A: Here is a list of some common issues that may lead to non-convergence
•You are asking the plant to output real power when there are no loads in the network. See Appendix K on how you can remedy this problem.
•Transformer and/or line that carries the power from the wind/solar plant to the network are not rated high enough. Sometimes an under-rated transformer will cause the solar and/or wind plants to shut down due to unusually high voltage at the device terminal.
•Frequently – but not always – modeling the unit transformer is beneficial for numerical convergence. Each converter-interfaced resource (CIR) or type-3 wind plant – that represents either a single physical device or an aggregate – should ideally be connected to the network through the wye winding of either a wye-delta or wye-wye-delta transformer. Modeling the neutral impedances for the wye winding(s) is not a problem.
•You can almost always omit the unit transformer for STATCOMs modeled as voltage-controlled current sources without any problems.
•Multiple units are connected through branches with very low impedance. Aggregating the units may solve this problem.
You can investigate these issues by examining the model data and some preliminary simulation results. The OneLiner Check | Network Anomalies command provides many tools that can be used to identify potential issues in the network model. A few items that tend to have more influence on the prefault voltage profile are:
● Transformers with incorrect phase shift (use the Check | Network Anomalies | Transformers with wrong phasing tool to find these)
● Generators with incorrect phase shift (use the Check | Network Anomalies | Generators with wrong reference angle tool to find these)
● Transformers with tap settings that are too high or too low for the modeled network condition (use the Check | Network Anomalies | Transformers with tap higher/lower than tools to find these)
● Network models with unreasonable load/generation balance - partial inclusion of loads and/or MW dispatch from Type-3,4 models can result in unreasonable current flows that affect the network voltages (you can set Type-3,4 MW dispatch to zero and select the fault option to ignore loads to test whether this is impacting convergence for a particular fault solution).
ASPEN is developing some OlxAPI Python scripts to assist in identifying items that can lead to prefault solution issues. When they become available, this toolset can be found at the ASPEN public GitHub repository (https://github.com/aspeninc) or in the OneLiner installation directory (default location below). Expected release of these tools is Q3 of 2024.
C:\Program Files (x86)\ASPEN\1LPFv15\OlxAPI\Python\PrefaultCheck