Permanent Magnet Linear Machine Research Articles

Force Ripple Compensation and Robust Predictive Current Control of PMLSM Using Augmented Generalized Proportional–Integral Observer

In this article, an augmented generalized proportional–integral observer (GPIO) is presented to estimate and then compensate for the disturbance/uncertainty both existing in the electrical and mechanical subsystems of the motion stage driven with an air-bearing permanent-magnet linear synchronous machine (PMLSM). First, a modeling method for the two subsystems, considering the disturbance/uncertainty and the integration of the measured outputs as extended states, is proposed. Second, to reduce the coupling effect of the observer gains and the measurement noises on the disturbance estimation dynamics, an augmented GPIO is designed and its convergence theorem is given. Furthermore, with the extended models, the augmented GPIO is developed for both the compensation of parameter mismatch in the predictive current control (PCC) and the force ripple estimation/suppression of the PMLSM. Finally, with the augmented GPIO, an improved PCC robustness test with time-varying parameter mismatch is conducted both in the single-current closed loop and the double-current closed loop with cascade position-current control. A simple and practical parameter-tuning procedure is also analyzed in detail for both the electrical and mechanical subsystems. The position trajectory tracking error is reduced largely with accurate and real-time force ripple compensation. Experimental setup and results are provided to validate the effectiveness of the proposed design method.

A Study on Linear Generator Characteristics in Free Piston Engine

The linear generator (LG) is integrated into a system that called the free piston linear generator (FPLG). In recent year, free piston engine that is studied by many researchers, has some advantages. Therefore, the application of the line generator in free piston for converting the chemical energy to electrical energy that can be used for plug-in hybrids to extend the range of operations as an alternative energy converter. Therefore, the optimizing of linear generator performance be able to significantly reduce the vehicle's fuel consumption. The parameters in permanent magnet linear electric machine (PMLEM) are designed by Maxwell software and the optimal parameters is carried out via the flux density. To achieve this goal, a linear generator in free piston engine with a flat structure and quasi-Halbach array flux structure was proposed. The simulation of linear generator is performed based on the speed ranges in the New European Driving Cycle (NEDC) for a mid-size car. In the study, a linear electrical machine (LEM) is designed by Maxwell software with translator that has various diameters. The results show that the suitable parameters for stator and rotor about 7.7 mm and 14 mm, respectively. Because the flux density for this design’s stator and rotor yoke avoids saturation state and generates the highest electrical output compared to the other states. Besides, the paper also examined the power output at different frequencies from 15 Hz to 50 Hz, corresponds to a velocity amplitude of 3.6 m/s to 12 m/s. The simulation result shows that the frequencies from 15Hz to 30 Hz with 4.8 m/s to 7.2 m/s (1200 rpm to 2100 rpm), respectively meets engine speed operation ranges in hybrid vehicle and these frequencies produce the power output that increases considerably about 7.5 kW at 30 Hz.

Design optimisation and performance investigation of novel dual three‐phase permanent‐magnet linear synchronous machines for a ropeless elevator system

A novel dual three-phase permanent-magnet linear synchronous machine (DTP-PMLSM) is proposed for the large capacity ropeless elevator, where two sets of windings have 30 electrical degrees phase shift in space. First, the topology of DTP-PMLSM with 12-slot/11-pole (12 s/11p) combination is introduced. Second, the influence of each main parameter on thrust force performance is investigated by single variable sweeping method, and then DTP-PMLSM is optimised by global optimisation method. Moreover, the electromagnetic performance is predicted and analysed by two-dimensional (2D) finite element method (FEM) in detail. Compared with conventional single three-phase PMLSM, the proposed DTP-PMLSM shows better force performance. Furthermore, the analysis results are compared with 3D FEM which includes the transverse end effect. Finally, a 12 s/11p prototyped machine is built and tested to validate the theoretical analyses.

