Introduction

With the continuous advancement of energy storage technologies, string energy storage systems have gained attention due to their unique topology and remarkable advantages. This article provides a detailed analysis of the structural features, benefits, and comparison of string energy storage systems with DC bus on-grid systems, offering readers a comprehensive understanding.

1. Topology of String Energy Storage Systems

A string energy storage system connects each battery cluster to a dedicated modular string energy storage inverter, which then connects to the grid on the AC side. In this topology, battery clusters are electrically independent on the DC circuit, sharing only centralized systems for fire protection, distribution, packaging, and cooling. Each inverter is paired with a single battery cluster, managing its charge and discharge processes individually.

Specifically, the DC output voltage of each battery cluster is converted to AC via a DC/AC module. These AC outputs are combined on a shared AC bus and eventually connected to the main grid through a step-up or step-down transformer.

2. Features of String Energy Storage Systems

2.1 Guaranteed Available Capacity

The core of the string energy storage system lies in the independent management of battery clusters. Since the charging and discharging processes of each cluster are independent and the DC-side voltages are isolated, common issues in DC bus on-grid systems, such as current imbalance and circulating currents, are avoided.

Even if a battery cluster experiences voltage drops, it does not affect the entire system's operation. The faulty cluster and its corresponding string inverter can be isolated, allowing the system to continue operating at a reduced capacity. This ensures a steady cash flow for the project and aligns with financial internal rate of return (IRR) expectations.

2.2 Extended System Lifespan

The electrical isolation between battery clusters on the DC side eliminates circulating and current imbalances commonly seen in DC bus on-grid systems. Even if significant voltage differences occur between battery clusters, they only impact the efficiency of the corresponding DC/DC rectifier module, without causing temperature increases in battery cells. This helps extend the battery lifespan.

Moreover, optimized thermal management design and advanced BMS (Battery Management System) balancing strategies improve battery consistency and health, enhancing the overall system lifespan.

2.3 Simplified Maintenance

The modular design and independent management of battery clusters in string energy storage systems make maintenance more convenient. If a non-critical fault occurs in a battery cluster, there is no need to shut down the entire system. The faulty cluster can be maintained individually.

During maintenance, procedures are limited to the specific cluster, with tasks like balancing and calibration being relatively straightforward. This saves time and cost while minimizing disruptions to system operations, and enhancing economic benefits.

3. Conclusion

String energy storage systems exhibit significant potential in the energy storage sector with their unique topology and multiple advantages. As technology advances and market demand grows, string energy storage systems are expected to see broader applications in the future.

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