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Research On Current And Power Quality Control Of Virtual Synchronous Generator Under Unbalanced Voltage

Posted on:2019-12-17Degree:MasterType:Thesis
Country:ChinaCandidate:C WangFull Text:PDF
GTID:2382330566498227Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
With the large-scale application of distributed power sources in the grid,the grid is developing in the direction of low inertia and low damping.Virtual Synchronous Generator(VSG)has become a research hotspot because of its ability to simulate the rotational inertia,damping and frequency regu lation of synchronous generator.The output current of the VSG will be unbalanced and the power will be oscillating under unbalanced grid voltage.The current balance control and power oscillation suppression strategy is proposed to achieve current balance and constant power without changing the characteristics of the VSG under unbalanced grid voltage in this paper.Firstly,the second-order mathematical model of the synchronous generator is established,and the workflow is analyzed to design the overall control structure of the VSG.The virtual governor,virtual excitation regulator and ontology models of the VSG are designed by using the active power-frequency droop characteristics of the synchronous generator governor,the reactive power-voltage droop characteristics of the excitation regulator and the second-order mathematical model to simulate the synchronous generator's rotational inertia,damping characteristics,frequency regulation and voltage regulation.Then,the parameters of the virtual governor,the virtual excitation regulator and the ontology model are designed using the root locus method by establishing a small signal model of the VSG.The mathematical model of VSG in grid-connected mode and islanding mode is established based on MATLAB/SIMULINK,and the effectiveness of virtual governor,virtual excitation regulator,rotational inertia and damping in the model is verified.Next,for the problem of unbalanced current and power oscillation of the VSG under unbalanced grid voltage,the current balance control and power oscillation suppression strategy is designed to achieve balanced current,constant active power and constant reactive power without changing the characteristics of the VSG.The current balance and power oscillation suppression control strategy mainly includes three parts: VSG module,positive and negative sequence current reference calculation module and current regulation module.The positive and negative sequence current reference calculation module is the core of the entire control method.Its design method is: According to the positive sequence circuit of the VSG main circuit structure,the positive sequence current refer ence is calculated;according to different control targets,the negative sequence current reference is calculated based on the instantaneous power theory.The current balance control and power oscillation suppression strategy is established to verify the validity of the current balance control mode,the constant control mode of active power and the constant control mode of reactive power based on MATLAB/SIMULINK.Finally,the effectiveness of grid-connected control strategy,islanding control strategy,current balance control and power oscillation suppression strategy are verified based on the VSG prototype.
Keywords/Search Tags:Virtual Synchronous Generator(VSG), unbalanced grid voltage, current balance, power oscillation suppression
PDF Full Text Request
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