Permanent Magnet Vernier Machine: A Review

Permanent magnet vernier machines (PMVMs) gained a lot of interest over the past couple of decades. This is mainly due to their high torque density enabled by the magnetic gearing effect. This study will provide a thorough review of recent advances in PMVMs. This review will cover the principle of operation and nature of magnetic gearing in PMVMs, and a better understanding of novel PMVM topologies using different winding configuration as well as different modulation poles and rotor structures. Detailed discussions on the choice of gear ratio, slot-pole combinations, design optimisation and role of advanced materials in PMVMs will be presented. This will provide an update on the current state-of-the art as well as future areas of research. Furthermore, the power factor issue, fault tolerance as well as cost reduction will be discussed highlighting the gap between the current state-of-the art and what is needed in practical applications

Linear Permanent Magnet Vernier Generators for Wave Energy Applications: Analysis, Challenges, and Opportunities

© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).Harvesting energy from waves as a substantial resource of renewable energy has attracted much attention in recent years. Linear permanent magnet vernier generators (LPMVGs) have been widely adopted in wave energy applications to extract clean energy from oceans. Linear PM vernier machines perform based on the magnetic gearing effect, allowing them to offer high power/force density at low speeds. The outstanding feature of providing high power capability makes linear vernier generators more advantageous compared to linear PM synchronous counterparts used in wave energy conversion systems. Nevertheless, they inherently suffer from a poor power factor arising from their considerable leakage flux. Various structures and methods have been introduced to enhance their performance and improve their low power factor. In this work, a comparative study of different structures, distinguishable concepts, and operation principles of linear PM vernier machines is presented. Furthermore, recent advancements and innovative improvements have been investigated. They are categorized and evaluated to provide a comprehensive insight into the exploitation of linear vernier generators in wave energy extracting systems. Finally, some significant structures of linear PM vernier generators are modeled using two-dimensional finite element analysis (2D-FEA) to compare their electromagnetic characteristics and survey their performance.Peer reviewe

Optimal Design of Special High Torque Density Electric Machines based on Electromagnetic FEA

Electric machines with high torque density are essential for many low-speed direct-drive systems, such as wind turbines, electric vehicles, and industrial automation. Permanent magnet (PM) machines that incorporate a magnetic gearing effect are particularly useful for these applications due to their potential for achieving extremely high torque density. However, when the number of rotor polarities is increased, there is a corresponding need to increase the number of stator slots and coils proportionally. This can result in manufacturing challenges. A new topology of an axial-flux vernier-type machine of MAGNUS type has been presented to address the mentioned limitation. These machines can attain high electrical frequency using only a few stator coils and teeth, which can simplify construction and manufacturing under certain conditions. Additionally, the inclusion of auxiliary small teeth within the stator main teeth can generate a noteworthy increase in output torque, making it a unique characteristic of this motor. By analyzing the operating principle of the proposed VTFM PM machine, possible pole-slot combinations have been derived. The process of designing an electric machine is complicated and involves several variables and factors that must be balanced by the designer, such as efficiency, cost, and performance requirements. To achieve a successful design, it is crucial to employ multi-objective optimization. Using a 3D FEA model can consider the impact of magnetic saturation, leakage flux, and end effects, which are not accounted for in 2D. Optimization using a 3D parametric model can offer a more precise analysis. Validating the machine\u27s performance requires prototyping a model and testing it under different operating conditions, such as speed and load, which is a crucial step. This approach provides valuable insights into the machine\u27s behavior, allowing the identification of any areas for improvement or weaknesses. A large-scale multi-objective optimization study has been conducted for an axial-flux vernier-type PM machine with a 3-dimensional (3D) finite element analysis (FEA) to minimize the material cost and maximize the electromagnetic efficiency. A detailed study for torque contribution has indicated that auxiliary teeth on each stator main teeth amplify net torque production. A prototype of optimal design has been built and tested

Development of a Linear Vernier Hybrid Machine for direct drive wave energy converters

