Common-Mode Equivalent Circuits for Analysis of Grounding Methods in Naval Power Systems

Power electronics are an enabling technology of future naval power systems. Although they enable wide-bandwidth control, they also introduce secondary issues such as common-mode (CM) currents through the ship hull. CM currents may cause interference with other systems (i.e. cathodic protection and degaussing) and negatively influence a ship's electromagnetic signature. Traditionally, highly-detailed models are constructed to quantify CM behavior, but such models are often computationally intensive and numerically stiff. This paper highlights an approach to simplify CM analysis and reduces the necessary modeling effort. Specifically, a method has been derived to transform the highly-detailed models into so-called CM equivalent circuits. The technique is applied to an example generation/propulsion system, enabling the reduction of a detailed model comprising thirty passive components, twelve switching devices, and three sources to a single source-RLC combination. The technique is validated through comparison of time-domain simulation results for the detailed and CM equivalent circuit models. Finally, it is utilized to evaluate grounding strategies being considered for future naval vessels, and it is shown that the grounding method selected has a significant impact on the location and magnitude of hull currents induced by a ship power system.