New sensor delivers accurate SOC estimation across all EV technologies

LEM has launched the new SMU family. The Single Monitoring Unit (SMU) brings previously unseen performance levels to all EV technologies – FHEVs, PHEVs and BEVs.

The new modular SMU family satisfies the requirements of automotive BMS designers who want to extend the maximum driving range of an electric vehicle as far as possible. The SMU continuously monitors vehicle parameters such as battery performance and safety systems. It also identifies anomalies and supports diagnostics, which enhances vehicle efficiency and ensures compliance with regulations.

The design of the new high-performance sensor recognises the necessity for the smallest possible components so that EVs can weigh less and travel further on a single charge. The compact SMU measures just 29.1mm (H) x 35.5mm (W) x 49.9mm (L), while the busbar thickness is 2mm to 3mm compatible. The integrated busbar keeps the size down and improves accuracy; it has been designed to accommodate various busbar dimensions.

The key to maximising EV driving range is accurate State of Charge (SOC) estimation, which means exactly determining the remaining battery capacity. Accurate SOC estimation helps optimise battery life and prevent unexpected power loss while improving user confidence and delivering efficient energy management.

The SMU is a Hall effect technology sensor in an open-loop configuration using the latest LEM9 ASIC. Designed by LEM to add intelligence at the Battery Disconnect Unit (BDU) level, the ASIC allows for the measurement of environmental factors while ensuring accurate sensor performance.

Many new features have been built into the SMU to optimise performance. For example, accuracy is improved by software algorithms that can correct or adjust measurement data to account for distortions or errors caused by mechanical stresses. This enhances the precision of the sensor's readings and makes it possible to reach 1% accuracy up to 1300A and <1.7% up to 1500A. The current range of up to +/-1500A is ideal for BMS applications.

Other features include digital calibration, which provides end-to-end (E2E) protection, improved offset/sensitivity calibration, and such diagnostic warnings as under- or over-voltage. In addition, malfunction is avoided by a dedicated safe state mode should topics such as sensitivity and offset drift, temperature measurement errors, or memory errors (RAM, FLASH, EEPROM, ROM) be detected. Also, the sensor's internal microcontroller includes a built-in algorithm to correct for any magnetic offset, ensuring more accurate and reliable sensor readings by eliminating errors caused by residual magnetism.

The new sensor's high isolation levels enable it to withstand voltage differences greater than 800 V between components or between the device and its surroundings. This improves safety and prevents electrical interference or damage.

Finally, unlike similar sensors on the market, the new SMU family complies with functional safety conditions. This means it satisfies the stringent Automotive Safety Integrity Level (ASIL) requirements built into the ISO 26262 standard for vehicle functional safety. The first version to enter the market is ASIL B ready with the possibility of extending it to ASIL C. ASIL B applies to systems where moderate safety risks are present, balancing safety with practicality in automotive design, and the new SMU family incorporates all the safety mechanisms and design processes that are required to address the risks associated with safety-critical automotive applications.

Jérémie Piro, global product manager BMS at LEM, says: "It's widely understood that the EV industry is continually looking to maximise driving range. BMS designers will welcome a new sensor that is not just compact but also ensures accurate SOC estimation, which are the two main factors. We are very excited that the new SMU family will bring previously unseen performance levels to the FHEV, PHEV and BEV sectors."