The transformation of passive distribution systems to more active ones thanks to the increased penetration of distributed energy resources, such as dispersed generators, flexible demand, distributed ...storage, and electric vehicles, creates the necessity of an enhanced test system for distribution systems planning and operation studies. The value of the proposed test system, is that it provides an appropriate and comprehensive benchmark for future researches concerning distribution systems. The proposed test system is developed by modifying and updating the well-known 33 bus distribution system from Baran & Wu. It comprises both forms of balanced and unbalanced three-phase power systems, including new details on the integration of distributed and renewable generation units, reactive power compensation assets, reconfiguration infrastructures and appropriate datasets of load and renewable generation profiles for different case studies.
Owing to the advantages of simple structure, higher power density and reliability, unidirectional five-level rectifiers are attractive solutions for high-power medium-voltage non-regenerative ...applications such as the electric vehicle charging pile, telecommunication power and lasers power. However, the existing five-level unidirectional rectifiers use more switching devices or flying capacitors (FCs). This will reduce the power density and increase complexity of the system. To address this issue, this paper presents a three-phase five-level unidirectional rectifier with reduced components. It uses only three active switches and one FC per phase. Compared with most similar rectifiers, the number of active switching devices and floating capacitors has been reduced by 25% and 50%, respectively. Consequently, the proposed rectifier has the comprehensive merits in term of simple structure and higher power density of the system. The operating principles of the proposed topology, control strategy, modulation scheme and comparison study are presented in depth. Finally, a 3 kW three phase experimental prototype is built to verify the validity and flexibility of the proposed topology.
The continuous granular flow under gravity extensively exists in chemical processes, and the dynamic behaviors of granular flow under different gas–liquid environments are investigated by synchronous ...slide‐type high‐speed photography. Results show that a hexagonal arrangement is observed after three‐stage densification in wet granular flow, while these structures are almost absent in the dry system. Further analysis shows that under the induction of liquid, the special cavity collapse in stage І is the pre‐condition of granular densification, and the subsequent densification in stage ІІ for the first time gives the experimental proof for the hypothesis that energy barriers exist and depend on the friction characteristics, and the cage effect in stage ІІІ provides a guarantee for the formation of a hexagonal contact network. Besides, three‐stage densification in the three‐phase system mainly occurs in the region with low gas and liquid velocities (G* < 0.716 and L* < 0.023 in this work).
Lightweight autonomous underwater vehicles (AUVs), powered by rechargeable batteries, are widely deployed in inshore surveying, environmental monitoring, and mine countermeasures. While providing ...valuable information in locations humans have difficulty accessing, limited battery capacity of such systems prevents extended mission times. In order to extend mission times, this paper proposes a three-phase wireless charging system that could be used in a field-deployable charging station capable of rapid, efficient, and convenient AUV recharging. Wireless charging should not, however, affect instrumentation located inside the AUV. Thus, a three-dimensional finite element analysis tool is employed to study the characteristics of magnetic fields inside the AUV during three-phase charging. Simulation results reveal that the magnetic field generated by the proposed three-phase coil structure is concentrated away from the center of the AUV, where instrumentation would nominally be located. Detailed circuit analysis and compensation method to achieve resonance on both transmitter's and receiver's sides are also given. To validate the proposed concept, a three-phase wireless charging system is developed. Experimental results demonstrate that the system is able to transfer 1.0 kW with a dc-dc efficiency of 92.41% at 465 kHz.
In this study, we use a combined CFD-Discrete Element Method to assess predictive capabilities and numerical implications of a coarse-graining technique in Wurster fluidised-bed coaters. We ...investigated both hydrodynamics and heat and mass transfer and conducted simulations of a full three-phase system for the original and three coarse-grained systems, analysing velocity distributions, macroscopic solid stresses, moisture content and phase temperatures. We achieved a logarithmic simulation speed-up by aggregating up to 64 original particles into each coarse grain. This was accomplished while maintaining fidelity to the original CFD-DEM system in terms of reproducing with high accuracy macroscopic granular flow properties in different regions of a coater (drying, tube and bed regions). By integrating a liquid spray and humid air, we demonstrated that the phase temperatures were accurately predicted within the coarse-grained system, with a high capability of delivering liquid spray distributions with the same uniformity and drying. We also give arguments for choosing a certain degree of coarse-graining as a compromise between a desired reduction of computational costs and a trustworthy reproduction of granular-flow physics encountered in different regions of a Wurster bed. Our findings pave the way to using CFD-DEM to industrially-scaled Wurster-bed systems, which is currently unfeasible due to prohibitive computational costs.
Display omitted
•Logarithmic simulation speed-up in CFD-DEM via coarse-graining (particle scaling).•Modelling of solid, gas, and liquid phases in the Wurster fluidised-bed coating process.•Evaluation of granular flow rheology, with analysis of inter-phase momentum, heat, and mass transfer.•Experimental validation of CFD-DEM predictions with PEPT data.
