Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> The paper explains two new theories of the linear induction motor, and indicates that the end effect exercises very adverse influence on motor performances, and proposes the compensated linear induction motor as a measure to eliminate. the end effect. <s> BIB001 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> This paper describes a new class of electric motor, with a field winding and an armature winding, both of which are on the stator. The motor has no brushes or permanent magnets. Its motor characteristics are shown to be similar to those of a DC machine. Control of the armature windings can be achieved with very simple electronic circuits resulting in a very low cost and reliable variable speed drive. An experimental flux switching motor has been constructed and tested in conjunction with two new power converter circuits. <s> BIB002 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> This paper describes a technique for minimizing the detent force using the finite element method. The detent force of the whole stator core is the total of two magnetic forces arising at both side edges of a stator core. Computed results show the phase difference between the two magnetic forces. Therefore, we can cancel out the two forces by adjusting a stator length to minimize the detent force. The stator with the smooth formed edge shape is also contrived to reduce the detent force in the practical use. The detent force of this model is successfully minimized by proposed method. <s> BIB003 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> This study focuses on the development of a robust Petri-fuzzy-neural-network (PFNN) control strategy applied to a linear induction motor (LIM) drive for periodic motion. Based on the concept of the nonlinear state feedback theory, a feedback linearization control (FLC) system is first adopted in order to decouple the thrust force and the flux amplitude of the LIM. However, particular system information is required in the FLC system so that the corresponding control performance is influenced seriously by system uncertainties. Hence, to increase the robustness of the LIM drive for high-performance applications, a robust PFNN control system is investigated based on the model-free control design to retain the decoupled control characteristic of the FLC system. The adaptive tuning algorithms for network parameters are derived in the sense of the Lyapunov stability theorem, such that the stability of the control system can be guaranteed under the occurrence of system uncertainties. The effectiveness of the proposed control scheme is verified by both numerical simulations and experimental results, and the salient merits are indicated in comparison with the FLC system <s> BIB004 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> A field-programmable gate array (FPGA)-based adaptive backstepping sliding-mode controller is proposed to control the mover position of a linear induction motor (LIM) drive to compensate for the uncertainties including the friction force. First, the dynamic model of an indirect field-oriented LIM drive is derived. Next, a backstepping sliding-mode approach is designed to compensate the uncertainties occurring in the motion control system. Moreover, the uncertainties are lumped and the upper bound of the lumped uncertainty is necessary in the design of the backstepping sliding-mode controller. However, the upper bound of the lumped uncertainty is difficult to obtain in advance of practical applications. Therefore, an adaptive law is derived to adapt the value of the lumped uncertainty in real time, and an adaptive backstepping sliding-mode control law is the result. Then, an FPGA chip is adopted to implement the indirect field-oriented mechanism and the developed control algorithms for possible low-cost and high-performance industrial applications. The effectiveness of the proposed control scheme is verified by some experimental results. With the adaptive backstepping sliding-mode controller, the mover position of the FPGA-based LIM drive possesses the advantages of good transient control performance and robustness to uncertainties in the tracking of periodic reference trajectories. <s> BIB005 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> A two-dimensional time-stepping finite element analysis of a single-sided linear induction motor (LIM) used in transportation systems is presented in this paper. The analysis model taking into account the transverse edge effect and primary moving is proposed. The thrust and normal force are calculated at different speeds using Maxwellpsilas stress tensor. The simulation results are found to be a good prediction to the thrust characteristics. <s> BIB006 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> In rotating machines, no end effects occur because of their cylindrical geometry, which has no ends in the direction of movement. In linear motors, however, either the rotor or the stator has a finite length, and end effects occur because of the part having finite length