With the implementation of the national dual carbon strategy, energy storage technology has rapidly developed as an important support for energy structure transformation. With the continuous growth of market demand, the application of energy storage integration technology in segmented scenarios is also deepening. Among them, the four technology routes of centralized, string, distributed, and high-voltage cascade each demonstrate unique advantages and applicable scenarios, playing a crucial role in promoting the efficient utilization of renewable energy sources and ensuring the stable operation of the power system.
Centralized energy storage: a solid support for large-scale scheduling
Centralized energy storage typically has a large capacity and volume per device, and is assembled in a containerized manner. The system structure consists of Pack batteries connected in series to form battery clusters. Multiple battery clusters are connected in parallel on the DC side, and then converted into AC power by an energy storage converter. After being stepped up by a transformer, they are connected to the power grid. The centralized energy storage system is compact in structure, large in capacity, simple in control logic and high in efficiency. It is easy to realize centralized allocation and optimization of large-scale energy, and plays an important role in grid side energy storage and large-scale renewable energy power stations.
In large-scale applications, centralized energy storage can balance the supply and demand of the power grid, improve power quality and stability. In addition, centralized energy storage has reduced equipment and operation costs through large-scale procurement and centralized management, demonstrating significant economic benefits. However, centralized energy storage also faces some challenges. For example, the difference in internal resistance between battery clusters during long-term operation may lead to circulation problems, affecting system efficiency and safety. At the same time, the large capacity of individual units also means that once a failure occurs, it may have a wider impact and pose higher requirements for operation and maintenance.
String based energy storage: a flexible and efficient distributed solution
Unlike centralized energy storage, string based energy storage technology adopts a modular design, with each energy storage unit having independent control and management functions. This decentralized architecture endows string based energy storage with high flexibility and scalability, suitable for application scenarios such as industrial and commercial user side, zero carbon parks, new energy distribution and storage, and substation energy storage.
In practical project applications, string type energy storage can be accurately configured according to different energy generation and consumption patterns, improving the efficiency and reliability of the entire system. In addition, the string type energy storage system adopts a cluster by cluster management approach. When the system fails, it can quickly and accurately locate a single cluster, reducing the risk of system shutdown; Each battery cluster is individually controlled for charging, discharging, and thermal management to avoid the influence of circulating currents, with good temperature uniformity, long battery life, and stable system operation.
The string type energy storage system adopts a modular design, which has the advantages of convenient transportation, fast installation, and flexible expansion, greatly reducing operation and maintenance costs and difficulties. It has good adaptability to complex terrain and dispersed energy layouts, and demonstrates excellent safety and reliability. But compared to centralized systems, string systems use more optimizers and monitoring devices, making system integration and debugging more complex and overall more expensive.
Distributed energy storage: DC isolation+centralized inverter
Distributed energy storage is a way of parallel operation of multiple battery clusters. Each battery cluster is converted into a consistent voltage through a DC/DC transformer and connected in parallel on the DC side. The DC current is then converted into AC through a PCS energy storage converter. Unlike centralized systems, distributed systems use DC/DC for each battery cluster.
By increasing DC/DC isolation in distributed energy storage systems, DC arcing, circulating current, and capacity loss caused by DC parallel connection are avoided, greatly improving system safety and efficiency. The disadvantage is that the system requires two-stage inversion, which increases energy loss. In addition, due to the need for parallel and interconnected regulation of this technology route, installation and commissioning are relatively complex, which requires high requirements for power station management and operation.
High voltage cascaded energy storage: no parallel structure, no need for upgrading
The high-voltage Federal Reserve energy system consists of multiple energy storage units, each consisting of an H-bridge and an independent small battery stack. Each phase is connected in series with multiple energy storage units to a certain voltage and directly connected to the AC power grid. The advantages are that there is no need for a step-up transformer, reducing system losses, minimizing footprint, no need for parallel connection between battery clusters, and eliminating inter cluster circulating current problems.
The high-voltage cascade scheme, as a new technological route, needs to be validated through operation. A project scale of over 5MW is economically viable, and can only output voltage levels of 6kV/10kV/35kV. The electromagnetic environment is complex, and higher requirements are placed on BMS control. In addition, placing the DC and AC sides of the high-voltage cascade technology route in the same position increases the difficulty of operation and maintenance, and poses certain safety risks.
Conclusion
Currently, string type energy storage has been widely used in household storage and industrial and commercial fields, while centralized energy storage dominates in the field of large-scale storage. However, with the continuous changes in market demand, distributed systems and high-voltage cascade systems are gradually penetrating into the field of large storage. The selection of technology route requires comprehensive consideration of multiple indicators such as economy, safety, stability, and operational efficiency. It is crucial to choose a suitable energy storage system integration technology route for specific application scenarios.
