Electric Motors 5

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Prof. Dr. -Ing. Ralph M. Kennel Wuppertal University Page 1

EXPERT SYSTEMS AND SOLUTIONS

Email: [email protected]

[email protected]

Cell: 9952749533www.researchprojects.info

PAIYANOOR, OMR, CHENNAI

Call For Research Projects Final

year students of B.E in EEE, ECE, EI,

M.E (Power Systems), M.E (Applied

Electronics), M.E (Power Electronics)

Ph.D Electrical and Electronics.

Students can assemble their hardware in our

Research labs. Experts will be guiding the projects.



Elektrical Machines and Drives

Wuppertal University

Tutorial 2

Sensor less Motor Drives

Ralph M. Kennel




Reasons for Industrial Applications

of Drives with Encoderless Control:

� Cost

� Reliability

� Robustness




Industrial Drives with Sensorless Control

since several years / decades sensorless control is investigated

and published on conferences and magazines

- acceptance in industry, however, is rather low

Why ?new ideas and concepts are interesting for industry,

only if they do not result in higher cost or higher effort!!!

What does that meanf or industrial drives with sensorless control ?

no additional or more powerful processors / controllers no additional hardware or additional sensors (e. g. voltage sensors)

no increased installation effort with respect to parameter adjustments




introduction

� f undamental model methods

� high f requency injection methods

sensorless control of electrical machines

� machine response on high f requency injection voltages

� tracking of magnetic saliencies / anisotropies

practical results

� experiences with industrial drives

conclusions

Sensor less (Encoder less) Motor Drives




Categories of Machine Models for ÄSensorless³ Control




Basic Principlesof Encoder less Control

high f requency injectionfundamental model

� simple realisation

� does not work at frequency 0

� parameter dependencies

current injection voltage injection

� measuring voltage is high enough

� additional voltage sensors

stationary current response

� standard microcontroller sufficient

� very small measuring current

transient current response

� no additional hardware

� very short measuring time




stator rotor

mechanicswhen knowing voltage uS

as well as current i S

it should be possible

calculate speed [

Fundamental Model of an Induction Machine




Calculation of Speed by Fundamental Model

is not Practicable for Very Low Speeds

... because

� the voltage signal becomes very small

� errors between real voltage and values used f or calculation

cannot be avoided and become more signif icant

� DC components of these errors

let the integrators f or f lux calculation drif t away

the calculated speed gets more and more incorrect

is an encoder/resolver the only feasable solution ??




� this is basically a current injection method

voltage sensors are necessary !!!

� it is possible to use current derivativesinstead of motor voltages

measuring current derivatives, however ,

by standard current transducers is not really possible

� but, industrial current transducershave a current derivative available internally

can this be made avail abl e for c ustomer s ???

Signal Injection Methodaccording to J. Holtz, H.Pan, etc.




INFORM method

according to M. Schroedl(Technical University of Vienna, Austria)

� this is basically a transient voltage injection method

currents have to be sensed at specif ic times !!!

� when using standard current transducers

these cannot be synchronized with PWM

the hardware of a standard industrial drive

has to be changed

neverthel ess this method comes c l ose to i nd ustr i al need s !




Stationary Signal Injection Methodsaccording to R. Lorenz, S.-K. Sul, R. Kennel, etc.

� the basic idea is

to use the electrical machine itself as a resolver !!!

� a resolver is nothing else but an electrical machine

can we operate the motor itself like a resolver ?

� if the machine itself is a resolver (encoder)

is that really an Äencoder less³ control ???

g ood i dea ± but does i t work ???




R esolver

Stator u

e

Rotor u

R

Stator u2

Stator u

1

R1

R2

S1 S3

S4

S2

u2(K

K

TT0

u1(K

K

TT0

Tamagawa

injection of a

stationary (sinusoidal)

high f requency signal

sensing of a two-dimensional

stationary (sinusoidal)

signal response




Stationary Signal Injection Methodsaccording to R. Lorenz, S.-K. Sul, R. Kennel, etc.

� the basic idea is

to use the electrical machine itself as a resolver !!!

� a resolver is nothing else but an electrical machine

can we operate the motor itself like a resolver ?

