Ultracapacitor Cell Voltage Control for Low-Loss Active Balancing
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Solution Overview
Problem
Ultracapacitor cells in series strings experience voltage imbalances due to self-discharge, leading to energy loss and reduced lifetime, as traditional passive balancing methods consume excess current and deplete cells when idle.
Innovation Solution
An ultracapacitor module with active capacitor cell voltage control, utilizing a bidirectional DC/DC converter, voltage sensors, and electronically controlled switches to maintain voltage balance and adjust float voltage based on load status, reducing energy loss and extending cell lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive balancing with resistor ladder is used, then voltage balance is maintained, but energy is continuously consumed and cells are depleted during idle periods
Solution Approach 1:
The system dynamically switches between passive balancing (resistor ladder) and active balancing (DC/DC converter) modes based on operational state. During charging, active balancing redistributes energy efficiently; during idle periods, the system can disconnect or reduce balancing activity to minimize energy consumption while maintaining voltage balance.
Solution Approach 2:
The system changes the balancing parameter from continuous energy dissipation (passive) to controlled energy redistribution (active). The DC/DC converter adjusts power flow parameters to balance cell voltages without continuous energy loss, and can modify float voltage based on load status to optimize energy retention.
2Reliability
If passive balancing with resistor ladder is used, then voltage balance is maintained, but ultracapacitor cell lifetime is reduced due to continuous discharge
Solution Approach 1:
The system dynamically adapts balancing activity based on cell state and operational requirements. During idle periods, the active balancing system can reduce or suspend discharge activity compared to continuous passive balancing, thereby reducing cumulative stress on cells and extending lifetime while maintaining voltage balance when needed.
Solution Approach 2:
The system changes the balancing parameter from continuous energy dissipation (passive) to controlled energy redistribution (active). The DC/DC converter adjusts power flow parameters to balance cell voltages without continuous energy loss, and can modify float voltage based on load status to optimize energy retention.
3Loss of energy
If active balancing with DC/DC converter is used, then energy consumption is reduced, but device complexity increases
Solution Approach 1:
The DC/DC converter is designed to perform multiple functions: active cell balancing during charging, voltage regulation during idle periods, and support for load demands. This multi-functionality justifies the added complexity by eliminating the need for separate passive balancing circuitry and providing superior energy efficiency across all operational states.
Solution Approach 2:
The DC/DC converter acts as an intermediary between the ultracapacitor cell stack and the electrical load/bus. It mediates energy flow to actively balance cell voltages during charging and can regulate float voltage based on load status, reducing energy consumption while managing the complexity through centralized control.
4Power
If float voltage is maintained at high level, then energy availability is improved, but cell lifetime is reduced due to voltage stress
Solution Approach 1:
The system dynamically adjusts float voltage based on real-time load status and cell state. During high-demand periods, float voltage is maintained at higher levels to ensure energy availability. During idle or low-demand periods, float voltage is reduced to minimize voltage stress and extend cell lifetime, optimizing the trade-off between power and durability.
Solution Approach 2:
The system changes the float voltage parameter dynamically based on operational conditions. The controller monitors load status and adjusts float voltage accordingly - higher during active use for energy availability, lower during idle periods to reduce voltage stress and preserve cell lifetime.
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 active balancing system efficiently maintains voltage balance, reduces energy consumption, and prolongs ultracapacitor cell lifespan by selectively discharging cells and adjusting float voltage according to load conditions, minimizing energy loss during idle periods.
Implementation Method 1
a bidirectional boost/buck DC/DC converter, wherein the ultracapacitor cell stack and the DC/DC converter are configured to be connected in series with a voltage supply bus of a vehicle
Implementation Method 2
two or more voltage sensors configured to determine a voltage value of each of the two or more ultracapacitor cells in the series circuit
Implementation Method 3
two or more electronically controlled switches each connected in series with a bleed resistor, wherein one of the electronically controlled switches and bleed resistors are connected in parallel with each of the ultracapacitor cells
Data Source
AI summary
An ultracapacitor module includes an ultracapacitor cell stack containing ultracapacitor cells connected in series and a bidirectional boost/buck DC/DC converter. The cell stack and the converter are configured to be connected in series with a voltage bus of a vehicle. The ultracapacitor module includes voltage sensors configured to determine a voltage value of each ultracapacitor cell. The ultracapacitor module includes electronically controlled switches connected in series with a bleed resistor. The electronically controlled switches and bleed resistors are connected in parallel with each of the ultracapacitor cells. The ultracapacitor module includes an electronic controller that communicates with the converter, the voltage sensors, and the switches. The electronic controller is configured to determine the voltage of each ultracapacitor cell via the voltage sensors and operate the switches to selectively discharge at least one of the ultracapacitor cells to bring the voltage of the discharged ultracapacitor cell closer to one of the other ultracapacitor cells.