Motor control is required in large number of industrial and domestic applications such as
transportation systems, rolling mills, paper machines, textile mills, machine tools, fans, pumps,
robots, and washing machines. Systems employed for motion control are calleddrives and may
employ any of the prime movers. Drives employing electric motors are known as electric drives.
Nowadays, in electric power stations generating large amounts of electric energy for
agriculture, industry, domestic needs, and electrified traction facilities and in driving all kinds of
working machines, electric motor is essential, which is the predominant type of drive so the term
electric drive being applied to it.
Electric drive becomes more popular because of its simplicity, reliability, cleanliness,
easiness, and smooth control. Both AC and DC motors are used as electric drives; however, the
AC system is preferred because:
It is cheaper.
It can be easily transmitted with low-line losses.
It can be easy to maintain the voltage at consumer premises within prescribed limits.
It is possible to increase or decrease the voltage without appreciable loss of power.
In spite of the advantages of AC motor, sometimes DC motor is used because:
In some processes, such as electrochemical and battery charging, DC is the only type of power that is
The speed control of DC motors is easy rather than AC; thus, for variable speed applications such as lift
and Ward Leonard system, the DC motors are preferred.
DC series motor is suited for traction work because of high starting torque.
1.2 BLOCK DIAGRAM OF ELECTRIC DRIVE
1-φ and 3-φ, 50-Hz AC supplies are readily available in most locations. Very low power drives
are generally fed from 1-φ source; however, the high power drives are powered from 3-φsource;
some of the drives are powered from a battery