l34 Three-Phase Induction Motor Starting Methods for Single-Phase Induction Motor
Induction Motor Scalar Control
-
Upload
divinelight -
Category
Documents
-
view
4.894 -
download
34
description
Transcript of Induction Motor Scalar Control
![Page 1: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/1.jpg)
INDUCTION MOTORScalar Control(squirrel cage)
MEP 1422
ELECTRIC DRIVES
![Page 2: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/2.jpg)
Scalar control of induction machine:
Control of induction machine based on steady-state model (per phase SS equivalent circuit):
Rr’/s+
Vs
–
RsLls Llr’
+
Eag
–
Is Ir’
Im
Lm
![Page 3: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/3.jpg)
Scalar control of induction machine
r
s
Trated
Pull out Torque(Tmax)
Te
ssmratedrotor
TL
Te
Intersection point (Te=TL) determines the steady –state speed
![Page 4: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/4.jpg)
Given a load T– characteristic, the steady-state speed can be changed by altering the T– of the motor:
Scalar control of induction machine
Pole changing Synchronous speed change with no. of polesDiscrete step change in speed
Variable voltage (amplitude), frequency fixedE.g. using transformer or triacSlip becomes high as voltage reduced – low efficiency
Variable voltage (amplitude), variable frequencyUsing power electronics converter Operated at low slip frequency
![Page 5: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/5.jpg)
Variable voltage, fixed frequency
0 20 40 60 80 100 120 140 1600
100
200
300
400
500
600
Tor
que
w (rad/s)
Lower speed slip higher
Low efficiency at low speed
e.g. 3–phase squirrel cage IM
V = 460 V Rs= 0.25
Rr=0.2 Lr = Ls = 0.5/(2*pi*50)
Lm=30/(2*pi*50)
f = 50Hz p = 4
![Page 6: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/6.jpg)
Variable voltage, variable frequency
Constant V/f
Approximates constant air-gap flux when Eag is large
Eag = k f ag
f
V
f
Eag ag = constant
Speed is adjusted by varying f - maintaining V/f constant to avoid flux saturation
![Page 7: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/7.jpg)
Variable voltage, variable frequency
Constant V/f - assuming constant airgap flux
0 20 40 60 80 100 120 140 1600
100
200
300
400
500
600
700
800
900
Tor
que
50Hz
30Hz
10Hz
![Page 8: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/8.jpg)
Variable voltage, variable frequency
Constant V/f
Vrated
frated
Vs
f
![Page 9: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/9.jpg)
Constant V/f – open-loop
VSIRectifier
3-phase supply IM
Pulse Width
Modulators*+
Rampf
C
Variable voltage, variable frequeny
V
![Page 10: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/10.jpg)
Constant V/f – open-loop
Variable voltage, variable frequeny
Simulation example: 460V, 50Hz, 4 pole, Rs = 0.25, Rr = 0.2, Lr=Ls= 0.0971 H, Lm = 0.0955,
0 20 40 60 80 100 120 140 160 180 200-100
0
100
200
300
400
500
600
Steady state T-
![Page 11: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/11.jpg)
Constant V/f – open-loop
Variable voltage, variable frequeny
Simulation example: 460V, 50Hz, 4 pole, Rs = 0.25, Rr = 0.2, Lr=Ls= 0.0971 H, Lm = 0.0955,
0 20 40 60 80 100 120 140 160 180 200-100
0
100
200
300
400
500
600
Steady state T- and transient T- characteristic – without ramp limitter
![Page 12: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/12.jpg)
Constant V/f – open-loop
Variable voltage, variable frequeny
Simulation example: 460V, 50Hz, 4 pole, Rs = 0.25, Rr = 0.2, Lr=Ls= 0.0971 H, Lm = 0.0955,
0 20 40 60 80 100 120 140 160 180 200-100
0
100
200
300
400
500
600
Steady state T- and transient T- characteristic – with ramp limitter
![Page 13: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/13.jpg)
1Variable voltage, variable frequency
Constant V/f
Problems with open-loop constant V/f
At low speed, voltage drop across stator impedance is significant compared to airgap voltage - poor torque capability at low speed
Solution:Boost voltage at low speedMaintain Im constant – constant ag
![Page 14: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/14.jpg)
0 20 40 60 80 100 120 140 1600
100
200
300
400
500
600
700
Tor
que
50Hz
30Hz
10Hz
Constant V/f
Variable voltage, variable frequeny
![Page 15: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/15.jpg)
with compensation (Is,ratedRs)
0 20 40 60 80 100 120 140 1600
100
200
300
400
500
600
700
Tor
que
Constant V/f
• Torque deteriorate at low frequency – hence compensation commonly performed at low frequency
• In order to truly compensate need to measure stator current – seldom performed
Variable voltage, variable frequeny
![Page 16: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/16.jpg)
with voltage boost at low frequency
Constant V/f
Vrated
frated
Linear offset
Non-linear offset – varies with IsBoost
Variable voltage, variable frequeny
![Page 17: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/17.jpg)
Constant V/f
Variable voltage, variable frequeny
Poor speed regulation
Solution:Compesate slipClosed-loop control
Problems with open-loop constant V/f
2
![Page 18: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/18.jpg)
Constant V/f – open-loop with slip compensation and voltage boost
VSIRectifier
3-phase supply IM
Pulse Width
Modulator
VboostSlip speed calculator
s*++
++ V
Vdc Idc
Rampf
C
Variable voltage, variable frequeny
![Page 19: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/19.jpg)
Constant air-gap flux
A better solution : maintain ag constant. How?
ag, constant → Eag/f , constant → Im, constant (rated)
Rr’/s+
Vs
–
RsLls Llr’
+
Eag
–
Is Ir’
Im
Lm
maintain at rated
Controlled to maintain Im at rated
Variable voltage, variable frequeny
![Page 20: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/20.jpg)
Constant air-gap flux
Variable voltage, variable frequeny
0 20 40 60 80 100 120 140 1600
100
200
300
400
500
600
700
800
900T
orqu
e
50Hz
30Hz
10Hz
![Page 21: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/21.jpg)
sr
mlr
rlr
m I
sR
)LL(j
sR
LjI
,I
1T1
j
1TjI
I
sR
L1
j
sR
LjI
s
rr
rslip
rslipm
s
rr
r
r
rr
m
,I1Tj
1T1
j
I mrslip
rr
rslip
s
• Current is controlled using current-controlled VSI
• Dependent on rotor parameters – sensitive to parameter variation
Constant air-gap flux
Variable voltage, variable frequeny
![Page 22: Induction Motor Scalar Control](https://reader033.fdocuments.in/reader033/viewer/2022061117/54675220b4af9fda3f8b53be/html5/thumbnails/22.jpg)
Constant air-gap flux
VSIRectifier
3-phase supply IM
*
+
+ |Is|slip
C
Current controller
s
PI
+
Variable voltage, variable frequeny
r
-