EV current sensors are basic components. They perform two major tasks. They help us to know how much energy we use. Also, the second task is avoiding overcurrents. Therefore, current sensors are a major sub-systems of a battery design.
EV current sensors can include resistive or magnetic elements based on their structure. We use these elements for sensing the current to be measured. Thus, current sensor manufacturers make current sensors as two separate electrical paths: one is for the measurement current, the other one is for the signal conditioning.
Current Sensor Structure
Let’s focus on battery current sensors. Battery systems provide DC current. So, the battery current sensors perform DC current measurements. There are two main types of battery current sensors.
Shunt sensor-based current measurement devices use resistive elements. Therefore, this type of current sensor is usually non-isolated, unless the signal conditioning circuit has isolation.
Typically shunt sensors are robust and highly accurate. They have a simple structure. So, they are rather robust against thermal, mechanical, and electrical overloads. If we design the signal conditioning circuit well, the shunt sensors are perfect current sensors for automotive battery systems.
The other type of battery current sensor uses electromagnetic elements and measures the magnetic field of current. Therefore, by their nature, these types of current sensors are isolated. However, these sensors measure the current indirectly. Because of this, the accuracy could be less than the shunt sensors.
There are also two major types of magnetic field-based current sensors. Hall sensors use a ferromagnetic core to concentrate the magnetic field. Fluxgate sensors also use a concentration core. However, fluxgate sensors have more complex signal conditioning circuits.
Boundary Conditions
Current sensors are critical elements for maintaining the safety of a battery system. Battery management systems are highly dependent on the current information to determine State of Charge (SOC), State of Health (SOH), and State of Power (SOP). Therefore, accuracy and cumulative errors on coulomb counting are key aspects when selecting current sensors. Besides, it is important how durable the current sensor is against environmental conditions such as thermal, mechanical, electrical, and electromagnetic disturbances. Similarly, we can list the boundary conditions affecting the current sensor selection:
- Duty cycle
- Electrical Isolation
- Signal conditioning
- Temperature dependency
- Overload protection
- Thermal and mechanical loads
- Automotive Safety Integrity Level (ASIL) of current measurement
- Measurement and communication speed
References
- IVT Modular Datasheet, Isabellenhütte Heusler GmbH & Co. KG, 04.01.2017, accessed 01.02.2022
- CAB Current Sensor, LEM Holding SA, accessed 01.02.2022