Three-phase symmetrical short circuit current characteristic analysis of doubly fed induction generator with crowbar protection

Abstract

When there has a sudden drop of grid voltage, crowbar protection circuit is a widely used method to improve the low voltage ride-through ability of wind turbines with doubly fed induction generator (DFIG), which is commonly used in wind power. This paper studied three-phase symmetrical short circuit current characteristics of DFIG with crowbar protection in depth, and simulations have been made in PSCAD/EMTDC. The analysis and simulation results show that, the output short circuit current concerns with crowbar resistance, dc-link voltage clamp effect and control strategies of the grid side converter (GSC). Short circuit current characteristics of a DFIG wind turbine become complicated because of the responses of GSC, when the dc-link clamp effect occurs. The GSC will also provide a high current to the short circuit point. However, when necessary restrictions have been introduced, short circuit current of DFIG wind turbine can be substituted by stator winding short circuit current of the DFIG whether the dc-link clamp effect occurs or not. Thus, on the basis of previous analysis results, we got short circuit current expressions of a DFIG under no dc-link clamp effect, when short circuit occurred at the normal operation. And an impedance voltage source model was proposed and has been verified at last.