| With the rapid development of society and science,the contradiction between the shortage of traditional energy,environmental pollution and the development of human society and economy is more and more intense.Distributed power generation equipment has attracted more and more attention because of its advantages such as pollution-free and renewable.But the renewable energy also has the disadvantages of dispersion and intermittency,which affect the stable operation of the system.Therefore,this paper studies the core equipment of microgrid-energy router.By designing the circuit topology,control strategy and system level coordination control strategy of each port,the power generated by renewable energy can be rationally utilized and scheduled,and the system can run stably and efficiently.Firstly,based on DC microgrid,a multi-port energy router based on DC bus architecture is designed in this paper,and the overall topology of the energy router is introduced.The AC side interface uses a three-phase full-bridge voltage converter,and the DC side interface uses a non-isolated Buck-Boost converter to achieve multi-direction energy flow and power balance between ports.At the same time,I established their mathematical model and analyzed the working principle.Secondly,Virtual Synchronous Generator(VSG)is used to control the grid-connected port,and active frequency loop and reactive voltage loop are designed.Compared with droop control in Matlab/Simulink platform,the results show that under load mutation,The frequency change under VSG control shows more obvious inertia.On this basis,through root locus and simulation analysis,the influence of virtual inertia J and virtual damping D on system stability is obtained.Therefore,an improved VSG control based on J and D adaptive is designed.The simulation results show that compared with the traditional VSG control,the improved VSG control reduces the frequency overshoot by 20% and the active power overshoot by 90%,which embodies the excellent control performance.At the same time,the pre-synchronization control is introduced into VSG control,and the effectiveness of the pre-synchronization control on the seamless switching between the system and offgrid is verified by simulation comparison.Thirdly,the working characteristics of photovoltaic,diesel generator and energy storage in DC side are analyzed.The PV port adopts variable step size perturbation observation method;As an emergency port,diesel generator can supplement the electric energy in time when the system power is insufficient;The energy storage device adopts the hybrid energy storage system of battery and supercapacitor,which has the advantages of long service life,large capacity and high power density.On this basis,I propose energy storage SOC balancing to improve sagging control,and this control can automatically adjust the droop coefficient of each energy storage according to the SOC state of each energy storage so as to change the output power and achieve the effect of SOC balance.The simulation was built on Matlab/Simulink simulation platform to verify the effectiveness.、Finally,the working mode of the energy router and the reason of DC bus fluctuation are analyzed.On this basis,the grid connected and off-grid bus voltage hierarchical coordination control is designed respectively.The selection principle of grid side power is designed to reduce the fluctuation of grid side power,considering various factors such as SOC state of energy storage,peak cutting and valley filling,and port failure.The bus voltage fluctuation threshold was set as 2%,5% and 10% respectively,and the grid-connected mode and off-grid mode were subdivided into 9 and 7 main working states.Finally,it is verified by Matlab/Simulink and experimental platform.The results show that the system can adjust the port control timely in the face of load sudden change,equipment failure,off-grid switching,peak and valley normal section switching,emergency access and other sudden situations,so that the system is fast and stable,and also verifies the effectiveness of the proposed control strategy. |
