Monitoring and controlling temperature, voltage, current, and electromagnetic interference (EMI) help ensure the efficiency and safety of key electric vehicle (EV) components.
This article explores how embedded EV sensors accurately measure operating temperatures, highlighting the benefits and tradeoffs of air and liquid cooling solutions. It also discusses the crucial role of regulators, current limiters, and safety mechanisms in managing voltage and current fluctuations. Lastly, the article reviews the primary sources of EMI and outlines various mitigation techniques, including shielding and filtering.
Tracking thermal levels across primary EV systems
Most primary EV systems rely on embedded temperature sensors (Figure 1) to continuously monitor and control fluctuating thermal levels. For example, sensors integrated into lithium-ion (Li-ion) battery management systems (BMS) track temperature, state of charge (SOC), and state of health (SOH) to prevent thermal runaway. Similarly, temperature sensors monitor onboard chargers (OBCs), ac-dc converters, traction inverters, and power distribution units (PDUs).
Figure 1. Various types of EV temperature sensors. (Image: PROSTECH)
Additionally, temperature sensors monitor crucial drivetrain components, including electric traction motor inverters, stators, and rotors. They also monitor the thermal levels of regenerative braking systems, infotainment systems, and advanced driver-assistance systems (ADAS), such as LiDAR and onboard cameras (machine vision). Lastly, sensors measure the temperature of heating, ventilation, and air conditioning (HVAC) systems, as well as thermal management components, including cooling loops, plates, and heat sinks.
Many automotive manufacturers use a combination of contact and non-contact temperature sensors. Contact sensors, such as thermocouples and resistance temperature detectors (RTDs), provide direct temperature measurements of critical components.
In contrast, fiber optic sensors gauge thermal levels in high-voltage areas that are susceptible to EMI. Non-contact sensors and methods, including infrared thermography and laser-based pyrometry, monitor complex thermal behaviors.
Controlling and dissipating thermal buildup
Traction motors operate at around 90% efficiency, meaning a 70-kW motor generates approximately 7 kW of heat that must be dissipated using air cooling, water jackets, or oil spray systems. Smaller traction motors often rely on air cooling, which reduces temperatures by 176° to 284° F (80° to 140° C) across thermal interfaces. Larger motors use liquid-based solutions like water jackets, which circulate water around the stator to dissipate heat through a radiator.
Oil spray systems in direct contact with critical motor components provide optimal heat transfer while also cooling the gearbox. Advanced motor designs may incorporate oil-cooled rotors alongside water jackets or oil spray systems to optimize thermal dissipation.
EV manufacturers equip Li-ion battery packs with either active or passive cooling systems. Although less efficient, passive cooling (such as natural airflow or heat sinks) minimizes complexity, weight, and power consumption. Active cooling, including forced air or liquid cooling, increases efficiency at the cost of added system complexity and power consumption. Forced air cooling provides moderate efficiency, whereas liquid cooling (Figure 2) use water and ethylene glycol, is the most effective but also the most costly option.
Figure 2. A liquid-cooled Li-ion battery bank from a Chevy Bolt. (Image: Advanced Thermal Solutions)
Many EV thermal management systems use a combination of liquid and air cooling to dissipate excess heat from PDUs, OBCs, traction inverters, and regenerative braking systems. Liquid cooling is common for power electronics, such as traction inverters, onboard chargers, and PDUs.
Infotainment systems and ADAS typically use air cooling, although some high-performance ADAS components may require more advanced liquid-based solutions. Lastly, HVAC systems incorporate coolant loops and heat exchangers to regulate cabin temperature and manage the thermal load of other critical systems.
Detecting and managing voltage and current fluctuations
Voltage and current fluctuations in EV Li-ion battery traction packs can result from varying load demands, temperature changes, and dynamic SOC and SOH. The BMS continuously monitors these parameters to ensure stable power delivery and prevent imbalances that could lead to thermal runaway.
High-precision shunt resistors and Hall effect sensors track voltage and current at the cell, module, and pack levels, providing accurate, real-time data to maintain safe operating conditions and optimize charge and discharge cycles. Monitoring individual battery cell voltages and currents safeguards the powertrain, including the OBC, which incorporates additional sensors as shown in Figure 3.
