What is a battery energy storage system?

Battery energy storage systems (BESSs) have gained significant attention during the past decades, due to low CO 2 emission and the mature development of battery technologies and industry . In order to gain high voltage/capacity, the BESS usually uses multiple low voltage/capacity batteries in series/parallel connections .

What is a battery energy storage system (BESS)?

Battery energy storage systems (BESSs) are widely utilized in various applications, e.g. electric vehicles, microgrids, and data centres. However, the structure of multiple cell/module/pack BESSs causes a battery imbalance problem that severely affects BESS reliability, capacity utilization, and battery lifespan.

How can a battery imbalance be mitigated?

Therefore, the battery imbalance issue can be potentially mitigated via reconfigurable circuits commuting at relatively low frequencies i.e hundred Hz (depending on the size of the batteries and capacitors). Rather than introducing either passive or active equalizers.

How do battery topologies provide fault tolerance?

The last one employs both connection methods hierarchically to obtain different terminal voltages. Such capability is achieved by using power switches to modify battery connectivity . Some of these topologies provide fault tolerance by selectively switching ON/OFF and isolating faulty batteries.

Why is battery maintenance important?

The maintenance also addresses two aspects: fault tolerance and fault/dead battery replacement. Battery fault would either stop the system operation or even damage the system . Moreover, the replacement of fault/dead batteries is also a challenge due to the fixed configuration. Finally, battery imbalance issues are also critical in BESS.

Where is circuit protection located in a battery rack?

This circuit protection is usually at the battery protection unit (BPU), which is found at the top of the battery rack (see Figure 1(C)), and consists of the aggregated energy from each of the modules. The circuit protection at this level is usually rated at a higher system voltage than the voltage in each module.