goodwe-addon/goodwe_controller/DECISIONS/SAFETY-136-slow-meter-settle.md

SAFETY-136 - a slow meter gets a gentler loop until the last move shows

Status: for review. Code: app/settle.py, a call in Controller.cycle() (app/ctl_cycle.py). Tests: test_safety136.py. No option, no text change.

Problem. On a 5 s meter, Home Assistant readings 10-15 s late are not found (SAFETY-129): they look like a slow battery (R2-1), and a hold does not help (a perfect one cut the export of the oven by 7 %, SAFETY-129 review). With moving loads the loop answers the same stale error at each cycle and overshoots: an oven, a kettle and hob, the owner's day or a step export 3-10 times what they do with no lag. The fix is a calmer loop, not a detector.

Decision. After a move of 150 W or more, a loop on a slow meter runs at half its gain until the meter has fallen by half of that move, or for 2 cycles. Slow is judged from the readings that arrive: the usual gap between them, over the last 60 s and at least 5 readings, is over 3.75 s (the limit of SAFETY-128's fast meter fit). It counts arrivals, not changes of value: on the recorded day at 1-2 s the value-based test (MeterFit.slow()) called 24 % of the cycles slow, because the recorded house repeats a value for 5 s or more, and the commands then differed from base. So there is no option. At a meter with a usual gap of 3.75 s or less (1-3 s) it is false, the tuning is never touched and the commands are those of the tree before. A meter that Home Assistant passes on only when its value changes looks as slow as its changes are far apart, as it does to SAFETY-128's fits: a 1-2 s meter with a value that holds for 5 s or more is then treated as slow, and the loop is gentler for it (the cost below). With no lag the meter shows a move at the next reading, so the wait ends at once.

Candidates (SAFETY-129 sim, real cycle(), 5 s meter, sum over oven, kettle and hob, owner shape over the oven and over the heat pump, step down, step up, flat; export Wh, lag 0 / 10 s / 15 s; base 64 / 340 / 363):

Candidate, only at a slow meter	0 s	10 s	15 s	Import Wh, 0 / 10 / 15 s
gain 0.4	97	201	299	97 / 224 / 301
gain 0.3	128	185	322	132 / 232 / 293
step limit 500 W	118	285	293	110 / 325 / 324
cut fast, raise slowly (0.6 / 0.3)	55	140	226	140 / 332 / 345
ignore 1 cycle after a move	93	216	325	90 / 240 / 291
ignore 2 cycles after a move, unless the meter showed half	69	206	277	62 / 240 / 354
half gain for 2 cycles after a move, unless the meter showed half	67	189	296	62 / 223 / 288

A lower gain for good, a step limit and a fixed ignore all make a 5 s meter with no lag worse (export +30-110 Wh, quarter peak up to 150 W): that is the common case. Cutting fast and raising slowly moves export to import and peak. Waiting only while the last move has not shown costs nothing with no lag. Ignoring the meter (the 2-cycle line) was worse than half gain where the plant is slow, not the readings late: a 12 s dead time with one inverter went from 250 to 841 Wh import and a quarter peak of 206 to 1 509 W, so the loop keeps following at half gain.

What it gives (5 s meter; the pull request and the report have each scenario). Export summed over the seven houses: 10 s late 340 -> 189 Wh (-44 %, import 363 -> 223), 15 s late 363 -> 296 Wh (-19 %, import 281 -> 288), together -31 %. At 15 s the oven and the owner's oven are not better (92 / 39 Wh against 91 / 37), the kettle and the steps are. No lag: export 64.4 -> 66.5 Wh (kettle +2), import and peak the same.

What it costs. The loop follows a real step more slowly: half gain for up to two cycles after each move of 150 W or more. Of the 136 sim runs (every SAFETY-129 review scenario and its 15 harm runs), 56 at 4-10 s meters differ from base. Together their export is 10 363 -> 9 559 Wh (-8 %) and import 8 389 -> 7 835 Wh (-7 %). Only 5 export more than 1 Wh and 14 import more: export by at most 11.5 Wh (a 10 s battery lag, +10 %), import by at most 17 Wh (a 12 s dead time, one inverter, +7 %), and the quarter average by at most 35 W, except two import quarters: +73 W (10 s meter, 10 s dead time, export -59 Wh) and +40 W (dead10_p6, -6 to 34 W, export -68 Wh). Slow batteries with a dead time of 8-10 s export 5-39 % less; a 12 s dead time is the same. READINGS_LATE holds are the same seconds in every run.

Live, a 1-2 s meter can be judged slow. Through Home Assistant on change, a value that holds for 4-10 s makes a 1 s meter slow. In 20 rig scenarios the commands were those of base. On the recorded day (1 s, N=1, 1 day, repeats dropped; its values hold about 5 s) it was slow in 33 % of cycles, half gain in 83 cycles, 15 422 commands in both trees, 4 016 with another value (at most 190 W apart), cost 0.61 EUR in both (review of SAFETY-136).

Does not change. Meters of 1-2 s: the same commands in all 63 runs (34 at 1 s, 29 at 2 s), and the recorded-day digests (see the report). The late verdict, the hold and the freeze tests. 15 s late is only partly helped, and 30 s late is the hold's (SAFETY-129).