The conversion of AC to DC is done by Battery Energy Storage System (BESS). It is power electronic devices control system and batteries.
We use batteries for storing purpose, the working of the battery is the conversion of electrical energy into chemical energy. Batteries are charged and discharged by DC power. Bidirectional power electronic devices are for regulating power flow between batteries and energy systems 8. Based on what type of battery we are using it has various benefits and drawbacks like cost, weight, size, power, and energy capability.
Lithium-Ion, Lead-Acid, Nickel-Cadmium, Nickel Metal Hydride are the significant kinds of energy storage technologies. High discharge rates are achieved by Lead-Acid batteries. Long life, high energy density, charge or discharge efficiency is high are the qualities of sodium sulfur batteries. Nickel Cadmium (NiCd) batteries are one of the good in all qualities and it requires low maintenance than the lead-acid batteries 9 10.
But these kind of batteries is high in cost when compared to the lead-acid battery. Nickel Metal Hydride (NiMH) batteries are used in hybrid electric vehicles and telecommunication applications because of the compact batteries and light in weight. Lithium-Ion batteries have highest energy density. They are used in cellular phones, computers, etc.
and development of this technology is used in distributed energy storage applications. Because of its sizes availability on small, medium and large-scale renewable energy systems. During the coupled operation, changes in the outputs of wind and solar PV generation 11 12 will change the output of BESS and BESS must neutralize by rapid changes in output power. Rate variation control or ramp rate control is applied for an associated coupled system to smooth their power fluctuations.
The information is observed by the battery energy system controller. It estimates the State of Charge (SoC) and capability of each battery cell and keeps all the cells to run in the designed SoC range.