Design and Analysis of Tubular Slotted Linear Generators for Direct Drive Wave Energy Conversion Systems

Linear generator utilization in a wave energy converter (WEC) is an attractive alternative to a rotary generator. This paper presents the design of a permanent magnet linear machine (PMLM) for WEC applications in low wave power areas. In this paper, the wave height and vertical speed of Malaysian water is used for the simulation and design. Two design variants are introduced which are tubular PMLM with no spacer (TPMLM-NS) and tubular PMLM with spacer (TPMLM-S). Finite element analysis (FEA) has been conducted to investigate the performance and to refine the main dimensions of the design in terms of split ratio, pitch ratio and tooth width. The FEA results are then validated using an analytical method which is established according to the design’s magnetic field distribution. Based on main dimension refinement, it can be deduced that both the split ratio and the pitch ratio have a significant influence on the airgap flux density and back EMF of the design. The obtained FEA results also reveal that the TPMLM-NS variant is capable of producing 240 V back EMF, 1 kW output power with satisfactory efficiency. Consequently, this indicates the capability of the design to convert wave energy with good performance. Additionally, good agreement between the analytical predictions and FEA results was obtained with a low percentage of error, thus providing concrete assurance of the accuracy of the design.

Design and Analysis of a Linear Memory Machine for Ocean Wave Power Generation

In this paper, a permanent magnet (PM) linear memory machine is proposed for ocean wave power generation. A notable feature of this machine is its online tunable mnemonic flux. This enables it to operate efficiently in a wide speed range and makes it suitable for the variable-speed wave-power generation. Moreover, this machine has both the PMs and the windings arranged in its stator so that it does not need slip rings or brushes. The proposed machine is also robust and cost-effective because it has a simple translator of slotted steel. In this paper, the configuration and working principle of the linear memory machine are firstly introduced. The results of a parametric analysis are presented to investigate the effects of the proposed machine’s geometric parameters. The performance of the proposed machine is then analyzed using time-stepping finite element method (TS-FEM).

Investigation of New IPM Linear Machine Configuration with Low Permanent Magnet Used

Permanent magnet (PM) machines have received numerous attentions, since they are distinguished by many desirable features including simple construction and high efficiency. However, high price of the permanent magnet material may be considered as the main problems of such machines. Hence, the demand of PM machine with high efficient PM materials used is increased. In this study a new configuration of PM linear machine with high efficient PM material utilization, named as V-shape interior PM linear machine is investigated. The mentioned machine has been compared to the conventional I-shape counterpart. In order to perform sensible comparison, I-shape and V-shape machines have been designed with identical main design specifications. It has been observed that the V-shape topology shows better PM material utilization. It should be noted that about 43% higher efficient PM used is obtained by the V-shape machine compared to the conventional I-shape corresponding. It should be noted that the V-shape machine has been designed with about 51.6% less total permanent magnet volume compared to I-shape machine. Moreover, the introduced machine offers less cogging force as well as thrust force ripple than that of the conventional machine.

A Dynamic Model for Bearingless Flux-Switching Permanent-Magnet Linear Machines

This article deals with dynamic models for three-phase bearingless flux-switching permanent-magnet (FSPM) linear machines. This machine type can be used to build a magnetically levitating long-range linear drive system, whose rail does not need any active materials apart from iron. A dynamic machine model is developed by means of equivalent magnetic models, taking into account air-gap variation and magnetic saturation. The effects of these phenomena are analyzed using finite-element method (FEM) simulations of a test machine. The parameters of the proposed model can be identified using the FEM or measured data. The model can be applied to real-time control and time-domain simulations. The model is validated by means of experiments.

A Novel Negative-Sequence Current Injection Method for Reducing LVPMM Electromagnetic Thrust Ripple Considering Static Longitudinal End Effect

The thrust force ripple of a linear motor includes positioning force and electromagnetic thrust ripple. Compared to the conventional rotary motor, linear vernier permanent magnet machines (LVPMM) break at both ends, leading to three-phase asymmetry. This article focuses on the elimination of the electromagnetic thrust ripple caused by the special structure of the LVPMM, and an asymmetrical current control strategy using in power grids is introduced to the drive system. However, unlike power grids working at a fixed frequency, the drive system of the LVPMM needs variable speed operations, and some improvements are made to the original method. High bandwidth of current loop is guaranteed, and the stability of the control system is achieved with the proposed method. Experimental results obtained are presented. It verifies that the asymmetrical current control strategy reduces electromagnetic thrust ripple by more than 67%.

