Identification and performance simulation of a hybrid i.c.-engine/battery electric automotive power train. Part 2: The electric traction system

Abstract

This paper, and its companion, describe the identification, modelling and simulation of the drive-train components in a hybrid i.c.-enginelbattery electric car. This paper concentrates on the electric traction system and describes the identification of discrete transfer functions that relate motor current and motor shaft torque to the input demand to the power electronic controller. All the traction system transfer functions identified are related to a theoretical unalysis of the DC traction system and both full- and reduced-order models are derived. In the identification procedure the non-linear gains are identified separately to the system dynamics which leads to system transfer functions that are ideally suited for controller design. It is shown thut the power electronic controller has three distinct operating modes, and transfer functions are identified for each mode. Simulated results are compared with test data and the identified transfer functions shown to describe the behaviour of the electric traction system accurately. A method to predict motor torque by measuring armature current and field current is also presented. With the identified system transfer functions it is possible to design a control unit which will control the torque from the electric traction motor in a smooth manner.