Permanent Magnet Electrical Machines Research Articles

Hollowed windings for an improved cooling of permanent magnet electrical machines

Hollowed windings for an improved cooling of permanent magnet electrical machines

A novel electro-hydraulic unit design based on a shaftless integration of an internal gear machine and a permanent magnet electric machine

In recent years, increasingly stringent emission regulations have spurred an electrification trend in off-highway vehicle technology. To address challenges such as the high cost of power electronics components, limited battery capacity, and the substantial modifications required for the vehicles, there is a pressing need to develop high-speed, cost-effective, compact, and efficient electro-hydraulic units capable of powering vehicle functions. In response to these demands, this paper introduces an innovative morphology for an electro-hydraulic unit and outlines the integration method for a crescent-type internal gear machine with a permanent magnet synchronous electric machine. The proposed morphology aims to minimize component count through a shaftless solution while incorporating a cooling system that utilizes the same working fluid as the hydraulic machine. The design approach utilizes a genetic algorithm optimization process to maximize overall energy efficiency and compactness. Insights gained from the optimization results shed light on the relationship between key design parameters and unit performance, enhancing the understanding of this electro-hydraulic unit. A prototype of the unit was manufactured and tested, demonstrating a volumetric efficiency ranging from 81 % to 97 % at a maximum rotational velocity of the pinion of 6000 rpm. These results validate both the morphology and the design approach, indicating the feasibility of designing compact electro-hydraulic units that leverage hydraulic machines with higher maximum rotational velocities than commercially available counterparts as a mean to enhance efficiency and compactness.

Innovative Design of Cooling System for a High-Torque Electric Machine Integrated with Power Electronics

The growth of electrical machine applications in high-torque environments such as marine propulsion and wind energy is encouraging the development of higher-power-density machines at ever higher efficiencies and under competitive pressure to meet higher demands. In this study, numerical simulations are performed to investigate the characteristics of air cooling applied to a 3 MW high-torque internal permanent magnet electric machine with integrated power electronics. The whole system of the main machine and two converters at either end are modelled with all details. Effects of different parameters on the total pressure drop and air flow rate to the machine and converters are examined. Results show that by changing the converter outlet hole size, the air flow rate to the machine and converter can be adjusted. Air guides and pin vents reveal excellent performance in the distribution of air to laminations and windings with a penalty of some increase in pressure drop, which is more pronounced when using smaller outlet holes. Furthermore, the air return manifold increases the pressure drop and causes a reduction in air flow rate to the converter. Insulation between compression plate and laminations is an unavoidable component used in electric machines and acts as a thermal insulator. However, it can also significantly augment pressure drop, especially in combination with smaller outlet holes. Thermal studies of the integrated power electronics illustrate that components’ temperatures are less than the temperature limit, confirming enough air through the converter. Analysis of power electronics in the case of fan failure provides the operational time window for the operators to respond.

Operational Analysis of an Axial and Solid Double-Pole Configuration in a Permanent Magnet Flux-Switching Generator

There are two main beneficial characteristics that doubly salient permanent magnet (PM) electrical machines present for aircraft applications: armature windings and PMs excitation sources placed on the stator side (maintenance and thermal management), and having a clear-cut rotor without PMs or excitation windings (vulnerable at high speeds due to associated centripetal mechanical stresses). Within this framework, a doubly salient permanent magnet (DSPM) generator was conceived by optimizing the stator size and rotor structure to minimize the torque ripple and maximize the root-mean-square (RMS) voltage value per turn of each generator phase. Firstly, a comparison between the 2D and 3D finite element method (FEM) models is made considering the results of 3D finite element analysis (FEA) as our benchmark in order to understand the accuracy of the 2D results against our benchmark model, the 3D one. A multi-objective design strategy based on a 2D FEA is made, it is set to have characteristics closest to optimal for a Boeing 767 turbine, that is, the necessary electromotive force for a required power of 90 kW at 3000 rpm, feeding a simplified Boeing 767 electrical power distribution system. The results show that the machine could not deliver the required power at 3000 rpm since the 2D FEA demonstrates that the 2D model gives optimistic results when compared with the 3D FEM model. However, with a 3D FEA of the machine feeding the aircraft load, it was seen that the machine’s efficiency is 92%, suggesting that this machine can be a plausible solution.

