Research On Droop Control Strategy Based On Virtual Flux In Microgrid

It is very important to find a way to generate electricity from clean energies due to the deterioration of environment and the increase demand for electricity.Microgrid technology exactly provides powerful supplement and support for traditional power supply by integrating distributed generation units,energy storage devices and converters effectively.In order to give full play to the advantages of microgrid,it is essential to study some advanced control strategies.In this paper,droop control strategy is studied.In traditional voltage-frequency droop control method,complicated multiple feedback loops,PI regulators,Park transformation are used.More seriously,there are larger frequency deviation in this method.Considering the aforementioned problems,an improved virtual flux droop control method is proposed.Further,active and reactive power allocation problems based on flux control are studied.The main work of this thesis is as follows:Firstly,traditional voltage and frequency droop control method is deduced,and the mathematical model of interface inverters is constructed and decoupled.On this basis,a droop controller is designed based on the “power-voltage-current” three-loop control strategy.The performance of traditional voltage droop control is verified by MATLAB/Simulink.Secondly,the inherent deficiencies in traditional droop control method are analyzed and a new virtual flux droop control method is derived.In consideration of the slow response speed of flux droop controller,an improved average power calculation method is proposed.In addition,conventional flux trajectory division method is replaced with an improved one to reduce flux ripples.At last,the simulation verification of improved flux droop control sheme is carried out on the MATLAB simulation platform.Finally,the application of flux-angle droop control strategy in parallel inverters is analysed in detail.The factors that affecting active power sharing are analysed.Based on this,a novel active load sharing strategy is proposed,which can achieve accurate active power allocation and zero frequency deviation simutaneously.Similarly,the factors that affecting reactive power sharing are analysed and a novel reactive load sharing strategy is proposed,which can ensure accurate reactive power sharing and voltage recovery control.The two kinds of power control strategies are both simulated by MATLAB/Simulink and the effectiveness of them is also proved.