Though microgrid technology has many advantages, stable operation with paralleled distributed generation (DG) must be ensured with proper controls. Droop control ensures distributed loading of DGs, but it has some lim...
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ISBN:
(纸本)9781538627570
Though microgrid technology has many advantages, stable operation with paralleled distributed generation (DG) must be ensured with proper controls. Droop control ensures distributed loading of DGs, but it has some limitations, namely, a large frequency deviation may occur if a large load demands reactive power sharing, the errors due to disproportional line impedance, etc. In order correct the voltage and frequency steady-state deviations of controlled inverter-based microgrids, the secondary control is needed. This paper proposes primary and secondary control for islanded microgrids (MGs) based on the P-V/Q-f droop control strategy. Based on the droop control method and the inverter's double-loop control, the primary control of hierarchical structure controls the distributed generations and loads, while secondary control allows restoration and improvement of the quality of frequency and voltage magnitude after each load change. The virtual impedance is proposed in order to improve the power sharing performance, by redesigning the converters' equivalent output impedance as pure resistance. An islanded MG test system consisting of four DGs is built in MATLAB and RT-EVENTS of OPAL-RT Technologies to illustrate the design approach. The effectiveness of the proposed control methodology is verified by offline simulation.
In this paper, a droop control strategy is presented for accurate power sharing between parallel connected inverters in an AC microgrid in autonomous mode. The proposed strategy is based on the droop control technique...
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In this paper, a droop control strategy is presented for accurate power sharing between parallel connected inverters in an AC microgrid in autonomous mode. The proposed strategy is based on the droop control technique...
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ISBN:
(纸本)9781509015948
In this paper, a droop control strategy is presented for accurate power sharing between parallel connected inverters in an AC microgrid in autonomous mode. The proposed strategy is based on the droop control techniques P-f/Q-V and P-V/Q-f, with a virtual impedance and using monitored quantities directly at the inverter. This droop control approach can be used in microgrids where communications are not reliable or not available. It allows for maintaining voltage and frequency stability and for regulating the power flows between the primary energy sources and the common AC bus. The design methodology of the control scheme under study is based on grid-supporting-grid-forming controls using multi-loop dq control. The time domain simulation is conducted, in the MATLAB/Simpowersystems environment and the RT-EVENTS toolbox from OPAL-RT is also used to model the inverters. Resulting waveforms show that the proposed method can allocate both real and reactive powers effectively and can enhance the stability of a micro-grid in the autonomous operation mode.
Bottom fishing equipment employed by scallopers and trawlers routinely damage or break important Navy Oceanographic cables resulting in substantial repair coats and unacceptable system interruption. The Civil Engineer...
Bottom fishing equipment employed by scallopers and trawlers routinely damage or break important Navy Oceanographic cables resulting in substantial repair coats and unacceptable system interruption. The Civil Engineering Laboratory (CEL), sponsored by the Naval Facilities Engineering Command (NAVFACENGCOM), has been developing and validating an engineering concept for a Deep Ocean Cable Burial (DOCB) system. This DOCB system will providethe Navy with an efficient, effective and reliable means of burying cables 3-feet deap in ocean mediments, at speeds not less than one knot, to water depths of 6,000 feet. The DOCB system b a remotely controlled machine which underruns and buries existing (previously laid) cables. It is powered and controlled from a surface ship via an electromechanical umbilica cable. The machine is self-propelled by ducted thrusters and supported on water lubricated skids. The excavation system computer an orbital vibrating plowshareand a vertical waterjet. Full-scale field testing at CEL baa keyed on three areas: •. Quantifying the reduction in drawbar force achieved by applying orbital vibration to an upward cutting plowshare. •. Evaluating a Vertically impinging jet nozzle for depth of a cut M a function of jet operating parameters. •. Demonstrating the effect on the soil drag of a flat-bottomed skid due to forcing a thin layer of water between the skid and the seafloor. The field teats of an orbital vibratory plow were performed in a 1 to 2 psi clay simllar to that found on the ocean floor. The results showed that a 70% reduction in drawbar force was achieved by applying an elliptical orbital vibration. It was also shown that the vibration feature would split or push aside buried rocks which would have stalled a conventional stationary plow. The water jet tests demonstrated that a 2 1/2-in. nozzle cuts 36-in. deep in 1 to 2 psi clay. The nozzle pressure was 75 psi and flow was 1,200 gpm. The water jet did not produce a clearly defined trench, b
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