基于可变频变压器的双馈风电系统低电压穿越控制

摘要

在电网电压发生跌落故障期间,基于Crowbar电路的双馈风力发电( DFIG)系统需吸收大量无功功率。为提高DFIG风电机组并网运行稳定性,提出增设可变频变压器( VFT)新方案。 VFT由双馈电机、直流电机及驱动器构成。 Crowbar电路动作后,通过控制低电压穿越( LVRT)期间的VFT转速来抑制系统转差率,减小系统无功功率吸收量,基于 MATLAB/Simulink 平台,进行了暂态仿真研究。结果表明,故障期间在Crowbar电路起动后,所提控制策略能避免系统从电网中吸收过量无功功率,避免发电机转差率越限,有助于电网电压的恢复,DFIG风电机组的LVRT性能提高。%The vast grid reactive power would be absorbed by the crowbar-based doubly-fed induction generator ( DFIG) wind turbine when grid voltage dip fault. To improve the stability of power grid with DFIG wind turbines, a new low voltage ride-through ( LVRT ) control strategy was proposed for DFIG wind turbine by adding a variable frequency transformer ( VFT) between DFIG and grid. The VFT was composed of a doubly-fed induction machine, a DC motor and its drive system. During the crowbar circuit active, the slip of DFIG could be restrained with controlling the rotary speed of VFT during LVRT to reduce the amount of reactive power consumption. With MATLAB/Simulink simulation platform, the dynamic process of DFIG system was simulated during the voltage sag. The simulation results showed that the amount of reactive power absorbed by DFIG system from grid could be decreased and the slip ratio of DFIG could be limit below the critical value with the proposed control strategy during voltage sag, which contributes to the recovery of the grid voltage and improves the LVRT performance of DFIG wind turbine.