Understand the sources of electromagnetic interference in electric vehicles
Understanding the origins of electromagnetic interference (EMI) in electric vehicles (EVs) is crucial for addressing the challenges posed by electrical noise sources. EMI and electrostatic discharge (ESD) are the two main types of interference that can disrupt the operation of electronic circuits within vehicles. In the context of wirelessly connected vehicles, radiated noise, specifically radio frequency interference (RFI), becomes a significant aspect in identifying EMI sources.
EMI is present in all types of vehicles, including older internal combustion engines and modern EVs. As the electronic content of cars increases, so does the potential for EMI sources and the number of vulnerable systems. To better understand potential EMI sources in an EV, it is essential to clarify key terminology and concepts.
EMI refers to unwanted electromagnetic fields that can disrupt electronic circuits. Electromagnetic compatibility (EMC) is closely associated with EMI and indicates that a circuit or system is unaffected by the presence of EMI. EMC implies immunity to EMI emissions, while susceptibility highlights that a system may be prone or vulnerable to EMI, potentially affecting its reliability and safe operation.
ESD is another type of EMI involving high-voltage, short-duration pulses that create fast voltage transients. These transients can emit high levels of energy. ESD occurs irregularly compared to most EMI emissions. Crosstalk is another form of EMI, where signals from one PCB trace or wire couple to another.
Understanding that no component is ideal is crucial for preventing and identifying EMI. This includes considering the wiring, interconnects, and PCBs, which can introduce parasitic elements that propagate EMI. For example, passive components such as capacitors exhibit inductance, DC resistance, and impedance in addition to their nominal capacitance.
Component leads can act as antennas at high switching frequencies, and capacitors beyond their self-resonant frequency behave more like inductors. These attributes must be considered in design to identify the source of EMI, as the dominant noise source may not always be the direct cause.
EMI propagates from a source to a susceptible receiving system through conducted emissions, inductive coupling, and capacitive coupling. Conducted emissions flow directly between the source and receiver through an electrical connection. However, noise can also propagate through inductive and capacitive coupling, where parasitic capacitance or mutual inductance induces unwanted artifacts or disturbances in nearby signals.
Capacitive coupling can occur between long PCB traces or signal wires, inducing noise in adjacent signals. Inductive coupling arises from mutual inductance between wires, transferring artifacts from one wire to another. Careful PCB layout design is crucial for controlling EMI, particularly for circuits operating at high frequencies and with high impedance inputs.
Common impedance coupling is another form of EMI, occurring when minor noise artifacts generated by one circuit function are superimposed on its power rail, impacting other connected circuit functions. This can lead to erroneous operation, which is critical in safety-critical systems like advanced driver assistance systems (ADAS).
In EVs, virtually any electronic-based system can emit EMI, from infotainment touchscreens to battery management systems. High-power DC/DC converters and inverters used in EV drivetrain electronics generate constant high-frequency switching inputs and dynamic voltage transients during acceleration. These voltage transients can propagate throughout the vehicle systems, cables, and interconnects, potentially damaging sensitive electronics.
Systems such as ADAS, global navigation satellite systems (GNSS) navigation, tire pressure monitoring sensors, and collision-avoidance radar are susceptible to EMI. Battery management systems and onboard chargers, as high-power electronic circuits in EVs, are also potential sources of EMI. Conducted EMI from cables and interconnects attached to power electronic systems can cause erratic and unreliable behavior.
RFI immunity is essential for EV systems. Infotainment systems with Bluetooth and Wi-Fi connectivity can potentially affect the operation of other wireless-based functions, such as GNSS navigation or Bluetooth-connected blind spot detection mirrors. With the increasing deployment of wireless-based vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2X) networks, ensuring vehicle systems are immune to interference from roadside base stations is crucial.
All vehicles must comply with internationally recognized EMC legislation before being sold, following standards such as ISO 11451/2, CISPR 12/25, and SAE J551-x. Specialist EMC consultancies and test houses can assist in pre-compliance testing and achieving full compliance with the required standards. Anechoic chambers are used for prescribed tests defined by the respective standards, accommodating vehicles equipped with EMI receivers, spectrum analyzers, and ESD equipment.
