Parallel Battery SOC Correction via Segmented BMS Logic
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Solution Overview
Problem
In parallel State Of Charge (SOC) systems for batteries, cell voltage sensing errors can lead to inaccurate SOC calculations, causing energy consumption issues and imbalances among packs, especially when voltage values indicate 0-0.5V, resulting in a widened SOC range and incorrect energy management.
Innovation Solution
A system with sub-Battery Management Systems (BMS) connected to each sub-pack calculates individual SOC values and a main BMS determines the final SOC by averaging or taking the minimum/maximum values based on sub-pack SOC calculations, while identifying and correcting voltage sensing errors by summing valid cell voltages and applying a correction rate to minimize SOC changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple battery packs are connected in parallel to increase capacity, then the energy storage capability is improved, but the SOC measurement precision deteriorates due to voltage sensing errors
Solution Approach 1:
The battery system is divided into multiple sub-packs, each managed by a dedicated sub-BMS with independent voltage sensing. This segmentation isolates sensing errors to individual sub-packs, preventing error propagation across the entire parallel system and maintaining overall SOC measurement precision while preserving increased energy capacity.
Solution Approach 2:
The main BMS acts as an intermediary that collects SOC data from multiple sub-BMS units, validates the readings, and determines the final SOC value. This intermediary layer filters out erroneous voltage measurements by comparing readings across multiple sub-packs and applying correction algorithms, thereby maintaining measurement precision in the parallel configuration.
2Speed
If voltage sensing is used to calculate SOC, then the calculation speed is improved, but the reliability deteriorates when voltage values are 0-0.5V due to sensing errors
Solution Approach 1:
The system preemptively detects voltage sensing errors by monitoring for abnormal voltage readings (0-0.5V range) before they significantly impact SOC calculations. When such errors are detected, the main BMS applies correction algorithms or switches to alternative SOC estimation methods, preventing unreliable voltage-based calculations from compromising overall system reliability.
Solution Approach 2:
The main BMS continuously monitors SOC values from multiple sub-BMS units and provides feedback on the consistency of readings. When voltage sensing errors are detected through feedback mechanisms, the system adjusts calculation weights or switches to current integration methods, maintaining reliable SOC calculation while preserving the speed advantages of voltage-based estimation under normal conditions.
3Measurement precision
If SOC correction is applied to fix sensing errors, then the measurement precision is improved, but the device complexity increases due to multiple BMS units and correction algorithms
Solution Approach 1:
The BMS is segmented into modular sub-BMS units, each handling a specific sub-pack. This modular architecture distributes the complexity of error correction across multiple simple units rather than requiring one complex centralized system. Each sub-BMS performs basic SOC estimation locally, while the main BMS handles coordination and correction, reducing individual unit complexity while maintaining overall precision.
Solution Approach 2:
Each sub-BMS unit independently performs preliminary SOC estimation and error detection on its own sub-pack, providing self-service functionality. This distributes the correction workload and reduces the processing burden on the main BMS. The modular self-service approach maintains high measurement precision while managing system complexity through distributed intelligence rather than centralized complexity.
Data Source
AI summary
A SOC correcting system in a parallel structure of multiple packs in which a plurality of sub-packs having serially connected cells are connected in parallel. The system includes sub BMSs connected to each of the sub-packs a main BMS connected to each of the sub BMSs to collect the SOCs calculated in each of the sub BMSs and to transmit a final SOC to a vehicle SOC to a vehicle controller. When an average SOC to each SOC of the sub-packs is less than 50%, the main BMS determines a minimum value among the SOCs of the sub-packs as a final SOC, and when the average SOC to each SOC of the sub-packs is 50% or more, the main BMS determines a maximum value among the SOCs of the sub-packs as a final SOC.