•Dependence of harmonic spectrum of PV current on solar irradiance is considered.•Update of PV current harmonic spectrum is included in the optimization problem.•Optimization problem is solved by ...both probabilistic and deterministic methods.•Optimal PV penetration levels are obtained in unbalanced distribution systems.•PV and load uncertainties are considered in the optimization problem.
Photovoltaic (PV) system is one of the most important technologies among the renewable energy resources. With the increasing penetration of PV systems in distribution networks, harmonic distortions also rise due to the inevitable effects of PV inverters. Therefore, determination of the optimal PV penetration level is a vital issue in terms of preventing power quality problems. In this paper, probabilistic and deterministic approaches are proposed to determine the optimal penetration levels of PV systems in unbalanced distorted distribution networks by taking into account the uncertainty of load profile and the intermittent characteristic of PV system output power due to changes in solar irradiance. The Interior Point (IP) method is applied to solve the optimization problem in conjunction with the Monte Carlo Simulation (MCS) and K – means clustering, respectively. The methodology is based on the dependence of the harmonic spectrum of PV injected current on solar irradiance. The harmonic power quality parameters are calculated by using loop frame of reference based three phase harmonic power flow method in the unbalanced distribution network, where the nonlinear loads and PV systems are interfaced. The allowable PV penetration levels are determined based on power quality parameters comprising of total harmonic voltage and individual harmonic voltage distortions, and RMS bus voltage limits.
The bridge arms of traditional three-phase multilevel converters are independent of each other; thus, more active switches and passive diodes are required. In order to reduce the number of devices, a ...coupled three-phase converter architecture, which is suitable for both dc-ac and ac-dc converters, is presented. Based on this architecture, a ten-switch three-phase three-level (10S-3P-3L) inverter is proposed in this article. The proposed topology employs only ten active switches and no additional diodes, which helps to cut size, weight, and costs of system. The proposed space vector modulation enables 10S-3P-3L inverter to operate full modulation indexes. A comparison between the proposed inverter with some existing topologies in terms of device voltage and current stresses, conduction loss, switching loss, and other parameters is made to highlight its excellent performance. Moreover, the experimental results from a 3-kW experimental prototype reveal that the proposed inverter offers superior power quality.
Display omitted
•Low growth rate and competing heterotrophs continue to challenge nitrification.•Low liquid velocity and higher carrier fraction in riser enhance nitrification.•A three phase ...mathematical model was applied for predicting low liquid velocity.•Geometry, aeration, and carrier characteristics were major design criteria.•Construction of a 1000L pilot plant verified the design and liquid velocity.
In this study, a 1000L pilot scale internal loop airlift bioreactor was operated and compared to a mathematical model to determine the best design for optimal supply of oxygen for nitrification and sufficient air for biomass fluidization. The design model is based on parameters such as geometry, carrier density, and airflow of the 1000L pilot scale bioreactor. The model predicts a range of superficial air velocities (0.009–0.013m/s) under which the airlift bioreactor was fluidized. Three superficial air velocities (0.009m/s, 0.011m/s and 0.013m/s) were experimentally tested in the pilot plant and the obtained circulation velocities were compared with the predicted design scenarios. The predicted velocity was in agreement with the measured velocity. The aim of the mathematical model and the calculations of different geometry scenarios was to define the optimal geometry design for the physical model. The results show that the ratio of the cross-sectional area between the riser and the downcomer of 1.33 resulted in the lowest superficial liquid velocity of 0.076m/s in the riser at a relative low superficial air velocity of 0.011m/s and a carrier density of 1030kg/m3. This bioreactor design enabled longest retention time of particles in the oxygenated riser.
In this article, a robust three-phase grid synchronization technique has been proposed for rapid detection of fundamental frequency, phase, and amplitude. The widely accepted phase locked-loop (PLL) ...algorithms possess complex architectures and require tedious tuning process for attaining a good stability margin. In order to surpass the shortfalls of PLL algorithms, a computationally efficient, stable, and open-loop scheme has been reported in this article. A novel two consecutive samples based frequency estimator is developed for fast detection of the fundamental frequency. Moreover, an efficient hybrid prefiltering approach is implemented based on the demodulation of the grid voltage signal. Additionally, the combination of a delayed signal cancellation operator and a band-pass filter allowed rapid rejection of dc-offset and harmonics, respectively. In the event of a grid voltage imbalance, the instantaneous symmetrical component method is a rescuer for the rejection of the fundamental negative sequence component without any delay. Subsequently, overall transient response time of the scheme is observed to be improved. On the other hand, the fundamental positive sequence component facilitates the estimation of amplitude and phase angle information. Importantly, the dynamic performance of the proposed scheme has been experimentally validated in presence of various grid disturbances.
PDF
