Dual-Use of Onboard Chargers to Achieve Controllable DC Bus Voltage for Electric Vehicles

The power flow architecture in electric vehicles must prioritize high efficiency and power density while consistently delivering the rated torque-speed envelope. In traditional setups, where the battery is directly connected to the traction inverter’s dc link, the torque-speed envelope diminishes as the battery discharges. To address this limitation, adding a dc-dc converter between the battery and the traction inverter can help maintain torque-speed capabilities. However, this approach requires the dc-dc converter to handle the full traction power, making the system bulkier and less efficient. This paper introduces an alternative solution: leveraging the onboard charger to regulate the inverter dc-link during motoring. The analysis demonstrates that even with the onboard charger rated at only 15% of the traction motor’s power, the system can maintain the rated torque-speed envelope down to a 20% battery state of charge (SOC). The paper explains the functionality of the proposed architecture, supplemented by efficiency color maps showing a 2% improvement across the torque-speed envelope. Experimental results comparing the conventional boost converter with the proposed architecture corroborate the analysis.