Battery Management System Active Interrogation for SOC and SOH
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Solution Overview
Problem
Existing methods are ineffective in accurately determining the State of Charge (SOC) and State of Health (SOH) of battery packs containing hundreds of cells, which is crucial for efficient operation of energy storage systems in electric vehicles and power grids.
Innovation Solution
A Battery Management System (BMS) that uses a switching power converter, voltage sensing circuit, and processor to generate pre-determined current signals and measure voltage responses, processing the data to estimate the SOC and SOH through impedance spectrum analysis, allowing for precise characterization of battery packs without disrupting the electrical load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If active interrogation methods are used to determine SOC and SOH of battery packs, then measurement precision is improved, but device complexity increases due to the need for switching power converters and additional control circuitry
Solution Approach 1:
The switching power converter serves dual functions: it acts as a power management device for charging/discharging the battery pack and simultaneously functions as an active interrogation device for SOC and SOH estimation. By injecting predetermined current signals during normal operation and analyzing the voltage responses, the same hardware infrastructure is utilized for both power delivery and diagnostic purposes, eliminating the need for separate testing equipment.
2Device complexity
If battery packs are tested using conventional methods, then device complexity is reduced, but measurement precision deteriorates for battery packs containing hundreds of cells
Solution Approach 1:
The battery pack itself serves as the testing device by utilizing its inherent switching power converter to generate interrogation signals. The system performs self-diagnosis by injecting current signals through the existing power converter and measuring the resulting voltage responses across the battery cells, eliminating the need for external testing equipment while maintaining high measurement precision for large-scale battery packs.
3Measurement precision
If battery packs undergo charge and discharge cycles for SOC determination, then measurement accuracy is improved, but loss of time increases due to the duration of complete cycles
Solution Approach 1:
Instead of requiring complete charge-discharge cycles, the system uses periodic injection of predetermined current signals at specific frequencies during normal operation. The switching power converter applies these periodic signals and the system measures the resulting voltage responses, allowing SOC and SOH estimation to be performed rapidly without waiting for full charge-discharge cycles to complete.
Solution Approach 2:
The system performs preliminary characterization of the battery pack by analyzing the impedance spectrum obtained from small-signal perturbations before full charge-discharge cycles are initiated. This preliminary action provides initial SOC and SOH estimates that can guide subsequent operations, reducing the need for time-consuming complete cycles for routine monitoring.
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
Enables accurate estimation of SOC and SOH, facilitating timely replacement of battery packs, improving the efficiency and range of electric vehicles, and maintaining grid stability by determining the degradation and charge capacity of battery packs.
Implementation Method 1
The pre-determined signal is generated as a result of the switching power converter supplying current to the battery pack (referred to as 'charging') or the battery pack supplying current to the switching power converter (referred to as 'discharging')
Implementation Method 2
A voltage signal output by the battery pack in response to the current signal is measured
Implementation Method 3
The measured current and voltage signal data are processed to obtain an estimation of an impedance spectrum for the battery pack
Data Source
AI summary
A characteristic, such as State Of Health (SOH) or State Of Charge (SOC), is estimated for an Energy Storage System (ESS) by supplying a pre-determined signal to the ESS, measuring a response signal output by the ESS, and obtaining an impedance spectrum of the ESS. In one example, the ESS is one of several electrochemical battery packs of an electric vehicle. The pre-determined signal is a current signal generated by a switching power converter that transfers charge from the battery pack to other battery packs or transfers charge from the other battery packs onto the battery pack. The pre-determined signal is generated without disrupting any load supplied by the battery packs. The battery pack outputs a voltage signal in response to receiving the pre-determined current signal. A processor obtains an impedance spectrum using the current and voltage signals, and thereby obtains an SOH and SOC estimate of the battery.