Linear Electric Machine Research Articles

Work at the Kharkiv Electromechanical and Turbo-Generator Plant on the project of electromagnetic torpedo tubes (1936–1938)

The article, based on archival documents of the Kharkiv Electromechanical Plant, highlights the activities of scientists of this enterprise during 1936–1938 on the project to create electromagnetic systems for bubble-free torpedo firing, which in today is completely new information for historians of science and technology, and for specialists in the field of electrical machine engineering too. This project arose as a result of a confluence of several circumstances, one of which was the need of the Soviet naval submarine fleet on the eve of World War II to improve itself torpedo armament with systems that would not reveal submarines when firing torpedoes from a submerged. Another circumstance was that since 1934 the Kharkiv Electromechanical Plant was the main enterprise in the Union of the Soviet Socialist Republic for the production of electromechanics for ships of all classes and for all coastal defense facilities, and therefore its administration and the scientific and technical personnel who were involved in defense issues at the plant, were aware of this problem. At the same time, some of the latter, working part-time at the Kharkiv Electrotechnical Institute, from the first half of the 1930s, along with the studies problems of rotary electric machines, actively developed the direction of electric machines with the axial [linear] direction of rotor movement, and achieved significant results in this. Thus, by 1936, conditions had been formed when meeting the need to provide Soviet submarines with bubble-free torpedo firing systems became theoretically possible through the use of electromagnetic torpedo launching according to the methods developed by Kharkiv scientists for linear electric machines, and by torpedo tubes whose corresponding equipment for which’s could be manufacturing at Kharkiv Electromechanical Plant. However, this theoretical possibility required practical confirmation, for which the “Magnetic Torpedo Pusher” project was organized, carried out by the same specialists who were engaged in the study of linear electric machines both at the Kharkiv Electromechanical Plant and at the Kharkiv Electrotechnical Institute. The purpose of the project was to select a possible version of the fundamental design of an electromagnetic torpedo tube and test the functionality created according to the chosen design option using model experiments. Studies have shown that pushing a torpedo out of a torpedo tube within the framework of the modes established by the customers of the project is possible with the help of a running magnetic field, however, the electromagnetic method of launching a torpedo does not make it completely bubble-free, but only leads to a decrease in the volume of the air bubble formed during the firing. Wherein, the use of electromagnetic launch of torpedoes on existing and designed projects of Soviet submarines turned out to be impossible due to significant changes in the weight and size characteristics of the electrical power equipment, that need to be installed in this case. Meanwhile, the same degree of reduction of the air bubble without any significant additional costs has already been achieved in the designs of pneumatic torpedo tubes of Stalinets-type submarines, projected by order of the Soviet Union by German and Holland designers, which completely deprived the project of torpedo tubes with electromagnetic action of its attractiveness, and led to its closure. At the same time, despite the unsuccessful result of this project in the context of creating a bubble-free torpedo firing system, its implementation allowed Kharkiv scientists to validate and verify the methods they created for calculating and designing linear electric machines, as well as to determine the optimal designs of magnetofugal stators, which was subsequently used in the creation special electromechanical equipment for the mining and construction industries.

Approximation of electromagnetic force axial distribution in “single excitation coil – permanent magnet runner” module based on modified Kloss function

An elementary part of various electromagnetic devices or linear electric machines is a module consisting of an excitation coil and a permanent magnet (PM runner). The electromagnetic force axial distribution in this “single excitation coil – PM runner” module is usually determined by numerical field calculations at discrete runner positions. When solving the mathematical model, a table containing discrete values of the electromagnetic force axial distribution is usually used (the so-called lookup table). The authors of this article decided to find a simple analytic function that approximates the calculated discrete electromagnetic force function with technically sufficient accuracy and the smallest possible number of coefficients. After many attempts, they proposed the modified Kloss function with 2 coefficients denoted as S′ and M′, the values of which for the best approximation have to be determined using the optimization algorithm e.g. the Hooke–Jeeves algorithm. This analytical function reflects perfectly the nature of the discrete electromagnetic force axial distribution determined by the numerical field calculations and approximates the discrete function with fully satisfactory accuracy.

