Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <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> BIB001 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> Detent force produced in permanent magnet linear machines generally causes an undesired vibration and noise. This paper analyzes detent force and thrust in permanent magnet linear synchronous motor by using various detent force minimization techniques. A two-dimensional finite-element analysis is used to predict detent force and thrust due to structural factors and nonlinearity. Moreover, moving node techniques for the drawing models is used to reduce modeling time and efforts. <s> BIB002 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> 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. <s> BIB003 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> In this paper a multiobjective design optimization of an air-core linear permanent magnet synchronous motor is presented. Thrust, thrust ripple and consumed magnet volume are chosen as objectives for design optimization. A 2D finite element analysis is carried out to evaluate the optimization results. <s> BIB004 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> Although air-core linear permanent-magnet (PM) synchronous motors are widely used in precision applications because of their advantages such as fast dynamics, lack of detent force, and negligible iron loss, they basically suffer from low developed thrust, thrust ripple, and excessive use of permanent-magnet materials, all of which lead to undesirable performance and high production cost. In this paper, we analyze performance characteristics of an air-core linear PM synchronous motor by varying motor design parameters in a layer model and a d-q model of the machine. We propose a multiobjective design optimization to improve thrust, thrust ripple, and consumed magnet volume independently and simultaneously by defining a flexible objective function. A genetic algorithm is employed to search for optimal designs. The results confirm that desirable thrust mean and substantial reduction in magnet volume and thrust ripple can be achieved. We draw several design conclusions from the motor analysis and design optimization. Finally, we carry out a time-stepping finite-element analysis to evaluate the effectiveness of the machine models and the optimization method. <s> BIB005 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> The thrust ripple in a permanent magnet linear synchronous motor (PMLSM) is mainly generated by the detent force that is caused by the interaction between the permanent magnet (PM) and the iron core without input current in armature winding. This paper proposes two different techniques to minimize the detent force in a PMLSM. One is to choose an optimal constructive design; the other is to employ a current compensator. In this paper, we investigate the performance of detent force minimization using both of them. The effectiveness is verified by both numerical and experimental results. <s> BIB006 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <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> BIB007 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> To make the ropeless elevator system become practical, one of the most important requirements is the high force density. The slotted iron core type permanent magnet linear synchronous motor (PMLSM) seems to be the best choice except the large detent force. Therefore, in this paper we will investigate the characteristics of detent force, normal force, and thrust of PMLSM under different motor topology structures. Finally, the long stator double-sided slotted iron core type PMLSM with fractional slot winding is selected for the best performance. <s> BIB008 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> Generally, the discontinuous armature permanent magnet linear synchronous motor (PM-LSM) is composed by the stator block (accelerator, re-accelerator, and decelerator) and the free running section. However, the stationary discontinuous armature design involves the velocity variation of the mover during drive when the armature’s non-installation part changes over to installation part as a result of the outlet edge of the armature. Therefore, we considered deforming the shape of the outlet edge at the armature and apply skew on the permanent magnet by displacing the two magnet segments of each pole. This paper presents the results of a threedimensional (3-D) numerical analysis with a finite element method (FEM) of the force exerted by the outlet edge. <s> BIB009 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> Permanent magnet linear synchronous motor (PMLSM) for rope-less hoist system, which has the advantages of simple structure, small volume, high force, unlimited hoisting height and speed, is a research focus and difficulties in the vertical hoist field. In this paper, according to the key technical problems of PMLSM for rope-less hoist system, a design scheme of direct driving high-speed elevator is proposed, and then a small-sized home elevator prototype drove by PMLSM is built. Experimental results show the safe and stable operation performance of the experimental device, with good prospects for the development and application of PMLSM rope-less hoist system. <s> BIB010 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> This paper analyzes the thrust characteristics of the investigated permanent magnet linear synchronous motor (PMLSM) and discusses their differences with those of rotary motors. It shows that the main components of the thrust ripple are second, fourth, and sixth harmonics, which is produced by end-effect, not the 12th harmonic caused by cogging. The ripple suppression abilities of magnet step-skew method are analyzed through skew factors of thrust harmonics and effective electromagnetic thrust. The optimal step number and skew angle for PMLSM are studied with comparison to those of rotary motor. A 2-D FEM algorithm for the asymmetric PMLSM model analysis is investigated, with which the aforesaid skew step number selection and optimal skew angle are validated. <s> BIB011 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> The reduction of the ripple of driving force is required for the practical utilization of linear