Research On Control Strategy For Synchronverter Under Non-ideal Condition

With the development of renewable energy,distributed power are increasingly connected to the power grid,which cause some stability problems to the amplitude and frequency of the power grid.Therefore,the Synchronverter arise at the historic moment.It can transplant internal model of synchronous generator into the inverter,through the introduction of the virtual moment of inertia and damping coefficient,make inverters have the inertia characteristics of frequency modulation and voltage regulation characteristics.When the grid voltage amplitude or frequency fluctuation occurs,by changing the amount of the output power,the Synchronverter can also be involved in the power system frequency modulation of the voltage regulation,improve the capacity of power system for distributed power.This paper firstly analyzes the electrical characteristics and the mechanical properties of synchronous generator,and the feasibility of transplanting synchronous motor control strategy into the inverter control.Then,by setting the model for the Synchronverter,this paper introduces the mathematical model of the Synchronverter,and the control strategy of it.In order to achieve the Synchronverter smooth interconnection between grid and off-grid,two kinds of existing control strategy are introduced: preliminary synchronization control strategy is used,or the self-synchronized synchronverter,and gives the corresponding implementation process.Under the condition of non-ideal power grid,the output power of synchronous inverter will oscillate and the grid current will also be distorted.The analysis shows that the negative sequence components and harmonic components in the grid voltage are the cause of the current distortion.In order to extract negative sequence components and harmonic components of voltage in non ideal power grid,the sinusoidal amplitude integration method is introduced,and its basic principle and realization method are expounded,and the feasibility of detecting the positive sequence and negative sequence and the harmonics of the voltage base wave in the power grid is verified by simulation.Then,on the basis of analyzing the control strategy of synchronous inverter with current inner loop,a control strategy of specific sub voltage feedforward is proposed to eliminate the voltage imbalance of the power grid and the disturbance of harmonics to the grid current.The feasibility of the control strategy is verified by simulation experiments.In this thesis,simulation model of the Synchronverter is built in MATLAB/Simulink,and the selection principle of the parameters of the Synchronverter controller is introduced.In addition,an experimental platform controlled by TMS320F28335 is established for experimental justification.A prototype is designed based on the control requirements of the Synchronverter.The preliminary experimental results of the previous theoretical analysis and control strategy are carried out through the prototype.