Stability Analysis Of DC Microgrid Based On Improved Droop Control

As the world continues to grow rapidly,the demand for energy is increasing.However,the traditional fossil energy is exhausted for a day,so the research and practice of new energy power generation technology has gradually become a hot spot.As the best way to receive distributed new energy such as wind energy and solar energy,microgrid technology is also deepening its research.Compared with the AC microgrid,the DC microgrid has become the focus of microgrid research because it does not need to consider the system frequency,the intermediate conversion link and the simple and flexible control structure.Each power generating device,energy storage device and load in the DC microgrid is connected to the DC bus via an inverter,and the stability of the DC bus voltage represents the power balance of the system.Therefore,how to coordinate the balance of source,load and storage,and safe,reliable and economical operation control of the system is a key point of DC micro-network research.Moreover,the lack of inertia caused by a large number of power electronic devices in the DC microgrid and the uncertainty of new energy output have brought greater challenges to the stability of the system.Therefore,it is very necessary to conduct an in-depth study on the stability of the DC microgrid system.Droop control is an important operation control method in microgrid,this paper introduces its principle in detail and analyzes the contradiction between current distribution accuracy and voltage adjustment of traditional droop control.Aiming at solving this contradiction,the deformation of the drooping curve is made "with the straight line",and the problem is solved by this nonlinear droop control strategy.Then,the principle of nonlinear drooping strategy is analyzed and the design principle of drooping curve is proposed.Based on this,a polynomial nonlinear droop control strategy is proposed,and the drooping parameters are configured and the voltage compensation link is designed.Then the small-signal modeling of the DC microgrid system is carried out.The stability of the system is studied by the small-signal analysis method,and the influence of the line parameters on the stability of the system is obtained.Finally,the superiority of the proposed nonlinear droop control is verified by simulation and the advantages and disadvantages of different voltage compensation links are analyzed and compared.The research on the stability of DC microgrid mainly focuses on small signal stability,and the research on large signal stability is still in its infancy.In this paper,the large-signal model of the DC microgrid system with multiple droop controlled micro-sources is established,and the principle of the mixed potential function method is introduced in detail.Then,the large-signal stability of the DC microgrid system is analyzed by the mixed potential function method,and the large signal stability criterion of the system is calculated.Based on the criterion and the proposed nonlinear droop control strategy,a quadratic polynomial droop control strategy is proposed to improve the stability of the system and analyze the principle of improving the stability of the system.Finally,the simulation results prove the validity of the obtained large signal stability criterion and show that the proposed nonlinear droop control strategy improves the system’s large signal stability.In summary,this paper proposes a nonlinear form of improved droop control strategy to solve the contradiction problem of DC microgrid system,and then uses the mixed potential function method to study the large signal stability of the system,and finally combined with the improved droop control to improve the system’s stability.It’s proved that the strategy enhances the stability of the system,which provides some help for the operation control and stability of the DC microgrid.