Parallel Battery Pack Charging and Equalization Beyond Voltage Flat Regions
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Solution Overview
Problem
In power supply systems with multiple battery assemblies connected in parallel, achieving full charge state and effective equalization of cell voltages is hindered by differences in internal resistance, particularly in batteries with a voltage flat region in their OCV-SOC characteristic, leading to incomplete SOC estimation and unequalization.
Innovation Solution
A power supply system with a controller that charges each battery assembly to a fully charged state and performs equalization control using converters, ensuring all battery assemblies are fully charged and voltage equalized, with a predetermined period for equalization based on self-discharging variation or impedance, effectively addressing the voltage flat region challenge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If equalization control is performed in the voltage flat region, then the control process continues, but the SOC is not precisely estimated and variation in SOC is not effectively eliminated
Solution Approach 1:
The controller charges each battery assembly to a fully charged state before performing equalization control. This preliminary charging action ensures that the battery operates outside the voltage flat region where SOC estimation is inaccurate, thereby enabling effective equalization control.
Solution Approach 2:
The system dynamically adjusts the charging state of each battery assembly individually using its dedicated converter, ensuring that each battery reaches a fully charged state before equalization. This dynamic adjustment allows the system to adapt to differences in internal resistance and charge characteristics of each battery.
2Quantity of substance
If multiple battery assemblies are connected in parallel, then the system capacity increases, but all battery assemblies cannot be charged to the fully charged state due to differences in internal resistance
Solution Approach 1:
The system segments the battery system into multiple independent battery units, each consisting of a battery assembly and its own converter. This segmentation allows each battery to be charged independently to a fully charged state, overcoming the limitations of parallel connection where uniform charging is difficult to achieve.
Solution Approach 2:
Each converter is designed to perform multiple functions: it can charge its associated battery assembly to a fully charged state and also perform equalization control. This multi-functionality ensures that all batteries can be brought to the optimal charge state regardless of their individual characteristics.
3Loss of time
If equalization control is performed without full charging, then the control time is reduced, but the voltage equalization is not effective due to the voltage flat region
Solution Approach 1:
The system performs preliminary charging to a fully charged state before executing equalization control. This ensures that the battery is in a state where voltage changes are meaningful and SOC estimation is accurate, making the subsequent equalization control effective.
Solution Approach 2:
The system replaces traditional voltage-based equalization control with SOC-based control. By using SOC as the control target and performing equalization based on SOC differences rather than voltage differences, the system achieves accurate equalization even in batteries with voltage flat regions.
Data Source
AI summary
A power supply system is a power supply system that performs charging and discharging between the power supply system and an external system. The power supply system includes a plurality of battery units and a controller. The plurality of battery units include a plurality of battery packs and a plurality of converters provided corresponding to the plurality of battery packs. The plurality of battery units are connected together in parallel. The controller controls the plurality of converters to charge each of the plurality of battery packs to a fully charged state. For each of the plurality of battery packs, the controller is configured to perform equalization control to equalize voltages of cells included in the battery pack when the battery pack is charged to the fully charged state.