Linear Permanent Magnet Research Articles

Evaluation of magnetic orientation in dual-stator linear permanent magnet vernier machine for wave energy conversion

The Permanent Magnet Vernier Machine (PMVM) is favored for wave energy conversion due to its high torque production at low speeds and straightforward design. This study introduces the innovative Dual Stator Linear Permanent Magnet Vernier Machine (DSLPMVM) with concentrated winding. In this design, permanent magnets (PMs) are strategically placed on both the stator and a segmented translator, enhancing system reliability. The stator utilizes a simple PM layout, while the translator features a Halbach array. This research advances the DSLPMVM’s performance through the optimal placement and orientation of magnets, alongside a meticulous selection of tooth types. The paper rigorously evaluated all possible magnetic orientations and eight distinct stator tooth models. Detailed comparisons of flux linkage, back electromotive force (back-EMF), inductance, efficiency, power factor (PF), and force were conducted to identify the most effective designs.

Non‐linear coordinated control of LPMG‐based direct drive wave energy conversion system with supplementary energy storage system based on feedback linearization

AbstractThe linear permanent magnet generator (LPMG)‐based direct drive wave energy conversion system (DDWECS) works under perpetual fluctuations of ocean waves. Short‐term energy storage, such as electrochemical energy storage, is usually adopted in a supplementary energy storage system (SESS) to buffer power fluctuations. Since the investigated DDWECS consists of various non‐linear components such as insulated gate bipolar transistors (IGBTs)‐based power electronic converters, the unremitting changes of system working conditions caused by ocean wave effects will degrade the dynamic performance with conventional linear controllers which are implemented via local linearization around a single working condition. This paper proposes the multiple feedback linearization based non‐linear coordinated control (MFLNCC) scheme for coordinating non‐linear plants in DDWECS with SESS such as the machine‐side converter (MSC), the grid‐side converter (GSC) and DC/DC converter in SESS. The enhanced dynamic performance of the proposed MFLNCC in DDWECS with SESS is validated under different scenarios.

Double-Sided Single-Set Winding Coordinated Active Levitation Control of Linear Permanent Magnet Motor Considering Mover Air-Gap Offset

Double-Sided Single-Set Winding Coordinated Active Levitation Control of Linear Permanent Magnet Motor Considering Mover Air-Gap Offset

Optimal hydraulic PTO and linear permanent magnet generator for a floating two-buoy wave energy converter

A fully coupled fluid-structure-power take-off model is used to investigate the optimal energy capture of a floating two-buoy wave energy converter excited by regular waves and irregular waves. The system incorporates hydraulic power take-off and a linear permanent magnet generator. By considering the coupling relationship between the power take-off parameters for regular waves, a power take-off parameter interval is determined for the optimization model. Parametric optimization of the hydraulic power take-off and linear permanent magnet generator systems is proposed, based on response surface methodology in conjunction with central combination design for sensitivity analysis and optimal configuration of different parameters. The methodology efficiently predicts optimal electric efficiency while reducing the requirement for multiple boundary element simulations. It is found that a model with predicted optimal configuration of the hydraulic power take-off system can achieve 10 % more electrical efficiency than that with linear permanent magnet generator. Comparison between the energy capacities of the different systems indicates that a device with linear permanent magnet generator attains higher energy conversion efficiency within a wider power take-off bandwidth. This study provides guidance for the design and selection of efficient power take-off systems for floating two-buoy wave energy converters.

Analytical modelling of the linear transverse flux permanent magnet motor using magnetic equivalent circuit method

AbstractThe authors propose an analytical modelling approach for the linear transverse flux permanent magnet motor using the magnetic equivalent circuit method. The main focus of this study is to predict the phase flux‐linkage characteristic of the motor. Essential equations required for implementation of the model and how to solve it are described clearly so that someone can use it easily. A typical motor is selected to apply the proposed model and simulation results, including static characteristics of flux‐linkage and thrust, are presented. To validate the developed analytical model, the discussed motor is also analysed with 3D finite element method using MAXWELL software and the obtained simulation results are compared to each other.

