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Variable Frequency Control of a Photovoltaic Boost Converter System with Power Quality Indexes Based on Dynamic Phasors
摘要： Dynamic phasors modeling technique has demonstrated to be a good methodology for modeling oscillatory dynamic systems such as electric machines, power electronics and FACTS. Its main advantages are accuracy and fast simulation. However, something that has not been much exploited, is that Fourier coefficients can be used to compute the voltage module at some specific frequency for example, and with this extra information design new control algorithms to improve the behavior of the system. In this work, an extended model of a PV-boost converter system is developed, considering the main harmonics of the system that appear for a wide range of operation. Then, with this extra information contained in the harmonics, two new approaches are proposed: 1) Design of a variable frequency control of the boost converter to improve the quality of the output voltage under irradiation and load changes, and 2) Definition of power quality indexes for monitoring oscillatory behavior. Simulation results demonstrate the proposal effectiveness, establishing the mathematical basis and analyzing the dynamics of a 12.8 kWp photovoltaic system under different scenarios of operation.
关键词： variable frequency control,Dynamic phasors modelling,PI controllers,photovoltaic boost converter,power quality indexes
更新于2025-09-12 10:27:22
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Numerical modelling and experimental validation of thermal history of titanium alloys in laser beam melting
摘要： During selective laser melting processes parts will heat up with each layer depending on the geometry and surrounding powder material. This leads to process boundary conditions that are not certainly defined and can induce unstable melt pool sizes. These will have an influence on surface roughness and dimensional accuracy. One way to deal with this is an individual adaptation of process parameters, but without knowing the exact thermal boundary conditions in each layer one will not be able to adapt the parameters properly. In this paper a model for prediction of the macroscopic temperature history is presented and experimentally calibrated. A sample with characteristic features like overhanging’s was designed. These samples were produced by selective laser melting and simultaneously monitored by an infrared camera to calibrate the boundary conditions of a numerical model. This lays the foundation for part individual adaption of process parameters to improve the quality of SLM parts.
关键词： Experimental Validation,Numerical Modelling,Titanium Alloys,SLM
更新于2025-09-12 10:27:22
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Model assisted closed-loop control strategy for selective laser melting
摘要： Selective laser melting is a growing technology for the production of complex metal parts. However, the workpiece heat conduction differs for different points due to its geometry, which results in a varying melt pool temperature and a varying part quality. A desired closed-loop control of the melt pool temperature is currently missing, because the production machines have no suitable sensors or the slow measurement hinders the in-process control. For this reason, a novel control approach is presented and verified by a proof-of-concept experiment. The control consists of a model-based feedforward control using a finite element heat simulation in combination with a robust feedback control employing a pyroelectric sensor. Simulation and experimental results prove a reduction of the temperature deviation of up to 73 % compared to an open-loop approach for the tested demonstration geometry. The feedback control concept is further shown to be capable of achieving cycle durations <50 μs, which enables in-process control.
关键词： Control,feedback control,simulation,modelling,selective laser melting
更新于2025-09-12 10:27:22
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Efficient micro processing with high power femtosecond lasers by beam engineering and modelling
摘要： Hybrid femtosecond lasers today deliver output powers of several hundred watts. Translating the available power into high-speed micromachining requires new approaches such as beam delivering tools with suitable synchronization of the laser pulses. We study the interest of rapid scanning systems or multi-beam shaping but also a rapid estimation of the ablation efficiency using a simple engineering model.
关键词： femtosecond processing,femtosecond ablation modelling,high power ultra fast lasers,beam shaping
更新于2025-09-12 10:27:22
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Study of correlation between edge roughness and gas flow characteristics in laser beam fusion cutting
摘要： Fiber laser fusion cutting trials on AISI 304 stainless steel sheets of 10 mm thickness were performed with the aim to gain further insights into the striation formation process on cut edges. The study is based on a factorial Design-of-Experiment (DoE) approach with consideration of laser power, focal plane position, gas pressure, nozzle stand-off and nozzle diameter as control factors. Analyzed responses include the achievable cutting speed, the cut kerf geometry and the cut edge roughness. In addition, numerical simulations of the cutting gas flow were carried out for adapted kerf geometries and gas parameters. The evaluation of these results reveals strong correlations between experimental roughness values and the numerically computed rear-directed shear stress component within the transition zone between cutting front and cut edge surface. This finding supports the hypothesis that the particular characteristics of the boundary layer zone of the cutting gas flow affects the structure and roughness of cut edges.
关键词： Laser beam fusion cutting,edge roughness,modelling and simulation,gas flow characteristics,design-of-experiments
更新于2025-09-12 10:27:22
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Multi-material modelling for selective laser melting
摘要： Selective Laser Melting (SLM) is a powder-bed Additive Manufacturing (AM) process which uses a laser beam to fully melt the powders layer upon layer to build a 3D part. While most studies are conducted on SLM using single material, the application of multi-materials using this technology can offer more advantages than the conventional manufacturing methods. Complex multi-materials parts can be built which conventional manufacturing methods are unable to due to their restriction in design of freedom. However, the SLM process has its own limitations in producing multi-material parts. Since SLM uses a powder bed to build parts, the use of different powder materials in the powder bed will result in contamination of the unused powder, rendering unnecessary wastages. Therefore, using modelling techniques to attain the optimized parameters before conducting the actual experiment to verify its validity will aid in reducing wastages, leading to cost saving. To study the effects of the interface of different materials during the laser scanning, a model was simulated to observe the melting process. An open-source LAMMPS (Large-scale Atomic Molecular Massively Parallel Simulator) software uses Molecular Dynamics (MD) to simulate the melting process. The materials used for the simulations are iron (FE) and aluminum (Al). The modelling is extended to multiple layers to allow the observation of the bonding between layers.
