Allegro电流传感器IC和铁磁芯的高电流测量：涡流的影响
Allegro电流传感器IC和铁磁芯的高电流测量：涡流的影响
由Yannick Vuillermet，
雷竞技竞猜下载Allegro MicroSystems欧洲有限公司
一世ntroduction
用周围的铁磁核心测量汇流条电流的技术是常识。对于高于200A的高电流测量，Allegro建议使用A136x系列的线性IC，例如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“使用Allegro Hall效应传感器IC设计用于设计高电流传感应用的集中器指南”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.
磁芯和Allegro A1367
测量原理
一世deally, the magnetic field,H, in the air gap is perfectly proportional to the input current,一世, 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, SC, 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.
涡流基础知识
涡流是Lenz的定律的直接影响，其指出通过不同磁场引起的电流的方向和大小是它产生磁场
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.
这些涡流产生诱导的磁场，与激发磁场相对的磁场HEDexc。这在传感器级别测量，作为降低的核心灵敏度，sC或其他方式
说，电流测量误差。
在散装磁芯中
为了减少涡流，有必要切割核心中的电流路径。这是通过使用具有薄片的层叠芯来实现。这些床单必须从每个床隔离
其他。
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.
eddy currents: rolled (left) and stacked (right)
Typical Application Using Allegro A1367LKT Linear Sensor IC
这里考虑使用Allegro A1367LKT线性传感器IC的典型高电流应用。该应用中的最大峰值电流为600A。几何形状如图4所示。沿Z轴的核心长度为6毫米。芯由铁磁材料制成，例如晶粒化硅钢，典型的磁性特性如图5所示。初始相对渗透率为10000，饱和磁极化为1.8吨。注意，为了简单起见，不考虑磁滞。芯电阻率为45μΩ/ cm。
The DC core sensitivity, SC, is evaluated from 0 to 600 A. Figure 6 reports the expected measured field at the A1367 Hall plate location and the expected core sensitivity. The core magnetic sensitivity is constant up to the maximum current, as expected. The core sensitivity is around 2.36 G/A. In bipolar mode, the A1367 uses a ±2 V output span. Consequently, the IC sensitivity is ~1.4 mV/G, and the recommended A1367 part option would be A1367-LKTTN-2B-T. Figure 7 displays the core magnetization at maximum DC current; the magnetization
没有达到饱和度。
Now, a sinusoidal current is supplied to the bus bar with a 600 A peak value.
评估三个核心：
- Bulk
- 沿Z方向层压在0.375 mm床单中
- 沿Z方向层压在0.250mm板上
图8报告磁芯灵敏度衰减Δ过频率。百分比，频率f的衰减定义为：
S.C_fis the core magnetic sensitivity at frequencyF。S.CDC是DC和10 A中的核心磁性敏感性。在散装核心中，敏感性会降低非常迅速，频率非常好：在100 Hz，这已经很大（> 5％）。否则说，批量核心仅适用于近DC测量。
根据所需的精度，层压芯可使用多达几kHz。正如预期的那样，更薄的纸张导致更好的交流表演。
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
流动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.
作为直接后果，由于其高谐波含量，可以通过显着延迟测量输入电流步骤。请注意，衰减和滞后是由于涡流
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下衰减约300a。这可以通过涡流引起的芯的早期饱和来解释。300 a以下，
衰减仅是由于浓缩器中的涡电流，其在图5的线性区域工作。在300a时，涡流局部产生饱和的高磁场
核心。因此，核心磁敏度已经在300a下降，而核心通常在DC中的600℃下饱和。在比较核心磁化时清晰可见
From 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表示在5kHz和600A的0.375mm叠层芯的截面内的涡流幅度密度。
在600个AC电流下频率
laminated core with 0.375 mm thick sheet
laminated core with 0.375 mm thick sheet
结论
The analysis shows:
- 由于核心灵敏度改变和输入电流和所产生的磁场之间的相移，涡流诱导电流测量误差。
- 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.
- 建议叠层磁芯，用于频率高达几kHz的AC测量，纸张几百μm，距离几个左几
percent. - 对于给定的应用，最坏情况的测量误差是最大的应用频率和最大应用电流。
Allegro工程师可以帮助客户根据电流和频率范围设计最佳磁芯。联系您当地的Allegro Micro雷竞技竞猜下载systems技术
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。