Overview

If an electric vehicle is to operate efficiently and effectively it is essential that the total vehicle system is optimised at all times to ensure that the energy available is used as effectively as possible. The amount of energy available is normally much less than that in a gasoline-powered vehicle, but the performance needs to be comparable if the electric vehicle is to operate on the road system at the same time as conventional vehicles.

In the early days of electric vehicles only the electric motor speed and torque were controlled and this was done by switching batteries in and out to give coarse voltage control and by variation of field and armature resistance of the DC motors universally used at that time. Typical basic control circuits for series, shunt and compound DC motors are shown in Chapter 3. Figure 3.3. These control techniques were adequate to make the early electric vehicles competitive, but once the internal combustion engine was fully developed in the first decade of the 20th century (see Chapter 2), the performance of vehicles using this form of propulsion was so much improved that electric vehicles ceased to be of any interest. When they appeared again in small numbers in the 1960s the early methods used for the control of DC motors were still in use. They were eventually superseded by more efficient chopper techniques which permitted a much finer control of power to the motor armature than was possible by battery switching and resistance variation.