Non-Dissipative Battery Balancing via Voltage Converters
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Solution Overview
Problem
High-voltage energy storage systems in electrified transportation, such as electric vehicles, face challenges in maintaining charge balance across energy storage elements due to differences in capacity and state-of-charge, leading to reduced system efficiency and accessible energy capacity.
Innovation Solution
A non-dissipative energy storage system with a high-voltage section, a low-voltage section, and voltage converters, where a controller determines power converter inputs to balance charge states by minimizing a cost function, ensuring maximal balance without energy loss, using bidirectional or unidirectional DC-DC power converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If energy storage elements are connected in series to achieve high voltage, then system voltage increases, but charge balance across cells deteriorates due to capacity differences
Solution Approach 1:
The system segments the high-voltage energy storage into multiple series-connected elements while introducing individual control pathways for each element through voltage converters, allowing independent charge management of each cell while maintaining high system voltage
Solution Approach 2:
Voltage converters are introduced as intermediary devices between the series-connected energy storage elements and the low-voltage bus, mediating power flow to enable charge balancing of individual high-voltage cells without disrupting the overall series configuration
2Measurement precision
If conventional battery management systems check each cell individually, then charge balance monitoring improves, but system complexity increases
Solution Approach 1:
The voltage converters serve multiple functions simultaneously: they enable charge balancing of individual high-voltage cells, provide power conversion to the low-voltage bus, and facilitate state-of-charge monitoring, thereby achieving precise charge balance monitoring without proportionally increasing system complexity
Solution Approach 2:
The system uses the existing voltage converters, which are necessary for power management, to also perform charge balancing functions, allowing the system to monitor and balance cell charges without adding separate dedicated balancing hardware
3Reliability
If dissipative balancing methods are used to equalize charge states, then charge balance improves, but energy loss increases
Solution Approach 1:
Instead of dissipating excess energy from overcharged cells as heat, the system recovers this energy by transferring it through voltage converters to undercharged cells or to the low-voltage bus, thereby achieving charge balance while recovering rather than wasting energy
Solution Approach 2:
The system changes the balancing approach from dissipative (resistive) to regenerative by altering the power flow parameters, using controllable voltage converters to redirect excess energy from high-charge cells to low-charge cells, transforming the balancing process from energy-consuming to energy-neutral
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 achieves efficient energy balancing, maximizing the accessible energy capacity of the storage system while reducing energy losses and operational costs, enabling improved battery pack utilization with existing electronic systems.
Implementation Method 1
Each of the voltage converters can be electrically connected between one of the high-voltage energy storage elements and the low-voltage bus and operable to convert power between a high-voltage level of the high-voltage section and a low-voltage level of the low-voltage section
Data Source
AI summary
The integration of the auxiliary power module (APM) functionality into non-dissipative balancing hardware of a high voltage battery or supercapacitor pack enables a more cost-effective non-dissipative balancing system while maintaining a similar complexity in topologies. The system uses state-space equations and three control problems to balance high-voltage energy storage elements and charge low voltage energy storage elements. Two optimization based controllers are employed to optimize both balancing and charging simultaneously.