introduction to Electrical Drives Day 2.pptx

DRIVES AND VARIABLE FREQUENCY DRIVES
(VFD)

Presentation or section title
2
DAY 2
ELECTRICAL DRIVES

3
DRIVES :System employed for motion control.
What are Electrical Drives?
Electrical drives are systems that control the motion of electrical motors by adjusting
power and operational parameters: Drives employing electric motors!
The classification of electrical drives can be done depending upon the various components
of the drive system. Now according to the design, the drives can be classified ACCORDING
TO APPLICATIONS OR TYPE OF POWER SUPPLY.
According to applications; classified into three types such as single-motor drive, group
motor drive and multi motor drive. The single motor types are the very basic type of drive
which are mainly used in simple metal working, house hold appliances etc.
Group electric drives are used in modern industries because of various complexities. Multi
motor drives are used in heavy industries or where multiple motoring units are required
such as railway transport. If we divide from another point of view, these drives are of two
types.
According to power supply: AC drive and DC drive
Based on Speed and Based on Control Parameters
ELECTRICAL DRIVES

4
AC drives are used to control the speed of an electric motor, such as a three-phase induction
motor, by changing the frequency of the electrical supply to the motor.AC drive is also known
as Variable Frequency Drive (VFD) or Variable Speed Drive (VSD) (VSD).
DC motor Drives
It is essentially a speed control system for a DC electrical motor that supplies voltage to the
motor in order for it to operate at the desired speed.
There are two types of DC drives:
Analogue DC drives and Digital DC drives.
Precision control is possible with digital DC drives
ELECTRICAL DRIVES

5
Electrical drives consist of several key parts: load, motor, power modulator, control unit,
Sensing Unit and source. These components work together to drive the system. Loads can
vary and have specific requirements.
ELECTRICAL DRIVES

6
ELECTRICAL DRIVES
The power source (supply) in the above diagram provides the system with the
necessary energy.
The converter and the motor interact to one another, and the power source
controls the motor’s voltage, frequency, and current.
The power modulator controls the source’s output power. It directs power from the
source to the motor in such a way that the motor transmits the load’s required
speed-torque characteristic.
During transient operations such as
• Starting,
• Braking, and
• Speed reversal,
the excessive current drawn from the source is reversed.
The excessive current drawn from the source may cause it to overload or cause a voltage
drop.

7
ELECTRICAL DRIVES
As a result, the power modulator limits the source and motor current.
The power modulator converts energy based on the needs of the motor, for example, if
the source is DC and an induction motor is used, the power modulator converts DC to
AC.
It also selects the motor’s mode of operation, either motoring or braking.
CONTROL Unit
The power modulator, which operates at low voltage and power levels, is controlled by
the control unit.
The power modulator is also controlled by the control unit. For the protection of the
power modulator and the motor, it generates command signals.
An input command signal from an input to the control unit that adjusts the operating
point of the drive.

8
ELECTRICAL DRIVES
Sensing Unit
It detects specific drive parameters such as motor current and speed. It is primarily
required for either protection or closed loop operation.
Electric Motor
This primarily converts applied energy (source) into mechanical motion. The significant
proportion of DC motors used in electric drive systems are in
•Series,
•Shunt, and
•Compound form,
whereas AC motors are slip ring induction motors. In some cases, stepper motors or
brushless DC motors are used.

9
ELECTRICAL DRIVES
Load
The system load is specified based on the torque/speed characteristics of the system,
such as pumps, machines, and so on.
In terms of torque-speed characteristics, the electric motor and load are compatible.

10
ELECTRICAL DRIVES
ADVANTAGES OF THE ELECTRIC DRIVE
•Electric drives are environmentally friendly because they emit no smoke, fumes, or ash. As a result,
electric drives are best suited for subway and tube railways.
•Electric drives are versatile because their performance can be effectively controlled by Electronic
devices such as SCRs, IGBTs, and microcontrollers.
•There is a wide range of torque, speed, and power available.
•Electric drives are smaller and take up less space.
•They do not require any warm-up time and can be used immediately.
•Electric drives can be controlled remotely.
•A consistent source of drive.
•Powered by electrical energy, which has several advantages over other energy sources.
•Adaptable to a variety of operating conditions, including submersion in liquid, explosive chemical or
mining environments, radioactive environments, and so on.
•Electric drives have a high schedule speed and traffic handling capacity, requiring less terminal space.

