I am trying to apply phase shift control to my H bridge inverter but I get these spikes in the picture I don't know why. And it getting worse if I apply inductive load
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1\$\begingroup\$ Welcome! Please post a schematic. How are you driving it? \$\endgroup\$winny– winny2023-11-04 14:09:28 +00:00Commented Nov 4, 2023 at 14:09
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\$\begingroup\$ Hello, it is normal H bridge, and I am using UCC21520 \$\endgroup\$Deia Deen– Deia Deen2023-11-05 01:34:04 +00:00Commented Nov 5, 2023 at 1:34
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\$\begingroup\$ What voltage is being shown on the scope? It does not look like Vab of the phase-shifted full-bridge (refer post below from @Andyaka). Is it possibly the output after the transformer, ie: the transformer secondary? Does your circuit even have a transformer? Please show the schematic, and on that schematic please show where the scope probe is placed. \$\endgroup\$Fabio Barone– Fabio Barone2023-11-05 13:26:09 +00:00Commented Nov 5, 2023 at 13:26
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I am trying to apply phase shift control to my H bridge inverter but I get these spikes in the picture I don't know why.
You appear to have too much dead-time when you should have either the top two MOSFETs activated or, the bottom two MOSFETs activated. The dead-time will result in an energy spike being carried by the internal bulk diodes within each MOSFET to the power rails and, that is partially defeating the object of phase-shifted PWM.
It's only a problem in resonant converters because you want to keep resonant current circulating when you are not actively driving current. So, if you have too much dead-time, you will pass too-much resonant circuit energy back to the supply rails and, this somewhat defeats the objective; you have to put that energy back in again during the next active part of the cycle. This creates extra MOSFET losses and, of course, you want to avoid that.
So, you need to improve your control method.
it getting worse if I apply inductive load
Yes, this will certainly happen. What you probably need to consider is this: -
The circuit part of the image was taken from here. You need to make the dead-time areas as short as is necessary to avoid shoot-through. But, inevitably, there will be a little glitch especially when you have inductive/resonant loads.
But, this looks too much: -
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\$\begingroup\$ Thank you so much for your reply, I will reduce the deadtime and see \$\endgroup\$Deia Deen– Deia Deen2023-11-05 01:35:06 +00:00Commented Nov 5, 2023 at 1:35
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\$\begingroup\$ I just tried to reduce the deadtime and nothing happened even when I increase the deadtime no change. But I have noticed something. When I increase the deadtime too much the phase shift cancelled and the output is a square wave again. By the way I am using resistive load. Because at inductive load the waveform is terrible \$\endgroup\$Deia Deen– Deia Deen2023-11-05 02:00:58 +00:00Commented Nov 5, 2023 at 2:00
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\$\begingroup\$ @DeiaDeen is that it? You've hit a small bump in the road and stopped? I can't read your mind and get a mental image of your controller's schematic and neither can I tell what you have done to modify the timing. I can only tell you what the problem looks like to me on the very limited information you have provided so, if we are done here, please take note of this: What should I do when someone answers my question. If you are still confused about something then leave a comment to request further clarification. \$\endgroup\$Andy aka– Andy aka2023-11-05 09:37:33 +00:00Commented Nov 5, 2023 at 9:37
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\$\begingroup\$ Sorry, I don't have the privilege to vote up and I didn't know about acceptance. For the dead time I am using DSP launchpad 28379D. I am using embedded coder inside simulink to transform my block diagram in to code. I used EPWM block and it has the ability to add deadtime between signals. Also there is phase shift property I can phase shifting one leg with respect to the other. Sorry again for little details I didn't want to waste your time. \$\endgroup\$Deia Deen– Deia Deen2023-11-05 10:55:45 +00:00Commented Nov 5, 2023 at 10:55
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1\$\begingroup\$ @DeiaDeen it's the little details that are important in engineering. Just as important as the big details. In fact, all the detail is important! However, and unfortunately, I can't advise on your method of control because I design hardware mainly and I have no idea how an embedded coder will work. If you cannot see stuff changing on the oscilloscope screen when you tweak the parameters then, it sounds like the implementation isn't working. \$\endgroup\$Andy aka– Andy aka2023-11-05 11:05:28 +00:00Commented Nov 5, 2023 at 11:05