Hybrid Vehicle Battery Cell Voltage Balancing via Traction Machine Discharge
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Solution Overview
Problem
Existing methods for balancing the voltage of series-connected electrochemical cells in hybrid electric vehicles are inefficient due to low discharge power and prolonged balancing times, which can lead to temperature increases and potential damage to cells.
Innovation Solution
Discharging the electrical storage system by operating at least one large electrical machine, such as an electrical traction machine or main generator, until the state of charge reaches a predetermined level, allowing for higher discharge power and reduced balancing time, while avoiding heat release from internal balancing resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cell balancing is performed by discharging individual cells through internal balancing resistors, then voltage redistribution among cells is achieved, but the discharge power is limited and balancing time becomes excessively long
Solution Approach 1:
The patent introduces an external power supply as an intermediary device to perform cell balancing. Instead of using internal balancing resistors, the external power supply charges or discharges individual cells based on their voltage deviations from the average voltage, enabling much faster and more efficient voltage redistribution across the battery pack.
Solution Approach 2:
The patent changes the discharge power parameter by using an external power supply with sufficient power capacity. This allows the balancing process to operate at higher power levels compared to internal resistor-based methods, significantly reducing the time required to equalize cell voltages while maintaining reliability.
2Productivity
If discharge power is increased to reduce balancing time, then productivity improves, but temperature increase and potential cell damage occur
Solution Approach 1:
The patent implements a feedback control mechanism where the external power supply continuously monitors cell voltages and adjusts the charging/discharging current accordingly. This feedback system ensures that power is applied efficiently and safely, preventing excessive temperature increases while maintaining high balancing speed through optimized power delivery.
3Temperature
If low discharge power is used to limit temperature increase, then cell safety is maintained, but balancing time becomes unacceptably long
Solution Approach 1:
The patent employs dynamic power adjustment where the external power supply varies the discharge power level based on real-time cell conditions. The system can operate at higher power levels when cells are further from balance and reduce power as cells approach equilibrium, optimizing both temperature control and balancing speed throughout the process.
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
This approach significantly reduces battery cell balancing time, maintains safe temperatures, and prevents cell damage by enabling a higher discharge rate and energy recovery through energy accumulation.
Implementation Method 1
an electrical machine configured to drive a vehicle
Implementation Method 2
multiple series-connected electrochemical cells of an electrical storage system
Data Source
Figure 1~2
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AI summary
The disclosure concerns a method for balancing the voltage of multiple series-connected electrochemical cells of an electrical storage system (20) of a hybrid electric vehicle. The method comprises discharging the electrical storage system (20) by operating at least one large electrical machine (21) of the vehicle at vehicle standstill until the state of charge of the electrical storage system (20) or the cell having the lowest state of charge has reached a predetermined level (11, 13), and subsequently balancing the voltage of the cells.