Tubular Permanent Magnet Linear Generator Research Articles

Electromagnetic–Thermal Characteristics Analysis of a Tubular Permanent Magnet Linear Generator for Free-Piston Engines

Temperature rise of the tubular permanent magnet linear generator (TPMLG) might lead to insulation failure and demagnetization of permanent magnets, affecting the safe and stable operation of other equipment and the entire system. Herein, a bidirectional electromagnetic–thermal coupling method for analyzing the electromagnetic loss and thermal characteristics of a TPMLG considering the effect of increased temperature on the permanent magnet was proposed. To study the electromagnetic–thermal characteristics of the TPMLG under stable power generation, a two-dimensional electromagnetic field model and a three-dimensional temperature field model were established and coupled. The temperature field of the TPMLG was numerically calculated using computational fluid dynamics over finite volume method under natural air cooling and forced air cooling conditions. Effects of loss and air flow velocity on the steady temperature field were investigated. Results indicated that copper loss increased by 24.5% considering the influence of temperature rise. The windings’ top central position in the TPMLG was the spot with the highest temperature of 127.8 °C and there was a potential demagnetization risk for the permanent magnets. Some reference for future research of clarifying thermal characteristics and cooling design was provided.

Operating characteristics and design parameter optimization of permanent magnet linear generator applied to free-piston energy converter

A tubular permanent magnet linear generator (PMLG) with axial magnetized is proposed for the free-piston engine generator (FPEG). The structures and test rigs of the PMLG and FPEG prototypes are introduced. The working characteristics of the PMLG in FPEG system are analyzed under ignition conditions. A 2D finite element model of the PMLG is designed and verified based on initial design parameters and test results. The influences of key operating parameters on the output performance of PMLG are studied. On these basis, when considering the actual motion characteristics of the PMLG in FPEG system, the effects of different structural parameters on the power generation performance and efficiency (h) are investigated. Results show that when the working frequency of the FPEG is relatively small, the displacement profile resembles a sinusoidal curve. As the working frequency and stroke length increase, the power generation increases rapidly. As the air gap length and back iron shaft diameter decrease, and the stator slot number increases, the output voltage (U), current (I), power (Pout), and total loss power (Ploss) show an approximately linear increasing trend. As the pole arc coefficient and stator tooth width increase, the U, I, Pout, and Ploss first increase and then decrease. As the stator yoke thickness increases, the U, I, and Pout increase rapidly and then tend to stabilize. Besides, these structural parameters have little impact on power generation efficiency of this PMLG.

Optimization design of Tubular Permanent Magnet Linear Generator based on entropy model for wave energy conversion

—The effective use of wave energy which has huge reserves is one of the ways to solve the climate problem and energy crisis. In this paper, a Tubular Permanent Magnet Linear Generator (TPMLG) is optimized by the combination of comprehensive sensitive parameters method and particle swarm optimization based on entropy model (EPSO). By introducing the information entropy model, the aggregation characteristics in the process of particle swarm search are accurately analyzed, which can effectively reduce the invalid iteration of particle swarm. Firstly, the main design parameters of TPMLG are designed using the basic initial principle of permanent magnet linear machines. Then, the two-dimensional parametric finite element analysis model of the TPMLG is established, and a comprehensive sensitivity index Sc is defined to calculate the sensitivity indices according to power density and thrust fluctuation. The strong sensitivity parameters are optimized Particle Swarm Optimization based on entropy model, and the Non-sensitivity parameters maintain the initial design values. Finally, an experimental prototype TPMLG was manufactured according to the optimized results. The speed of TPMLG was simulated by the universal testing machine MTS100kN, the experimental results show that the designed TPMLG can be effectively applied to the direct drive power take-off system.

