general discussion of ED

1. ED First lecture

2. What is Electrical Drives
?????????????
Motion control is called as drives.
It may use any of the prime mover such as diesel
engine, gas or steam turbine , steam engine or any
electrical motors etc.

3. Electrical Drives
Drives are systems employed for motion control
Require prime movers
Drives that employ electric motors as
prime movers are known as Electrical Drives

4. History of Electrical Drives:
• In year 1838,Prof B.S.Lakobi tested a DC
motor supplied from a storage battery and
used it to drive a screw propeller on a boat.

5. SOME Examples of ELECTRICAL DRIVES
Electrical
drives
Industrial
applications
Textile mills Transportation Machine tools
Domestic
applications
fans
Washing
machines

6. Advantages of Electrical Drives
• Have flexible control characteristics
• Available in wide range of torque , speed and
power
• Not pollute the environment
• Adaptable in almost any operating conditions
• Can operate in all the four quadrant of
operations
• Smooth speed control

7. AC and DC Drives:
Advantages of DC drives:
• DC motors are very versatile for the purpose of
speed control
Disadvantage of DC drives :
• Sparking at the brushes limit both the highest
speed of operation and design capacity of
motor.
• Also the ripple content of the motor current
due to processes of rectification impairs the
commutation capability of the motor.

8. Disadvantages of AC Drives:
• In past AC motors were mainly used in fixed speed
applications
• When controlled using conventional methods , only
stepped speeds are possible with a limited range of
speed control.
Advantages of AC Drives:
With thyristor power converter ,the variable voltage and
variable frequency supply the speed control of
Induction motor is making AC drive competitive with
DC drives.

9. Conventional electric drives (variable speed)
• Bulky
• Inefficient
• inflexible

10. Electrical Drives Block diagram

11. Components of Block Diagram
• Power source
• Power Processor/power modulator
• Motor
• Load
• Control unit
• Sensing unit

12. Power Source
• Single phase AC
• Three Phase AC
• DC supply

13. Power Modulator:-
• Modulates flow of power from the source to the
motor in such a manner that motor is imparted
speed torque characteristics required by the load
• During transient operations , such as starting,
braking and speed reversal . It restricts the source
and motor current within permissible value
• Converts electrical energy of the source in the
form suitable to motor.
• Selects the mode of operation

14. Selection Criteria for Electric Machines
• Cost
• Thermal Capacity
• Efficiency
• Torque-speed profile
• Acceleration
• Power density, volume of motor/Torque to
weight ratio
• Ripple, cogging torques
• Peak torque capability

15. Requirement of an adjustable speed Drive:
• Stable operation: The speed torque
characteristics of the motor should be such
that stable operation of the drive is assured
in all four quadrants.
• The drive motor should also have a good
transient response.

16. Load:-
• The load has certain torque speed
characteristic
• A motor having speed torque characteristic
and capabilities compatible to the load
requirement is chosen

17. Example of cranes and hoist drives
Requirement of Drives:
The motion of the crane hook is in all three
dimensions
In crane drives , the acceleration and
retardation must be uniform . This is more
important than the speed control
For exact positioning of the load creep speed
must be possible.

18. classification of power modulator:
(a)Converters:
Need for converter arises when nature of the
available electrical power is different than what is
required for the motor.
1.ac to dc converter
2.dc to dc converter
3.Inverters
4.cycloconverters

19. (b)Variable impedances
Variable resistors are commonly used for the
control of dc and ac drives.
Can be controlled manually or automatic .
Stepless variation of resistance can be
obtained using a semiconductor switch in
parallel with a fixed resistance; variation of
duty ratio of the switch gives a stepless
variation in effective value of the resistance.

20. (c)Switching Circuits:
Need:-
For changing motor connections to change it’s
quadrant of operation
For operating motors and drives according to
predetermined sequence
To disconnect motor when abnormal
conditions occur

21. IInd lecture
Dynamics of Electrical Drives:
Torque equations
Four quadrant operation
Equivalent values of Drive parameter

22. Equivalent motor load system
Motor Load
Speed
J = polar moment of inertia of motor load system shaft referred to motor
m =Instantaneous angular velocity of motor shaft
Te= Instantaneous value of developed motor torque
Tl= Instantaneous value of load torque , referred to motor shaft
Te Tl

23. General Torque Equation
Translational (linear) motion:
Rotational motion:
dt
dv
MF 
F : Force (Nm)
M : Mass (Kg )
v : velocity (m/s)
T : Torque (Nm)
J : Moment of Inertia (Kgm2 )
 : angular velocity ( rad/s )
LT
dt
d
JT 


24. Torque Equation: Motor drives
dt
d
JTTor
dt
d
JTT LeLe


0 Le TT Acceleration
0 Le TT Deceleration
0 Le TT Constant speed
Te : motor torque (Nm) TL : Load torque (Nm)

25. • Drive accelerate or decelerate depends
upon whether Te is greater or less than Tl .
• During acceleration motor should supply
not only the load torque but additional
torque component
dt
d
J


26. Four quadrant operation
Speed conventions:-
Motor speed is considered +ve ,when rotating in
the forward direction.
forward direction :
• for the drive which operate only in one
direction, their normal speed taken as it’s
forward speed.
• for up-down motion drive, up speed is
taken as forward speed.

