| With the continuous increase of renewable energy power generation.Renewable energy generation reduces the inertia of the power system,and it is difficult to maintain the power balance of the short-term system.Renewable energy generation reduces the operating inertia of the system to a certain extent,and thus reduces the power quality of the system to a certain extent.This thesis studies micro-grid power quality control technology based on virtual synchronous generator(VSG).By studying the control strategy of grid-connected inverter in microgrid.The distributed power gridconnected inverter has similar output characteristics of the synchronous generator,and at the same time improves the power quality of the microgrid.Synchronous generators in power systems provide sufficient inertia and damping characteristics for the system.These characteristics of the synchronous generator improve the anti-interference ability for the change of the initial potential and inherent potential of the system.The high penetration of the inverter reduces the total inertia and damping of the system.If the inertia in the power system decreases,the system frequency change rate will increase to a certain extent.Even when a small fluctuation occurs,the system may trip.Therefore,the system becomes more sensitive to failure/interference.The power quality of the power grid has deteriorated.In order to solve the above problems,this thesis mainly studies:(1)The thesis analyzes the current domestic and foreign research status of VSG.The existing technical difficulties of the virtual synchronous generator are analyzed.The key technologies and corresponding control strategies of virtual synchronous generator control are summarized.(2)Study the working principle of renewable energy power generation and grid-connected inverters in the microgrid.Through the establishment of mathematical models and equivalent circuit models.Analyze the control method of the distributed power inverter control system.A control strategy of virtual synchronous generator to improve the stability of power system is proposed.Through the proposed control strategy,the corresponding model of the synchronous generator is compared with the virtual synchronous generator control model.Through reasonable analysis and approximate equivalence,according to the active and reactive output characteristics of synchronous generators.The control model of active frequency and reactive voltage characteristics of virtual synchronous generator is established.(3)Establish a micro-grid virtual synchronous generator control model.First,the virtual synchronous generator control of the optical storage system in the microgrid is studied.Establish virtual inertia of optical storage system and virtual governor model.Secondly,study the virtual synchronous control strategy of wind power generation.Study the virtual inertial control of wind turbines.Additional inertial control.Finally,a virtual inertial control based on power tracking optimization is obtained.Study the impact of wind turbines on the system damping in the microgrid.Take appropriate control to enable the wind turbine to respond quickly to changes in the system frequency.Through the virtual synchronous power generation control method,the problem of insufficient inertia and damping of the power system caused by the large-scale wind power grid connection of the microgrid system is solved.Improve the damping characteristics of the system.Give the system a controllable inertial response.Improve the frequency and voltage stability of the power grid.(4)Aiming at the problems of voltage deviation and frequency deviation in the microgrid.Establish a virtual synchronous generator frequency control model based on uncertain factors.This model is applied to micro-grid control of virtual synchronous generators.When the microgrid is in the island operation state and the grid-connected operation two modes.To a certain extent,it can improve the anti-interference ability of the system frequency and voltage under the conditions of interference and uncertain fluctuations in the microgrid.Finally,the microgrid power quality control based on virtual synchronous generator is modeled by Matlab/simulink software.Simulate the proposed control method.It is verified that the method proposed in this paper can improve the safety and stability of system operation and improve the power quality of microgrid. |
