induction motor iliustrated in fig. 1 we distinguish the following frequency conversion chain: e ac utility grid 50/60 Hz, e dc link voltage across filter capacitor ...
At healthy steady-state operation of the inverter-fed induction motor iliustrated in fig. 1 we distinguish the following frequency conversion chain: e ac utility grid 50/60 Hz, e dc link voltage across filter capacitor modulated with 6th harmonic ofthe line frequency 300/360 Hz, at motor terminals smewave PWM voltage of a variable fundamental frequency In a customary range up to several hundred Hz, carrier commutation frequency (1-20 W ) superimposed on ac stator currents with an interaction of 5th and 7th harmonics in the upper overmodulation range, e sinusoidal &stributed air-gap flux density wave rotating at fundamental inverter frequency, shaft angular velocity with frequency components resulting from motor torque harmonics, elasticity and mechanical resonances of load. 0
circuit and Gating signal faults cause base drive blocking state of the corresponding transisto[. Since in steady state inductive load of machine can not support any dc voltage, the polarity of the current is biased (positive or negative) for the whole cycle. The resulting dc offset current is, because of symmetry equally divided between healthy phase currents. As phase motor current, due to the bipolar modulation principle, is composed of a transistor current with a compllementary free-wheeling diode current, an opened diode or blocked transistor manifest similar wveform transients. lniiibited drive control to the whole one inverter leg leads to the single-phase motor operation. Remaining phase currents assume reverse polarity sequences introduang puiisation of motor torque.
at each stage of this power transfer chain a fault may be developed distorting the spectral content of the energy carrying state variables. Thus, we classlfy primary faults, as is depicted in Fig. 1, into groups according to: Power failures such as line to ground short circuit faults, open phase circuit faults due to phase fuse blown, transitory supply voltage sags and outages, Dc bus faults as diode rectlfier breakdown, decrease of filter capacitance, voltage sensor and ground faults, PWM inverter w i n g signal faults such as wiring disconnection or power driver inhibited, transistor and diode open, -short circuits, fatigue parametric failures of power semiconductors (eg. ICEreverse collector current or VCEA increase), cwiing fan damage, Induction motor faults of stator winding insulation degradation, mechanical breakage, ground failures, rotor strikes, broken bars, air-gap eccentricities, excessive shaft vibrations or locked rotor. 0
Input supply faults disturb three-phase rectlfier operation introducing 2nd line harmonic in the dc link voltage spectra. as in Fig. 2. In the process of modulation this frequency component is transferred in a form of positive and negative phase sequences to motor currents generating a pulsating torque. Similar process may be observed during ageing of the electrolytic filter capacitor. Loss of capacitance increases the amplitude of 6th line har~nonicon its voltage spectra. UcnM
Transistor-diode short circuit or motor phase to ground faults require immediate withdraw of gate signal from the inverter (Fig. 4).At conducting transistor branch machine phases are interconnected by the bypass diodes developing large dc component current. At a motor-phase to ground short circuit unidirectional braking current, charging filter capacitor flows through the diodes of healthy phases to the third phase connected to ground. Post inverter shut-down current analysis is used to determine short circuit location.
111. SPACE VECTOR APPRQACK
For the diagnosis of above mentioned faults we propose to apply the space vector concept, as an efficient tool of visual and Jgorithmic inspection of three-phase variables. By the acquisition of phase currents in a system of natural fixed to the stator coordinates, satisfying the condition C,4sA(d+ I , B ( d + GcW = 0 we define a cunrent space vector as in [S]
Cl)
where the factor 2iB guarantees, for the case of sinusoidal waves, equality of the space vector amplitude and the
amplitude of instantaneous per phase waves. Since ( 2 ) constitutes a transformation of instantaneous quantities OP a three-phase system on a complex plane, the space vector liocus can be obtained by plotting real and imaginary components of the vector under consideration Sonie particular examples are next treated analytically.
1012
yielding an elliptic trace ofthe end In the case of sinusoid and sj"etric
currents
as is computed for p = 3 749 in Fig. 5
w r phase the end p i n t of the vector perpendicular to the axis of Iacking
..L-
phase ep if in (3)
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.
