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8/12/2019 Seminar im thermal

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A NONINTRUSIVE THERMAL

MONITORING METHOD FORINDUCTION MOTORS FED BY

CLOSED - LOOP INVERTER

DRIVES


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OVERVIEW

Introduction

Principle

Terminal voltage estimation

Real time signal processing techniques

Experimental validation

Conclusion

References


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INTRODUCTION

Closed loop induction motor drives are widely

used in traction applications and industrial

processes

Accurate thermal monitoring not only protects

the induction machines from overheating, but

also boosts the usage and performance of the

overall drive system

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INTRODUCTION(Contd)

Recently used thermal monitoring schemes forinduction motors are

Embedded temperature sensors

High-order thermal model-based methods Parameter-based methods

Motor-model-based methods

Signal-injection-based methods

The relationship between the resistance and the

temperature is

..(1)

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PRINCIPLE

Fig 1.Simplified diagram of dc current injection in a closed-loop induction

motor drive

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PRINCIPLE(Contd)

Contains an outer low-bandwidth speed-regulating loop and inner high-bandwidth

current-regulating loop.

DC currents can be injected into the three-phasewinding of the induction machine by

superimposing a sine-wave component onto the

current command id*and iq*

id*=Idc cos.....................................(2.a)

iq*= Idc sin .................................(2.b)

is the transformation angle of the dq

reference frame.4


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PRINCIPLE(Contd)

The dc currents injected into the motorswindings are

ia = Idc................................................(3.a)

ib = 0.5Idc.........................................(3.b)

ic = 0.5Idc.........................................(3.c)

Once currents in (2) have been injected into the motorsstator winding, the stator resistance can be calculated asfollows (Yconnection assumed) Rs

Rs= ................................................(4)

and are dc components of Vab and ia

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PRINCIPLE(Contd)

To track the stator temperature over time, thestator resistanceR0 is first estimated at room

temperature t0

The winding temperature ts,

ts = (t0 + k1 )(Rs/Ro)-k1............................(5)

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Fig 2.Estimated stator temperature using the dc injection method

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TERMINAL VOLTAGE

ESTIMATION An accurate extraction of the dc component in

the line voltage vab is critical for calculating the

stator resistance of the induction machine

In typical closed-loop inverter drives,the

terminal voltages are estimated from the

commanded PWM duty cycle and the measured

dc bus voltage asVaN = DaVdc

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TERMINAL VOLTAGE

ESTIMATION(Contd...)

Where Da is the phase-A duty cycle

generated by the current regulator

Vdc is the measured dc bus voltage

VaN is the average phase-A voltage over

a period of the PWM carrier, with

respect to the negative rail of the dc bus

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A. EFFECT OF DEAD TIME ON

DC VOLTAGE ESTIMATION

Fig 3.a)Current flowing outward b)Current flowing inward c)Reducereffective voltage d)Increased effective voltage

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A. EFFECT OF DEAD TIME ON DC

VOLTAGE ESTIMATION (Contd...)

Fig 4.Contribution of dead time on terminal voltage .No dc current offset

Fig 5.Contribution of dead time on terminal voltage .Positive dc current offset11


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A. EFFECT OF DEAD TIME ON DC

VOLTAGE ESTIMATION (Contd...)

Fig 6.Contribution of dead time on terminal voltage. Positive dc

current offset and smaller current amplitude

Equation (6) is therefore modified to

if ia> 0, VaN = (Da Ddt)Vdc

if ia< 0, VaN= (Da+ Ddt )Vdc........................... (7)

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B.EFFECT OF DEVICE VOLTAGE DROP

ON DC VOLTAGE ESTIMATION

Fig 7.a)Current flowing outwards b)Current flowing inwards13


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B.EFFECT OF DEVICE VOLTAGE DROP ON

DC VOLTAGE ESTIMATION(Contd...)

Fig 8.Contribution of device voltage drop on terminal voltage

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B.EFFECT OF DEVICE VOLTAGE DROP

ON DC VOLTAGE ESTIMATION(Contd...)

