Battery SOC Measurement Using Adaptive Current and Voltage Switching
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Solution Overview
Problem
Existing battery management systems face challenges in precisely measuring State Of Charge (SOC) due to accumulative errors over time, especially during long-term battery operation, and are influenced by self-discharge and current measuring sensor inaccuracies, leading to significant errors in both SOCi and SOCv measurements.
Innovation Solution
A method using a simple equivalent circuit model and an adaptive digital filter to measure SOC by obtaining current, voltage, and temperature data, filtering these using a low pass filter, and calculating Open Circuit Voltage (OCV) to accurately determine SOC, with the option to set SOC based on either SOCi or SOCv depending on the battery's current state, thereby reducing errors and improving precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SOCi is used for measuring battery charge state, then short-term precision is improved, but accumulative error increases over time
Solution Approach 1:
The patent dynamically switches between SOCi and SOCv measurement methods based on the battery's operating state. When the battery is in a static state (low current), SOCv is used for high accuracy. When the battery is in a dynamic state (high current), SOCi is used. This dynamic adaptation resolves the contradiction by utilizing the strengths of each method in appropriate conditions.
Solution Approach 2:
The patent changes the measurement parameter from current-based (SOCi) to voltage-based (SOCv) depending on the operating conditions. By monitoring current magnitude and battery state, the system transitions between measurement parameters to maintain both short-term precision and long-term reliability.
2Productivity
If current measuring sensor is used for SOC calculation, then SOCi calculation is enabled, but errors cannot be corrected when sensor has trouble
Solution Approach 1:
The patent introduces voltage measurement as an intermediary method to correct errors when current sensor data is unreliable. When the battery is in a static state, SOCv provides a reference value that can correct accumulative errors from SOCi calculation, even when the current sensor has troubles or drift.
Solution Approach 2:
The system uses feedback from voltage measurements to continuously correct SOCi calculation errors. By comparing SOCi with SOCv when the battery is static, the system can detect and correct accumulative errors, maintaining long-term reliability even with imperfect current sensor data.
3Measurement precision
If complex battery models are used for SOC measurement, then measurement precision is improved, but device complexity increases
Solution Approach 1:
Instead of using a continuously complex model, the patent applies a simple model (SOCi) most of the time and only switches to a more accurate method (SOCv) when necessary (during static periods). This partial application of the more accurate method achieves high precision without the continuous complexity of sophisticated models.
Solution Approach 2:
The patent changes the measurement approach based on operating parameters rather than using a single complex model. By switching between SOCi and SOCv based on current and voltage parameters, the system achieves high precision with simple calculation methods appropriate for each operating condition.
Data Source
AI summary
This invention is related to a method and an apparatus for choosing SOCi (State Of Charge based on current) or SOCv (State Of Charge based on voltage) as the SOC (State Of Charge) of a battery depending on a condition in a battery management system by using an equivalent circuit model. In this invention, a method for measuring SOC of a battery in a battery management system is characterized by comprising the steps of: obtaining voltage data and temperature by measuring the current, voltage and temperature of a battery; calculating SOCi by accumulating the current data; calculating open circuit voltage by using an equivalent circuit model which simply presents the current data, the voltage data and the battery through an electric circuit; calculating SOCv by using the temperature data and the open circuit voltage; and choosing at least one of the SOCi and the SOCv as SOC of the battery by using the SOCi and the SOCv based on the judgment on the current state of a vehicle for a certain time interval.