Abstract
The modular multilevel converter (MMC) is now the most attractive topology for medium and high voltage power conversion applications with several advantages over the traditional voltage source converter (VSC). However, due to a large number of sub-modules (SMs) in the MMC, system reliability is a big challenge in its practical application, where each SM may be considered as a potential point of failure. In this paper, a reliability evaluation based on the Markov model is proposed for the MMC. The failure rates of the power electronic devices and SMs are firstly analyzed. Then, the Markov model and the state transition equation of the system are built in detail. A general reliability evaluation function is established, in which the mean time to failure and reliability evaluation of the MMC with redundant SMs are also discussed. Finally, a practical direct current (DC) distribution example for reliability evaluation is analyzed, and the results verify that the reliability evaluation based on the Markov model could provide a useful reference for project design.
Highlights
The offshore wind power has been widely developed in Europe, China, the United States and Australia [1]
Voltage source converter (VSC) based high voltage direct current (HVDC) transmission systems, including multi-terminal HVDC systems, are widely applied to transmit the power [2, 3], in which the modular multilevel converter (MMC) topology attracts the most attention of researchers [4]
In a practical power system project, it is always difficult to provide a precise reliability evaluation for MMC because there is a large amount of power electronic components
Summary
The offshore wind power has been widely developed in Europe, China, the United States and Australia [1]. There is a big motivation to find a solution for reliability evaluation and submodule (SM) redundancy configuration of the MMC. Using the k-out-of-n: G model and Gamma distribution, a reliability function of MMC was established [15], wherein the failure rates of SM components were based on the experience-hypothesis. The Markov model is proposed to analyze the failure rates of the MMC and its SMs, based on a graphical representation of system states. A general function for reliability evaluation of the MMC is given. The mean time to failure and reliability evaluation of the MMC with a redundant SM are both discussed.
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