Abstract
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.
Highlights
The modular multilevel converter (MMC) has been widely used in high voltage direct current (HVDC) transmission systems due to its advantages of easy expansion of voltage and capacity level, low harmonic content, low switching frequency, and low operational losses [1]–[3]
When the short-circuit fault occurs to the press-pack Insulated Gate Bipolar Transistor (IGBT)-based MMC submodule, the capacitor of the submodule discharges through the path of the positive terminal of the capacitor-IGBT1-IGBT2-the negative terminal of the capacitor
When the short-circuit fault occurs, the transient overcurrent flows through the MMC submodule busbar, which generates a strong electromagnetic field around the busbar
Summary
The modular multilevel converter (MMC) has been widely used in high voltage direct current (HVDC) transmission systems due to its advantages of easy expansion of voltage and capacity level, low harmonic content, low switching frequency, and low operational losses [1]–[3]. Y. Cai et al.: Improved Multiphysics Analysis Model failure mechanism of the MMC submodule busbar under the short-circuit fault, it is necessary to analyze the coupled electromagnetic-thermal-mechanical field of the busbar. In [18], the coupled electromagnetic-thermal-mechanical field model of the three-phase rectangular busbar was studied, and the influence of multiphysics coupling factors on the temperature and deformation calculation results of the busbar was analyzed. The coupled electromagnetic-thermal-mechanical field of the busbar has been studied in the exiting research, the coupled multiphysics model for short-circuit fault analysis is imperfect Some detailed features such as the dynamic electromotive force and plasticity, which significantly influences the failure analysis of the busbar, haven’t been taken into account.
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