具有较低复杂度和开关频率的MMC混合排序均压算法

模块化多电平换流器(MMC)在世界范围内的直流输电中应用已经十分广泛,其中电容电压均衡控制策略是MMC应用的关键技术与难点。文中首先提出了一种分两组的组间比较排序法,称为OF排序法。该方法排序的最大时间复杂度为N-1,但该方法的使用范围受限。因此,在此基础上又提出了一种新型MMC混合排序均压算法。该算法在大幅降低排序时间复杂度的同时还能够降低器件的开关频率。以厦门柔性直流输电工程为例,验证了该算法在多种工况下的正确性。最后,通过仿真计算出新型混合排序均压算法的时间复杂度约为1.45 N,优于现有的其他MMC均压排序算法,并且仿真结果显示该算法还能降低开关频率,约为传统冒泡法的1/2。

Hybrid Sorting Algorithm with Low Complexity and Switching Frequency for Capacitor Voltage Balanced Control of Modular Multilevel Converter

The modular multilevel converter(MMC)is applied in the DC transmission system all over the world, while the capacitor voltage balanced control strategy stands out for its difficulty and complexity. This paper presents a sorting algorithm based on a comparison between two groups, called the OF sorting algorithm. The maximum time complexity of the method is N-1, but the algorithm is unlikely to be practical because of its limited range of application. Therefore, a new hybrid sorting algorithm for capacitor voltage balanced control of MMC is proposed to reduce the time complexity and device switching frequency. The effectiveness of the proposed algorithm under various conditions is verified based on the Xiamen MMC-HVDC project. The time complexity of the new hybrid sorting algorithm is 1. 45N, which is better than that of other existing MMC sorting methods for about half reducing the switching frequency compared with the traditional bubble sorting method.