Balck Start Strategy Of Isolated Microgrid Based On Virtual Synchronous Machine Control

When the power grid experiences long-term and large-scale power outages due to faults,it will have a serious impact on various aspects of the economy,electricity safety and social order within the region,endangering social security.In order to be able to reduce the economic loss and quickly restore the power supply,a black-start scheme for the isolated microgrid can be used to ensure the stable operation of the primary load within the isolated microgrid system.Therefore,a black-start scheme for the isolated microgrid based on two energy storage systems is developed in this thesis,the primary load inside the isolated microgrid system is predicted,a control strategy for a single energy storage system is designed,and two energy storage systems in parallel are connected to form an isolated microgrid system to provide sufficient and reliable power for the primary load.The specific research contents are as follows:First,a black-start scheme for the isolated microgrid based on serial recovery for two energy storage systems is designed to plan the whole black-start process.In addition,the time series method is used to predict the primary load within the isolated microgrid system,clarify the primary load value within the system,and further determine the number of start-up units of the energy storage system,which effectively avoids the problem of black-start failure and improves the reliability of power supply.Secondly,by comparing and analyzing common three-level inverter circuit topologies,T-type three-level inverters are selected as the circuit topology of the energy storage system,and the power loop with virtual synchronous generator control,the voltage loop with quasi-proportional resonance control and the current loop with proportional control are designed for a single T-type three-level inverter,which makes the T-type three-level inverter have certain damping and inertia.The stability of the T-type three-level inverter is further improved.In addition,the working principle of parallel pre-synchronization control strategy of two T-type three-level inverters is studied to avoid the inrush current generated when two T-type three-level inverters are connected in parallel,which leads to the black start failure of the isolated microgrid.Finally,the simulation model of two T-type three-level inverters is built in Matlab/Simulink simulation software,and the experimental platform of two T-type three-level inverters with STM32F407ZGT6 as the core control chip is also built to verify the feasibility of the isolated microgrid black-start scheme and control strategy designed in this thesis.By predicting the primary load in the isolated microgrid system and starting the isolated microgrid according to the predicted load value,a stable isolated microgrid system is established,it verifies that the isolated microgrid black-start scheme and its control strategy are reasonable and feasible under the linear load and nonlinear load conditions.