Upload
bitswhoami
View
220
Download
0
Embed Size (px)
Citation preview
8/17/2019 Inverter Lecture 4
1/38
( DC to AC Converters)
PWM Inverters
Inverters
8/17/2019 Inverter Lecture 4
2/38
Voltage Source Inverters : Pulse
Width Modulated Inverters
EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
2
8/17/2019 Inverter Lecture 4
3/38
Single-phase half-bridge inverter
nics R. Femi, Lecturer, EEE Department
3
8/17/2019 Inverter Lecture 4
4/38
rms value of the fundamental component
1,3,5,..
2sin so
n
V v n t
n
4
nics R. Femi, Lecturer, EEE Department
= 1.273
Vs=Vd
8/17/2019 Inverter Lecture 4
5/38
Square-Wave Mode of Operation
EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department5
8/17/2019 Inverter Lecture 4
6/38
6
Single Phase Inverter Square-wave
V dc
Q1
Q2
Q’ 1
Q’ 2
vout
+
+
-
-
q1(t)
q2
(t)1-q1
(t)
1-q2(t)
vout(t)
-Vdc
Vdc
dcdcout V V V 27.14
1
t
1,3,5,..
4sindco
n
V v n t
n
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
7/38
7
THD = 0.48
Characteristics: - High harmonic content.
- Low switching frequency.
- Difficult filtering.
- Little control flexibility.
Single Phase Inverter Square-wave
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
8/389
Pulse-Width Modulated VSI
Objective of PWM
Disadvantages of PWM
Increase of switching losses due to high PWM frequency
Reduction of available voltage
EMI problems due to high-order harmonics
Control of inverter output voltage
Reduction of harmonics
8
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
9/38
Voltage Control of Single-Phase Inverters
Commonly-used Techniques Single-Pulse-Width-Modulation
Multiple-Pulse-Width-Modulation
Sinusoidal-Pulse-Width-Modulation
Modified-Sinusoidal-Pulse-Width-Modulation
9 EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
10/38
Single-Pulse-Width-Modulation
10 EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
11/38
One Pulse per Half-Cycle
Pulse Width Controls the Output Voltage
11
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
12/38
Carrier and Reference Signals
Compare the Reference Signal with the Carrier
Frequency of the Reference Signal determines the frequencyof the Output Voltage
Modulation Index (amplitude modulation ratio) = M = Ar/Ac
Gate PulseGate Pulse
EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department 12
8/17/2019 Inverter Lecture 4
13/38
rms value of the Output Voltage
1
22
2
2
2( )
2
0 180
0
o s
o s
o s
V V d t
V V
V V
13 EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
Quasi Square wave Inverter
8/17/2019 Inverter Lecture 4
14/38
Fourier Series for the Output Voltage
1,3,5,...
4( ) sin sin2
so
n
V nv t n t n
14 EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
15/38
Multiple-Pulse-Width-Modulation
15 EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
16/38
Multiple Pulses per Half-Cycle of Output Voltage
16
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
17/38
Gate Signal Generation
Compare the Reference Signal with the Carrier
Frequency of the Reference Signal determines the Output Voltage
Frequency Frequency of the Carrier determines the number of pulses per half-
cycle
Modulation Index controls the Output Voltage
EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department 17
8/17/2019 Inverter Lecture 4
18/38
Gate Signals and Output Voltage
Number of pulses per half cycle = p = f c/2f o = mf /2
where mf = frequency modulation ratio
18 EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
19/38
rms Value of the Output Voltage1
2( ) / 2
2
( ) / 2
2( )
2
0 1
0
2
0
0
p
o s
p
o s
o s
pV V d t
pV V
M
T
p
p
V V
19 EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
20/38
Fourier Series of the Output Voltage
1,3,5,...
2
1
( ) sin
4 3sin sin ( ) sin (
4 4 4
o n
n
p
sn m m
m
v t B n t
V n B n n
n
20 EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
21/38
Sinusoidal Pulse-Width Modulation
In multiple-pulse modulation, all pulses are the same width
Vary the pulse width according to the amplitude of a sine
wave evaluated at the center of the same pulse
21 EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
22/38
Generate the gating signal
2 Reference Signals, vr , -vr 22
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
23/38
Comparing the carrier and reference signals
Generate g1 signal by comparison with vr Generate g4 signal by comparison with -vr
23 EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
24/38
Comparing the carrier and reference signals
24
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
25/38
Potential problem if Q1 and Q4 try to turn ON
at the same time!
25 EEE/INSRT F342 - Power ElectronicsR. Femi, Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
26/38
If we prevent the problem
Output voltage is low when g1 and g4 are
both high
26
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
27/38
This composite signal is difficult to generate
27
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
28/38
Generate the same gate pulses with one
sine wave
28
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
29/38
Alternate scheme
29
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
30/38
rms output voltage
Depends on the modulation index, M
2
1
p
m
o S S m
pV V V
Where δm is the width of the mth pulse
30EEE/INSRT F342 - Power Electronics
R. Femi, Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
31/38
Fourier coefficients of the output voltage
2
1
4 3
sin sin sin4 4 4
1, 3, 5,..
pS m m m
n m m m
V n
B n n n
n
31
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
32/38
Pulse-Width Modulation (PWM)
Fig. 5 Pulse-width modulation.10
32
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
33/38
I. Voltage Source Inverter (VSI)B. Pulse-Width Modulated VSI (3)
Inverter output voltage
When vcontrol > vtri, VA0 = Vdc /2
When vcontrol < vtri, VA0 = -Vdc /2
A01A0
10
Vof componentfrequecnylfundamenta:)(Vwhere,
,2/
)(
dc
A
tri
control
V
V of peak
v
vm
Modulation Index (m)
Control of inverter output voltage
Amplitude is controlled by the peak value of vcontrol
Fundamental frequency is controlled by the frequency of vcontrol
PWM frequency is the same as the frequency of vtri
33
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
8/17/2019 Inverter Lecture 4
34/38
34
Characteristics: - High harmonic content.
- Low switching frequency.- Difficult filtering.
- More control flexibility.
THD = 0.3
Example with Vout-1=1.21Vdc
Single Phase Inverter Single Phase Inverter
SquareSquare--wave “Modulation” (4)wave “Modulation” (4)
EEE/INSRT F342 - Power Electronics R. Femi,
Lecturer, EEE Department
O L f S i h M d DC AC
8/17/2019 Inverter Lecture 4
35/38
One Leg of a Switch-Mode DC-AC
Inverter
EEE/INSRT F342 - Power Electronics
R. Femi, Lecturer, EEE Department35
S th i f Si id l O t t b
8/17/2019 Inverter Lecture 4
36/38
Synthesis of a Sinusoidal Output by
PWM
EEE/INSRT F342 - Power Electronics
R. Femi, Lecturer, EEE Department36
8/17/2019 Inverter Lecture 4
37/38
EEE/INSRT F342 - Power Electronics
R. Femi, Lecturer, EEE Department37
8/17/2019 Inverter Lecture 4
38/38
Details of a Switching Time Period
EEE/INSRT F342 - Power Electronics
R F i L EEE D38