase the effectiveness of applying RSM to oil-immersed transformer cooling system design. Details of implementation of the studied transformer are also presented.

This paper applied the finite-element method (FEM) with topological data structures to the optimization of electrical devices. A generic modifiable graph data structure is built according to the graph-theoretic foundation for these data structures. The employed topological FEM avoids rebuilding of the mesh in traditional FEM method while geometrical variations happen. It is an effective algorithm which can save computer storage and working time when applied to successive optimization. The effectiveness is verified by numerical example and comparison of the topological FEM with traditional FEM on storage load and working time is shown in this paper.

Permanent magnet biased axial-radial magnetic bearing (ARMB) can realize axial and radial suspension simultaneously. It has a compact configuration with the volume and weight reduced. However, its magnetic field distribution is quite complicated, its bias and control magnetic field are coupled. In order to design the magnetic bearing accurately, this paper divides the leakage and soft magnetic material routes according to the 2D FE simulation, establishes the accurate magnetic circuit including the leakage and soft magnetic material reluctance. The circuit can be used to observe the flux distribution in each route, verify and regulate the magnetic bearing structure parameter, so the FE computation efforts of the basic structure parameter are significantly reduced. An experimental sample was designed, 3D FE simulation and experiments were processed to test the prototype. The results confirm that the design method is reasonable and correct.

In the design and practical application of highspeed permanent magnet synchronous machine (HSPMSM), there is a multi-parameter, strongly coupled relationship between the machine and the drive. Drive harmonics have a significant impact on machine losses and thus on the overall efficiency. First, a 100kW, 60krpm machine and drive system is modelled accurately to study the strongly coupled electromagnetic field of the motor and drive. The model includes an accurate model of the slot conductor, which facilitates the calculation of AC copper loss. An electromagnetic field-circuit coupling model of the HSPMSM, which enables the study of the high coupling regulation between the machine and the drive. Second, based on the comparison between the ideal sine wave current source and the drive harmonic power supply, the effect of the drive harmonic on various losses of the machine is studied, such as AC copper loss, stator core loss, permanent magnet (PM) and sleeve eddy current loss. The laws and coefficients of the effect of drive harmonics on the various loss of the machine are obtained, which is of great significance for the design and development of HSPMSMs. It provides a useful reference for the design, development and application of HSPMSMs.

The transformer of fly-back switching power convertor traditionally has a ferrite core with an air gap for energy storage and energy transfer. The excessive air gap in traditional fly-back transformer will increase leakage flux, resulting in more losses and lower efficiency. This paper presents a novel structure in which a part of the ferrite core is replaced by a plurality of coil units. The port of each coil unit is connected to a capacitor. The inductance and capacitance values of the coil unit are properly designed so that the resonant frequency of the unit is close to the operating frequency of the fly-back circuit. Near the resonance frequency, the equivalent impedance of the input winding increases significantly. In order to achieve a larger imaginary part and a smaller real part of the equivalent impedance of the winding, the number of turns and the arrangement of the coil unit need to be adjusted. In the case study of this article, the equivalent impedance of the input winding is about 10 times its self-inductance at the operating frequency of the fly-back circuit. The new structure enhances the energy storage, and then increases the output power, as well as reduces the amount of ferrite core.

Based on an Alopex optimization algorithm and a response surface model (RSM), a hybrid sub-region methodology is presented to solve the optimal design problems of permanent magnet (PM) machines. The Alopex optimization method is processed both in subspace and in global solution space. In order to decrease the computing time, a multi quadric radial basis function (MQRBF) is embedded in the optimization. The proposed method speeds up the convergence rate while keeps the accuracy of the solution. A numerical experiment is given to validate the efficiency and effectiveness of the method.