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Control Strategies And Grid-forming Characteristics Of Microgrid Inverters

Posted on:2017-07-15Degree:MasterType:Thesis
Country:ChinaCandidate:Y N ZhangFull Text:PDF
GTID:2392330590468114Subject:Electrical engineering
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Different from synchronous generator interface,power electronic interface device used by distributed micro-source in micro-grid system lacks of inertia.Overload capability is very poor too.Slight power fluctuations may lead to serious problems of power quality.Furthermore,the position of micro-source relatively dispersed,and the line impedance is mainly resistive.Those undoubtedly bring the application of traditional droop control new problems.This dissertation proposes an improved droop control strategies based on virtual synchronous generator and analyzes its parallel operation characteristic.(1)In order to solve micro-source inverter's problem of lacking of inerter,learning from operating characteristics of synchronous generators,rotor motion equation,characteristics of primary frequency as well as characteristics of voltage regulator are introduced to construct virtual synchronous generator control strategy.The new virtual synchronous generator control strategy better simulate the external characteristics of synchronous generator,which improves the dynamic response of micro-source inverter.(2)A novel adaptive virtual synchronous generator control strategy is designed in this paper,which can flexibly adjust the inerter time constant according to need.It plays an important role when the micro-grid operating in islanded mode.The new control strategy can effectively reduce the rate of change in frequency when system load fluctuations and Guarantee less adjustment time at the same time.For the introduction of the damping coefficient affecting active power-frequency droop characteristic,setting the corresponding feedforward compensation,effectively improve the micro-source inverter active allocation performance.An improved droop control strategy based on virtual reactance is proposed based on analysis of power distribution characteristics using the traditional droop control.This method introduces stator voltage equation to the existing droop control,which makes micro-source inverters equivalent output impedance inductive,solving the problem of output power coupling.So droop control can be applied to low-voltage micro-grid system.(4)Reactive power-voltage droop control module has been improved to solve the unequal distribution of load reactive power problem caused by the line impedance.The new module compensates the voltage drop and Sustain voltage within a certain range,which can improve precision of the load power distribution between the micro-source inverter and ensure the quality of power supply.
Keywords/Search Tags:Micro-grid, Micro-source, Droop Control, Virtual Synchronous Generator, Virtual Reactance
PDF Full Text Request
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