Hall current sensor-open loop Hall solution
Latest update time：2020-07-24
Reads：
It has been raining for nearly a month. Although it is humid, the weather is quite cool. Autumn will begin in less than half a month. This is the first summer where the air conditioner has not been turned on. In the cool summer, drink some Coke and continue reading. .
This time we summarize several common solutions for bus current detection on BMS.
Current detection is an essential function of BMS, and there are clear requirements for it in "GB/T 38661_2020 Technical Conditions for Battery Management Systems for Electric Vehicles".
Hall current sensor solution
First, you need to understand
the concept of the Hall effect
: When a small current Ic passes through a semiconductor perpendicular to the external magnetic field, the carriers are deflected, and an additional electric field is generated in the direction perpendicular to the current Ic and the magnetic field B, thereby generating a potential difference at both ends of the semiconductor. VH, this phenomenon is the Hall effect, and this potential difference VH is also called the Hall voltage. (Picture from LEM official website)
Specifically, you can take a look at this video (from Baidu Encyclopedia):
Online principle explanation
: Applying a magnetic field perpendicular to the direction of the current to the semiconductor will cause the electrons and
holes
in the semiconductor to
be subject to
Lorentz forces
in
different directions
and gather in different directions.
Between
the gathered
electrons
and holes
An electric field will be generated. After the electric field force and the Lorentz force are balanced, they will no longer gather. At this time, the electric field will cause the subsequent electrons and holes to be affected by the electric field force and
balance out the Lorentz force generated by the magnetic field, so that Later electrons and holes can pass smoothly without deflecting
. This phenomenon is called the Hall effect. (Pictures come from the Internet)
Furthermore, how to use the Hall effect to measure current?
Because the Hall voltage is proportional to the magnetic field strength and the small current passing through the semiconductor, if we provide a constant small current passing through the semiconductor, then the Hall voltage is only proportional to the magnetic field strength, and a certain functional relationship can be established between the two.
Then, if
the magnetic field generated by the large current to be measured in the bus bar
is applied around the semiconductor above (the magnetic field is perpendicular to the current inside the semiconductor), then a certain functional relationship will be produced between the Hall voltage and the large current to be measured, The Hall voltage can be used to represent the current to be measured.
The above is a bit convoluted, so I suggest you read it several times.
Common Hall effect current sensors include open loop and closed loop. There seems to be another technology called Eta Hall current sensor, but it is less common.
Open Loop Hall Current Sensor
The basic structure is as shown below (sourced from the Internet). The current Ip to be measured passes through the wire, and Ip generates a magnetic field. This magnetic field is concentrated in the magnetic core. There is an air gap on one side of the magnetic core, and a semiconductor is placed in the air gap. Hall element, which is used to sense the magnetic field strength at the air gap.
Continuing the analysis, a constant small current Ic is passed through the semiconductor Hall element, so that according to the Hall effect, a Hall voltage will be generated at both ends of the semiconductor. After amplification and conditioning, it is output to the outside, and Ip can be calculated. size. (Picture from LEM official website)
In summary, the advantages of open-loop Hall current sensors are low cost, small size and weight, and relatively low power consumption; the disadvantages are slightly poorer accuracy and larger zero-point offset; actually look at the product and feel its parameters. (The picture below comes from LEM official website)
Summarize:
There is a lot of content in this area, and it will take several chapters to be written, and the benefits are quite large; all the above are for reference only.
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