What are the sources of EMI in Electric Vehicles (EV) ?

There are two types of electrical noise sources within vehicles: electromagnetic interference (EMI) and electrostatic discharge (ESD).

Radiated noise is a particularly challenging aspect of today's wirelessly connected vehicles, and Radio Frequency Interference (RFI) is a key part of discovering sources of EMI.EMI is present to some degree in all types of vehicles, including fuel-efficient and electric vehicles.

As the number of automotive electronics and ECUs increases, so does the number of potential sources of EMI and the number of vulnerable systems.

EMI is any unwanted electromagnetic field that can disrupt the operation of electronic circuits. Electromagnetic compatibility (EMC) is a term closely related to EMI and indicates that the behavior of a circuit or system is unaffected by EMI.EMC infers immunity to EMI radiation, while susceptibility (another term often used when discussing EMI) emphasizes that the reliability and safe operation of a system may be susceptible to EMI.

Electrostatic discharge (ESD) is another type of EMI that involves high-voltage, short-duration pulses that produce rapid voltage transients. These fast transients result in high levels of emitted energy. In contrast to most EMI emissions, ESD occurs irregularly. Crosstalk, in which signals from one PCB alignment or wire are coupled to another PCB alignment or wire, is another type of EMI. No ECU (controller) is ideal, including all the wiring, interconnections, and circuitry of the PCB. passive devices are particularly susceptible to devices that are subject to parasitic components that can propagate EMI. For example, capacitors have inductance, DC resistance and impedance in addition to nominal capacitance. Component leads make excellent antennas at high switching frequencies, while outside of their self-resonant frequency, capacitors are more like inductors than capacitors, and attributes such as these are key considerations in design. For example, the main source of noise may be driving the microcontroller pins of the clock IC, but the signal chain in the relevant components may be the culprit of the coupling noise, such as alignment, capacitor placement location.

1, electromagnetic interference coupling Electromagnetic interference propagates from a source to a susceptible receiving system there are several main methods. Conducted radiation flows directly between the source and receiver through an electrical connection, and noise can propagate through inductive coupling and capacitive coupling.

EMI has different propagation paths between the source and the sensitive circuitry Capacitive coupling: parasitic capacitive coupling between long PCB alignments or signal lines may be sufficient to induce unwanted noise artifacts. This may be the clock signal adjacent to the analog sensor output, even though the clock signal may only be between 0-3VDC and the analog sensor output may be millivolts. Even if the clock signal induces only a few tens of microvolts to the analog signal, it can lead to inaccurate, unstable and unreliable measurements, and can potentially disrupt the stable operation of the system.

Inductive coupling: Mutual inductance between two wires can also cause artifacts on one wire to be transferred to the other. Circuits operating at high frequencies and high impedance inputs are particularly susceptible to disruption. At the same time, PCB layout is an important catch for controlling EMI. It is necessary to keep noise-sensitive analog circuits away from high-voltage circuits, digital logic circuits and power conversion circuits.

Common impedance coupling: If multiple power supply networks are located within a complex system, such as the electronic control unit (ECU) of an electric vehicle. Common impedance coupling occurs when small noises generated by one circuit function are superimposed on its power supply network. When that power connection is routed to other circuit functions, the noise can affect their operation. For example, small variations in the supply voltage in an operational amplifier or analog-to-digital converter will result in erroneous operation, which is critical in the performance of advanced driver assistance systems (ADAS).

2. Potential Noise Sources in Electric Vehicles

Almost any electronics-based system within an electric vehicle emits EMI, from the infotainment touchscreen to the battery management system. However, some functional systems may generate higher levels of EMI noise than others. High-power DC/DC converters and MCUs in an EV's "triple power" system generate constant high-frequency switching inputs, and MCUs also generate highly dynamic voltage transients during acceleration.

The magnitude of the voltage transients can be widely propagated through vehicle systems, cables and interconnections, and can cause severe damage to sensitive electronic equipment. Vulnerable systems include Advanced Driver Assistance System (ADAS) functions, Global Navigation Satellite System (GNSS) navigation, tire pressure monitoring sensors, and collision avoidance radar - basically any circuit that uses an analog small signal chain. Battery management systems and OBCs are other examples of high-power electronic circuits used in EVs (radiation is an important influence). Conducted EMI from cables and interconnects connected to power electronics systems can also lead to unstable and unreliable behavior, as mentioned earlier.

In electric vehicles, motor controllers, OBCs and DCDCs are the hardest hit by the EMC of the three power systems, and rectification is something that takes a lot of time and effort.

Vehicle systems also need to be free from RFI. Infotainment systems often integrate Bluetooth and Wi-Fi connectivity. Drivers can pair their cell phones with infotainment systems for hands-free calling and screen mirroring of their favorite navigation apps or media players. Despite the relatively low power levels of these wireless protocols, there is still the potential to impact the operation of another wireless-based feature, such as GNSS navigation or Bluetooth-connected blind-spot detection mirrors. As wireless-based vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2X) networks are increasingly deployed, it is critical to ensure that vehicle systems are not interfered with by these roadside base stations.

All vehicles must comply with internationally recognized EMC regulations prior to sale. Relevant standards include GB/T18387, ISO7637, ECE R10, ISO11451/2, CISPR12/25, and SAE J551-X, amongst others (typically corporate standards are higher than these national or international standards). Sometimes the help of EMC professional consulting firms and testing organizations is needed to complete the EMC rectification and fully meet the requirements. In the actual product development process, EMC rectification has always been a very important work in the development of automotive products, especially for vehicles to be exported to Europe and North America.