Control and Operation of the Battery-enabled Direct-current Fast Charging Station for Electric Vehicles

This dissertation presents, develops, and evaluates a system architecture and its control structure that mitigates impact of the Electric Vehicles’ (EVs) Direct-Current Fast-Charging (DCFC) station on its host weak Alternating Current (AC) grid. The DCFC station includes multiple DCFC units, a Battery Energy Storage System (BESS), a solar-Photovoltaic (PV) system, and a grid-interface Voltage-Sourced Converter (VSC). The proposed control system, i.e., combination of Local Controllers (LCs) and Supervisory Controller (SC) contains the station dynamics within the station and thus prevents dynamic impact of the DCFC units and other internal sources, such as solar-PV generation, on the host grid. Unlike a conventional station, this enables interfacing the proposed DCFC station to the legacy AC distribution grid, irrespective of the grid weakness and technical limits. A discrete-event control-based Supervisory Controller (SC) for the DCFC station is synthesized, evaluated, and verified to (i) limit the station’s power based on grid-imposed requirements, (ii) coordinate operation of controllable units within the station, (iii) operate the station in either grid-connected mode or islanded mode, and (iv) dynamically adjust power flows inside the station between grid, PV unit, DCFC units, and BESS to satisfy the EVs charging requirements and when applicable charge BESS or export PV power to the grid. Time-domain simulation results, in PLECS software platform, are presented to assess the dynamic performance of the proposed SC subject to various discrete events/transitions. The results demonstrate robustness of the proposed control system to large-signal disturbances and discrete events/transitions. The proposed control system performance, i.e., LCs and SC, is experimentally validated using a two-layer real-time control Hardware-in-the-Loop (HIL) setup. The power circuit of the DCFC station is simulated in real-time in OPAL-RT platform. The LCs and the SC of the DCFC station are implemented in industrial CompactRIO (cRIO) controller and a Programmable Logic Controller (PLC) PLCnext-controller, respectively. The control system performance is tested in case of islanded and grid-connected modes of operation of the station, subject to various disturbances and SC transitions, to verify the functionality of the implemented controls and readiness for final deployment and field tests.Ph.D.2021-06-22 00:00:0