EV Precharge Mode for Cold Battery Conditioning
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Solution Overview
Problem
Electric vehicle batteries may be unable to accept charge due to conditions such as extreme temperatures, imbalances, or internal faults, preventing the power circuitry from energizing the power buses and transferring power from an AC source.
Innovation Solution
The implementation of a precharge mode in electric vehicle charging systems, where a precharge circuit pumps charge onto the power bus from a 12V voltage source until a setpoint voltage is reached, enabling a current source charger to charge the battery once it is conditioned to accept power, and allowing ancillary features to be powered even if the battery is not chargeable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the battery is in an unchargeable condition (too cold, too hot, imbalanced, or faulty), then the battery cannot accept charge or energize power buses, but the vehicle still needs to power ancillary features and eventually charge the battery
Solution Approach 1:
The precharge mode performs preliminary conditioning of the battery by pumping charge onto the power bus from a 12V voltage source before enabling the current source charger. This preliminary action brings the battery to a condition where it can accept charge, even when initially unchargeable due to temperature, imbalance, or faults.
Solution Approach 2:
A precharge circuit acts as an intermediary between the 12V voltage source and the battery, and between the power bus and the current source charger. This intermediary component enables power transfer and battery conditioning when direct charging is not possible, bridging the gap between unchargeable battery states and charge acceptance.
2Reliability
If a precharge circuit is added to condition batteries before charging, then batteries in unchargeable states can be brought to chargeable conditions, but the device complexity increases
Solution Approach 1:
The precharge circuit is integrated into the existing charging system architecture, serving multiple functions: conditioning unchargeable batteries, enabling power bus energization, and preparing the battery for subsequent charging. This multi-functionality reduces the need for separate dedicated systems and minimizes overall complexity.
Solution Approach 2:
The precharge mode utilizes the vehicle's existing 12V voltage source to condition the battery itself, rather than requiring an external conditioning system. The battery is brought to chargeable conditions using resources already available within the vehicle, reducing the need for additional external equipment.
3Ease of operation
If the battery cannot energize power buses or accept charge due to extreme conditions or faults, then charging cannot proceed, but ancillary features still need to be powered
Solution Approach 1:
The precharge mode performs preliminary power delivery to the power bus from the 12V voltage source before battery charging is enabled. This allows ancillary features to be powered in advance, ensuring vehicle functionality is maintained even when the battery cannot initially accept charge or energize the power buses.
Data Source
AI summary
A system comprises an EVSE and an electric vehicle having a precharge mode. To charge a battery, the vehicle is connected to the EVSE. In some cases, the battery is unable to energize power buses. For example, if the battery is too cold and has insufficient charge, then the battery will not energize the power buses. If the battery cannot energize the power buses, then a precharge mode is enabled. During the precharge mode, charge is pumped onto two power buses until a setpoint voltage is reached. For example, a precharge circuit pumps charge onto one power bus and a power converter pumps charge from that bus onto a second bus. Once the setpoint voltage is reached, a current source charger is enabled, and energy stored on both buses is used to facilitate the turn-on of the charger, the precharge mode is disabled, and the EVSE charges the battery.