Power Transfer Limit Exceeded by OPF
The Optimal Power Flow (OPF) solution involves iteration between a linear program (LP) to adjust controls (usually generation) and a non-linear power flow. If an AC OPF is performed over a very large Area (or Super Area), the LP may attempt to dispatch generators in a manner that exceeds voltage stability margins (PV) or maximum power transfer limits. This causes the non-linear power flow solution to fail and the process to abort. Techniques to address this include adding interface limits, adding dispatchable area transactions with limits, or returning to the original power flow state and manually stepping the generation in small increments towards the dispatch chosen by the LP. With the third technique, the incremental power flow states will often violate transmission limits that were not violated in the original power flow state and were thus not part of the original LP constraint set. The OPF process may be able to then restart from one of these incremental states and move in a direction that does not cause voltage stability margins to be exceeded. The attached slides explain the process and the attached spreadsheet enables the manual stepping of generation.
October 17, 2023