Scalable Integrated Drive System for Battery Electric Vehicles

Abstract

Conventionally, electric powertrain in battery electric vehicles are designed and optimized for a particular vehicle category and performance requirements. In this thesis the design of an electric powertrain using two different type of machine is proposed which can be implemented across passenger vehicle categories and provide various performance levels. One of the machine will be high efficiency and the other capable of providing high peak power. The powertrain is dimensioned by analysing existing combustion engine based as well as battery electric vehicle specifications along with wheel load analysis performed on simplified vehicle models using standard drive cycles. Two different vehicle models representing a small and medium sized car is used. The acceleration requirements of various drive cycles are observed to mainly determine the peak power of the powertrain. A V-shaped interior permanent magnet machine is designed to support most of the drive cycle requirements with an electromagnetically excited synchronous machine to provide overloading capabilities. To compare the proposed drive system with the two different machines, a third machine using the same V-shaped magnet geometry is designed to represent a conventional electric powertrain. The proposed drive system is observed to achieve similar torque speed operating boundary as the centralized drive using single machine. The peak efficiency of the centralized drive motor was observed to be higher and the efficiency contours were wider as expected. However, the average operating efficiency of the centralized drive machine was found to be inferior to the proposed design. It was observed that the proposed design of the powertrain can result in higher operating efficiency while providing a scalablity of peak power.