entering or exiting the magnetic field. End effects occur as magnetic waves having attenuation, and play a major role in the performance of linear induction motors (LIMs), especially at high speeds. As the speed increases, efficiency decreases because of longitudinal end effects. This decrease in efficiency has a braking effect. In high-speed maglev devices, such as trains, the efficiency and performance of the LIMs become very important. We report on our investigation of end effects by the finite-element method. <s> BIB007 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> This paper presents the comparison of four linear switched reluctance machines (LSRMs) as possible candidates for application in vertical elevators. Linear induction and linear synchronous machines have been presented and experimentally tested in vertical elevators. In this paper, four longitudinal LSRM configurations are presented and designed to operate as propulsion actuators in a vertical elevator prototype. Two of the four configurations have been presented earlier in horizontal propulsion experiments, and a third one has been proposed for application in vertical elevators. All four LSRMs are designed for similar static force profiles to allow for their comparison. The designed LSRM configurations are compared by using finite-element analysis and dynamic control simulations. The stator, translator, and copper winding weight and dimensions, footprint area, active material weight, normal forces and payload capabilities for all four configurations are contrasted. The configuration with the highest payload capability is chosen for implementation in an experimental prototype. The prototype vertical elevator is 1.27 m tall with a 1-ft-tall elevator vehicle with no counterweights and uses two LSRM setups on each side. The experimental correlation of propulsion force and inductance is presented to validate the theoretical design method used in this research. <s> BIB008 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> This paper compares the performance and material costs of two candidate tubular permanent magnet topologies, viz., quasi-Halbach magnetized moving magnet and flux switching (moving-iron) machines for applications in active vehicle suspension. Both machines are optimally designed for the same operating conditions and under the same volumetric and thermal constraints. It is shown that while the flux switching machine has a robust mover structure, it has relatively low force capability and suffers from higher manufacturing cost, and a heavier moving armature which impacts on the performance of active suspension. <s> BIB009 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> An outline of the different fields of application for linear motors in transportation is given. The different types of linear motors are described and compared. The current status of the different linear motors used in the transportation sector is analyzed. Finally, a look at worldwide activities and future prospects is presented. <s> BIB010 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> Fields, Forces, and Materials for LEMs Review of Electromagnetic Field Theory Forces in Electromagnetic Fields of Primitive LEMs Magnetic, Electric, and Insulation Materials for LEMs Electric Conductors and Their Skin Effects Insulation Materials for LEMs Magnetostriction Effect LEMs Methods of Approach Summary References Classifications and Applications of LEMs Linear Induction Machines Linear Synchronous Motors for Transportation Industrial Usage Linear Synchronous Machines Solenoids and Linear Oscillatory Machines Summary References Linear Induction Motors: Topologies, Fields, Forces, and PowersIncluding Edge, End, and Skin Effects Topologies of Practical Interest Specific LIM Phenomena Dynamic End-Effect Quasi-One-Dimensional Field Theory Summary of Analytical Field Theories of LIMs Finite Element Field Analysis of LIMs Dynamic End-Effect Compensation Summary References Linear Induction Motors: Circuit Theories, Transients, and Control Low-Speed/High-Speed Divide LIM Circuit Models without Dynamic End Effect Flat SLIMs with AL-on-Iron Long (Fix) Secondary Flat SLIMs with Ladder Secondary Tubular SLIM with Ladder Secondary Circuit Models of High-Speed (High Goodness Factor) SLIMs Low-Speed LIM Transients and Control Control of Low-Speed LIMs High-Speed LIM Transients and Control DTFC of High-Speed LIMs Summary References Design of Flat and Tubular Low-Speed LIMs Introduction Flat SLIM with Ladder Long Secondary and Short Primary Tubular SLIM with Cage Secondary Summary References Transportation (Medium- and High-Speed) SLIM Design Introduction Urban SLIM Vehicles (Medium Speeds) High-Speed (Interurban) SLIM Vehicles Design Optimization Design of SLIM: Urban Vehicles Summary References DC-Excited Linear Synchronous Motors (DCE-LSM): Steady State, Design,Transients, and Control Introduction and Topologies dc Exciter (Inductor) Design Guidelines Stator (Armature) Core Design DCE-LSM Parameters and Performance Circuit Model for Transients and Control Field-Oriented Control