Earth Resistance Measurement Using Adaptive Injection Frequency
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Solution Overview
Problem
Existing methods for measuring earth resistance in battery charging systems are ineffective due to network noise and varying load conditions, making it difficult to distinguish between the injected signal and noise components, especially with limited current intensity, which affects user safety.
Innovation Solution
A method that injects alternating current signals at predetermined frequencies, detects phase-shift angles, and adjusts frequencies based on threshold comparisons to optimize measurements, adapting to changing load conditions and network noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current signal is injected into the network to measure earth resistance, then the measurement can be performed, but network noise and disturbances make it difficult to distinguish the injected signal from noise components
Solution Approach 1:
The patent implements dynamic frequency selection by monitoring the network environment and adapting the injection frequency in real-time. The system detects whether the network is in a static or dynamic state and adjusts the measurement frequency accordingly, transitioning between fixed and adaptive frequency modes to optimize signal detection amidst varying noise conditions.
Solution Approach 2:
The patent changes the frequency parameter of the injected current signal based on network conditions. By selecting different frequencies (e.g., 50Hz, 100Hz, 200Hz, or higher) depending on the detected noise environment, the system optimizes the distinguishability of the measurement signal from background noise, thereby improving measurement accuracy.
2Reliability
If the current intensity used for measurement is limited to little more than 1 mA due to regulatory constraints, then user safety is ensured, but the ability to determine the injected signal component becomes difficult
Solution Approach 1:
The patent performs preliminary detection of network noise characteristics and selects an optimal injection frequency before conducting the actual measurement. By pre-assessing the electromagnetic environment and choosing a frequency with minimal interference, the system ensures that even the limited 1 mA current can produce a detectable signal above the noise floor.
Solution Approach 2:
The system continuously monitors the voltage signal and compares it against expected characteristics of the injected current. By using feedback mechanisms to identify the correlation between the injected signal and detected voltage, the system can accurately determine the measurement component even when the current intensity is limited to safety levels.
3Ease of operation
If a fixed frequency is used for signal injection, then the measurement procedure is simple, but the system cannot adapt to varying load conditions and network noise
Solution Approach 1:
The patent transitions from a static frequency selection approach to a dynamic one where the injection frequency is continuously adapted based on real-time monitoring of network conditions. The system detects changes in load characteristics and noise levels, then automatically adjusts the measurement frequency to maintain optimal performance across varying operational scenarios.
Solution Approach 2:
The system autonomously monitors its own operating environment and self-adjusts the measurement parameters without external intervention. By implementing self-diagnosis of network conditions and automatic frequency selection, the system maintains both operational simplicity for the user and adaptability to changing conditions through automated decision-making algorithms.
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 and efficient earth resistance measurement by dynamically adjusting frequencies to minimize capacitive and inductive interference, ensuring reliable safety monitoring.
Implementation Method 1
injecting a first alternating current signal between a first neutral node and a second earth node... detecting a first voltage signal representing an electrical potential difference between said first and second nodes... calculating an earth resistance value as a function of said first voltage signal
Implementation Method 2
detecting a value of a phase-shift angle between said first current signal and said first voltage signal in the current measurement cycle
Data Source
AI summary
A method for measuring an earth resistance in a battery charging system connected to or connectable to a power grid; includes injecting a first alternating current signal between a first, neutral, node and a second, earth, node, detecting a first voltage signal representing an electrical potential difference between said first and second nodes, calculating an earth resistance value as a function of said first voltage signal, determining a new injection frequency for a subsequent measurement cycle. The determining of a new injection frequency includes detecting a value of the phase shift angle between the first current signal and the first voltage signal in the current measurement cycle, comparing the value of the phase shift angle with at least a first, upper threshold value and/or at least a second, lower threshold value and determining said new injection frequency at least partly as a function of the comparisons.