`runpm_ac_opf()` does not converge when angle shift over transformer is `< -60°` or `> 60°`

[kornerc]

Bug report checklist

• Searched the issues page for similar reports

• Read the relevant sections of the documentation

• Browse the tutorials and tests for usefull code snippets and examples of use

• Reproduced the issue after updating with pip install --upgrade pandapower (or git pull)

• Tried basic troubleshooting (if a bug/error) like restarting the interpreter and checking the pythonpath

Issue Description and Traceback

When the absolute value of an angle shift over a transformer is greater to 60 degree, the OPF does not converge when running runpm_ac_opf().

This might be caused by the hardcoded angle check of 60 degrees in the function get_branch_angles in the file to_pm when the parameter correct_pm_network_data is True.

pandapower/pandapower/converter/pandamodels/to_pm.py

Line 284 in 7b972fc

angmin = -60.

pandapower/pandapower/converter/pandamodels/to_pm.py

Line 288 in 7b972fc

angmax = 60.

Expected Behavior

OPF converges

Reproducible Example

import pandapower as pp


def create_net() -> pp.pandapowerNet:
    min_vm_pu = 0.9
    max_vm_pu = 1.1
    max_loading_percent = 80.0

    net = pp.create_empty_network()
    b1 = pp.create_bus(net, vn_kv=110., min_vm_pu=min_vm_pu, max_vm_pu=max_vm_pu)
    b2 = pp.create_bus(net, vn_kv=20., min_vm_pu=min_vm_pu, max_vm_pu=max_vm_pu)
    pp.create_transformer(net, hv_bus=b1, lv_bus=b2, std_type="25 MVA 110/20 kV", max_loading_percent=max_loading_percent)
    pp.create_ext_grid(net, bus=b1)
    load = pp.create_load(net, bus=b2, p_mw=1.0, min_p_mw=1.0, max_p_mw=1.0, min_q_mvar=0.0, max_q_mvar=0.0, controllable=True)
    pp.create_poly_cost(net, element=load, et="load", cp1_eur_per_mw=1.0)

    return net

def main():
    net = create_net()

    original_shift_degree = net.trafo.iloc[0]["shift_degree"]
    net.trafo["shift_degree"] = 60.0

    results = []

    for shift_degree in (59.0, 60.0, 61.0, original_shift_degree, -59.0, -60.0, -61.0, -original_shift_degree):

        net.trafo["shift_degree"] = shift_degree

        try:
            pp.runpm_ac_opf(net, opf_flow_lim="I")
            converged = True
        except pp.OPFNotConverged:
            converged = False

        pp.runpp(net)

        results.append((shift_degree, converged, net.res_trafo.at[0, "va_lv_degree"].item()))

        

    for shift_degree, converged, angle in results:
        print(f"shift_degree: {shift_degree} | voltage_angle: {angle:.1f} -> converged: {converged}")

if __name__ == "__main__":
    main()

Output:

shift_degree: 59.0 | voltage_angle: -59.3 -> converged: True
shift_degree: 60.0 | voltage_angle: -60.3 -> converged: False
shift_degree: 61.0 | voltage_angle: -61.3 -> converged: False
shift_degree: 150.0 | voltage_angle: -150.3 -> converged: False
shift_degree: -59.0 | voltage_angle: 58.7 -> converged: True
shift_degree: -60.0 | voltage_angle: 59.7 -> converged: True
shift_degree: -61.0 | voltage_angle: 60.7 -> converged: False
shift_degree: -150.0 | voltage_angle: 149.7 -> converged: False

Installed Versions

• Operating System name/version: Windows 11
• pandapower version: 3.5.3
• python version: 3.13.5
• pandas version: 2.3.3
• numpy version: 2.3.5

Label

• Relevant labels are selected