1MWh battery energy storage system connected to distribution network: Design, modeling, and control

Battery energy storage system (BESS) is recently becoming a strong candidate for being a system component of modern smart grids. In this thesis, a two-stage 1MWh BESS connected to a 34.5 kV distribution grid is designed and simulated. The power stage of the system consists of a three-phase wye-connected 11-level cascaded H-bridge (CHB) converter and a DC-DC converter for each submodule of CHB converter. At first, a recent literature survey is given about BESS components focusing mainly on the battery storage unit in hierarchal order from cell to pack in terms of modeling, design, and wiring diagrams. Then, CHB converter topology is compared with other power electronic interfaces in terms of storage capacity and switching elements. It is shown that CHB converter topology minimizes the number of series connected batteries. The modeling details of the power circuit of the BESS as well as its control system based on decoupled current control to exchange active and reactive power between the BESS and the grid are described. Finally, a nonlinear state feedback exact linearization controller is designed to control the bidirectional buck-boost converter in each submodule to charge/discharge the batteries. It is also shown that this controller can stabilize the dc-link capacitor voltage. Simulation tests is then performed to test the capability of the designed system to exchange active/reactive power with the distribution grid while charging and discharging the battery.