Dynamic Power Limiter Limitations
This Script takes full advantage of the Dynamic Power Limiter (DPL) capability of the OpenDTU-OnBAttery project: https://github.com/helgeerbe/OpenDTU-OnBattery
What it does is actually split the total house consumption into separate parts and deliver them to separate OpenDTU-OnBattery units, each of them using each DPL to control one inverter.
So, at the end, it all comes to the Dynamic Power Limiter (DPL).
Since you will probably looking at the results very closely, you may experience fluctuations and "oscillations" while the systems try to achieve "zero feed throttle" (Nulleinspeisung).
And sometimes you may feel disapointed, realising that this Script and the DPL do not balance the "zero feed throttle" (Nulleinspeisung) as well as you would expect. If you are a perfectionist, you will notice the oscillations and start trying to understand whether there is an error in your setup. This Wiki article is aimed at you, in order to spare you hours of frustration... (and do not ask us how we know about it).
Although it is understandable you may consider the cause of error to be in this Script's programming (or, the DPL programming), there are some other areas you need to first examine! We have listed some cases below.
In Summary: There are Limitations! Not due to the programming of OpenDTU-OnBattery Dynamic Power Limiter (DPL) but, due to inverters' design and behaviour. In most cases, if you leave enough margin, DPL will keep the "zero feed throttle" (Nulleinspeisung) despite the oscillations and you will hardly notice this behaviour.
Community member peff74 made some interesting observations:
On close inspection of the performance of the Hoymiles HM-700, I noticed that an inverter with many Inputs connected to the battery, has a brief power dip of 50W about once a minute.
You can only see this on the electricity meter itself, as it spits out 2 values per second.
If the information one of these power dips reaches the OpenDTU-OnBattery, the DPL will proceed to the necessary adejustmnets and later back again. Result --> oscillation.
I have noticed this particularly strongly at power levels around 100-200W and when many Inputs are connected whereas as of 250W, the oscillations seems to disappear.
The problem only exists in the 15-35% relative limit range. Whereby it occurs most strongly around 25%.
You can see it clearly in the live view. The limit has not changed, however inverter power jumps almost 20W per channel from one moment to the next:
We can not confirm whether this problem as a general issue of all inverters, or something related to a specific model or specific Firmware Version.
On a HM600 for example, the fluctuation happens also in the area of 15%-35% but, at much smaller scale ~6-7W per Input.
All Hoymiles inputs should be connected to the battery
What happens if:
- "All DC+ cables" do not have the same length? or
- "All DC- cables" do not have the same length? or
- "All DC+ & DC- cables" do not have the same length?
SW-Niko and spcqike were kind enough to write some explanations:
First of all, different length of cables = different losses.
It makes sense therefore, that all DC- cables have the same length and all DC+ cables have the same length.
In Summary: Have same length DC- cables 👍
A more detailed explanation is here: https://github.com/helgeerbe/OpenDTU-OnBattery/wiki/HOYMILES
One member describes: The string inputs to the inverter were completely assymettric (I was too busy one Sunday afternoon to put things together again that I mixed a set of cables):
In Summary: With 128 Watt "imbalance" [800Watt (402,8+398,5) on one side and 672Watt (336,1+335,9) on the other], it will be impossible for DPL to achieve "zero feed throttle" (Nulleinspeisung) with precision - expect a lot of fluctuations
More exhaustive explanations and examples you will find at the Wiki of the OpenDTU-OnBattery project: https://github.com/helgeerbe/OpenDTU-OnBattery/wiki/Dynamic-Power-Limiter-Limitations