Figure 3. An OBC current sensor. (Image: PROSTECH)
Current and voltage sensors monitor EV regulators and current limiters, ensuring a stable power supply under varying load conditions and optimizing the performance of the traction motor, inverter, and auxiliary systems. To prevent catastrophic failures, sensors are deployed throughout the drivetrain, ADAS, infotainment, HVAC, and thermal systems, detecting overcurrents, short circuits, and voltage spikes that may result from damaged wiring or loose connections.
Together with regulators and current limiters, electronic fuses, circuit breakers, and isolators use sensor data to initiate protective actions and minimize overheating risks that could lead to electrical fires. These actions typically involve disconnecting batteries from the circuit, shutting down affected power electronics, and isolating critical subsystems during fault scenarios, such as collisions or severe electrical issues.
Notably, artificial intelligence (AI) and machine learning (ML) are increasingly crucial in monitoring and controlling EV voltage and current, as well as managing power flow and load balancing across various systems. Optimizing current distribution helps prevent voltage imbalances and mitigate risks like contact welding, nuisance tripping, and battery degradation, while extending EV range.
Additionally, AI-driven systems can now predict and prevent a wide range of safety risks, such as overheating, cell imbalances, and voltage irregularities, before they become critical issues.
Minimizing EMI in EV systems
EMI in EVs originates from multiple sources, such as power converters, electric motors, battery currents, high-voltage interconnects, and ADAS. Power converters using insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), silicon carbide (SiC), and gallium nitride (GaN) devices operate at medium to high frequencies, which, if unshielded, can interfere with various wireless systems such as the BMS.
High-current cables, fluctuating impedance, and high-power levels in electric motors also generate EMI, while ADAS radar and LiDAR systems emit electromagnetic radiation that can impact other vehicle systems.
Minimizing EMI and ensuring compliance with automotive industry standards, such as CISPR25 and SAE J551-5, requires a combination of sealants and gaskets (Figure 4), as well as shielding, filtering, and other design strategies. EMI mitigation includes the use of Class X and Class Y capacitors for high-voltage subsystems, while high-efficiency switching techniques, such as zero-voltage switching, reduce EMI in power converters and motors.
Figure 4. EV Li-ion battery traction packs with highlighted seal and gasket system providing EMI shielding and thermal management. (Image: H2TC)
Shorter interconnect lines, multiple PCB layers, and split ground planes minimize emissions, with differential signal lines and shielded connectors rejecting common-mode noise. Flexible circuit boards and robust EMI-resistant enclosures protect critical components, and grounding brushes and shaft grounding rings prevent electrical charge buildup in motors.
Lastly, lightweight conductive shielding materials, such as graphene and MXene composites, demonstrate excellent EMI shielding capabilities, with hybrid aerogels achieving shielding effectiveness up to 86.9 dB and foam composites reaching 53.8 dB in the X-band frequency range.
Conclusion
Keeping EV temperature, voltage, and EMI within optimal levels ensures key components operate efficiently, reliably, and safely. Advanced sensors and a combination of air and liquid cooling systems are deployed throughout EV systems to monitor temperature and dissipate excess heat. Sensors, along with regulators and current limiters, manage voltage and current fluctuations, while electronic fuses, circuit breakers, and isolators help prevent catastrophic failures. Lastly, EV manufacturers employ shielding, filtering, and other design strategies to minimize EMI and comply with international safety standards.
Related EV Engineering content
- What Role Do Advanced Sensors Play in EVs?
- How Do You Measure and Manage a Thermal Load?
- What Role Do Isolators Play in Electric Vehicles?
- What EV Battery Management System (BMS) Architectures Are Used Today?
- What Are the Biggest Challenges for EV Battery Thermal Management?
References
- Temperature Measurement in High-Voltage Environments, IMC
- A Manufacturer’s Guide to EV Thermal Management & Sensor Technology, Amphenol
- Automotive Electrification and Power Supply Design, Mistral
- EV Sensors and EMI Compatibility, Amphenol
- Understanding the Thermal Behavior of EV Batteries, IMC
- Keeping it Cool: Thermal Management Solutions for Electric Traction Motors, Ansys
Filed Under: FAQs, High Voltage Systems (> 60 VDC), Power Management, Thermal Management System