A low-cost approach to determine the optimum conductor plate thickness of linear permanent magnet eddy current brakes

This paper proposes a low-cost approach to determine the optimum Conductor Plate (CP) thickness without needs for mathematical models and large data volumes, which means that 0.6 times of the Standard Depth of Penetration (SDoP) can be directly selected as the optimum CP thickness without calculation. Firstly, the SDoP is introduced. Then, the influences of speed and conductivity on the optimum CP thickness are investigated. Finally, the relationship between the SDoP and the optimum CP thickness is found. The optimum CP thickness can be selected directly according to the relationship without mathematical models and large data volumes. It not only guarantees high braking force, but also reduces the weight of the LPMECBs as much as possible.

Comparative Analysis of Normal Force Characteristics and Dynamic Influence of Linear Flux-Switching Permanent Magnet Motor for Rail Transit

Comparative Analysis of Normal Force Characteristics and Dynamic Influence of Linear Flux-Switching Permanent Magnet Motor for Rail Transit

Linear permanent magnet electrodynamic suspension system: Dynamic characteristics, magnetic-mechanical coupling and filed test

This study investigates the dynamic electromagnetic characteristics and thermo-mechanical coupling effect of the linear permanent magnet electrodynamic suspension system (PMEDS) via high-speed test rig. Besides, a physical prototype weighing 1.5 tons along with a 50-m linear copper guideway is developed and tested. Firstly, the topology structure along with fundamental operation model is introduced, followed by establishing the analytical model. Subsequently, a multi-functional test rig is utilized to experimentally determine its speed characteristics, lateral stability, and vertical vibration, while also validating the simulation and analytical models. Additionally, thermo-mechanical coupling analysis is conducted through co-simulation, experimentation and calculation to determine the dependence of temperature on the levitation and drag forces. Finally, a prototype vehicle integrated with auxiliary components, is fabricated and tested on a copper guideway. The vehicle is suspended freely via levitation force in the air above 30 mm, with tested suspension height generally aligning with dynamic simulation results.

Optimal gear ratio selection of linear primary permanent magnet vernier machines for wave energy applications

AbstractLinear permanent magnet vernier generators offer a high capability of force density, making them appealing configurations for wave energy harvesting systems. In absolute terms, the performance of these machines is significantly influenced by the selection of slot/pole combinations based on the magnetic gearing effect. For the first time, this paper aims to investigate the impact of different gear ratios on a wide array of linear primary permanent magnet vernier machines (LPPMVMs) with different slot/pole combinations based on fair criteria to offer a more comprehensive understanding of gear ratio selection. To find the optimal number of slots and poles, the response surface methodology is adopted to obtain a robust design and make a fair comparison among LPPMVMs with optimum design characteristics using a cost‐effective approach for the fast and reliable optimisation process. The higher gear ratios result in higher thrust force capability. This will help establishing a new route toward faster develpment of advanced LPPMVMs. The power loss models of LPPMVMs are studied to predict their steady‐state and transient thermal behaviours, verifying their stability and safety, while a simple external forced convection method can be utilised. To verify the model, finite element analysis is exploited to confirm the electromagnetic and thermal analysis results and provide a more exhaustive investigation.

Asymmetric air gap fault detection in linear permanent magnet Vernier machines

PurposeThe aim of this paper is to introduce an accurate asymmetric fault index for the diagnosis of the faulty linear permanent magnet Vernier machine (LPMVM).Design/methodology/approachThree-dimensional finite element method is applied to model the LPMVM. The geometrical and physical properties of the machine, the effect of stator and translator teeth, magnetic saturation of core and nonuniform air gap due to asymmetric fault are taken into account in the simulation. The air gap asymmetric fault is proposed. This analytical method estimates the air gap flux density of an LPMVM.FindingsThis paper presents an analytical method to predict the performance of a healthy and faulty LPMVM. The introduced index is based on the frequency patterns of the stator current. Besides, the robustness of the index in different loads and fault severity is addressed.Originality/valueIntroducing index for air gap asymmetry fault diagnosis of LPMVM.

