Stability Analysis And Power Coordination Control Strategy Research Of DC Microgrid

To solve the energy crisis caused by the massive use of traditional fossil energy,the development and full utilization of new energy generation such as solar and wind power has become the inevitable trend of future energy,and microgrid is the main utilization method of new energy generation.Compared with the AC grid,the DC microgrid has the advantages of high conversion efficiency and no need to consider frequency and reactive power,which has become a popular research field.Therefore,it is important to analyze and focus on the stability and power coordination control of DC microgrids.To study the operation control technology of DC microgrid,it is necessary to build a DC microgrid that can reflect the operation characteristics of distributed power supply.Based on the physical characteristics of the micro power supply,the mathematical models of photovoltaic cells,liquid flow cells and electrolytic hydrogen production were built,and the controller of grid-connected inverter was designed,and a DC microgrid system containing a variety of distributed power sources was built.For the stability problem of DC microgrid with constant power load,a hybrid passivitybased control with improved current inner loop is proposed in this paper.By injecting virtual damping,the influence of negative impedance characteristics of constant power load on system stability is alleviated.The Lyapunov eigenvalue method is used to estimate the power boundary of the DC microgrid,and the influence of different control strategies on the system stability was analyzed and compared.Compared with the traditional voltage-current dual loop control,the proposed hybrid passivity-based control system has a higher power boundary under the same dynamic performance,and the system stability is improved.Power coordination control is also the focus of research on DC microgrid.It is necessary to coordinate different types of power sources in the microgrid to ensure the power balance.For power distribution of hybrid energy storage system,frequency division response control based on second-order filter is adopted in this paper to realize frequency division response of battery and supercapacitor and self-recovery of supercapacitor’s state of charge.To solve the power distribution problem of multiple energy storage systems,an SOC balancing control based on improved voltage reference value is proposed in this paper.The battery adjusts its output power according to its own state of charge,and achieves SOC balancing of the battery rapidly under the condition of no communication.For a variety of controllable resources in the microgrid,a bus voltage hierarchical control is adopted to realize multiple distributed power source adaptive switching operation mode,ensure power balance in the network,and realize multi-source coordinated and stable operation of the DC microgrid.In this thesis,a DC microgrid system containing distributed units such as photovoltaic cells,liquid flow cells,and electrolytic hydrogen production is established for simulation and semiphysical simulation verification.Based on the small signal model,the influence of constant power load on system stability is analyzed.A hybrid passivity-based controller is proposed to improve the system stability.Three power allocation strategies are designed to realize multisource coordinated operation of the microgrid.The correctness of the proposed hybrid passivity-based control and power coordination control is proved by MATLAB/Simulink simulation and RTLAB real-time simulation.The hardware-in-the-loop experiment is carried out to prove the effectiveness of the proposed control strategy to improve the system stability.