Research On VSG Operation Control Applied To Micro Grid Inverter

Usually,using new energy to generate electricity needs to use power electronic conversion technologies before incorporating into the power grid or providing power for the loads,so as to meet the power standards.However,the power electronic equipment dose not have the inertia(J)and damping(D)characteristics of the generator.Especially with the continuous expansion of distributed energy sources,the introduction of a large number of power electronic converters will make this deficiencies more pronounced.Previous control techniques such as V/f,Droop and other control strategies have not solved the problem.Therefore,some scholars proposed a virtual synchronous generator technology(VSG)that uses a mathematical model to simulate the external characteristics of a synchronous motor.In general,the VSG that uses mathematical modeling simulates the characteristics of damping,inertia,voltage and frequency regulation.In a word,it further simulates the inertia and damping characteristics of the synchronous generator based on the Droop control strategy to make sure that the power electronic converter have the same external characteristics as the synchronous generator.This paper mainly focuses on three important points in VSG inverter technology.The main contents are as follows:1.Research on the key parameters of the VSG.The small signal analysis expression about the power control of VSG was established,and the important parameters were studied and the value rules were concluded.Finally,a 20kW VSG control model was established in MATLAB/Simulink,and the theoretical analysis was verified by Simulation.2.The second part of the research in this paper is the research on adaptive J and D.According to the functional expression of VSG,the mathematical function between the absolute value of the frequency change rate(|dfldt|)of VSG and J was obtained.At the same time,according to the relationship between J and D,the mathematical function between |df/dt| and D is further obtained.According to the two functions,the control structure diagrams of adaptive J and D was designed,and the parameters involved in the functions were analyzed and the method of value selection was summarized.Finally,it was verified and analyzed by using MATLAB/Simulink and experimental platform.3.The third part of the research in this paper is about the switching between VSG control and PQ control.In the case of grid-connected condition,taking into account the disadvantages of VSG control performance under frequency disturbances and the characteristics of PQ control under the same condition,the combined mode between VSG and PQ was obtained.In the switching strategy,this paper studies two kinds of switching modes respectively,which are switched via the current inner loop of the voltage and current control layer,and switched via the power control loop of the VSG functional layer.The second switching method,which is the control model adopted by the experiment,is the control structure re-designed after summarizing in the simulation modeling process of the first method.The two switching models were analyzed and compared by MATLAB/Simulink modeling,and the second model was verified through experimental platform.