Research On Modeling Of DC Microgrid And Bus Voltage Regulation Technology

In this paper,the modeling and analysis of DC microgrid are carried out.During the operation of DC microgrid,the DC bus voltage is easily affected by the power fluctuation of distributed generation,load switching and high-order harmonics.Therefore,it is necessary to suppress the DC bus voltage fluctuation to maintain the bus voltage at a relatively stable level.The main research contents include:Through the analysis of the mathematical model and topological structure of photovoltaic,wind distributed generation and energy storage device,a simulation model of DC microgrid composed of photovoltaic distributed generation,wind distributed generation,energy storage device and grid connected inverter is constructed.Among them,the photovoltaic distributed generation model adopts the constant duty cycle disturbance observation Maximum Power Tracking(MPPT),the wind distributed generation model adopts the variable duty cycle disturbance observation MPPT control mode,and the energy storage device model adopts the voltage and current double closed-loop control mode.By studying the topology and control mode of grid connected inverter,the L-type,LC type and LCL type filters are compared.On this basis,the mathematical model of LCL grid connected inverter is established.According to the principle of constant PQ,the grid connected operation mode is controlled,and the existing V/F droop control is improved.DC bus voltage fluctuation includes disturbance type fluctuation and oscillation type fluctuation.Aiming at disturbance type fluctuation,by analyzing its mechanism,power balance is maintained based on energy storage system,and a complete DC microgrid control mode is formed by combining with grid connected inverter control strategy to suppress it;Aiming at the oscillation type fluctuation,the double closed-loop active damping control method based on grid connected current and capacitor current is used to design the control system and match the system damping to suppress the oscillation.Finally,through Simulink simulation experiments,the grid connected,islanded control mode and grid connected constant PQ active damping control mode based on energy storage system are verified respectively,and it is proved that they can restrain the disturbance type and oscillation type fluctuations.