of DCE-LSM Note on PM + DCE-LSM Summary References Superconducting Magnet Linear Synchronous Motors Introduction Superconducting Magnet Technical Field and Circuit Theory of SM-LSM Normal and Lateral Forces SM-LSM with Eight-Shape-Stator Coils Control of SM-LSM Summary References Homopolar Linear Synchronous Motors (H-LSM): Modeling, Design,and Control H-LSM: Construction and Principle Issues DC Homopolar Excitation Airgap Flux Density and AC emf E1 Armature Reaction and Magnetization Synchronous InductancesLdm and Lqm Longitudinal End Effect in H-LSM Preliminary Design Methodology by Example H-LSM Model for Transients and Control Vector Thrust (Propulsion) and Flux (Suspension) Control Summary References Linear Reluctance Synchronous Motors: Modeling, Performance Design,and Control Ldm, Lqm Magnetization Inductances of Continuous Secondary(Standard) L-RSM Ldm, Lqm Magnetization Inductances for Segmented Secondary L-RSM Ldm, Lqm (Magnetization) Inductances in Multiple Flux BarrierSecondary L-RSM Reduction of Thrust Pulsations dq (Space Phasor) Model of L-RSM Steady-State Characteristics for Vector Control Strategies Design Methodology for Low Speed by Example Control of L-RSM Summary References Linear Switched Reluctance Motors (L-SRM): Modeling, Design, and Control Practical Topologies Principle of Operation Instantaneous Thrust Average Thrust and Energy Conversion Ratio Converter Rating State Space Equations and Equivalent Circuit Small Signal Model of L-SRM PWM Converters for L-SRMs Design Methodology by Example Summary References Flat Linear Permanent Magnet Synchronous Motors A Few Practical Topologies Multilayer Field Model of Iron-Core F-LPMSMs with Sinusoidal emfsand Currents Magnetic Equivalent Circuit (MEC) Theory of Iron-Core F-LPMSM Analytical Multilayer Field Theory of Air-Core F-LPMSM Cogging Force and Longitudinal End Effects dq Model of F-LPMSM with Sinusoidal emf Steady-State Characteristics for Typical Control Strategies F-LPMSM Control Design Methodology of L-PMSM by Example Summary References Tubular Linear Permanent Magnet Synchronous Motors A Few Practical Topologies Fractionary (q <= 1) Three-Phase AC Winding Technical Field Theory of T-LPMSM Circuit dq Model of T-LPMSM Advanced Analytical Field Theories of T-LPMSMs Core Losses Control of T-LPMSMs Design Methodology Generator Design Methodology Summary References Multi-Pole Coil Three- or Two-Phase Linear PM Reluctance Motors Few Practical Topologies Technical Theory of Flux-Reversal IPM-Primary LPMRM Numerical Example 14.1: FR-LPMRM Design Transverse-Flux LPMRM Technical Theory Example 14.2: TF-LPMRM Example 14.3: TF-LPMRG Energy Converter Summary References Plunger Solenoids and Their Control Introduction Principles Linear Circuit Model Eddy Currents and Magnetic Saturation Dynamic Nonlinear Magnetic and Electric Circuit Model PM-Less Solenoid Design and Control PM Plunger Solenoid Case Study: PM Twin-Coil Valve Actuators Summary References Linear DC PM Brushless Motors Introduction Topology Aspects Principle and Analytical Modeling Geometrical Optimization Design by FEM Air-Core Configuration Design Aspects Design for Given Dynamics Specifications Close-Loop Position Control for a Digital Video Camera Focuser Summary References Resonant Linear Oscillatory Single-Phase PM Motors/Generators Introduction Coil-Mover LOMs (LOGs) PM-Mover LOM(G) Iron-Mover Stator PM LOMs Linear Oscillatory Generator Control LOM Control Summary References Multiaxis Linear PM Motor Drives Large x-y (Planar) Motion PM Drive Topologies Modeling of Large Travel Planar Linear PM Drives with RectangularAC Coils Planar Linear PM Motor Micron Positioning Control for MillimeterRange Travel Six DOF Control of a MAGLEV Stage Multiaxis Nanometer-Positioning MAGLEV Stage Summary References Attraction Force (Electromagnetic) Levitation Systems Competitive Topologies Simplified Analytical Model Analytical Modeling of Longitudinal End Effect Preliminary Design Methodology Dynamic Modeling of ALS Control State Feedback Control of ALS Control System Performance Assessment Control Performance Example Vehicle Lifting at Standstill Robust Control Systems for ALSs Zero Power Sliding Mode Control for PM-Assisted ALSs Summary References Repulsive Force Levitation Systems Superconducting Coil RFLS: Competitive Technologies Sheet Secondary (Track) Normal-Flux RFLS Normal-Flux Ladder Secondary RFLS Null-Flux RFLS Dynamics of RFLS Damping RFLS Oscillations Repulsive Magnetic Wheel Coil-PM Repulsive Force Levitation System PM-PM Repulsive Force Levitation System Summary References Active Guideway MAGLEVs Introduction DC-Excited Iron-Core LSM MAGLEV Vehicles (Transrapid) Supercon MAGLEVs Iron-Core Active Guideway Urban PM-LSM MAGLEVs Active Guideway Multimover Doubly Fed LIM MAGLEV IndustrialPlatforms Summary References Passive Guideway MAGLEVs Introduction LIM-MAGLEVs H-LSM MAGLEV (Magnibus) Potential Improvements on Magnibus System Transverse-Flux PM-LSM MAGLEVs DC-Polarized L-SRM MAGLEVs Multiphase (True Brushless) Linear Reluctance Machine MAGLEVs Summary References Index <s> BIB011 