應用於家用電線量測之可撓式電流感測器之自我校正模型

Abstract

本論文針對應用於家用導線之非侵入可撓式電流感測器感測置放位置的偏 差產生的偵測值失真提出一個自我校正模型。電流感測器元件為三十圈、線寬 30 μm 及線距30 μm 的矩形電感。根據法拉第定律，置放於電線上方之電流感 測器會因通過電線之電流所產生之磁場產生感應電動勢。然而，依據感測器放置 位置的不同會使得產生之感應電動勢有所不同，造成用感應電動勢計算電線電流 值大小值會產生失真。此外，感應電動勢的大小也會因電線外層PVC 厚度的不同 而感應出不同大小之感應電動勢，此也是造成量測失真的原因。爰此，本論文提 出一電感陣列結構使感測器具備自我校正量測失真的功能。 此自我校正模型包含水平位置校正及PVC 厚度分析兩部分。由實驗及理論可 知，感應電動勢大小隨感測器位置之變化會呈二次曲線關係。因此，我們設計三 個連續的電感陣列電感彼此間距 0.5 mm，以此三組數據導出一個二次曲線來計 算各電感的置放位置及此PVC 厚度下最大之感應電動勢的值。在電線另一側即電 感陣列下方再置放一電感，移除家用電線後對此電感通1000 Hz 的交流電流。藉 此，我們可從上方電感處量測出另一感應電動勢。由實驗及理論可知，上下電感 間距大小會與感應電動勢呈一個三次曲線關係。藉由改變上下電感間距之大小， 我們可量測出此三次曲線方程式。將關聯於PVC 厚度的感應電動勢代入此三次曲 線方程式中，可將對應之PVC 厚度計算出來。最後將最大感應電動勢及PVC 厚度 這兩項參數代入理論推導之數學公式計算電流值大小，由實驗驗證計算得出的電 流值大小與實際通過電線內之電流大小誤差僅小於4%。故此校正模型解決了原 型非侵入可撓式電流感測器偵測失真的問題。

This work presents the reliable issues of non-intrusive flexible current sensor tag, made up by 30-turns rectangle coils with 30 μm and 30 μm wire width and spacing respectively, for the power detection of household two-wire power cables. The detection mechanism based on Faraday`s law is to measure the induced voltage signals of the coils as a result of the 60 Hz household current in the power cable. For real applications, the reliability issue may occur due to the misplacement of the tag on the power cable that would cause derived-value errors during measurement. There are two major critical factors affecting the detection reliability, which are the horizontal misplacement of the sensor tag, and the thickness variance of PVC-coated power line, respectively. Therefore, it requires a particular self-calibration scheme to reduce the detection error for solving the reliable issues of non-intrusive flexible current sensor. The calibration scheme in this work contains the correction of horizontal misplacement and the analysis of power cable thickness. In the part of horizontal misplacement, we propose a quadratic polynomial equation to correlate the relation between the induced signals and horizontal positions of the sensor tag placed on the power cable. Using the polynomial equation, we can detect the horizontal shift and correct the sensor tag to the right position. For the part of cable-thickness analysis, we devise two coils on the both sides of the power cable. By applying an AC current signal in one of the coils and simultaneously detecting the induced signal on the other, we can also derive a cubic polynomial equation to estimate the relation of the induced voltages and the distance between two coils. Thus, we can analyze the gap variance from coil to core of the power line PVC coating. Through the proposed self-calibration scheme, less than 4 percent detection error can be realized. We think the scheme can improve the reliability to facilitate the flexible sensor tag for practical use.