关键词： Multi-material modelling,Additive Manufacturing,Selective Laser Melting
更新于2025-09-12 10:27:22
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Integrative modelling and optimisation of a desiccant cooling system coupled with a photovoltaic thermal-solar air heater
摘要： An integrated model of a desiccant cooling system with a hybrid photovoltaic thermal collector-solar air heater (PVT-SAH) was developed and coupled with a building model to enable a performance evaluation and optimisation of the system. A double pass PVT-SAH system that incorporates heat pipes was used to increase the air temperature of the PVT-SAH outlet in order to regenerate the desiccant in a desiccant wheel. The integrated model was then used to quantify the performance of the hybrid desiccant cooling system in terms of Solar Fraction (SF) and the Coe?cient of Performance (COP) and its response to the various sizes of PVT-SAH systems. The model outputs showed that the selection of the PVT-SAH design parameters can be critical in improving the system’s utilisation in a desiccant cooling process. For a commercial building case study in a hot and humid climate, the annual Solar Fraction and the electrical COP of the cooling system reached up to 96.6% and up to 19.8 respectively, when the design of the PVT-SAH was optimised. The optimal electrical COP was higher than those for non-optimal designs that ranged from 0.6 to 15.1. The minimum size of the PVT-SAH that is required for the hybrid desiccant cooling system to exceed a typical COP for commercial buildings (2.6–3.0) was found to be 0.35 m2 per m2 of the conditioned ?oor area.
关键词： Desiccant cooling system,Integrated modelling of solar desiccant systems,Photovoltaic thermal collector-solar air heater,Design optimisation
更新于2025-09-12 10:27:22
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Thickness validation of modeling tools for laser cutting applications
摘要： Laser cutting of metal sheets is a well-established industrial process, however, major process changes are constantly being introduced by newer technologies, e.g. new laser technologies, higher power sources, polarization and beam shaping control units, and gas flow optimizations. The multi-physical nature of the laser cutting process makes detailed simulations complex and demanding in terms of computational and implementation efforts. The gap between accurate modeling and industrial requirements makes an experimental approach often more economically realistic. Nevertheless, efficient assessment models that utilize a trade-off between model complexity and accuracy of the response to be assessed are attractive. Such models can be used for further technological development by efficiently supporting engineers in designing and selecting optical systems. This paper revisits model assumptions of an in-house developed laser cutting model as it is validated for larger thicknesses. This model assesses polarization and beam shaping effects on the cutting performance of thin sheets. In this work, dedicated cutting experiments to assess the maximum cutting speed of stainless steel 304L of 2, 6, and 10 mm thickness for a wide range of focal point positions are conducted and compared to the model prediction. The results show that R2 of this comparison decreases from 0.99 for 2 mm thickness, to 0.58 for 10 mm. It can be concluded that the trend prediction accuracy degrades for thicker plates. Analysis of the experiments and simulation data for 10 mm plates reveals two possible phenomena that become more important with thickness: multiple reflections and instability of the melt flow dynamics.
关键词： Thickness,Modelling,Prediction,Maximum cutting speed,Laser cutting
更新于2025-09-12 10:27:22
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[IEEE 2019 8th International Conference on Modeling Simulation and Applied Optimization (ICMSAO) - Manama, Bahrain (2019.4.15-2019.4.17)] 2019 8th International Conference on Modeling Simulation and Applied Optimization (ICMSAO) - Thermal Analysis in Laser Surface Alloying of Ti6Al4V with TiC
摘要： Laser Surface Alloying employs high laser power density to melt alloying material and a portion of the underlying substrate to form an alloyed layer over substrate. As melting temperature of Ti alloys is very high, it poses difficulty in alloying using conventional methods. Titanium alloys are vulnerable to induced thermal stresses at high temperature. In this study thermal analysis of laser surface alloyed Ti6Al4V with TiC at different laser power and laser spot diameter is modelled. Melt pool depth and developed thermal stresses at different process parameters are predicted. Subsequently, model is verified with published experimental results. It is observed that developed model is adequate in predicting pool depth with 6.43% error. The von-Mises stress is observed to be lower than the yield strength of the material, indicating less possibility of thermally induced cracks.
关键词： Thermal stress,Numerical modelling,Pool depth,Laser surface alloying,Thermal analysis
更新于2025-09-12 10:27:22
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Finite element prediction and validation of residual stress profiles in 316L samples manufactured by laser powder bed fusion
摘要： Laser powder bed fusion (LPBF) processes continue to grow in popularity and much progress has been made in recent years. However, due to the extreme thermal gradients present, significant residual stresses are inevitable and can be detrimental during component service. Critical to mitigating these stresses effectively is the ability to model the thermo-mechanical process accurately and efficiently. A simplified FE modelling methodology has been developed and applied to a cylindrical component built in both the horizontal and vertical orientations. The resulting distortion of the parts following a slitting process was compared with those predicted by the model and good agreement to within 5% was found. The final stress fields in the components were predicted by the model and then examined to assess the principal stresses driving the distortion and the causes of difference in results between the two build orientations.
关键词： LPBF,residual stress,finite element modelling,Laser powder bed fusion,distortion
更新于2025-09-12 10:27:22