Current Issue : October - December Volume : 2016 Issue Number : 4 Articles : 5 Articles
In a low-voltage islanded microgrid powered by renewable energy sources, the energy storage systems (ESSs) are considered\nnecessary, in order to maintain the power balance. Since a microgrid can be composed of several distributed ESSs (DESSs), a\ncoordinated control of their state-of-charge (SoC) should be implemented, ensuring the prolonged lifespan. This paper proposes a\nnew decentralized control method for balancing the SoC of DESSs in islanded microgrids, without physical communication. Each\nDESS injects a current distortion at 175Hz, when its SoC changes by 10%. This distortion is recognized by every DESS, through\na phase-locked loop (PLL). In order to distinguish the origin of the distortion, each DESS injects a distortion of different time\nduration. This intermediate frequency has been selected in order to avoid the concurrence with the usual harmonics. The DESSs\ntake advantage of this information and inject a current proportional to the SoC. Implementing this strategy, a comparable number\nof charging/discharging cycles for each DESS are achieved. Furthermore, an active filter operation, implemented in the dq rotating\nframe for each individual harmonic, is integrated in the control of the distributed generation units, supplying nonlinear loads with\nhigh-quality voltage. The effectiveness of this method is verified by detailed simulation results...
A 360Ã? twisted helical capacitance sensor was developed for holdup measurement in\nhorizontal two-phase stratified flow. Instead of suppressing nonlinear response, the sensor was\noptimized in such a way that a ââ?¬Ë?sine-likeââ?¬â?¢ function was displayed on top of the linear function. This\nconcept of design had been implemented and verified in both software and hardware. A good\nagreement was achieved between the finite element model of proposed design and the approximation\nmodel (pure sinusoidal function), with a maximum difference of +1.2%. In addition, the design\nparameters of the sensor were analysed and investigated. It was found that the error in symmetry\nof the sinusoidal function could be minimized by adjusting the pitch of helix. The experiments of\nair-water and oil-water stratified flows were carried out and validated the sinusoidal relationship\nwith a maximum difference of +1.2% and +1.3% for the range of water holdup from 0.15 to 0.85.\nThe proposed design concept therefore may pose a promising alternative for the optimization of\ncapacitance sensor design....
The adoption of silicon carbide (SiC)\nMOSFETs and SiC Schottky diodes in power converters\npromises a further improvement of the attainable power\ndensity and system efficiency, while it is restricted by several\nissues caused by the ultra-fast switching, such as phase-leg\nshoot-through (ââ?¬Ë?crosstalkââ?¬â?¢ effect), high turn-on losses,\nelectromagnetic interference (EMI), etc. This paper\npresents a split output converter which can overcome the\nlimitations of the standard two-level voltage source\nconverters when employing the fast-switching SiC devices.\nA mathematical model of the split output converter has been\nproposed to reveal how the split inductors can mitigate the\ncrosstalk effect caused by the high switching speed. The\nimproved switching performance (e.g. lower turn-on losses)\nand EMI benefit have been demonstrated experimentally.\nThe current freewheeling problem, the current pulses and\nvoltage spikes of the split inductors, and the disappeared\nsynchronous rectification are explained in detail both\nexperimentally and analytically. The results show that, the\nsplit output converter can have lower power device losses\ncompared with the standard two-level converter at high\nswitching frequencies. However, the extra losses in the split\ninductors may impair the efficiency of the split output\nconverter, which is verified by experiments in the\ncontinuous operating mode. A 95.91% efficiency has been\nachieved by the split output converter at the switching\nfrequency of 100kHz with suppressed crosstalk, lower turnon\nlosses, and reduced EMI.\nIndex Termsââ?¬â?Silicon carbide (SiC), split output\nconverters, crosstalk, efficiency, electromagnetic\ninterference (EMI).\nI....
In this paper power electronics used in PV power generation systems have been reviewed and\nmodelled. PV systems need converters for maximum power point tracking, power conditioning,\nvoltage step-up/down as necessary, and for storage charge-controlling. Inverters are needed for\nAC loads and for utility grid interfacing. The four basic DC-DC converters commonly used with PV\nsystems have been reviewed and modelled. Different DC-AC inverter types and operational architectures\nhave also been reviewed with the two-stage DC-AC inverter, with the point of common\ncoupling (PCC) at the inverter input, suggested as the most cost-effective and efficient architecture\nfor PV-based communal grids. This is because only one inverter is used for the entire system as\nopposed to an inverter for every module string, resulting in higher efficiencies, low cost, and low\nharmonic distortions when compared to systems with PCC at AC terminal. The aim of power conversion/\ninversion is to extract maximum power possible from the PV system and where necessary,\nto invert it at close to 100% as possible. Highlight: 1) DC-DC converters are necessary for power\nconditioning in PV systems; 2) DC-AC inverters are necessary for AC loads and for utility grid interfacing;\n3) DC-AC inverters are also used to control the PV systems when grid connected; 4) Best\ninverter configuration cost-effectively and efficiently allows easy system modifications....
In industries DC motor drives are very essential due to their high performance applications such\nas its reliability, ease of control, low cost and simplicity. And speed control of these motors is very\neasy due to power electronic AC-DC converters. These power electronic converters are with\nprominent low power factor and higher Total Harmonic Distortion (THD). These converters operate\nonly for short time resulting non-sinusoidal waveform. This problem of harmonic distortion\ncan be mitigated by reshaping the non-sinusoidal waveform to pure sine wave. Different wave\nshaping techniques have been developed by using different filters among which one is tuned passive\nfilter. This paper proposed power factor improvement and harmonic mitigation of AC-DC\nconverters based on separately excited DC motor using tuned passive filter. In this context experimental\nmodel is designed and results are analyzed by power quality analyzer....
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