Vehicle SOC Estimation via Dynamic Current Integration and Voltage Correction
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Solution Overview
Problem
Conventional state of charge (SOC) estimation methods for secondary batteries in externally chargeable vehicles inaccurately calculate the SOC, leading to premature cessation of charging or discharging, which reduces the vehicle's electric-only travel distance and inefficient energy utilization.
Innovation Solution
A vehicle system that includes a controller for estimating SOC by integrating current and open-circuit voltage measurements, accounting for internal resistance and polarization variations, and switching between different SOC estimation methods based on charging and discharging cycles to accurately determine the battery's state of charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SOC estimation methods are used for externally charged batteries, then the estimation process is simple, but the SOC estimation accuracy deteriorates leading to premature cessation of charging
Solution Approach 1:
The patent applies dynamics by switching between different SOC estimation methods based on the battery's operational state. The controller determines whether the battery is in a charging-only state, discharging-only state, or alternating state, and selects the appropriate estimation method for each state. This dynamic adaptation resolves the contradiction by using simple current integration when appropriate and more complex voltage-based methods only when necessary, thereby maintaining accuracy without unnecessary complexity.
Solution Approach 2:
The patent changes the estimation parameters based on operational conditions. When the battery is in a stabilized state (charging or discharging continuously without alternation), the system uses current integration with open-circuit voltage correction. When the battery alternates between charging and discharging, the system switches to methods that account for polarization effects. This parameter change strategy maintains high SOC estimation accuracy while avoiding unnecessary computational complexity in stable operating conditions.
2Productivity
If conventional SOC estimation methods are used, then the control system is simple, but the electric-only travel distance is reduced due to premature charging cessation
Solution Approach 1:
The controller dynamically selects estimation methods based on the battery's charging/discharging state. By using current integration during stable charging phases and switching to polarization-compensated methods during transitions, the system accurately determines when the upper SOC limit is reached. This prevents premature charging cessation and maximizes the electric-only travel distance while maintaining reliable charging control.
Solution Approach 2:
The system continuously monitors battery current, voltage, and temperature to determine the operational state and selects the appropriate SOC estimation method accordingly. This feedback mechanism ensures that the controller accurately tracks the actual SOC, preventing premature cessation of charging and thereby extending the vehicle's electric-only travel distance while maintaining reliable charging control.
3Measurement precision
If current integration method is used alone, then the calculation is simple, but polarization causes voltage deviation leading to inaccurate SOC estimation
Solution Approach 1:
The patent dynamically switches between current integration method and voltage-based estimation methods depending on the battery's operational state. During stable charging or discharging phases, current integration is used for simplicity. During transitions or when polarization effects are significant, the system switches to methods that correct for voltage deviations, thereby maintaining accurate SOC estimation and optimizing energy utilization efficiency.
Solution Approach 2:
The system changes estimation parameters based on the determined operational state. When polarization is detected (through voltage-current relationship analysis), the system adjusts by incorporating voltage-based correction or switching to open-circuit voltage methods. This parameter adaptation maintains high SOC estimation accuracy while minimizing energy loss by using the most appropriate method for each operating condition.
Data Source
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AI summary
A vehicle (1) includes a chargeable and dischargeable battery (B1), a current sensor (11-1) for detecting electric current of the battery, and a controller (30) for estimating a state of charge of the battery and controlling charging and discharging of the battery based on the state of charge. In a first operation mode in which charging and discharging cycles are repeated, the controller (30) estimates an open-circuit voltage of the battery and determines the state of charge based on a value obtained by correcting the open-circuit voltage based on polarization. In a second operation mode in which one of charging and discharging is continued, the controller (30) determines the state of charge based on a result of integration of the current detected by the current sensor. In this way, the vehicle can be provided in which the secondary battery can be charged with and discharge a large amount of energy and can be effectively used.