The Juxtaposition of Our Future Electrification Solutions: A View into the Unsustainable Life Cycle of the Permanent Magnet Electrical Machine

Electrification is increasing in prevalence due to the importance placed on it for achieving global net zero targets. This has led to the proliferation of electrical mobility, including the wide-scale production of passenger vehicles, personal mobility devices and recent announcements regarding electrically powered aircraft, as well as in energy production. Electrical machines provide a cleaner source of energy during operation in comparison to their traditional fossil-based alternatives. The uncertainty and lack of transparency hanging over these green credentials can be attributed to how these products are manufactured and then disposed of at the end of their life. For them to be a truly sustainable solution, improvements need to be made across their entire life cycle. With the projected increase in their numbers due to the advancement of electrification, this current life cycle is not sustainable, directly opposing the intention of these products. This paper will introduce the current demand and challenges. It will also present these motors broken down into their constituent parts and follow each through their typical lifecycle. This paper presents the typical current life cycle of permanent magnet electrical machines, demonstrating the environmental issues associated with the current linear life cycle, and proposing alternative practices, to ease the environmental burden.

Enhancing Heat Transfer Efficiency in Permanent Magnet Machines through Innovative Thermal Design of Stator Windings

This paper investigates innovative methods for enhancing heat transfer efficiency in high-power permanent magnet electrical machines. The objectives are to quantify the effects of increasing the air speed, increasing the turbulence intensity, and introducing the spacing between windings on cooling performance. The cooling of stator windings is studied through experimental wind tunnel testing and Computational Fluid Dynamics (CFD) modelling. The CFD model is validated against wind tunnel measurements to within 4 Kelvin (K). The results demonstrate that each enhancement method significantly improves the cooling capability. Increasing the air speed from 10 m/s to 40 m/s reduces the winding hotspot temperature by 34%. Introducing a high turbulence intensity of 40% leads to a 21% lower hotspot temperature compared to 0.5% turbulence intensity. Creating a 1.5 mm spacing between coils also substantially improves convection and conduction heat transfer. Overall, combining these optimised design parameters yields over a 40% reduction in hotspot temperature compared to the original design. This research provides practical guidance for maximising heat transfer efficiency in high-power permanent magnet machines, without increasing complexity. The findings will lead to higher machine efficiency, reliability, and longevity for aerospace and other applications.

Study on the Influence of a Combined-Halbach Array for the Axial Flux Permanent Magnet Electrical Machine With Yokeless and Segmented Armature

To increase torque density, a combined-Halbach array for the axial flux permanent magnet machine (AFPMM) with yokeless and segmented armature (YASA) is presented in this paper. Firstly, the YASA machine models with conventional axial magnets and combined-Halbach array magnets are established by using 3-D finite-element method (FEM). Then, the torque, torque per magnet-volume and no-load back electromotive force (back-EMF) are calculated, and the performance of two machines are analyzed and compared. It is demonstrated that the combined-Halbach array can improve the torque density of the machine and the utilization rate of the magnets. Finally, the combined-Halbach array rotor is optimized, where the rotor with unequal-thickness magnets is established, and its torque density is calculated under different thickness. The results show that the combined-Halbach array with unequal-thickness magnets can decrease the amount of permanent magnet materials, thus improve the utilization of magnets and reduce the costs.

Analyzing heat transfer in Axial Flux Permanent Magnet electrical machines: A literature review on the discretization methods-FVM and FDM

Axial Flux Permanent Magnet (AFPM) machines have gained significant attention due to their high power density, efficiency, and compact design. However, effective heat transfer analysis is critical for optimizing their performance and reliability. This paper presents a comprehensive literature review on the application of discretization methods, specifically the Finite Volume Method (FVM) and Finite Difference Method (FDM), in the thermal analysis of AFPM machines. The fundamentals of FVM and FDM are briefly explained, followed by an exploration of their applications in AFPM machine thermal analysis. The advantages and limitations of using these methods are discussed, and a comparison between FVM and FDM is provided. Advanced discretization techniques, such as the Finite Element Method (FEM), and coupled thermal-electromagnetic analyses are also examined. The paper highlights studies that have utilized FVM or FDM in developing optimized designs and effective thermal management strategies for AFPM machines. Lastly, potential future research directions are identified, including the development of more efficient discretization methods, the incorporation of advanced materials, and the investigation of novel cooling techniques. This review offers valuable insights into the current state of research and potential future directions in the thermal analysis of AFPM machines using discretization methods.

