Download singhper1997 - EPrints@IIT Delhi

Performance Analysis of a Low Cost Vector Controlled
Induction Motor Drive: A Philosophy for Sensor Reduction
B.N.Singh', Bhim Singh and B.PSingh
Dept. of Electrical Engineering, IIT Delhi
Hauz Khas, New Delhi 1110016
INDIA
Abstract: This paper deals with the reduction of overall cost
of a current controlled voltage source inverter fd Vector
Controlled Ind uction Motor Drive (VCIMD). For this purpose
an attempt has been made here to examae Le possibility of
such elininatiodreduction in the number of sensors. The
performance anal~sis of the VCIMD system (22 kW cage
induction motor) is carried out and with the belp of simulated
resdtr. the effectiveness of the prOpO5ed elininationlreduction
of sensors is assessed.
I. WTRODUCTION
Despite of many advantages, the cost of Vector
Controlled Induction Motor Drive (VCIh4D) system has
been one of the factors coming in the way of its wider
acceptance. The requirement of precise, accurate and high
resolution speed sensor has been mainly responsible for the
high cost [ 1 -21 of the system. It may be realid that the use
of speed sensor, not only escalates the cost but also affects
the robustness and reliability [l-21 of the system especially
in hostile environment wherein special cabling and care are
required. Moreover, in some cases due to lack of accessibility,
it may not be feasible to install a speed sensor. These
problems have motivated the researchers [1-41 to make
attempts to eliminate the use of the speed sensor in the
VCiMD system.
The system can be further simplified and its cost may be
reduced by decreasing the number of sensors USBd for sensing
voltagedcurrents in addition to the speed sensor. The
majority of the earlier attempts [l-3,5] mainly aimed at the
elimination of speed sensor only. While Xue et al [4] have
attempted to reduce the number of voltage and current
sensors in addition to elimination of the speed sensor,
however, their model is based on the field quantities.
In view to eliminate/reduce as many sensars as could be
possible [ 1-61 a need is felt to evolve a simpIe flux model
for the purpase of speed estimation, thereby facilitating the
elimination of the use of a speed sensor. The costly speed
sensor is replaced by voltagdcurrent seflsors along with a
suitable algorithm. In addition to this it is also attempted to
reduce the number of voltagdcurrent sensors used in the
system. With this end view, an attempt has been made to
examine the possibility of eiimination/reLhrction of number
of sensors to reducing the cost of the VCW system. The
performance analysis of the drive system is carried out and
thz simulated results has demonstrated th eadveness of
the proposed eliminatiodreduction of sensurs.
n. ELIMINATION/REDUCTION OF SENSORS
It has already been mentioned that a VCIMD system
requires a number of electrical and mechanical sensors. Qute
often some of these sensors are c4stly and therefore, it
becomes desirable to take qeps to eliminate or reduce the
number of sensors used without leading to any deterioration
in the level of perfommnce. The eliminahdreduction in
number of sensors is effected in the following manner. (1)
Elimination of speed sensor, in case h the complete
elimination is not possible then its replacement by an
alternative indirect cheaper sensor.
Ambrish Chandra and Kamal Al-Haddad
*&ole de technologie superiere
4750, avenue Henri-Julia Montreal
(Quebec) H2T 2C8 CANADA
(2) Reduction of number of voltage and current sensors
used wherever possible by making use of the symmetry etc.
For example, in a three phase balanced system, sensing of
3-phase voltage and current is made only for two phases
and from these the required quantity for the third phase are
derived.
(3)Further reduction in the number of sensors used for
sensing voltage and current is possible by sensing both the
dc llnk voltage and current and hng the switching funct~ons
of inverter switches, the three phase voltages and currents at
the output of inverter are derived.
In order to effect the eliminaticdreductioii of sensors
one can take the following steps:
To start with the elimination of qxea sensor is made. It
maybe mentioned that this particuiar sensor is relatively
more costly and hence its elinunation will lead to substantial
reduction in the cost. Therefore the speed sensor is replaced
by a flux model and which needs the use of two additional
voltage sensors. The reduction of number of voltage sensors
to be used in a VCIMD system is also made. The two ac
terminal voltage sensing is carried out by only one voltage
sensor in the dc link alongwith switching status of the
inverter devices.
