Dual-DC-Bus Battery Rack Equalization Without Capacity Loss
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Solution Overview
Problem
Battery inverter systems face challenges in balancing the state of charge between battery racks during equalization processes, which can temporarily reduce system capacity and require disconnecting racks from the DC bus, impacting power provision and operational availability.
Innovation Solution
A transfer circuit with two separate DC buses, a main and a secondary bus, where the DC/DC converter has a lower rated power than the inverter bridge, allows for intra-battery equalization without significantly impacting power capacity, using a control circuit to disconnect and reconnect racks between the buses for balancing and energy supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a battery rack is disconnected from the DC bus for intra-battery equalization, then the state of charge balance between cells is improved, but the system capacity and power provision are reduced
Solution Approach 1:
The patent segments the battery system into multiple battery racks connected in parallel to the DC bus. This allows individual racks to be disconnected for equalization while others remain operational, maintaining system capacity. The segmentation enables selective maintenance without complete system shutdown.
Solution Approach 2:
The patent introduces a transfer circuit as an intermediary between battery racks and the DC bus. This transfer circuit enables controlled disconnection and reconnection of individual racks during equalization processes, allowing the system to maintain operational racks while performing maintenance on disconnected ones, thus preserving overall system capacity.
2Stability of the object's composition
If a battery rack is disconnected for equalization, then cell charge balance is achieved, but operational availability is reduced
Solution Approach 1:
By segmenting the battery system into multiple parallel racks, the patent ensures that disconnecting one rack for equalization does not compromise the operational availability of the entire system. Other racks continue to provide power, maintaining system reliability during maintenance operations.
Solution Approach 2:
The patent implements preliminary balancing of the disconnected rack's state of charge to match the DC bus voltage before reconnection. This preliminary action prevents harmful equalization currents upon reconnection, ensuring safe and reliable reintegration of the rack into the operational system.
3Use of energy by moving object
If additional energy is supplied through the inverter bridge for equalization, then the battery rack can be fully charged, but the inverter is unavailable for regular operation
Solution Approach 1:
The patent extracts the equalization function from the inverter bridge by implementing dedicated transfer circuits and DC/DC converters between battery racks and the DC bus. This extraction allows equalization to occur independently through the transfer circuit, preserving inverter availability for regular power conversion operations.
Solution Approach 2:
The transfer circuit serves multiple functions: it enables intra-battery equalization, facilitates energy transfer between racks, and maintains system connectivity without requiring inverter intervention. This multi-functionality allows the inverter to remain available for its primary operations while the transfer circuit handles equalization tasks.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach minimizes the impact on power provision capacity during equalization, enabling continuous operational readiness by balancing state of charge and supplying necessary energy, while reducing the need for additional converters and maintaining system availability.
Implementation Method 1
a first power exchange can take place between a plurality of battery racks, which are connected via a first DC bus to an inverter bridge, and at least one battery rack, which is connected via a second DC bus to the inverter bridge
Data Source
AI summary
The application describes a transfer circuit or system with a first DC bus for connecting a plurality of battery racks to an inverter bridge for a first power exchange with an AC grid. The transfer circuit or system has a second DC bus which is connected to the first DC bus via a DC/DC converter. The transfer circuit or system is arranged to disconnect at least one battery rack of the plurality of battery racks from the first DC bus and to connect it to the second DC bus for performing an intra-battery equalization process. The application also describes a system with a transfer unit and a method for performing an intra-battery equalization process.