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对于双馈式风电机组而言,当采用转子励磁这一类控制方法进行低压穿越(low voltage ride-through,LVRT)时,根据具体控制方法的不同,其LVRT能力不同。但是由于转子电压幅值的限制,使得转子励磁控制方法存在一个极限。为了分析不对称电压跌落故障下转子励磁控制方法的极限,该文以最小化转子电流为目标,基于最优控制理论设计了一种转子励磁最优控制方法。基于该方法可以得到不对称故障下转子励磁控制方法的极限,进而衡量转子励磁控制下系统对于不对称故障的穿越能力。最后以典型的1.5MW双馈式风电机组为例,分析了3种不对称故障下转子励磁控制的故障穿越能力。由分析结果可得:在相同的电压跌落深度下,相间短路故障最难穿越,两相接地故障次之,单相接地故障最容易穿越。
For DFIGs, the LVRT capability varies according to the particular control method when LVRT (LVRT) is adopted. However, due to the limit of the rotor voltage amplitude, there is a limit to the rotor excitation control method. In order to analyze the limit of the rotor excitation control method under the condition of unsymmetrical voltage drop, this paper aims at minimizing the rotor current. Based on the optimal control theory, a rotor excitation optimal control method is designed. Based on this method, the limit of the rotor excitation control method under asymmetrical fault can be obtained, and then the system’s ability of crossing the system under asymmetrical fault can be measured. Finally, taking a typical 1.5MW doubly-fed wind turbine as an example, the failure traversal ability of the rotor excitation control under three kinds of asymmetrical faults is analyzed. According to the analysis results, under the same voltage drop depth, the shortest interphase fault is the most difficult to cross, the second phase is the earth fault, and the single phase earth fault is the easiest to cross.