Design Considerations of DC-Link Capacitors in NPC Inverters for Electric Vehicles

摘要

The dc-link capacitor of traction inverters in electric vehicles is a key component. In this paper, the dc-link capacitor current harmonics of an NPC inverter are identified as crucial design elements. In a first step, these harmonics are derived analytically and an electrical and thermal model of the capacitor are deducted. Secondly, the neutral-point balancing is evaluated. A new balancing scheme is proposed and its impact on the inverter harmonics is analyzed. The analytical considerations are verified on a test-bench setup. Finally, design rules are given to determine suitable dc-link capacitors.