27. Torque conventions:-
+ve torque: the torque which produce
acceleration or +ve rate of change of speed
in forward direction.
-ve torque -deceleration

28. MOTORING AND BRAKING
• Motoring: converts Electrical energy into
mechanical energy
• Braking: converts mechanical energy into
Electrical energy and thus oppose the
motion.

29. 4Q OPERATION
SPEED
TORQUE
I
III
II
IV
TeTe
Te Te
FMFB
RM
RB
F: FORWARD R: REVERSE M : MOTORING B: BRAKING

30. 4Q OPERATION: HOIST SYSTEM
Convention:
Upward motion of the cage: Positive speed
Weight of the empty cage < Counterweight
Weight of the full-loaded cage > Counterweight
Principle:
What causes the motion?
Motor : motoring P =T = +ve
Load (counterweight) : braking P =T = -ve

31. Four functions of hoist
1.Movement of loaded cage upward
2.Lowering of the loaded cage
3.Upward empty cage
4 downward empty cage

32. Counterweight
Counterweight
Counterweight Counterweight
Empty Cage Loaded Cage
Loaded CageEmpty Cage
speed
Te
Tl
speed Tl
Te
speed
Tl
Te
Tl
speed
Te

33. 4Q OPERATION: LIFT SYSTEM
You are at 10th floor, calling
fully-loaded cage from gnd floor
You are at gnd floor, calling
empty cage from 10th floor
You are at 10th floor, calling
empty cage from gnd floor
You are at gnd floor, calling
Fully-loaded cage from 10th floor
Torque
Speed
FMFB
RM RB

34. 1.8. MULTIQUADRANT OPERATION
Mode of
operation
Forward
motoring
Forward
regenerati
ve braking
Reverse
motoring
Reverse
regenerati
ve braking
Speed, r + + - -
Torque, Te + - - +
Electric
power flow
+ - + -

35. 3rdlecture

36. Loads with rotational motion:
Motor driving two loads, one coupled directly to it’s shaft and other through a gear
with n1 and n2 teeth:
Motor
Te
Load 1,
Tl1
Load 2,
Tl2
J1
J2
m
m
m1
n1
n2
Equivalent values of Drive parameters
Motor
Te
Jequ
Equivalent
Load , Tlequ
m

37. Notations used are:
Jeq and Teq = moment of inertia and torque of the equivalent system
J1,Tl1 and wm= parameters of the load directly coupled
J2,Tl2 and wm1= parameters of the load coupled through a gear
Gear ratio
If the losses in the transmission is neglected , then the kinetic energy due
to equivalent inertia must be the same as the kinetic energy of various
moving parts .Thus:
Or
a1 = wm1/wm = n1/n2 Eq1
1
2
2
2
1
2
2
1
2
1
2
1
mmmequ wJJJ  
2
2
11 JaJJequ 

38. If in addition to load directly connected to the
motor with inertia J1,
there are m other load with moment of inertias
J2,J3…………Jm with gear teeth ratio of
a2,a3……………..am then :
mmequ JaJaJaJJ 2
3
2
22
2
11 .....................

39. Power at the loads and motor must be same . If
transmission efficiency of the gears be η
From eq1
If m loads of torques Tl1,Tl2,Tl3……………..Tlm are
coupled through gear ratio of a2,a3……………..am
then :

2
11
l
leq
T
aTT 


 11
1
ml
mlml
T
TT 
m
m
m
lll
leq
T
a
T
a
T
a
T
aTT

1
3
4
3
2
3
2
1
2
11 ............................... 


40. Load with translational motion
J1
V1
Motor Load Rotational to linear
motion transmission
Mass
M1force
F1

41. Let us consider a motor driving two loads
,one coupled directly to it’s shaft and other
through a transmission system converting
rotational motion to linear motion.
Or
2
1
11
2
1









m
equ
V
MJJ

1
2
1
2
1
2
2
1
2
1
2
1
vMJJ mmequ  

42. Similarly power at motor and load should be same ,
so:-
Or







m
leq
w
vF
TT 11
1.







 11
1.
vF
wTwT mlmeq


43. Components of Load Torques(Tl)
1.Friction torque TF :
friction will be present at the motor shaft and
also in various part of the load.
2.Windage torque Tw :
Wind generates a torque opposing the motion.
3. Torque required to do the useful mechanical
work Tl

44. • wm
•
Tf

45. m Tv Tc
• Ts
• Torque
Components of Frictional torque:

46. Tv: viscous friction
= Bm
Tc = coulomb friction
Ts = additional torque at standstill friction
Windage torque 2
mw CT 

47. Hence load torque
as is negligible
Hence equation becomes:
2
mcmLl TBTT  
2
mcT 
mL BT
dt
d
JT 



48. Classification of load torques