LEM sensor for accurate SOC estimation across all EV technologies

Designed to deliver high performance for electric vehicles (EVs), the new SMU family is compatible with Full Hybrid Electric Vehicles (FHEVs), Plug-in Hybrid Electric Vehicles (PHEVs), and Battery Electric Vehicles (BEVs).

The SMU family is specifically engineered to meet the needs of automotive battery management system (BMS) designers aiming to maximise the driving range of EVs. By continuously monitoring vital parameters such as battery performance and safety systems, the SMU enhances vehicle efficiency, detects anomalies, and supports diagnostic processes – all while ensuring compliance with safety regulations.

One of the features of the new SMU sensor is its compact design. Measuring just 29.1 (H) x 35.5 (W) x 49.9mm (L), the unit integrates a busbar with a thickness range of 2 to 3mm. This design reduces the sensor's size while improving accuracy, and it is adaptable to various busbar dimensions, making it a highly versatile solution for EV applications.

Accurate estimation of the State of Charge (SOC) is crucial for optimising battery life and ensuring efficient energy management in EVs. The SMU’s precision in SOC estimation helps prevent unexpected power loss and extends battery life, increasing user confidence and vehicle reliability.

The SMU sensor is based on Hall effect technology in an open-loop configuration and incorporates LEM’s latest LEM9 Application-Specific Integrated Circuit (ASIC). This technology adds intelligence at the Battery Disconnect Unit (BDU) level, allowing for the measurement of environmental factors while maintaining the sensor's accuracy.

The SMU family has several advanced features aimed at optimising performance. One key improvement is the integration of software algorithms that correct measurement data for distortions or errors caused by mechanical stress. This enhancement allows the sensor to achieve 1% accuracy up to 1300A and less than 1.7% accuracy up to 1500A, making it ideal for BMS applications with a current range of up to +/-1500A.

Additional features include digital calibration for end-to-end (E2E) protection, offset and sensitivity calibration, and diagnostic warnings for conditions such as under- or over-voltage. To further ensure reliability, the SMU includes a safe state mode that activates in case of detected issues like sensitivity drift, temperature measurement errors, or memory errors. The internal microcontroller also has a built-in algorithm to correct magnetic offset, eliminating errors caused by residual magnetism and ensuring more accurate readings.

The sensor's high isolation levels allow it to withstand voltage differences greater than 800V between components, enhancing safety and preventing electrical damage.

A key differentiator of the new SMU family is its compliance with stringent functional safety standards. The sensor is designed to meet the Automotive Safety Integrity Level (ASIL) requirements of the ISO 26262 standard, which governs functional safety in vehicles. The first version of the SMU is ASIL B ready, with potential for extension to ASIL C. This ensures that the SMU meets the safety needs of critical automotive applications, balancing high performance with practical safety measures.

Jérémie Piro, Global Product Manager BMS at LEM, commented on the significance of the new product: “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.”