| In recent years,countries around the world,represented by China,have actively undertaken the goal of carbon neutrality and vigorously developed renewable energy,represented by wind and solar energy.With the increase of the penetration proportion of new energy in the power grid,a large number of new energy power electronic equipment connected to the grid changes the inertial support of the original large power grid,affecting the safe and reliable operation of the power system.In order to solve this problem,some scholars proposed the Virtual Synchronous Generator(VSG)control strategy.Through the change of control strategy,grid-connected inverter adopts the operation characteristics of traditional synchronous generator,so as to support the frequency and voltage of the grid and maintain the stability of the system.This thesis studies the stability of microgrid inverter based on virtual synchronous generator in isolated island mode.The main contributions are stated as follows:(1)The power oscillation mechanism of the parallel multi-VSGs system meeting the future development trend of integrated power supply,power grid,load and energy storage is analyzed,and the conditions of power distribution according to capacity are deduced,and the small signal state space model of the parallel VSGs is established when the microgrid island is running.The influence of key parameters such as moment of inertia and damping coefficient on the stability of the system is analyzed theoretically,and the correctness of the analysis is verified by simulation.(2)The mixed potential function analysis method applied to large signal stability analysis is introduced.The nonlinear model of the parallel-VSGs is derived.Based on the mixed potential method,the mixed potential function is established.The Lyapunov function is reconstructed according to the mixed potential function,and its threedimensional relationship diagram with the output voltage of multiple machines is drawn by MATLAB.The progressive stability domain of the system is given,which provides a new idea and method for the large signal stability analysis of the multi-VSGs system.The effectiveness of the proposed mixed potential method is verified by simulation analysis.(3)The coupling model of single virtual synchronous generator was established,and the coupling degree of dual power control loop of virtual synchronous generator was quantitatively analyzed based on the relative gain matrix method,and the influence of key parameters such as output inductance,output active power and voltage loop on coupling was analyzed.Since the traditional virtual impedance cannot simultaneously solve the problem of power allocation by capacity and decoupling,a control method based on virtual electromagnetic torque compensation is proposed in this paper,which can effectively suppress the transient power oscillation phenomenon of the parallelVSGs system and decouple the system through adaptive inductance design.The effectiveness of the proposed method is verified by simulation and experiment.(4)An experimental platform of parallel-VSGs isolated island running system with full digital control based on TMS320F28835 chip is built,and the effectiveness of the algorithm and stability control of the virtual synchronous generator is verified by single-VSG,multi-VSGs and multi-working condition experiments of the system on the experimental platform. |
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