Reliability Evaluation for the Press-pack Submodule in MMC-HVDC Application

Modular Multilevel Converter (MMC) is a key component of flexible HVDC system. The press-pack IGBT has many advantages and it is suitable for flexible high-voltage power transmission. However, after a long period of thermal cycling, fatigue damage will occur in each component, which can reduce the reliability of the sub-module (SM). To this end, this paper proposes a approach of lifetime estimation and reliability evaluation for MMC press-pack SMs. Through analyzing the electrical model and heat dissipation path, a thermal equivalent network is formed and adopted to calculate the junction temperature of each component. Next, rainflow counting algorithm and the LESIT model are employed to estimate the lifetimes of press-pack IGBTs (PPI) and DC-link capacitor (DCLC). Afterwards the Monte Carlo method is adopted to obtain the lifetime Weibull distribution of each component. The distribution parameters are adopted to evaluate reliability of the SM. Finally, the related factors and comparison of the SMs lifetime are analyzed, and the conclusion is expressed.