Linear Machines for Long Stroke Applications—A Review

This document reviews the current state of the art in the linear machine technology. First, the recent advancements in linear induction, switched reluctance and permanent magnet machines are presented. The ladder slit secondary configuration is identified as an interesting configuration for linear induction machines. In the case of switched reluctance machines, the mutually-coupled configuration has been found to equate the thrust capability of conventional permanent magnet machines. The capabilities of the so called linear primary permanent magnet, viz. switched-flux, flux-reversal, doubly-salient and vernier machines are presented afterwards. A guide of different options to enhance several characteristics of linear machines is also listed. A qualitative comparison of the capabilities of linear primary permanent magnet machines is given later, where linear vernier and switched-flux machines are identified as the most interesting configurations for long stroke applications. In order to demonstrate the validity of the presented comparison, three machines are selected from the literature, and their capabilities are compared under the same conditions to a conventional linear permanent magnet machine. It is found that the flux-reversal machines suffer from a very poor power factor, whereas the thrust capability of both vernier and switched-flux machines is confirmed. However, the overload capability of these machines is found to be substantially lower than the one from the conventional machine. Finally, some different research topics are identified and suggested for each type of machine.

A Novel Tubular Partitioned Stator Flux-Reversal Permanent Magnet Linear Machine for Direct-Drive Wave Energy Generation

A novel tubular partitioned stator flux-reversal permanent magnet linear machine (PS-FRPMLM) is proposed for direct-drive wave energy generation. It consists of four flat PS-FRPMLMs and a moving aluminum tube, which not only combines the merits of permanent magnet machines and flux-reversal machines but also overcomes the space constraint between the permanent magnets and electric loadings. First, the topology and the operation principle are presented. Then, the proposed machines with different slot/pole combinations, i.e., 6/4, 6/5, 6/7, and 6/8, are optimized to obtain the maximum no-load electromotive force (EMF). Furthermore, the performances of these proposed machines are compared with those of conventional tubular FRPMLMs in both no-load and on-load states. The results show that this novel structure possesses lower cogging force, better PM utilization, and higher efficiency in the on-load state, which proves it to be suitable for application in direct-drive wave energy generation. Finally, a prototype of a single flat PS-FRPMLM is tested to verify the predicted finite element (FE) results.

Magnetically Nonlinear Dynamic Models of Synchronous Machines and Experimental Methods for Determining Their Parameters

This paper deals with rotary and linear synchronous reluctance machines and synchronous permanent magnet machines. It proposes a general method appropriate for determining the two-axis dynamic models of these machines, where the effects of slotting, mutual interaction between the slots and permanent magnets, saturation, cross-saturation, and—in the case of linear machines—the end effects, are considered. The iron core is considered to be conservative, without any losses. The proposed method contains two steps. In the first step, the dynamic model state variables are selected. They are required to determine the model structure in an arbitrarily chosen reference frame. In the second step, the model parameters, described as state variable dependent functions, are determined. In this way, the magnetically nonlinear behavior of the machine is accounted for. The relations among the Fourier coefficients of flux linkages and electromagnetic torque/thrust are presented for the models written in dq reference frame. The paper presents some of the experimental methods appropriate for determining parameters of the discussed dynamic models, which is supported by experimental results.

Design and Analysis of a Flux-Concentrated Linear Vernier Hybrid Machine With Consequent Poles

In low-speed applications, variable-reluctance permanent magnet machines are often proposed due to their efficient use of magnet material and high torque density. This becomes even more important in large linear applications, where the translator is longer than the stator. Often, however, very low power factors are experienced by this class of machines. This paper proposes a V-shaped flux concentrated version of a consequent pole linear Vernier hybrid permanent magnet machine and compares it to a surface-mounted magnet variant. Using finite-element analysis validated by two laboratory prototypes, it is shown that the flux-concentrated version increases the airgap flux density, which potentially leads to an improvement in the force density and efficiency or can be used to increase the operating power factor.

