Stability of a dc Distribution System for Power System Integration of Plug-In Hybrid Electric Vehicles

This paper proposes a method for enhancing the stability of a dc distribution system that integrates plug-in hybrid electric vehicles (PHEVs) with an ac power grid. The dc distribution system is interfaced with the host ac grid via a voltage-sourced converter and can also embed photovoltaic (PV) modules. Thus, bidirectional dc-dc electronic power converters act as battery chargers and interface the PHEVs with the dc distribution system, while PV modules are interfaced with the dc distribution system via unidirectional dc-dc converters. The dc distribution system is expected to be more efficient and economical than a system of ac-dc battery chargers directly interfaced with an ac grid, but it is prone to instabilities due to the constant-power property of the dc-dc converters. Using a nonlinear control strategy, the proposed stability enhancement method mitigates the issue of instability by altering the power setpoints of the battery chargers, bidirectional dc-dc converters, without a need for changing system parameters or hardware. The paper presents mathematical models for the original and modified systems and demonstrates that the proposed technique expands the stable operating region of the dc distribution system. Simulation results demonstrate the effectiveness of the proposed method for a study system in the PSCAD/EMTDC software environment.