| DC microgrid can flexibly and reliably combine distributed power supply.It outputs DC form of electricity,regardless of frequency and phase.And the control structure is simple,which can improve the quality of power consumption,reduce system losses,and have obvious advantages in development.The interface converters of each power generation unit and energy storage unit in the DC microgrid are the basic and key link to connect the system and achieve various control objectives.Therefore,for the proposed DC microgrid system structure,aiming at achieving stable operation of the system and fully utilizing distributed generation of power generation,based on model building the power conversion control strategies of each unit system applicable to this system are studied.In this paper,a DC microgrid consisting of permanent magnet direct drive system,photovoltaic power generation system,buffer energy storage system and alkaline water electrolyzer is studied.The hydrogen production load can adapt to the intermittent fluctuations of power supply,and better utilize the wind and photovoltaic power generation that cannot be consumed,and is clean and environmentally friendly.Firstly,the structure of the DC microgrid system adopted in this paper is designed,and the two operating modes of the system,namely the wind power grid-connected operation mode and the wind-solar hybrid hydrogen production operation mode are analyzed.Then modeling,simulating and analysis of each unit of photovoltaic power generation system,battery energy storage system,and permanent magnet direct drive wind power generation system,and the control of the interface converters of each part were studied.The simulation verifies the correctness of the control strategy when each unit system works alone.The photovoltaic system realizes the MPPT effect well with the improved variable step perturbation and observation method and the CVC control can realize the power adjustment.The battery system uses a constant voltage charge and discharge control method to achieve the voltage regulator control.Wind power system MPPT control adopts the optimum tip speed ratio method.The machine side converter adopts dynamic indirect current and speed control combined with ZDC control and feedforward decoupling control.The grid-side inverter adopts feedforward decoupled grid-based voltage-oriented vector control in the dq coordinate system.When the wind power in grid-connected operation mode can meet the grid connection requirements.Finally,the model of hydrogen production load of the electrolyzer used in the system is determined.After verifying the correctness of the working characteristics of the simulation model,it is connected to the DC microgrid system,and establish the simulation model of the whole system.In addition,the off-grid model of the system has been coordinated controlled with the system bus output voltage reaching the requirements for hydrogen production and system stability.Based on Matlab/Simulink software,it verifies whether the running results of the system model under various operating conditions meet the system requirements and the feasibility of the control strategies. |
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