Energy Converter Research Articles

A Unified Model of a Virtual Synchronous Generator for Transient Stability Analysis

A virtual synchronous generator (VSG) is prone to transient instability under a grid fault, which leads to the loss of synchronization between the new energy converter and grid, and threatens the operation safety of high-proportion new energy grids. There are a variety of control models in the existing VSG control, including active and reactive power models, which lead to their different transient stabilities. However, the evolution characteristics, correlation between different models of VSG, and the internal mechanism affecting transient stability have not been fully studied. To this effect, this paper analyzes their evolution characteristics based on the existing mainstream VSG control models and establishes a unified VSG model and its equivalent correspondence with other models. Then, the phase plane method is used to comprehensively analyze and compare the transient stability of the VSG unified model with other models. It is pointed out that the key factors affecting the transient stability of different models are three links of primary frequency regulation, reactive power regulation and reactive power tracking. Finally, the correctness of the established VSG unified model and the conclusion of transient stability analysis is verified by experiments.

Current Loads on a Horizontal Floating Flexible Membrane in a 3D Channel

A 3D analytical model is formulated based on linearised small-amplitude wave theory to analyse the behaviour of a horizontal, flexible membrane subject to wave–current interaction. The membrane is connected to spring moorings for stability. Green’s function approach is used to obtain the dispersion relation and is utilised in the solution by applying the velocity decomposition method. On the other hand, a brief description of the experiment is presented. The accuracy level of the analytical results is checked by comparing the results of reflection and the transmission coefficients against experimental data sets. Several numerical results on the displacements of the membrane and the vertical forces are studied thoroughly to examine the impact of current loads, spring stiffness, membrane tension, modes of oscillations, and water depths. It is observed that as the value of the current speed (CS) rises, the deflection also increases, whereas it declines in deeper water. On the other hand, the spring stiffness has minimal effect on the vibrations of the flexible membrane. When vertical force is considered, higher oscillation modes increase the vertical loads on the membrane, and for a mid-range wavelength, the vertical wave loads on the membrane grow as the CS increases. Further, the influence of the phase and group velocities are presented. The influences of CS and comparisons between them in terms of water depth are presented and analysed. This analysis will inform the design of membrane-based wave energy converters and breakwaters by clarifying how current loads affect the dynamics of floating membranes at various water depths.

Constructal Design Applied to an Overtopping Wave Energy Converter Locate on Paraná Coast in Brazil

This research aims a numerical and geometrical investigation about an Overtopping Device Wave Energy Converter (OTD-WEC). Constructal Design method was employed to perform a geometric evaluation of this OTD-WEC submitted to ocean waves with similar characteristics of the coastal region of Paraná State – Pontal do Paraná city in southern Brazil, located 41 km from the coast and 30 m water deep. It was analyzed two different significant wave heights, HS1 = 1.25 m and HS2 = 1.50 m. In each set, it were simulated 10 cases with different ramp angles, totaling 20 numerical simulations. The main goal was to evaluate the influence of the ramp angle on the water mass flow rate entering the reservoir. Therefore, through the Construtal Design, the degree of freedom (DOF) H1/L1 (ratio between the height and length of the ramp) was varied, considering a constant area of the ramp. For the numerical analysis, a two-dimensional computational model was employed using the commercial software Ansys Fluent, which is based on the Finite Volume Method (FVM). The multiphase Volume of Fluid (VOF) model was applied to tackle with the water-air interaction. The results showed that the best geometric configurations happened for those cases with smaller ramp angles. In addition, a reconfiguration of the ramp angles, keeping the area fixed, allowed a significant improvement in the OTD-WEC available power.

