Fourier Transform Isolation Impedance Measurement for EV Noise Rejection

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Solution Overview

Problem

Existing isolation measuring systems in electric vehicles and hybrid electric vehicles are unable to accurately monitor AC impedance and detect fault conditions based on capacitance, as they are prone to noise interference and temperature-related issues, particularly affecting capacitor values.

Innovation Solution

An AC impedance measurement system using a Fourier transform-based algorithm to calculate phase and amplitude, which determines isolation impedance by sending a sinusoidal excitation signal, time-stamping the response waveform, and processing it with a Discrete Fourier Transform to extract noise-rejected amplitude and phase information, while also employing self-calibration methods to address initial tolerance and temperature coefficient errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of moving object

If AC method or DC method is used to monitor isolation resistance, then continuous monitoring capability is achieved, but measurement precision deteriorates due to strong noise from electrical drive train

Engineering Contradiction:

Improvecontinuous monitoring capabilityVSAvoidmeasurement precision

Core Design Contradiction:

Duration of action of moving objectVSMeasurement precision

Solution Approach 1:

The patent introduces an intermediary signal processing approach by using a known excitation signal and Fourier transform as a mediator to separate the measurement signal from noise. The excitation signal serves as a reference that allows the system to identify and extract the response signal characteristics even in the presence of strong electrical noise from the drive train, thereby maintaining measurement precision during continuous monitoring.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces traditional time-domain analysis methods with frequency-domain analysis using Fourier transform. This substitution allows the system to analyze the frequency spectrum of the response signal, where the excitation signal's frequency components can be clearly distinguished from random noise, thus improving measurement precision while maintaining continuous monitoring capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Device complexity

If traditional measurement methods are used, then device complexity is low, but reliability deteriorates because fault conditions based on capacitance cannot be detected

Engineering Contradiction:

Improvedevice complexityVSAvoidreliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent transitions from single-parameter DC resistance measurement to multi-parameter AC impedance measurement by adding the frequency dimension. By measuring both resistance and capacitance through AC impedance analysis, the system can detect fault conditions that manifest as capacitance changes, thereby improving reliability without significantly increasing device complexity since the same hardware platform is used.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Ease of manufacture

If component values are used without calibration, then ease of manufacture is high, but measurement precision deteriorates due to initial value tolerance and temperature coefficient problems

Engineering Contradiction:

Improveease of manufactureVSAvoidmeasurement precision

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent implements a self-calibration mechanism where the system automatically measures the actual values of capacitors and resistors during operation and uses these measured values for subsequent measurements. This self-service approach compensates for initial value tolerances and temperature coefficient variations without requiring manual calibration, maintaining ease of manufacture while significantly improving measurement precision.

Inventive Principle:

Principle #25Self-service

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 approach provides high accuracy in measuring isolation resistance and capacitance, effectively rejecting noise and accounting for temperature-related changes, thereby ensuring reliable isolation impedance measurement in electric vehicles.

Implementation Method 1

uses an extraction algorithm based on a Fourier transform to calculate phase and amplitude and then utilizes the calculated phase and amplitude to determine the isolation impedance

Methodology Applied

Scientific EffectFourier transform:

Implementation Method 2

The isolation impedance comprises leakage resistance and total capacitance that are coupled in parallel between the high voltage system and the chassis

Methodology Applied

Scientific EffectElectrical impedance:

Data Source

PatentUS10852334B1Isolation impedance measuring system and method using fourier transform and component value self calibration

Publication Date: 2020.12.01 MAXIM INTEGRATED PROD INC

AI summary

Embodiments of the present invention disclose methods and systems in a vehicle having high voltage (HV) for measuring isolation impedance in an EV or HEV utilizing an AC impedance measurement system. The method utilizes an extraction algorithm based on a Fourier transform to calculate phase and amplitude and then utilizes the calculated phase and amplitude to determine the isolation impedance. The isolation impedance comprises leakage resistance and total capacitance that are coupled in parallel between the high voltage system and the chassis. Embodiments of the present invention also provide a method and systems for component value self-calibration.