Study On Control Strategy Of Micro-grid Inverter Based On Virtual Synchronous Generator

In the new period of the profound change of world energy pattern and constantly strengthened environmental constrains,the scale of domestic wind power and photovoltaic power generation technology is increasing rapidly.As a new inverter control strategy with good grid-connection characteristics,virtual synchronous generator(VSG)technology develops rapidly.However,it becomes a new challenge to design and optimize the control strategy of inverters based on virtual synchronous generator.In view of the above problems,the operation characteristics and operation control strategy of microgrid inverters based on virtual synchronous generator have been investigated in this thesis,and shown as follows:(1)The typical topology of the microgrid is analyzed,and the mathematical model of microgrids in the two-phase stationary coordinate system and two-phase rotating coordinate system is established;The influences of key parameters,such as moment of inertia,damping coefficient,droop coefficient dynamic and static response and stability of control systems and so on have been investigated by the root locus method.The effective ranges of key parameters have been obtained,to provide an important reference for algorithm design.Meanwhile,a MATLAB simulation platform has been established,by which the validity of the design has been verified.(2)The common adaptive parameter schemes of virtual synchronous machine are analyzed.Introducing the hyperbolic tangent function,an adaptive parameter selection method with progressive upper and lower boundary has been analyze,to avoid the dramatical variation of moment of inertia resulting in system unstability when conventional adaptive parameter methods based on frequency change rate are used,and the simulation results show that this method can not only realize the dynamic characteristics of control systems but also ensure the parameter change in a safe range.(3)The circulation problem of parallel systems in practical application is studied,and it is pointed out that the circulation problem is essentially a power distribution problem.In order to reduce the circulation caused by mismatching of line impedance and improper selection of control parameters,realize accurate power distribution in parallel virtual synchronous system,the configuration principle of control parameters and virtual impedance strategy of parallel virtual synchronous system under different capacity ratio is studied.Simulation results show that the proposed method is effective and the virtual impedance can restrain the circulation.(4)Two 5k W virtual synchronous generator experiment platforms were built,and the grid-connected,isolated and parallel operation experiments were completed.The experimental results verified the correctness and effectiveness of control strategy for virtual synchronous generator studied in this thesis.This thesis has 80 pictures,8 tables,and 96 references.