Dynamic Stability of Constant Power Loads In Electrified Propulsion Systems

Power electronic converters are essential to the electrification of transportation including marine propulsion. In the literature, it is widely agreed that converter-based distribution systems are prone to instability due to the high-bandwidth control systems and weak onboard grids. One main dynamic issue in onboard DC distribution systems is the increasing share of electric motor drives and the corresponding constant power load behaviors with negative incremental resistance. In this work, the source converter is modeled using an average-value model with feedback control loops for two different types of configurations: back-to-back and a decentralized propulsion drive. The two systems are linearized and the eigenvalues are obtained for variations in power flow and DC voltage controller gain. Based on the analysis, the two configurations show very different characteristics when the source converter model is included. The results indicate that both power system configurations are heavily affected by the DC voltage control proportional gain rather than the CPL. The results could contribute to stability preserving design and tuning of hybrid power systems for future vessels.