Constructal Design Applied to an Overtopping Wave Energy Converter Locate on Paraná Coast in Brazil

This research aims a numerical and geometrical investigation about an Overtopping Device Wave Energy Converter (OTD-WEC). Constructal Design method was employed to perform a geometric evaluation of this OTD-WEC submitted to ocean waves with similar characteristics of the coastal region of Paraná State – Pontal do Paraná city in southern Brazil, located 41 km from the coast and 30 m water deep. It was analyzed two different significant wave heights, HS1 = 1.25 m and HS2 = 1.50 m. In each set, it were simulated 10 cases with different ramp angles, totaling 20 numerical simulations. The main goal was to evaluate the influence of the ramp angle on the water mass flow rate entering the reservoir. Therefore, through the Construtal Design, the degree of freedom (DOF) H1/L1 (ratio between the height and length of the ramp) was varied, considering a constant area of the ramp. For the numerical analysis, a two-dimensional computational model was employed using the commercial software Ansys Fluent, which is based on the Finite Volume Method (FVM). The multiphase Volume of Fluid (VOF) model was applied to tackle with the water-air interaction. The results showed that the best geometric configurations happened for those cases with smaller ramp angles. In addition, a reconfiguration of the ramp angles, keeping the area fixed, allowed a significant improvement in the OTD-WEC available power.

Modeling and optimization for arrays of water turbine OWC devices

The large-scale implementation of wave energy conversion requires the installation of parks of devices. We study the problem of optimizing park layout and control for wave energy converters of the oscillating water column type. As a test case, we consider a device with a Wells turbine working in water. First, a novel model based on a nonlinear ordinary differential equation is derived to describe the behavior of the water column and used to estimate the power matrix. Then, its linearization is derived in order to enable the fast simulation of large parks of devices. The choice of the hydrodynamic model allows obtaining the gradient of the power with respect to the positions through an adjoint approach, making it especially convenient for optimization. We consider in particular the case of interaction with the piles of a floating wind energy plant. The results from the developed computational framework allow us to draw interesting conclusions about park layout design. In particular, we observe that mutual interaction effects can be significant even in parks made up of devices of small size, and that wave reflection from the piles of an offshore structure can improve energy production.

Ocean wave energy harvesting: Utilizing buoy float to induce dielectric elastomer deformation and electret vibration for power generation

The dielectric elastomeric polymer material, characterized by its high energy output, resilience, mechanical compliance, lightweight, damage tolerance, and low cost, demonstrates significant potential as an innovative sustainable energy converter. It seamlessly adapts to the ever-changing climatic conditions of the ocean, converting the violent impacts of wave kinetics into electrical energy. This paper proposed a viable electret and dielectric elastomer wave energy harvester to convert ocean wave energy into electricity and aims to achieve self-priming operation in the conjugate components. The output voltage from the electret also functions as the bias voltage for the dielectric elastomer, based on the intrinsic variable capacitance electric translation principle. The dielectric elastomer's deformation, equivalent to variable capacitance, successfully converted the mechanical energy from the ocean waves into electrical energy. The ocean wave energy conversion is evaluated using a system-level approach, incorporating theoretical, simulation, and experimental models. In addition, electric power generation is assessed with parameters such as output voltage, electret surface potential, and bias voltage. Essentially, the electric energy produced by the electret generator can serve as the bias voltage source for the dielectric elastomer generator, providing a self-sustaining solution for ocean wave energy harvesting. The innovative power device envisions various potential configurations for ocean-based power generation.

Structural Integrity Analysis of Marine Dynamic Cables: Water Trees and Fatigue

Abstract Offshore power cables are typically designed to have a service life of around 25 years. A pattern is emerging where these cables only last 10 years or even as little as two. The main consensus as to why the service life is so short is due to a combination of fatigue and fretting/wear damages of the copper conductors and water treeing in the insulation material. This study presents a method that can be used to analyze the structural integrity of dynamic subsea power cables and estimate their service life determined by the factors above. The numerical simulation models developed and used to carry out global and local fatigue analyses of dynamic subsea power cables are presented, together with methods and models for assessing fretting, wear, and growth of water tree defects. A methodology for structural integrity assessment that includes all these factors is proposed. A dynamic subsea power cable connected to a wave energy converter is used as the case study for comparison of the service life when these factors are considered compared to when, e.g., the growth of water trees is excluded. A numerical sensitivity analysis demonstrates that the value of the seawater's electrical conductivity and the insulation material's threshold stress-intensity factor greatly influence the cable's service life.

