基于改进快速排序算法的MMC均压控制策略

模块化多电平换流器(modular multilevel converter,MMC)由于其自身具有输出电平数高、开关频率低、波形质量好等优势而被广泛研究和使用。子模块电容的电压均衡问题是MMC的重点研究方向之一。传统均压方法随着子模块数目增加,将极大增加开关元件频率损耗和控制器运算量。该文提出了一种基于改进快速排序算法的均压策略,通过实时监测子模块电容电压,设置子模块电压间的离散度指标,继而控制排序模块的开通和保持。同时,通过排序算法的优化,使控制器在多模块时计算效率大大增加,降低硬件要求。在PSCAD/EMTDC仿真平台搭建MMC-HVDC模型进行仿真验证。仿真结果表明,改进的均压控制方法能够在维持系统特性相对均衡的同时,有效提高运行速度,降低子模块开关频率。

Voltage Balancing Control Strategy for Modular Multilevel Converter Based on Improved Quick Sort Algorithm

Modular multilevel converter (MMC) has a widely application and research because of its advantages of high output level, low switching frequency and good waveform quality, etc.The voltage balance of sub-module capacitor is one of the key research directions of MMC.While traditional voltage balancing method will greatly increase the frequency loss of switching element and controller operation with the increasing of the number of sub-modules.This paper puts forward an optimized capacitor voltage balancing strategy for MMC based on improved quick sort algorithm, which can trigger or maintain control scheduling module by real-time monitoring the voltage of sub-module capacitor, setting the discrete degree index of sub-modules voltage.At the same time, through the optimization of the sorting algorithm, the calculation efficiency of controller in multi-modules is greatly increased and the hardware requirements is reduced.Finally, this paper builds the MMC-HVDC model in PSCAD/EMTDC simulation platform to simulate and verify the algorithm.The simulation results show that the improved voltage balancing control method can significantly improve the running speed and reduce the switching frequency of sub-module without noticeablly influencing the system performance.