1.2 Drive Technology Trends 3
1.2 Drive Technology Trends
This sections aims to provide the reader with an overview of technology
trends associated with key components of the electrical drive as shown in
Fig. 1.1. Most importantly the objective in each of the ensuing subsections
is to identify important developments and trends of key drive elements such
as the machine, converter and controller.
1.2.1 Electrical Machines
The primary electro-mechanical energy converter of the drive is the electrical
machine, which must be controlled in accordance with the industrial pro-
cesses in which the unit is deployed. Modern electrical drives typically use
one of the three electrical machine types shown in Fig. 1.3.Thesemachine
types are referred to as the induction (asynchronous), PM synchronous and
switched reluctance machine and are shown in Fig. 1.3 consecutively from
top to bottom and will be discussed extensively in this book. Both asyn-
chronous and synchronous machine configurations depicted in Fig. 1.3 are
shown with the typical three-phase winding, which is located in the stator
slots of the machine. Note that other machine types including the brushed DC
machine are also still in use. Of the three configurations shown in Fig. 1.3,
the induction machine is most commonly found in industrial drives. This
can be attributed to the inherent robustness of the machine itself and the
presence of tried and proven drive components which form the basis of a
reliable drive. Above all, the emergence of fast, low-cost digital processors
and micro-controllers has been instrumental in achieving this market posi-
tion, given that these units are able to accommodate well established con-
trol algorithms such as field-oriented control. The end result is a brushless
and in many cases (position) sensorless induction machine drive with dy-
namic performance that outperforms that of the classical brushed DC ma-
chine.
An important performance parameter of the machine is the power density,
i.e., the output power to weight ratio in (kW/kg). The power density over
the past century has steadily increased from 0.02
kW
/kg at the beginning of
the 20
th
century to 0.15
kW
/kg by 1970, according to an ‘S’ curve as typi-
cally found in maturing technologies. The expectation at that time was that
further substantial increases in power density were unlikely. Consequently,
power density values were expected to level off around the 0.16
kW
/kg value,
given the need to keep operating temperatures within acceptable levels. The
importance of this statement follows from Fig. 1.4, which shows the relation-
ship between operating temperature and lifetime. Hence, according to this
figure, a life-time of, for example, 80 000 h can be expected provided operat-