An Improved Calculation Method for Dynamic Characteristics of Electromagnetic Repulsion Mechanism Based on Series Armature Equivalence

The bypass switch is an important component for protecting the modular multilevel converter submodule in the flexible DC transmission system. Due to the low impedance of the flexible DC system, the fault current rises rapidly, imposing strict requirements on the closing speed of the bypass switch. As a linear actuator, the electromagnetic repulsion mechanism (ERM) can be a solution for the mechanical part of the bypass switch. At present, the ERM is primarily designed and optimized by the finite element method (FEM) and the equivalent circuit method (ECM). However, the FEM suffers from limitations such as low computational efficiency, large resource consumption, and model modification, while the inductance and inductance gradient required by the ECM are difficult to obtain. Moreover, the ECM divides the armature into multiple regions, resulting in highly ill-conditioned inductance matrix and inductance gradient matrix, which increases the risk of numerical errors. In this regard, a series armature equivalent method (SAEM) is proposed in this article to calculate the dynamic characteristics of ERM. First, the principle of SAEM is introduced, and the formulas of the electrical parameters are given. The calculation accuracy of the electrical parameters is verified by the FEM. Then, the dynamic characteristics of the ERM calculated by the ECM, the SAEM, and the FEM, are compared with the experimental results. The results indicate that SAEM has similar accuracy to the ECM, and it has more advantages in numerical stability. In addition, the SAEM has more advantages in calculation efficiency than the ECM and the FEM.