PB-vines issues

Results 4 issues of


                                            PB-vines

[bug] pc.from_mpc no longer works.

### Bug report checklis - [X] Searched the [issues page](https://github.com/e2nIEE/pandapower/issues) for similar reports - [X] Read the relevant sections of the [documentation](https://pandapower.readthedocs.io/en/latest/about.html) - [X] Browse the [tutorials](https://github.com/e2nIEE/pandapower/tree/develop/tutorials) and [tests](https://github.com/e2nIEE/pandapower/tree/develop/pandapower/test) for...

bug

Convergence Issues

### Feature Checklist - [X] Searched the [issues page](https://github.com/e2nIEE/pandapower/issues) for similar reports - [X] Read the relevant sections of the [documentation](https://pandapower.readthedocs.io/en/latest/about.html) - [X] Browse the [tutorials](https://github.com/e2nIEE/pandapower/tree/develop/tutorials) and [tests](https://github.com/e2nIEE/pandapower/tree/develop/pandapower/test) for usefull...

timeseries OPF w/distributed slack

### Feature Checklist - [x] Searched the [issues page](https://github.com/e2nIEE/pandapower/issues) for similar reports - [x] Read the relevant sections of the [documentation](https://pandapower.readthedocs.io/en/latest/about.html) - [x] Browse the [tutorials](https://github.com/e2nIEE/pandapower/tree/develop/tutorials) and [tests](https://github.com/e2nIEE/pandapower/tree/develop/pandapower/test) for usefull...

Distributed Slack with ACOPF - Multiple connected slacks in one area found. This would probably lead to non-convergence of the OPF. Therefore, all but one slack (ext_grid) were changed to gens. To avoid undesired behaviour, rather convert the slacks to gens yourself and set slack=True for only one of them.