A Comprehensive Generalized Theory and Classification of Multiphase Systems for Rotating and Linear Electric Machines

A Comprehensive Generalized Theory and Classification of Multiphase Systems for Rotating and Linear Electric Machines

On-load magnetic field calculation for linear permanent-magnet actuators using hybrid 2-D finite-element method and Maxwell–Fourier analysis

PurposeThe purpose of this study is to present a novel extended hybrid analytical method (HAM) that leverages a two-dimensional (2-D) coupling between the semi-analytical Maxwell–Fourier analysis and the finite element method (FEM) in Cartesian coordinates.Design/methodology/approachThe proposed model is applied to flat permanent-magnet linear electrical machines with rotor-dual. The magnetic field solution across the entire machine is established by coupling an exact analytical model (AM), designed for regions with relative magnetic permeability equal to unity, with a FEM in ferromagnetic regions. The coupling between AM and FEM occurs bidirectionally (x, y) along the edges separating teeth regions and their adjacent regions through applied boundary conditions.FindingsThe developed HAM yields accurate results concerning the magnetic flux density distribution, cogging force and induced voltage under various operating conditions, including magnetic or geometric parameters. A comparison with hybrid finite-difference and hybrid reluctance network methods demonstrates very satisfactory agreement with 2-D FEM.Originality/valueThe original contribution of this paper lies in establishing a direct coupling between the semi-analytical Maxwell–Fourier analysis and the FEM, particularly at the interface between adjacent regions with differing magnetic parameters.

Design and Analysis of a Linear Electric Generator for Harvesting Vibration Energy

This paper provides a proof of concept for a linear electric generator that can be used to harvest energy from various sources of linear motion, such as vibrations, free-piston engines and wave energy. The generator can be used to power small electronic devices, such as sensors, or charge household batteries. The literature was reviewed to develop an understanding about the applications, control methods, excitation methods and mechanics of rotating and linear electric machines. A bidirectional, two-sided linear machine was designed with two stator cores and a single mover core. The stator windings and mover winding can be independently excited, allowing for three modes: no mover excitation, a DC excited mover, and an AC excited mover. Simulation results showed that the magnetic flux generated by DC excited stator cores were concentrated in the centre of the mover core. The use of two stator cores eliminates lateral flux in the mover core when it is not excited, minimising attraction and repulsion forces. Parametric analysis showed that flux cutting occurred in all operation modes, verifying that the generator will produce power when operating. Hardware tests produced an output current when the machine was electrically and mechanically excited, verifying the proposed design.

Design, scalable construction, and test of optimal linear Halbach arrays for mobile applications

Design, scalable construction, and test of optimal linear Halbach arrays for mobile applications

Linear Electric Machines, Drives, and MAGLEVs Handbook [Book News

Linear Electric Machines, Drives, and MAGLEVs Handbook [Book News

Two-Dimensional Analytical Model and Control of Linear Induction Motor

Through electromagnetic forces, Linear Electric (Electromagnetic) Machines (LEMs) can directly convert electrical energy into linear mechanical kinetic energy (vice versa). Linear motion is especially common in industry. LEM was developed in his 19th century, but did not become widely used in industry until 1960 because it required power electronics (no mechanical transmission) for control. However, LEMs require power electronics for linear position, speed, and/or force control to achieve better performance than rotary electric motors with mechanical transmissions. After 1960, LEM continued to improve. The lift and drive forces of a two-phase Linear Induction Motor (LIM) are controlled by varying the phase angle between the two phases. In this article, we derive the magnetic flux density, secondary current density, and propulsion and levitation force densities in the air gap. The mean force equation is derived by summing the force density over a quadratic length using two dimensional magnetic field analysis and is used to simulate the performance of a linear induction motor. We investigate the effect of changing the phase angle on the secondary current density, perpendicular magnetic flux density component, and tangential magnetic flux density component. Furthermore, these phase-shifting effects are extended to include his two components of force (levitation and propulsion). Calculations are performed using MATLAB programs and displayed graphically. Keywords Density; Magnetic flux; Magnets; Electric

Performance and Cost Comparison of Drive Technologies for a Linear Electric Machine Gravity Energy Storage System

