Research On Secondary Voltage Control Of DC Microgrid

By integrating distributed power sources,the microgrid can effectively deal with power quality problems caused by intermittent and random energy sources.The DC microgrid has unique advantages in energy utilization,control difficulty,and transmission costs,and is expected to become the main solution for low-voltage microgrids and building power supply systems.The droop control can distribute the load power of the DC microgrid without interconnection.However,due to the influence of line impedance and droop coefficient,there is a contradiction between DC bus voltage control accuracy and load distribution accuracy that is difficult to coordinate.Dealing with the two problems of voltage stability and reasonable load distribution is the difficulty of DC microgrid energy management.Therefore,based on the analysis of the principle of droop control and the existing problems in existing research,this paper proposes a secondary voltage control strategy for droop control.The proposed secondary voltage control strategy is implemented in two stages: in stage one,the goal is to restore the DC bus voltage.According to the sensitivity relationship between the reference voltage of the droop control and the DC bus voltage,the voltage reference value increment of the droop control is adjusted to restore the DC bus voltage to the target value.In the second stage,on the premise of maintaining the constant DC bus voltage,the power of each power supply is adjusted again,so that the proportion of the load distribution meets the requirements of the system operation.Combined with the proposed secondary voltage control strategy,an equivalent model of DC microgrid system is established.Through the large-signal analysis method and the small-signal analysis method to study the steady state of the system,the conditions for stable operation of the system are obtained,and the factors that affect the stability are analyzed.Finally,the thesis takes two low-voltage microgrid systems as examples to carry out simulation research to verify the effectiveness and adaptability of the proposed method.The research shows that the proposed voltage control strategy can effectively restore the DC bus voltage and distribute the load power according to the set proportion.The proposed strategy effectively solves the problems of traditional droop control,and can realize the distribution of load power in the early stage of accurately controlling the DC bus voltage;and the system stability is not affected by the matching of the droop coefficient and line resistance,which greatly improves the system operation Flexibility and adaptability.