Model 702 - Should absorption ratings and setting be a negative number

[bobfox]

Currently VarMaxAbsRtg is unsigned. Absorption is in the name but it seems more intuitive for the setting to be negative. The var ratings in quadrants 2 and 3 in model 120 are signed and expected to be negative.

[FW22]

At SMA we treat all parameters related to reactive power absorption as signed and use negative values. Even if this might be confusing because of the term “max”.

[FW22]

Reactive power absorption applies to quadrants 3 and 4 (not 2 and 3 as you stated). And my understanding of IEEE1547 is, that this standard covers active power feed-in quadrants 1 and 4 only. As such, the 702-VarMaxAbsRtg is the equivalent to 120-VArMaxQ4 and 702-VarMaxInjRtg is the equivalent to 120-VArMaxQ1. There is no 702-equivalent for 120-VArMaxQ2 ans 120-VArMaxQ3. Please correct me if I missed something...

[bobfox]

You are right of course. I was thinking about active power relative to the quadrants for some reason. I meant 1 and 4 for reactive power.

We need to change the VarMaxAbsRtg and VarMaxAbs from uint16 to int16.

[bobfox]

After discussion in the SunSpec Modbus workgroup today, the consensus is to leave the VarMaxAbsRtg and VarMaxAbs unsigned. The following factors led to favoring this approach:

• Leaving it unsigned keeps the type and range consistent with the var injection rating.
• The direction of flow is contained in name.
• 1547-2018 does not seem to indicate that the rating should be expressed as a negative number.
• It is also the approach taken with the charge ratings.