Energy storage is a crucial technology for facilitating the integration of renewable energy sources (RES), such as wind and solar energy, into the electrical grid. The challenge of maintaining a balance between incoming and outgoing grid power can be effectively addressed by integrating energy storage technologies with inherently intermittent RES. A range of viable options for storing energy from RES currently exists, among which the Linear Electric Machine Gravity Energy Storage System (LEM-GESS) stands out as a promising choice. The LEM-GESS stores energy in a shaft using piston masses based on the concept of gravity. This paper presents the performance and cost analysis of different linear machines employed as the main drive units in a dry gravity energy storage system. Specifically, linear permanent magnet flux switching machine demonstrates the best performance in terms of overall system cost when considering a 20 MW/10 MWh system and optimizing for the minimum levelized cost of storage (LCOS). Noteworthy findings reveal that the LEM-GESS cost is highly sensitive to system efficiency, with factors such as material cost and power factor also influencing the LCOS. Designs with modest secondary height, low usage of copper and magnet materials on the primary of the LEM, and a high power factor are preferred to minimize the LCOS. In conclusion, the LEM-GESS with a permanent magnet machine drive option is a highly promising and cost-effective technology for supporting the integration of RES into the grid.

Improvement on Thrust Control for Start-Up and Piston Motion of Free-Piston Linear Generator

Free-piston linear generators (FPLGs) without a crank mechanism are promising to be used in hybrid vehicles due to their unique operation characteristics. However, the FPLG currently still faces challenges in the start-up and piston control. In this paper, the start-up and operation process of FPLG are analyzed deeply and the improved thrust control strategies for the linear electric machine (LEM) are presented accordingly. First, the mechanism that the vibration center shifts under the general constant thrust resonance starting method is revealed, considering the asymmetric potential energy caused by non-linear compression spring effect in the combustion chamber. Then, a compensation thrust iteratively adjusted by the vibration offset is added to stabilize the swing center during start-up. Next, the coupling effect between the dead centers under single-stroke independent thrust control method is analyzed, by modeling the piston motion from the aspect of energy flow. Accordingly, an improved thrust control method for coupling suppression is presented to enhance the accuracy and robustness of piston motion. Finally, the performance of the proposed method is verified by controlling a permanent- magnet linear synchronous machine (PMLSM) in experiments and simulations.

Biofilm prevention in the generator of a direct drive wave energy converter

Power take off in a wave energy converter has a number of unique requirements. It must convert low speed oscillating motion into electricity in a reliable, low maintenance manner. A direct drive system, where the electrical machine is optimised to operate at low speed, has the potential to offer a mechanically robust and simple solution. Similar to a hydraulic power take off, the only regular maintenance would be to inspect and replace the seal between moving parts. One strategy for removing regular maintenance is to have an unsealed system, i.e. one where sea water is allowed throughout the electrical machine. A fully flooded electrical machine has benefits in terms of cooling, but poses challenges relating to reliability, corrosion, biofouling and lubrication.
 Biofilm refers to a thin layer of fouling organisms which can interfere with the operation of components. Recent work has found that submerged surfaces can be kept free of biofouling using projected ultraviolet (UV) light from LEDs. This paper discusses the testing procedure and impact of the UVC irradiation on biofilm prevention within the active part of an electric generator in a systematic manner, with a view to accelerate its translation to full-scale applications.
 A prototype generator is being developed which will be installed in the North Sea, consisting of a submerged linear tubular electrical machine. A magnetic tubular translator will oscillate within a cylinder that houses stator coils. Lubrication will be by way of solid polymer bearings. In order that the active part of the electrical machine can oscillate smoothly, it is imperative that biofilm is prevented from colonising on the bearing surface, which also makes up the magnetic gap of the electrical machine.
 The system will have a slow reciprocating oscillation, with a peak speed of perhaps 2m/s. For most wave energy converters there will be brief static periods twice in every wave, and in calm seas these could be prolonged to several hours or even days. In low energy sea states oscillation amplitude could be less than the fully rated amplitude, meaning different parts of the bearing surface could be exposed for different amounts of time.
 Early-stage work is underway to investigate the use of UV irradiation in the active part of the electrical machine and bearing surface as biofilm prevention. Flat panels (600mm x 220mm) are used to simulate the original surfaces between moving parts. To achieve biofilm growth, an artificial slime farm was deployed which allows test panels to be subjected to a continuous dynamic flow. The light source of UV irradiation was provided by Light Emitting Diodes (LEDs) with 278nm wavelength. The effectiveness of the biofilm prevention by UVC were evaluated by Image Analysis
 The results indicate that UVC can significantly control biofilm presence on the panels. It also has demonstrated that intermittent UV can achieve successful biofilm prevention on submerged surfaces. However, observations indicate the actual UVC light intensity may perform below the manufacturer’s specifications, and this could lead to a detrimental effect on its biofilm control performance.