Optimal Design Method of Post-Assembly Magnetizing Device with Field–Circuit Coupling Analysis

Post-assembly magnetization can significantly simplify the manufacturing of the rotor of permanent magnet (PM) electrical machines. The optimization of the post-assembly magnetizing device using finite element analysis (FEA) is time-consuming; therefore, a globally optimal solution aiming at achieving an adequate magnetizing level and minimal energy consumption is difficult to achieve. In this paper, a field–circuit coupling analysis (FCCA) model is proposed to optimize the auxiliary stator-type magnetizing device for interior permanent magnet synchronous machines (IPMSMs). A reasonable simplification of the highly saturated magnetic circuit is made based on FEA results so that the magnetic equivalent circuit (MEC) model can be established. On the other hand, the eddy currents in the PMs are equivalent to an eddy current short-circuit; thus, by converting the field calculation into a circuit calculation, the time cost can be reduced significantly, which greatly improves the speed of multi-objective optimization of the magnetizing device with multiple degrees of freedom. A V-type IPMSM is taken as a study case, and its post-assembly magnetizing device is optimized with the proposed method. FEA and experimental results show that the PMs are fully magnetized, while the required energy consumption is greatly reduced when compared with an existing magnetizing device.

Performance Analysis of Distributed HTS Armature Winding Direct Drive Wind Generator With Active Magnetic Shielding Layer

High-temperature superconducting (HTS) electrical machine has higher torque density and higher efficiency than permanent magnet electrical machine, showing a great application prospect in the field of offshore wind power generation. However, if there is applied magnetic field acting on the wide plane of HTS tape perpendicularly, the current-carrying capacity of the HTS tape will be greatly reduced, resulting in the performance limitation of the HTS electrical machine. In order to reduce the negative effect of the applied magnetic field on the HTS tape, this paper proposes a new distributed HTS armature winding direct drive wind generator (DHTSAW-DDG) with active magnetic shielding layer. In this paper, the topology and working principle of the DHTSAW-DDG is clearly illustrated, meanwhile, the basic electromagnetic performances of the DHTSAW-DDG are carefully analyzed and compared with the counterpart with the copper armature winding. The results show that the active magnetic shielding layer made of HTS material can significantly weaken the negative effect of the applied magnetic field on the current-carrying capacity of the HTS tape. The electromagnetic performance of the HTS electrical machine can be significantly improved, if the distributed HTS armature winding and the active magnetic shielding layer are adopted. The torque density and the power factor of the proposed DHTSAW-DDG with active magnetic shielding layer can increase approximately 40% than the copper armature winding electrical machine with same topology.

Design Factors of High-Speed Turbo-Electric Distributed Propulsion System

Turbo-electric Distributed Propulsion (TeDP) is a promising concept to achieve the operational goals of more electric aircraft. The application of TeDP architecture can achieve the desired weight reduction of an aircraft power system. The use of a superconducting machine is expected to provide the workaround for the weight issue, but its current state of technology has not yet been extensively tested for aircraft applications. Another more practical option is to directly couple the aircraft's propeller system to a high-speed permanent magnet (PM) electrical machine, eliminating the gear part that also contributes to the total weight. A critical part of the design for a high-speed PM machine is choosing the optimum magnet configurations. This study used finite element modelling to analyze the impact of scaling the PM’s critical parameters on the weight and machine speed. A prototype testing of a 2-KW high-speed machine, suitable for a Remotely Piloted Aircraft System (RPAS), was developed and tested. The results confirmed the following critical parameters that should be carefully designed to achieve the optimum output, such as the (a) number of winding turns, (b) stack length, (c) sleeve thickness, and (d) terminal voltage.

