Battery Pack SOC Estimation Without a Current Sensor
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of a battery pack in power tools are inaccurate due to high current measurement errors, leading to potential safety issues and requiring costly current sensors, which also increase energy consumption and temperature rise.
Innovation Solution
A method for estimating SOC based on real-time current using a battery pack database, built through an equivalent circuit model, which includes RC models and acquired parameters like OCV, polarization voltages, and internal resistance, without the need for current detection devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current sensor is used to measure real-time current for SOC estimation, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the current sensor from the system by using alternative measurement approaches. It measures voltage across known resistance elements (internal resistance and external load resistance) to calculate current indirectly, thereby removing the need for dedicated current sensors while maintaining measurement capability
Solution Approach 2:
The patent introduces voltage measurement as an intermediary method to obtain current information. Instead of directly measuring current, it measures voltage across resistance elements and uses Ohm's law to derive current, serving as an indirect measurement pathway that avoids the need for current sensors
2Measurement precision
If current sensor is used for accurate current measurement, then SOC estimation accuracy is improved, but energy consumption increases
Solution Approach 1:
The patent removes the energy-consuming current sensor from the system and replaces it with voltage measurement circuits that consume less power. The approach uses existing voltage measurement capabilities to derive current information, eliminating the continuous power requirement of active current sensing elements
3Reliability
If current sensor is used for real-time current detection, then SOC estimation reliability is improved, but temperature rise occurs
Solution Approach 1:
The patent extracts and removes the current sensor that causes temperature rise from the system. By using voltage measurement across resistance elements instead of direct current sensing, it eliminates the source of excessive heat generation while maintaining the ability to obtain accurate current data for SOC estimation
4Measurement precision
If noise compensation method is used to improve SOC estimation accuracy, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent enables the battery pack to self-characterize its own electrical parameters by performing standardized charge-discharge cycles and measuring voltage-current relationships. This self-testing approach builds an internal electrical characteristic database that the system uses for accurate SOC estimation without requiring external noise compensation equipment
Solution Approach 2:
The patent performs preliminary characterization of the battery pack's electrical characteristics during manufacturing or initial use through standardized charge-discharge tests. This pre-established electrical characteristic database is stored and used for subsequent SOC estimations, eliminating the need for real-time noise compensation systems
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides accurate and efficient SOC estimation, reducing errors to less than 8% in discharging and 4% in charging processes, enhancing safety and reducing costs by eliminating the need for current sensors.
Implementation Method 1
acquiring battery pack internal resistance of the battery pack under different working conditions
Implementation Method 2
acquiring undetermined parameters in the equivalent circuit model include direct current (DC) internal resistance, polarization resistance, and polarization capacitance of the battery pack
Data Source
AI summary
A battery pack and a state of charge (SOC) estimation method of the battery pack are provided. The method includes estimating an SOC of the battery pack based on a real-time current flowing through the battery pack, where the real-time current is estimated according to real-time parameters of the battery pack, at least part of the real-time parameters of the battery pack are capable of being acquired by querying a battery pack database with at least partially data preset. With the preceding technical solution, a battery pack can be provided which has a low cost and can accurately estimate the SOC of the battery pack without a current detection resistor.