基于Haar小波变换重构开关序列的MMC子模块电容值在线监测方法

Online Monitoring Method for Sub-Module Capacitance in Modular Multilevel Converter Based on Haar Wavelet Transform Reconstruction Switch Sequence

电容器作为模块化多电平换流器(MMC)系统子模块核心部件,因长期工作于交流、大功率的工作环境,使其成为最容易失效的部件之一。因此,电容器健康状态的实时监测对MMC系统可靠运行具有重要意义。该文提出一种基于Haar小波变换重构开关序列的MMC子模块电容值在线监测方法,首先,通过对MMC系统实测的电容器电压信号进行Haar小波变换重构出子模块投入与切除的开关序列;其次,基于重构的开关序列提取电容器的充电时段电压信号,并结合桥臂实测电流信号实现电容器容值在线反演计算;最后,通过MMC系统工况模拟平台验证了该文所提方法的准确性和有效性。该方法仅需控制系统原有采集的电容电压和桥臂电流信号为监测方法输入,即可实现对电容器容值的评估,去除了对开关信号的需求,极大地降低了监测的难度,为MMC系统电容器的健康状态监测和主动运维提供了方法和数据基础。

As the core component of the modular multilevel converter(MMC)systemsub-module(SM),the capacitoris one of the most fragile components due to its long-term working environment of high-frequency and high-power.Therefore,real-time monitoring of capacitor status is very important to ensure the reliable operation of the MMC system.In this paper,an online monitoring method for SM capacitance in MMC based on Haar wavelet transform reconstruction switch sequence is proposed.Firstly,the input and excision switch sequence of submodule is reconstructed by Haar wavelet transform on the capacitor voltage signal of the MMC system.Secondly,the voltage signal during charging period of the capacitor is selected based on the reconstructed switching sequence,and the capacitance value is monitored online combined with the bridge current signal.Finally,the accuracy and effectiveness of proposed method are verified by the MMC system working condition simulation platform.The proposed method can evaluate the capacitance through the capacitor voltage and arm current signals from the control system,which greatly reduces the difficulty of monitoring by removing the need for switching signals.It provides theoretical and method support for capacitor condition monitoring and active operation and maintenance of the MMC system.