textbook: bin wu, ‘high-power converters and ac drives’, wiley - ieee press, 2006 ee8407 topic 6...
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1 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
Power Converter Systems
Graduate Course EE8407
Ryerson Campus
Bin Wu PhD, PEng
ProfessorELCE DepartmentRyerson University
Contact Info Office: ENG328Tel: (416) 979-5000 ext: 6484Email: bwu@ee.ryerson.ca http://www.ee.ryerson.ca/~bwu/
2 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
CHB Inverter Fed Drive Source: Toshiba - General Electric
H-bride power cells
Topic 6
Multilevel Cascaded H-Bride (CHB) Inverters
3 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
Lecture Topics
• H-Bridge Inverter
• CHB Inverter Topologies
• Phase Shifted PWM
• Level Shifted PWM
• PWM Scheme Comparison
Multilevel CHB Inverters
4 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• To increase inverter operating voltage without devices in series
• To minimize THD with low switching frequencies fsw
• To reduce EMI due to lower voltage steps
Why Use Multilevel Inverters?
Switching frequency for high power converters:
fsw = 60Hz ~ 1000Hz
Multilevel CHB Inverters
5 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
N
dC
CascadedH-bridge (CHB)
Inverter
dC
Two LevelInverter
dC
Flying CapacitorInverter
dC
Neutral PointClamped (NPC)
Inverter
dC
~ ~
~
~
• Per-Phase Diagram
Multilevel Inverter Topologies
6 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• H-bridge Power Cell
dCdV
1S
2S
3S
4S
1D
2D
3D
4D
1g 3g
2g4g
A
B
P
N
ABv
H-Bridge Inverter
7 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
H-bridge Power Cell
• Typical Industrial Applications
0
0
0
M
30
30
30
A
B
C
Neutral
H-bridge
Phase ShiftingTransformer
UtilityGrid
Five-level CHB inverter
dCdV
1S
2S
3S
4S
1D
2D
3D
4D
1g 3g
2g4g
A
B
P
N
ABv
H-Bridge Inverter
8 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Bipolar Modulation
Bipolar PWM:
vAB from -Vd to +Vd
or from +Vd to -Vd
dCdV
1S
2S
3S
4S
1D
2D
3D
4D
1g 3g
2g4g
A
B
P
N
ABv1gv
3gv
dV
dV
0
-1.0
1.0
0
BNv
ANv
0
ABv
dV
1ABv
2
mv crv
0
0.2
0.4
0.6
12 fm32 fm 32 fm
2fm 2fm 23 fm 14 fm
1n
dn VVAB /
0
(a) Waveforms
(b) Harmonic spectrum
dV
n1 10 20 30 40 50 60
H-Bridge Inverter
9 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Bipolar Modulation (FFT)
d
n
V
VAB
0.2
0.4
0.6
0.8
0.2 0.4 0.6 0.8
2fm
00
32 fm
12 fm
0.707
fm
am
1n
H-Bridge Inverter
10 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Unipolar Modulation (1)
0
-1.0
1.0
mv
2
1gv
3gv
0
BNv
ANvdV
dV
0
ABv
dV
0
0.2
0.4
dn VVAB /
32 fm 32 fm14 fm
0.6
12 fm
mv crv
1n
(b) Harmonic spectrum
(a) Waveforms
n1 10 20 30 40 50 60
dCdV
1S
2S
3S
4S
1D
2D
3D
4D
1g 3g
2g4g
A
B
P
N
ABv
• Two modulation waves
vm and vm-
• One carrier wave vcr
• Unipolar PWM:
vAB from 0 to +Vd
or from 0 to -Vd
H-Bridge Inverter
11 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• One modulating wave: vm
• Two carrier waves: vcr and vcr-
dCdV
1S
2S
3S
4S
1D
2D
3D
4D
1g 3g
2g4g
A
B
P
N
ABv
0
-1.0
1.0
0
ABv
dV
mv crv
crv
1gv
3gv
• Unipolar Modulation (2)
H-Bridge Inverter
12 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Five-Level CHB Inverter
Converters in cascade, but no switching devices in series.
