兆瓦级风电变流器在低穿时热负荷再分配调制策略研究

多电平拓扑结构风电变流器中,三电平中点钳位型拓扑是在海上兆瓦级风电系统中最有应用前景的。然而,随着风电机组电网适应性的需求越来越多,对变流器系统的可靠性要求也越来越高。针对这个问题,本文首先对兆瓦级三电平中点钳位型风电变流器在低电压穿越时的热负荷分布进行了分析,然后提出了一种改进的空间矢量调制方法,在该方法作用下可以使得各个功率器件热负荷重新分布。为了验证该调制方法的有效性,设计了相关试验,试验结果表明,在新的调制策略作用下,变流器在低电压穿越时各个功率器件的热负荷趋于均衡,最大热应力功率器件的结温也在正常范围内,该方法在改变热负荷的同时,还增强了对中点电位的控制能力,而这是中点钳位型变流器的关键技术之一。

Study on Modulation Strategy of Thermal Load Redistribution of Megawatt Wind Power Converter at Low-voltage Ride-through

In the wind power converter with multiple level topological structures,three-level neutral-point-clamped (NPC) converter is a promising multilevel topology in offshore megawatt wind power generation systems. However,with the growing requirements by grid adaptability,the requirement to the reliability of converter becomes a more and more high. In view of this issue,in this paper,the thermal load distribution a megawatt three-level NPC wind power inverter in the low-voltage ride-through(LVRT)is analyzed. Then,a kind of improved method for space vector modulation is proposed and related test is designed, under which the thermal load of each power element is redistributed. It is shown by the test result that under the action of new modulation strategy,the thermal load of each power element at low voltage ride through of converter tends to balance,the temperature of power element with maximum stress is also within normal range. This method, at the time of changing thermal load,also increase the control ability to the neutral point potential and this is one of the key techniques of the neutral point clamped topology.