• What is an Electric Drive?

An Electric Drive can be defined as, a system which is used to control the movement of an
electrical machine. This drive employs a prime mover such as a petrol engine, otherwise diesel,
steam turbines otherwise gas, electrical & hydraulic motors like a main source of energy. These
prime movers will supply the mechanical energy toward the drive for controlling motion
An electric drive can be built with an electric drive motor as well as a complicated control system
to control the motor’s rotation shaft. At present, the controlling of this can be done simply using
the software. Thus, the controlling turns into more accurate & this drive concept also offers the
ease of utilizing.
The types of electrical drives are two such as a standard inverter as well as a servo drive.
A standard inverter drive is used to control the torque & speed. A servo drive is used to control the
torque as well as speed, and also components of the positioning machine utilized within
applications that need difficult motion.
• Block Diagram of Electric Drive
The block diagram of an electric drive is shown below, and the load in the diagram signifies
different kinds of equipment which can be built with an electric motor such as washing machine,
pumps, fans, etc. The electric drive can be built with source, power modulator, motor, load, sensing
unit, control unit, an input command.
The types of electrical drives are two such as a standard inverter as well as a servo drive. A standard
inverter drive is used to control the torque & speed. A servo drive is used to control the torque as
well as speed, and also components of the positioning machine utilized within applications that
need difficult motion.
• Block Diagram of Electric Drive
The block diagram of an electric drive is shown below, and the load in the diagram signifies
different kinds of equipment which can be built with an electric motor such as washing machine,
pumps, fans, etc. The electric drive can be built with source, power modulator, motor, load, sensing
unit, control unit, an input command.

Fig. Basic block of Electric Drives

• Power Source
The power source in the above block diagram offers the necessary energy for the system. And both the
converter and the motor interfaces by the power source to provide changeable voltage, frequency and
current to the motor.

• Power Modulator
This modulator can be used to control the o/p power of the supply. The power controlling of the motor can
be done in such a way that the electrical motor sends out the speed-torque feature which is necessary with
the load. During the temporary operations, the extreme current will be drawn from the power source.
The drawn current from the power source may excess it otherwise can cause a voltage drop. Therefore the
power modulator limits the motor current as well as the source.
The power modulator can change the energy based on the motor requirement. For instance, if the basis is
direct current & an induction motor can be used after that power modulator changes the direct current into
alternating current. And it also chooses the motor’s mode of operation like braking otherwise motoring.

• Load
The mechanical load can be decided by the environment of the industrial process & the power source can
be decided by an available source at the place. However, we can choose the other electric components
namely electric motor, controller, & converter.

• Control Unit
The control unit is mainly used to control the power modulator, and this modulator can operate at power
levels as well as small voltage. And it also works the power modulator as preferred. This unit produces the
rules for the safety of the motor as well as power modulator. The i/p control signal regulates the drive’s
working point from i/p toward the control unit.

• Sensing Unit
The sensing unit in the block diagram is used to sense the particular drive factor such as speed, motor
current. This unit is mainly used for the operation of closed loop otherwise protection.

• Motor
The electric motor intended for the specific application can be chosen by believing various features such
as price, reaching the level of power & performance necessary by the load throughout the stable state as
well as active operations.

• Advantages of Electrical Drives

• The advantages of electrical drives include the following.
• These dries are obtainable with an extensive range of speed, power & torque.
• Not like other main movers, the requirement of refuel otherwise heat up the motor is not
necessary.
• They do not contaminate the atmosphere.
• Previously, the motors like synchronous as well as induction were used within stable speed
drives. Changeable speed drives utilize a dc motor.
They have flexible manage characteristics due to the utilization of electric braking.
At present, the AC motor is used within variable speed drives because of semiconductor converters
development.

• Disadvantages of Electrical Drive

The disadvantages of electrical drives include the following.

• This drive cannot be used where the power supply is not accessible.
• The power breakdown totally stops the entire system.
• The primary price of the system is expensive.
• The dynamic response of this drive is poor.
• The drive output power which is obtained is low.
• By using this drive noise pollution can occur.
• Applications of Electrical Drives
The applications of electrical drives include the following.

• The main application of this drive is electric traction which means transportation of materials
from one location to another location. The different types of electric tractions mainly include
electric trains, buses, trolleys, trams, and solar-powered vehicles inbuilt with battery.
• Electrical drives are extensively used in the huge number of domestic as well as industrial
applications which includes motors, transportation systems, factories, textile mills, pumps, fans,
robots, etc.
• These are used as main movers for petrol or diesel engines, turbines like gas otherwise steam,
motors like hydraulic & electric.

