| Referring to our country coal is main power supplies, renewable energy such assolar energy and wind energy are given special attention by researchers aiming toresolve conflicting between dry up of coal and increasing requirement of power supply.Microgrid is a helpful complementarity to the utility grid, it can not only solveimpacting to the utility grid by the distributed generation, but also can improve thepower supply quality greatly, promote reliability and security of power supply. So itpossesses extensive application field and prospect. Based on researches of home andabroad scholar, this thesis focuses on the microgrid, voltage stability, photovoltaicsystem short-term power forecasting and islanding detection have been researched.Discussing the feasibility and necessity of optimizing our national microgridbased on analyzing development of renewable energy and requirement of society.Aiming at security and reliability of microgrid, isolating voltage source converterstructure was adopted, for required isolation and voltage boosting. The microgrid candisconnect from the utility grid and transfers into intentional islanding operation modeor unintentional islanding operation mode when a fault occurs in the main grid. Whenislanding occurs, the power balance between supply and demand does not match, sothat voltage will fluctuate on point of common coupling at the moment. thecooperative control strategy of the voltage controller and other controllable microsources is studied based on voltage source converter structure. The voltage controllerresponds in milliseconds by the primary control, it should play an important role inmaintaining the frequency and the voltage of the microgrid during islanded operation.In islanded operation, by proper power-balancing action of the voltage controller, thefrequency and the voltage of the microgrid can be regulated at the normal values.However, the control capability of the voltage controller for balancing betweengeneration and consumption may be limited by its available system capacity. Therefore,the power output of the voltage controller should be brought back to zero as soon aspossible by the secondary control in order to secure the maximum energy reserve. Study on the droop control without connection line of grid-connected inverter andsharing load power between DGs in secondary control fused with the deducedstate-space models of the microgrid including all the converters, improving reliabilityof optimization DG.Take photovoltaic array system for example, study on particularity anduniversality of microgrid key technology. Based on discontinuousness, uncertainty ofoutput power, recurrent neural networks output power forecasting model waspresented. Because gradient algorithm has some shortcomings such as low precisionsolutions,slow search speed and easy convergence to the local minimum points.Dynamic Ant Colony algorithm and Self-Adaptive Ant Colony algorithm are first usedto determine the weight of recurrent neutral networks, then gradient algorithm is usedto regulate the weight to find the best weight. These algorithms can be applied to keyparameter forecasting in addition to photovoltaic array system.Integrated active current disturbing and voltage positive feedback islandingdetection method was proposed and designed. None detection zone was reduced by themethod, furthest avoiding unintentional islanding operation and damage to powersystem security. According to the simulation, faster detection speed was realized.The system of regulating voltage of PCC use the active power and reactive powersupplied from the voltage controller corresponding to different voltage level microgridwere researched. Two mode regulation including active power hysteresis moderegulation and integrated active and reactive power mode regulation of voltagecontroller were conducted. Experimental studies were conducted on low-voltage andmedium-voltage system which indicating well engineering application value of twomode regulation...
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