Research On Transient Stability Optimization Control Of Virtual Synchronous Generator

Under the influence of increasing energy crisis,the scale of new energy microgrids involved in power systems is increasing day by day,which brings unprecedented pressure on power systems.The virtual synchronous generator(VSG)uses the control system to simulate the dynamic characteristics of the traditional synchronous generator(SG),which can make the distributed system interact with the grid friendly,so it has been widely used.However,in weak networks with high resistance ratio,the application of VSG technology is facing severe challenges due to complex working conditions such as large voltage drop,sudden change of high-power load or given power in gridconnected state.Therefore,in order to promote the development of VSG technology,efforts must be made to improve the reliability of the application of VSG control algorithm,so that VSG has the ability to operate under the condition of large interference.According to the above capability requirements,in this paper,the problems of low voltage ride-through(LVRT)and frequency response speed of VSG are explored in depth.The main contents are as follows:Firstly,the electromagnetic transient model of traditional SG in grid fault is analyzed.Then referring to the natural operation mechanism of SG in grid fault and using the advantages of VSG control technology,a novel LVRT control strategy based on virtual self-inductance flux linkage is proposed from the perspective of the switch law.This control strategy can restrain the transient sudden change of grid-connected current to assist grid-connected inverter to adjust the output voltage quickly and realize the LVRT of VSG.The proposed scheme fully exploits the simulation of natural characteristics of SG by VSG,and can cope with various complex working conditions.Then,according to the frequency response characteristics of VSG grid-connected system under the condition of sudden change of given power or load,a mainstream adaptive moment of inertia control strategy and its inherent shortcomings are introduced.The background that the power decoupling control scheme based on virtual impedance technology is adopted by most microgrid systems with high resistance ratio is considered.In this paper,a method of adjusting VSG inertia with adaptive virtual impedance is proposed from the perspective of virtual impedance.It can improve the output frequency response speed of VSG grid-connected system.Finally,the above two schemes work together to further improve the frequency response curve and obtain the deep optimization of the transient stability control of the system.Finally,in this paper,the basic functions of VSG control algorithm are tested by using the rapid prototype controller experimental platform.The experimental results show that the feasibility of VSG algorithm has been preliminarily verified.