AC Motor Control and EV Applications
Pulse-Width Modulation andInverter
Chapter 10
Switching Turn-on / off Losses
On loss Conduction loss Off loss
VCE
IL
VCE
IL On
Off
t
t
(a) (b)
Pole and Line-to-line Voltages
Line to linevoltages
Polevoltages
Q3
Q2
Q4
Q6
Q5
Q6
Q2
Q1Q1
Q3
Phase Voltages
Motorphase
voltages
vas
t
vbs
t
vcs
t
vsn
t
2Vdc /3Vdc /3
2Vdc /3Vdc /3
2Vdc /3 Vdc /3
Vdc / 6
-Vdc / 6
Six Step Operation
Sinusoidal PWM
Vdc /2
-Vdc/2
Van
Sa 1
0
Vdc/2
-Vdc/2
Van
+ -comparator
Addition of 3rd Order Harmonics
3rd order harmonics lowers the peak of the fundamental component.
Addition of 3rd order harmonicsprovide a room to increase the fundamental component.
Overmodulation
Over modulation area
360
180
Overmodulatedwave form
Space Vector PWM
V1 (1,0,0) V2 (1,1,0) V3 (0,1,0) V4 (0,1,1) V5 (0,0,1) V6 (1,0,1)
q
asds
bs
cs
V1(1,0,0)
V2(1,1,0)V3(0,1,0)
V4(0,1,1)
V5(0,0,1) V6(1,0,1)
Sector 1
Sector 2
Sector 3
Sector 4
Sector 5
Sector 6
V0(0,0,0)
V7(1,1,1) 2/3Vdc
s
SVPWM
Overmodulationregion
Small voltage
Max.voltage
Space Vector PWM (sector 1)
Sector 1
V2(1,1,0)
V1(1,0,0)
Va
V0(0,0,0) Va1
Va2
Space Vector PWM
1 1 1 1 1 1 00
1 1 1 10 0 0 0
1 10 0 0 0 0 0
Ts
Sector 1
0 1 1 1 1 0 00
1 1 1 10 1 1 0
1 10 0 0 0 0 0
T2
Sa
Sector 2
V0 V3 V2 V7
T1
Sb
Sc
Sa
Sb
Sc
V0 V1 V2 V7
T1 T2
Ts
0 0 1 1 0 0 00
1 1 1 10 1 1 0
1 10 0 1 1 0 0
Ts
Sector 3
Sa
Sb
Sc
V0 V3 V4 V7
T1 T2
Space Vector PWM
0 0 1 1 0 0 00
1 1 1 10 0 0 0
1 10 1 1 1 1 0
T2
Sa
Sector 4
V0 V5 V4 V7
T1
Sb
Sc
Ts
0 1 1 1 1 0 00
0 1 1 00 0 0 0
1 10 1 1 1 1 0
Ts
Sector 5
1 1 1 1 1 1 00
0 1 1 00 0 0 0
1 10 0 1 1 0 0
T2
Sa
Sector 6
V0 V1 V6 V7
T1
Sb
Sc
Sa
Sb
Sc
V0 V5 V6 V7
T1 T2
Ts
SVPWM
Sector Finding Method
START
Y
N
YSector 2
N
YSector 1
N
Sector 3
YSector 5
N
Y
Sector 6
N
Sector 4
Sector 1
Sector 2
Sector 3
Sector 5
Sector 4 Sector 6
Overmodulation
Overmodulationregion
SPWM versus SVPWM
SPWM
SVPWM– Voltage Usage : 15.5% increase– No of switching decreases.
Current Sampling
1 1 1 1 1 1 00 11 1 1 1 100
(a) Symmetric (b) Asymmetric
currentaveragecurrent
currentsampling
averagecurrent
current
currentsampling
Vdc /2
-Vdc /2
0
Sa
Sa ’
0-Vdc
(b) Ias <0
Vdc /2
0
Sa
Sa ’
0
(a) Ias >0
Vdc
Gate signalwith
dead time
Terminalvoltage
Dead timevoltageerror
Gate signalwith
dead time
Terminalvoltage
Dead timevoltageerror
i
i
Original PWM
Original PWM
Dead Time Effects Depending on Current Direction
Dead Time Effects on Current
Zero Current Clamping
(a)
Distortedvoltageby dead time
current
(b)
Distortedvoltageby dead time
current
(b) Ias <0(a) Ias >0
Sa
Sa ’
With dead timecompensation
Original PWM
Original PWM
Gate signalafter providingdead time
Sa
Sa ’
With dead timecompensation
Gate signalafter providingdead time
Dead Time Compensation
LED
Encoder
Photo TR
ABZ
Slit
Disk
1 2 3 4 1 2 3 4
Encodersignal
Referencepulses
(a) (b)
Speed
Mea
sure
men
t erro
r
M-method T-method
Frequency
M/T Method
1-Input, 2-Output Resolver
Rotating coilStationary coil
+
+
Flux linkageRotary transformer
Output 1
Output 2Input
Resolver Signal Processing
LPF PI V/Fconverter
demodulator
Pulsecounter
to processor
+
-
PI+
-
Current Sensors
+-
+
-
(a) Voltage type (b) Current type
PI
Rotating coil
Stationary coil
AC sourcefor rotor excitation
+
+
Flux linkage
Rotary transformer
Input 1
Input 2
Output