synchronous motor for ropeless elevator. In addition, it is important to increase the driving force and reduce the weight of motor. In this paper, two kinds of movers for the air-cored linear permanent magnet (PM) synchronous motors are optimized, one is Halbach-type Linear PM motor (HTLPM) and the other is yoke-type air-core linear PM motor (YTLPM), by using the Evolution Strategy (ES) method. Multi-objective results in terms of the reduction of ripple and weight and the increase of driving force are also discussed. <s> BIB012 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <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> BIB013 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> Due to the advantages of gearless, high thrust density and high efficiency, PM linear synchronous motor (PMLSM) has attracted more and more attentions recently, which is pretty suitable for the long stroke transportation systems. In order to simplify structure and improve thrust force performance, a novel PMLSM with segmented-armature and non-overlapping windings is proposed. The analytical formula of thrust force is derived based on energy method and harmonic method, which is validated by two-dimensional finite element method (FEM). It is found that (3m+1) order and (3m+2) order harmonic components of thrust force are eliminated, while the 3m order ones are amplified. Moreover, the selection principles of slot-pole number combination and interval distance are obtained. Finally, the thermal analysis shows the novel structure has better heat radiation than that of the conventional one. The result shows the novel structure has excellent driving performance, simple manufacture processes, possibility of modular production and good heat radiation compared with conventional PMLSM. <s> BIB014 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> New detent-force minimization methodologies for a 6/4 double-sided interior permanent-magnet flat linear brushless motor configured with alternate teeth windings are presented in this paper. Based on the superposition principle, the end-effect and cogging forces are separately minimized using two different techniques. The end-effect force is reduced by a new 2-D optimization using the step-shaped end frames in the slotless stators. The cogging force is minimized through a destructive interference using the slot-phase shift between the upper and lower stators. Each technique is verified experimentally, and the optimal design parameters are formulated using Fourier series. The total detent-force reduction of 94% is achieved as compared with the base model. The steady-state force after applying these new detent-force-free techniques is demonstrated with actual measurements, and also compared with the finite-element analysis result and analytic solution. <s> BIB015 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> This study focuses on optimisation design of permanent magnet linear synchronous motors that are applied in laser engraving machines with no cutting force. Traditional analytical optimisation method based on magnetic field with particle swarm optimisation algorithm was introduced to obtain the best combination of motor structure parameters. By contrast, the novel optimisation design method – Taguchi method based on orthogonal array was proposed to optimise the thrust and thrust ripple. After the design of experiments using finite-element analysis, the relative importance of each design parameter was estimated in detail. Experimental results of prototype can certify the superiority and validity of Taguchi optimisation method. <s> BIB016 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <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> BIB017 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> Two permanent magnet linear machines, i.e. partitioned stator flux reversal permanent magnet (PS-FRPM) and conventional switched flux permanent magnet (SFPM) linear machines, are compared, in terms of electromagnetic performance and demagnetization withstand capability. It is found that compared to the conventional SFPM linear machine, the PS-FRPM linear machine shows lower cogging force, higher thrust force capability, better PM utilization, and lower thrust force ripple. Moreover, it possesses better demagnetization withstand capability. <s> BIB018 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> This paper discusses the traction performance of a single-side linear induction motor and a single-side coreless Halbach permanent magnet linear synchronous motor (PM-LSM) for the mid- and low-speed maglev train. Based on a typical mid- and low-speed maglev transit system, the overall performance of the two kinds of propulsion motors was analyzed by the finite element method. By comparing the performance of the single-side coreless Halbach PM-LSM at different magnetization direction of the PMs of the Halbach array, the optimal angle between the magnetization direction of two adjacent PMs was found. In order to achieve the higher propulsion efficiency of the single-side coreless Halbach PM-LSM, various cross-sectional shapes of the conductor were analyzed. The analytical results indicate that the coreless Halbach PM-LSM is more suitable for the mid- and low-speed maglev train in urban rail transit system. <s> BIB019 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> Linear machines (LMs) produce linear motion without any intermediate transmission mechanisms, thus the whole electromechanical system has simple structure and its efficiency is high. Because of such merits, linear machines have been studied for a long time and rapidly developed in recent years. Due to the characteristic of open structure, linear machines have more diversity than rotary machines in terms of machine topologies. Accounting for the wide applications of linear machines, e.g. Maglev train, precision machine tools, semiconductor processing device, automatic equipment, logistic transport line, ropeless lifter, compressor, etc., this paper reviews the most applied linear machines including machine topologies, operating principle and features. In addition, the influence of end effects and the corresponding reduction methods are also summarized. Finally, several commercial applications are exemplified. <s> BIB020 