GoodWe: Fix battery charging with PV when constraint is active

[iseeberg79]

Problem

When an external controller (e.g., evcc) sets a discharge constraint via setActivePowerLessOrEquals(0) to keep the battery neutral, the GoodWe handler incorrectly charged the battery with available PV power instead of allowing PV to supply household consumption first.

Root Cause

In handleRemoteMode(), when activePowerSetPoint == 0 and PV was available, the condition pvProduction >= activePowerSetPoint (e.g., 300 >= 0) triggered CHARGE_BAT mode, routing PV to battery instead of household loads.

Fix

Added explicit handling for constraint case (activePowerSetPoint == 0) to return DISCHARGE_BAT, 0 (neutral), allowing PV to serve household consumption before any battery interaction.

Test Coverage

• Fixed semantically incorrect test case
• Added CHARGE_BAT test with proper PV surplus calculation
• Added constraint test case (activePowerSetPoint == 0)
• Added real-world evcc scenario test (GitHub evcc#22827)

Reference

• evcc GitHub Discussion: FENECON Speichersperre - falsches Verhalten (?) evcc-io/evcc#22827

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #3509      +/-   ##
=============================================
+ Coverage      59.57%   59.63%   +0.06%     
  Complexity       105      105              
=============================================
  Files           3006     3006              
  Lines         130472   130474       +2     
  Branches        9639     9640       +1     
=============================================
+ Hits           77720    77789      +69     
+ Misses         49848    49770      -78     
- Partials        2904     2915      +11     

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[iseeberg79]

@sfeilmeier, I would appreciate if you could review this. I've analyzed the issues related to evcc usage, referencing both the KACO implementation (https://community.openems.io/t/setactivepowerlessorequals-verhalten/10697/7) and the GoodWe (FENECON) implementation (already referenced). Sadly I've not found a solution for the KACO device as it looks like it's not about the implementation by OpenEMS (probably related to firmware/external library?). I cannot fiddle out the reason for PV routing for those.

It's related to the prevent discharge function implemented by the opemens template in evcc.

Because I have no hardware to test, you need to take it as theoretical work and someone else needs to the testing. It's additional unit tests are based on real-world scenarios and proove to solve the issue. Users having issues are FEMS users and because of this a test is not possible easily.