7/22/2019 Chapter 4 - Inverters
1/67
7/22/2019 Chapter 4 - Inverters
2/67
7/22/2019 Chapter 4 - Inverters
3/67
7/22/2019 Chapter 4 - Inverters
4/67
7/22/2019 Chapter 4 - Inverters
5/67
7/22/2019 Chapter 4 - Inverters
6/67
7/22/2019 Chapter 4 - Inverters
7/67
7/22/2019 Chapter 4 - Inverters
8/67
7/22/2019 Chapter 4 - Inverters
9/67
7/22/2019 Chapter 4 - Inverters
10/67
7/22/2019 Chapter 4 - Inverters
11/67
7/22/2019 Chapter 4 - Inverters
12/67
7/22/2019 Chapter 4 - Inverters
13/67
7/22/2019 Chapter 4 - Inverters
14/67
7/22/2019 Chapter 4 - Inverters
15/67
7/22/2019 Chapter 4 - Inverters
16/67
7/22/2019 Chapter 4 - Inverters
17/67
7/22/2019 Chapter 4 - Inverters
18/67
7/22/2019 Chapter 4 - Inverters
19/67
7/22/2019 Chapter 4 - Inverters
20/67
7/22/2019 Chapter 4 - Inverters
21/67
7/22/2019 Chapter 4 - Inverters
22/67
7/22/2019 Chapter 4 - Inverters
23/67
7/22/2019 Chapter 4 - Inverters
24/67
7/22/2019 Chapter 4 - Inverters
25/67
7/22/2019 Chapter 4 - Inverters
26/67
7/22/2019 Chapter 4 - Inverters
27/67
7/22/2019 Chapter 4 - Inverters
28/67
7/22/2019 Chapter 4 - Inverters
29/67
UTM
7/22/2019 Chapter 4 - Inverters
30/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
30
UTM
Si l
7/22/2019 Chapter 4 - Inverters
31/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
31
Full bridge (single phase) is built from two half -bridge leg. The switching in the second leg is delayed by 180 degreesfrom the first leg.
Single-phase,
Full-bridge
UTM
7/22/2019 Chapter 4 - Inverters
32/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
32
UTM
7/22/2019 Chapter 4 - Inverters
33/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
33
Three-Phase Inverter
Each leg(Red, Yellow,Blue) is delayedby 120degrees.
A three -phaseinverter withstar connected
load is shownon the right
UTM
Three phase
7/22/2019 Chapter 4 - Inverters
34/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
34
Three phaseinverter
waveforms
UTM
Three Phase
7/22/2019 Chapter 4 - Inverters
35/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
35
Three PhaseInverter
Waveforms(6 steps output
VL-N)
UTM
7/22/2019 Chapter 4 - Inverters
36/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
36
3-phase Inverter - Analysis
R total = R + R/2 = 3R/2
iTotal = V s /R total = 2V s /3R
Van = V cn = i Total .R/2 = V s /3
Vbn
= - iTotal
.R = - 2Vs/3
UTM
7/22/2019 Chapter 4 - Inverters
37/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
37
3-phase Inverter - Harmonics
THD i is load dependent.The output voltage magnitude can only be controlled by V DC ,and switching frequency controls the output frequency.Harmonics of order three and multiples of three are absent
Example:
VDC = 100 V,Output fundamentalfrequency = 60 Hz,Load R-L series
Y- connected withR = 10 ohm andL = 20 mH,determine the THD i .
