I am trying to design a seven level asymmetrical cascaded H bridge inverter using two H bridges with voltage E and 2E. How can I design the switching pulses for the inverter using level shift PWM technique?
From random search in google most papers on asymmetrical inverters use XOR gate logic for switching pulse generation(a reference sine wave is compared with a triangular wave and passed through a comparator and than a XOR gate is used) but no explanation have been provided on how and why it is developed.
Dear Maulik Kandpal,
Can you please share the circuit diagram and switching sequence you are planing to use.
with that i might be able to help you with design of pulse generation.
BTW are you trying to simulate or hardware implementation ?
Dear Maulik Kandpal,
I agree with Mr. shrinivas, can you please share the circuit diagram and switching sequence you are planing to use.
There are a lot of literature are available for this, but first we have to know your requirements.
and, also the second point you are doing for the simulation or for hardware.
please specify.
Hi
Hopefully you have access to Matlab and you can see the Simulink example in attachment.
You need 6 shift carriers (-3 to -2, -2 to -1, -1 to 0, 0 to 1, 1 to 2, 2 to 3)
you compared the carrier with a reference varying between -3 and 3
You sum the result of each comparaison to obtain a signal varying between 0 to 7.
each value correspond to a switching pattern according to your configuration
To add a bit of selfpromoting, and if you read french, you can also see the effect of choosing the most appropriate carrier pattern in my Master thesis
http://espace.etsmtl.ca/301/2/GR%C3%89GOIRE_Luc-Andr%C3%A9.pdf
pages 20 and 21
Follow up answer to your follow question:
Maulik: please tell me how do this multiport switch works?
The multiport is pretty much just a switch case; according to the first input (between 0 and 6) one of the vectors is chosen.
Maulik: how have you decided the switching for inverter?
each H-Bridge has 3-states. +V, 0, -V. In SimPowerSystem the corresponding vectors are [1 0 0 1] [1 0 1 0] [0 1 1 0].
Maulik: why have you taken the constant value as [-3,2]?
The constant values of [-3:2], not [-3,2], yields the following vector [-3 -2 -1 0 1 2] used to level-shift the carriers
Maulik: Should not switching be when reference sine wave is greater than carrier wave?
Either would work, just use which ever your comfortable with.
Thanks...but I am still not clear on working of multiport switch.Could you please explain a bit more on multiport switch working taking your model as reference .
Secondly why have you set the multiport input sequence as
[0 1 1 0 0 1 1 0] - 3V
-V
-2V
0
2V
V
3V
Could you explain the reason for choosing this particular sequence?Why not(-3,-2,-1,0,1,2,3)?
if the first input of the multiport is 0, the first vector (-3V) is applied.
if the first input of the multiport is 1, the second vector (-2V) is applied (not -V unlike what you believe).
and so on
the sequence is indeed (-3,-2,-1,0,1,2,3)
For [1001]= V, [1 0 1 0]=0 and [0 1 1 0]=-V are we numbering the switches of H bridge horizontally or vertically as shown below.
1 2 or 1 3
3 4 2 4
Secondly I've interpreted
1st input
[0 1 1 0 0 1 1 0]= [0 1 1 0] for 1st H bridge(-V) and [ 0 1 1 0] for second H bridge(-2V) which gives -V+-2V=-3V
2nd input
[0 1 1 0 0 1 0 1]= [0 1 1 0] for 1st H bridge(-V) and [ 0 1 0 1] for second H bridge(0) which gives -V+-0=-V
3rd input
[0 1 0 1 0 1 1 0]= [0 1 0 1] & [0 1 1 0] =0+-2V=-2V
Please explain what am I doing wrong
the numbering is
1 3
2 4
as for the second question I assumed the first H-bridge to be 2V and the second H-bridge to be 1V
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