Linear Generator Research Articles

Modelling of a wave-to-wire system for a wave farm and its response analysis against power quality and grid codes

A single wave energy converter (WEC) produces a low and fluctuating power, and the use of a permanent magnet linear generator (PMLG) as an electric power take-off unit can make the situation worse because the power produced from a PMLG varies with each incident wave. The use of a short-term energy storage unit as an energy buffer will become necessary to mitigate the fluctuating power. However, the addition of the energy storage system will further increase the cost of the WEC. This paper proposes a modelling strategy for the wave-to-wire system of WEC arrays, consisting of Archimedes wave swings coupled with PMLGs, to analyze its power output quality and grid compliance without the integration of any energy storage system. The measured hydrodynamics of ocean waves are used for the analysis of the system. The developed model for the wave-to-wire system is tested under various scenarios for its power output quality while maintaining grid code compliance. The flicker level at the point of common coupling for the wave farm is evaluated for grids of varying strength. The simulation results show that the proposed configuration of the wave-to-wire system can be integrated with the grids of sufficient strength, without the need for expensive energy storage units, while complying with the grid code in the respective countries, such as Ireland, UK and Nordic countries. The main contributions of this paper are (i) a new modelling strategy to analyze a wave-to-wire system, (ii) simulation studies to analyze the power quality and grid code compliance of a wave-to-wire system, (iii) recommendations for the required grid strength to integrate wave farms to the grid. • A PMLG based wave farm is modelled for its smooth integration with the grid. • Modelling strategy for the wave-to-wire system of WEC arrays. • The wave energy flux density is evaluated for the selected site. • The flicker level at the point of common coupling for the wave farm is evaluated for grids of varying strength. • Grid integration without the need for expensive storage units, while complying with the grid codes.

Performance evaluation of surface riding wave energy converter with linear electric generator

In this study, we devised a new WEC (wave energy converter) called SR-WEC (Surface Riding WEC). The SR-WEC consists of two bodies: the outer cylinder with an armature assembly (body #1) and a magnet assembly (body #2) sliding inside the armature. For the SR-WEC, the relative sliding displacement and velocity are caused by gravity acceleration and the outer cylinder's motions, and they lead to electrical power generation. To evaluate its performance, a numerical simulation tool was developed, which solves the fully-coupled floater-mooring-generator dynamics. During the developing stage, the appropriate hydrodynamics model, sliding mechanics model, mooring dynamics model, and LEG (linear electric generator) electro-magnetic model were independently developed and then fully coupled in time domain to account for the cross-coupling interactions among them. Then, the developed simulation tool was verified component by component against various laboratory tests. Subsequently, systematic parametric studies were conducted with several important design parameters under various wave conditions to enhance power generation. After that, the average output power was evaluated in enlarged operational wave conditions. The present SR-WEC is particularly designed to be efficient at low sea states, which is good since they cover the majority of typical annual sea states.

Performance simulation by a nonlinear thermodynamic model for a Free Piston Stirling Engine with a linear generator

In the present study, an RE-1000 Free Piston Stirling Engine (FPSE) combined with a Permanent Magnet Linear Synchronous Machine (PMLSM) was analyzed. First, a nonlinear thermodynamic model of the FPSE was developed and validated. Based on this model, gas temperatures and pressures in different parts of the system and also its thermal efficiency can be calculated. Then, the PMLSM was modeled. At the next step, the systems were combined, and the results of the adapted controlled combined system were presented. Finally, by modifying the reference velocity parameters (amplitude and frequency), respecting the physical limitations of the system, it is possible to find the optimum operating point. At this optimum operating point, the efficiency of the system is maximum. The results also showed that this optimum point happened when the summation of the pistons’ strokes (power piston stroke + displacer piston stoke) was at its maximum amplitude.

