Electrical Motors1

8/3/2019 Electrical Motors1

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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


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BS

L

N S

The Generator : Transform

mechanical power into electrical

power

The Motor: Transform electrical

power into mechanical power

SL.BEmf

BS

L

I

N SB

IL

BL.IF

N S

B

L

I

F

lossesP

P

P

PEfficiency

output

output

input

output

Electrical Machine Principle


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UR

IR I

s

Emf, R, L

Tm

Ir

cstv

Electrical characteristics

IrkTmvIsk

v &

vvkE

Ir

cstv

k

Ir.RUr

DC Motor (Brush)


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DC Motor (Brush)

UR

IR I

s

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

Pros and Cons


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tsrsinHrHskTm

0Tm sr

Synchronous Machine

0r s

Asynchronous Machine

sr

ssr

sjeHsHs rjeHrHr

AC Motors


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cosIsEkTm v

IsEv

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 Tr

2Tr

3

W1W

3

W2 VDC

DC Brushless MotorSynchronous Motors


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DC Brushless Motor control

DC Brushless Motor

Inverter

Converter

Position sensor

PWM

Current

control

Speed corrector

PWM switches


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DC Brushless Motor

Pros and Cons

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.


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Stepper MotorSynchronous Motor


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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 themagnetic 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

sn

2

1

3

ns

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


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Stepper Motor

Pros and Cons

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


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The rotor of an induction motor consists of windings or more often a copper

squirrel cage

The stator flux speed

s

s

sS

The slip ratio

The rotor speed

AC Induction Motor


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S

Tm

01

%40Efficiency

AC Induction Motor simple phase

AC Induction Motor

Variable field Two fields, rotating in opposite direction

B=B1+B2

S

Tm

01

s

sS


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The maximum torque2

s

Ev

Nr

kmaxT

sNrRrmaxS

S

Tm

To

0Smax1

Tmax

Stable field

Rr1

AC Induction Motor three phases

222

sNrg/Rrg/Rr

sEvkTm

AC Induction Motor

Stable field

Rr2>Rr1


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Scalar control system for driving Asynchronous Motors

2

s

Ev

Nr

kmaxT

csts

Ev If &cstr

cstmaxTTm

Power

Inverter

PWM

Rotating speed

sensor

AC Induction Motor


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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


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AC Induction Motor

Pros and Cons

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 effectAsynchronous behavior

Resistor rotor is large


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qr1I..kT

rr2d

dt

dTrkI

DC motor (Brush) electricalcharacteristics

Vector control interest in driving Motors

AC Induction Motor

AC d i


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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

S ifi bl f h O S li i


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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 resinknow how

necessary)

Choice of oil is important

Reliability/lifetime

High temperature, High pressure, shocks & vibrations

Limited size and limited available power

Price constrains

S ifi bl f h OFS li i


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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 :

S


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Comparative chart

Motor type DC Brushless Stepper DC Brush Ac InductionThree 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

S


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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 timecontrol of the

motor:

- Operate with

the required

torque

- Insure the

control of the

motor current

Open loop

System

Its a simplecontrol, if the

load torque is

small

compared to

output motor

torque

DC Brush

20 at lowpower (PMIT).

Much better

for high power

Open loop

System

Simple control

Closed Loop

System

A real timecontrol of the

motor:

- Operate with

the required

torque

- Insure the

control of the

motor current

Summary

S


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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


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Electrical Motors1

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