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <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> BIB021 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> Phase-shift or pole-shift method can reduce the detent force of the double-sided permanent magnet linear synchronous motor (DS-PMLSM) dramatically. However, this method causes a decrease in thrust and an increase in normal force simultaneously. To overcome this drawback, a novel slot-shift structure whose slots on the two sides of the primary component are staggered by an optimal distance is proposed in this paper. The models of the detent force including the end force and cogging force is established theoretically, and then verified by finite element analysis. The windings in the upper primary and the lower primary are arranged differently to improve the average thrust. The thrust characteristics of the DS-PMLSM under different shifted distances are analyzed and compared in detail. Furthermore, the primary component employing two kinds of core laminations is proposed to reduce both the dc component and ripple of the normal force. Finally, a DS-PMLSM prototype is tested, and the experimental results are compared with the analytical results to verify the effectiveness of the theoretical and simulation research. <s> BIB022 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <s> Traditionally, straggering the primaries of the double-sided permanent magnet linear synchronous motor (DS-PMLSM) is beneficial in helping to reduce the detent force caused by the longitudinal end effect, but leading to a reduction of the average thrust. To overcome this disadvantage, this paper provides a novel DS-PMLSM, which adopts the structure of staggering two primaries and rearranging windings. First, the characteristics of the voltage and detent force are analyzed theoretically and verified by finite element (FEM) simulations. The inductance, thrust, and normal forces are then compared with the traditional DS-PMLSM. Furthermore, the geometrical parameters are optimized to improve the thrust. Finally, one DS-PMLSM prototype is tested. The detent force and back electromotive force tested results verify the effectiveness of the topology proposed in this research. <s> BIB023 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <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> BIB024 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <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> BIB025 </s> Linear Machines for Long Stroke Applications—A Review <s> IV. LINEAR PERMANENT MAGNET MACHINES <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> BIB026
In the same way as in permanent magnet RMs, LPMSMs show an excellent thrust force density, efficiency, power factor and controllability BIB014 , BIB015 , BIB019 . Their advantages make them a strong candidate for applications such as ropeless elevators BIB008 , BIB010 , BIB012 , factory automation BIB009 and high precision machine tooling BIB012 - BIB020 . However, LPMSMs are also affected by the end effect. Apart from the previously cited phase unbalance and flux density reduction, the end effect is also source of an additional thrust force ripple component known as end force or end effect force in LPMSMs. This force affects them even at no load condition BIB006 , BIB022 , BIB026 . Depending on the relative position between the primary and the secondary parts, the magnets on one side or another will attract the machine ends with more strength, generating the end effect ripple. The no load thrust ripple, also known as detent force, is the result of the sum of the conventional slot effect or cogging force and the end effect force BIB022 , BIB026 , BIB020 . As LPMSMs have to deal with multiple detent force ripple sources, several different solutions have been tested in order to reduce the open-circuit thrust pulsation, e. g. skewing magnets, adjusting the primary length, and slot shifting BIB002 , BIB011 , BIB015 , BIB026 . A comprehensive analysis of the performance of a LPMSM with different step-skew configurations is reported in BIB011 . Cai et al. mention that the optimal skew angle to suppress the cogging is different from the optimal angle to suppress the end force. The orders of end force harmonics are low, an thus, suppressing those via the skew would also lower the average thrust force. A two dimensional detent force reduction method is showed in BIB015 . The authors achieve a reduction of 94 % in the detent force ripple by employing two different primary lengths to suppress the end force and a slot-shift method to deal with the slot effect. The performance of a segment-shifted machine can be improved with a rearrangement of the windings BIB022 , BIB023 , BIB026 . As the average thrust force is reduced with the increase of phase or pole shifting distance, the authors suggest that rearranging the winding configuration in the different primary sides can be a good solution for reducing the detent force without losing any force production capability. Modern optimisation techniques have also been applied to LPMSMs. A genetic algorithm is employed to optimise an air-core LPMSM via different objective function configurations in BIB004 , BIB005 . The results clearly improve the performance of the original motor. A combination of Taguchi method and Finite Element Method (FEM) is employed in BIB016 . The authors compare the resultant machine with the optimal machine obtained from the optimisation via an analytical model and particle swarm optimisation. The results show that the combination of Taguchi method with FEM can produce better results than the previous optimisation method. Due to the high cost of PM materials, the material cost of LPMSMs can be prohibitive in long stroke applications BIB009 . In the last decades, a new family of linear PM machines, known as flux-switching machines BIB017 , BIB013 , BIB021 , BIB024 , BIB007 , BIB001 - BIB018 , BIB018 -  , and primary PM Vernier machines BIB003 - BIB025 are drawing much attention. All these machines consist of an active primary that contains both windings and magnets, and a passive secondary with no PMs or copper, similar to that of LSRMs. Although these machines are still a type of LPMSM, they are grouped in a different section in this document.