世界各国的风电并网导则均要求并网风机具备低电压穿越(low voltage ride-through,LVRT)的能力.传统的LVRT协调控制方案是将故障期间的不匹配能量全部储存到风机转子上以维持直流母线电压的恒定,这种方案没有考虑风机转速越限的问题.该文根据中国国标要求,对传统LVRT协调控制方案中永磁同步电机的升速问题进行详细的理论计算,结果表明该方案下多数风机在恶劣故障期间都会转速越限,从而威胁机组的安全.基于此结论,首先提出一种先存储后卸荷的协调控制方案,该方案能够保证风机转速不越限,但仍会使风机转速在恶劣故障期间达到限值,并且难以对卸荷电路的冲击电流进行优化.为了最大程度上抑制风机转速上升以及更好地优化卸荷电路,最终提出一种变桨距与比例卸荷结合的新型优化LVRT协调控制方案.最后对提出的几种LVRT协调控制策略进行仿真对比研究,验证了理论的正确性和控制方案的有效性.
Many countries' grid guidelines require that the grid-connected wind turbines must have low voltage ride through (LVRT) capability. Traditional LVRT coordinated control scheme saves all mismatching energy in the rotor of wind turbine during fault to keep DC bus voltage steady, which does not consider the possibility that the rotor speed may exceed the limit. Considering the requirements of grid guidelines in China, this paper provided detailed calculation of the question whether the rotor speed of permanent magnet synchronous generator (PMSG) would exceed the limit. The result shows that under this scheme many rotors' speed will exceed the upper limit when serious fault occurs. Considering this conclusion, this paper firstly proposed a discharging after storing scheme. This scheme could protect the rotor speed from exceeding the limit, but with which the rotor speed would reach the limit during serious fault. Furthermore, this scheme did not well optimize the impact current of discharging circuit. To deal with these problems, a new optimized coordinated control scheme which combines pitch adjustment and proportional discharging was finally proposed. The comparison simulation of the proposed LVRT coordinated control schemes shows the correctness of the theory and the effectiveness of control schemes.