Current Sharing Analysis and Evaluation of Parallel DC-Link Capacitors in Vehicle Motor Drive

Abstract

In electric vehicle inverter systems, the DC-link capacitor bank becomes a critical obstacle to high power density due to its large volume. DC-link capacitor bank commonly adopts a multi-core parallel structure. The challenges exist in the current sharing of parallel capacitor cores because of the imbalance of stray parameters in the busbars. A current sharing analysis method aiming at thermal stress for capacitor banks in high-power-density inverters based on the characteristic matrix is proposed in this paper. First, the design basis of DC-link capacitors is given theoretically. Then, the complex coupling impedance model between multiple ports on capacitor busbars is mathematically derived by the matrix method, revealing the current resonance phenomenon of parallel capacitor cores affected by stray parameters. Next, three capacitor banks are evaluated by the proposed current sharing model. The influence of capacitor core arrangement and terminal position on current sharing is explored, which can guide capacitor banks’ high-power-density structure and heat dissipation design. Finally, an experimental platform is built with customized capacitor samples. The experimental results are consistent with the analysis results of the model, verifying the proposed method.