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Fig 5 MOdeLling &ator p h m winding isohtion
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case considered in the section 3-D.
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1;. kXipp&i, C; I ~ r m d k i C. . 'l'u~ai. "1ntcgry;dcd:&biap&~c iirr failure i&mtiIi&icm m pcwcr cnnv&as". in Proceedings N/ the I Y9.5 EH? Conference. Sevilla, vol 3 , m).270-274. 171 I; I.. iioadlcy, "AC drive cq)waldim during pcwa failures, I'aril, 2" P o w r Conver.rron & Inkdligem Morion, vol. 6 , no. 4, JullAuy 1 9 9 4 . ~1RR-189,no.5,ScplOct. . iY94.pp.258-262. "InvcJiipialim of fault m o d s cfvokagc-icd 181 I).K&a and R K . k. inverter sysiun for h?du&immam dxivc". it8 Proceedtngx 01 / h e 992 EE/?-LAS Conference, I loii.im Texa., pp. 863-866. [9\ MY.Kaimiakcfimki rlrd 11. 'l'unia, Au/omo/ic coplfroi ofconvenerfed drives, ElscVrep Amdudam-Lmdm-NY-Tokyo; 1994, pp 5 6 3 n applicalim tP PWM m v t s l m to [ 101 li, P a s m "'l'rmsimt dY&s i kdudicm mdors", UNI? Trans. lndusrrynpplicaiions. vol. 28. nn 5. */Od 1 9 9 2 . ~ 1095-1101. . [ 1 11 M Raikavr;Sti, R. Sazemy, "Ciraut-ximttxi models of ac m & m w fw ccnvatcr - madiiae syskam cJmuIalitn",In Proceedings ofthe 1995 Ef'E Conference, S e d i a , vol3, pp 50-55. 1121 C. S&uitze, h/L T d i m "'ihc r d i q u e of m6eEgaLP modules", European Power Eiectronm and Drives J o u m d , vol. 4, no. 2 , Jun 1994,pp. 27-32. [ i 3 ] R. S ~ m yK ,. Iwm, M Wmkwsl;i, "TCAD a simulaticm package fix powm eledrcmc systemsn, in Proceedings of the 1993 EPE Conference, Brightm. vol7,pp. 1.6. Li4] R. S z m y , P J. &?an, K. I w e , "M&'hg and s i m u l a t m of ela(r;cal drive at n d and facif mditicns", in Proceedings uf the I995 EPE Conskrence, S e d l a , vol3, pp. 580-585. [ 151 P. Vas, Parame!er estinialion, condition monitoring and diugnosis ofeiecwical machines, C l a r e " Prm Oxford; 1993,pp. 360 (161 I, Ban&LB atis,E.N. HuUey, "Ahowledgebased. system fm OD$ne fault $lagnosis ofpower invmprer circuits fx ac maQloe drive", in Proceedings ofthe 199.9 EPE Con]:, Sevilla, vol3, pp 334-339
j61
qlnudc I-s [AI 61 IKJ2
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p11= f-A (dst31 0
ZllplilUde I-* IA1 0,042
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2.756 iJ 175 0.194 0.052 0.068 0.055 0.077
-171.4
amplitude
5 i 2 3
0.055 2.534 0.155 0.223 0.062 0.057 n 023 0 076
7
-72.0 29.9
0 00 I 0.11 0
hmmic m
6
48.0 -133.1 -51.4 -IY 6
0 168.0
0 024
5
phaw -& I k3l
6.442
0.067 0 00 i
4
phasc I.-& [dcgl 0
phaw I-.sA &yi
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145.1 121.4
125 2
li
68.6
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W. CONCLUSIONS
Sources of malfunction in the converter-fed ac drive may be detected by signal analytical redundancy in the time auld frequency domain. In a voltage source inverterfed induction motor h v e , numerous fmfts related to Wure, dc bus, PWM inverter and induction ne cm be diagnosed from the senso standard control variables as stator currents filter VOl ase-howledge inspection of the motor current space vector trajectory ~ m b i i n e dwith the Fourier sePles spectra constitutes a ~ ~ e n ~ tool, ~ cwhich a ~ may ~ Q on-~ oApration.
1016
