This article summarizes several common bus current detection schemes on BMS.

Current detection is a fundamental function of BMS, which is explicitly required in GB/T 38661 2020 Electric Vehicle Battery Management System.

Hall current sensor scheme

Firstly, we need to understand the concept of the Hall effect: when a small current IC passes through a semiconductor perpendicular to the external magnetic field, carriers will be deflected and an additional electric field perpendicular to the direction of the current IC will be generated. Magnetic field B generates a potential difference VH at both ends of the semiconductor. This phenomenon is called the Hall effect, and the potential difference VH is also known as the Hall voltage.

Specifically, you can take a look at the online explanation of the principle: If a magnetic field perpendicular to the direction of the current is applied to a semiconductor, the electrons and holes in the semiconductor will be subjected to Lorentz forces in different directions, and then an electric field will be generated between the concentrated electrons and holes. After the electric field force and Lorentz force are balanced, the electric field will cause the electrons and holes behind to experience the electric field force, and balance the Lorentz force generated by the magnetic field, so that the electrons and holes behind can pass smoothly without deviation. This phenomenon is called the Hall effect.

In addition, how to use the Hall effect to measure current? Since the Hall voltage is proportional to the magnetic field strength and the small current flowing through the semiconductor, if we provide a constant small current through the semiconductor, then the Hall voltage is only proportional to the magnetic field strength and has a certain functional relationship that can be established between the two. Then, if the magnetic field generated by the high current to be measured in the bus is applied to the upper semiconductor (the magnetic field is perpendicular to the current inside the semiconductor), some functional relationship between the Hall voltage and the high current becomes the generation of the measured current, and the Hall voltage can be used to indicate the measured current. The above is a detour, it is recommended to read it more 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 not very common. The following figure shows the basic structure of an open-loop Hall current sensor. A magnetic field will be generated in the wire through the measured current IP. The magnetic field is concentrated in the magnetic core and there is an air gap on one side of the magnetic core. Place semiconductor Hall elements in the air gap to sense the magnetic field strength at the air gap.

Continuing the analysis, in semiconductor Hall elements, a constant small current IC is used. Therefore, according to the Hall effect, there will be a Hall voltage at both ends of the semiconductor, which is amplified and adjusted before being output to the outside. The magnitude of this voltage can then be used to calculate the percentage of IP.

Generally speaking, the advantages of open-loop Hall current sensors are low cost, small size, light weight, and low power consumption. The disadvantage is slightly lower accuracy and larger zero offset. Take a look at the product

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