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> Linear permanent magnet machines have been increasingly used in several applications that require high reliability and good dynamic characteristics. In this paper, a novel double-sided design of a 3φ permanent magnet flux-switching linear synchronous machine (FSLSM) with a yokeless translator is proposed. It is found that the proposed design can achieve more than 50% higher thrust than a conventional FSLSM and excellent linearity even under high excitation currents. Optimization of the proposed machine is performed using individual parameter optimization and is compared with results from global optimization using genetic algorithm (GA). Force analysis of the proposed design is performed to establish the mechanical integrity of the design. The proposed FSLSM is most suitable for long-stroke applications and intermittent oscillatory type applications. <s> BIB012 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> Linear flux-switching permanent magnetic (LFSPM) machines are good choices for long stroke applications. These machines deliver high thrust force density in addition to the machine structure where permanent magnetics (PMs) and windings are all on the short mover. For LFSPM machines, their performance is always affected by big thrust force ripple. In this paper, for two C-core LFSPM machines of high thrust force capability, including a 6/13 C-core LFSPM (6/13LFSPM-C) machine and a sandwiched C-core LFSPM (SLFSPM-C) machine, and a thrust force ripple reduction method is proposed. The proposed method is developed by reducing the slot effect component of the cogging force based on staggered stator tooth, and suppressing the thrust force ripple caused by unbalanced three phase back-electromagnetic forces (EMFs) based on two end PMs. Based on finite element analysis (FEA) results, both C-core LFSPM machines can achieve small thrust force ripples as well as high sinusoidal back-EMFs, and at the same time, maintain high thrust force capability with the proposed method. It was also found that, the improved SLFSPM-C machine exhibited the same thrust force capability as the improved 6/13LFSPM-C machine, but with a much smaller thrust force ripple. <s> BIB013 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> The 18 papers in this special section focus on the technology of linear electric (electromagnetic)machines (LEMs). LEMs were introduced at the turn of the last century. They have been conceived to convert electrical energy into mechanical energy (or vice versa) as a direct linear motion through electromagnetic forces. LEMs are reversible devices,meaning that they can work as bothmotors and generators. Although feasible, linear alternators are currently explored for limited applications (e.g., Stirling motor). On the contrary, linear motors or actuators are electromagnetic devices capable of producing direct (without any link or interposition) linear motions of the following types: in a unique direction, short-stroke motion, oscillatory motion, and step-by-step motion. Correspondingly, exactly as in the rotating counterpart, different types of linear motors have been devised: linear synchronous motors (LSMs) in its versions with excitation winding, with permanent magnets (PMs) LSMs or without both (linear reluctance motor = LRM), linear induction motors (LIMs), and linear stepper motors. <s> BIB014 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> To incorporate the merits of simple and robust movers of induction linear motors and higher power factor and high efficiency of permanent magnet linear motors, a new long primary double-sided linear flux-switching permanent magnet (DSLFSPM) motor is proposed, investigated, and quantitatively compared with linear induction motors (LIM) for the electromagnetic launch system. First, the topology, operation principle, and electromagnetic performance of the DSLFSPM motor have been investigated. Then, in order to analyze the LIMs comprehensively, three LIMs have been designed based on the same overall dimensions and other key parameters. Finally, the electromagnetic performance of DSLFSPM motor and LIMs have been compared and summarized. The results show that the DSLFSPM motor has some merits such as higher efficiency, higher power factor, more robust mover, larger thrust force, and smaller force ripple than LIM motors. In order to validate the simulation results, a small-scale prototype of DSLFSPM motor has been built and measured. <s> BIB015 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> A fifth-order dynamic continuous model of a linear induction motor (LIM), without considering “end effects” and considering attraction force, was developed. The attraction force is necessary in considering the dynamic analysis of the mechanically loaded linear induction motor. To obtain the circuit parameters of the LIM, a physical system was implemented in the laboratory with a Rapid Prototype System. The model was created by modifying the traditional three-phase model of a Y-connected rotary induction motor in a d–q stationary reference