Permanent Magnet Linear Generator Research Articles

An Experimental Comparison between an Ironless and a Traditional Permanent Magnet Linear Generator for Wave Energy Conversion

Permanent Magnet Linear Generators (PMLGs) are currently being studied for sea wave energy harvesting. Typically, a PMLG consists of an iron-made armature and a moving translator. The permanent magnets adoption produces parasitic effects, such as cogging force, and the machine weight increment. A solution could be the adoption of an ironless configuration, accepting a power density reduction. This paper investigates the use of ironless PMLGs in sea wave energy conversion systems by an experimental comparative analysis between an iron PMLG prototype and an ironless PMLG prototype, which share the same geometry. The main electrical and mechanical parameters (resistance, mass, and magnetic fields) were preliminarily measured. Subsequently, open-circuit and load tests were carried out to compare the induced voltages, the energy transferred to a resistive load, efficiency and the load average power. The reported comparison shows that iron PMLG performances are significantly superior to the ironless ones during the open-circuit tests, as expected. However, the analysis carried out through the load tests shows that the cogging force significantly limits the energy production, obtaining similar values in both machines. Therefore, the experimental tests justify the use of ironless machines in sea wave energy harvesting, where the maximization of energy production is a relevant target.

A Novel Structure of Tubular Staggered Transverse-Flux Permanent-Magnet Linear Generator for Wave Energy Conversion

This paper presents a novel linear generator structure of three-phase tubular staggered transverse flux permanent magnet linear generator (TSTF-PMLG) for wave energy conversion. Compared with conventional TF-PMLGs, the new structure has a simpler magnetic flux path, high mechanical strength, low cogging force and more suitable for low-speed direct driven situation. In the primary of TSTF-PMLG, a nonuniform teeth steel sheets structure is used and steel sheets of different phases are in different angel so that the groove can be separated by staggered steel sheets in the plane perpendicular to the direction of movement. By the analytical model, the operation principle of the proposed linear generator is explained. Then through the finite element analysis, the distribution of the main flux and leakage flux, the no-load characteristics and output power of TSTF-PMLG are analyzed in detail. And the influence of the lamination factor on the output characteristics of the TSTF-PMLG is obtained. Subsequently the appropriate design parameters of the TSTF-PMLG are selected. During the TSTF-PMLG processing, the method of mixing silicon steel sheets and fiberglass board is used to limiting the lamination factor. Finially, a prototype of 150 W rated power and 79% rated efficiency is presented. And the experimental results verify the theoretical analysis.

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.

The Novel Low Reluctance Superconducting Permanent Magnet Linear Generator for Oceanic Wave Energy Extraction

In this paper, the low reluctance superconducting direct drive linear generator (DDLG) for harvesting oceanic wave is presented. At first, a permanent magnet DDLG is designed in the ANSYS/Maxwell environment. The DDLG with both the copper and superconducting winding are characterized with finite element analysis. The DDLG is analyzed with the conventional and recently developed M5 Carlite magnetic cores. High graded neodymium iron boron permanent magnet, N46SH is selected for the DDLG to create strong magnetic field. It is analyzed that the proposed superconducting DDLG with M5 Carlite magnetic core and N46SH permanent magnet produces 294 kW more electrical power compared to that of the DDLG with copper conductor. It is also found that the stator size of the proposed DDLG is much smaller than the conventional one for designing the winding with superconducting tape.

Modeling and Design of a Multiport Magnetic Bus-Based Novel Wind-Wave Hybrid Ocean Energy Technology

This article proposes a multiport magnetic bus (MMB)-based novel wind-wave hybrid ocean energy technology (HOET). The ocean waves are mixed frequency waves and generate unique frequency spectra. The wave energy converters (WECs) connected to the linear permanent magnet generators generate voltages with varying amplitudes and frequencies due to the variation of the wind speed and direction. The proposed MMB of the proposed compact wind-wave HOET can provide galvanic isolation and allow a high-frequency operation of the MMB. A decoupled voltage and current control architecture is proposed to regulate the voltage and current waveforms in the high-frequency inverter modules of the MMB that can integrate multiple WECs. An Archimedes wave swing-based conversion method is utilized for the modeling and the design of the proposed WEC. A damping controller is designed to extract the maximum power from the irregular waves. For the wind-energy generation system, a doubly fed induction generator-based technology is considered. The simulation and the laboratory-scale experimental results validate the potential and the applicability of the proposed wind-wave HOET as an effective means to harness ocean energy.