It is further appreciated that the three phase currents at
the output of the inverter are the segments of & link current.
Therefore, these currents (in. i, and id are derived from
the sensed dc link current (i,) and swtching functions of
the inverter. The complete scheme is given in Fig. I, in
which the drive system requires only two sensors one for the
voltage and the other for the current at dc link. The
performance of the proposed dnve system shown in Fig. 1,
has been analpd with a view to examining the effective~less
of elimination and reduction of sensors. The detailed
mathematical model for reductiodelimination of individual
sensors is described in Reference [7J.
I. RESULTS AND DISCUSSIONS
The simulated results of a 22 kW VCIMD system are
shown in Figs. 2 to 5 from which the following important
observations are made.
A. Response of Estimat0r.s
Response of estimators namely speed estimators, voltage
estimator and current estimator is shown in Figs. 2 to 4.
1) Response of Speed Estimator: The response of flux
model which acts as a speed estimator is shown in Fig. 2 for
the proposed VCIMD system. It is observed from Fig. 2,
that the estimated quantities such as synchronous speed w.
of the motor, slip speed wan,
exactly match with their
computed counterparts throughout the operating range of
the drive. This confirms the validity of the developed flux
madel employed fbr the speed estimation in this investiganon.
2) Response 011 bitage Estimator: The methodology used
For the purpose of estimation of voltage waves at the output
of CC-VSI has been described in Reference [7]. This
methodology is applied while simulating the performance
of a VCIMD system with reduced number of sensors. The
response of the voltage estimator is presented in Fig3. Part
(a) of this figure shows the PWM ac voltage constructed
with the help of technique for voltage estimation. It is
observed that the inverter switches are made ON/OFF at a
high switching freqi-lncy and this is reflected fiom the shape
of the PWM ac voltage wave shown in this part. This is
necessary to maintain the currents through the motor
windings with the desired shape. Because the speed estimator
requires the sinusoidal voltage signals for the purpose of
accurate estimation of the rotor speed, therefore, a filter is
used over the PWM ac voltage waves. The filter is simulated
while carrying out the performance analysis of the system.
The filtered wave of voltage at the output of the CC-VSI is
shown in part (b) for the case of phase 'a'. It is observed
from this figure, that the inverter switching pattem affects
both the magnitude and frequency of voltage during the
transient operation of the drive such as starting and speed
reversal. Inverter impresses a voltage of constant magnitude
and frequency during the steady state running of the drive
in each direction. In order to show the variation of stator
currect with the estimated voltage, the time variation of
computed and mimated currents for phase 'a' is shown in
parts(c) and (d) of this figure. These two figures reveal a
feature of the drive system which is related to its controlled
fiequency starting and braking
3) Ke.vpn.ve ?f Curmnt Estimator: The simulated response
of the current estimator is shown in Fig.4. Th~s figure show
the computed and estimated values of current for the 'a'
phase of inverter output. part (a) of this figure shows the
reference current i-* for the phase 'a' generated from the
vector control sauctwe of the drive. While parts @) and (c)
show the computed current for phase 'a' and computed dc
link current, respectively. Part (d) of this figure, shows the
estimated current for the phase 'a..
B. Response oj'l Y'I:\iD
Fig5 shows the response of a 22kW, VCIh4D system
with only two sensors namely one voltage and one current
sensor at dc link. It is revealed from this figure that the drive
exhibits a controlled fiquency startinglregenemive bralang
which helps in impraing the response of the system. It takes
155 mS for starting with PID speed controiler and time for
speed reversal is found to be 180 mS. Peak value of
starting/reversal current is found to be 113.0 A While the
*r(n)
Inverter Outputvb1tag«
and Current Formttioa,
Filtering and Rotor Sp«atd
Eat imat ion
r(n)
Field Weakening
motor has 19.0 A (peak) current during its no load running
in either direction at a set speed of 210 rdsec:.
