LC Active Cell Balancing for Series Battery Capacity Limits
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Solution Overview
Problem
High-voltage battery modules with series-connected low-voltage cells face capacity limitations due to charge imbalances caused by internal and external factors, leading to inefficient charging and discharging, as the weakest cell determines the overall capacity and state of charge, resulting in incomplete utilization of stronger cells.
Innovation Solution
An active cell balancing system using a circuit with transistors and an inductor-capacitor (LC) circuit, coupled with a control circuit, transfers charge between cells to equalize state of charge, allowing all cells to fully charge or discharge by phase-shifted switching of driver signals, enabling efficient energy storage and retrieval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cells are connected in series to achieve high voltage, then voltage is improved, but capacity is limited by the weakest cell
Solution Approach 1:
An LC circuit is introduced as an intermediary energy storage element between battery cells. The LC circuit temporarily stores electrical energy and releases it to weaker cells, enabling charge redistribution without requiring direct cell-to-cell connections. This mediator approach allows the system to overcome the capacity limitation imposed by the weakest cell while maintaining series connection for high voltage operation.
2Quantity of substance
If charge is transferred from stronger cells to weaker cells, then capacity utilization is improved, but charge imbalance occurs
Solution Approach 1:
The system employs periodic switching of transistors to control charge transfer between cells. By alternately connecting and disconnecting the LC circuit to different cell pairs, the system periodically redistributes charge while monitoring and maintaining overall charge balance. This periodic action allows stronger cells to recharge weaker cells without creating permanent charge imbalance, as the switching pattern ensures equitable charge distribution over time.
3Productivity
If active cell balancing is implemented, then energy storage efficiency is improved, but system complexity increases
Solution Approach 1:
The LC circuit serves multiple functions: it acts as an energy storage element, a charge redistribution medium, and a temporary buffer for charge balancing operations. The same LC circuit and transistor switching mechanism are used for both voltage stabilization and charge equalization across cells. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby limiting the increase in system complexity while achieving improved energy storage 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
The active cell balancing system enhances the total charge capacity of the battery module by ensuring all cells are utilized equally, increasing energy storage and retrieval efficiency by redistributing charge across cells, thereby overcoming the limitations imposed by the weakest cell.
Implementation Method 1
A first transistor is coupled between a first battery terminal and a capacitor terminal. The second transistor is coupled between the capacitor terminal and a second battery terminal.
Implementation Method 2
The third transistor is coupled between a third battery terminal and an inductor terminal. The fourth transistor is coupled between the inductor terminal and a fourth battery terminal.
Data Source
AI summary
A system includes a first battery, a second battery, an integrated circuit, a capacitor, and an inductor. The first battery has first and second battery terminals. The second battery has a third and fourth battery terminals. The second battery terminal is coupled to the third battery terminal. The integrated circuit includes a first transistor, a second transistor, a third transistor, and a fourth transistor. The first transistor is coupled between the first battery terminal and a capacitor terminal. The second transistor is coupled between the capacitor terminal and the second battery terminal. The third transistor is coupled between the third battery terminal and an inductor terminal. The fourth transistor is coupled between the inductor terminal and the fourth battery terminal. The capacitor and the inductor are coupled in series. The capacitor is coupled to the capacitor terminal and the inductor coupled to the inductor terminal.