Galvanically Isolated Charge Balance System Using MEMS Switch
Solution Overview
Problem
Existing charge balancing systems for multicell batteries are inefficient, particularly when only one or a few cells are undercharged, as they either discharge all cells to balance them or require complex switch matrices for active charging, leading to suboptimal performance.
Innovation Solution
A galvanically isolated charge balance system utilizing a MEMS switch to connect a flying capacitor to a voltage supply and a biasing circuit with a variable conductance switch, allowing for selective charging or discharging of cells to a predetermined level, enabling efficient charge balancing across multiple cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If passive discharge balancing is used to bring all cells into balance, then battery life is improved, but efficiency deteriorates when only one or a few cells are undercharged because the majority of cells must be discharged unnecessarily
Solution Approach 1:
Instead of discharging overcharged cells to match undercharged cells (traditional approach), the invention inverts the approach by charging undercharged cells to match the voltage level of overcharged cells. This is achieved by connecting the flying capacitor to undercharged cells through the galvanically isolated MEMS switch, transferring charge selectively to only those cells that need it, thereby eliminating unnecessary discharge of other cells and improving energy efficiency while still achieving charge balance for extended battery life
Solution Approach 2:
The invention extracts the charge balancing function from the main battery system by using a separate flying capacitor that can be selectively connected to individual cells through the galvanically isolated MEMS switch. This allows charge to be transferred only to the specific undercharged cells that need it, rather than affecting the entire battery system, thus extracting the inefficiency of unnecessary discharge operations
2Loss of energy
If active charge balancing using a flying capacitor is used to charge undercharged cells, then efficiency is improved, but device complexity increases due to the requirement of a complex matrix of switches
Solution Approach 1:
The galvanically isolated MEMS switch acts as an intermediary between the flying capacitor and the battery cells, providing galvanic isolation while enabling selective charge transfer. This single intelligent switch replaces the complex matrix of switches traditionally required, simplifying the device architecture while maintaining the efficiency benefits of active charge balancing. The MEMS switch's ability to provide galvanic isolation eliminates the need for additional isolation circuits that would further increase complexity
Solution Approach 2:
The galvanically isolated MEMS switch performs multiple functions simultaneously: it provides galvanic isolation between the control circuitry and the battery cells, enables selective connection of the flying capacitor to individual cells, and controls the charge transfer process. This multi-functionality consolidates what would traditionally require multiple separate components and switch matrices into a single device, dramatically reducing system complexity while maintaining active charge balancing efficiency
3Manufacturing precision
If a complex matrix of switches is used for selective charge application, then charge balancing precision is improved, but ease of manufacture deteriorates
Solution Approach 1:
The galvanically isolated MEMS switch serves as an intermediary that simplifies the manufacturing process while maintaining charge balancing precision. By providing a single controlled connection point between the flying capacitor and each cell, it eliminates the need to manufacture and assemble complex switch matrices, reducing manufacturing complexity while preserving the ability to precisely control charge transfer to individual cells through the MEMS switch's controlled activation
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 allows for efficient charge balancing by selectively adjusting the charge on undercharged cells while minimizing unnecessary discharge of overcharged cells, improving battery life and reducing complexity in multicell battery systems.
Implementation Method 1
A galvanically isolated charge balance system uses a galvanically isolated MEMS switch for selectively connecting a flying capacitor to a voltage supply
Implementation Method 2
A galvanically isolated charge balance system uses a galvanically isolated MEMS switch for selectively connecting a flying capacitor to a voltage supply to charge an associated cell
Implementation Method 3
a biasing circuit for setting a variable conductance switch to adjust the charge on the associated cell to a preselected level
Data Source
AI summary
A galvanically isolated charge balance system for a multicell battery includes a balancing circuit associated with each cell; each balancing circuit including a flying capacitor; a variable conductance switch; and a biasing circuit for the variable conductance switch; and a galvanically isolating MEMS switching device for selectively connecting the flying capacitor to a voltage supply to charge it to a predetermined voltage and to the biasing circuit for setting the variable conductance switch to adjust the charge on its associated cell to a preselected level.