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用Allegro电流传感器IC和铁磁芯测量大电流：涡流的影响

作者：Yannick Vuillermet，
雷竞技竞猜下载Allegro微系统欧洲有限公司

我ntroduction

用周围的铁磁芯测量母线电流的技术是常识。对于200 A以上的大电流测量，Allegro建议使用A136x系列的线性IC，如A1367, in conjunction with a magnetic core (Figure 1). This document focuses on alternating current (AC) effects on the current measurement. AC input currents tend to generate eddy currents in the magnetic core. These eddy currents alter the measured magnetic field and consequently decrease current measurement accuracy.

有关核心设计的更多详细信息，请参阅“Allegro霍尔效应传感器IC大电流传感应用集中器设计指南”雷竞技最新网址[1], available on the Allegro website.
Note that all results in this document come from electromagnetic simulations performed in Ansys Maxwell software.

f级igure 1 — 图1:典型的嗨gh-current sensing system with
磁芯与快板A1367

测量原理

我deally, the magnetic field,小时, in the air gap is perfectly proportional to the input current,我, in the bus bar or currentconducting wire. Thus, it is enough to measure this magnetic field with a linear magnetic field sensor and to characterize the coefficient between the input current and the magnetic field to measure this input current. This coefficient, S_C级, is called the coupling factor or the core sensitivity. However, this coupling factor is only constant over a limited range of current and frequency. Any change of this coefficient leads to input current measurement error. Typical accuracy requirements are in the range of a few percent of the measured current.

涡流基础

涡流是伦茨定律的直接影响，伦茨定律指出，由变化磁场在导体中感应的电流的方向和大小，使其产生磁场
that opposes the change that produced it. In an AC current sensor application using a ferromagnetic core, eddy currents are induced inside the core as a response of the tangential varying magnetic field. Figure 2 shows a YZ cross section that schematically represents the eddy currents in a bulk core.

这些涡流产生一个感应磁场Heddy，与激励磁场H相反_exc公司. 这在传感器水平上测量为降低的核心灵敏度S_C级，或其他
说，是电流测量误差。

图2：大块磁芯中涡流的示意图 — Figure 2: Schematic view of eddy currents
在大块磁芯中

为了减少涡流，有必要切断铁芯中的电流路径。这是通过使用薄板层压核心来实现的。这些板必须与每个板进行电气隔离
other.

The lamination can be done in the Y direction by rolling or in the Z direction by stacking sheets (Figure 3). Eddy currents still flow, but with a reduced magnitude.

图3：层压芯和相应的eddy currents: rolled (left) and stacked (right) — 图3：层压芯和相应的
eddy currents: rolled (left) and stacked (right)

Typical Application Using Allegro A1367LKT Linear Sensor IC

这里考虑了使用Allegro A1367LKT线性传感器IC的典型大电流应用。此应用中的最大峰值电流为600 A。几何结构如图4所示。沿Z轴的芯子长度为6 mm。磁芯由铁磁性材料制成，如晶粒取向硅钢，具有典型的磁特性，如图5所示。初始相对磁导率为10000，饱和时的磁极化为1.8t。注意，为了简单起见，不考虑磁滞。岩心电阻率为45μΩ/cm。

The DC core sensitivity, S_C级从0到600 A进行评估。图6报告了A1367霍尔板位置的预期测量场和预期堆芯灵敏度。磁芯的磁灵敏度是恒定的，直到最大电流，如预期的那样。核心灵敏度约为2.36 G/A。在双极模式下，A1367使用±2 V输出量程。因此，IC灵敏度约为1.4 mV/G，建议A1367零件选项为A1367-LKTTN-2B-T。图7显示了最大直流电流下的磁芯磁化；磁化
未达到饱和。

**Figure 6: DC core magnetic performance**

Now, a sinusoidal current is supplied to the bus bar with a 600 A peak value.

评估了三个核心：

Bulk
沿Z方向用0.375 mm薄板层压
沿Z方向用0.250 mm薄板层压

Figure 8 reports the magnetic core sensitivity attenuation δ over frequency. The attenuation, in percent, at frequency f is defined as:
方程式
S码_{C级_f}is the core magnetic sensitivity at frequencyf级.S码_C\直流电是磁芯的磁灵敏度，单位为直流和10 A。在体磁芯中，灵敏度随频率迅速降低：在100 Hz时，这已经非常显著（>5%）。否则，大块磁芯仅适用于近直流测量。

叠层磁芯的使用频率可高达几千赫，这取决于所需的精度。正如预期的那样，薄板越薄，交流性能越好。

Figure 9 displays the phase shift between input current and the magnetic field measured in the air gap. Figure 9 indicates that the magnetic field measured by the IC is lagging the AC current
f级lowing in the bus bar. In a laminated core, this lag can be up to a few electrical degrees for current frequency above a few kHz.

直接的结果是，由于输入电流阶跃的高次谐波含量，可以测量出明显的延迟。注意衰减和滞后是由涡流引起的
只有物理。具有无限带宽的完美磁场传感器也会看到这些效果。

The attenuation versus the input current is reported in Figure 10 for a 0.375 mm sheet laminated core. A very interesting phenomenon is visible on this plot. At low frequency, the attenuation
在电流上是恒定的，而衰减在5 kHz时下降约300 A。这可以用涡流引起的磁芯早期饱和来解释。低于300 A，
衰减只是由于集中器中的涡流造成的，集中器在图5的线性区域工作。在300 A时，涡流会在局部产生一个高磁场，使电流饱和
核心。因此，磁芯的磁灵敏度在300A时已经降低，而磁芯在直流时通常饱和在600A以上。这是显而易见的，而比较核心磁化
f级rom Figure 7 and Figure 11. Note that the “noise” visible on the core magnetization mapping of Figure 11 is not real but due to the simulation mesh.

图12表示5 kHz和600 a下0.375 mm层压铁芯截面内的涡流幅值密度。

图8:600 A交流电流下铁芯灵敏度衰减与频率的关系 — 图8：岩心灵敏度衰减
与600 A交流电流下的频率对比

图10：铁芯灵敏度衰减与电流的关系，带0.375 mm厚薄板的层压铁芯 — Figure 10: Core sensitivity attenuation vs. current,
laminated core with 0.375 mm thick sheet

Figure 11: Core magnetization at 600 A, 5 kHz, in tesla, laminated core with 0.375 mm thick sheet — Figure 11: Core magnetization at 600 A, 5 kHz, in tesla,
laminated core with 0.375 mm thick sheet

**图12:5 kHz和600 A，YZ横截面下，0.375 mm薄板芯内的涡流幅值密度**

结论

The analysis shows:

由于磁芯灵敏度的改变以及输入电流和产生的磁场之间的相移，涡流会导致电流测量误差。
Eddy currents are reduced by core lamination: the thinner the sheets, the better the behavior over frequency.
Bulk magnetic cores are only for DC measurements or very slow AC, roughly less than 10 Hz.
建议将叠层磁芯用于频率高达几kHz的交流测量，片材厚度为几百μm，所需精度在几kHz左右
percent.
对于给定的应用，最坏情况下的测量误差是在最大应用频率和最大应用电流下。

Allegro工程师可根据电流和频率范围，协助客户为其应用设计最佳的磁芯。请联系您当地的Allegro Microsystems技术人员雷竞技竞猜下载
center for assistance.

[1]“Guidelines for Designing a Concentrator for High-Current Sensing Applications with an Allegro Hall-Effect Sensor IC”,
//www.wasanxing.com/en/insights-and-innovations/technical-documents/hall-effect-sensor-ic-publications/current-sensor-concentrator.

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