Enhancements of Wave Power Absorption with Arrays and a Vertical Breakwater

The capability of the in-house transient wave-multibody computational tool, ITU-WAVE, is extended to predict the wave power absorption with Wave Energy Converters (WECs) arrays placed in front of a vertical breakwater. The hydrodynamic forces are approximated by solving boundary integral equation at each time interval. The reflection of incoming waves due to a vertical wall is predicted with method of images. The constructive or destructive performance of WECs arrays with different array configurations is measured with mean interaction factor. The behaviour of the hydrodynamic forces of each WEC due to a vertical wall effect shows considerable differences than those of WECs arrays without a vertical wall. When the wave power absorption with WECs arrays with and without a vertical wall effect are compared, the numerical results show that WECs placed in front of a vertical wall have much greater effects on wave power absorption. This can be attributed to the hydrodynamic interaction, standing waves, and nearly trapped waves in the gap between a vertical wall and WECs arrays. The analytical and other numerical results are used for the validation of present ITU-WAVE computational results for exciting and radiation forces, and mean interaction factor of WECs arrays which show satisfactory agreements.

Enhanced Electron Emission Performance and Air-Surface Stability in ScO-Terminated Diamond for Thermionic Energy Converters.

Diamond with negative electron affinity (NEA) and low work function surfaces are suggested as a suitable material for electron-generation applications in vacuum, in particular, as the emitter electrode in thermionic energy converters. Such NEA surfaces can be fabricated by evaporating and then annealing submonolayers of a suitable metal in vacuo onto bare or oxidized diamond. Among the metals studied, scandium termination of bare diamond (100) and (111) surfaces is recently reported to give the largest NEA values reported to date for a metal-diamond system, as well as being thermally stable to 900°C. It is now shown that preoxidized (100) diamond functionalized with 0.25monolayers of Sc also produces a large NEA value of -1.02eV with low work functions (<3.63eV). Moreover, this surface is thermally stable to 700°C and can withstand exposure to air for extended periods. Here, the structural and electronic properties of this Sc─O-functionalized diamond surface are characterized in detail using a variety of surface-science techniques. The results suggest that this material may be the ideal candidate for the fabrication of commercial thermionic energy conversion devices, e.g., for solar-power generation, as well as for various other electronic devices that rely upon electron emission.

Low-voltage DC collection grids for marine current energy converters: Design and simulations

Marine current energy represents a globally abundant yet largely untapped renewable energy source, offering greater predictability than other sources such as wind. Consequently, it has the potential to play a vital role in the green transition. A critical consideration for harnessing marine current energy is the design of the electrical grid to accommodate multiple turbines. Therefore, this paper presents a study that explores three types of DC collection grids (series, parallel, and star) for a specific marine current energy converter. A simulation model developed for the marine current energy converter is introduced and utilized to assess these topologies for grids comprising ten identical turbines subjected to varying water speeds. The designed topologies are intended for low-voltage and nearshore applications. The simulation results demonstrate that the series collection grid requires a significantly higher DC grid voltage compared to the other topologies for the turbines to operate correctly. Additionally, the study reveals that all three grid topologies can effectively transmit power to the distribution grid with similar power losses.

An extensive qualitative and quantitative multi criteria analysis for a hybrid renewable energy system applied to tribal zone - based primary health centres, and maximizing the societal parameters