A Novel Fault Tolerance Structure of Arc Linear Flux Switching Permanent Magnet Motors Based on Redundant Winding

This paper presents a novel structure of the arc linear flux switching permanent magnet motor based on the redundant winding to inhibit the rises of the motor losses and temperature due to the open circuit fault tolerance. Firstly, the structural characteristic of the arc linear flux switching permanent magnet motor is introduced. Then, the fault tolerance current of single phase open circuit fault is calculated for different winding connection forms. The fault tolerance performances under different conditions are compared from a special view of motor temperature rises. Finally, a novel structure for fault tolerance enhancement is proposed, which can effectively improve the freedom degree of the fault tolerance current by using the redundant winding. This novel structure takes full advantage of the circumferential air gap between the arc stator. The calculation results show that the novel structure can allow the fault tolerance of open circuit fault has little influence on the motor copper losses and temperature rises while maintaining the on-load torque.

Unbalanced magnetic pull in angular eccentricity magnetic screw

AbstractThis paper investigates the unbalanced magnetic force (UMF) produced by angular eccentricity in a magnetic screw. The principle of eccentricity is briefly outlined and an analytical expression that can be used to predict UMF of a magnetic screw is established. A 3D magnetic screw model with helically magnetized permanent magnets (PM) has been built and simulated in ANSYS Maxwell with different angular eccentricities. Comparing the finite elements (FE) simulation and analytical calculation results, there is a certain difference in the UMF of the magnetic screw, which is also caused by the asymmetry of the magnetic screw structure. It has been shown that compared to the linear tubular PM motor with the same thrust force capability, the magnetic screw has a much small UMF, which greatly simplifies the mechanical design of the magnetic screw.

Novel Virtual Winding Current Controller for Suppression of Linear Permanent Magnet Machine Electromagnetic Thrust Ripple

Thrust force ripple, including no-load detent force and electromagnetic thrust ripple, worsens the precision of linear permanent magnet machine (LPMM) control system. Asymmetrical current injection algorithm has been proposed for the suppression of electromagnetic thrust ripple, and the key point of the algorithm is positive- and negative-sequence (PNS) current closed-loop control. To achieve better steady-state and dynamic performance, a novel high-bandwidth current controller is proposed in this paper. A dual three-phase control system composed of three-phase virtual winding and the three-phase LPMM is introduced. According to the dual three-phase topology, PNS components are decoupled by a novel coordinate transformation, and the proposed controller avoids the use of filters or sophisticated algorithms for extraction of PNS currents. Experimental results based on a linear vernier permanent magnet machine (LVPMM) are presented. It verifies that the asymmetrical current control strategy based on the novel PNS current controller reduces electromagnetic thrust ripple by more than 60% compared with symmetrical three-phase current control.

Performance Investigation and Improvement of Linear Vernier Permanent Magnet Motor for Servo Application

With its high thrust density and low force ripple, the linear vernier permanent magnet motor (LVPMM) is regarded as a good competitor for linear servo applications. However, typical LVPMMs have shortcomings, such as phase imbalance, a long distributed-winding end, and low power factor. The goal of this work is to present a thorough analysis-based approach for performance enhancement that addresses all three flaws while enhancing the LVPMMs high thrust density advantage. Thanks to the proper slot/pole-pair combination, Halbach array PM, and a special three-modular structure, the proposed LVPMM improves thrust density by 28%, reduces force ripple to 1.2%, increases power factor by over 40%, and nearly eliminates three-phase imbalance when compared with those of a conventional LVPMM. Manufacturing and testing a 2.2 kW/2200 N prototype has confirmed the viability of the theoretical analysis and improvement process.

