Page 34 - Electric Drives and Electromechanical Systems

26 Electric Drives and Electromechanical Systems

FIG. 1.14 Overview of the electrically operated functions supplied in a current petrol powered car.

multi-voltage system with some functions remaining at 12 V, and others operating from
voltages as high as 48 V, (Kassakian et al., 1996), this will allow for the reduction in
cabling volume as a higher voltage results lower current draw.

1.4.2 Electric vehicles

Electric cars were first developed in the early 1900’s and were widely used, until the
introduction of low cost, mass produced petrol engine cars by Ford. It is only recently with
increasing concerns about the environment that there has been a determined move to
replace petrol and diesel vehicles with all electric versions. Currently vehicle can be
supplied in two main versions, a hybrid, where a small petrol engine supplements the
energy stored in the battery to allow increased range and less dependence on charging
points, or the pure electric vehicle that depends solely on the stored energy in the battery.
Electric machines drives are a key part of the three enabling technologies for electric
vehicles and hybrid electric vehicles, the other being the batteries and overall control
system. The basic characteristics which are required of the electrical motor and its
associated drive system include:

A high torque density and power density
High torque at low-speed with the capability for starting and driving up hill, in
addition the availability of high power at high-speed is required for safe driving.
High efficiency over the required torque and speed ranges, particularly at low
torque operation
High reliability and robustness for given the environment
Acceptable costs, particulary those assocated with the battery.

The actual drive motor used is a company specific decision as while the induction
motor, permanent-magnet synchronous motor or switched reluctance motor can pro-
vide the required characteristics.