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Research On Reactive Power Sharing Control Strategy Of AC Microgrid In Islanded Mode

Posted on:2018-09-04Degree:MasterType:Thesis
Country:ChinaCandidate:Q Y WangFull Text:PDF
GTID:2322330536480492Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
To solve the problem of the stability of distributed microsource,scholars put forward the theory of microgrid.Along with the development of microgrid,problems emerge in endlessly,such as reactive power sharing problem of microgrid in islsnded operating mode,voltage unbalance of inverter output and point of common coupling(PCC)due to the unbalanced load in microgrid.Therefore,it is of great significance to study the inverter interface control technology to solve the problem mentioned above.Droop control can make use of the local information,and the communication requirement is low,so it is an important method to realize the power sharing of parallel inverters.However,it may lead to the coupling between active power and reactive power when the line impedance of the microgrid appears as resistance,so as to impact the effect of droop control allocating reactive power.In addition,the inverter output impedance and line impedance can not be distributed according to capacity ratio strictly will result in reactive power sharing problem of the inverter.Virtual impedance do solve the problem of reactive power sharing that is the traditional droop control can not do,but how to set the virtual impedance has been a difficulty.Virtual impedance includes virtual resistance and virtual reactance.Aiming at the problem of virtual resistance seting,a virtual negative resistance method is proposed to eliminate the voltage drop caused by the line resistance;Aiming at the problem of virtual reactance seting,a control strategy of reactive power sharing is proposed by using the parameters of the inverter output.In this paper,the inverter with simple circuit structure is selected as the reference inverter,others are selected as target inverters.The virtual reactance of the target inverter is determined by the output voltage,droop coefficient,line reactance of the reference inverter and target inverter,however the virtual reactance of reference inverter is adjusted according to the inductor.In the two cases of balanced load and unbalanced load,the proposed method can improve the reactive power sharing accuracy of conventional droop control.Aiming at the problem of system voltage unbalance under unbalanced load conditions,the paper put forward a coordinated control method which can compensates the voltage unbalance of the inverter output and PCC simultaneously.The method compensates the inverter output voltage at first,it will not compensatevoltage unbalance degree of the PCC until the voltage unbalance degree of the inverter output meets the standard of power supply.This method can improve the voltage unbalance degree between the inverter output port and the PCC simultaneously.The simulation results in MATLAB/Simulink verify the validity of the proposed method.
Keywords/Search Tags:reactive power sharing, virtual impedance, droop control, parallel inverters, voltage unbalance compensation
PDF Full Text Request
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