PhD ThesisThe work presented in this thesis concerns the development of linear electric machines for use with wave energy converters. The machine topology selected, the Linear Vernier Hybrid Machine, is extensively investigated, specifically looking at alternative magnet configurations. Topologies are evaluated by their generation capabilities at low velocities, as demanded by Direct Drive Wave Energy Converters. Attention is mainly focused on improving the electromagnetic performance and reducing the magnet mass. A new topology of the Linear Vernier Hybrid Machine is proposed for these purposes, known later as Inset Magnet Consequent Pole machine. Tapered ferromagnetic poles are employed in this topology, which have shown a great impact on minimising the inherent pole-to-pole leakage flux as well as the unwanted cogging force. Further investigation into the Inset Magnet Consequent Pole machine focuses on improving the power factor through modifications made to the machine structure with no increase in the mass magnet, steel or copper used. Two novel variants with the added benefit of flux concentration effect are proposed and described. Finite Element Analysis is used to optimize, analyse and compare the electromagnetic performances for the three investigated machines. Considering the complexity of manufacturing and number of components, two selected topologies are built and tested in the laboratory, the Inset Magnet Consequent Pole machine and V-shape Consequent Pole machine. The experimental results are compared to the simulation results to validate the design. In general, a good agreement is shown between the predicted and measured results. Afterwards, the experimental results obtained from the two prototypes are compared with each other. These results verify that the proposed V-shape Consequent Pole topology is superior in terms of no-load back EMF, force and power factor, while it exhibits lower cogging force in comparison with the Inset Magnet Consequent Pole topology. It is therefore concluded that the V-shape Consequent Pole machine is the best compromise between power factor, efficiency and ease of manufacture. It has half the number of components per pole of the best machine design presented, yet delivers 91% of the force density and 93% of the power factor. The last part of this thesis investigates the feasibility of using the proposed V-shape Consequent Pole machine as an alternative design for an existing wave energy device developed by Uppsala University to assess the effect of employing this sort of machine on Abstract ii the overall machine size and costs. Five variants of the V-shape Consequent Pole machine are described and comparedTechnical and Vocational Training Corporation, Saudi Arabi

Development of high force dense linear generators for wave energy converters

PhD ThesisThe main concern of this thesis is the development of force dense linear generators for a Direct Drive Wave Energy Converter. Linear machines for direct drive power take-off systems are required to deliver very high force in order to harness the significant amount of power from the low velocity oscillation of an ocean wave. Therefore, the linear Vernier Hybrid Machine is investigated for its simple design structure and high force density at low speed, due primarily to the inherent magnetic gearing. Attention is focused on improving the performance of the existing linear Vernier Hybrid Machine and developing new variant topologies with higher force density. An improved E-core stator design, optimised permanent magnet dimensions and new segmented translator structure have been proposed which improve the machine performance in terms of mass and magnet utilisation. The implementation of a pole shifting method is shown to provide a significant reduction in the cogging force. Two cylindrical variants with three-dimensional flux paths are also developed from the improved E-core Vernier Hybrid Machine, which further improves the force with similar magnet mass and current density. Furthermore, a new combination of Halbach magnets arrays and Consequent Pole topology are employed in the flat E-core structure, known later as Halbach Consequent Pole Vernier Hybrid Machine, which significantly improves the flux density by reducing the inherent pole-to-pole leakage and thus further improve the force density and power factor of the machine. A cylindrical variant of the flat Halbach Consequent Pole topology has been designed and analysed to prove the performance improvement of the cylindrical versions compared to the flat. The flat Halbach Consequent Pole and two small scale cylindrical variants of the E-core Vernier Hybrid Machines have been built and tested in the laboratory. The flat prototype is built from laminated steel and both the cylindrical machines are made of Soft Magnetic Composites to allow the three-dimensional flux path. All the experimental results are shown to provide good agreement with the static and dynamic generator performance predictions. Finally, this thesis compares the performance of three flat and three cylindrical Vernier Hybrid Machine topologies for various axial lengths and air-gap diameters and investigate the feasibility of using them for a wave energy devic

