Distributed Sub-Voltage Adapters for ESS Circulation Current Control
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Solution Overview
Problem
Existing energy storage systems (ESSs) face limitations in voltage balancing, leading to inefficiencies such as excessive heating and power loss due to circulation currents between energy strings, and high costs and complexity in power electronic devices for energy balancing.
Innovation Solution
The proposed energy storage system incorporates a voltage adapter with distributed sub-voltage adapter units, allowing for flexible configuration and multiple functions like voltage/energy balancing, protection, and efficient energizing at various levels. This system reduces the number of actively controlled devices and overall complexity compared to traditional ESSs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-isolated voltage adapters are used to balance voltage levels in energy storage systems, then voltage balancing capability is improved, but the system complexity and cost increase due to requiring multiple actively controlled devices
Solution Approach 1:
The voltage adapter is divided into multiple distributed sub-voltage adapter units, each handling a portion of the total voltage. This segmentation allows voltage balancing to be achieved through simpler, lower-voltage components rather than requiring a single complex high-voltage adapter, thereby reducing overall system complexity while maintaining voltage balancing capability
Solution Approach 2:
Secondary energy storage blocks are introduced as intermediary elements that facilitate voltage balancing between primary energy storage blocks. These secondary blocks act as mediators that can absorb or release energy to equalize voltage levels across different strings, enabling voltage balancing without requiring complex active control devices in every string
2Power
If traditional voltage adapter arrangements are used for energy balancing, then voltage regulation is achieved, but excessive heating and power loss occur due to circulation currents between energy strings
Solution Approach 1:
The system maintains equipotential conditions between parallel energy strings by using the secondary energy storage blocks to equalize voltage levels. When all strings are kept at the same voltage potential, circulation currents are eliminated, preventing the excessive heating and power losses that would otherwise occur
Solution Approach 2:
The control system continuously monitors voltage levels across different energy strings and adjusts the operation of sub-voltage adapter units and secondary energy storage blocks accordingly. This feedback mechanism ensures that voltage imbalances are detected and corrected promptly, preventing the development of circulation currents that would cause energy losses
3Reliability
If multiple redundant energy blocks are used to ensure system availability, then reliability is improved, but cost and device complexity increase
Solution Approach 1:
The secondary energy storage blocks serve multiple functions: they enable voltage balancing between strings, provide backup capacity to maintain system availability, and can be used for energy arbitrage or ancillary services. This multi-functionality allows the system to achieve high reliability without requiring proportional increases in redundant primary energy storage blocks, thereby reducing overall system complexity and cost
Data Source
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AI summary
An energy storage system is provided comprising at least one energy string. Each energy string comprises a voltage adapter comprising a plurality of distributed sub-voltage adapter units, each having a primary side and a secondary side. Each energy string further comprises a primary energy storage block having at least one energy storage device. The primary sides of the plurality of distributed sub-voltage adapter units and the primary energy storage block are configured to be connected in series. The energy storage system further comprises at least one secondary energy storage block having at least one energy storage device. The secondary side of at least one sub-voltage adapter unit of the plurality of sub-voltage units is configured to be connected with one of said at least one secondary energy storage block.