DC Fast Charging Current Control Under Thermal Limits
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Solution Overview
Problem
The existing power systems for automotive vehicles face challenges in managing the direct current charge to traction batteries, particularly during DC fast charging, where high input currents can exceed thermal management limits, leading to potential hardware stress and prolonged charge durations.
Innovation Solution
Implementing a Filtered I-Squared (FIS) strategy that monitors current utilization over varying time windows, allowing the system controller to gradually limit the maximum charge current to prevent FIS capacity depletion, thereby optimizing charge duration and preventing hardware overload.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high input current is applied to charge the traction battery during DC fast charging, then charge duration is reduced and charging speed is improved, but thermal management limits are exceeded causing hardware stress and potential damage
Solution Approach 1:
The system dynamically adjusts the charge current magnitude based on real-time monitoring of current input/output and FIS capacity status. The controller continuously modifies the current limit command to the EVSE, transitioning from static current limits to dynamic adaptation that responds to changing battery conditions and thermal states.
Solution Approach 2:
The system implements a feedback mechanism where the controller monitors the average magnitude of current input/output over a predefined time window, calculates FIS capacity remaining, and uses this information to adjust the charge current limit. This closed-loop control ensures thermal management limits are maintained while optimizing charging speed.
2Reliability
If the maximum charge current is limited to prevent thermal overload, then hardware protection is improved, but charge duration increases and charging efficiency decreases
Solution Approach 1:
The system performs preliminary action by monitoring current utilization and calculating FIS capacity remaining before thermal damage can occur. The controller proactively adjusts current limits based on predicted FIS capacity depletion, preventing hardware stress before it happens while minimizing charge duration extension.
Solution Approach 2:
The system changes the parameter of charge current magnitude dynamically based on FIS capacity status. Instead of using a fixed current limit, the controller adjusts the current parameter in real-time based on the calculated FIS capacity remaining, allowing higher currents when capacity is available and lower currents when approaching limits.
3Productivity
If FIS capacity is allowed to deplete completely, then maximum charge current can be applied continuously, but thermal management limits are exceeded and hardware stress increases
Solution Approach 1:
The feedback mechanism monitors FIS capacity remaining and provides continuous information to the controller. When FIS capacity approaches depletion thresholds, the system automatically reduces charge current to prevent hardware stress, ensuring sustainable high-efficiency charging without exceeding thermal limits.
Solution Approach 2:
The FIS capacity calculation acts as an intermediary between the charge current input and the battery thermal state. By monitoring current utilization through FIS, the system indirectly manages thermal stress without direct temperature sensing, allowing optimization of charge efficiency while preventing hardware damage.
Data Source
AI summary
One or more controllers limit direct current output by electric vehicle supply equipment to charge a traction battery of a vehicle according to a filtered current squared capacity remaining of the traction battery, which may be defined for a window of time having a predefined duration and be based on an average current input to or output from the traction battery.