| With the widespread use of distributed photovoltaic and wind power generation systems for grid-connected power generation,their grid-connected stability and power quality have received increasing attention.Distributed power supply is generally connected to the distribution network through a grid-connected converter and operates in the form of a micro-grid.The safety and stability of the power system will be greatly effected by the interface characteristics of the distributed power supply.Therefore,the interface unit to improve the control of the inverter is continuously developing.Based on this,scholars have proposed the Virtual Synchronous Generator(VSG)control.The VSG control introduces virtual inertia and damping based on the droop control to achieve active inertia response,which makes it has similar performance comparing with synchronous generator.This topic has carried on the research in the industrial demonstration microgrid construction with the stable operation parameter selection of the virtual synchronous control energy storage system,the parallel stable operation of multiple energy storage control units,and the problems in multiple application integration control.The main work of the full text is as follows:(1)This paper first summarizes the research status and operational control of microgrid,introduces the background and development of VSG,and describes its research status and application in microgrid.(2)The overall structure and model of the optical storage microgrid are constructed.The detailed mathematical model derivation of the energy storage system and the photovoltaic system is performed.Based on this,the control strategy is analyzed.The simulation model was built on the Simulink platform to verify the VSG control characteristics.(3)The stability of the grid-connected energy storage system controlled by a single VSG has been analyzed in this paper.A method for determining impedance boundary of grid-connected converters under this control is proposed.At the same time,the impedance boundary conditions of the power control performance,stability limit,allowable variation range of system load,and small-signal stability of the grid-connected converter are also satisfied.The virtual impedance configuration method is also given to enable the system to obtain good dynamic control performance and stability.(4)Based on the stability of a single VSG grid connected,the stability of grid-connected operation of the energy storage system controlled by two VSGs is analyzed.The expression of the system transfer function is derived from the equivalent circuit diagram and the stability of the subsystem is analyzed.Considering the mutual influence between subsystems,we use the Gershgoirin disc theory to discuss the stability of the overall system.(5)The application of an industrial photovolatic-battery-diesel microgrid in a factory has been designed.The system response characteristics of peak load shifting,off-grid switching,diesel engine operating mode,load switching,and photovoltaic output change has been verified and a real load and grid connection experiment of energy storage converters was conducted. |
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