Battery Pack Cell-Level State Estimation via Bar Delta Filter
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Solution Overview
Problem
Existing electric vehicle battery systems lack accurate cell-level insights for estimating state of charge (SOC) and state of power (SOP), leading to inaccurate maximum travel estimates under non-ideal conditions.
Innovation Solution
An automotive battery system with a controller implementing a bar delta filter to update SOC estimates based on balancing currents across series-connected cells, allowing for precise charge and discharge management within defined power limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If battery pack level SOC estimation is used, then system simplicity is maintained, but measurement precision of cell-level SOC and SOP deteriorates
Solution Approach 1:
The patent divides the battery pack into individual cell-level monitoring units. Each cell is equipped with its own voltage sensor and SOC estimation algorithm, allowing independent tracking of state of charge and state of power for each cell. This segmentation enables precise cell-level measurements while maintaining overall system manageability through modular architecture.
Solution Approach 2:
The patent introduces a cell-level current sensor as an intermediary measurement device that directly measures the current flowing through each individual cell. This intermediary measurement approach provides accurate cell-level current data for SOC estimation without requiring complex pack-level calculations, thereby improving measurement precision while keeping the monitoring system relatively simple.
2Reliability
If ideal condition assumptions are made for travel estimation, then calculation simplicity is maintained, but reliability of maximum travel estimates deteriorates under non-ideal conditions
Solution Approach 1:
The patent implements a feedback mechanism where actual cell-level voltage, current, and temperature measurements are continuously compared with estimated values from the SOC and SOP algorithms. The estimation system uses this feedback to continuously update and refine its predictions, allowing accurate maximum travel estimation under varying non-ideal conditions without requiring overly complex modeling.
Solution Approach 2:
The patent dynamically adjusts estimation parameters such as cell capacity, internal resistance, and efficiency factors based on real-time operating conditions including temperature, charge/discharge rate, and cell age. This parameter adaptation enables reliable travel estimation across different environmental and operational conditions while maintaining reasonable system complexity through standardized adjustment algorithms.
Data Source
AI summary
A controller discharges a traction battery according to power limits defined by output that is indicative of a state of charge of the traction battery and is updated by a bar delta filter according to a balancing current. The balancing current is associated with each cell of a string of series connected cells of the traction battery and represents a deviation of an estimated current through the cell from a total current of the string.