To account for the effect of device voltage drop,(7) is further improved to

if ia> 0, VaN= (Da Ddt)Vdc (Da Ddt)VIGBT(ia) (1 Da+ Ddt)Vdiode(ia)

if ia< 0, VaN= (Da+ Ddt )Vdc+(Da + Ddt)

Vdiode(ia)+ (1 Da Ddt )VIGBT(ia)............ (8)

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C. EFFECT OF DIFFERENT

DEVICE TURN-ON/TURN-OFF

TIME DELAY

Fig 9. Contribution of different turn-ON/turn-OFF delay on terminal

voltage.

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C. EFFECT OF DIFFERENT

DEVICE TURN-ON/TURN-OFF

TIME DELAY(Contd...) To account for the effect of device turn-

ON/turn-OFF time difference, (8) is furtherimproved to

if ia > 0, VaN = (Da Ddt+ Ddly)Vdc

(Da Ddt+ Ddly)VIGBT(ia)

(1 Da+ Ddt Ddly)Vdiode(ia)

if ia< 0, VaN = (Da+ Ddt Ddly)Vdc+ (Da+ Ddt Ddly)Vdiode(ia)

+ (1 Da Ddt+ Ddly)VIGBT(ia)...(9)

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REAL-TIME SIGNAL

PROCESSING TECHNIQUES

Fig. 10. Signal process techniques for extracting dc current and voltage. (a) DC

current extraction. (b) DC voltage extraction.

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EXPERIMENTAL VALIDATIONA.EXPERIMENTAL SETUP

Fig. 11. Experimental setup for the proposed thermal monitoring method.

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B. MEASURED MOTOR WAVEFORMS

Fig. 12. d- and q-axis current before and during dc current injection. (a) id

reference and measurement. (b) iq reference and measurement.

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MEASURED MOTOR WAVEFORMS(Contd...)

Fig. 13. Stator voltage and current before and during dc current injection.

(a) Waveform of vab . (b) Waveform of ia

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Fig. 14. DC components of stator voltage and current. (a) DC component

of vab . (b) DC component of ia .

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Fig. 15. Motor torque and speed before and during dc current injection. (a)

Electromagnetic torque. (b) Measured motor speed.

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C TEMPERATURE ESTIMATION AT


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C. TEMPERATURE ESTIMATION AT

A SINGLE OPERATING

CONDITION

Fig. 16. Stator winding temperature estimation at constant operating

condition.

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D TEMPERATURE ESTIMATION


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D. TEMPERATURE ESTIMATION

WITH VARIABLE OPERATING

CONDITIONS

Fig. 17. Stator winding temperature estimation with variable load level.

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TEMPERATURE ESTIMATION


CONDITIONS(CONTD.....)

Fig. 18. Stator winding temperature estimation with variable motor speed.

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CONDITIONS(CONTD...)

Fig. 19. Stator winding temperature estimation with variable dc bus

voltage.27


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CONCLUSION

A simple method is proposed for injecting dccurrent into closed-loop drive-fed induction

machines without interrupting normal operation.

The major technical difficulty of dc-injection-based thermal monitoring, which is

inconsistency in resistance estimation, has been

overcome by carefully analyzing and

compensating for the effects of inverternonidealities.

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ADVANTAGES

Nonintrusive

Easy to use

Accurate

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REFERANCES

[1] Siwei Cheng, Yi Du, Jose A. Restrepo,Pinjia Zhang, andThomas G. Habetler, ANonintrusive Thermal Monitoring Method

for InductionMotors Fed by Closed-Loop Inverter Drives,IEEE

Trans. Power Electron.,vol. 27, no. 9, Sept. 2012.

[2] A. Boglietti, A. Cavagnino, M. Lazzari, and M. Pastorelli, A

simplified thermal model for variable-speed self-cooled industrialinduction motor,IEEE Trans. Ind. Appl., vol. 39, no. 4, pp. 945

952, Jul./Aug. 2003.

[9] IEEE Standard Test Procedure for Polyphase Induction Motors

and Generators, IEEE Standard 112-2004 (Revision of IEEE

Standard 112-1996),pp. 179.

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