考虑冗余系统时变故障率和更新过程的MMC可靠性建模及其应用

针对现有模块化多电平换流器(modular multi-level converter, MMC)可靠性计算中未充分考虑冗余系统故障率时变性和缺乏考虑更新过程,从而不能科学衡量MMC可靠性的问题,提出了一种考虑MMC冗余系统故障率时变性并引入N阶梯更新过程的MMC可靠性建模方法。首先,从冗余程度、冗余方式角度细化MMC冗余系统的分类,建立可靠度与故障率间的数学解析关系来量化表征冗余系统故障率时变的变化特性,分析传统马尔科夫模型所计算的冗余系统故障率过小而导致可靠性计算结果偏高的不合理问题;其次,利用N阶梯故障率取代传统MMC冗余系统的时变故障率,并同时引入更新过程理论推导MMC的平均无故障工作时间(mean time to failure, MTTF)和稳态可用度公式,以此修正传统MMC可靠性参数计算结果偏高的问题。最后,以半桥子模块的MMC为例,验证了所提方法的有效性和可行性。

MMC Reliability Modeling Considering Time-Varying Failure Rate and Renewal Process of Redundant System and Its Application

In view of the problem that the existing research on reliability of modular multi-level converter (MMC) does not fully consider time-varying failure rate of redundant system, and lacks the evaluation method for renewal process, which can not scientifically measure the reliability of MMC, this paper proposes an MMC reliability modeling method considering the time-varying failure rate and N-step renewal process of redundant system. Firstly, from the perspective of redundancy degree and redundancy mode, the classification of redundant systems is refined. According to the classification above, the mathematical analytical relationship between reliability and failure rate is established, which indicates the characteristics of the time-varying failure rate of redundant system. It is pointed out that the failure rate of redundant system obtained by traditional methods is too small. Then, N-step failure rate is used to replace the time-varying failure rate of MMC redundant system. At the same time, the renewal process theory is introduced to deduce the mean time to failure (MTTF) and steady-state availability formula of MMC, so as to correct the problem that the calculation results of traditional methods are too high. Finally, the converter of half-bridge sub-module is taken as an example to verify the effectiveness and feasibility of the proposed method.