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The Grid-connected Control Strategy For Microgrid And Analysis Of Stability

Posted on:2009-01-13Degree:MasterType:Thesis
Country:ChinaCandidate:T ZhangFull Text:PDF
GTID:2132360278963836Subject:Power system and its automation
Abstract/Summary:PDF Full Text Request
Along with economic development, technical progress and requirements for environment, the traditional power production and transmission are changing gradually. The technology of distributed generation (DG) is quickly applied to the distribution systems. In order to reduce the adverse effect caused by DG units and make full use of the positive assistance function of DG units, the systemic approach, in which the generator and the matched load are regarded as a subsystem or a"microgrid", is adopted. The microgrid serves the distribution system, and can operate both in the grid-connected mode and the islanded mode and smoothly switch between the two modes.In this paper, some distributed sources are introduced and the models of three-phase synchronous generator, microturbines, wind turbines and fuel cell generation are illustrated. In addition, two interface models between synchronous generator and power electronic facilities are presented according to different generation forms of DG units. The wireless parallel mode is adopted in the parallel operation of DG units in the microgrid. An self-adaptive pre-synchronization scheme is put forward to solve the starting phase error of the wireless parallel DG units. The digital phase locked technology is adopted in this system, which can not only lock the phase and frequency of output voltage, but also effectively enhance the capability of immunizing to interference of the system.This paper mainly researches the grid-connected control strategy for microgrids. The automatic quasi-synchronization device plays an important role in the power system of grid-connected. This paper also analyses the conditions of grid-connected, which means the difference of magnitude,frequency and phase of the voltages between the two sides of breaker must be small enough. The differential phase must be zero at the moment of closing breaker when the frequency and magnitude of the microgrid is satisfied. For using the invariant advanced insertion time to make the differential phase between microgrids and the public network is 0 degrees at the moment of grid-connected. In addition, the conditions that the active power and load satisfy when the microgrid stably operates in the grid-connected mode are verified by deducing. Furthermore, the strategies of over frequency generator removal and under frequency load shedding are put forward in this paper. Finally, the above-mentioned viewpoints are verified with the PSCAD/EMTDC based simulation tests.
Keywords/Search Tags:microgrid, wireless parallel, automatic quasi-synchronization, grid-connected, stability
PDF Full Text Request
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