Multidimensional Mission-Profile-Based Lifetime Estimation Approach for IGBT Modules in MMC-HVdc Application Considering Bidirectional Power Transfer

Modular multilevel converter (MMC) applied in high-voltage direct current (HVdc) field consists of numerous submodules (SMs) and supports bidirectional power transfer, leading to the diverse mission and temperature profiles among SMs and insulated gate bipolar transistor (IGBT) modules. In this article, an IGBT lifetime estimation approach in terms of the bidirectional power transfer of MMC is proposed. The temperature profile of each module is translated based on the multidimensional mission profile, including arm current, heatsink temperature, active power, and reactive power. In this way, the average junction temperature and junction temperature fluctuation of each SM can be readily estimated according to the power transfer direction. Furthermore, both the line-frequency and low-frequency fatigue are considered in the estimation process by using corresponding lifetime models. The proposed lifetime estimation method is compared with the traditional power loss average method and one-direction power transfer method by the application of the multidimensional mission profile of the practical Nanao project. The results show the bidirectional power transfer has a big influence on the damage distribution inside SM. The lower IGBT, upper free-wheeling diode (FWD), and lower FWD suffer considerable degradation under bidirectional power transfer conditions. Moreover, bond wire fatigue is the dominant degradation mechanism in MMC-HVdc application.