Battery Isolation Monitoring with Fast Noise-Resistant Voltage Estimation

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Solution Overview

Problem

Monitoring electrical isolation between high voltage batteries and chassis ground in electric vehicles is complicated by noise, making it challenging to detect isolation faults and prevent electrical shocks.

Innovation Solution

A configurable voltage divider circuit and microcontroller-based system that estimates settled chassis voltages using sampled values and calculates isolation impedance, allowing for quick detection of faults even in the presence of noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional isolation monitoring methods are used, then isolation faults can be detected, but the monitoring is complicated by noise from vehicle operation

Engineering Contradiction:

Improveisolation fault detectionVSAvoidnoise interference

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies periodic action by using alternating voltage polarity sequences (positive and negative voltage steps) to excite the isolation impedance. By periodically switching the voltage polarity and measuring the resulting current responses, the system can distinguish true isolation faults from noise through pattern recognition. The periodic excitation allows the system to accumulate measurements over multiple cycles and filter out random noise while detecting consistent fault patterns.

Inventive Principle:

Principle #19Periodic action

2Measurement precision

If waiting for chassis voltage to settle before measurement is made, then measurement accuracy improves, but measurement time increases

Engineering Contradiction:

Improvechassis voltage measurementVSAvoidsettling time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent applies preliminary action by performing multiple voltage measurements at intermediate time points before the chassis voltage fully settles. Instead of waiting for complete settling, the system takes preliminary measurements during the transient phase and uses these to calculate the final settled voltage value. This approach allows the system to obtain accurate measurements without waiting for the full settling time, thereby reducing measurement time while maintaining precision.

Inventive Principle:

Principle #10Preliminary action

3Loss of time

If multiple voltage measurements are taken during transient phase, then settled voltage can be estimated quickly, but measurement complexity increases

Engineering Contradiction:

Improvefault detection timeVSAvoidmeasurement and calculation process

Core Design Contradiction:

Loss of timeVSDevice complexity

Solution Approach 1:

The patent applies feedback by using the preliminary voltage measurements taken during the transient phase to calculate and update the estimated settled voltage value. The system continuously refines its estimate of the settled voltage based on the intermediate measurements and the known RC time constant characteristics. This feedback mechanism allows the system to quickly converge on an accurate settled voltage value without waiting for full settling, reducing fault detection time while managing complexity through algorithmic efficiency.

Inventive Principle:

Principle #23Feedback

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 robust and efficient monitoring of isolation impedance, reducing the time required for fault detection and minimizing the impact of noise, thereby ensuring user safety by promptly alerting for potential electrical shocks.

Implementation Method 1

a voltage divider circuit that is configurable

Methodology Applied

Scientific EffectVoltage division: Ohm's Law

Implementation Method 2

sampling a first chassis voltage for less than a settling time of the first chassis voltage

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Data Source

PatentUS11833910B2Dynamic isolation monitoring with low sensitivity to noise

Publication Date: 2023.12.05 ANALOG DEVICES INT UNLTD CO

AI summary

A method of monitoring a battery system includes connecting a voltage divider circuit to a battery of the battery system; measuring a first battery voltage; sampling a first chassis voltage for less than a settling time of the first chassis voltage and estimating a settled value of the first chassis voltage using sampled values of the first chassis voltage; changing a configuration of the voltage divider circuit; measuring a second battery voltage; sampling a second chassis voltage for less than a settling time of the second chassis voltage and estimating a settled value of the second chassis voltage using sampled values of the second chassis voltage; and determining isolation impedance of the battery to a chassis using the first and second battery voltages and the estimated settled values of the first and second chassis voltages.