frame. The discrete-time LIM model was obtained through the continuous time model solution for its application in simulations or computational solutions in order to analyze nonlinear behaviors and for use in discrete time control systems. To obtain the solution, the continuous time model was divided into a current-fed linear induction motor third-order model, where the current inputs were considered as pseudo-inputs, and a second-order subsystem that only models the currents of the primary with voltages as inputs. For the discrete time model, the current-fed model is discretized by solving a set of differential equations, and the subsystem is discretized by a first-order Taylor series. Finally, a comparison of the continuous and discrete time model behaviors was shown graphically in order to validate the discrete time model. <s> BIB016 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> Switched reluctance motor (SRM) is gaining more interest in the last decades due to its simple and robust structure. SRMs are classified into conventional SRMs (CSRMs) and mutually coupled SRMs (MCSRMs). CSRMs are based on single-phase excitation and torque is generated by the variation of self-inductance with rotor position. MCSRMs are based on multi-phase excitation and torque is produced by the rate of change of both self- and mutual inductances. MCSRM has the advantages of using the standard voltage source inverter at balanced current operation, when the sum of the phase currents is zero, while CSRM requires an asymmetrical converter. This paper presents the state-of-the-art review of MCSRMs, including operating concept, winding, and pole configurations, control methods by using different current waveforms, performance comparison of MCSRM configurations, modeling methods, and future work for improving MCSRM performance. <s> BIB017 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> Linear induction motors (LIMs) have been extensively adopted in urban railway transportation given their nonadhesion thrust and simple stator structure. However, these LIMs undergo unfavorable power factor and efficiency considering their copper and eddy losses. Recently, linear flux-switching permanent-magnet motors (LFSPMs) have attracted the attention of researchers due to their high power density, simple structure, easy heat dissipation, high efficiency, and high power factor. However, so far, no quantitative comparison exists between LFSPMs and LIMs of the size 1:1 to prove the feasibility of LFSPMs to be used in railway transit systems. Therefore, a comparative analysis between the two motors is conducted in this paper. First, this paper investigates the LIMs for railway transit using the finite element method (FEM). Second, the LFSPMs for railway transit is designed and optimized. Third, the electromagnetic performance of the two motors is compared and analyzed through the FEM. Finally, a small-sized prototype of the LFSPMs is constructed to validate the FEM results. It is concluded that LFSPMs offer a favorable thrust force, have high efficiency, and high power factor but have large normal force and force ripple. Therefore, applying LFSPM requires a reliable supporting device and a shock absorber. <s> BIB018 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> 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. <s> BIB019 </s> Linear Machines for Long Stroke Applications—A Review <s> I. INTRODUCTION <s> The longitudinal end effect of the double-sided permanent magnet linear synchronous motor (DS-PMLSM) causes a large end force. To overcome this drawback, this paper proposes a novel DS-PMLSM structure, in which the upper or lower primary component is shifted by a certain distance. First, the end-force model of the DS-PMLSM is established, based on which, the influences of the staggered structure on the fundamental and higher order end-force components are analyzed. Following this, the DS-PMLSMs with different slot–pole combinations are divided into four categories, and the design principles of possible winding arrangements are discussed. Furthermore, the staggered structures are applied to four slot–pole combinations, namely 21-, 15-, 20-, and 16-pole/18-slot. The back electromotive forces, detent forces, thrusts, and normal forces of the four combinations are analyzed and compared through the finite-element method. The electromagnetic and output characteristics of the novel DS-PMLSM are also compared with the traditional DS-PMLSM prototype to verify the effect of the proposed structure on suppressing the end force. <s> BIB020
