Issue in pandapower backend when the generator representing the slack bus is moved

[BDonnot]

When the generator representing the slack bus in pandapower backend is changed of location (with change_bus) it sometimes lead to issue with negative generation and in most cases the kirchoff's law, as "seen" by grid2op is not verified and the total generation is not enough to sustain the total demand.

The script to reproduce the bug is:

with warnings.catch_warnings():
    warnings.filterwarnings("ignore")
    env = grid2op.make("rte_case14_realistic", test=True)
action = env.action_space({"set_bus": {"generators_id": [(-1, 2)], "lines_or_id": [(0, 2)]}})
obs, reward, done, info = env.step(action)
assert not done
assert np.all(obs.prod_p >= 0.)
assert np.sum(obs.prod_p) >= np.sum(obs.load_p)
p_subs, q_subs, p_bus, q_bus = env.backend.check_kirchoff()
assert np.all(np.abs(p_subs) <= self.tol_one)
assert np.all(np.abs(p_bus) <= self.tol_one)

Correct behavior: this script run without issue.

Current behavior:

assert np.all(np.abs(p_subs) <= self.tol_one)
AssertionError

This problem does not arise with lightsim2grid backend (https://github.com/BDonnot/lightsim2grid). It is likely due to a "ghost" generator being still modeled in pandapower where the slack bus used to be.

[BDonnot]

Fixed in version 0.9.0.