EV Power Supply Current Limiting for Cell Safety and Mobility
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Solution Overview
Problem
Pure electric vehicles (EVs) without an engine cannot travel when the relay cut-off is activated due to anomalies in the measurement circuit, even if the battery itself is not anomalous, leading to safety concerns and reduced user convenience.
Innovation Solution
A power supply system for electric vehicles that includes a power storage unit, voltage, current, and temperature measurement units, and a controller that determines a current limit value to suppress cell deterioration and ensure safety, allowing the vehicle to continue operating even with measurement circuit anomalies by transitioning to a degenerate mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If relay cut-off is activated when measurement circuit has anomaly, then safety is improved, but vehicle mobility is lost
Solution Approach 1:
The system applies partial action by selectively limiting current only in the affected cell group while allowing other cell groups to continue normal operation. This resolves the contradiction by maintaining partial vehicle mobility rather than complete shutdown, achieving a balance between safety and usability when measurement anomalies occur.
Solution Approach 2:
The battery system is divided into multiple cell groups with independent current measurement circuits. When one measurement circuit fails, only the corresponding cell group is affected, while other groups continue normal operation. This segmentation allows the vehicle to maintain mobility while ensuring safety in the affected segment.
2Reliability
If relay cut-off is activated to prevent cell deterioration, then cell safety is improved, but user convenience deteriorates
Solution Approach 1:
The system limits current only to the extent necessary for safety in affected cell groups while allowing full current in unaffected groups. This partial action approach maintains user convenience for essential vehicle operations while ensuring cell safety in the problematic areas.
Solution Approach 2:
The controller dynamically adjusts current parameters based on measurement circuit status. When anomalies are detected, current limits are changed only for affected cell groups, allowing the vehicle to continue operating with modified parameters rather than complete shutdown, thus maintaining user convenience while ensuring safety.
3Reliability
If current limit value is determined based on voltage, current, and temperature measurements, then cell deterioration is suppressed, but system complexity increases
Solution Approach 1:
The controller performs multiple functions using the same measurement data: it monitors for anomalies, determines current limit values, and manages charging/discharging operations. This multi-functionality approach suppresses cell deterioration through comprehensive monitoring without proportionally increasing system complexity, as existing measurement infrastructure is utilized efficiently.
Data Source
AI summary
Power supply system mounted in electric vehicle includes voltage measurement unit that measures a voltage of each of a plurality of cells to ensure both safety of an electric vehicle and convenience of a user. Current measurement unit therein measures a current flowing through the plurality of cells. Temperature measurement unit therein measures a temperature of the plurality of cells. Controller therein determines a current limit value defining an upper limit of a current for suppressing cell deterioration and ensuring safety based on the voltage, the current, and the temperature of each of the plurality of cells measured by voltage measurement unit, current measurement unit, and temperature measurement unit respectively, and that notifies a higher-level controller in electric vehicle of the determined current limit value.