Research On Frequency Secondary Control Strategy Of Low Voltage Independent Microgrid Inverters

In recent years,the development and application of microgrid has received a lot of attention,because the microgrid is an effective organization form for clean and pollution-free,intermittent distributed generation(DG).Energy storage devices are an important part of balancing microgrid power generation,and are also an important means to stabilize intermittent energy power fluctuations and maintain stable operation of microgrid systems.Conventional present droop control is an important performance of method for the isolated in microgrids,and is widely used because it has the advantages of not requiring a communication system and "plug and play".However,due to the randomness and volatility of the distributed power supply and the switching of the load,the frequency control capability of the droop control in the independent microgrid is limited,and the frequency stability of the microgrid system cannot be guaranteed,which will affect the power quality of the system,so it needs to be increased.Frequency secondary control adjustment.In this paper,the low-voltage optical storage independent microgrid system is taken as the research object,and the research on frequency recovery is carried out:Firstly,the research and summary of the common control strategies of microgrids and the research status of frequency secondary control at home and abroad are studied and summarized,and the control strategy of interconnected lines is mainly studied.The structure and basic principle of the optical storage independent microgrid system are expounded,and the model is built.The power transmission of the droop control energy storage inverter is studied and analyzed.Secondly,the basic principle of traditional droop control is analyzed,and the power outer loop controller and voltage-current dual-loop controller model are established.For the low-voltage microgrid droop control,there are active and reactive power coupling and line impedance mismatch.Add virtual impedance loop to meet the traditional droop control application conditions and achieve power decoupling,improve power distribution accuracy,and add filter inductor The link improves the stability of the system.The analysis concludes that the traditional droop control has the limitation of small system inertia.For the droop control,there is a difference adjustment.To adjust the local control stable operation point,a frequency compensation secondary control strategy based on weak communication is proposed,and the proportional integral link is used to form the frequency.The feedback compensation eliminates the frequency deviation.The stability of the control system is analyzed by establishing the frequency small signal model.The Matlab/Simulink simulation platform is used to verify that thesecondary controller improves the system frequency deviation elimination,but the control speed is slow.Finally,in order to improve the frequency secondary regulation speed,an adaptive quadratic control strategy is proposed based on adjusting the active-frequency droop coefficient.In the droop control,adaptive control is integrated,and local information is utilized by recursive least squares method(RLS).Adaptive modulation of the droop coefficient speeds up system frequency recovery without communication.In order to verify the feasibility and effectiveness of the proposed control strategy,a simulation model of low-voltage optical storage independent microgrid system was built in Matlab/Simulink,and the adaptive secondary control and frequency compensation secondary control were compared under different working conditions.Adapting to secondary control improves the autonomy and dynamic response performance of system frequency regulation.