Stability Analysis And Research On Active Damping Control Strategy Of DC Microgrid

As a reliable way of renewable energy consumption,distributed generation has become a hotspot in the current power industry.In order to maximize the efficiency of distributed generation,DC microgrid has attracted increasing attention for its outstanding advantages.In DC microgrid,DC or AC loads are mostly connected to DC bus through power electronic converter,which is characterized by constant power load.Owing to the negative damping characteristic of constant power load in DC microgrid,the DC bus voltage is prone to oscillation and even instability with the large number of CPL access.,which restricts the application of DC microgrid.Therefore,it is vital to analyze the influencing factors of the stability of DC microgrid and explore the methods to improve its stability.The stability of DC microgrid is studied in depth in this paper.The main work and achieved research results are as follows:(1)The mathematical model of each component unit of DC microgrid and the control mode of corresponding power electronic converter are analyzed.The model of DC microgrid,including distributed power unit,battery energy storage unit,constant power load unit and grid connected converter unit is established,which lays a foundation for further research.(2)A small signal model of the DC microgrid is derived and the relationship between system stability and the parameters of DC system,such as DC bus capacitance,load power,droop coefficient and current-loop controller parameters is revealed.Based on the high sensitivity of droop coefficient,the active damping control strategy is proposed to compensate the droop coefficient and improve the system stability margin.Qualitative analysis from Nyquist curve and quantitative analysis from sensitivity are conducted to compare the application effect of virtual resistance in different source converters,which shows that the proposed control strategy has a better improvement for the system stability when applied to the grid-side converter.(3)Aiming at the problem of inadequate compensation of the original active damping control and the instability caused by load power variation and DC bus voltage deviation created by excessive droop coefficient compensation,an adaptive active damping control strategy with voltage self-recovery characteristic is proposed.The power influence factor is introduced to make the virtual resistance increase with the increasing of load power,and the compensation term is added to the original droop control expression.It can be seen from the stability analysis that the DC microgrid could operate safely and stably and the DC bus voltage could be restored to the rated value whenever the load power fluctuates.(4)The model of DC microgrid is built and simulated in MATLAB/Simulink,while the real-time simulation is carried out in RT-LAB.The results show that the proposed control strategy could effectively improve the stability of DC microgrid and the voltage quality of DC bus.