Transient Stability Criterion And Voltage Recovery Control Technology Of Flexible DC Power Grid

In the flexible DC grid,the transient recovery characteristic of DC voltage is the key to analyzing the stability criterion and fault ride-through capability of the system.Based on the transient stability criterion and voltage recovery control technology during the DC fault,it also provides the main basis for the operating time of the DC breaker and the rapid fault removal and isolation.The paper mainly studies the transient stability of the flexible DC power grid after disturbance or failure,and the recovery control strategy during the transient change of the DC voltage.Based on the static stability characteristics,the stability criterion that the system needs to fulfil during the transient process is proposed.Aiming at the control strategy of the converters,voltage recovery control strategy with varying droop coefficients is proposed.At the same time,in the complex network,each converter adopts a step-by-step voltage control strategy to increase the additional discharge power value during DC grid faults and ensures that the system still has the ability to establish stable operation after disturbance or fault recovery.The research contents of this paper:(1)Firstly,the dynamic model of the flexible DC grid is established in this paper.By analyzing the load trajectory of the system operating point after the load power and DC voltage fluctuations,the stable operation mechanism of the DC grid is explained.(2)Secondly,the principle of power balance that should be followed in the transient stability recovery of flexible DC grid is proposed,and the DC voltage limit and DC fault cut-off time are calculated to obtain the transient stability criterion of DC grid.(3)By analyzing the DC power grid stability limit parameters,the DC voltage transient recovery control technology is proposed to increase the DC voltage transient stability margin.(4)Finally,the correctness of the transient stability criterion and voltage recovery control strategy of the proposed DC grid is verified by constructing the flexible DC simulation system,which provides a basis for evaluating the transient stability.