基于频带能量的模块化多电平换流阀中金属化薄膜电容器失效检测方法

Failure Detection Method for Metalized Polypropylene Film Capacitor in Modular Multilevel Converter Based on Band Energy

金属化薄膜电容器(metallized polypropylene film capacitor,MPPF)是模块化多电平换流阀(modular multilevel converter,MMC)中最薄弱的部件之一,准确地评估其可靠性对柔性直流输电系统的安全稳定运行十分重要。针对MPPF电容老化后聚丙烯膜熔融导致等效串联电阻(equivalent series resistance,ESR)增大,进而增加电容损耗,加速电容老化的问题,文中提出一种利用电容输出电压高频带能量来表征ESR增加,并在不同服役周期后对比能量变化从而判断电容的老化状态的方法,建立基于频带能量的MPPF电容失效检测模型。文中详细分析电容在MMC系统中的运行机理,并从MPPF电容结构的角度分析电容的失效机理;在建立的MMC系统仿真平台上研究ESR变化与电容输出电压高频带能量之间的规律;在此基础上,建立MPPF电容失效检测模型,并通过实验验证所提方法与模型的可行性和有效性。与现有方法相比,该方法只需电容器电压信息即可评估其当前失效程度,且适用于大部分开关电路中电容器的失效检测,尤其解决了传统方法成本高、算法复杂且普适性不足的问题。为模块化多电平换流阀中MPPF电容的状态监测和寿命评估提供一定的理论基础和技术支撑。

Metallized polypropylene film(MPPF)capacitor is one of the weakest components in modular multilevel converters(MMC). The accurate assessment of its reliability is crucial for the safe and stable operation of flexible DC transmission systems. The melting of the polypropylene film during the MPPF capacitor’s degradation will increase the equivalent series resistance(ESR), then increase the power loss of the capacitor and accelerating the aging process of it. To solve the problem, a method was proposed to characterize the increase of the ESR by utilizing the high frequency band energy of output voltage. The aging status of the capacitor can be judged by comparing the band energy after different service period. A failure detection model based on the band energy was finally established. The operation principle of capacitors in MMC system was studied, and the failure mechanism of the MPPF capacitor was analyzed. An MMC simulation model was established to find the relationship between the ESR and the high frequency band energy of capacitor’s output voltage. A failure detection model of the MPPF capacitor was established,the feasibility and the validity of the proposed method and model were also verified through experiment. Compared with existing researches, this method can evaluate the failure status of the capacitor only with its output voltage. This method is also suitable for failure detection of capacitors in most switching circuits, and it especially solves the problem of high cost, complicated algorithm and poor universality in traditional methods. The intended outcome of this paper will lay scientific and technological foundation for condition monitoring and lifetime assessment of MPPF capacitors in modular multilevel converters.