Architecture and Working Principle of Battery Energy Storage System (BESS)

With the development of renewable energy and the rapid advancement of the global energy transition, Battery Energy Storage System (BESS) is playing an increasingly important role in modern energy systems. Adopting advanced lithium-ion battery technology, BESS stores electric energy in batteries and distributes it on demand when needed, thereby helping maintain the stable operation of the power grid. Meanwhile, it can be integrated with renewable energy power generation devices to achieve more efficient energy management. This article will provide a detailed introduction to the basic architecture of the Battery Energy Storage System and the working principles of its key components.

The structure and energy flow of the BESS system are shown in the figure below. PCS is a bidirectional DC/AC converter,

BESS consists of the following key components:

1. Battery Pack

A battery pack is formed by multiple cells connected in series and parallel (with a cell voltage range of 2.5V to 3.65 V), which is responsible for storing and releasing electric energy. To increase the battery voltage, battery packs are connected in series to form battery racks or battery clusters (with a voltage of up to 1500VDC). To boost energy capacity, battery racks/clusters are connected in parallel to form battery containers (usually 20 feet in size, with a capacity of approximately 5 MWh).

Cell types include lithium-ion batteries, lead-acid batteries and other types, and batteries with different performances are generally selected according to specific application scenarios.through which energy flows from photovoltaic panels to batteries, loads and the power grid.

2.Battery Management System (BMS)

The BMS (Battery Management System) is a core system designed to monitor and manage batteries with a host of vital functions. By real-time monitoring of battery parameters including voltage, current and temperature, the BMS keeps the battery operating within safe limits and effectively avoids risks such as overcharging, over-discharging, short circuits and overheating. Furthermore, it leverages intelligent charge-discharge strategies and balancing management technologies to optimize battery performance and extend service life. It also adopts passive or active balancing technologies to eliminate the "cask effect" caused by inconsistent power levels among individual battery cells. Meanwhile, the BMS is capable of estimating the State of Charge (SOC) and State of Health (SOH) of the battery, delivering precise support for the safe operation and performance optimization of batteries. The block diagram of the BMS system shown below intuitively illustrates its overall functions and components. For more details, please refer to the stackable BMS solutions on the Infineon official website.

3.Power Conversion System (PCS)

PCS serves as an intermediate device between energy storage components (such as large DC battery packs) and the AC power grid, undertaking bidirectional electric energy conversion with its operating principle covering charging and discharging modes.

In charging mode, the PCS converts alternating current from the power grid into direct current and stores the electric energy in batteries. Alternatively, it employs a DC/DC converter to adjust direct current to the voltage and current suitable for battery charging, so as to realize efficient battery charging.

In discharging mode, the PCS transforms direct current from batteries into alternating current to supply power to electrical loads or feed electricity into the power grid. In another scenario, a DC/DC converter first modulates the direct current from batteries to the voltage and current matching the operating requirements of the inverter, after which the DC/AC inverter converts the conditioned direct current into alternating current. Based on application demands, PCS is categorized into residential, industrial and commercial, and large-scale energy storage station types. Widely deployed in households, enterprises and large-scale energy storage systems, it has become an indispensable core component of modern energy systems. The figure below illustrates the block diagram of the PCS system, which explicitly displays its core components and working mechanism. For more details, please refer to the introduction of Power Conversion System (PCS) on Infineon's official website.

4.Energy Management System (EMS)

The Energy Management System (EMS) is an intelligent system designed to monitor, control and optimize the energy flow and consumption of energy systems. EMS collects real-time data including battery charging and discharging status, temperature, voltage and current through sensors. It adopts data analysis technology to monitor system operation, identify potential problems and improve energy utilization efficiency. In addition, EMS can intelligently dispatch energy storage facilities according to energy demand, electricity prices, grid load and other conditions to achieve efficient energy consumption. It also features fault detection and safety protection functions, which can timely warn of abnormalities such as battery overcharging and overdischarging, and support remote control and linkage protection to ensure the safe operation of the system. According to specific application requirements, the EMS monitoring platform can adopt C/S (Client/Server) or B/S (Browser/Server) architecture. The figure below shows the topology diagram of the EMS system of an energy storage power station and the monitoring platform of the energy storage EMS, presenting the overall system architecture as well as the detailed modes of energy flow and management.

5.Auxiliary System

The auxiliary system of the energy storage system is the key to ensuring the safe and stable operation of the system, which includes the following components: The temperature control system efficiently manages battery temperature through air cooling or liquid cooling to prevent overheating or undercooling from affecting battery performance and service life. The fire protection system is equipped with fire detection and automatic fire-extinguishing devices (such as heptafluoropropane, gas and dry powder fire extinguishers) to quickly respond to potential fire hazards and guarantee operational safety. The power distribution cabinet undertakes power distribution and circuit protection functions to avoid equipment damage caused by faults. The combiner cabinet collects electric energy from battery modules and transmits it to power conversion equipment, while providing real-time monitoring and safety protection. These auxiliary subsystems work in coordination to ensure the efficient, safe and stable operation of the energy storage system under various conditions.

The Battery Energy Storage System (BESS) realizes efficient energy storage, intelligent scheduling and safe energy management through the coordinated operation of battery packs, BMS, PCS, EMS and auxiliary systems. While supporting the stable operation of the power grid, BESS is deeply integrated with renewable energy, providing solid support for improving energy utilization efficiency and promoting global energy transition, and will continue to play a vital role in the energy system in the future.