Remote electrification enhances the quality of life quality of people in remote areas, with no access to electricity through distributed coverage of electricity. Due to the irregular and unbalanced fuel cost and impracticable expansion of the grid, hybrid integrated renewable energy sources become dependable substitute for remote electrification. The necessity of uninterrupted power dispatch is a prime factor for primary health centres, located in tribal and remote areas. This article proposes an integrated primary analysis like financial, production, quantity and environmental, applied to an optimum sizing of a hybrid standalone renewable energy source, which might be carried out in eight primary health centres, situated in the Gudalur Zone in Nilgiris District, Tamil Nadu, India. Four different criteria were inspected in this study, as standard loading, boost up loading, step down loading and complete renewable loading. In addition, every criterion was assessed with four kinds of PV tracking arrangements. The peak load requirement of power and energy, for eight primary health centres, was around 121.08 kW and 907.96 kWh/day respectively. HOMER Pro Micro-grid Analysis Tool was used, to analyze the different primary parameters of this study. The foremost financial parameters like COE (Cost of Energy) and NPC (Net Present Cost), could range from 0.102 to 0.118 $ per kWh and from 0.4047 to 0.5708 Million $ respectively. Annual energy production of solar PV could vary from 318.5 to 427.65 MWh. The main quantity parameter like percentage of excess electricity was obtained from 13.3 to 21.5% annually. The leading emission parameters like CO2 and CO were reported to range from 1700 to 4502 and from 7.98 to 28.1 kg per year respectively. Generator and fuel parameters, key properties of energy storage and converter, were also analyzed extensively. In addition, sensitivity analysis and social parameters were also discussed in this study. The result of this work gives a conceptual and flexible design of structure, to make possible the continuous power supply to the remote tribal area - based primary health centres, under in all situations.

Energy Maximization Absorption of Wave Energy Converter Based on Fourier Pseudo-Spectral Method and Adaptive Dynamic Programming

In this paper, a novel noncausal control framework to address the energy maximization problem of wave energy converters (WECs) with physical constraints is proposed. The energy maximization problem of WECs is a constrained optimal control problem. The proposed control framework converts this problem into a reference trajectory-tracking problem through the Fourier pseudo-spectral method (FPSM) and utilizes the online tracking adaptive dynamic programming (OTADP) algorithm to realize real-time trajectory tracking for practical use in the ocean environment. Using the wave prediction technique, the optimal trajectory is generated online through a receding horizon (RH) implementation. A critic neural network (NN) is applied to approximate the optimal cost value function and calculate the error-tracking control by solving the associated Hamilton-Jacobi-Bellman (HJB) equation. The proposed WEC control framework improves computational efficiency and makes it feasible for the online control of the WEC in practice. Simulation results show the effects of the receding-horizon implementation of FPSM with different window lengths and window functions, while verifying the performances of tracking control and energy absorption of WECs in two different sea conditions.

The Influence of Wave Characteristics, Tides, and Installation Conditions of L-Shaped OWC Wave Energy Converter on Energy Absorption Capability

The Influence of Wave Characteristics, Tides, and Installation Conditions of L-Shaped OWC Wave Energy Converter on Energy Absorption Capability

Feasibility Study of a Nonlinear Wave Energy Converter With Variable Buoy Geometry

Feasibility Study of a Nonlinear Wave Energy Converter With Variable Buoy Geometry

Viscous effects on the hydrodynamic performance of a two-body wave energy converter with a damping plate

In this study, the hydrodynamic forces and power absorption performance of an autonomous underwater vehicle (AUV)-based two-body wave energy converter (2BWEC) are investigated. A theoretical model is developed within the framework of linear potential flow to solve for added mass, radiation damping, and wave excitation force using the matched eigenfunction expansion method (MEEM). A computational fluid dynamics (CFD) model is employed to account for vortex-shedding effects of the floater and inner cylinder with a damping plate under various excitation conditions. Empirical formulas for supplementary added mass and drag coefficients caused by flow separation are proposed based on curve-fitting the differences between CFD results and MEEM calculations. These formulas are integrated into motion equations to enhance accuracy in evaluating the power absorption of the 2BWEC. It has been found that in the context of viscous flow, both the added mass and damping coefficients are increased, particularly for the inner cylinder with a damping plate. In addition, the viscous hydrodynamic coefficients exhibit strong dependence on the Keulegan–Carpenter number, while showing insensitivity to changes in the frequency parameter β. The supplementary (viscous) added mass provides additional inertia for the AUV with a limited mass itself, which is advantageous for the power absorption of the AUV-based 2BWEC. Conversely, the presence of viscous damping from the damping plate impedes wave energy capture.

