Optimal Dimensioning of DC Link Capacitor for Traction Machine and Drive Cycles

DC link capacitors in DC/AC inverters can be bulky and expensive. Reducing capacitor size can improve power density and reduce the cost of the inverter. The capacitor size depends on the voltage and current stress experienced by the capacitor in operation. Dimensioning the capacitor current stress for all loads can result in significant oversizing. An optimized dimensioning of the DC link capacitor current stress for a specific load, e.g., the traction machine, and load cycle, e.g., a drive cycle, is presented for a passenger electric vehicle and an electrified heavy-duty truck. The analysis considers two types of traction machines: a permanent magnet synchronous machine (PMSM) and an electrically excited synchronous machine (EESM). Four different DC link designs, two for each application, are evaluated in simulations by considering the capacitor lifetime. Simulation results show that a 25% reduction in capacitor size is possible without negatively affecting the lifetime using the proposed method.