Design, Modeling, and Control of Rotating and Linear Electric Machines for Automotive Applications

The automotive industry is one of the main employers in industrialized countries [...]

Non-linear and multi-domain modelling of a free piston engine with linear electric machine

In the current technological era, with the rapid advances in low-carbon power generation solutions, there has been renewed interest in the Free Piston Engine (FPE) as a viable thermal propulsion technology. However, describing and capturing the intrinsic non-linear dynamics of the FPE is computationally challenging and, understandably, is generally characterised by a simplified linear description, which may inherently omit the dominant dynamics.Consequently, this study considers the non-linear and multi-directional nature of the coupled translation loads during motoring and power generation. Thus, presenting a non-linear and multi-domain description of the FPE. The proposed model was implemented in an opposed-piston free-piston engine configuration and validated during motoring and generating against experimental data captured from a prototype with identical parameters. The simulation results strongly correlate to the experimental data with similar translator displacement, in-cylinder pressure and bounce chamber pressure traces. Furthermore, the study demonstrated that the proposed modelling approach captured the dominant dynamics of the FPE and proved satisfactory accuracy and performance. In addition to validating the proposed modelling approach, this paper concludes with a simulation study that demonstrates the embedding of a novel surrogate Chemical Kinetics (CK) description of the hydrous ethanol auto-ignition process and the resultant influence on the FPE dynamics, most importantly, on gaseous emission formation.Therefore, this paper aims to extend the current knowledge in this novel and emerging technology by considering the characteristic non-linearity and multi-directional nature of its coupling with multi-physical domains such as mechanical, chemical and electrical.

Trajectory-Regulation-Based Segmented Control for Dead Center Positions Tracking of Free-Piston Linear Generator

Free-piston linear generator (FPLG), as a novel energy converter, has attracted wide attention due to its unique operating characteristics. However, the high-precision and robust tracking of the dead center positions in the presence of frequent combustion variation is still a tricky problem. In this respect, in this article, we present a trajectory-regulation-based segmented control (TRBSC) to actively control the linear electric machine (LEM) of FP LG. The target stroke is divided into the high-speed zone and low-speed zone, where active tracking of the input reference trajectory of LEM and free damped motion are performed separately. Especially, the input trajectory is selected as a variable sinusoidal reference velocity profile, which is adjusted by the combinations of the dead center errors. The segmented control decouples the specific interaction between the dead center positions and velocity curve, reducing the heavy dependence of the algorithm on speed tracking accuracy. A full theoretical analysis is provided with emphasis on the regulation rules of the reference speed profile based on the modeling of the displacement profiles. The performance of the TRBSC is experimentally verified on an 18 kW permanent-magnet linear synchronous motor setup in motoring mode.

A Comprehensive Review of the Free Piston Engine Generator and Its Control

Review A Comprehensive Review of the Free Piston Engine Generator and Its Control Patrick Brosnan 1, Guohong Tian 1, * , Umberto Montanaro 1, and Sam Cockerill 2 1 School of Mechanical Engineering Sciences, University of Surrey, Surrey GU2 7XH, UK 2 Libertine FPE Ltd., Sheffield S9 1DA, UK * Correspondence: g.tian@surrey.ac.uk; Tel.: +44-1483-300-800 Received: 2 February 2023 Accepted: 10 March 2023 Published: 23 March 2023 Abstract: The Free Piston Engine (FPE) is a unique machine with a higher thermal efficiency than its counterpart, the Conventional Reciprocating Piston Engine (CPE). The unique piston motion of the FPE is not constrained kinematically like the CPE with its connecting crankshaft and rotational inertial masses. Moreover, when directly coupled to the Linear Electric Machine (LEM) to harness electric energy production, the Free Piston Engine Generator’s (FPEG) characteristic motion, now being dynamically constrained, permits an extensive range of piston trajectory profiles to be exploited during operation. In addition, exploring varied piston trajectories during the development stages may be vital in reducing in-cylinder combustion emissions through strategies such as Low-Temperature Combustion (LTC) and Homogeneous Charge Compression Ignition (HCCI). This review paper will focus on the key motivations and drivers for continued FPEG development. It will also highlight and review its distinct advantages and challenges in being a viable solution as a future zero-carbon engine technology. Finally, FPE fundamentals, alongside its rich history, will be introduced, clearly presenting how academia and industry have described and controlled its intrinsic non-linear dynamics.