• Comparison between AC Drives and DC Drives

Characteristics AC Drives DC Drives
Definition AC drives (also known as VFD) convert DC drives only convert the input
the AC supply to DC using converter AC supply to the DC using
(rectifier) and invert it back from the DC converter circuit based on
to the AC using inverter to run the AC rectifier to run the DC motors.
motors.
Control AC drives control AC output from AC DC drives control DC output
input. from AC input.
Main Supply & AC Drives run by AC power supply i.e., DC Drives run by DC power
Voltage single phase and three phase AC supply i.e. Batteries and supplies
voltages. sources of DC voltages.
Self-Start Not self-starting Self-Starting
Circuit Design The circuit design of AC drives is little The circuit design of DC drives
bit complex due to the inverter and is less complex due to the single
converter which convert AC to DC and power conversion i.e. It converts
invert back DC to AC then. AC to DC only once.
Power and AC drives power and control circuits are DC drives power and control
Control Circuits complex in design as compared to the DC circuits are simple in design as
drives. compared to the AC drives.
 Breaking / The breaking and acceleration The breaking mechanism of DC
Acceleration mechanism of AC drives can be drives can be control by applying
controlled by changing the supply resistance at rotor side.
frequency (FS).
Speed Control Speed control is done by changing the Speed control is done by
supply frequency. armature and field control.
Speed Limitation Maximum speed can be achieved. The speed is limited because of
commutator used in the motors
for commutation.
Motor Speed in Up to 10k RPM Up to 2.5k RPM
RPM
Speed Regulation ~1% speed regulation is achievable in 1% speed regulation is not
motors run by AC drives. possible to achieve in motors run
by DC drives.
Speed Torque It is complex to adjust the speed torque It can be achieved easily.
curves.
Starting Torque Low High
Inverter / AC drives have both inverter and DC drives have converter and
Converter converter. chopper circuits. It doesn’t need
an inverter.
Commutator and No need of commutation but slip rings in No slip rings but Commutation is
Slip Rings AC drives. needed in DC drives.
Rectification No need of rectification circuit. Rectifier circuit is must.
Battery AC drives won’t be connected directly to DC drives can be connected and
Operation the batteries as some additional run directly through batteries
components and circuits are needed to do (providing DC voltage).
so.
Transformer AC drives can be directly connected to In DC drives, transformer is
the transformer (mains supply). needed at voltage higher than
100V.
Power usage AC drives consume less power as DC drives consume more power
compared to DC drives. as compared to AC drives.
Brushes Life High (about 10k hours) Low (about 3k hours)
span
Noise Operation of AC drives is noisy. Operation of DC drives is less
noisy.
Harmonics Inverter used in AC drives produces Converter used in DC drives
harmonics on both sides i.e., supply and doesn’t generate harmonics.
load.
Spark AC drives are spark free and can be DC drives can’t be used in wet
used in wet environment. areas due to generated spark in
the burses.
Dynamic High Low
Response
Maintenance Less More and frequent
 Size, Weight & Large Small
Power Rating
Cost AC drives are more expensive while the DC drives are less expensive
motors used in AC drives are less while the motors used in DC
expensive e.g., squirrel cage motor. drives are little bit expensive.
General uses AC drives used in almost all areas with DC drives are used in few areas
vast applications. as compared to AC drives.

• Comparison between individual drives and group drive

Point of Individual Drive Group Drive
Comparison
Motor required Separate motor is required to drive One single motor is required to
each individual machine. drive a common shaft.
Total power As each machine requires a separate As it needs only a single motor,
required in H.P. motor. Thus, the total sum of powers thus the total power in HP
(in HPs) is more. required for complete section is
lesser.
Overload The individual drive system has less The group drive system has high
capacity overload capacity. overload capacity.
Safety The operation of individual drive is The operation of group drive is
safe. not safe.
Speed control In individual drive, the speed of each In group drive, the speed control
motor can be controlled separately. of individual machine is not
possible.
System The individual drive system has clean The group drive system has
Appearance appearance. clumsy appearance.
Layout The layout of individual drive can be The layout of group drive is
changed, i.e. a new machine can be fixed and cannot be changed.
installed as per requirement and space
available.
Extension In individual drive more separate In case of group drive, future
machines can be added in future. extensions are not possible.
Effect of fault Fault in one machine does not disturb Fault in the main motor drive
operation of other machines. stops operation of all machines.
Power loss Individual drives have less power Power losses are more in the
losses. group drives.
Cost Cost involved in individual drive is For group drive, the cost is much
much more. less.
Applications Individual drives are used in lifts, Group drives are used in
cranes, shapers, lath machines, etc. workshops, paper mills, textile
mills, etc.