Incoherent and Collective Thomson Scattering for the Determination of Electron and Ion Properties in Low-Temperature Plasma

In this lecture an overview of applications of incoherent Thomson scattering (TS) as well as collective Thomson scattering (CTS) will be given. These are the most accurate methods for measuring the electron and ion properties, because the method is direct and non-intrusive. A CTS system based on the fundamental wavelength of a seeded Nd:YAG laser, being developed for the high density, low-temperature plasma of the linear plasma generator Magnum-PSI will be described also. The small Debye length of dense low temperature plasma enables application of CTS at relatively short laser wavelength. The combination of this CTS system and existing incoherent TS system enables determination of electron density and temperature as well as ion temperature and plasma velocity of the near surface plasma. In this lecture, the theoretical background and experimental challenges of the work will be given along with some examples that demonstrate the capabilities of such systems.

Structural optimisation based on a snake‐like wave energy convertor with magnetoelectric transducer

Snake-like wave energy conversion (WEC) is a new type of WEC that combines raft WEC and magnetoelectric transducer. This type of WEC uses the magnetoelectric transducer, which is designed based on the permanent magnet linear generator and Halbach permanent magnet array, as its power take-off unit. The purpose of this study is to design a matching magnetoelectric transducer for WEC in common wave conditions and test its performance. The hydrodynamic model of the snake-like WEC is established to study the motion of WEC in regular waves. The equivalent magnetic circuit model of the magnetoelectric transducer is set up to optimise its ability to harvest wave energy in the ocean. Taking the maximum damping coefficient (cm ·max) as the optimisation goal of the magnetoelectric transducer, the induced voltage and output power of the magnetoelectric transducer in relatively uniform and sinusoidal motion can be calculated by simulation software. Finally, a prototype of the magnetoelectric transducer was made and its performance was tested. The experiment shows that the magnetoelectric transducer has a good ability to harvest wave energy, and snake-like WEC has wide applicability.

Simulasi Monte Carlo dalam Memprediksi Tingkat Lonjakan Penumpang (Studi Kasus di PT. Tri Arga Travel)

Tri Arga Travel is a company engaged in transportation services. The company really prioritizes the quality of service to consumers. So that on holidays there is usually a surge in passengers that cannot be predicted by the company. This greatly affects service to passengers. The purpose of this research is to predict the surge rate of PT. Tri Arga Travel, making it easier for the leadership of PT. Tri Arga Travel to take a policy when there is a surge in passengers in the future. The data used in this study is data on the number of passengers in 2017, 2018, and 2019 with the aim of padang-perawang. Then, the data is processed using the Monte Carlo method. The Monte Carlo method is a simulation method that uses random numbers obtained from the Linear Congruential Generator (LCG) to predict the rate of passenger spike in the following year by utilizing the previous year's passenger data. The results obtained from testing the Monte Carlo simulation can be seen that in July it is predicted that there will be a surge in passengers with an average level of accuracy of 86.74%. With a fairly high level of accuracy, the application of the Monte Carlo method can be used as a recommendation to predict the level of passenger spikes and also help in improving services to prospective passengers of PT. Tri Arga Travel.

Improving electric power generation of a standalone wave energy converter via optimal electric load control

This paper aims to investigate electric dynamics and improve electric power generation of an isolated wave energy converter that uses a linear permanent magnet generator as the power take-off system, excited by regular or irregular waves. This is of significant concern when considering actual operating conditions of an offshore wave energy converter, where the device will encounter different sea states and its electric load needs to be tuned on a sea-state-to-sea-state basis. To that end, a fully coupled fluid-mechanical-electric-magnetic-electronic mathematical model and an optimization routine are developed. This proposed time-domain wave-to-wire model is used to simulate the hydrodynamic and electric response of a wave energy converter connected to specific electric loads and also used in an optimization routine that searches optimal resistive load value for a wave energy converter under specific sea states. Sample results are presented for a point-absorber type wave energy converter, showing that the electric power generation of a device under irregular waves can be significantly improved.

