Battery Cell Voltage Ripple Estimation via Impedance Ratio
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Solution Overview
Problem
Existing electricity storage systems with series-connected cells face challenges in accurately measuring ripple voltage fluctuations using expensive and large-sized circuits, especially when charged by low-spec chargers, leading to increased system size and cost, particularly in applications like electric vehicles and stationary storage.
Innovation Solution
A management device with a cell voltage measurement unit, total voltage measurement unit, and controller that estimates cell voltage ripples by multiplying the detected total voltage ripple by the internal impedance ratio of each cell, allowing for accurate monitoring within an allowable voltage range using an inexpensive and small-scale circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a highly accurate voltage measurement circuit is used to measure cell voltage ripple, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent segments the voltage measurement function into two parts: (1) a simple ADC measures the total voltage of all series-connected cells, and (2) the control unit separately measures the internal impedance of each cell and calculates individual cell voltages through computation. This segmentation allows using a low-precision ADC for total voltage measurement while achieving high-precision individual cell voltage measurement through mathematical calculation based on measured internal impedances.
Solution Approach 2:
The patent replaces the traditional electrical measurement approach (using high-precision voltage measurement circuits for each cell) with a computational approach. Instead of directly measuring each cell voltage with high-precision hardware, the system measures total voltage and internal impedances, then substitutes the direct measurement with calculation based on the relationship between voltage, current, and internal impedance.
2Measurement precision
If a highly accurate voltage measurement circuit with high sampling frequency is used, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent segments the measurement and calculation functions: the ADC only needs to sample total voltage at a moderate frequency, while the control unit performs high-frequency ripple analysis by combining total voltage ripple measurement with individually measured cell internal impedances to calculate each cell's voltage ripple.
Solution Approach 2:
The patent substitutes the need for high-frequency sampling hardware with computational processing. The control unit measures internal impedances and uses these along with total voltage ripple to calculate individual cell voltage ripples, replacing the need for expensive high-speed ADCs and analog front-end ICs.
3Quantity of substance
If the number of series-connected cells is increased, then the electricity storage capacity is improved, but the circuit size and system cost increase
Solution Approach 1:
The patent makes the voltage measurement system universal by using a single ADC to measure total voltage for all series-connected cells, rather than requiring separate measurement circuits for each cell. The control unit then universally applies the same calculation method (using total voltage and individual cell internal impedances) to determine all individual cell voltages, making the system scalable to any number of cells without proportionally increasing circuit size.
Solution Approach 2:
The patent substitutes hardware multiplication (one voltage measurement circuit per cell) with computational multiplication (one total voltage measurement plus individual impedance measurements processed through calculation). This allows the system to handle any number of series-connected cells without increasing the number of physical measurement circuits, enabling scalability while controlling circuit size.
Data Source
AI summary
A cell voltage measurement unit measures a voltage of each of a plurality of cells that are series-connected. A total voltage measurement unit measures a total voltage of the plurality of cells. A controller manages an internal impedance of each of the plurality of cells. The controller detects a ripple of the total voltage measured by the total voltage measurement unit, estimates a ripple of each cell voltage by multiplying the detected ripple of the total voltage by a ratio of the internal impedance of each cell to a resultant internal impedance of the plurality of cells, and determines whether the ripple of each cell voltage is within an allowable voltage range.