Physics-Informed Generative Adversarial Network-Based Modeling and Simulation of Linear Electric Machines

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.

Dynamic Characteristics and Demonstration of an Integrated Linear Engine Generator with Alternative Electrical Machines

A linear engine generator with a compact double-acting free piston mechanism allows for full integration of the combustion engine and generator, which provides an alternative chemical-to-electrical energy converter with a higher volumetric power density for the electrification of automobiles, trains, and ships. This paper aims to analyse the performance of the integrated engine with alternative permanent magnet linear tubular electrical machine topologies using a coupled dynamic model in Siemens Simcenter software. Two types of alternative generator configurations are compared, namely long translator-short stator and short translator-long stator linear machines. The dynamic models of the linear engine and linear generator, validated with lab-scale prototypes, are applied to investigate the influence of alternative topologies of the generator on system performance. The coupled model will facilitate the early design phase and reveal the optimal match of the key parameters of the engine and generator. Then, experimental tests on an integrated compressor cylinder-generator prototype were successfully performed, and it is shown that this concept is feasible and electrical power and compressed working fluid, such as air, can be generated by this prototype.

Power flow in the air gap of linear electrical machines by utilisation of the Poynting vector: Part 2 ‐ simulations

Different types of linear generators are simulated and their power flow in the air gap is investigated. The results are compared to the analytical expressions derived in Part 1. The simulations and the analytical expressions in Part 1 show the same general behaviour, but the magnitudes are lower for the analytical expressions. One explanation for the difference in magnitude can be that the harmonics of the electric and magnetic fields contribute to the power flow, which is not accounted for in the analytical expressions. Due to results from Part 1, it is investigated if changing the number of poles can decrease the tangential power flow while the normal power flow stays the same. As was suspected, changing the number of poles affected several other factors, which lead to an increase in the normal power flow when increasing the number of poles, even though the electrical power was the same. The tangential power flow also decreased for three out of four generators. Thereby, increasing the number of poles while keeping the same length of the machine, at the cost of reduced pole-pitch, should be done with precaution.

Design, build and testing of an integrated compressor-generator

An alternative source of on-board electricity generation in hybrid propulsion systems is a free piston engine. If the electrical machine can be fully integrated with the combustion engine, it may be able to offer a denser source of power conversion than conventional engines, fuel cells and batteries. This paper presents the modelling, development and testing of the linear engine generator concept, where a linear electrical machine is physically integrated within the compressor of a free piston engine. The challenges of mechanical integration of these two usually separate components to form a generator-compressor unit is discussed and demonstrated. The concept is shown to be capable of generating electricity whilst simultaneously compressing a working fluid such as air for use in the expander cylinder.

Assessment of Electrical Power Generation of Wave Energy Converters With Wave-to-Wire Modeling

Direct-drive wave energy converter (WEC) and buoy control algorithms have shown great potential for renewable wave energy extraction in ideal conditions. However the actual power take-off (PTO) impacts are barely considered in the WEC design. This paper highlights the demands of designing the WEC wave-to-wire control from a global point of view by studying the actual PTO impacts. A permanent magnet linear electrical machine (LEM) PTO unit is simulated and controlled to fulfill the WEC buoy control requirements. Several state of the art control algorithms, which include singular-arc (SA) control, shape-based (SB) control, model predictive control (MPC), and proportional-derivative (PD) control, are applied to maximize the wave energy production (mechanical energy). Multiple types of electrical PTOs, including ideal PTO, unlimited PTO and limited PTO, are all implemented to evaluate WEC wave-to-wire performances. Further, the PTO copper loss model and the PTO actual efficiency maps are introduced and studied to improve the electrical PTO operation efficiency. To further assess the control schemes in various wave conditions, one-year PacWave ground-truth data is applied as well. Numerical simulations are conducted using MATLAB/Simulink and the Simscape toolbox. The electrical PTO unit is composed of a LEM, an ideal inverter, and an ideal energy storage system. The results show that the actual PTO will impact the constrained controls (MPC and SB) less comapring to unconstrained controls (SA and PD). Although SB can produce the maximum energy with the limited PTOs, it is not robust for all wave conditions. At the end of the paper, the possible solutions for improving the WEC wave-to-wire performances are also provided.