Linear generators for direct drive marine renewable energy converters

This thesis is concerned with the development of linear generators for use as the power take off mechanism in marine renewable energy converters. Delivering significant power at the low velocities demanded by wave and tidal stream energy converters requires a large force, which must be reacted by an electrical machine in a direct drive system. Attention is focused on the development of two novel topology linear permanent magnet machines suitable for use in this application. For each topology, models are presented that are capable of predicting the force characteristics and dynamic generator performance. The models, which are verified experimentally, reveal significant behavioural differences between the two topologies. The designer is thus provided with an interesting choice when considering a direct drive power take off strategy. In short, a variable reluctance machine is shown to develop a high shear force in its airgap, offering the potential of a compact generator, yet its performance is hindered by a poor power factor and the presence of significant airgap closure forces. The second machine, an air cored stator encompassing a permanent magnet translator, is shown to lend itself favourably as a generator, but only at the expense of requiring a large quantity of magnetic material and developing a significantly lower shear stress. Mechanical issues involved in the direct integration of linear electrical machines into the marine environment are examined. Details of two existing marine renewable energy devices are used to hypothesise about the characteristics of realistic sized generators of both the topologies investigated. Direct drive power take off is shown to represent a feasible alternative to the complex systems frequently proposed in these applications

Power Converter of Electric Machines, Renewable Energy Systems, and Transportation

Power converters and electric machines represent essential components in all fields of electrical engineering. In fact, we are heading towards a future where energy will be more and more electrical: electrical vehicles, electrical motors, renewables, storage systems are now widespread. The ongoing energy transition poses new challenges for interfacing and integrating different power systems. The constraints of space, weight, reliability, performance, and autonomy for the electric system have increased the attention of scientific research in order to find more and more appropriate technological solutions. In this context, power converters and electric machines assume a key role in enabling higher performance of electrical power conversion. Consequently, the design and control of power converters and electric machines shall be developed accordingly to the requirements of the specific application, thus leading to more specialized solutions, with the aim of enhancing the reliability, fault tolerance, and flexibility of the next generation power systems

Mathematical Models for the Design of Electrical Machines

This book is a comprehensive set of articles reflecting the latest advances and developments in mathematical modeling and the design of electrical machines for different applications. The main models discussed are based on the: i) Maxwell–Fourier method (i.e., the formal resolution of Maxwell’s equations by using the separation of variables method and the Fourier’s series in 2-D or 3-D with a quasi-Cartesian or polar coordinate system); ii) electrical, thermal and magnetic equivalent circuit; iii) hybrid model. In these different papers, the numerical method and the experimental tests have been used as comparisons or validations

Superconducting generators for large direct-drive wind turbines

This thesis further improves upon the original 10 MW design of the double claw pole generator, by systematically addressing its shortcomings. The original design is a fully iron cored machine with a stationary superconducting field winding. Its structure allows it to be highly modular, reliable and cost-effective. Its main disadvantages are, when compared to other superconducting generator designs, its weight and efficiency. The double claw pole generator is a large diameter iron-cored axial-flux machine, due to these features a very stiff mechanical structure is required to main the air gap clearances, which leads to a very heavy structural mass. A novel stator design is introduced, which partially deviates the air gap closing forces into the radial direction, reducing the axial component of forces. This enabled the structural mass to be reduced from 126 tonnes to 115 tonnes. Secondly, the field core of the double claw pole machine was replaced by an inner stator. The additional stator increases the electric loading of the machine while also further increasing its modularity and improving the generator efficiency. With a target efficiency of 95 %, the power output of the generator was increased from 10 MW to 11.5 MW, while maintaining the same machine diameter and axial length. To further increase the power density and modularity, the possibility of stacking machine modules was explored. Stacking two standardised modules concentrically was found to result in a smaller and lighter machine than the original design. Additionally, the standardised modules, due to their smaller size, greatly simplify the transportation of the generator. The addition of the inner stator was found to be a very promising design. It improves the original concept of the machine in terms of power density, efficiency and modularity. It is believed that this makes the design even more competitive in the high-temperature superconducting generator market. Finally, detailed electromagnetic modelling of superconductors was performed in the electromagnetic environment relevant to electrical machines. Particular focus was put on the dynamic loss mechanisms in superconducting field windings. Through the new knowledge gained on the loss characteristics, the cooling requirements can be better understood, potentially increasing the reliability of superconducting windings and their associated cooling systems