Electric Drive-Parts Pros and Cons of Electric Drives Classification of Electric Drives Selection of Electric Drive Four- Quadarant Control

1.  Electric Drive-Parts
 Pros and Cons of Electric Drives
 Classification of Electric Drives
 Selection of Electric Drive
 Four- Quadarant Control

2. • Systems employed for motion control are called
as Drives.
• It may employ any of prime movers such as diesel
or petrol engines, gas or steam turbines, steam
engines, hydraulic motors and electric motors, for
supplying mechanical energy for motion control.
• Drives employing electric motors are called as
Electrical Drives.

4.  Power Modulator :
• The power modulator regulates the output
power of the source.
• The power modulator converts the energy
according to the requirement of the motor
• e.g.if the source is DC and an
induction motor is used then power
modulator convert DC into AC.
• It also selects the mode of operation of the
motor, i.e., motoring or braking

5.  The electric drive system, the power modulators can
be any one of the following
◦ Controlled rectifiers (ac to dc converters)
◦ Inverters (dc to ac converters)
◦ AC voltage controllers (AC to AC converters)
◦ DC choppers (DC to DC converters)
◦ Cyclo converters (Frequency conversion)

7. Control Unit :
• The control unit controls the power modulator which
operates at small voltage and power levels. The
control unit also operates the power modulator as
desired.
• It also generates the commands for the protection of
power modulator and motor. An input command
signal which adjusts the operating point of the drive,
from an input to the control unit.
Sensing Unit :
• It sensesthe certaindrive parameter like
motor current and speed.
• It mainly required either for protection or for
closed loop operation.

8. • The electrical drives are available in a wide
range of torque, speed and power.
• The electrical drive does not pollute the
environment.
• It can operate in all four quadrants of speed
torque plane.
• They can be started instantly and can
immediately be fully loaded.
• They have flexible control characteristic and
can be employed to automatically control
the drive.
• No need for mechanical gears as speed has
been changed electrically

9. • The power failure completely disabled the whole of
the system.
• The application of the drive is limited because it
cannot use in a place where the power supply is not
available.
• It can cause noise pollution.
• The initial cost of the system is high.

10.  According to Mode of Operation
◦ Continuous duty drives(: paper mill drives, compressors, pumps.)
◦ Short time duty drives(motors used for opening and closing lock gates and bridges)
◦ Intermittent duty drives (rolley buses )
 According to Means of Control
◦ Manual
◦ Semi automatic
◦ Automatic
 According to Number of machines
◦ Individual drive
◦ Group drive
◦ Multi-motor drive

11. • If several group of mechanisms or machines are organized on
one shaft and driven or actuated by one motor, the system is
called a group drive or shaft drive.
Advantage : Most Economical
Disadvantage : More Faults and Low Efficiency
Individual Drive
• If a single motor is used to drive or actuate a given
mechanism and it does all the jobs connected with
this load , the drive is called individual drive.
• Each motor is driven by its own separated
motor with the help of gears , pulleys etc.
Disadvantage: Power loss occurs

12. • Each operation of the mechanism is taken care of by
a separate drive motor.
• The System contains several individual drives each of
which is used to operate its own mechanism.
Advantage :
• Each Machine is driven by a separated motor it can be run
and stopped as desired.
• Machines not required can be shut down and also
replaced with a minimum of dislocation.
• There is a flexibility in the installation of different
machines.
Disadvantage:
• Initial high cost

13.  According to Dynamics and Transients
◦ Uncontrolled transient period
◦ Controlled transient period
 According to Methods of Speed Control
◦ Reversible and non-reversible uncontrolled constant
speed.
◦ Reversible and non-reversible step speed control.
◦ Variable position control.
◦ Reversible and non-reversible smooth speed control.

14.  Choice of an electric drive depends on a number of factors. Some of the important factors are.
1. Steady State Operating conditions requirements
Nature of speed torque characteristics, speed regulation, speed range, efficiency, duty
cycle, quadrants of operation, speed fluctuations if any, ratings etc
2. Transient operation requirements
 Values of acceleration and deceleration, starting, braking and reversing performance.
3. Requirements related to the source
 Types of source and its capacity, magnitude of voltage, voltage fluctuations, power
factor, harmonics and their effect on other loads, ability to accept regenerative power
4. Capital and running cost, maintenance needs life.
5. Space and weight restriction if any.
6. Environment and location.
7. Reliability.