Design and Optimization of an Improved T-shape Linear Permanent Magnet Machines

Design and Optimization of an Improved T-shape Linear Permanent Magnet Machines

Optimal Energy Management System Control of Permanent Magnet Direct Drive Linear Generator for Grid-Connected FC-Battery-Wave Energy Conversion

The Wave Energy Conversion System (WECS) control strategy is presented in this study to make sure the system operates at its best under fluctuating wave resource situations. The suggested system consists of a MOPSO based MPC approach, a point absorber WEC oscillating in heave, back-to-back power converter for grid connections, and a linear permanent magnet generator. Despite the benefits of model predictive control, problems including switching frequency variations, steady-state errors, high processing costs, and constrained prediction horizons continue to exist. The article presents a method that incorporates the switching control action into the cost function while maintaining the finite nature of a model predictive control to handle the switching frequency issue. In order to minimise switching frequency variations while also addressing other control goals, such as regulating the direct current linked voltage and controlling the flow of active and reactive power, the switching control weight factors are optimised. In order to increase power quality, a fuel cell-based short-term energy storage system is also included to direct current link between the back-to-back converters.

Performance Improvement in a Linear Primary Permanent Magnet Vernier Machine by Modular Unit Shift Effect

This article investigates the effects of modular unit shift on the detent force and mutual to self-inductance ratio in the modular linear primary permanent magnet vernier (MLPPMV) machine. First, the winding connection and slot/pole combinations for the modular design is discussed. Then, the relationship of the phase shift and modular unit spacing is given. The operation principle of the MLPPMV machine is analyzed from the perspective of the air-gap field modulation theory. Moreover, the analytical expressions of the modular unit shift and phase shift angle for the MLPPMV machine are derived. Afterwards, the back EMFs, detent forces and inductances are comparatively analyzed. The investigation reveals that the reasonable modular unit shift has significance to improve the electromagnetic performances. Furthermore, the finite element method is adopted to evaluate. Finally, a prototype of MLPPMV machine is built. Experiments are carried out on a linear test bench, verifying the theoretical analysis.

Quantitative Comparison of Modular Linear Permanent Magnet Vernier Machines with and Without Partitioned Primary

Quantitative Comparison of Modular Linear Permanent Magnet Vernier Machines with and Without Partitioned Primary

Eddy Current Braking Force Analysis of a Water-Cooled Ironless Linear Permanent Magnet Synchronous Motor

The ironless linear permanent magnet synchronous motor (ILPMSM) is highly compact, easy to control, and exhibits minimal thrust fluctuations, making it an ideal choice for direct loading applications requiring precise positioning accuracy in linear motor test rigs. To address the issue of temperature rise resulting from increased primary winding current and to simultaneously enhance thrust density while minimizing thrust fluctuations, this paper introduces a bilateral-type ILPMSM with a cooling water jacket integrated between the dual-layer windings of the primary movers. The primary winding of the motor adopts a dual-layer coreless structure where the upper and lower windings are closely spaced and cooled by a non-conductive metal cooling water jacket, while the dual-sided secondary employs a Halbach permanent magnet array. The motor’s overall braking force is a combination of the electromagnetic braking force generated by the energized windings and the eddy current braking force induced on the cooling water jacket. This paper specifically focuses on the analysis of the eddy current braking force. Initially, the motor’s geometry and working principle are presented. Subsequently, the equivalent magnetization intensity method is employed to determine the no-load air gap magnetic density resulting from the Halbach array. An analytical model is then developed to derive expressions for the eddy current density and braking force induced in the water-cooling jacket. The accuracy of the analytical method is validated through finite element analysis. Then, a comparative analysis of the braking forces in two primary cooling structures, namely the inter-cooled type and the two-side cooled type ILPMSM, is conducted. Moreover, the characteristics of the eddy current braking force are thoroughly examined concerning motor size parameters and operating conditions. This paper provides a solid theoretical foundation for the subsequent optimization design of the proposed motor.

Analytical model for double-sided linear permanent magnet inner armature synchronous machine with slot-less stator at on-load in different patterns of magnetization

Analytical model for double-sided linear permanent magnet inner armature synchronous machine with slot-less stator at on-load in different patterns of magnetization