Permanent Magnet Generator Testing for Low-Power Off-Grid Oscillating Water Column Wave Energy Converters

Permanent Magnet Generator Testing for Low-Power Off-Grid Oscillating Water Column Wave Energy Converters

Performance analysis of a novel hybrid device with floating breakwater and wave energy converter integrated

As a kind of clean energy, wave energy has attracted increasing attention in recent years. However, due to its high cost and low efficiency, wave energy has not been widely commercialized worldwide. According to previous research works, the combination of wave energy devices and floating breakwaters can reduce the cost of wave power generation devices efficiently. In this paper, a hybrid device with wave energy converter (WEC) and flexible porous floating breakwater integrated is proposed. The hydrodynamic performance of this device is studied by numerical simulation based on Reynolds-Averaged Navier–Stokes (RANS) method which has been validated through experimental results. Based on this, a series of numerical simulations are performed under different power take-off stiffness (KPTO) and different power take-off damping coefficient (CPTO) to calculate the motion and transmission coefficient of the device. By comparing the numerical results, the influence of KPTO and CPTO of the hybrid device on its wave attenuation performance and energy conversion efficiency are analyzed. The results indicate that under the incident waves of period 0.56 s and 0.89 s, the recommended value of KPTO is 3.0 N/m and 0.5 N/m respectively. While for incident waves of period 0.56s, in order to achieve better wave attenuation performance and power generation efficiency, the recommended value of CPTO should be between 10.55 Ns/m and 14.23 Ns/m. On this basis, the influence of the size of breakwater on the wave attenuation performance and power generation efficiency of the hybrid device is also discussed. Moreover, through a cost analysis, it can be inferred that the utilization of the baseline model is more economically viable.

Analysis of Resonance Efficiency According to Length and Entrance Depth of Channel Resonance Part of Multi-Resonance Wave Energy Converter

Multi-resonance wave energy converter can generate efficient power generation by complexly utilizing the resonance phenomenon of waves even when waves propagate normally. As the wave is amplified by resonance, the power generation efficiency of the multi-resonance wave energy converter increases, and the shape of the resonance part needs to be optimized to maximize power generation efficiency. The multi-resonance wave energy converter amplifies waves in the seiche resonance part and the channel resonance part. In this study, CFD numerical experiments were performed under various conditions such as the length and location of the channel resonance part to analyze the sensitivity for each condition and derve the optimal shape of the channel resonance part.

Developing an optimization framework for capacity planning of hydrogen-based residential energy hub

— This paper introduces a comprehensive modeling approach for optimizing the capacities of various energy converters and storage systems within a residential Energy Hub (EH). The model focuses on minimizing energy supply costs to customers while maximizing the utilization of renewable and hydrogen-based technologies. Through the optimization process, we determined that implementing CHP units in the EH could reduce total costs by approximately 78% with green tax incentives and by 46.7% without them. Additionally, the inclusion of an incentive to the EH resulted in a 27.2% reduction in total costs imposed on subscribers.The study also evaluates the impact of uncertainties in photovoltaic (PV) electricity generation, demonstrating the benefits of using stochastic optimization over deterministic methods. The results indicate that the economic advantage of this approach over deterministic methods is 86.75%–95.74% greater, depending on the scenario. Sensitivity analysis further reveals that the investment costs of fuel cells significantly influence the optimal capacity design and economic viability of the EH model.

FVCOM-CFD model-based study of hydraulic turbine arrays in Mount Putuo tidal current energy test site

In recent years, China has started to vigorously promote the research of tidal energy power generation technology; and during site testing of tidal energy converters, the distributed tidal energy converters will produce a certain effect on the flow field of the sea area. In this paper, on the basis of a tidal current energy test site established in the sea area between Mount Putuo Island and Hulu Island in Zhoushan city, Zhejiang Province, a far-field mathematical model of a three-dimensional FVCOM model was established, and in conjunction with the TSE evaluation method optimized by incorporating flow characteristic parameters. Compared to traditional assessment methods, the research aims to mitigate the influence of shallow water high-flow-speed regions and complex terrain in the test site area. Use the analysis results as CFD input conditions to perform pseudo-instantaneous numerical simulation to investigate the impact of different deployment angles on the power characteristics of hydraulic turbines, thereby providing ideas for optimizing the arrayed arrangements of tidal energy converters.