Complementary Switch pairs: S11 and S41;
S31 and S21;
S12 and S42;
S32 and S22;
1Hv
2Hv
N
21S
11S
41S
31S
22S42S
32S12S
E
E
E
E
E
E
A B C
O
LOAD
H1
H2
CHB Inverter Topologies
13 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Output Voltage and Switching Status (five-level)
Waveform of vAN is composed of five voltage levels: 2E, E, 0, -E, and -2E
1Hv
2Hv
21S
11S
41S
31S
22S42S
32S12S
E
E
A
H1
H2 N
Switching State Output Voltage
ANv 11S 31S 12S 32S 1Hv 2Hv
2E 1 0 1 0 E E 1 0 1 1 E 0 1 0 0 0 E 0 1 1 1 0 0 E
E
0 0 1 0 0 E 0 0 0 0 0 0 0 0 1 1 0 0 1 1 0 0 0 0 1 1 1 1 0 0 1 0 0 1 E -E
0
0 1 1 0 -E E 0 1 1 1 -E 0 0 1 0 0 -E 0 1 1 0 1 0 -E
-E
0 0 0 1 0 -E -2E 0 1 0 1 -E -E
CHB Inverter Topologies
14 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Seven- and Nine-Level Inverters (Per phase diagram)
1Hv
2Hv
21S
11S
41S
31S
22S42S
32S12S
E
E
A
H1
H2
3Hv
23S43S
33S13S
E
H3 N
1Hv
2Hv
E
E
A
3HvE
4HvE
N
(a) Seven-level inverter (b) Nine-level inverter
CHB Inverter Topologies
15 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Unequal dc Bus Voltages
(a) Two-cell seven-leveltopology
(b) Two-cell nine-leveltopology
1Hv
2Hv
21S
11S
41S
31S
22S42S
32S12S
E
E2
A
H1
H2 N
1Hv
2Hv
21S
11S
41S
31S
22S42S
32S12S
E
E3
A
H1
H2 N
CHB Inverter Topologies
16 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
Switching State Output Voltage
ANV 11S 31S 12S 32S 1HV 2HV
3E 1 0 1 0 E 2E
1 1 1 0 0 2E 2E
0 0 1 0 0 2E
1 0 1 1 E 0
1 0 0 0 E 0 E
0 1 1 0 -E 2E
0 0 0 0 0 0
0 0 1 1 0 0
1 1 0 0 0 0 0
1 1 1 1 0 0
1 0 0 1 E -2E
0 1 1 1 -E 0 -E
0 1 0 0 -E 0
1 1 0 1 0 -2E -2E
0 0 0 1 0 -2E
-3E 0 1 0 1 -E -2E
• Unequal dc Bus Voltages (Two-cell seven-level topology)
(a) Two-cell seven-leveltopology
1Hv
2Hv
21S
11S
41S
31S
22S42S
32S12S
E
E2
A
H1
H2 N
CHB Inverter Topologies
17 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Carrier Based PWM – Phase Shifted
Amv
1crv 2crv 3crv
11gv
31gv
1Hv
12gv
32gv
2Hv
13gv
33gv
3Hv
0
ANv
E
3E
0
1.0
-1.0
E
1crv 2crv 3crv
E
321 HHH vvvvAN
• # of voltage levels: m = 7
• # of carriers: mc = m - 1 = 6
• Phase shift: 360° / mc = 60°
Carriers for H1 bridge:vcr1 and vcr1-
Carriers for H2 bridge:vcr2 and vcr2-
Carriers for H3 bridge:vcr3 and vcr3-
m = 7
Phase Shifted PWM
18 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Inverter Waveforms (7-level, phase shifted)
1Hv
2Hv
3Hv
0
ANv
0
ABv
3E
6E
• Switching occurs at different times• fsw(device) = 60 mf = 600Hz
• Inverter phase voltage levels: 7• Low EMI
• Line-to-line voltage levels: 13• Close to a sinusoid• Low THD
Phase Shifted PWM
19 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• FFT (7-level, phase shifted)
• Lowest harmonics: around 2mf
• Lowest harmonics: around 6mf
• Containing triplen harmonics
• No triplen harmonics• Equivalent fsw(inverter)
= 60(6mf ) = 3600Hz
0
0.04
0.08 12 fm14 fm 16 fm
0
0.04
0.08
36 fm96 fm 96 fm
0
0.04
0.08 16 fm76 fm 76 fm
dn VV /H1
dANn VV /
dABn VV /
THD = 53.9%
THD = 18.8%
THD = 15.6%
1 n10 20 30 40 50 60 70 80
1 n10 20 30 40 50 60 70 80
1 n10 20 30 40 50 60 70 80
Phase Shifted PWM
20 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Harmonic Content (7-level, phase shifted)
00.2 0.4 0.6 0.80
am
0.1
0.2
0.3
d
n
V
VAB
16 fm
56 fm 76 fm
116 fm
x
y 2241.x
y
1n
Phase Shifted PWM
21 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Carrier Based PWM – Level Shifted• # of voltage levels: m = 5
• # of carriers:
mc = m - 1 = 4
IPD provides the best harmonic profile.
