ac motor control and ev applicationsphome.postech.ac.kr/user/cmdlab/acmc(ch3).pdf · 2014-04-07 ·...
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AC Motor Control and EV Applications
Induction Motor Basics
Chapter 3
Squirrel Cage of an Induction Motor
End Ring
Rotor Bar
S
N
Loop 2Flux Increasing;
Current flowsso as to oppose tothe PM flux increase.
Magnet moving direction
Loop 1Flux Decreasing;
Current flowsso as to oppose tothe PM flux decrease.
Rotationaldirection
Squirrel Cage of an Induction Motor
End Ring
Rotor Bar
Stator Flux
Stator Flux
Laminated Sheets for Stator and Rotor Cores
Assembled IM Rotor
Flux Linking between Stator and Rotor Windings
as
as ’
ar
ar ’
End ring conductor
Air gap
Secondary windingPrimary winding
Steady State Model
Air gap power:
Circuit Simplification and Torque
Vs
rs Lls
Lm
Llr
rr /s
Vs
rs Lls
Lm
Llr
rr /sIrIs
Torque Speed Curve
Starting torque
Breakdowntorque
Motoring Regenerating
Linear in s
Te
s=1 s=0 m
e
Torque-Speed Curve
Starting torque
Breakdowntorque
Plugging Motoring Regenerating
Linear in s
s=1 s=0sm
s=1 s=0
Rated torque
Rated current
Locked rotor current
(a)
(b)
Breakdown Torque
Breakdowntorque
Breakdown Torque for Different Rotor Resistance
Breakdown torque is independent ofrotor resistance.
(Nm)
(b)
00.10.20.30.40.50.60.70.80.910
50
100
150
200
250
Slip
Torq
ue
(a)
(b)
Torque-Speed Curve Based on Simplified Model
Vs254V, 60Hz
rs =0.1
0.25/s
Lls =3mH Lls =3mH
Lm = 150mH
rs =0.1 Lls =3mH Lls =3mH
0.25/sLm =
150mHVs
254V, 60Hz
(a) (b)
Stable/Unstable Regions
UnstableRegion
StableRegion
Te
s=1 s=0e
Larger load
Smaller loadA
A’
A’’
sm
B
0.8571.2
Parasitic Torque Caused by 5th and 7th Harmonics
0
7th5th
Slip
Torque
Parasitic torque
Slot, Zigzag and End-Turn Leakage Flux
Zigzag leakage
Slot leakage
End turn leakage
(a) (b)Mutual flux
Shaft
Stator
Rotor
Circle Diagram
Circle Diagram for Different Slips
Min. PFangle
Ratedcurrent
Currentyieldingbreakdowntorque
Currentat locking
Rotor Slot Leakage Flux at Zero Slip
J barxx
xxx
(a) (b) (c)
Rotor Slot Leakage Flux at None Zero Slip
J bar
x x
xx
xx
x
Jbar
Isl hbar hbar
Bx
(a) (b) (c)
Current Displacement
Current Displacement of a Deep Bar
(a) (b)
Flux Lines over Double Cage Rotor
(a) (b)
High Slip : rr is large Low Slip : rr is small
Rotor Types and NEMA Classification
Doublecage
Deep wedge
Round
100
200
slip00.51
0
Class A
Class D
100
200
300
Class C
Class B
10050
Class A motors have high efficiency and high stiffness.Class D motors have high starting torque, but low efficiency.
Line Starting
Soft Starter
3 phase AC input
Induction motor
va
vb
vc
(b)
va
vb
vc
(c)
(a)
Gating signal
va
vb
vc
Speed variation range
Variable Voltage Control
VVVF Control
VVVF implies that flux level is kept constant so that it does not saturate the motor iron core.
PI Inverter
limiter
V/Ftable-
P/2
+
Motor
Speedsensor
0 Low frequency cut off
High voltage limit
Voltage boostregion
ConstantV/F
Slip Based VVVF Speed Controller