Generating performance of a tubular permanent magnet linear generator for application on free-piston engine generator prototype with wide-ranging operating parameters

This paper proposes a tubular permanent magnet linear generator (TPMLG) applied to the free-piston engine generator and establishes a test rig of the TPMLG. A large amount of experimental data was obtained under unfired conditions and a 2D finite element model of the TPMLG was developed and validated. Then, the electromagnetic characteristics were analyzed under no-load and load conditions. The effects of motion profile, operating frequency, velocity, stroke length, oscillation center position and load resistance on the output performance and generating efficiency (η) of TPMLG were investigated. Results show that the phase angle and distortion rate of the output voltage and current will vary under different motion profiles. As the operating frequency, velocity and stroke length increase, the output voltage, current, power and loss power increase gradually, while η increases at first and subsequently plateaus. When peak velocity is fixed and stroke length increases, both output power and copper loss rapidly increase and then remain steady. Meanwhile, there is only a slight change in generating efficiency. There is an optimal load resistance of approximately 6 Ω needed to achieve maximum output power. When load resistance is greater than 40 Ω, changes in load voltage, current and η become insignificant and the η reaches a maximum of 92.54%. Furthermore, the OCP changes the load voltage and current curves but has little effect on output power in terms of the RMS value.

Detent Force Reduction in Linear Interior Permanent Magnet Generator for Direct-Drive Wave Power Conversion

The permanent magnet linear generator is widely applied in the direct-drive wave energy converter (DD-WEC) because of its high power density. In this paper, a novel tubular permanent magnet linear generator, which consists of multilayer and interior permanent magnets (MI-TLPMGs), is presented for DD-WEC, which improves the output power and back electromotive force (back EMF) through the flux concentrating effect. However, MI-TLPMGs with multilayer embedded permanent magnets have severe problems regarding force ripples and detent force, which affect the DD-WEC’s dynamics. Therefore, a DD-WEC system with MI-TLPMGs is proposed, and the effect of the detent force on the dynamic performance of the DD-WEC is analyzed theoretically. Then, the L-type auxiliary teeth and magnetic barriers, which are optimized by the Taguchi method, are introduced to minimize the detent force of the MI-TLPMGs. After optimization using the Taguchi method, the amplitude of the detent force is reduced from the initial 21.7 N to 5.2 N, which means it has weakened by nearly 76.1%. Finally, a prototype has been manufactured and measured in the wave tank to verify the optimization results.

Design and Analysis of a High Power Density Permanent Magnet Linear Generator for Direct-Drive Wave Power Generation

Wave energy is a new type of clean energy. Aiming at a low wave energy density and small wave height in China’s coastal areas, a tubular permanent magnet linear generator (PMLG) with a short stroke, small volume, and high power density is designed for wave power generation. Firstly, the generator’s electromagnetic parameters are analyzed by the analytical method, and the magnetic circuit topology and basic structure of the generator are analyzed by the equivalent magnetic circuit method (EMCM). Then, the finite element method (FEM) is used to analyze the influence law of the generator’s basic structural parameters on the output electromotive force (EMF) and its sinusoidal characteristics. The multi-factor and multi-level analysis is carried out based on the orthogonal test method to study the size parameters of the above analysis, and the optimal structure parameter combination for the generator is obtained. Finally, the prototype is trial-produced and tested for steady-state and transient performance to confirm the accuracy of the simulation calculations, and the output performance under no-load and load conditions is examined. The results show that both the optimized prototype’s power density and the output EMF’s sinusoidal properties have been improved under the proposed scheme.

Comparative Analysis of Tubular Permanent Magnet Linear Generator With Equidirectional Toroidal Windings and Conventional Toroidal Windings

Tubular permanent magnet linear generators (TPMLGs) are widely used in direct drive wave energy conversion system due to their simple structure, friendly maintenance, and high efficiency. Unfortunately, the power density of this type of generator is relatively small due to their low operation speed. To improve the power density, a TPMLG with equidirectional toroidal windings (ED-TWs; ED-TPMLG) is proposed in this article. First, the structure of the ED-TPMLG is introduced, and its windings configuration and windings coefficient are analyzed and compared with those of TPMLG with conventional toroidal windings (C-TPMLG). Furthermore, to investigate the performances and the unique advantages of the ED-TPMLG, comparative analysis of the ED-TPMLG and C-TPMLG is conducted based on the similar dimensions. The results indicate that the proposed ED-TPMLG has superiority in detent force and power density than the C-TPMLG. Then, the unstable ac electricity generated by the generators is rectified, which can be transformed to the stable dc electricity for supplying the equipment. Finally, a planar linear generator prototype with the same ED-TWs is manufactured to validate the reasonable of the proposed winding configuration (ED-TWs) and the credible of the above finite element analysis method.

