Batteries are among the promising electrical energy storage technologies for industrial and commercial applications. These energy storages have been used for making intermittent renewable resources dispatchable and controllable. They also used in various applications such as uninterruptable power supply and power peak shaving. The power peak shaving process shifts a power demand from peak time to a low demand time via using the stored energy in batteries. In this process, the batteries store energy during off-peak times when the power demand and generation cost is low. The peak shaving process increases the transmission line capacity at peak-time which in turn increases flexibilities in management of transmission line capacities. Thus, peak shaving can potentially defer the reinforcement of a line and/or postpone the establishment of a new line in the power system. It also postpones the immediate needs for development of new power plants to meet ever-increasing demand in a power system. Economically, the main challenge in proliferations of battery energy storage systems is the high investment cost which necessitates advance charge/discharge control methods to increase the lifetime of the batteries. Battery balancing which equalizes the state-of-charge of the batteries is among the key control methods to increase the lifetime of the batteries. Battery balancing needs dc/ac power converters with multi-terminal at dc-side. Thus, the main technological challenge in the implementation of high power converter for energy storage system is introducing suitable topologies for megawatts power exchanges at high voltage level with multiple dc terminals. This thesis investigates the battery energy storage systems for power peak shaving applications and presents a multi-terminal power converter topology based on a half-bridge switch configuration. In the first part of the thesis various energy storage systems and their applications in transmission and distribution systems are investigated. Then, by focusing on the peak shaving application and its requirements (such as energy density, life time/cycles, and charging/discharging capacities) the suitable storages including lead-acid and sodium sulfide batteries are introduced and investigated in more details. The second part of the thesis briefly investigates various power converter topologies for high-power and medium voltage applications. Then, a multi-terminal topology is proposed based on half-bridge switch cells as a suitable converter topology for energy storage applications. Compare with conventional cascade full-bridge topologies, the proposed half-bridge topology provides twice dc-terminals with the same number of switches which are used in full-bridge topologies. Thus, the suggested half-bridge topology can potentially enhance the lifetime of the energy storage system via battery balancing among more battery modules. The performance of the proposed topology and the validity of its control method have been verified via the time domain simulation of a three-phase study system with four cells in each phase. Furthermore, a grid-connected single-phase prototype with four 12-V/6-Ah leads-acid batteries are implemented to practically test the suggested power flow and battery balancing control systems. Keywords: Battery Energy Storage System, Multi-level converter, Power Peak shaving, Real/Reactive Power Control, State-Of-Charge (SOC)-Balancing, Voltage Balancing