Research On Energy Management Predictive Control Of DC Microgrid Clusters

DC microgrid is a regional power supply system that integrates renewable energy,energy storage devices,interface converters and loads.It can realize energy conversion between source and load by virtue of corresponding operation control technology.However,its inherent characteristics such as small capacity and weak anti-disturbance ability will affect the reliable operation of the system.Therefore,the interconnection of DC microgrids to form clusters has been rapidly developed as an effective means to improve system reliability.DC microgrid clusters mostly adopt hierarchical control strategies.Among them,the tertiary control has a lower control bandwidth due to the higher control level,and it cannot achieve fast dynamic response speed when encountering loads change and mode switching conditions.Therefore,in order to ensure reliable and economical operation of the system,the energy management of the cluster needs to be optimized.In response to the above problems,the thesis focuses on the improvement strategy of the tertiary control.First,focus on the energy management of the cluster,a hierarchical control strategy applied to the DC microgrid cluster is analyzed.According to the physical characteristics of the renewable energy unit and the Energy Storage Unit(ESU)in the DC microgrid,the introduction of primary control and secondary control in the grid realizes the independent distribution of energy among micro-sources and the dynamics of the DC bus voltage consistent;The tertiary control strategy is adopted in the grid to make the load current in the cluster and the So C(State of Charge)eventually converge to achieve the goal of energy balance.The feasibility of the proposed hierarchical control strategy was verified by simulation.Secondly,in order to improve the slow dynamic response of traditional tertiary control strategies,a distributed tertiary control strategy based on predictive function control(PFC)is proposed.When a large signal disturbance occurs in the DC microgrid cluster,aiming at the energy management problem at the system level,the proposed improvement strategy can achieve the DC bus voltage change and energy balance on a smaller time scale,so as to improve system reliability and stability,thus to extend the life of power electronic devices to reduce system maintenance costs.The proposed improved tertiary control strategy was verified by simulation.Finally,three DC microgrid interconnection experimental platforms based on DSP28335 digital controller and Buck/Boost interface converter are built,and the experimental waveforms of distributed tertiary control based on PFC are given,to verify the effectiveness of the proposed PFC strategy.In order to compare the superiority of the proposed strategy,the relevant experimental waveform acquisitions of primary control,secondary control and traditional tertiary control have been completed.The experimental results show that the PFC controller has a faster dynamic response speed than thetraditional PI controller when performing large signal disturbances such as mode switching and load changing.