| The rapid development of industry and technology requires strong support from the energy industry.Nowadays,it is imperative to use abundant new energy and renewable energy sources to replace traditional energy due to scarce fossil energy and polluted environment.It not only can effectively alleviate the energy crisis and environmental degradation,but also can be used as a future energy development strategy to meet the sustainable development of human society.With the continuous research on micro-grid technology,the development and utilization of new energy is promoted.As the hub of new energy and large power grid,inverter plays an important role in the safe and stable operation of micro-grid,and its control process has the advantage of extremely high response speed.However,due to the lack of inertia and damping,the frequency of the system changes too much to be stable after disturbance.By analyzing the operation characteristics of synchronous generators in large power grids,virtual synchronous generator technology is introduced to improve the stability of the system.However,the transient process of the system will be affected by the key parameters of the virtual synchronous generator,so that the dynamic response of the system can’t take into account rapidity and stability.Therefore,the inverter of the control algorithm of virtual synchronous generator is taken as the research object in this thesis.Aiming at the insignificant improvement of the system stability under the traditional virtual synchronous generator control,a virtual synchronous generator parameter adaptive control strategy is proposed.The main research contents are as follows:(1)The basic concepts and background is described in detail.Micro-grid is basically introduced and the differences between the three traditional inverter control schemes are explained.In order to better realize the friendly grid connection of the micro-grid and maintain the stability of its independent operation,the virtual synchronous generator technology with inertia and damping characteristics is introduced.The current research status of this technology is introduced.(2)The mathematical model of the virtual synchronous generator is established and analyzed.A virtual synchronous generator model based on the second-order mathematical model of the synchronous generator is established.The structural characteristics is analyzed to design the P-f controller and Q-U controller of the virtual synchronous generator.The characteristics of the synchronous generator and the virtual synchronous generator are analyzed to clarify the differences.(3)The small-signal of virtual synchronous generator is analyzed.The off/grid smallsignal model of virtual synchronous generators is established and the root locus is analyzed on key parameters to clarify the relationship between parameter changes and system stability.The dynamic response processes of each key parameter are analyzed to verify the correctness of the small-signal theoretical analysis by building the MATLAB/Simulink simulation models.Subsequently,the consistency of the droop control of the same simulated synchronous generator and the virtual synchronous generator control is analyzed to verify the superiority of the virtual synchronous generator control method by simulation models.(4)The parameter adaptive control strategy of virtual synchronous generator is proposed.Due to the similarity of the simulation,the power angle curve and angular frequency oscillation curve of the synchronous generator are analyzed to find a certain correlation between the rotational inertia,damping coefficient of the virtual synchronous generator and the amount and rate of the change about system output frequency.Based on the mutual relationship,an adaptive control strategy for the rotational inertia and damping of the virtual synchronous generator is proposed and the MATLAB/Simulink simulation model of the scheme is built.Through the above analysis and simulation verification,the correctness of the proposed virtual synchronous generator moment of inertia and damping adaptive control strategy and the effectiveness of improving the system stability performance are proved.The contradiction between rapidity and stability in the process of system dynamic response are weaken to provide reliable guarantee for the safe and stable operation of power system. |
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