Abstract:
When the Crowbar protection is put into serious failure to avoid overcurrent in the converter, the fault characteristics of doubly fed induction generator(DFIG) will have significant differences from traditional power supply, causing challenges to the electrical safety design of renewable systems. Due to the uncertainty of the fault time, in order to simplify the selection and dynamic stability verification of existing equipment with DFIG connected to the power system, it is necessary to calculate the peak current of DFIG considering different fault time. Based on the time-domain expression of the fault current under the crowbar protection input, the influence of the fault time on the various components of the current and the peak current is deeply explored. On this basis a DFIG current peak calculation method considering different fault time is proposed. This method first derives the analytical formula for the peak value at a certain fault time, achieving rapid calculation of the peak value. Then, aiming at the non-linear problem of peak value calculation when the fault time changes, a method of setting discrete steps and gradually solving is proposed to obtain the peak value considering different fault time. Finally, the simulation of DFIG integrating infinity system is carried out in MATLAB/Simulink platform. The results indicate that the errors between the calculated values of the proposed method and simulated values are relatively small, thus verifying the correctness of the calculation method in this paper.