Research On Frequency Regulation Scheme Of Islanded Microgrid

With the penetration of distribution generators linked on middle or low voltagegrid, the disadvantage is more and more obvious, therefore it encourages thedevelopment of microgrid. The microgrid can operate on grid connected andislanded mode. The microgrid must be converted to the operation mode which hasthe ability of regulation the frequency to guarantee the normal operation, andprepare to the resynchronization when it operate on islanded mode. So the projecton the frequency regulation method of islanded microgrid is built under the help of“863” planning.Firstly, model the commonly used intermittent new resources. The two stagethree phase grid connected photovoltaic power system adopts MPPT and active,reactive decoupled control is built, and analyzed the characteristics of its operation.The math model of wind generation power system using doubly fed inductiongenerator (DFIG) is analyzed in detail, study the maximum power point tract(MPPT) control under fixed blade angle and the decoupled control of power, whichbuilt the base of following research.Secondly, research on the frequency control strategy of microsources inmicrogrid. The frequency control scheme of battery system based on powerelectrical converter is searched. The control method introduced voltage and currentfeedback of equal load is proposed which benefit the power quality. The firstfrequency control of DFIG considering the variable wind speed is designed whichreduces the frequency error of microgrid system; Starting from the function of windturbine, The MPPT control under variable blade angle is proposed using the fittedcurve of the perfect blade top speed ratio with maximum output power of windturbine. The polynomial relation between blade and maximum wind energycoefficient is fitted, thereupon the relation between maximum power of blade angleis built. Based on those, the secondary frequency control of DFIG is proposed. Thesimulation results indicate the frequency controller developed the frequency quality.Lastly, a frequency regulation method is proposed concerning the economy andregulation speed for islanded microgrid. Classify the microsources to preferentialand conventional generating sets depending on the various operated characteristicsof every microsourses. The different microsources have the various mission andpriority of frequency regulation. Through setting sufficient criteria to control thepreferential microsources to participate the frequency regulation, and theconventional microsources take part in the frequency control after the preferentialone reach the power limit. The simulation results demonstrate the validity and necessary of frequency scheme for islanded microgrid.