基于双馈风电场的三相短路电流计算及保护方法

Calculation and protection method for a three-phase short circuit fault current based on a doubly-fed wind field

新能源发电技术在电力系统中逐渐占据越来越大的比重。为了实现电力系统安全运行的稳定性,需要了解系统故障的影响,根据双馈风力发电机的撬棒动作情况以及相关暂态特性完成短路电流计算。通过建立双馈风力发电机模型,并根据双馈风力发电机在三相短路故障期间投入的撬棒保护,对风机内在机理的动态变化进行分析,精确计算定转子磁链在故障期间的变化情况,从而得到撬棒动作时的新三相短路电流计算方法。最后通过PSCAD/EMTDC进行仿真验证,并利用Matlab检验计算方法的精确度。同时根据风场的低电压穿越能力与电流保护装置的特性,提出一种针对双馈风电场的低电压穿越保护方案。该方案根据低电压穿越能力的电压变化要求以及短路电流的大小协作完成对线路的保护,以便清除故障后风场电压可以及时恢复并且保持并网运行,且在一定程度上可应对低电压穿越能力的延时问题。

New energy power generation technology gradually occupies an increasingly large proportion of power system.In order to achieve the stability of power system safe operation,it is necessary to understand the impact of system failures.The short-circuit current calculation is completed according to the crowbar action and related transient characteristics of doubly-fed induction generation.By establishing a doubly-fed induction generation model,and using the crowbar protection during a three-phase short-circuit fault,the dynamic changes of the internal mechanism of the wind turbine are analyzed,and the changes of the stator and rotor flux linkage during the fault are accurately calculated,to complete the new three-phase short-circuit current calculation method when the crowbar is in motion.Finally,a simulation is carried out by PSCAD/EMTDC,and the accuracy of the calculation method is tested by Matlab.At the same time,according to the low voltage ride-through capability of the wind farm and the characteristics of the current protection device,a low voltage ride-through protection scheme for a doubly fed wind farm is proposed.The scheme helps complete the protection of the line according to the voltage change requirements of the low voltage ride-through capability and the size of the short circuit current so that the wind field voltage can restore in time and maintain the grid-connected operation after clearing the fault.To a certain extent,it can cope with the delay problem of the low voltage ride-through capability.