Design of Linear Magnetic Position Sensor Used in Permanent Magnet Linear Machine With Consideration of Manufacturing Tolerances

This paper proposes the design of a linear magnetic position sensor (LMPS) to detect the mover position of the permanent magnet linear synchronous machines (PMLSMs). The working principle of the LMPS is based on the well-known Hall-Effect. The Hall-Effect-based design of LMPS is considered because it provides a low cost and relatively harsh environment susceptible alternative for the position detection for long track PMLSM system. The initial design was performed using 3D-finite element analysis and genetic algorithm-based deterministic optimization. Based on the initial model, four LMPS were manufactured and tested under the output constraint of peak flux density > 0.1T and total harmonic distortion < 3%. From the test results, it is concluded that the manufactured LMPS suffered significant deviation in output compared to the simulation model. These anomalies arise because of the manufacturing tolerances. To further improve the design and manufacturing process of the LMPS considering the effect of tolerance, a reliability-based robust design optimization (RBRDO) of the LMPS is proposed. The results of RBRDO confirms its usefulness for the design process of the LMPS in terms of undesired design non-compliance cost and great robustness without sacrificing the accuracy of the output signal.

Modeling and Analyzing a Novel Dual-Flux-Modulation Consequent-Pole Linear Permanent-Magnet Machine

A novel dual-flux-modulation consequent-pole linear permanent-magnet (DFM-CP-LPM) machine is proposed in this paper, which can be regarded as the combination of a linear flux-switching PM machine and a linear vernier PM machine. Via two sets of interoperable PMs mounted on both the primary and the secondary, the proposed machine can work in a dual-flux-modulation mode, achieving higher thrust density. Meanwhile, the consequent-pole structure is introduced, reducing approximately half of the PM usage compared to a conventional surface-mounted linear PM vernier machine (LPMVM), which will greatly reduce the cost. In this paper, the configuration and the operation principle of the novel DFM-CP-LPM are presented. Then the optimization and several thrust ripple reduction methods are introduced to improve the performance of the machine. Thermal analysis is also carried out to check the demagnetization risk of primary PMs, due to the heat from coils. Finally, the proposed machine is compared to a conventional LPMVM and a consequent-pole linear vernier permanent magnet machine with only PMs set on the secondary. The results verify the superiority of the proposed DFM-CP-LPM.

Power‐take‐off topology comparison for a wave energy converter

Wave Energy Converters (WECs) generally use a Mechanical Power-Take-Off (MPTO) involving hydraulics or gearing to optimise the extraction of energy from the incoming waves before converting it into electrical energy via a high speed rotating generator. This simplifies the design of the Electrical Power Conversion System (EPCS). Further, it facilitates the use of mechanical energy storage such as hydraulic accumulators to reduce the peaky nature of the power flow and allows the WEC resonant frequency to be tuned for maximum energy capture. This work compares two power electronic converter topologies for an Electrical PTO (EPTO). This EPTO is intended to replace the aforementioned MPTO and generator with a Permanent Magnet Linear Machine (PMLM) directly coupled to the WEC. The compared topologies comprise either a Current Source Converter (CSC) or a Voltage Source Converter (VSC) as the generator interface working in combination with a DC-DC converter and an Energy Storage System (ESS). The principle differences between the two topologies are explored and losses are evaluated in a modular EPCS working with a WEC. Wide-bandgap power electronic switches are assumed for both topologies over a range of switching frequencies. The evaluation concludes that the CSC topology is advantageous at higher switching frequencies.

Investigation into linear generators with integrated magnetic gear for wave energy power take off

This work presents a new wave energy converter power take off (PTO) system that combines two recent developments in drive train technology, the consequent pole linear vernier hybrid permanent magnet machine and the linear magnetic gear. The combined system is fully realised in three-dimensional finite element method and compared to a similar direct drive machine. While the resulting system is lighter, reducing the active material mass by 30%, and more efficient, the system requires larger amounts of high cost permanent magnet material and increased PTO complexity. It is summarised that while such a system could be recommended in certain conditions, it is not viable for general application.