11
DISADVANTAGES OF ELECTRIC DRIVE
•Installing an electric drive has a high capital cost
Electric drives are only appropriate for electrified tracks.
•Additional control circuitry is required for electric drives.
•Electric drives can occasionally cause noise pollution.
•The dynamic response of electric drives is poor.
•A power outage can render an electric drive completely inoperable.
•The output power of an electric drive is limited.
ELECTRICAL DRIVES Contd.

12
APPLICATIONS OF DRIVES
•This drive’s primary application is electric traction, which is the transportation of materials from
one location to another. Electric tractions include electric trains, trams, buses, trolleys, and solar-
powered vehicles with built-in batteries.
•Electrical drives are widely used in a wide range of domestic and industrial applications,
including motors, transportation systems, factories, textile mills, pumps, fans, robots, and so on.
•These are used as primary movers in gasoline or diesel engines, turbines (gas or steam), and
hydraulic and electric motors.

13
1.Reversible types drives
2.Non reversible types drives.
This depends mainly on the capability of the drive system to alter the direction of the flux
generated. So, several classification of drive is discussed above.

14
AC motor drives are referred to as variable frequency drives,
adjustable frequency drives, inverter drives, vector drives,
direct torque control drives, and closed-loop drives.
Regardless of how an AC drive is referred to, its primary
function is to convert the incoming supply power to an
altered voltage level and frequency that can safely control the
motor connected to the drive.
AC motor drives are designed to operate 3φ AC motors
regardless of whether the drive is designed for 1φ power (115
VAC or 230 VAC), 3φ power, or DC power. The speed of an AC
motor is determined by the number of stator poles and the
frequency of the AC power supply.
AC motor drives control the speed of a motor by varying the
frequency of the power applied to the motor. See Figure 1.
The lower the frequency applied to a motor, the slower the
motor speed. For example, an AC motor rated for 1730 rpm at
60 Hz operates at 1730 rpm at 60 Hz, 865 rpm at 30 Hz, and
432.5 rpm at 15 Hz.
Variable Frequency Drive
(VFD)
Figure 1. An AC motor drive controls the speed
of a motor by varying the frequency of the power
applied to the motor.

15
The three main components of an AC motor drive are: the converter, DC bus, and inverter.
NOTE: The converter (rectifier) receives incoming AC voltage and changes it to DC voltage. If
the AC input voltage is different from AC output voltage sent to a motor, the converter must
first step up or step down the AC voltage to the proper voltage source level. For example, an
electric motor drive supplied with 115 VAC that delivers 230 VAC to a motor requires a step-up
transformer to increase the input voltage. A drive supplied with 230 VAC would be stepped
down to deliver 115 VAC. See Figure 2.
The DC bus filters the voltage and maintains the proper DC voltage level. The DC bus may also
deliver DC to the inverter for conversion back to AC. The inverter controls the speed of a
motor by controlling frequency and controls motor torque by controlling the voltage sent to
the motor.
AC Motor Variable Frequency
Drive Components
Figure 2. The three main sections
of an AC motor drive are the
converter, DC bus, and inverter.

16

17
A converter is an electronic device that changes AC voltage into DC
voltage. Converters in electric motor drives are 1φ full-wave rectifiers,
1φ bridge rectifiers, or 3φ full-wave rectifiers. Small AC motor drives
supplied with 1φ power use 1φ full-wave or bridge rectifiers. Most
electric motor drives are supplied with 3φ power, which requires 3φ
full-wave rectifiers. See Figure 3.
AC Motor Drive Power Converter Requirements
In order for a converter to deliver the proper DC voltage to the DC bus
of an AC motor drive, the converter must be connected to the proper
power supply. AC motor drives operate satisfactorily only when
connected to the proper power supply. The power supply must be at
the correct voltage level and frequency and must also provide enough
current to operate an AC motor drive at full power. When a power
supply cannot deliver enough current, the available voltage to an AC
motor drive drops when the drive is required to deliver full power.
Converters
Figure 3. AC motor drive voltage should be
measured under no-load and full-load
operating conditions to determine whether a
drive is underpowered.

18
Current to an AC motor drive is limited by the
size of the conductors to the drive, fuse and
circuit breaker sizes, and the transformer(s)
delivering power to the system. The supply
voltage to an AC motor drive must be checked
when additional loads or drives are installed,
serviced, or added to a system. To determine
whether an AC motor drive is underpowered, the
voltage at the drive is measured under no-load
and full-load operating conditions. See Figure 4.
A voltage drop greater than 3% between no-load
and full-load conditions indicates that the AC
motor drive is underpowered and/or
overloaded.
Converters
Figure 4. The three main sections
of an AC motor drive are the
converter, DC bus, and inverter.