Equivalent Transformation Between Axial- and Radial-Flux Permanent-Magnet Machines

In this paper, an equivalent transformation approach for permanent-magnet (PM) electrical machines using coordinate transformation theory is presented. With the proposed method, an axial-flux PM (AFPM) machine can be transformed to an equivalent radial-flux PM (RFPM) machine or vice versa. The main purpose of proposing such a transformation method is to simplify the design of AFPM for specific applications. Besides, according to the working space requirement, the shape of PM machines can be changed while maintaining magnetic performances. The proposed transformation theory is based on the basic magnetic theory and the theoretical derivation is presented in detail. The resulted transformation equations for RFPM and AFPM machines with surface-mounted PMs are friendly to engineers. Moreover, an AFPM machine is used to validate the proposed theory, both FEM and experimental results have good agreement with the results of the proposed method. With the equivalent transformation theory, engineers could design, simulate and evaluate the AFPM machines with an exist well-developed machines.

Characteristics of Permanent-Magnet Electric Machines with Slotted and Slotless Stator Design

Characteristics of Permanent-Magnet Electric Machines with Slotted and Slotless Stator Design

Study on AC Copper Losses in an Air-Cored Axial Flux Permanent Magnet Electrical Machine With Flat Wires

In this article, we propose the calculation method of ac copper losses of air-cored axial flux permanent magnet (AFPM) electrical machine with flat wires fed by pulsewidth modulation (PWM) inverters. The ac copper loss due to armature currents in air-cored electrical machines is significant when these machines are driven by PWM inverters. Besides, the exposure of windings to the inhomogeneous alternating rotor magnetic field causes ac copper loss. Analytical formulas are efficient tools to evaluate these losses but few pieces of literature have reported the derivation in such machines. To address this issue, the formulas of aforementioned ac copper losses are derived based on Maxwell's equations and Poynting theorem. As for end windings, the ac copper loss caused by armature current is calculated analytically, while the rotor-induced ac copper loss is calculated by aid of static three-dimensional finite-element analysis (FEA). The interaction of load current and rotor-induced eddy current is also studied. A 12-slot-16-pole air-cored AFPM machine is analyzed with the proposed method, and the analysis is validated by time-transient FEA simulations and prototype experiments. The influence of modulation ratio on ac copper loss due to armature current of the AFPM machine is also discussed.

Electromechanical engineering education and science in Republic of Moldova

The work is a summary of the history of the industry and education development of electrotechnics in the Republic of Moldova during the independence period. With the national renaissance, the process of professional training in the electrotechnical field began to take on a natural national face - training in the Romanian language. Scientific research is determined by the subject of special submersible and permanent magnet electric machines, renewable energy sources, but also by new directions such as the development of adjustable electromechanical systems for the automation and efficiency of technological processes and traction systems of electric passenger vehicles.

Analysis of Flux Density and Iron Loss Distributions in Segmented Magnetic Circuits Made With Mixed Electrical Steel Grades

This article presents the potential contribution of segmented stator magnetic circuits of rotating permanent magnet electrical machines with concentric winding. Two magnetic materials are mixed: FeSi non-oriented electrical steel and FeSi grain-oriented electrical steel (GOES). The choice of using GOES is based on the high performance it offers in terms of permeability and iron losses compared to conventional non-oriented grain electrical steel (NOES), particularly when GOES is magnetized in the rolling direction (RD). The goal is to analyze the contribution of the mixed magnetic circuit on the losses and electromagnetic torque but also the drawbacks due to the cut process and the assembly. The behavior of the magnetic field at the junction between the segments is studied by comparing different geometrical connection shapes and compared to a reference magnetic circuit fully made with NOES sheets. This comparison is experimentally made with a model representative of the existing phenomena in an electrical machine. In addition, numerical calculations using finite elements software are carried out by considering both the magnetic anisotropy and the saturation of the GOES.

