DC/DC Converter And DC Bus Voltage Stability Control Based On Virtual DC Motor

With the continuous development of renewable energy,DC microgrid has become a research hotspot of scholars at home and abroad in recent years.As an important part of the DC microgrid,the energy storage device plays a role in balancing the system power fluctuations.Two different voltage levels need DC/DC converters to connect.The selection and control of the DC/DC converter at the energy storage port will have a direct impact on the safe and stable operation of the DC microgrid.Therefore,this paper focuses on the DC/DC converter at the energy storage port,selects a current-type push-pull DC/DC converter and its control method to carry out research.The main research contents include the following aspects:Firstly,the topology of the selected current-type push-pull DC/DC converter is briefly introduced.The working principle of the converter is divided into six modes according to time,and the working process of each mode circuit is analyzed in detail.The front and rear stages of the converter are equivalent respectively.Based on the two equivalent circuits,the control method of combining the voltage and current dual closed-loop control of the frontstage and the voltage single loop phase shift control of the post-stage is given.On this basis,each controller is designed and the operating characteristics of the converter are verified by simulation.Secondly,in view of the lack of inertia in the DC microgrid and the sudden change of the DC bus voltage when the power fluctuation occurs in the system,the method of adding virtual DC motor control to the post-stage control of the selected converter is proposed,so that the DC/DC converter at the energy storage end can simulate the inertia characteristics of the DC motor,thus providing inertia support for the system.Based on the modeling and analysis of virtual DC motor,the parameter adaptive virtual DC motor control is proposed,and the simulation results show that the proposed control can improve the shortcomings of the conventional virtual DC motor control sacrificing the dynamic response speed of the system.Then,the mechanism is analyzed that the secondary ripple current generated by the inverter connected to the DC microgrid is conducted to the energy storage device.By establishing the output impedance model of the front-stage of the converter,the secondary ripple current suppression method is proposed,which is to add additional filters to the feedback loops of the voltage outer loop and the current inner loop in the converter frontstage control,and the method is verified by simulation.Finally,build the physical platform of the selected converter,complete the experiment of the converter’s working characteristics and virtual DC motor control.The main circuit model of DC/DC converter and inverter is built in the hardware-in-the-loop experimental platform,and the proposed secondary ripple current suppression method is verified experimentally.