Battery Load Leveling System with Ultracapacitor Buffer
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Solution Overview
Problem
Existing battery load leveling systems for electric vehicles are less effective in providing high power levels over extended periods, especially during acceleration under heavy loads and climbing steep grades, due to limited energy storage in ultracapacitors and inefficiencies in matching output voltage with traction drive requirements.
Innovation Solution
A battery load leveling system that includes a first and second battery, a passive storage device, and a unidirectional conducting apparatus, with a battery switching circuit that connects the batteries in either a lower voltage parallel or higher voltage series arrangement to optimize energy delivery and storage, using a pre-charge circuit and current limiting switch to manage current flow and recharge the ultracapacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional batteries are used to provide high current during acceleration, then power delivery capability is improved, but battery terminal voltage drops and efficiency decreases
Solution Approach 1:
The energy storage system is segmented into two distinct components: conventional batteries for energy storage and ultracapacitors for power delivery. This segmentation allows each component to operate in its optimal performance range, with the ultracapacitor handling high-current transient demands and the battery providing sustained energy, thereby resolving the contradiction between power delivery and energy efficiency
Solution Approach 2:
The ultracapacitor acts as an intermediary between the battery and the traction motor. It buffers the high-current transient demands, preventing direct high-current draws from the battery that would cause voltage drops. The ultracapacitor absorbs and releases energy during transient events, mediating the interaction between the battery and load to maintain battery terminal voltage and efficiency
2Power
If ultracapacitor is used to provide additional power during high current situations, then power delivery is improved, but energy storage capacity is limited by voltage difference
Solution Approach 1:
The system merges the ultracapacitor and battery into a hybrid energy storage system where both components work together. The ultracapacitor provides high-power transient support while the battery provides sustained energy. This combination allows the system to achieve both high power delivery capability and adequate energy storage capacity, overcoming the limitation of the ultracapacitor's restricted energy storage due to voltage differences
3Productivity
If battery voltage is maintained at nominal level during constant speed operation, then control circuit efficiency is improved, but voltage drops when high current is drawn
Solution Approach 1:
The ultracapacitor is pre-charged to a voltage slightly higher than the battery voltage during constant speed operation. This preliminary charging state prepares the ultracapacitor to immediately respond to high-current demands without causing battery terminal voltage drops. When acceleration is required, the pre-charged ultracapacitor can instantly deliver the necessary current, maintaining battery voltage stability and ensuring control circuit efficiency
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system enhances energy storage capacity and efficiency, allowing for increased power delivery during high-demand situations while extending battery life and reducing costs by decoupling the traction battery from the DC link, thus improving overall drive system efficiency.
Implementation Method 1
a unidirectional conducting apparatus coupled in series electrical circuit with the passive storage device and poled to conduct current from the passive storage device to the load
Implementation Method 2
a passive storage device, a unidirectional conducting apparatus coupled in series electrical circuit with the passive storage device
Implementation Method 3
a battery switching circuit that connects the first and second batteries in either a lower voltage parallel arrangement or a higher voltage series arrangement
Data Source
AI summary
A battery load leveling system for an electrically powered system in which a battery is subject to intermittent high current loading, the system including a first battery, a second battery, and a load coupled to the batteries. The system includes a passive storage device, a unidirectional conducting apparatus coupled in series electrical circuit with the passive storage device and poled to conduct current from the passive storage device to the load, the series electrical circuit coupled in parallel with the battery such that the passive storage device provides current to the load when the battery terminal voltage is less than voltage on the passive storage device, and a battery switching circuit that connects the first and second batteries in either a lower voltage parallel arrangement or a higher voltage series arrangement.