E-Mobility Engineering 015 l EMotive Scarab off-road truck dossier l In Conversation: Giulio Ornella l Hall effect and magnetic sensors focus l Challenge of batteries for heavy-duty EVs l Alpha Motor Corporation digest l Automated charging insight l HVAC systems focus

As Hall effect and magnetic sensor technology continues to develop, Nick Flaherty reports on the growing uses for these devices in EVs Pole stars T he Hall effect has been the mainstay of magnetic sensing since it was discovered by US physicist Edwin Hall in 1879. he effect describes the creation of an electric field in a conductor that carries a current and is placed perpendicular to a magnetic field. The fact that the induced voltage is proportional to the magnetic field provides a measurement that is used to control brushless motors and the position of almost anything that rotates. The design of the conductor has been optimised with different configurations for different applications. Some sensors use a single plate, others a cross-shape or multiple plates. Yet others use different materials, particularly graphene, a ‘2D’ version of carbon that is a single atom thick. This improves the sensitivity by reducing the errors that can come from having a thickness to the sensing layer. Multiple Hall effect sensors have also been integrated onto a single chip in an array of thousands of sensors. This can be used to measure the quality of the magnets used in an EV design, ensuring that motors or sensors do not fail owing to a faulty magnet. The sensors have traditionally been used for measuring the alternation, or repeated occurrence, of the magnetic poles within a rotor in a motor, with three sensors typically at a 120º angle to measure the speed and position of the rotor. But the increasing sensitivity of the sensors, through the integration of more processing on the chip, new structures or new materials, is seeing more uses for them in EVs, particularly in measuring the current in and out of the battery pack. This is increasingly important for fast charging, where accurate measurement of the hundreds of amps flowing into the battery pack is essential to protecting the battery cells in the pack. Hall effect sensors are also used for load balancing of cells, providing more flexibility than existing shunt sensors. Shunts are essentially resistors in series, and so introduce losses. Coreless Hall effect sensors measure the magnetic field generated by the currents that are flowing and so are non-invasive and virtually lossless. However, the sensors can be sensitive to variations in temperature, so maintaining their accuracy is a key challenge. Other magnetic sensing technologies are also being adopted in EVs, from the giant magnetoresistance (GMR) effect to inductive sensors that use the tracks on a PCB as the sensor. With a traditional Hall effect sensor, there are two conductor plates with a voltage between them exposed to a magnetic field. This field can be from a current or a magnet to measure the speed of rotation of a rotor. The key is that this is a well-established simple, reliable and robust technology, which is seen as a key requirement for automotive designs. With EVs there is a focus on measuring the higher magnetic field strengths that come from higher currents. These can come from the voltage of battery packs increasing to 900 V and above, and from fast chargers boosting the current flow into the vehicle at higher voltages. Current monitoring is also vital in home chargers for safe operation. These higher voltages and currents create more sources of noise and stray fields, requiring more signal processing. With Hall effect devices based on standard CMOS silicon chip technology, this processing can be added to the chip. This integrated processing also reduces the risk of external noise reducing the accuracy Magnetic sensors can be used for rotational or linear measurements in many areas of an EV and its charging infrastructure (Courtesy of Melexis) 34 Autumn 2022 | E-Mobility Engineering