-1.0
0
1.0mv
2
3
1crv
(a) In-phase disposition (IPD)
2crv
3crv
4crv
2 3
(b) Alternative phase opposite disposition (APOD)
mv
2
(c) Phase opposite disposition (POD)
mv
-1.0
0
1.0
1crv
2crv
3crv
4crv
-1.0
0
1.0
1crv
2crv
3crv
4crv
IPD
APOD
POD
Level Shifted PWM
22 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
cr1v
cr2v
cr3v
g11v
g31v
1Hv
12gv
32gv
2Hv
13gv
33gv
3Hv
0
ANv3E
mAv
-cr1v
-cr3v
-cr2v
3H2H1HAN vvvv
E
E
E
• # of voltage levels: m = 7
• # of carriers: mc = m - 1 = 6
• fsw(device):
- not equal to fcr, and
- not the same for all switches.
• Device conduction angle:
- not equal.
• Necessary to swap switching
pattern.
• Gating Arrangement (7-level)
Level Shifted PWM
23 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Inverter Output Voltages (seven-level)
• m = 7
• vAB close to a sinusoid • Low THD, low EMI
• fsw(inv) = fc = 3600Hz
• Switching occurs at different times
• fsw(device) = fcr /mc =
600Hz (avg)
1Hv
2Hv
3Hv
0
ANv
0
ABv
0
0.04
0.08
0
0.04
0.08
2fm8fm8fm
16fm16fm
3E
6E
2 4
2 4
THD = 18.6%
THD = 10.8%
6fm 6fm
dABn VV /
dANn VV /
1 n10 20 30 40 50 60 70 80
1 n10 20 30 40 50 60 70 80
Level Shifted PWM
24 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Prototype at Ryerson (Seven-level CHB Inverter)
Level Shifted PWM
25 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Measured Waveforms (IPD, 7-level)
Inverter phase voltage vAZ Line-to-line voltage vAB
Level Shifted PWM
26 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• PWM at Low ma
- Phase shifted PWM:
THD = 96.7%
- Level shifted PWM:
THD = 48.8%
• At ma = 0.2:
1Hv
2Hv
3Hv
0
ANv
0
ABv
E
2E
1Hv
2Hv
3Hv
0
ANv
0
ABv2E
E
(a) Phase-shifted modulation
(b) Level-shifted modulation (IPD)
THD = 96.7%
THD = 48.8%
PWM Scheme Comparison
27 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
• Total Harmonic Distortion (THD)
am0.2 0.4 0.6 0.80
20
40
60
80
THD(%)
Phase-Shifted PWM
Level-Shifted PWM (IPD)
Hz600, devswfSeven-level Inverter
PWM Scheme Comparison
28 Textbook: Bin Wu, ‘High-Power Converters and AC Drives’, Wiley - IEEE Press, 2006
EE8407 Topic 6
Comparison Phase-shifted Modulation
Level-shifted Modulation (IPD)
Device Switching Frequency Same for all devices Different Device Conduction
Period Same for all devices Different
Rotating of switching patterns No required Required THD of inverter output
line-to-line voltage Good Better
Low Order Harmonics No Yes
(Very low amplitude)
• Summary
PWM Scheme Comparison
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