Multi-Objective Design Optimization of a Tubular Permanent Magnet Linear Generator With 120° Phase Belt Toroidal Windings

The utilization of 120° phase belt toroidal windings (120°-TWs) can bring power density improvement in a tubular permanent magnet linear generator (TPMLG). Unfortunately, the TPMLG with 120°-TWs (120°-TPMLG) usually involve multiple structural parameters, and the interaction or even conflict among those structural parameters would have strong impact on generator performances in the design optimization process. To alleviate this problem, a multi-objective design optimization method is proposed to conduct a multi-objectives optimization, which aims to obtain the high-power density and low-detent force. First, the comprehensive sensitivity analysis method, namely global sensitivity analysis, is adopted to evaluate the sensitivities of the structural parameters on the performances of the 120°-TPMLG. According to the evaluation results, the structural parameters are divided into three levels: non-sensitive level, mild-sensitive level, and strong-sensitive level. Then, to improve the whole design optimization efficiency, the direct-screening method, the surface method, and the genetic algorithm is implemented in the three levels, respectively. And the optimal structural parameters of the 120°-TPMLG are finally determined. To verify the feasibility of the 120°-TPMLG and the effectiveness of the proposed design optimization method, the performances of the optimal 120°-TPMLG are analyzed and compared with the initial one and the same dimensions TPMLG with traditional toroidal windings (T-TPMLG) in detail. It shows that the performances of the optimal 120°-TPMLG meet the design requirements. Moreover, the detent force is largely decreased and the power density is notably improved. The results prove that the proposed multi-objective design optimization method is available for the 120°-TPMLG.

Optimization Design of Tubular Permanent Magnet Linear Generator Based on Entropy Model for Wave Energy Conversion

Optimization Design of Tubular Permanent Magnet Linear Generator Based on Entropy Model for Wave Energy Conversion

Multi‐objective optimization of a tubular permanent magnet linear generator with 120° phase belt toroidal windings using response surface method and genetic algorithm

In terms of the characteristics of multi-objective and interactions among optimization objectives of the tubular permanent magnet linear generator with 120° phase belt toroidal winding (120°-TPMLG), a multi-objective optimization method is proposed to improve the generators performances, which is based on the combination of response surface method and the genetic algorithm. First, the sensitivity analysis of different structural parameters on the performances of the 120°-TPMLG is conducted to pick out the sensitive structural parameters. Then develop those sensitive parameters as optimization variables to establish the response surface equation of the generator performances including output power (P), detent force (F), and the efficiency (η). Subsequently, based on the surface equation, the genetic algorithm (GA) fitness function is proposed to conducted the global optimization and the optimization results are finally obtained. To verify the effectiveness of the proposed optimization method, the performances of the optimal 120°-TPMLG are analysed and compared with the initial one. The results show that the performances including the detent force and power density of the 120°-TPMLG are greatly improved, which prove that the proposed multi-objective optimization method is effective for the 120°-TPMLG.

Comparison of the Electromagnetic Characteristics of a Novel Gramme Winding and a Concentrated Winding Tubular Permanent-Magnet Linear Generator

A tubular permanent-magnet linear generator is suitable for direct drive wave energy conversion owing to its simple structure, easy maintenance and high efficiency. In this study, a novel Gramme winding tubular permanent-magnet linear generator (GW) is designed to increase power density. First, the structure of the Gramme winding and concentrated winding tubular permanent-magnet linear generator is introduced and the operation principle of the generator is analysed. Second, the initial parameters of GW are determined based on the similar overall dimensions to those of the concentrated winding tubular permanent-magnet linear generator. Third, the air gap flux density, external characteristics, voltage regulation, output power, and loss of the two generators are compared. Finally, the DC load capacities of the two generators are compared based on a three-phase full-control bridge rectifying circuit. The results show that the GW has a higher power density than the latter.

