Bipolar DC network Constant power load Convergence evaluation DC grid DC networks Derivative-free Electric grounding Electric load flow Electric power transmission networks Iterative methods Monopolar Monopolar and bipolar constant power load Power-flow solution Triangular-based formulation bipolar DC networks convergence evaluation monopolar and bipolar constant power loads power flow solution triangular-based formulation Atomic-force-microscopy Chemical analysis Cobalt Cobalt ferrites Correlative microscopies Correlative microscopy Crystal atomic structure Defects Dichroism Domain wall pinning Domain walls