Two-Stage Charge Equalization for Series Battery Strings
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Solution Overview
Problem
Existing charge equalization apparatuses for series-connected battery strings are complex and voluminous, leading to increased production costs and voltage stress on components, as they require multiple switches and separate DC-DC converters for each battery cell, which complicates the charging process and reduces efficiency.
Innovation Solution
A two-stage charge equalization apparatus using a shared second DC-DC converter for each battery module, with a current conversion switch module and microprocessor to control the direction and path of the charge current, reducing the number of switches and voltage stress by dividing the battery string into modules and using a first DC-DC converter to output a lower voltage for the entire string.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate DC-DC converters and multiple switches are provided for each battery cell, then charge equalization can be performed on each battery individually, but device complexity and volume increase significantly
Solution Approach 1:
The battery string is divided into multiple battery modules, and the charge equalization system is segmented into a first DC-DC converter for the entire string and second DC-DC converters for each module. This segmentation allows shared resources while maintaining individual control capability.
Solution Approach 2:
The first DC-DC converter serves as a shared resource for the entire battery string, providing common power conversion functionality. The current conversion switch module enables a single second DC-DC converter to serve multiple battery cells by dynamically switching current paths, reducing the total number of converters needed.
2Reliability
If separate DC-DC converters are provided for each battery cell, then individual charge control is achieved, but volume and manufacturing cost increase
Solution Approach 1:
Multiple battery modules share the first DC-DC converter, merging the power conversion function at the string level. The current conversion switch module enables sharing of second DC-DC converters across multiple cells within a module, significantly reducing total converter count and system volume.
Solution Approach 2:
The current conversion switch module dynamically reconfigures current paths based on which battery cell requires charging, allowing a single second DC-DC converter to serve multiple cells sequentially. This dynamic switching enables resource sharing while maintaining individual cell control capability.
3Ease of operation
If multiple switches are used for each battery cell to control charge current direction, then precise current control is achieved, but the number of switches and voltage stress increase
Solution Approach 1:
The current conversion switch module serves multiple battery cells within a module through a single second DC-DC converter, making the switching components multi-functional. This reduces the total number of switches needed compared to having dedicated switches for each cell.
Solution Approach 2:
The current conversion switch module dynamically switches current direction and paths based on real-time battery state, enabling precise control with fewer components. The dynamic reconfiguration allows one switching module to handle multiple cells' control needs.
4Speed
If high voltage is applied to charge each battery cell individually, then charging speed is maintained, but voltage stress on components increases
Solution Approach 1:
The battery string is segmented into modules, and the charging process is divided into two stages: first DC-DC converter handles the entire string at string voltage, second DC-DC converters handle individual modules at lower module voltage. This segmentation reduces voltage stress on switching components while maintaining charging capability.
Solution Approach 2:
The system changes voltage parameters between stages: the first DC-DC converter operates at high string voltage, while the second DC-DC converters operate at lower module voltage. This parameter change reduces voltage stress on components in the second stage while maintaining overall charging 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
This approach simplifies the circuit, reduces complexity and volume, and maintains charging efficiency by sharing DC-DC converters between battery modules, while minimizing voltage stress and the number of switches, allowing for effective charge equalization across the battery string.
Implementation Method 1
a first DC-DC converter which is inputted with a total voltage of the battery string and outputs a voltage lower than the voltage inputted
Implementation Method 2
a second DC-DC converter which is inputted with an output of the first DC-DC converter and outputs a charge current for charging a particular battery cell
Data Source
Figure 1
Figure 2
Figure 3(a)~4
AI summary
A two-stage charge equalization apparatus for a series-connected battery string according to the present invention comprises a two-stage DC-DC converter including a first DC-DC converter which is inputted with a total voltage of the battery string and outputs a voltage lower than the voltage inputted; and a second DC-DC converter which is inputted with an output of the first DC-DC converter and outputs a charge current for charging a particular battery cell, wherein the battery string is divided into one or more battery modules having a plurality of battery cells connected in series and the second DC-DC converter is provided for each battery module; a current conversion switch module which forms a path of the charge current between the battery module and the second DC-DC converter to allow the charge current to be applied to the particular battery cell composing the battery module and controls an application direction of the charge current; and a microprocessor which determines a battery cell to be charged of a low-charged battery cell and controls the current conversion switch module to allow the charge current to be applied to the battery cell to be charged.