Coordinated control of DFIG subjected to grid faults

With the interconnection requirement for wind generation to the utility power system, it is of great importance that how to enhance the fault ride-through (FRT) capability of the doubly fed induction generator (DFIG) that are nowadays widely used in wind power plants. The FRT strategies based on active crowbar have been commonly used in practical engineering, but there are two problems remain unsolved. One is how to choose the crowbar activation time, the other is how to control the rotor-side converter after the crowbar disconnection. In fact, the precondition for solving these problems is to reveal the rotor fault current characteristics. In this paper, the main frequency components and their decaying characteristics of rotor current are analyzed. Further, a coordinated control strategy between the rotor-side converters and active crowbar is proposed to enhance the FRT capability of DFIG. The main idea is utilize the time constant of high-speed decaying component of rotor current as the reference of crowbar activation time, and the low-speed decaying current component considered as the bad factor of restarting the rotor-side converter. With the proposed strategy, the fault response of DFIG can be greatly improved. The minimum operational voltage limit of the DFIG´s fault ride-through is enlarged by 0.1p.u without increasing the converter rating. These performances have been demonstrated through the experimental tests based on the real time digital simulator (RTDS).