Performance of Linear Generator Designs for Direct Drive Wave Energy Converter under Unidirectional Long-Crested Random Waves

For generating electricity, direct-drive wave energy converters (WECs) with linear permanent magnet generators (LPMGs) have advantages in terms of efficiency, simplicity, and force-to-weight ratio over WEC with rotary generators. However, the converter’s work under approaching-real wave conditions should be investigated. This paper studies the performance of a pico-scale WEC with two different LPMGs under unidirectional long-crested random waves. Different significant wave heights (using data in the Southern Ocean of Yogyakarta, Indonesia) and peak frequencies are tested. The JONSWAP energy spectrum is used to extract the wave elevations, while the MSS toolbox in MATLAB Simulink is employed to solve the floater’s dynamic responses. Next, the translator movements are extracted and combined with the flux distribution from FEMM simulation and analytical calculation, and the output powers are obtained. An experiment is conducted to test the output under constant speed. The results show for both designs, different tested significant wave height values produce higher output powers than peak frequency variation, but there is no specific trend on them. Meanwhile, the peak frequency is inversely proportional to the output power. Elimination of the non-facing events results in increasing output power under both parameters’ variation, with higher significant wave height resulting in a bigger increase. The semi iron-cored LPMG produces lower power loss and higher efficiency.

Optimized design of a novel yokeless mover permanent magnet linear generator for free‐piston stirling engines applied to solar cogeneration systems

Considering the growing environmental issues, the use of renewable energy converters such as solar cogeneration systems has received more attention during recent years. Solar cogeneration systems convert the thermal energy of solar radiation into mechanical energy (by means of a free-piston Stirling engine) and then into electrical energy (by means of a linear generator). This paper introduces the novel yokeless mover permanent magnet linear generator (YMPMLG) to reduce mover mass, increase power density, increase thrust and decrease the normal force on the mover, which can make this generator a more suitable structure for operating in solar cogeneration systems. This paper is initiated with a comparative study of a YMPMLG with two reported prototypes in this field. Three generators with similar characteristics are simulated by the finite element method (FEM). The magnetic field flux density, power density, thrust coefficient, normal force, and efficiency parameters are analysed and compared in three generators. Following that, some dimensional parameters of the YMPMLG, including generator diameter and length and permanent magnet dimensions are optimized to achieve the highest possible power density and thrust coefficient using the ‘hybrid genetic and pattern search’ algorithm. The highest power density and efficiency are 0.58 kW/kg and 90.3%, respectively. In the end, the YMPMLG prototype has been tested to validate the results of the FEM method.

Design and analysis of a novel yokeless mover permanent magnet linear generator for free piston engine converter

Free piston engine generator (FPEG) is one of the recent solutions by researchers used in hybrid vehicles, which eventually can contribute to the reduction of environmental pollutants from public transports. The purpose of the this work is to introduce a novel dual-stator permanent magnet linear generator with yokeless mover (DSPMLG) to improve the key parameters of the linear generator used in FPEG systems. In this work, an analytical model of the DSPMLG magnetic field is developed to investigate magnetic field flux density distribution and for back-EMF prediction. Then, a two-dimensional (2D) model of the DSPMLG is put forth using the finite element method (FEM) to validate the analytical results. In the next section, 1D modelling and simulation of a two-stroke free-piston engine (FPE) with dual-piston structure is done using Ricardo’s WAVE software. The obtained results are used in the FEM simulation and prototype development in order to accurately evaluate the performance of the introduced generator in the FPEG system. Since the FPE velocity profile distorts the back-EMF, the effect of the velocity profile on back-EMF distortion is investigated using fast Fourier transform. Also, the DSPMLG is optimised for minimum back-EMF distortion, considering the maximum output power. To validate the simulation results, the DSPMLG is developed and the obtained experimental results have proper conformity with the simulation results. Finally, in order to weigh up the effectiveness of the proposed generator, its structure is compared with other reported structures in previous research studies based on the key indicators required for the linear generator used in FPEGs.

A Spiral Translator Permanent Magnet Transverse Flux Linear Generator Used in Direct-Drive Wave Energy Converter

Direct-drive wave energy converter (DD-WEC) simplifies the structure and improves the efficiency of wave energy conversion. Permanent magnet transverse flux linear generator (PMTFLG) combines the merits of transverse flux linear generator (TFLG) and permanent magnet linear generator (PMLG), and is suitable for low-speed high thrust density applications, like DD-WEC. However, it suffers from a significant demerit which is the high cost due to the rare earth permanent magnets (PMs). A stator-PM spiral translator PMTFLG (ST-PMTFLG) is proposed in this article. Armature winding and PMs are arranged in outer stator and inner stator, respectively while the translator is made of spiral steel blocks and nonmagnetic blocks. Similar to the magnetically geared machine, the proposed topology is suitable to be used in low-speed long-stroke application. Results show that ST-PMTFLG has advantages of low PM consumption and high thrust density. The thrust per PM volume of 12/11 ST-PMTFLG is 4.18 MN/m3.

