Electrical Motor

1. Electrical Motors : technologies and
driving electronics
Plan
 Introduction : Electrical Machine Principle
• Different Motors
DC Motor (Brush)
 Synchronous Motor
Stepper Motor
 AC Induction Motor
AC Motors :
• Drivers : Vector or scalar control
• Specific problems in High temperature High pressure
• Summary
DC Brushless Motor

2. B
S
L
N S
The Generator : Transform
mechanical power into electrical
power
The Motor: Transform electrical
power into mechanical power
 
S
L
.
B
Emf





B
S
L
I
N S
B
I
L
 
B
L
.
I
F






N S
B
L
I
F




losses
P
P
P
P
Efficiency
output
output
input
output
Electrical Machine Principle

3. UR
IR
Is
Emf, R, L
Tm
Ir
cst
v 

Electrical characteristics
Ir
k
Tm v 



Is
k
v 

 &
v
v k
E 



 
Ir
cst
v 

k
Ir
.
R
Ur 


DC Motor (Brush)

4. DC Motor (Brush)
UR
IR
Is
Emf, R, L
It needs a commutator and brushes (wear and high level of
maintenance.
The brushes of a dc motor have several limitations: brush life, brush
residue, maximum speed, and electrical noise generated.
Low level of reliability
Simple control
Now used for low power applications in air
Pro’s and Con’s

5.  
 











 t
s
r
sin
Hr
Hs
k
Tm
0
Tm  s
r 




Synchronous Machine
0
r 
 s



Asynchronous Machine
s
r 




s
s
r 



s
j
e
Hs
Hs 

 r
j
e
Hr
Hr 


AC Motors

6. 




 cos
Is
E
k
Tm v
Is
Ev Rs.Is
j.Ls..Is
Vs



Magnetic field
detector :
-Hall element
-optical sensors
(phototransistors)
-Resolver
N
S
H3
H2
H1
Magnet
Magnetic field detector
Tr1 Tr2
Tr3
W1
W3
W2 VDC
DC Brushless Motor
Synchronous Motors

7. DC Brushless Motor control
DC Brushless Motor
Inverter
Converter
Position sensor
PWM
Current
control
Speed corrector
PWM switches

8. DC Brushless Motor
Pro’s and Con’s
It is reliable
The motor torque is proportional to the current, allowing a full
torque control
The efficiency can reach 80 %
The angular velocity is high
It is driven in close loop mode, allowing a complete monitoring
and control (torque and speed).
It requires a motor resolver.
The driver electronics is complex.

9. Stepper Motor
Synchronous Motor

10. Motor Control Strategy
Phase 3 Phase 2
Phase 1
Controller Board
(t) rotor
2 3 1 2 3 1 2 3 1 2 3 1
S N S N S N S N S N S N
Rotor pole
Direction of the
magnetic field
generated by the
stator
Stator phase
30 
0  360 
180 
Motor step … 1 2 3 4 5 6 1 2 3 4 5 6 …
Stepper Motor
s
n
2
1
3
n
s
2
1
3
V
0 V
V
0 V
V
0 V
t
t
t
25 ms
Step 1 2 3 4 5 6
Phase 3
Phase 2
Phase 1
This figure shows one full
cycle for an input of 40
Hz (period = 25 ms) on
each motor wire
referenced to ground.
6 * 40Hz = 240
steps/second.
Therefore the
pulse rate is 240 PPS
The rotor speed is defined by
1200 rpm
Number of poles: NP = 4 poles

11. Stepper Motor
Pro’s and Con’s
It can be used for low speed and low torque applications
The efficiency is as 14 %
.
It is driven in open loop
The driver for this type of motor is simple
Pulse Rate/rotor speed
Torque
Holding Torque
Operating point

12. The rotor of an induction motor consists of windings or more often a copper
squirrel cage
The stator flux speed
s

s
s
S





The slip ratio
The rotor speed

AC Induction Motor

13. S
Tm
0
1
%
40
Efficiency 
AC Induction Motor simple phase
AC Induction Motor
Variable field Two fields, rotating in opposite direction
B=B1+B2
S
Tm
0
1
s
s
S






14. The maximum torque
2
s
Ev
Nr
k
max
T 








s
Nr
Rr
max
S



S
Tm
To
0
Smax
1
Tmax
Stable field
Rr1
AC Induction Motor three phases
   2
2
2
s
Nr
g
/
Rr
g
/
Rr
s
Ev
k
Tm







AC Induction Motor
Stable field
Rr2>Rr1

15. Scalar control system for driving Asynchronous Motors
2
s
Ev
Nr
k
max
T 








cst
s
Ev


If & cst
r 

cst
max
T
Tm 

Power
Inverter
PWM
Rotating speed
sensor
AC Induction Motor

16. Ev
Scalar method not accurate enough at very low speed
(RS.Is large at start)
AC Induction Motor
Scalar control system for driving Asynchronous Motors

17. AC Induction Motor
Pro’s and Con’s
The principal advantages for AC motor are its robustness and its price
(1/6 the price of a DC Brushless).
Scalar control method too much limited.
New methods such as ``Vector control`` has been successfully
introduced for motor control
Non linear behavior during saturation effect
Asynchronous behavior
Resistor rotor is large

18. q
r
1 I
.
.
k
T 










 r
r
2
d
dt
d
Tr
k
I
DC motor (Brush) electrical
characteristics
Vector control interest in driving Motors
AC Induction Motor

19. • Full motor torque capability at low speed
• Better dynamic behavior
• Higher efficiency up to 80 %, for each operating point in a wide speed
range
• High reliability
Vector control interest in driving Motors
AC Induction Motor

20. Specific problems of the OFS applications
 Motor modeling necessary to evaluate and optimize motor performances
(HT, HP)
 Electrical insulation (quality of the winding, type of resin…know how
necessary)
 Choice of oil is important
 Reliability/lifetime
 High temperature, High pressure, shocks & vibrations
 Limited size and limited available power
 Price constrains

21. Specific problems of the OFS applications
The breakdown of the Polyimide insulated copper wire when it is attacked by well bore fluid.
The insulation degenerates and causes electrical short circuit failure of the wire coils.
Failure Example :

22. • Comparative chart
Motor type DC Brushless Stepper DC Brush Ac Induction
Three phase
Price of Motor
(without the EL
driver)
9000 $
(CDA Intercop)
8000 $
(CDA
Intercop)
The cheapest 1600 $
(CDA Intercop)
Output Torque
Output Power
High power
High torque
and High speed
Low power
Low torque
and Low speed
Low power
Low torque
and Low speed
High power
High torque and
High speed
Summary

23. DC Brushless Stepper Ac Induction
Three phase
Efficiency
with
associated
driver (in T)
76  14  Up to 80 
Control
complexity
Closed Loop
System
A real time
control of the
motor:
- Operate with
the required
torque
- Insure the
control of the
motor current
Open loop
System
It’s a simple
control, if the
load torque is
small
compared to
output motor
torque
DC Brush
20  at low
power (PMIT).
Much better
for high power
Open loop
System
Simple control
Closed Loop
System
A real time
control of the
motor:
- Operate with
the required
torque
- Insure the
control of the
motor current
Summary

24. DC Brushless Stepper DC Brush Ac Induction
Three phase
Driver
Electronics
Complexity
Complex Simple Simple Complex
Motor
Position
Via a revolver Not possible Not possible Via a resolver
Reliability Good Medium Weak Good
Summary