A segmented traction drive system with a small dc bus capacitor

The standard voltage source inverter (VSI), widely used in electric vehicle/hybrid electric vehicle (EV/HEV) traction drives, requires a bulky dc bus capacitor, typically made of polypropylene films, to absorb the large ripple currents generated by the pulse width modulated switching actions and prevent them from damaging and shortening the battery's life. The dc bus capacitor presents a significant barrier to meeting the U.S. DRIVE targets for cost, volume, and weight for inverters. Currently the dc bus capacitor contributes up to 20% of the cost and weight of an inverter and up to 30% of an inverter's volume. The large ripple currents become even more problematic for the film capacitors (the capacitor technology of choice for EVs/HEVs) in high temperature environments as their ripple current handling capability decreases rapidly with rising temperatures. There is thus an urgent need to reduce the ripple currents. This paper presents a segmented traction drive system that can significantly decrease the ripple currents and thus the size of the dc bus capacitor.