Calculation On Tripping-off Condition Of DFIG During Three-phase Short Circuit Fault And Power Restoration Of Its Connected Distribution Network

Under the double pressure of energy and the environment, wind power technology has got more and more universal attention. In recent years, our country’s total wind power installed capacity ranks first in the world, and the annual increase of installed capacity is more than one-third of the world’s new capacity. There is no doubt that wind power has become the third-largest source of electricity since thermal power and hydropower. With the increasing proportion of wind power in power grid, the interactions of the wind turbine to the power grid has become a problem need to pay close attention to. Especially when the three phase short circuit fault occurs, which will seriously influence the safety and stability of the system, there’s been a series of problems to study and solve, including the effect of short circuit current on the wind turbine tripping off accident, and the impact from the wind turbine to the fault outage area power supply recovery when the line is break caused by fault isolation.In view of the three-phase short circuit problem, firstly, this paper deduces the terminal voltage expression of the wind turbine, analyses the influence from the transient characteristic of the current to the terminal voltage, and proves that the terminal voltage will experience oscillation damping by Matlab simulation. Secondly, according to the characteristic that voltage of the doubly-fed induction generator(DFIG) is under the control of the converter instruction value and the mechanism of wind turbine tripping off the net, establishes the wind turbine’s tripping-off model under steady state short circuit, and with the use of the stator voltage oriented vector control principle, the output power and injection current equations which can describe the doubly-fed induction generator’s external characteristic during low voltage ride through are deduced, so the terminal voltage can be solved using iterative method, and be used as the judgment basis of tripping off accident. Then uses the single wind turbine connected with the infinite power grid model and the multi grid-connected wind turbines short-circuit model as examples to study the influence factors of grid-tripping evaluation voltage, and the effect among wind turbines when some of them trip off the grid. The example results show that the wind turbine tripping-off accident caused by the short circuit has the risk of power grid voltage collapse.Finally, this paper researches the power supply recovery problems of the power distribution network containing wind turbines. Based on the hybrid algorithm of binary particle swarm with differential evolution, a mathematical model of power supply recovery is constructed and the reconfiguration, topology identification, isolated island partitioning, power flow calculation and objective function calculation are described in detail in the constructed model. A recovery strategy, which can rationally coordinate the distribution network reconfiguration with isolated island partitioning, is proposed, namely the isolated island partitioning is performed during the reconfiguration process, and by the means of establishing boundary matrix of isolated islands it can be judged whether the isolated island could exist or not during the reconfiguration, and the load loss obtained after the isolated island partitioning is regarded as a part of the objective function to make the results of reconfiguration and isolated island partitioning commonly impacting the global optimal solution, and make the two recovery modes possessing have their entirety. The effectiveness of the proposed algorithm is validated by simulation results of IEEE 33-bus distribution system, and the results make a further illustration that the tripping-off accident of the wind turbine has a bad impact on the power supply recovery reliability.