Vehicle SOC Display Logic for Sensor Drift and Early Charging
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Solution Overview
Problem
The accuracy of state of charge (SOC) calculation for power storage devices in electrified vehicles decreases over time due to integration of detection deviations from current sensors, leading to potential unexpected failures like lack of electricity.
Innovation Solution
A display system that includes a processor to calculate a display state of charge lower than the control state of charge when an index value indicating the degree of accuracy decrease exceeds a threshold, prompting the user to charge the vehicle earlier and preventing unexpected failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the control state of charge is calculated based on current sensor detection values, then the power storage amount can be monitored, but the calculation accuracy decreases over time due to integration of detection deviations
Solution Approach 1:
The system performs preliminary correction of the control SOC using the relationship with open circuit voltage before the calculation accuracy significantly deteriorates. By correcting the control SOC when the elapsed time exceeds the threshold, the system proactively prevents accumulation of integration deviations, thereby maintaining measurement precision without requiring continuous real-time correction.
Solution Approach 2:
The system establishes a feedback mechanism where the control SOC is periodically corrected based on the relationship with open circuit voltage. The correction value calculated from this relationship is fed back to adjust the control SOC, compensating for integration deviations that have accumulated over time. This feedback loop restores calculation accuracy without requiring complex real-time monitoring systems.
2Reliability
If the display state of charge is set equal to the control state of charge, then the display reflects actual charge level, but users may not charge in time and unexpected failures occur
Solution Approach 1:
The system applies preliminary anti-action by displaying a state of charge that is intentionally lower than the actual control state of charge. This creates a safety margin that prevents the vehicle from operating beyond the reliable charge level. By anticipating potential accuracy deterioration and setting the display SOC conservatively, the system prevents unexpected failures while maintaining reliable operation information for users.
3Measurement precision
If the control state of charge is corrected frequently using open circuit voltage relationship, then calculation accuracy is maintained, but system complexity and processing load increase
Solution Approach 1:
The system implements periodic correction of the control SOC based on the elapsed time from the last correction. Instead of continuous or frequent correction, the system corrects the control SOC at regular intervals determined by the threshold value. This periodic approach maintains measurement precision while minimizing system complexity and processing load by avoiding unnecessary correction operations.
Data Source
AI summary
The display system includes an instrument panel, a battery, a current sensor, and an ECU. The battery stores electric power for traveling of the vehicle. The current sensor detects a charge/discharge current of the battery. ECU calculates SOC of the battery according to the current sensor. SOC includes a control SOC used for charge/discharge control of the battery, and a display SOC displayed on the instrument panel and calculated according to the control SOC. When the index value indicating the degree of decrease in the calculation accuracy of the control SOC exceeds the threshold value, ECU starts a calculation process of calculating the display SOC lower than the control SOC.