Answer : THDi = 7 %
UTM
7/22/2019 Chapter 4 - Inverters
38/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
38
UTM
7/22/2019 Chapter 4 - Inverters
39/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
39
UTM
7/22/2019 Chapter 4 - Inverters
40/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
40
UTM
7/22/2019 Chapter 4 - Inverters
41/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
41
UTM
7/22/2019 Chapter 4 - Inverters
42/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
42
UTM
7/22/2019 Chapter 4 - Inverters
43/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
43
Pulse Width Modulation (PWM)
Objective PWM
- Control of inverter output voltage- Reduction of harmonics
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
- PWM frequency is the same as the frequency of V triangular
- Amplitude is controlled by the peak value of V control (Ma)
- Fundamental frequency is controlled by the frequency of V control
UTM
7/22/2019 Chapter 4 - Inverters
44/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
44
Pulse Width Modulation (PWM)
UTM
7/22/2019 Chapter 4 - Inverters
45/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
45
Triangulation Method(Natural Sampling)
Amplitudes of the triangular wave(carrier) and sine wave (modulating)
are compared to obtain PWMwaveform. Simple analoguecomparator can be used.(Introducedby Scnohung & Stemmler)
Basically an analogue method. Itsdigital version, known as REGULARsampling is widely used inindustry.(Introduced by Bowes)
Pulse Width Modulation (PWM)
UTM
7/22/2019 Chapter 4 - Inverters
46/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
46
PWM Types
Natural (sinusoidal) sampling (as shown on previous slide)
Problems with analogue circuitry, e.g. Drift, sensitivity,temperature, interference, etc . Regular sampling simplified version of natural sampling that results in simple digitalimplementation
Optimized PWM PWM waveform are constructed based on certain performancecriteria, e.g . THD. Harmonic elimination/minimisation PWM PWM waveforms are constructed to eliminate some undesirable
harmonics from the output waveform spectra. Highly mathematical in nature Space-Vector Modulation (SVM) A simple technique based on volt-second that is normally usedwith three-phase inverter motor drive
UTM
Modulation
7/22/2019 Chapter 4 - Inverters
47/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
47
ModulationIndex, Ratio
UTM
7/22/2019 Chapter 4 - Inverters
48/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
48
Modulation Index determines the output voltage fundamental
component
Modulation ratio determines the incident (location) ofharmonics in the spectra.
Modulation Index, Ratio
UTM
7/22/2019 Chapter 4 - Inverters
49/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
49
Regular Sampling (Asymmetric)
UTM
Asymmetric and
7/22/2019 Chapter 4 - Inverters
50/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
50
Asymmetric andsymmetric
regular sampling
UTM
7/22/2019 Chapter 4 - Inverters
51/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
51
UTM
Bipolar
7/22/2019 Chapter 4 - Inverters
52/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
52
BipolarSwitching
Output voltage alternatesbetween plus and minusthe DC supply, i.e
UTM
7/22/2019 Chapter 4 - Inverters
53/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
53
UTM
Unipolar
7/22/2019 Chapter 4 - Inverters
54/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
54
pSwitching
Extra Reading
http://sureshks.netfirms.com/article/apfc2/apfc2.htm#31
UTM
Unipolar switching
http://sureshks.netfirms.com/article/apfc2/apfc2.htmhttp://sureshks.netfirms.com/article/apfc2/apfc2.htmhttp://sureshks.netfirms.com/article/apfc2/apfc2.htmhttp://sureshks.netfirms.com/article/apfc2/apfc2.htmhttp://sureshks.netfirms.com/article/apfc2/apfc2.htmhttp://sureshks.netfirms.com/article/apfc2/apfc2.htmhttp://sureshks.netfirms.com/article/apfc2/apfc2.htmhttp://sureshks.netfirms.com/article/apfc2/apfc2.htm7/22/2019 Chapter 4 - Inverters
55/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
55
Unipolar switching
UTM
7/22/2019 Chapter 4 - Inverters
56/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
56
UTM
H i f bi l PWM
7/22/2019 Chapter 4 - Inverters
57/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
57
Harmonics of bipolar PWM
UTM
Harmonics of
7/22/2019 Chapter 4 - Inverters
58/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
58
bipolar PWM
UTM
PWM Spectra
7/22/2019 Chapter 4 - Inverters
59/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
59
PWM Spectra
UTM
PWM Spectra Observations
7/22/2019 Chapter 4 - Inverters
60/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
60
PWM Spectra Observations
The harmonics appear in clusters at multiple of the carrierfrequencies . Main harmonics located at :
f = k.p.( f m) where k = 1, 2, 3....where f m is the frequency of the modulation (sine) waveform.
