Development of Fast Onboard Chargers for Electric Vehicles

Abstract

Using electric vehicles (EVs) powered by renewable energy as a replacement for fuel vehicles is a key strategy to reduce greenhouse gas emissions. However, EV adoption faces two significant challenges: long charging times and range anxiety, both of which hinder the rapid replacement of fuel vehicles. Aiming at reducing charging time, increasing the charging power of on-board chargers (OBCs) and off-board chargers to increase charging speed is necessary. Since off-board chargers have no strict volume limitation, their power can be easily increased by increasing their volume. The available space for OBCs is limited, so it is difficult to increase their power by enlarging their size. To address this limitation, their power density should be increased.

A review of the literature reveals two main strategies to increase power density. The first strategy is to propose new topologies that reduce the size of OBC components. The second method involves minimizing power loss in OBC converters, thereby reducing the size of heatsinks. To achieve this research goal, some preliminary results are as follows. First, a new AC-DC topology with a small DC bus capacitor is proposed, increasing OBC power density. Second, two different power efficiency optimization methods are introduced for a four-switch buck-boost converter, which can be used in an OBC or a vehicle-to-vehicle charger. This method was verified through experiments. Third, a high power density capacitively isolated dual active bridge DC-DC converter is proposed for on-board charger applications. The power density is improved while maintaining the isolation function.

To address range anxiety, a drivetrain integrated vehicle-to-vehicle (V2V) buck-boost fast charger with soft switching is proposed. One of the proposed power efficiency optimization methods of four-switch buck-boost converter is implement in this V2V charger. With this method, vehicles can quickly share high power, thereby alleviating range anxiety within a few minutes.

In summary, with the proposed power efficiency improvements strategy and high power density topology, the OBC charger power can be increased, increasing the charging speed. The proposed V2Vpower-sharing method can share large energy within two vehicles rapidly, which reduces range anxiety.

Date of Award	7 May 2025
Original language	American English
Supervisor	VINOD Khadkikar (Supervisor)