Doubly-fed Wind Power System Low Voltage Through Simulation Technology

With the continuous growth of the installed capacity of wind turbine, the proportion accounting for grid also increases year by year, and the grid rules put forward higher requirements for wind power. The main research of the wind power technology is not only limited to running under the normal grid, but also through the wind turbine running under the power grid failure, and extends from the symmetrical fault to the asymmetric fault. The paper does a meticulous research on the doubly-fed wind turbine from the theoretical analysis and model simulation. It gains the following conclusions and results:(1) The mathematical model of DFIG and grid-side converter and rotor-side converter are created in the three-phase stator stationary reference frame and two-phase synchronous rotating reference frame. On the basis, grid-side converter vector control is suggested based on stator voltage orientation and rotor-side converter control strategy is suggested based on stator flux orientation.(2) Under the symmetrical grid voltage dips, doubly-fed induction wind power system operating characteristics and coping strategies are focused on. According to the principle of flux conservation, deduced the expression of the stator and rotor transient current. The fault response of doubly-fed wind power system is simulated in PSCAD/EMTDC.(3) As for rotor-side converter, a precise control model taking the stator voltage variation transients into account in the synchronous reference frame. Simulated analysis verifies the correctness and effectiveness of the proposed new vector control schemes under relatively small grid voltage drops.(4) The paper studies protection measures for DFIG wind generation systems under serious grid voltage sags. When the voltage drops in severe cases, the system has the rotor Crowbar protection circuit. The influence of resistor connected to rotor crowbar is analyzed. The timing of rotor Crowbar’s switching off is optimized. Based on the analysis, the appropriate cut out time and bypass resistor are obtained.