Development of low translator mass linear Vernier machine for wave energy power take off

This article proposes a new topology of double-sided linear Vernier permanent magnet (LVPM) machine with segmented translator structure. A combination of a typical Halbach array consists of two horizontally magnetised permanent magnets (PMs) sandwiched between a salient iron tooth and adjacent vertically magnetised PM pole with the aim of improving its electromagnetic performance. The coreless partitioned translator contributes to a significant reduction in mass and the associated cost. With the aid of finite element analysis (FEA), two LVPM machines with the same PM, and stator volume have been investigated, analysed, and compared. The results imply that the proposed LVPM is capable of producing higher force density, while it exhibits lower cogging force and force ripple compared to its counterpart.

Model Predictive Thrust Force Control of a Linear Flux-Switching Permanent Magnet Machine With Voltage Vectors Selection and Synthesis

To reduce the thrust force ripple of a complementary and modular linear flux-switching permanent magnet machine, a model predictive thrust force control (MPTFC) is developed and implemented in this paper based on the active voltage vectors selection (AVVS) and two-voltage-vector synthesis (TVVS). First, the active voltage vectors are screened and assigned to the specific sector, instead of traversing all the possible vectors, and consequently, significantly decrease prediction workload. Second, for the elimination of the weighting factor in the conventional MPTFC, the control object is transformed from the thrust force and stator flux to the stator flux only by using the load angle. Third, to achieve the steady-state performance improvement, the TVVS approach is applied in each control period, where the optimal TVVS and its dwell time are simultaneously obtained by only one cost function. Both simulated and experimental results verify that the steady-state performance improvement can be realized by the developed MPTFC through comparing with normal hysteresis current control and conventional MPTFC strategies.

Development of a Novel Transverse Flux Tubular Linear Machine With Parallel and Complementary PM Magnetic Circuit for Precision Industrial Processing

The transverse flux permanent-magnet (PM) linear machine has attracted much attention in high-performance direct-drive applications because of its high torque density and efficiency. However, due to its inherent large open-circuit flux leakage, the prominent cogging force makes it difficult to obtain a high accuracy in position and speed control, which restricts its potential for precision industrial processing applications. To overcome this problem, a novel transverse flux linear machine is proposed in this paper. The key is by creatively combining a consequent-pole mover design and a stator-segment-interlacing configuration in such a way that a parallel and complementary transverse magnetic circuit is realized for the moving PMs, which can effectively minimize the open-circuit leakage flux and cogging effect. In this paper, the machine structure, operation principle, and theoretical modeling are introduced, with its electromagnetic performance evaluated by using the finite-element method. A prototype is also built for the experimental verification, and relevant test results agree well with the finite-element predications.

Development and Analysis of Novel Flux-Switching Transverse-Flux Permanent Magnet Linear Machine

The flux-switching transverse-flux permanent magnet linear machine (FSTFPMLM) is proposed in this paper, combining the advantages of the transverse-flux linear machine and the flux-switching linear machine. First, the structure and operating principle of the FSTFPMLM is presented. Second, the magnetic field of a simplified FSTFPMLM is numerically computed by the three-dimensional (3-D) finite-element method (FEM). Third, the thrust characteristics of the machine, including the thrust force, cogging force, and force ripple, are numerically analyzed. The influence of structure parameters on the thrust characteristics has been analyzed by the 3-D FEM. The law of thrust, cogging force, and force ripple as the pole pitch ratio between primary and secondary, and the ratio between the tooth width and pole pitch of the secondary variable provides the guidance to design FSTFPMLM, which aims to achieve a larger thrust, smaller cogging and force ripple using less permanent magnet materials. The thrust force capabilities of FSTFPMLM are compared with other topologies of linear machines. Finally, the prototype and experimental setup have been developed, and the calculated results and the measured results are in good agreement.