Numerical Investigation of a Free-Piston Hydrogen-Gasoline Engine Linear Generator

The free-piston engine linear generator (FPELG) is being investigated by many researchers because of its high thermal efficiency and its variable compression ratio. However, all researchers focused on the FPELG characteristics with mono-fuel. Therefore, in this paper, the performance of the FPELG that has adopted gasoline with hydrogen as fuel is investigated. The method of coupling the zero-dimensional dynamics model with the multi-dimensional CFD (Computational Fluid Dynamics) combustion model was applied during the simulation process. According to the results, the piston TDC (Top Dead Center), the piston peak piston velocity, and the system operation frequency show a negative correlation with the increase of hydrogen fractions. However, the peak in-cylinder pressure was increased with the hydrogen volume fraction increase, due to the fast flame speed and short combustion duration characteristics of hydrogen. Meanwhile, the indicated efficiency of the free-piston engine was increased from 32.3% to 35.3% with the hydrogen volume fraction change from 0% to 4.5%, when the free-piston engine operates at stoichiometric conditions with fixed ignition timing. In addition, with the ignition timing advance increase, the piston TDC was decreased. The peak piston velocity and the peak in-cylinder pressure were in negative correlation with the ignition timing advance. While the engine indicated that the efficiency was increased with the equivalent degree of ignition timing from 20° to 16°. Therefore, the ignition timing of the FPELG under the spark-ignition combustion mode is supposed to be an effective and practical control variable.

Thrust Force Analysis of Slotless Permanent Magnet Linear Generator for Wave Energy Converter

The WEC (Wave Energy Converter) that uses a permanent magnet linear generator continues to develop. The most important thing to know in designing WEC with a linear electric generator is the thrust required by the linear generator itself. Therefore, this paper discusses and analyses the thrust that occurs in linear electric generators used in WEC systems. Linear electric generators are simulated using FEMM (Finite Element Magnetic Method) software. FEMM simulation is used to analyse the magnitude of the induced magnetic field received by the conductor at a certain position of the stator. The conductor is given a constant current so that it produces thrust force between the stator and translator; the magnitude of thrust force depends on the magnitude of the magnetic field at the position. In the design and analysis, conductors ware given 3A. The maximum thrust force in the linear electric generator design is 79N, and the average force is 75N, force ripple is 1,2%. The design of the permanent magnet linear generator was done, and the WEC system should produce thrust force at least equal to the force that the generator requires.

Designing of a generator for wave energy conversion for outdoor activities

Wave energy is one of the renewable resources with high availability area of the wave across the world. However, the wave power density in Malaysia is smaller compared to other countries with progressive development in Wave Energy Converter (WEC), which leads to wave energy utilization to produce pico-scale power generation for the benefit of outdoor activities. Thus, this paper is presenting the modeling of a tubular longitudinal permanent magnet linear generator for wave energy conversion for outdoor activities. This research aims to design a pico-scale linear generator with 100 W output power utilizing wave energy. The design is also intended to be a portable design with a weight that less than 20 kg, which compatible with outdoor activities. The generator is proposed by designing the different shapes of permanent magnets with slotless configuration. The designs are simulated using the Finite Element Analysis (FEA) to obtain the performance of flux distribution, flux linkage, and back EMF performance.

A study of a speed amplified linear generator for low-frequency wave energy conversion

This paper proposes a new method of speed amplification for a direct drive ocean wave energy converter. The relative speed of the stator and translator of a linear generator is doubled through a fixed pulley wheel mechanism. Analytical and simulation models of the system have been developed and simulated considering the mechanical damping and electrical damping coefficients. The models have been simulated in both the regular waves and irregular waves where hydrodynamic parameters for different heaving buoys are calculated from hydrodynamic boundary element analysis simulation using the ANSYS AQWA software. The relative displacement, output voltage and harvested power of the speed amplified wave energy converter system have been obtained in the frequency and time domains. The frequency and time domain models were validated through comparing the peak output power values at different frequencies. The generator parameters of electromagnetic coupling coefficient, or the power take-off (PTO) electrical damping coefficient and external resistance were studied to ensure an optimal wave-energy converter (WEC) design.

