Active Balancing Circuit for Series Battery Voltage Equalization
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Solution Overview
Problem
Large-capacity lithium secondary batteries connected in series face challenges in efficient charge/discharge due to differences in capacity and internal resistance, leading to low conversion efficiency and increased manufacturing costs, with existing solutions requiring separate discharge resistors and switching elements.
Innovation Solution
An active balancing circuit and algorithm that adjusts current at both ends of each battery to maintain constant voltage and current during charge/discharge, using a single bidirectional DC/DC converter and linear current source, allowing for simultaneous charging and discharging of batteries with different characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate discharge resistors and switching elements are used for each battery, then overcharge protection is improved, but manufacturing cost increases
Solution Approach 1:
The patent merges the discharge resistor and switching element functions into a single integrated module that serves multiple batteries. Instead of using separate components for each battery, a shared discharge path with a single switching element controls current distribution across multiple battery strings, reducing component count while maintaining overcharge protection capability
Solution Approach 2:
The discharge resistor is designed to serve multiple functions simultaneously: it acts as a discharge path for individual batteries, a balancing resistor for voltage equalization, and a protective element for overcharge prevention. This multi-functional design eliminates the need for separate dedicated components for each function
2Productivity
If DC/AC converter is used to regenerate power from discharged battery, then power recycling is enabled, but conversion efficiency deteriorates due to low battery voltage
Solution Approach 1:
The patent introduces an intermediate high-voltage capacitor bank as a mediator between the low-voltage discharged battery and the AC grid. The battery charges the capacitor at high current with minimal loss, then the capacitor discharges to the grid through a standard inverter, achieving efficient power transfer without direct DC/AC conversion from low-voltage battery
Solution Approach 2:
The patent replaces the inefficient direct DC/AC conversion mechanism with an electrostatic energy storage mechanism. Instead of using a DC/AC converter that suffers from low efficiency at low voltages, the system uses capacitor charging/discharging which has near-100% efficiency, substituting electromagnetic conversion with electrostatic energy transfer
3Device complexity
If multiple batteries with different capacities are charged by single bidirectional constant current source, then charging simplicity is improved, but charging uniformity deteriorates causing overcharge or overdischarge
Solution Approach 1:
The patent segments the charging system into multiple independent charging paths, each dedicated to a specific battery or battery string. Each path has its own current control that can be independently adjusted according to the battery's capacity and state of charge, allowing precise control while maintaining overall system simplicity through modular architecture
Solution Approach 2:
The patent implements dynamic current allocation where the constant current source automatically adjusts current distribution to each battery based on real-time voltage feedback. The system dynamically switches between constant current and constant voltage modes for different batteries, adapting the charging profile to each battery's characteristics while maintaining a single control source
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 solution enables efficient power conversion, reduces manufacturing costs, and minimizes size and weight by ensuring all batteries are charged and discharged at a set voltage, achieving over 80% energy efficiency and preventing overcharge/overdischarge.
Implementation Method 1
adding an active balancing circuit configured to add or subtract a predetermined amount of current at both ends of each of the secondary batteries
Implementation Method 2
a single bidirectional constant current source to charge and discharge the plurality of secondary batteries
Data Source
AI summary
An active balancing control apparatus and method with an active balancing algorithm to charge and discharge a plurality of batteries connected in series. The active balancing control apparatus may be designed to simultaneously charge and discharge a plurality of batteries, connected in series and having different charge/discharge characteristics, using an active balancing circuit. The apparatus may perform switching to achieve balancing of each of the batteries so that all the batteries may be charged at a maximum voltage.