Linear Machines (LMs) are electromechanical devices that, the same way as the Rotary Machines (RMs), convert electrical energy into mechanical energy and vice versa. Constructively, LMs are very similar to RMs. As described in Fig. 1 , linear machines could be referred as rotary ones that have been cut out radially, and flattened so that the stator and the rotor lay horizontally facing each other BIB011 . Historically, linear motion has been generated based on RMs and rotary to linear conversion mechanisms, such as sheaves or gears. Nonetheless, LMs are capable of producing linear motion directly, without any kind of mechanical interface BIB010 . High acceleration and deceleration rates can The associate editor coordinating the review of this manuscript and approving it for publication was Alfeu J. Sguarezi Filho . be achieved with linear machines, as there is no possibility of slipping BIB010 . Railway transportation systems such as the JFK-New York AirTrain or the Linimo MAGLEV are a potential application for this type of machines BIB011 . The lack of gears allows linear drives a smooth operation, with reduced noise and vibration levels BIB013 . High precision and comfort are also possible with these machines, because as there are no gears, there is no backlash BIB014 . Systemwise, the reduction of the amount of elements brings an enhancement of the reliability and the efficiency of linear motor driven systems BIB014 , together with a lower maintenance requirement BIB012 . However, as the magnetic circuit has a start and an end in the edges of LMs, a new phenomenon called end effect appears in these machines (see Fig. 2 and Fig. 3 ). This effect produces some undesirable behaviours in linear motors, and that is why it has been subject of research for a long time BIB001 . It happens because the flux escapes from the ends of the machine, reducing the flux density in the air-gap of these regions. This generates an asymmetry between the central and external poles of a linear machine, which complicates the control and the analysis of LMs BIB006 , BIB016 . Moreover, the end effect is also the reason why most of the linear motors have to deal with an unbalance between their phases BIB004 , BIB005 . Due to the fact that there are only two ends in the machine, and 2 phases in 3 phase machines are wound through the end slots, one phase works at a higher flux density than the other two , generating the phase unbalance. For every RM, there is a LM counterpart, so Linear Induction Machines (LIMs) BIB001 - BIB007 , Linear Switched Reluctance Machines (LSRMs) BIB008 - BIB017 , or Linear Permanent Magnet Synchronous Machines (LPMSMs) BIB003 - BIB020 , can be found in the literature. Besides the different machine types, several topologies are described in the literature. Flat or tubular shapes, single-sided or dual-sided structures, modular configurations... there are many different options for selecting the ideal machine for each application. In the last decade, a new and promising type of linear machine, Linear Primary Permanent Magnet Machine (LPPM), has emerged in the literature BIB013 , BIB012 , BIB015 , BIB018 , BIB009 , BIB002 - BIB019 . However, a comprehensive review of linear machines for long stroke applications has not been published yet. The available review papers summarise the content from the literature, and do not verify those contents with a direct comparison of different machine technologies. Moreover, a direct comparison of the main types LPPMs and a LPMSM under the same operating conditions has not been found in the literature. This paper first reviews the latest developments in linear machine technology. The capabilities and configurations of the different machine types are first presented. Then, based on the solutions found in the literature, some guidelines are listed to allow designers a fast configuration selection. A qualitative comparison of the main machine technologies is also given in terms of thrust density, shear stress, thrust per Permanent Magnet (PM) volume, thrust ripple and detent force, and PM immunity. In order to validate the qualitative comparison, the most promising LPPMs are then selected and compared under the same dimensions and linear loading. It has been found that even if the literature review gives a precise enough prediction of the relative performance, there are several facts that must be taken into account when selecting a machine technology. When comparing the thrust of the selected machines, it is found that a poor overload capability may limit the applications of some of the machines with a high rated thrust density. The lower overload capability is also found to be one of the main drawbacks of all the LPPMs when compared to a conventional LPMSM. In addition, the PM immunity term is also divided into two parts, because the results demonstrate that some machines exhibit a poor PM working point at no load operation, even if the variation of the operating point of the PMs is low in fault conditions. Finally, the low power factor is identified as the other main drawback of all LPPMs when compared to a conventional LPMSM. Sections II to V introduce the main machine technologies to date. Section VI summarises the different options to enhance a list of performances of linear machines. Section VII discusses the relative capabilities of the machines that have been found in the literature. The sizing and results of the selected machines are given in section VIII. Finally, in section IX the authors identify some of the remaining challenges and the most promising configurations for the selected machine technologies.