Damping Effect Coupled with the Internal Translator Mass of Linear Generator-Based Wave Energy Converters

The damping effect, induced inside the linear generator, is a vital factor to improve the conversion efficiency of wave energy converters (WEC). As part of the mechanical design, the translator mass affects the damping force and eventually affects the performance of the WEC by converting wave energy into electricity. This paper proposes research on the damping effect coupled with translator mass regarding the generated power from WEC. Complicated influences from ocean wave climates along the west coast of Sweden are also included. This paper first compares three cases of translator mass with varied damping effects. A further investigation on coupling effects is performed using annual energy absorption under a series of sea states. Results suggest that a heavier translator may promote the damping effect and therefore improve the power production. However, the hinder effect is also observed and analyzed in specific cases. In this paper, the variations in the optimal damping coefficient are observed and discussed along with different cases.

Comparison of Control Strategies and Electromechanical Devices for the Backpack Energy Harvesting System

This article provides a general overview on the control strategies and their implications for the backpack energy harvesting system. The control strategies include reactive control and resistive damping. The study is performed for three cases of electric generator: the direct drive linear generator, the rotary machine integrated with the trans-rotary magnetic gear (MITROMAG), and the rotary machine coupled with a mechanical rack and pinion (MRP). Equivalent circuits based upon electrical–mechanical analogies are employed to help understand the system dynamics under the two control strategies. It is shown that in all cases, upon reactive control, more power can be harvested; however, it comes at the cost of a higher velocity, peak power, and force requirement. Moreover, it is shown that for most of the operating points considered, the direct drive linear generator outperforms the geared electromechanical devices in terms of the harvested power. Furthermore, it is revealed that the low stiffness of the MITROMAG slightly increases its harvested power compared to the MRP under the resistive damping strategy.

A table of short-period Tausworthe generators for Markov chain quasi-Monte Carlo

We consider the problem of estimating expectations by using Markov chain Monte Carlo methods and improving the accuracy by replacing IID uniform random points with quasi-Monte Carlo (QMC) points. Recently, it has been shown that Markov chain QMC remains consistent when the driving sequences are completely uniformly distributed (CUD). However, the definition of CUD sequences is not constructive, so an implementation method using short-period Tausworthe generators (i.e., linear feedback shift register generators over the two-element field) that approximate CUD sequences has been proposed. In this paper, we conduct an exhaustive search of short-period Tausworthe generators for Markov chain QMC in terms of the t-value, which is a criterion of uniformity widely used in the study of QMC methods. We provide a parameter table of Tausworthe generators and show the effectiveness in numerical examples using Gibbs sampling.

Coupled Modeling and Advanced Control for Smooth Operation of a Grid-Connected Linear Electric Generator Based Wave-to-Wire System

The perpetual oscillations of ocean waves produce potential energy, which can be converted to electrical energy with the help of direct-drive linear generators. The fluctuating generated power poses a major challenge when it is supplied to the power grid. In this article, a supercapacitor provides the short-term energy storage to buffer and smooth out the power fluctuations. A new coupled model of a wave energy converter and a linear generator is proposed for its response characterization under varying system conditions. The developed model and an advanced control strategy are used to exhibit a smooth and stable operation of the wave-to-wire system. The generator-side converter is controlled to extract the maximum power from the waves and to minimize the generator losses by controlling its d -axis and q -axis currents. The grid-side converter is controlled to keep the dc-link voltage constant and to generate the required voltage waveforms at the point of common coupling. The performance of the proposed control strategy for the wave-to-wire system is investigated under different applied diffraction forces. The simulation results show that with the use of the proposed control scheme and the supercapacitor, the wave-to-wire system can operate in a smooth and stable operation under normal and fault conditions.