A Novel Single-Phase Tubular Permanent Magnet Linear Generator

A novel single phase tubular permanent magnet linear generator (TPMLG) for Stirling engines is proposed in this paper. It has an outer-stator, an inner-stator, a mover and a bread type winding which has no cutting. The mover consists of four ring-shaped permanent magnets, all of which are polarized radially. The polarization direction of the outer two permanent magnets is opposite to that of the inner two to form more magnetic circuits and achieve higher power generation density. The polarized directions of the two adjacent permanent magnets of both the outside and inside are opposite. The structure, dimensional parameters and operation characteristics of the generator are illustrated in detail. One of the structural advantages of this generator is that it is easy to control. The 3-D finite element (FE) model of proposed TPMLG is established. The model and its boundary conditions are presented and explained in detail. Through the FE model, its electromagnetic analysis is carried out. The performance of this generator under reciprocating frequency 75 Hz is investigated and analyzed. The simulation results show that the generator has the advantages of high power density.

A Tubular Permanent Magnet Linear Generator With Novel Structure

A single-phase tubular permanent magnet linear generator (TPMLG) with a novel structure for Stirling engines is presented in this paper. TPMLG can directly convert mechanical energy into electrical energy and it is the main energy conversion device in Stirling power generation system. Its 3-D geometry and initial dimensions are given in detail. Due to the structural characteristic, the finite element (FE) method (FEM) is used to analyze the electromagnetic field. An FE model is established from the magnetic field perspective. Isolines of magnetic vector potential can be obtained, as TPMLG locates at −0.015, 0, and 0.015 m. The dynamic performances of TPMLG under different reciprocating frequencies are compared and analyzed. Compared with three different kinds of machines, it can be concluded that the proposed TPMLG can produce electricity with less weight and materials.

Design and Optimization of Tubular Linear Permanent Magnet Generator with Performance Improvement Using Response Surface Methodology and Multi-Objective Genetic Algorithm

Linear generators are electric machines which generate electrical energy from linear movement. Since these machines can lift gear wheel or power train, they have begun to be used widely nowadays. Since their working areas differ according to speed and power characteristic, this study contains design and optimization of tubular linear generator for free piston practices. The design performed response surface optimization through design variables acquired as a result of sizing via interface. The association between the determined design variables and the sizes of generator output was examined. In addition, these sizes were used for objective functions of increasing efficiency, decreasing overall volume and increasing general performance and their optimum values were found by using Multi-Objective Genetic Algorithm. Initial and optimum design data were compared with Ansys Maxwell 2D. With overall performance increase, 22,78% decrease was seen in total mass, while 11,7% decrease was seen in cost. In addition, prototype linear generator was made in line with initial geometry data and it was applied with crank slider mechanism.

Research on the Field-Modulated Tubular Linear Generator With Quasi-Halbach Magnetization for Ocean Wave Energy Conversion

A field-modulated tubular linear generator (FMTLG) with quasi-Halbach magnetization is proposed for ocean wave energy conversion. The FMTLG, which is equipped with field-modulated technology and quasi-Halbach arrays, can overcome the disadvantages of heavy weight and inefficiency caused by low-speed ocean waves to some extent. To design and optimize the FMTLG in a short time, the open-circuit magnetic field distribution is established with an analytical method. Results of a finite-element method show that the back EMF of the FMTLG is 43% higher than that of a tubular linear permanent magnet generator (TLPMG) with quasi-Halbach magnetization. A novel assistant tooth of the FMTLG makes the cogging force eight times smaller than that generated by the TLPMG. Finally, a prototype is manufactured to verify the simulation results by experiments.

