You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Linear Machines for Long Stroke Applications—A Review 
Chapter Title:  V. LINEAR PRIMARY PERMANENT MAGNET MACHINES 
1. Abstract of Cited Paper (BIB001):  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. 
2. Abstract of Cited Paper (BIB002):  This paper proposes and investigates a new configuration of flux reversal linear synchronous motor(FRLSM). Two models are introduced and analyzed by 2-D finite element method(FEM) for simulation comparisons. Finite element analysis(FEA) shows that the proposed model generates about 239% higher thrust density than the basic model. 
3. Abstract of Cited Paper (BIB003):  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. 
4. Abstract of Cited Paper (BIB004):  A linear doubly salient permanent magnet (LDSPM) motor is particularly suitable for long stator applications due to its simple and low cost stator, which consists of only iron. This paper proposes a new LDSPM motor design with complementary and modular structure. The key of this structure is that the primary mover is composed of two modules whose positions are mutually four and one half of the stator pole pitch apart and there is a flux barrier between them. Hence, the back electromotive force (EMF) waveform and cogging force of the two modules have 180 electrical degree differences. This design results in the total cogging force being significantly reduced and the back-EMF of each phase becoming symmetrical because the even harmonics are canceled. For fair comparison, an existing linear LDSPM motor is designed based on the same electromagnetic parameters and compared by the means of finite element analysis (FEA). The results reveal that the proposed LDSPM motor can offer symmetrical back-EMF waveforms, smaller cogging force, lower force ripple, and higher magnet utilization factor than the existing one. 
5. Abstract of Cited Paper (BIB005):  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. 
6. Abstract of Cited Paper (BIB006):  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. 
7. Abstract of Cited Paper (BIB007):  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. 
8. Abstract of Cited Paper (BIB008):  A novel tubular transverse-flux flux-reversal permanent magnet linear motor (TTFFRPMLM) for long stroke applications is designed and analyzed in this paper, which not only has the low cost advantage of the existing flux-reversal motor (FRM) by combining both PMs and armature coils in short primary, but also can address the problem of complicated structure of the existing transverse-flux motor (TFM) by using rotating motor technology. The structure of the motor are introduced. The topology and operating principle of the motor are presented and analyzed. The performance of the motor is optimized by equivalent 2D finite element method (FEM). The simulation results of the 3D FEM prove the correctness and effectiveness of the motor topology and equivalent 2D FEM. The research work of this paper provides the theory basis for the engineering application of this novel motor. 
9. Abstract of Cited Paper (BIB009):  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. 
10. Abstract of Cited Paper (BIB010):  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. 
11. Abstract of Cited Paper (BIB011):  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.

Literature Review:
There are four main types of LPPMs currently in the literature. These machines are Linear Switched-Flux Permanent Magnet Machines (LSFPMs) BIB007 , BIB006 , BIB010 , BIB011 , BIB004 , BIB001 -  , BIB008 , Linear Flux-Reversal Permanent Magnet Machines (LFRPMs) BIB003 - BIB009 , Linear Doubly-Salient Permanent Magnet Machines (LDSPMs) BIB005 ,  and Linear Vernier Permanent Magnet Machines (LVPMs) BIB002 - BIB012 . Their structural advantage over conventional LPMSMs, i.e., the absence of PMs in the secondary, has brought a huge amount of research involving these LPPMs. In this section, their working principles and the latest research related to them are presented.