There also exist side-bands around the main harmonic frequencies. Amplitude of the fundamental is proportional to the modulation index.
The relation ship is given as:
V1= M IVin The amplitude of the harmonic changes with M I. Its incidence (location onspectra) is not. When p >10, or so, the harmonics can be normalized. For lower valuesof p, the side-bands clusters overlap-normalized results no longer apply.
UTM
Tabulated
7/22/2019 Chapter 4 - Inverters
61/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
61
BipolarPWM
Harmonics
UTM
Three phase Harmonics
7/22/2019 Chapter 4 - Inverters
62/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
62
Three-phase Harmonics
For three -phase inverters, there is significant advantage if M R
is chosen to be: Odd: All even harmonic will be eliminated from the
pole-switching waveform. triplens (multiple of three ( e.g . 3, 9, 15, 21, 27...):
All triplens harmonics will be eliminated from theline-to-line output voltage.
By observing the waveform, it can be seen that with odd M R,the line-to- line voltage shape looks more sinusoidal. As can be noted from the spectra, the phase voltage amplitudeis 0.8 (normalized). This is because the modulation index is 0.8.The line voltage amplitude is square root three of phase voltagedue to the three-phase relationship
UTM
Effect of Odd
7/22/2019 Chapter 4 - Inverters
63/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
63
and Triplens
P = 8 not a multiple of 3
VRY high harmonics
P = 9 Multiple of 3
VRY Low harmonicsMore Sinusoidal
p = 8, M = 0.6
p = 9, M = 0.6
UTM
Spectra: Effect of Triplens
7/22/2019 Chapter 4 - Inverters
64/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
64
Spectra: Effect of Triplens
A
B
0.83 (Line to line voltage)
Fundamental
p = 21, M = 0.8
UTM
Comments on PWM scheme
7/22/2019 Chapter 4 - Inverters
65/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
65
Comments on PWM scheme
It is desirable to have M R as large as possible.
This will push the harmonic at higher frequencies on thespectrum. Thus filtering requirement is reduced.
Although the voltage THD improvement is not significant,
but the current THD will improve greatly because the load
normally has some current filtering effect.
However, higher M R has side effects:
Higher switching frequency: More losses.
Pulse width may be too small to be constructed.
Pulse dropping may be required.
UTM
Example :
7/22/2019 Chapter 4 - Inverters
66/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
66
Example :
Q. A single-phase full-bridge inverter supplies a load of 10 W in series with aninductance of 31.8 mH. The inverter is supplied by a 380 VDC source.
(a) Sketch the inverter circuit as described above. (5 marks)(b) Calculate the rms value of the fundamental (n = 1) of the inverteroutput voltage assuming it is a square-wave. (3 marks)(c) Assuming a quasi square-wave output voltage waveform with a delayangle of 45, calculate the rms value of the fundamental and the twolowest order harmonics of the inverter output voltage. (5 marks)(d) Explain how the 7th harmonic of the inverter output voltage can beeliminated while maintaining the same rms value of the fundamental asobtained from (c). Then, plot the frequency spectrum of the inverter outputvoltage up to the 11th order (consider magnitude only). Label the
important parameters clearly. (7 marks)(e) Suggest and then describe a switching strategy for the inverter powerdevices that can shift the lower order harmonics in the inverter outputvoltage to the higher order side. Provide diagrams if necessary to supportyour suggestion. (5 marks)
UTM
7/22/2019 Chapter 4 - Inverters
67/67
UTMUNIVERSITI TEKNOLOGI MALAYSIA
The End
of Chapter 4
hank You
Top Related