Voltage-Controlled Battery Model for SOC and SOH Without Current Sensing
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Solution Overview
Problem
Existing methods for determining the state of charge (SOC) and state of health (SOH) of rechargeable batteries suffer from inaccuracies due to reliance on current-controlled models and the impracticality of current measurements during normal use, respectively.
Innovation Solution
A voltage-controlled dynamic mathematical battery model is used to determine SOC and SOH by measuring battery voltage, optionally with temperature, allowing for accurate calculation of battery current and capacity, using implicit systems of equations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current-controlled battery models are used for SOC determination, then the method can be implemented with available measurements, but the accuracy of SOC determination is insufficient due to measurement inaccuracies
Solution Approach 1:
The patent replaces current-controlled battery models with a voltage-controlled battery model. Instead of relying on measured battery current values as input, the new model uses measured battery voltage values to determine SOC. This substitution eliminates the dependency on inaccurate current measurements while maintaining the ability to calculate battery state through mathematical modeling.
Solution Approach 2:
The patent changes the controlling parameter from battery current to battery voltage. The voltage-controlled model expresses battery voltage as a function of state of charge and current, then inverts this relationship to determine SOC from voltage measurements. This parameter change fundamentally improves measurement accuracy by using voltage, which can be measured more precisely than current.
2Measurement precision
If battery current is measured to determine SOH during normal use, then SOH can be determined in practical operation, but current measurements cannot be obtained with desired accuracy
Solution Approach 1:
The patent replaces current-based SOH determination with a voltage-based approach. The voltage-controlled model calculates a model battery current as an output variable from voltage measurements, which is then used for SOH determination. This allows SOH to be assessed during normal operation using only voltage measurements, avoiding the need for accurate current measurements in practical applications.
3Measurement precision
If voltage-controlled dynamic mathematical battery model is used, then SOC can be determined with improved accuracy using only voltage measurements, but the model complexity increases
Solution Approach 1:
The patent employs a dynamic mathematical battery model that captures the time-dependent behavior of battery voltage. The model includes dynamic elements such as capacitance and resistance that account for transient effects during charging and discharging. This dynamic approach enables accurate SOC determination from voltage measurements while the model structure is optimized for practical implementation in battery management systems.
Data Source
AI summary
The invention relates to a method and a device for determining the state of charge (SOC) of a rechargeable battery (106) of a specified battery type, or a parameter physically related thereto, in particular a remaining charge amount Q contained in the battery, wherein the method operates by means of a voltage-controlled battery model (102), which is parameterized for the battery (106) in question or a corresponding battery type. It is merely necessary to measure the battery voltage Umeas and to provide it to the battery model (102) as an input variable. The invention further relates to a method and a device for determining the state of health (SOH) of a battery (102), wherein the battery model (102), which is also used to determine the SOC, provides a modelled battery current Imod. Modelled charge amounts during charging and discharging phases of the battery (106) can be determined therefrom and compared with measured charge amounts, which are determined from the measured battery current Imeas. Because the battery model (102) does not age, the SOH of the battery can thereby be determined.