� if the machine itself is a resolver (encoder)

is that really an Äencoder less³ control ???

now we do the same w i th an el ectr i cal AC machi ne




Fundamental Frequency Excitation

(in E- F coordinates)




High Frequency Excitation

(in E- F coordinates)




(F)c

(F)sa

(F)c(F)

s(F)

cs(F)c i l

i l i u [ j

dt

d r ! ¼

½

»¬«

!qs

ds( )s 0

0

l

l l

Machine Model for High Frequency Signals




High Frequency Behaviour of the Machine Model




injection of high f requency voltages

f undamental voltage phasor/vector

f undamental current phasor/vector

injected high f requency

voltage phasor/vector

high f requency

current phasor/vector (response)









high f requency










high f requency










high f requency





Injection of High Frequency Rotating Phasors

rotating voltage phasor uc elliptic current response i c




elliptic current response i c (rotating)

� machine responds

on a rotating voltage phasor

with an elliptic current response

� ellipse is correlated

with the geometric anisotropy

of the rotor

� rotor position inf ormation

is included

in the high f requency current

Position Information of Salient Rotors

in High Frequency Rotating Phasors




Saturation Anisotropy

of a Permanent Magnet Synchronous Machine

rotor f lux saturation of a

permanent magnet synchronous machine




Position Information of non-salient rotors

in High Frequency Rotating Phasors

� machine responds

on a rotating voltage phasor with an elliptic current response

� ellipse is correlated

with the saturation anisotropy

� rotor position inf ormation

is included

in the high f requency current elliptic current response i c (rotating)




Injection of High Frequency

Al ternating (Pu lsating) Voltage Phasors

composing an alternating (pulsating) voltage phasor

by two phasors rotating in opposite direction

advantage :

no rotational (HF) f ield

no additional torque




High Frequency Current Response

of a Synchronous Machine




Current Response

of a Misoriented System

voltage and current

show diff erent orientation !!




Current Response

under a Misorientation of 90°






Tracking the estimated angle of the rotor f lux by controlling i cq to 0

Tracking Scheme for Magnetic Anisotropies




tracking control of injection voltage





high f requency










high f requency










high f requency










high f requency









voltage phasor/vector high f requency










high f requency





step response of the PLL;

PLL is locked af ter ca. 10 -15 ms

Encoderless Control Structure









high f requency










high f requency










high f requency





the estimated angle can be used

f or f i el d or i entat i on as well as f or

speed or posi t i on control

of synchronous machines

control structureof an encoder less control

with alternating high f requency

signal injection




Stator Admittance in Complex Plane

trajectory of stator admittance(SMPMSM, carrier f requency f c = 0.5 kHz)

a) theoretisch b) experimentell

north and south polecan be distinguished



















Tracking Control

tracking of estimated rotor f lux angle by adjusting/controlling i cq to zero




Stator Admittance in Complex Plane

trajectory of stator admittance(SMPMSM, carrier f requency f c = 0.5 kHz)

a) theoretisch b) experimentell

north and south pol

ecan be distinguished




the concept of encoder less control as presented hereworks similar to radio broadcasting :

the inf ormation of rotor position

is modulated by a high f requency signal

the inf ormation is demodulated / extracted

f rom motor currents




� Synchronous Machines

Trager..

Position

Synchron–maschine

AM / FM Position

Demodulator

Trager..

PositionLaufer

Asynchron–maschine

?Position

Feld

..

PositionFeld

PositionLaufer..

Modulation of Carrier Signals by Electrcial Machines

� Induction Machinesworks f ine !!

f urther research to be done !!




Combination of

Field Oriented Control

and Encoderless Detection

of Rotor Position

� the estimated angle can be used

for f ield orientation as well as

for speed and/or position control

of synchronous machines

� high frequency test signals are superposed to

the fundamental stator voltage(s)

� drive control structure remains as before

� no additional sensors required

� the scheme is parameter independant



Prof. Dr. -Ing. Ralph M. Kennel Wuppertal UniversityPage 55

Drive with Speed Control

Sprungantwort der Drehzahlregelung




Step Response of Encoderless Position Control

Sprungantwort der Lageregelung




Results

� the tracking control scheme presented heresynchronizes on the saturation anisotropyof a synchronous machine.

� the tracking control schemeis not de pend i ng on any machi ne parameter .

� the size of additional software f or the tracking control is com parabl e to the software of a rotor model f or the f ield oriented control of an induction machine.

� the hi g h frequency c urrent si g nal can be measuredtog ether w i th the f undamental c urrent by the standard c urrent transd ucer s of a standard drive inverter.




Practical Experience with an Industrial Servo Drive

� training of a development engineer 2 x 1 week in our laboratory

Implementation of a sensor less control

into a servo drive of

� programming of additional sof twarein manuf acturerµs f actory

� delivery of prototypeaf ter ca. 3 months

� presentation on Hanover Fair in April 2006



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Electric Motors 5