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I am analyzing the interaction between a Li-ion battery model and the bidirectional inverter Type 48b in TRNSYS 18 and I observe an apparent power mismatch between inverter outputs and battery outputs, as well as non-intuitive SOC charging and discharging behavior.
Specifically:
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The inverter output “Power to or from battery” differs from the battery output “Battery power”
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The SOC follows the battery power, not the inverter power
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The battery may stop charging before reaching the upper SOC limit, and may also limit discharge while the inverter still assumes full battery support
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No power is dumped or exchanged with the grid
I would like to confirm whether this behavior is expected due to the internal control logic, efficiencies, and power limits of Type 48b and the battery model, and whether this configuration is valid for system-level energy simulations.
👉 A detailed explanation of the observed behavior, energy balance analysis, and graphical interpretation is provided in the Annex of the document.
Thank you for any clarification.
https://drive.google.com/drive/u/0/folders/16QT9ALbTxW-tqdslKJeRAflUTmMI0r-6
In this links are the anexx documents (simulation and pdf)
Luis,
Type48 can be a bit tricky and on the many times that it was doing something confusing and I took the time to walk through the code a line at a time, it turned out to be working correctly and that I was interpreting the meaning of one of the parameters incorrectly. One thing I would suggest doing is to make sure that you are using a short timestep (1-5 minutes). Since Type48 can only make one control decision per timestep running with a long timestep can result in poor setpoint maintenance or non convergence. Next, set all of the Type48 efficiencies (charge controller, inverter, etc.) to 1. This is a temporary measure just to prove to yourself that the component is working. Also make sure to disable the grid-charging priority parameters. Those can force the battery to continue charging all the way up even if it gets to a point where it could meet the load.
If you haven't found it, there is an example of implementing the Li-ion battery (Type549) with Type48 located in .\TrnsysXX\Tess Models\Examples\Electrical Library\ResidentialPVwithLi-IonBattery_v2a.tpf"
If none of the above works then please send the project to your distributor and they can look more in detail at what is going on.
kind regards,
~david