A Long-Range High Applicability Length Comparator for Linear Displacement Sensor Calibration

In this article, a long-range length comparator, applicable for both static- and dynamic-index calibrations of a linear displacement sensor, is presented. The comparator consists of an air-floating linear motion generator (LMG) and an interferometric optical length calibrator (OLC). A novel design of the LMG made by multisegment splicing is introduced, in which a two-level vibration isolation arrangement, a multiple sliders' setup, and an exoskeleton framework are adopted. The resulting linear motion can be extremely ideal even with a large stroke. The angular error is within 11.89 μrad covering the -2m range. The maximum operating speed and the acceleration of the LMG are 10 m/s and 20 m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. A dual-path optical design of the OLC is displayed, resulting in high environmental tolerance and a small trigger delay of 4.75 ns. The best accuracy of the comparator can be ±(0.041+0.106L) μm with a resolution of 0.3 nm. The maximum error and operation speed of a 2-m range exposed encoder were successfully calibrated, and the grating pitch deviation was also found, by which the effectiveness of the comparator is proven. The proposed length comparator introduces a possible solution, for how a long-range linear displacement sensor, can be calibrated with high accuracy, efficiency, and applicability.

Performance estimation of resonance-enhanced dual-buoy wave energy converter using coupled time-domain simulation

This paper presents the modeling methodology and performance evaluation of the resonance-enhanced dual-buoy WEC (Wave Energy Converter) by HEM (hydrodynamic & electro-magnetic) fully-coupled-dynamics time-domain-simulation program. The numerical results are systematically compared with the authors’ 1/6-scale experiment. With a direct-drive linear generator, the WEC consists of dual floating cylinders and a moon-pool between the cylinders, which can utilize three resonance phenomena from moon-pool dynamics as well as heave motions of inner and outer buoys. The contact and friction between the two buoys observed in the experiment are also properly modeled in the time-domain simulation by the Coulomb-friction model. Moon-pool resonance peaks significantly exaggerated in linear potential theory are empirically adjusted through comparisons with measured values. A systematic comparative study between the simulations and experiments with and without PTO (power-take-off) is conducted, and the relative heave displacements/velocities and power outputs are well matched. Then, parametric studies are carried out with the simulation program to determine optimum generator parameters. The performance with various wave conditions is also assessed.

Design of the swash-plate water hydraulic pump for environment-friendly actuator systems

This paper deals with a new development of a swash-plate hydraulic pump. It is particularly designed to aim its usage in applications where environmental impacts should be concerned. Thus, the pump is based on not mineral-based oil but simple tap water. The Electro-Hydraulic Actuator (EHA), a linear motion generator operated by an electric motor installed to the proposed pump, can be attractive and expandable to small-to-medium pressure applications. Water is clean and safe, and the size of EHA is relatively small. New design features of the pump including the no-shoe retainer, the inclination angle adjustment screw, the rotating cylinder block, and the simple assembly structure enabled EHA. The pump was designed to have its static pressure of 1.4 MPa and the volumetric flow rate of 10 × 103 mm3/s. To verify its performance, a series of experiments were constructed, and the maximum volumetric flow rate and pressure were found as 2935.87 mm3/s and 1.9 MPa, respectively. The maximum velocity of the actuator stroke was 9.35 mm/s. The EHA is controlled directly by the electric motor, and so a directional valve is not necessary. It is concluded the pump can be successfully used in small-to-medium pressure applications.

Analysis of Cascaded Buck–Boost Inverter for PMLG-Based Ocean Wave Energy Converter

The direct-drive Permanent Magnet Linear Generator (PMLG)-based Ocean Wave Energy Converter (OWEC) generates variable AC voltage, which cannot be directly utilized by the load. This paper presents a two-stage methodology to convert variable AC voltage to a constant amplitude AC voltage. First, a standard rectifier is used to convert variable AC voltage into variable DC voltage. After that, a cascaded buck–boost inverter is employed to achieve the constant frequency AC voltage. Systematic design and circuit analysis, along with working principle and voltage control strategy, are presented. A small scale laboratory prototype of PMLG associated with buck–boost inverter is developed to validate the proposed concept.

Research of a Hybrid Diesel Locomotive Power Plant Based on a Free-Piston Engine

This article describes one of the possible ways for improving the energy efficiency of shunting diesel locomotives. It means a replacing a traditional traction electric transmission with a diesel generator set with a hybrid transmission with a free-piston internal combustion engine and a linear generator. The absence of a crankshaft in an internal combustion engine makes it possible to reduce thermal and mechanical losses, which, in turn, leads to an increase in the efficiency of traction electric transmission of the diesel locomotive.