Research On Distributed Fixed-Time Secondary Control Strategy For DC Microgrid

As a new form of power grid,DC microgrids provide a very promising solution for the development and utilization of distributed generation.However,with the increasing penetration of random and intermittent distributed generation in DC microgrids,the control and management of the system is challenging.In the primary control of DC microgrids,the unknown impedance in the line and the variability of the load lead to voltage deviations and inaccurate current distribution problems.In addition,the uncertainty of distributed generation will reduce the economic efficiency of the system and prevent the economic distribution of power.Centralized communication is used in traditional secondary control,which shows the disadvantages of large computational burden,poor scalability,and sensitive to single point of failure.To address the above problems,this thesis proposes a distributed secondary control strategy based on the fixedtime consensus algorithm combined with the multi-intelligence consensus theory to achieve the stable and economic operation of DC microgrids.The main tasks include:Firstly,for the average voltage recovery problem,a fixed-time consensusbased voltage observer is designed to estimate the average voltage of each converter.Using the obtained average voltage information,a distributed secondary voltage regulator with fixed time convergence is proposed.By transferring information between adjacent distributed power supplies,the regulator gets the amount of voltage compensation that brings the average voltage of the system back to its nominal value.In addition,the fixed-time consensus algorithm improves the convergence speed and enhances the robustness of the system.The effectiveness of the proposed strategy is verified by simulation analysis.Secondly,for the current distribution problem,a fixed-time consensus-based distributed secondary current regulator is proposed to achieve the proportional current dispatch.Using the deviation between the per-unit currents of the converter,the output current of the converter can be effectively adjusted to achieve the proportional current dispatch.The stability as well as the fixed-time convergence of the proposed strategy is proved by Lyapunov stability theory.Simulation studies under different scenarios are designed to demonstrate the feasibility of the proposed control strategy.Finally,for the economic operation of DC microgrids,the economic scheduling problem considered by the tertiary control is introduced into the secondary control layer,which can realize the economic operation of the system and reduce the generation cost in a small time scale.Based on the principle of equal increment cost,a power regulator with fixed-time convergence is proposed considering the capacity limitation of distributed generation in the system.A typical DC microgrid testing system is established,and the effectiveness of the proposed strategy is verified by simulation studies.