Propulsion-Machine-Integrated Universal Onboard Chargers for Electric Vehicles

Abstract

Onboard level-1 and level-2 battery chargers are widely utilized in electric vehicles (EVs) for home overnight or office daytime charging. However, onboard level-1 and level-2 chargers suffer from power limitations and long charging time. On the other hand, high-power off-board chargers are utilized for fast charging, but they are bulky, expensive and require comprehensive evolution of charging infrastructures. Onboard chargers integrated with the propulsion systems of EVs provide a promising solution for fast charging of EV battery packs without contributing to additional weight and burden on the vehicle. This dissertation presents integrated charging systems, using the propulsion machine and its inverter for onboard battery charging. The proposed integrated onboard chargers do not need any modification of the propulsion systems to implement onboard battery charging. The integrated charging approaches are highly practical and applicable for commercial EVs in market. Initially, a single-phase propulsion-machine-integrated onboard charger is introduced and developed, which is capable of power factor correction (PFC) and battery voltage/current regulation without any bulky add-on passive components. The machine windings are utilized as mutually coupled inductors for PFC, and the inverter along with the machine windings constructs a two-channel interleaved boost converter. The input current ripple cancellation effect of the interleaved circuit is analyzed in detail, and the operation principles of the charging systems are presented. The feasibility of the single-phase integrated charger is proved by experimental results. Then, two approaches for three-phase propulsion-machine-integrated onboard charging are introduced and investigated. In the first approach, the charger topology is composed of a three-phase six-switch power electronics interface and the propulsion system. The proposed interface, mainly consisting of semiconductors, has small size and high power density, enabling onboard installment. The detailed operation modes of the topology are presented. In addition, the control-oriented modeling of the charging system is conducted, and a control system is designed to enable both the unity PFC and the battery voltage/current regulation. A 3.3kW prototype is designed, developed and tested for the validation of the proposed concept. The second approach is based on a three-phase three-switch power electronics interface, which is intended to be an even smaller interface. The power density of the three-switch interface increases by 40% in comparison to the first approach. The modeling and control strategy of the charging system are investigated and presented. A 5kW prototype is designed and built to validate the charging system and its control strategy.