Virtual Synchronous Control Technology For Microgrids

With the continuous development of society and industry,distributed new energy in the form of microgrid large-scale access to the modern power system,voltage source inverter as the representative of power electronics is also gradually replacing the traditional synchronous generator position,so that the modern power system is gradually towards the "high proportion of renewable energy" and "high proportion of power electronics "high proportion of power electronics" double high direction development.However,due to the lack of inertia support,the microgrid with new energy sources cannot effectively balance the voltage and frequency fluctuations,thus seriously threatening the stable operation of the microgrid system,and a large number of fluctuations in the microgrid even affect the normal operation of the power system.In order to improve the inertia level of microgrid system and provide support for the stable operation of modern power system,this paper proposes a virtual synchronized microgrid with autonomous inertia response capability,where all inverter and rectifier units inside the microgrid adopt the virtual synchronization control method,simulating the physical characteristics of synchronous machine,applying the inertia adaptive control method based on optimal self-turbulence,and responding to the microgrid in each phase of fluctuation in real time.It improves the robustness of the system,accelerates the response speed,and provides stable voltage and frequency support for the microgrid.The main work accomplished in this paper is as follows:First,the basic control algorithm of virtual synchronous generator and load virtual synchronous machine is studied,and the output impedance characteristics of its virtual excitation controller and virtual rotor controller are analyzed to summarize the same points of virtual impedance and synchronous machine sag characteristics.For the new generalized sag controller,the analysis and study of inertia performance are carried out to reveal the inner mechanism of inertia performance with the change of controller parameters and the law of influence of parameter change on inertia.Then,an adaptive controller with self-anti-disturbance and real-time adjustment is designed for the characteristics of the virtual generator.Compared with the traditional fixed inertia parameter control strategy and upper and lower bound control,the self-adaptive controller can rapidly and effectively respond to the disturbance in the system and improve the robustness of the system.Both simulation and experimental results verify the effect of the self-turbulence control method on the system frequency stability.Finally,a virtual synchronized microgrid system is established,and the concept of minimum inertia requirement of power system is introduced to evaluate and compensate the minimum inertia requirement of the microgrid system.When the disturbance occurs,the distributed generation unit,energy storage unit and load unit based on the virtual synchronization control technology will change their inertia magnitude in real time according to the inertia demand,and always meet the minimum inertia demand of the microgrid system.The simulation and experimental results validate that the proposed virtual synchronized microgrid system can meet the minimum inertia requirement in real time and ensure the stable operation of the microgrid system.