파력발전시스템의 간이 설계를 통한 파력발전용 리니어 발전기 설계에 관한 연구

In this paper, the design of linear generator for wave energy conversion is studied through wave energy system design. The wave energy system is designed through the mass and spring system. In the designed wave energy system, the specification of permanent magnet linear synchronous generator (PMLSG) is obtained using the principle of energy conversion. The basic design of PMLSG is performed considering the constraint of wave energy system considering the resistance load using the external circuit. Furthermore, the detent force of PMLSG is optimized using the parametric analysis. As a result, the PMLSG is designed considering the design of the wave energy system and optimization of the detent force.

Damping Studies on PMLG-Based Wave Energy Converter under Oceanic Wave Climates

Wave energy converters (WECs), which are designed to harvest ocean wave energy, have recently been improved by the installation of numerous conversion mechanisms; however, it is still difficult to find an appropriate method that can compromise between strong environmental impact and robust performance by transforming irregular wave energy into stable electrical power. To solve this problem, an investigation into the impact of varied wave conditions on the dynamics of WECs and to determine an optimal factor for WECs to comply with long-term impacts was performed. In this work, we researched the performance of WECs influenced by wave climates. We used a permanent magnet linear generator (PMLG)-based WEC that was invented at Uppsala University. The damping effect was first studied with a PMLG-type WEC. Then, a group of sea states was selected to investigate their impact on the power production of the WEC. Two research sites were chosen to investigate the WEC’s annual energy production as well as a study on the optimal damping coefficient impact. In addition, we compared the WEC’s energy production between optimal damping and constant damping under a full range of sea states at both sites. Our results show that there is an optimal damping coefficient that can achieve the WEC’s maximum power output. For the chosen research sites, only a few optimal damping coefficients were able to contribute over 90% of the WEC’s annual energy production. In light of the comparison between optimal and constant damping, we conclude that, for specific regions, constant damping might be a better choice for WECs to optimize long-term energy production.

Optimal Sliding Mode Control of Permanent Magnet Direct Drive Linear Generator for Grid-Connected Wave Energy Conversion

the key goal of this article is on the design and optimum sliding mode control for Grid-Connected direct drive extraction method of ocean wave energy by Multi-Objective Particle Swarm Optimization (MOPSO). A Linear Permanent Magnet Generator simulates the ocean wave energy extraction system, driven by an Archimedes Wave Swing. Uncontrolled three-phase rectifiers, a three-level buck-boost converter and 3 level neutral point clamped inverter are planned grid integration of Wave Energy Conversion device. The technique monitors the three-level buck-boost converter service cycle linked to the PMLG output terminals and decides the optimum switching sequence of 3 level neutral point clamped inverter to enable the grid relation. Simulations using Matlab/Simulink were carried out to test working of the wave energy converter after the suggested optimal control method was applied under various operating settings. Various simulation test results indicate that the proposed optimum control system is tested in both normal and irregular ocean waves. And it has been shown that the control method of the MOPSO sliding mode is ideal for maximizing energy transfer efficiency. Better voltage management at the DC-link and for achieving greater controllability spectrum was accomplished by the proposed Duty-ratio optimal control system.

Optimal Sliding Mode Control of Permanent Magnet Direct Drive Linear Generator for Grid-Connected Wave Energy Conversion

the key goal of this article is on the design and optimum sliding mode control for Grid-Connected direct drive extraction method of ocean wave energy by Multi-Objective Particle Swarm Optimization (MOPSO). A Linear Permanent Magnet Generator simulates the ocean wave energy extraction system, driven by an Archimedes Wave Swing. Uncontrolled three-phase rectifiers, a three-level buck-boost converter and 3 level neutral point clamped inverter are planned grid integration of Wave Energy Conversion device. The technique monitors the three-level buck-boost converter service cycle linked to the PMLG output terminals and decides the optimum switching sequence of 3 level neutral point clamped inverter to enable the grid relation. Simulations using Matlab/Simulink were carried out to test working of the wave energy converter after the suggested optimal control method was applied under various operating settings. Various simulation test results indicate that the proposed optimum control system is tested in both normal and irregular ocean waves. And it has been shown that the control method of the MOPSO sliding mode is ideal for maximizing energy transfer efficiency. Better voltage management at the DC-link and for achieving greater controllability spectrum was accomplished by the proposed Duty-ratio optimal control system.

