Abstract
This thesis presents a multifunctional battery energy storage system (BESS) with multiple auxiliary charging sources and its operation control. The DC-link voltage (400V) in the developed BESS is established from the 96V battery bank via an interleaving bi-directional DC/DC converter with two cells. Only single DC-link current sensing is required for making the current-mode controls of the parallel converters. Then a bilateral three-phase inverter is developed to generate 60Hz/220V AC output voltages. Through proper controls, the developed inverter possesses flexible power conditioning control capability. The developed BESS is arranged to possess the following functions: (1) Autonomous mode: the local loads are powered by the BESS with good waveform quality. (2) Grid-connected mode: The BESS is connected to the utility grid via synchronization process for conducting the following three operation modes: (i) Floating mode: The utility grid only supplies real power to the local load, and all load reactive as well as harmonic powers are compensated by the BESS; (ii) Discharging mode (or battery-to-grid (B2G) mode): The BESS supplies power to the local load and sends the preset power back to the utility grid; and (iii) Charging mode (or grid-to-battery (G2B) mode): The utility grid supplies power to the local load and also charges the battery. The BESS can compensate all load reactive and harmonic powers in grid connected operation. The battery bank of the developed BESS can be charged by an auxiliary charger system with multiple auxiliary charging sources through a common resonant isolated DC/DC converter. The three-phase AC sources are connected to the BESS via three-phase switch-mode rectifiers, such as three-phase single-switch (3P1SW) SMR and Vienna three-phase three-switch SMR. And the possible sources may include backup AC distribution network, wind generator, micro-turbine generator and flywheel generator, etc. As to the DC auxiliary charging sources, such as photovoltaic (PV) cell and solid-state fuel cell (SoFC), they are interfaced to the BESS by the developed interleaving buck-boost DC/DC converter. Moreover, the micro-grid and electric vehicle can be incorporated into the developed BESS to conduct their inter-connected operations.