# Why single phase AC output current is sinusoidal with a DC shift?

**URL:** <https://forum.plexim.com/t/why-single-phase-ac-output-current-is-sinusoidal-with-a-dc-shift/632>\
**Category:** PLECS\
**Tags:** phase, inductor, ac, single, sinusoidal\
**Created:** [March 4, 2019, 7:43pm UTC](https://forum.plexim.com/t/why-single-phase-ac-output-current-is-sinusoidal-with-a-dc-shift/632 "2019-03-04T19:43:08Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![snehathakur](https://avatars.discourse-cdn.com/v4/letter/s/cab0a1/32.png) [@snehathakur](https://forum.plexim.com/u/snehathakur)\
**Post date:** [March 4, 2019, 7:43pm UTC](https://forum.plexim.com/t/why-single-phase-ac-output-current-is-sinusoidal-with-a-dc-shift/632/1 "2019-03-04T19:43:08Z")

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Hi All

I am facing an issue with current source based converter circuit, Figure attached. The output load is single phase AC (240 V, 4 KW).

I am not getting a sinusoidal output current as expected, i.e. a sine wave varying with reference as zero, instead I am getting it with a DC offset.

My pulse control and other seems to be working fine, as when i replace the output with A DC source, I get the desired outputs. It’s with AC that the output current is not sinusoidal.

Am I missing grounding the circuit properly or anything like that? Any help would be appreciated.

Thanks  
Sneha Thakur

 ![schematic.png](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/1X/1e8d086692a7dfda354fdce89f701e98f0bbb33b.png)

 ![Capture.JPG](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/1X/1c4e7513734abd35853b826aae24dd8ebc8e12f5.jpeg)

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**Author:** ![tinivella](https://avatars.discourse-cdn.com/v4/letter/t/b77776/32.png) [@tinivella](https://forum.plexim.com/u/tinivella)\
**Post date:** [March 5, 2019, 9:18am UTC](https://forum.plexim.com/t/why-single-phase-ac-output-current-is-sinusoidal-with-a-dc-shift/632/2 "2019-03-05T09:18:47Z")

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how do you set the AC load?

do you have an integrator to keep avg(Vout)=0, really small DC error can create easy tens of amps on the output

where Iop comes from? L3?

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**Author:** ![snehathakur](https://avatars.discourse-cdn.com/v4/letter/s/cab0a1/32.png) [@snehathakur](https://forum.plexim.com/u/snehathakur)\
**Post date:** [March 5, 2019, 10:51am UTC](https://forum.plexim.com/t/why-single-phase-ac-output-current-is-sinusoidal-with-a-dc-shift/632/3 "2019-03-05T10:51:48Z")

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Hi Tinivella

I am just using a AC voltage source as the load. i do not have any integrator or so at the output.

Yes, the waveform shown in the figure is the current from inductor.

Can you Please elaborate a liitle more “integrator to keep avg(Vout)=0” about this?

Thanks

Sneha

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**Author:** ![tinivella](https://avatars.discourse-cdn.com/v4/letter/t/b77776/32.png) [@tinivella](https://forum.plexim.com/u/tinivella)\
**Post date:** [March 5, 2019, 11:49am UTC](https://forum.plexim.com/t/why-single-phase-ac-output-current-is-sinusoidal-with-a-dc-shift/632/4 "2019-03-05T11:49:04Z")

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I don’t know which control are you using, generally when you feed the AC grid you have to implement just a current control and the grid set the voltage.

Instead if you are trying to work as a voltage generator like the UPS do, the control must be more complex and you need to take care carefully to the DC voltage offset you generate with your inverter, just few hundred mV can produce the DC current you are showing, general concepts are here [https://books.google.ch/books?id=JCB0CQAAQBAJ&dq=mattavelli+ups+control&source=gbs\_navlinks\_s](https://books.google.ch/books?id=JCB0CQAAQBAJ&dq=mattavelli+ups+control&source=gbs_navlinks_s)

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<div class="post-metadata">

**Author:** ![snehathakur](https://avatars.discourse-cdn.com/v4/letter/s/cab0a1/32.png) [@snehathakur](https://forum.plexim.com/u/snehathakur)\
**Post date:** [March 5, 2019, 12:12pm UTC](https://forum.plexim.com/t/why-single-phase-ac-output-current-is-sinusoidal-with-a-dc-shift/632/5 "2019-03-05T12:12:38Z")

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Hi Tinivella

I am using charge control. And I have tried everything but still not able to sort out this issue.

Thanks

Sneha

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**Author:** ![tinivella](https://avatars.discourse-cdn.com/v4/letter/t/b77776/32.png) [@tinivella](https://forum.plexim.com/u/tinivella)\
**Post date:** [March 12, 2019, 3:06am UTC](https://forum.plexim.com/t/why-single-phase-ac-output-current-is-sinusoidal-with-a-dc-shift/632/6 "2019-03-12T03:06:25Z")

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I have never used this controller can you send me some ref?

if you enable only one controller voltage or current per time what does it happen?

if you enable just a PI voltage control how does it work? then the offset should be zero