Electronic pervasiveness in vehicles brings EMI challenges

August 06, 2019 //By Felix Corbett, TTI
Electronic pervasiveness in vehicles brings EMI challenges
The integration of more and more electronics in cars is being driven by automotive industry trends such as the ‘connected car’, increased used of ADAS (advanced driver assistance systems), and the drive towards semi- or even fully autonomous vehicles. The potential for EMI/EMC issues is therefore dramatically increasing with this growing pervasiveness of electronic systems and their physical proximity within the car. In addition, EMI will be an even greater issue in electrically powered vehicles that rely on high-current systems in the automotive drivetrain with the potential for significant transients.

Sources

Today’s modern car has more than a hundred processors running systems from critical drive-by-wire functionality to body electronics such as electric mirrors or door locks to in-car functionality such as mood lighting, heated seats or the infotainment system. This latter machinery introduces a host of communications signals coming in from external sources including GPS, radio broadcasts, cellular internet connectivity and data streaming via Wi-Fi or Bluetooth from mobile phones (figure 1). In addition, other signals are introduced from safety systems such as collision-avoidance radar or tyre-pressure monitoring, which is typically uses RF communication. All these create potential EMI problems and therefore signal interference protection is required for drive-by-wire functionality, or systems such as ADAS, which can make potentially life-changing decisions, or other safety devices. For example, there have been a host of reported incidents concerning the triggering of airbags by RF transmissions.

But this is not all: new technologies are being introduced in the coming years, such as the ‘Internet of Moving Things’ (IoMT). This will include Car-to-Car (C2C) and Car-to-Infrastructure (C2I) communication, providing a view of traffic conditions and potential hazards. These two technical initiatives will use IEEE802.11p, an automotive-specific version of Wi-Fi. Additionally, inside the vehicle, data is transferred via a wide range of buses and protocols, including: CAN (Controller Area Network) for routine functions; the MOSTTM (Media Oriented Systems Transport) protocol for multimedia; and FlexRayTM for critical controls such as braking and steering. Ethernet cabling is being used to transport these communications, but commonly two-wire unshielded cable is employed as it offers significant savings in weight compared to shielded multi-conductor cables.

Electric

The use of high-power motors and drives in electric vehicles will bring a further range of challenges. The battery’s DC bus is switched at high frequency to generate AC for traction motors; and switched-mode converters down-convert the bus voltage to 12 or 24V for ancillary equipment and the remainder of the electronics (Figure 1).

 


Figure 1. Electric vehicle powertrain (source – US DoE)

IGBTs will typically perform the DC switching at relatively low frequency to maintain efficiency. However, Silicon Carbide (SiC) based devices are increasingly being used and these can operate at much higher frequencies with good efficiency. This means a reduction in size of passive components such as magnetics and capacitors, thereby reducing cost and weight. But there is a penalty in terms of EMI, especially at higher frequencies.

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