IV CONCLUSIONS
The study has shown that the speed sensor used in
VCIh4D system can be successfully eliminated and the
number of voltage and current sensors can also be reduced
by using alternative algorithms.The speed sensor is eliminated with the help of aflw model based speed estimator
while the number of voltage and current sensors are reduced
with the help of voltage and current estimators. The flux
model proposed in this investigation is found to be simpler
and suitable for estimating the speed in all four quadrant
operation of the drive system. It has also been &sewed that
the quality of performance of VCIMD is not affected either
by elimination of andor reduction in the number of sensors.
The reduction in number of sensors helps in reducing the
cost of the drive system apart from simplifjmg the system.
V. REFERENCES
[1J
vdw
Coim Schauder. "Adaptive speed identifiCatio0 for
cxmtrol of inductim mdm aithotn rotatimal
transducers". "
!EE Trans. a0 Industry Applicatians. Vo1.28.
No.% pp. 1054inhi. srfuocz. 1992. 12}
L.B.Hrh;i od A
Kuw~~~wJ. "A fully digitized field witntrd
cxutrolled indudim motor drive usmg only currem sewms".
TFFF. Trans. m Industrial Eledl-aoics. W.39. No. 3. pp.241249. June 1992. 131
H. Tajima and Y. Hori. ".Speed
stmiorless field-caimtatim
cxntrol of the indudicn machine". IEE E Trans.m hduApplicatims. Vol. 29.
No. 1. pp. 175-180. Jan.&&.
1993. 141
Y. Xue. X. Xu. T.G. Hatiella and D.MDivm . -A
low cchi
flux orimted voltage s(xuce variable speed drive". IEE
Indue Applications Scriety Annual Meeting 1990. pp.410
415. 1990. IS]
H. Kuhola and R. M~LUIX . "Speed
~sorles~ field+itniLd
watrol d mdudimn m o r with rotor resislancr adaptaticn".
IEEE Trans. on
Industry Applications. Vol. 30. No. 5. pp.
1219-1224. svl/Od. 1994. 161
T.G. Chen and B.
W. Williams, "Dmvatim of mwcr line
current waveforms from the dc-lmk current of an inverter".
Prw. IEE R. B. Vol. 136. No. 4. pp. 196-204. July
1989. 171
H. N. Sin& "Investigatians m vedor antrolled
mdudico
mdor drive". ph. D. thesis. LLT. Delhi. Dec. 1995.
IG B T In v e r t e r
Filed Orientation and
Referen:* Current
. ■. . f t
qs
____ Generat ion ____
ids
i s*
and
Computation
Speed Controller
and V-,
u
r(n)
Re.1 Mematic of WlMD with Reduced Current and
Sensors and *out Mechanical Speed Sensor
TI33-1.2
Voltage
75: e .
1B0.0-
e.e
-Ts.e
Solid
line
estinated Discrete
corputed
- 300. e ■*--" ------- ■
0.00
line
0.72
0.0
-150.0
0.
0.24
0. 36
T I eI secsI
0.48
1
TB.e \
e.e
-TB.
e
ft
A
;1
n
\
11
V
ft
|
I
1
1
V |T /
8.61
Tisw
e.oo
(s*cs)
e.i?
T Il . I . C C . 1
Ftg.4
Transient
Response
of
35)3. 0-j
yvv
0.80
0.12 0.24
0.36
O.iO
-1E0.eJ
(<■<
"3ec'(?."£«"
*e."i2"
e!2i
0.36
a.-»B Fig.2 Response of Speed Estimator of a 22 kW VCIMD
System
0.00
~1.12
0.24
9.36
0.40
CurrentI.CC.1 Estimator
FQ.S Transient Response of a 22 kW VClMD System Hith
Reduced Number of Sensors
F1g.3 Transient Response of Voltage Estimator
TB3-1.3