An Improved Multiphysics Analysis Model for the Short-Circuit Fault Ride-Through Capability Evaluation of the MMC Submodule Busbar

The short-circuit fault is the severest fault that threatens the reliability of the modular multilevel converter (MMC) submodule busbar. When the short-circuit fault occurs, a huge overcurrent will flow through the busbar. Since the discharge time is very short and the discharge current is too large, the discharge current produces a strong skin effect on the busbar, resulting in overheating and deformation of the busbar, which may cause the permanent failure of the busbar. The busbar is the key component of the MMC submodule. It is therefore crucial to evaluate the fault ride-through capability of the MMC submodule busbar. The key feature of the short-circuit behavior of the busbar is that the large electromagnetic force is induced by the fault current, which causes the deformation of the busbar in a very short transient. The fast deformation of the conductor will generate the electromotive force induced current by the fast deformation of the conductor in a strong magnetic field. Plasticity of the conductor also significantly influences the deformation of the conductor. The existing researches on the failure mechanism of the busbar did not take these two important factors into account. This paper proposes an improved multiphysics analysis model which considers both the dynamic electromotive force and plasticity for analyzing the reliability of the MMC submodule busbar under the short-circuit fault. The fault current through the busbar is derived by numerical calculation. Utilizing the fault current as the input, an improved multiphysics analyzing model, which takes both features into account is proposed. Simulation results show that the dynamic electromagnetic force induced current and plasticity play dominant roles in the deformation of the busbar and are key factors that need to be taken into account in the short-circuit analysis of the busbar.