Electrochemical energy storage systems mainly consist of battery packs, battery management systems (BMS), energy management systems (EMS), energy storage inverters (PCS), and other electrical equipment.
BMS is one of the core components, mainly used for intelligent management and maintenance of each battery cell, real-time monitoring of battery SOC, SOH and other operating statuses, preventing safety risks to the battery itself or the system, and helping to ensure the safe and efficient use of energy storage batteries.
There are many types of BMS, and energy storage BMS was not very prominent among the many branches of BMS in recent years. However, with the rapid development of the energy storage industry, its market position has been greatly enhanced.
The energy storage BMS industry is a knowledge- and technology-intensive industry, involving multiple technical fields such as battery management technology, automatic control technology, power electronics technology and communication technology. It requires a lot of professional knowledge and experience accumulation and has high technical barriers. Among them, software algorithms and the combination of software and hardware are the core competitive elements.
This is why mature energy storage BMS products have an exceptionally complex structure.
Taking the intelligent BMS equipped in Huawei's string energy storage system as an example, the BMS system has a clear hierarchy and adopts a four-level structure, from bottom to top: module-level BMU, battery cluster-level BCU, system-level CMU, and subarray-level SACU. The four-level structure is progressive and realizes the monitoring, protection and intelligent management of the battery system.
Due to their design and structure, battery energy storage systems are characterized by a large number of batteries, system complexity, harsh operating environment, and high requirements for the anti-interference performance of the BMS.
Structurally, the energy storage system is composed of multiple battery clusters, each of which is integrated with multiple battery packs, and each battery pack is integrated with multiple cells through series and parallel connections.
Based on the structure of the energy storage system, the energy storage BMS forms a functional system with different specialized functions and clear hierarchical control for the four-level structure of the cell, battery pack, battery cluster, and the entire battery system.
The lowest layer is the most sophisticated BMU (Battery Pack Monitoring Unit). The BMU is the bottom-level worker of the BMS company, responsible for real-time monitoring and collection of battery operating information, such as temperature, voltage, current, SOC, SOH, etc. When abnormal information is detected, the battery pack optimizer controls the battery pack to switch off, so as to achieve safe operation of the energy storage system.
The third layer is the BCU (Battery Cluster Management Unit). The BCU is a mid-level manager in the BMS company, both doing its own work and overseeing its responsibilities. It manages the individual battery clusters integrated within the battery pack, directs the BMU to collect information from all battery packs within the cluster, and collects the voltage and current of the battery clusters itself to provide alarms and protection against abnormalities in the battery clusters during charging and discharging.
Because the BCU is the superior of the BMU, it can also directly command the BMU, issue control commands, perform balanced SOC control of battery packs within the battery cluster, independently switch out battery packs, achieve precise control, and optimize each pack individually.
The second layer is the CMU (Center for Energy Storage Management). The CMU is the senior executive of the BMS company, and its main responsibility is overall management. It oversees the BMU and BCU, manages the energy storage system composed of multiple battery clusters, analyzes and calculates data uploaded by the BMU and BCU, handles alarms and records and stores the data, and is also responsible for the equalization management between battery clusters, as well as SOC and SOH (State of Health) management.
Meanwhile, CMU is also responsible for collecting information from the environmental monitoring system of the energy storage system, such as the fire protection system, temperature control system, temperature and humidity sensors, and water immersion sensors. Then, it formulates reasonable temperature control strategies to improve battery temperature consistency, realize comprehensive fire early warning, protection and linkage of the energy storage system, provide highly reliable fire safety guarantee, and achieve effective prevention, early detection, effective isolation and protection of safety issues.
At the top level is the SACU (Smart Subarray Controller). The SACU acts as the chairman of the BMS company, responsible for coordinating the three-level protection across the entire BMS company, partially managing the PCS company, and fully considering the timing of protection unit actions, action delays, and the possibility of partial fault protection failures within the energy storage system. It designs the hierarchical action and linkage mechanism of protection. In addition, the SACU communicates directly with the EMS, receiving grid dispatch instructions and transmitting them to the PCS and CMU to meet grid dispatch requirements.
In the future, energy storage BMS may develop in the following directions.
First, weaken or even eliminate the BMS balancing function in energy storage systems. In centralized multi-parallel energy storage systems, the active balancing technology of the BMS can only balance a small amount of current, resulting in low effective utilization; the passive balancing capability is too weak and energy-intensive, which is detrimental to cost reduction and failure point reduction.
Second, the BMS active balancing circuit is changed to a DC boost circuit at the battery cluster level. In terms of measures, a DC-DC converter needs to be added, which will increase the cost, but the effective utilization rate and safety of the energy storage system will be improved.
Third, the energy storage BMS architecture is reformed by adopting string or modular energy storage technology, connecting a single battery cluster with a string or single module energy storage converter. Under this scheme, the BMS only needs a two-layer architecture, with one cluster managed at a time, which saves costs and improves work efficiency.