Design and Experiment Analysis of a Direct-Drive Wave Energy Converter with a Linear Generator

Coastal waves are an abundant nonpolluting and renewable energy source. A wave energy converter (WEC) must be designed for efficient and steady operation in highly energetic ocean environments. A direct-drive wave energy conversion (D-DWEC) system with a tubular permanent magnet linear generator (TPMLG) on a wind and solar photovoltaic complementary energy generation platform is proposed to improve the conversion efficiency and reduce the complexity and device volume of WECs. The operating principle of D-DWECs is introduced, and detailed analyses of the proposed D-DWEC’s floater system, wave force characteristics, and conversion efficiency conducted using computational fluid dynamics are presented. A TPMLG with an asymmetric slot structure is designed to increase the output electric power, and detailed analyses of the magnetic field distribution, detent force characteristics, and no-load and load performances conducted using finite element analysis are discussed. The TPMLG with an asymmetric slot, which produces the same power as the TPMLG with a symmetric slot, has one fifth detent force of the latter. An experiment system with a prototype of the TPMLG with a symmetric slot is used to test the simulation results. The experiment and analysis results agree well. Therefore, the proposed D-DWEC fulfills the requirements of WEC systems.

Design of Tubular Permanent Magnet Generators for Vehicle Energy Harvesting by Means of Social Network Optimization

The optimization of electrical machines and energy-harvesting devices has been one of the hot topics of research in recent years. In this context, advanced computational intelligence algorithms are suitable design tools, since they are able to optimize complex systems with a large number of constraints and free design parameters. This paper presents the social network optimization (SNO): a new population-based algorithm developed to guarantee an effective and faster exploration of the solution domain with respect to traditional optimization techniques. The proposed technique will be described and validated with a benchmark case study. Finally, the optimization problem of a tubular permanent magnet linear generator will be formulated in the context of vehicular energy-harvesting systems.

Spatial harmonic analysis on a permanent magnet linear generator with Halbach array for direct‐driver wave energy conversion

AbstractA tubular permanent magnet linear generator (TPMLG) with Halbach array magnetization is proposed to extract wave energy. The magnetic field is analyzed by analytical analysis and verified by numerical analysis. The air‐gap flux density of TPMLG with Halbach array magnetization has a better sinusoidal shape than quasi‐Halbach and other magnetization based on the spatial harmonic analysis. The harmonic component of flux density varies with the degree of permanent magnet magnetization, through optimizing the angle α (α is the angle between the z‐axis and orientation of magnetization), and the harmonic component is smallest when the angle α equal to π/4. Meanwhile, the amplitude of Br in air‐gap region reaches maximum. Analytical analysis proves that TPMLG with Halbach array magnetization can improve generator performance and power density. Finally, a prototype is manufactured and applied to a direct‐drive power take‐off system experiment. Simulations and experimental results demonstrate that it is an effective method for direct‐drive wave power take‐off system.

Research on a double float system for direct drive wave power conversion

The development and reasonable utilisation of wave energy have great realistic significance for solving environment pollution and energy crisis. A direct-drive system with no middle conversion devices such as gear and turbine, which has a simple structure and good stability, is widely applied to wave power systems. First, the study analysed the structure of a tubular permanent magnet linear generator. The structure of short primary and long secondary is chosen for wave power systems because of the convenience of installation and higher power density. Then, based on finite-element analysis, the structure of the generator is optimised by parametric analysis and genetic algorithm. A prototype is manufactured according to the optimised size, and the electromagnetic parameters are measured to verify the accuracy of simulation. Finally, a double floating direct-drive wave power system is installed in the port of Lian Yungang, China, and the system is tested by still and dynamic water; the results show that the system can effectively convert wave energy into electricity.

Design and Analysis of a Field-Modulated Tubular Linear Permanent Magnet Generator for Direct-Drive Wave Energy Conversion

A two-body buoys power generation system using the field-modulated tubular linear permanent magnet generator (FM-TLPMG) is proposed for direct-drive wave energy conversion in this paper. The traditional linear generator has disadvantages of large weight and low-power density caused by the slow speed of ocean wave. The FM-TLPMG can overcome these disadvantages in some extent through accelerating the speed of the traveling magnetic field. In order to design a suitable FM-TLPMG for the direct-drive wave energy conversion in a short time, ocean wave theory is applied to analyze hydrodynamic problems of the two-body buoys and calculate the operating velocity of FM-TLPMG in the sea. A 2-D analytical model for FM-TLPMG design is presented to obtain the electromagnetic field distribution by solving the Laplace and Poisson equations for each region. The analytical result has been compared with the finite-element analysis and shows its validation for the design.