19
Voltage drop is found by applying the following formula:
VD=VNL VFL
−
Where
VD=Voltage Drop (in V)
VNL=No Load Voltage (in V)
−
VFL=Full Load Voltage (in V)
−
Example: Calculating Voltage Drop
What is the voltage drop when an AC motor drive is measured to have 230 V
with no load and 226 V under full load?
Solution
VD=VNL VFL=230 226=4V
− −
When the supply voltage to an AC motor drive is measured, it is
recommended to check the measured voltage against the rated input
voltage of the drive. Large-horsepower AC motor drives are connected to the
high voltage to reduce the amount of current required.
Converters

20
AC voltage sources vary due to fluctuations within the power distribution system.
AC loads, including motor drives and motors, are designed to operate within a
specified voltage range. Operating outside the specified voltage range can cause
a motor drive to operate improperly and/or incur damage over time.
Electrical loads operating at low voltages are less likely to be damaged than loads
operating at high voltages. Operating at a voltage less than the rated voltage
causes lamps to dim, heating elements to produce less heat, computers to lose
memory and/or reboot, and motors to produce less torque. Although operating
at less than rated voltage is not desirable for electrical loads, it normally does not
cause damage.
Operating at higher than rated voltage causes lamps to fail, heating elements to
burn out (open), computer circuits to become permanently damaged, and motor
insulation to be destroyed.
AC loads are rated for proper operation at a voltage that is ±10% of the device’s
rated voltage. Because higher voltages are more damaging, some devices with
higher voltage ratings have a +5% to –10% voltage rating to protect them from
the high voltage side.

21
Tech Fact
Most drives display a “low voltage” fault when the drive turns off the motor due to a low
voltage condition. When troubleshooting a low-voltage fault, measurements are taken of the
voltage into the drive, the voltage out of the drive (using the MIN/MAX mode during a
complete cycle of the motor to determine whether there is a power feed or drive output
problem), and the drive’s DC bus voltage to eliminate a drive problem.
DC Buses
DC buses filter and maintain the proper voltage level. DC buses (links) include DC filter
components and are supplied with DC voltage by the converter. The capacitors and
inductors in the DC bus filter and maintain the proper voltage level. DC bus voltage is
typically about 1.4 times the AC supply voltage to an AC motor drive.
Circuit Protection
A bridge rectifier receives incoming AC supply power and converts the AC voltage to fixed DC
voltage. The fixed DC voltage powers the DC bus of the AC motor drive. To prevent damage to the
diodes in the converter and to the AC motor drive electronic circuits, protection against transient
voltages must be included in the drive.

22
A surge suppressor is an electrical device that provides protection from transient voltages
by limiting the level of voltage allowed downstream from the surge suppressor.
Surge suppressors are installed at service entrance panels, distribution panels feeding
motor drives, and/or the incoming power lines to a drive. Normally, a surge suppressor
consists of metal-oxide Varistors (MOVs) connected to the converter of a motor drive. See
Figure 5.
A Surge Suppressor
Figure 5. Metal-oxide Varistors (MOVs) are added to the converter of an AC
motor drive to reduce the amount of transient voltage entering the motor
drive.

23
MOVs are designed for surge suppression of damaging transient
voltages. When high-voltage transients enter an AC motor drive, MOVs
change electrical state from high resistance (open switch) to low
resistance (closed switch). In a low-resistance state, MOVs absorb
and/or divert transient voltage spikes.
NOTE: MOVs limit the level of transient voltages so voltages do not
exceed the maximum voltage rating of the rectifier diodes.
Capacitors
A capacitor is an electrical device designed to store a voltage charge by
means of an electrostatic field. Capacitance (C) is the ability to store
energy in the form of an electrical charge.
Capacitors in a DC bus are charged from rectified DC voltage produced
by the converter. Capacitors oppose a change in voltage and, when DC
bus voltage starts to drop, they discharge a voltage back into the
system to stop the drop-in voltage.
The main function of capacitors in a DC bus is to maintain proper
voltage levels when voltage fluctuates. See Figure 6.
Metal-oxide Varistors (MOVs)
Figure 6. Capacitors are added to filter or
smooth the DC bus voltage.

THANK
YOU

introduction to Electrical Drives Day 2.pptx

More Related Content

Similar to introduction to Electrical Drives Day 2.pptx (20)

More from beshelsunday (9)

Recently uploaded (20)

introduction to Electrical Drives Day 2.pptx