Parametric design of a resonant point absorber with a fully submerged toroidal shape

The parametric design of a resonant point absorber, equipped with a fully submerged toroidal shape and connected to a permanent magnet linear generator lying on the seabed, is performed to investigate the effectiveness of the new WEC device in terms of power production and cost of energy. After developing a non-linear time-domain model for the heave, surge and pitch motions of the floating buoy and the vertical motion of the Power Take-Off translator mass, a comparative analysis is performed among a reference WEC device and the new layout. The Annualised Energy Production of the WEC devices is assessed with reference to a candidate deployment site located in the western Mediterranean Sea. The scantling of the tensioned line, connecting the floating buoy to the Power Take-Off unit, is carried out based on both Ultimate and Fatigue Limit State design conditions. Subsequently, the Levelised Cost of Energy is determined and a sensitivity analysis is performed to detect a possible pathway to further reduce the power production costs. Based on current results, the new WEC device seems to be a promising layout to gain the EU target for the marine renewable energy sector that should be reached by 2025.

Multi-Physical Coupling Field of a Permanent Magnet Linear Synchronous Generator for Wave Energy Conversion

Permanent Magnet Linear Synchronous Generators (PMLSG) has high power density and high efficiency, which is always employed in industrial application field. However, as temperature increases, it is easy to cause demagnetization of the permanent magnet, and the applications of PMLSG is limited. In this paper, a PMLSG is optimized which is used in a low speed power generation system. Firstly, a multi-physical coupling field system is described, and introduced the main factors which affecting the design of the PMLSM. Secondly, a multi-physics optimization method based on Genetic Algorithm (GA) is to improve the power density and efficiency. At the same time reduce the material cost of the generator. The thermal model is established and analysis the losses of PMLSG. The conductive heat transfer coefficient is calculated. Then, a Finite Element Analysis (FEA) model is established, and the electromagnetic properties of PMLSG were analyzed. The results of the electromagnetic field calculation are imported into the transient thermal analysis model by FEA, and the temperature of each part for PMLSG are calculated. Finally, an experimental test platform is built for verifying the correctness of the analysis.

Study on the field strength and the output power of the dual Halbach magnet array-based linear generator using mix calculation methods

Ocean wave energy conversion is an emergent and highly important research topic in Vietnam. In an early research work, an experimental permanent magnet linear energy generator was developed and stu...

A Stator-PM Transverse Flux Permanent Magnet Linear Generator for Direct Drive Wave Energy Converter

Transverse flux permanent magnet linear generator (TF-PMLG) is widely used in direct drive wave energy converter (DD-WEC) because of its high power density. Traditional transverse flux machine (TFM) is designed and built in form of translator-PM. But translator-PM configuration needs a large amount of PM and the cost is high in long stroke application, like DD-WEC. Recently, the stator-PM linear machines have gained more attention for reducing the PM volume and improving the generator performances under low-speed conditions. In this paper, a novel stator-PM TF-PMLG for DD-WEC has been proposed. The fundamental configuration and operation principle of the generator are illustrated. Then, the expressions of the back EMF and the electromagnetic thrust are derived by magnetic circuit analysis. Main dimension parameters, such as PM thickness, central angle of the outer stator shoe and pole pitch are determined and optimized based on finite element analysis (FEA). This topology has advantages of low PM consumption and high power density, and is a suitable candidate for long stroke applications, like DD-WEC, in which a high power per PM volume is usually needed to reduce the amount of permanent magnet and ensure high power density.

A novel single‐body system for direct‐drive wave energy converter

Ocean wave energy has played a key role of the renewable energy. This study presents a novel single-buoy wave energy converter (WEC) with directly driven power take-off (PTO) system to overcome some difficulties that the PTO system in the conventional single-body direct-drive WEC (DD-WEC) is fully submerged under water and far away from the water surface. A rectangular buoy, a direct-drive PTO system with Halbach permanent magnet linear generator (HPMLG), and slide rails form the chief institutions of the WEC. The translator of the HPMLG is installed on the lateral surface of buoy, and the stator is mounted on the seacoast or the boats and ships. While wave drives the floating buoy to move, a relative movement between the translator and the stator of the HPMLG is caused. Then, the relative movement generates electricity. To explore theoretically its feasibility, the dynamics of the wave and the floating buoy is analyzed in detail. Thus, the structural parameters are analyzed and determined, and load performance is described. Furthermore, the finite element method (FEM) is used to conduct the performance evaluation of the HPMLG and traditional permanent magnet linear generator (TPMLG). The generated power of the HPMLG is 19% higher than the TPMLG under the same conditions. Lastly, Experiments of a fabricated prototype are conducted in the wave tank. Experimental results show that the prototype in this paper decreases these existing problems and is suitable for wave energy generation.