A mechanical flux weakening method via split rotor in permanent magnet aerospace alternators

Whilst permanent magnet (PM) electrical machines often offer very high power density, they suffer from the issue that the voltage output from the machine is a function of speed due to the fixed nature of the flux delivered by the PM poles within the machine. The best performance of PM machines achieved at lower speeds might not be achieved at higher speeds due to the fact that the voltage of the machine at high speeds is greater than the rating. In order to overcome this issue in PM machines, this paper proposes a mechanical flux weakening method via a split rotor. The key feature of the proposed scheme is that the fixed nature of rotor magnet flux can be altered by means of a simple mechanism that helps reduce the magnet flux by realigning part of the rotor at higher speeds. The rotor is axially split into two sections to achieve two states of field excitations: maximum and the least output depending upon the alignment between the rotor sections. A number of key 3-dimensional (3D) finite element (FE) simulations have been used to demonstrate the effectiveness of the proposed mechanical flux weakening approach. The results indicate that the split rotor method can be an alternative to more complicated mechanical flux weakening approaches in safety critical applications such as aerospace. Thus, a PM machine with split rotor could be used over a wide speed range without applying excessive voltages to the load at higher speeds in fault tolerant aerospace applications.

Design and Control of a New Compound Double-Rotor Electric Machine for Hybrid Propulsion System

In this article, a new compound consequent-pole double-rotor electric machine (CCPDRM) is proposed for hybrid propulsion system application. First, the operating principle and harmonic components in CCPDRMs are elucidated. The winding factor theory for conventional permanent magnet (PM) electric machines is further extended and applied in CCPDRMs. Then, this improved theory is adopted to investigate the structure and winding scheme requirement of the proposed CCPDRMs. In addition, the control strategy for the proposed CCPDRM is established. By utilizing a parameter sweep method, the variation trends of CCPDRMs’ torque density with respect to various geometrical parameters are revealed. Based on this, the structure of CCPDRMs is optimized to acquire a better electromagnetic performance. Next, the proposed CCPDRM is compared with a conventional compound bipolar double-rotor electric machine (CBDRM). It is found that the improved topology has a similar torque density but a much higher PM utilization factor and a lower PM demagnetization risk when compared with the CBDRM. Finally, a prototype is manufactured and tested in different operating modes. Furthermore, various mode-switching processes are performed to emulate the practical driving cycle of hybrid transportation. Both steady-state and dynamic mode-switching experimental results prove the effectiveness of CCPDRMs.

Experimental Study on Characteristics Variation of Permanent Magnets for High-speed Machine Applications

High-speed permanent magnet (PM) electric machines are widely used. However, their extreme operating conditions, e.g., high temperature and high mechanical stress, lead to variations of the PM characteristics and affect the machine performance. In the present study, an experimental device is designed to test the PM characteristics by simulating the stress and temperature conditions of high-speed machines. The experimental results indicate that the PM remanence not only varies at high temperatures, which is well known, but also changes under high mechanical stress. It is shown that the PM remanence increases with the mechanical stress but decreases with the temperature rise. Accordingly, a new demagnetization-curve model of the magnets under multiple stresses is refined to better express the PM characteristics. The performance of a high-speed PM machine is then analyzed as an example to indicate the necessity of the model refinement. The effects of the temperature and mechanical stress on the conductivity of the PMs are also examined. The experimental results indicate that the conductivity of the PM increases with the temperature and pressure.

Hybrid Excited Synchronous Machines

Hybrid excited synchronous machines (HESMs) combine permanent-magnet (PM) excitation and wound field (WF) excitation. The goal of hybrid excitation is to combine the advantages of PM excited machines and WF synchronous machines. HESM have been identified as one of the emerging technologies for modern energy conversion systems. They have been the subject of many review articles. The principle of hybrid excitation allows solving many drawbacks related to PM electric machines operation: flux weakening, energy efficiency, and PMs price fluctuation. It helps to introduce an additional degree of freedom in the design of synchronous machines, and allows therefore an easier adaptation of PM synchronous machines to a wider applications scope. To this additional degree corresponds the possibility of adjusting the contribution of the two magnetic field sources: PM and WF. The use of this technology for electric traction has been the subject of many scientific and technical contributions. In this contribution, the emphasis will be put on the use of these machines as generators in transportation applications and renewable energy applications. The design and operation of three particular structures will be presented. Two of them have been designed as generators for transportation applications, and the third one has been designed as generator for renewable energy conversion. All of them are flux switching hybrid excited synchronous machines (FSHESM).