Hi MARS
Thanks for sharing your schematic! But I still do not see how you have connected the voltage and current inputs to the ADE7754IC.
Please look at the below picture for a typical 4-wire wye connection.
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The attenuation network and VN pin connection is illustrated here:
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Please make sure that you have the grounds set up like this. The neutral must be grounded as shown. If the connections are made in such a way, adjusting the load shouldn't have any impact on the voltage channel or the supply voltage.
Regarding query1, there will be some inherent DC offset in the voltage channel and there is no HPF in the signal path. VRMS is actually a mean absolute value measurement and is accurate (within 0.5% error typically) upto FS/20. Are you able to meet this spec? With regards to the offset, if you can characterize it over mutiple parts and over temperature, you can come up with a way to compensate for it. Are you planning to do something like this? It is to be noted that the current channel has the HPF in its signal path; so, the power/energy computations will not be affected by the DC present on the voltage channel.
Regarding Query2, please check your schematic based on my figures (above). It is fine to have the HPFs and LPFs turned on (which is the default anyways). As per my earlier request, try to monitor the current, voltage and supply as you change the load. This will help you figure out if the load change is affecting any of the other signals. If you scope the SPI lines when the LCD "freezes", do you see any communication going on? This would help you figure out if it is only the LCD that is getting affected.
Regards
hmani
