Parallel Battery Pack Capacity Control Under Voltage and SOC Differences
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Solution Overview
Problem
In power storage systems with multiple battery packs connected in parallel, managing capacity accurately is challenging due to voltage and state of charge (SOC) differences, especially when some packs are not connected to the power line or have abnormalities, affecting the overall capacity calculation and usage of electrically driven moving bodies.
Innovation Solution
A management device that acquires monitoring data on voltage and SOC, individually controls switches based on voltage and SOC differences, and calculates the total capacity by including the potential contribution of packs not initially connected but capable of being switched on, ensuring accurate system capacity notification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a plurality of battery packs are connected in parallel to increase capacity, then the total energy storage and use time are improved, but inrush current flows between packs with OCV difference and measurement accuracy deteriorates
Solution Approach 1:
The system segments the battery pack management into individual pack monitoring and group management. Each battery pack is monitored independently for OCV and SOC, allowing accurate individual measurements that feed into the overall capacity calculation, resolving the measurement accuracy issue while maintaining parallel connection benefits
Solution Approach 2:
The system performs preliminary actions by sequentially turning on relays for battery packs with lower OCV before connecting packs with higher OCV. This preliminary sequencing prevents inrush current flow and establishes a controlled connection state that enables accurate capacity measurement from the beginning of operation
2Object-affected harmful factors
If relays are sequentially turned on according to OCV reduction to avoid inrush current, then harmful current flow is reduced, but device complexity and operation difficulty increase
Solution Approach 1:
The system implements feedback control by continuously monitoring OCV differences between battery packs and automatically adjusting relay states based on real-time measurements. This closed-loop feedback simplifies the control process compared to predetermined sequencing, as the system adapts to actual pack states while preventing inrush current
Solution Approach 2:
The management device performs self-service by automatically determining the connection sequence based on measured OCV values without requiring external intervention or complex predetermined scheduling. The system uses its own measurements to control its own operation, reducing overall system complexity
3Object-affected harmful factors
If battery packs with low voltage or abnormalities are not connected to avoid cross current, then harmful current flow is reduced, but the entire capacity cannot be accurately grasped
Solution Approach 1:
The management device acts as an intermediary that maintains capacity information for all battery packs including those not physically connected to the power line. By storing and calculating the capacity contribution of disconnected packs, the system provides complete capacity information to the user while the packs remain electrically isolated to prevent cross current
Solution Approach 2:
The system performs preliminary capacity calculation by including all battery packs in the total capacity computation, even those currently disconnected. This preliminary inclusion ensures accurate capacity information is provided upfront, with the understanding that disconnected packs will be reconnected when their voltage levels become appropriate
Data Source
AI summary
An acquisition unit of management unit acquires monitoring data including at least one of voltage and state of charge of a plurality of power storage packs connected in parallel. A switch controller can individually control on/off of a plurality of switches based on a voltage difference between the plurality of power storage packs or an SOC difference between the plurality of power storage packs. When calculating the entire capacity of the plurality of power storage packs, a capacity calculator also adds the capacity of power storage pack connected to a switch in an off state in a case where the switch can be controlled to an on state in future.