Abstract
In the field of high voltage level applications, modular multi-level converter (MMC) has the definite advantages of low power loss and modularity and there have been many studies on its reliability. Some researches focus on the degradation of physical characteristics in the lifetime prediction of key devices, but the degradation of physical characteristics has not been directly used in the research of MMC system level reliability. The traditional exponential distribution failure rate is constant while the Monte Carlo method assumes the random distribution of multiple devices. Neither of these two methods can describe the reliability of a single device with physical characteristics degradation. This article presents a system level MMC reliability analysis and design method based on MMC mission profile and insulated-gate bipolar transistor (IGBT) lifetime degradation. According to the IGBT current and power loss in MMC, the annual mission profile and junction temperature result are analyzed by rainflow counting algorithm. In terms of device degradation, the thermal network updating method is used to calculate the life of IGBT in different time, and the reliability analysis method based on exponential distribution is improved. To optimize the redundancy design of the system, the multi-objective function optimization is processed.
Highlights
Modular multi-level converter (MMC) [1] which is widely used in high voltage direct current (HVDC) field has obvious advantages in hydropower generation
In terms of the component level failure rate and reliability analysis, the annual temperature mission profile and the power mission profile under MMC operation condition are processed by the rainflow algorithm at first
The thermal network updating is implemented to calculate the lifetime in sections, and the time-varying failure rate for single device degradation can be obtained as an input of the failure rate conversion method
Summary
Modular multi-level converter (MMC) [1] which is widely used in high voltage direct current (HVDC) field has obvious advantages in hydropower generation. Due to the failure rate of traditional exponential distribution is constant, the reliability analysis cannot be accurate in actual working condition. From device level lifetime prediction to system level reliability, a Monte Carlo method is proposed to analyze system level reliability [9] based on the working condition profile. G. Lv et al.: Reliability Analysis and Design of MMC Based on Mission Profile for the Components Degradation. According to the annual mission profile and power mission profile, this article starts at the aspect of key device degradation, evaluates IGBT and capacitor damage with working conditions. To improve the reliability evaluation method under the traditional exponential distribution, a failure rate conversion method based on the actual working condition mission profile and aging analysis is proposed in this article. After comparing the reliability analysis results with Monte Carlo method, multi-objective function optimization is executed to design redundancy based on reliability, and the optimal number of redundancy modules in economy as well as reliability is given correspondingly
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