With the increasing penetration of renewable energy generators(REGs)the fault current characteristics of the grid are greatly altered by large-scale REGs. Traditional relay protection schemes are being challenged. The study on the fault characteristics of REGs depends on the employed converter's control strategies employed

but these strategies differ from manufacturer to manufacturer and are seldom

if ever

made public. As a result

how to reveal the fault current characteristics has become a quite difficult problem. In this paper

focus is on the inverter-interfaced REGs(IIREGs). A coordinated control strategy for gird-tie inverter and DC-link chopper is firstly proposed to ensure IIREGs can ride through severer asymmetrical faults(the imbalance degree is about 100%). On the basis of this

the correlation between the inverter's control strategies and the IIREGs' fault current characteristics is analyzed. Further

the expression of the steady fault current from IIREGs is derived theoretically

which is independent of the inverter's control structures and its parameters. Finally

based on the experimental test bench

both the FRT capability and the short-circuit current expression of IIREG are verified. Moreover

by studying the fault current characteristics of IIREGs as influenced by various fault types and locations as well as short-circuit capacity level of the connected grid

the differences between IIREGs and synchronous generators are revealed. The results can be used for evaluating existing relay protection strategies and developing protection configuration and setting principles. This work is supported by National Basic Research Program of China(973 Program)(No. 2012CB215206)

the Fundamental Research Funds for the Central Universities(No. 2014QN20)and State Grid Corporation of China(No. JB71-15-042).