Dynamic Characteristic Analysis And Current Stability Control Strategy Of Grid Connected Inverter

With the continuous development of distributed generation technology such as solar energy and wind energy,grid connected inverter as the energy interface between distributed power and large grid,its large-scale access to the grid,its stable operation and control directly affect the power quality and stability of the grid.The grid connected inverter usually controls the current injected into the grid by the current loop,and usually runs in the under damped state,which makes the inverter prone to generate impulse current in the transient process,especially when the grid connected is started,its over-current is more obvious;at the same time,in order to suppress the harmonic effect brought by the high-frequency switch,the output current of the inverter is usually filtered by the filter and connected to the grid However,the LCL type grid connected filter in common use has serious resonance problems.Generally,series resistance is used to increase its damping to suppress the instability caused by resonance.However,the series damping resistance method will reduce the high-frequency harmonic attenuation rate from 60 dB drop every 10 octave to 40 dB drop every 10 octave,and the high-frequency harmonic attenuation effect will be poor.The above problems will bring many unstable factors to the grid-connected inverter system and reduce the quality of the grid-connected current.Therefore,an in-depth analysis of the dynamic characteristics of the grid-connected inverter is performed to suppress its existing unstable factors,improve and optimize its current Stability control strategy is especially critical to further improve the dynamic quality of grid-connected current.The main content is detailed as follows:(1)Firstly,the three-phase voltage source inverters(VSI)are analyzed,the corresponding switch dynamic model is established,and the voltage and current double closed-loop control is given considering the system dynamic performance requirements Parameter design process,simulation results show that it has good static and dynamic characteristics.(2)Then an active damping control strategy based on the dynamic voltage information of DC side is proposed to solve the problem of over-current in the transient starting process of three-phase VSI.It can not only effectively suppress the emergence of impulse current,but also improve the robust stability of the system.Simulation results confirm the truth of the proposed control strategy.(3)Aiming at the problems of the resonance damping control strategy of the LCL grid-connected filter,six improved grid-connected filter damping control structures are deduced based on the parallel resistance method,and the analysis of amplitude-frequency characteristics shows that the improved damping structure has better High frequency attenuation performance,which can provide a reference for the design of new filters and damping links.(4)Finally,this paper focuses on the research of the improved capacitance split parallel resistance method,and makes an in-depth analysis on the damping effect,power loss,high-frequency harmonic suppression effect,etc.the simulation results show that it can retain the high-frequency harmonic attenuation effect of-60 dB drop every 10 octave and effectively reduce the damping loss,so its comprehensive performance is better than the traditional series and parallel resistance method.