Dynamic State of Charge Control for Hybrid Battery Systems
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Solution Overview
Problem
Existing on-board electrical systems in motor vehicles, particularly those with lead and lithium batteries, face inefficiencies in energy storage and service life due to restrictive state of charge thresholds, leading to larger, more expensive lithium batteries being used to meet storage requirements.
Innovation Solution
A method that allows the lithium battery to be temporarily operated above 80% state of charge during driving, with a second upper threshold value, and adjusts the state of charge based on temperature, enabling optimal use of energy storage while ensuring service life, and uses the lead battery for discharge when parked.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the lithium battery is restricted to a state of charge between 20% and 80% to ensure service life, then the battery longevity is improved, but the energy storage capacity is reduced requiring larger battery design
Solution Approach 1:
The patent applies dynamics by making the state of charge thresholds adjustable based on operating conditions. The control device dynamically adapts the upper threshold value - using 80% during normal operation to protect service life, and allowing up to 100% during driving phases when recuperation is active. This dynamic threshold adjustment resolves the contradiction by optimizing both service life and energy storage capacity according to real-time operational context.
Solution Approach 2:
The patent changes the parameter of state of charge thresholds based on operational mode. During driving with recuperation, the upper threshold is changed from 80% to 100%, allowing full utilization of battery capacity. During parking or non-recuperation phases, the threshold reverts to 80% to preserve service life. This parameter change strategy enables the system to achieve both long service life and maximum energy storage when needed.
2Quantity of substance
If a larger lithium battery is used to meet energy storage requirements, then the energy storage capacity is improved, but the cost and vehicle weight increase
Solution Approach 1:
By dynamically adjusting the state of charge thresholds based on operational context, the patent maximizes the utilization of the existing lithium battery capacity. During driving phases with recuperation, the battery can be charged to 100%, effectively increasing the usable energy storage without adding physical battery capacity. This reduces the need for larger, heavier battery packs.
3Quantity of substance
If the lithium battery operates above 80% state of charge during driving, then the energy storage capacity is improved, but the service life may be compromised
Solution Approach 1:
The patent applies periodic action by alternating between different state of charge thresholds based on driving cycles. During recuperation phases, the battery is charged to higher levels (up to 100%). During parking or non-recuperation phases, the threshold is reduced to 80% to allow discharge and rest. This periodic variation in threshold levels allows the battery to periodically access full capacity while periodically resting at lower levels, preserving service life.
Solution Approach 2:
The control device proactively manages the state of charge by lowering the threshold to 80% in advance during parking phases, allowing the battery to discharge and rest before the next driving cycle. This preliminary action prevents continuous high-state-of-charge operation, protecting service life while still allowing full capacity utilization during subsequent driving phases.
4Duration of action of stationary object
If the state of charge threshold is dynamically adjusted based on temperature, then the service life is improved, but the control system complexity increases
Solution Approach 1:
The patent changes the state of charge threshold parameter based on temperature measurements. When temperature exceeds a predefined threshold, the upper state of charge limit is reduced to protect the battery from thermal stress. This simple parameter adjustment based on temperature feedback provides effective thermal management without requiring complex control algorithms, balancing service life protection with acceptable system complexity.
Data Source
AI summary
The disclosure relates to a method for controlling an electrical system of an electrically drivable motor vehicle, wherein the electrical system includes at least one lead battery and at least one lithium battery. Initially, a lower and a first upper threshold value for a state of charge of the lithium battery are determined. Then, a second upper threshold value which is higher than the first upper threshold value is determined. During the driving operation of the motor vehicle, a state of charge of the lithium battery is set between a lower and a second upper threshold value. When the motor vehicle is switched off, the state of charge of the lithium battery is determined. If the state of charge of the lithium battery is higher than the first upper threshold value, the state of charge of the lithium battery is lowered to the first upper threshold value.