A primer: Understand the importance of EMI and EMC in EVs
In our world of high-speed connectivity and wireless communication, the importance of electromagnetic compatibility (EMC) has never been stronger. This is particularly relevant for battery electric vehicle applications, where dynamic drivetrains create significant high voltage transients (dV/dt).
The basic concepts of electromagnetic interference (EMI) (the problem) and electromagnetic compatibility (the solution) are apparent in all applications. A strong understanding of EMI and EMC is vital for any automotive engineering team. The significant increase in vehicle networking architectures and wireless connectivity uncovers the potential impact of unwanted noise on vehicle applications.
Electromagnetic fields are everywhere. Whenever a time-varying high-frequency current flows through a wire or printed circuit trace, magnetic flux lines (H-field) and an electric field (E-field) surround the conducting medium. When transferred to another PCB track or cable, these electromagnetic fields manifest as an unwanted signal – or noise – that can interfere with that circuit's operation.
An electrostatic discharge (ESD) is another form of EMI, something we have all experienced when exiting a car or from any other friction-related movement at some time or another. ESD tends to be of irregular frequency, whereas EMI typically occurs constantly. Any high-voltage, short-duration (high dV/dt) transients can cause erratic operation or even permanent damage to sensitive electronic systems.
Any complex electronic circuit will have multiple potential sources of EMI, from clocks, analog signal input lines, relay switching, microcontroller interfaces, and DC/DC converters. EMI can cause problems within the system generating it, as well as in other completely unrelated systems. EMI may occur regularly or only sporadically. This makes locating the source of EMI a time-consuming task that requires test equipment such as a spectrum analyzer.
There are two main ways EMI may transfer to another system: as conducted or radiated emission. A radiated emission usually come from signals operating at radio frequencies, like microcontroller data lines, clocks and wireless transceivers. PCB traces and interconnecting wires become extremely effective antennas above 30 MHz.
Conducted emissions can occur from the inductive, capacitive or common impedance coupling. The noise artifacts interfere with other systems or functions. Crosstalk between signal lines by either inductive or capacitive coupling is another term used to describe EMI. Common impedance coupling often occurs in power supply rails, where small load-related voltage fluctuations from one circuit function become superimposed on shared power connections to other system parts.
Types of electromagnetic emissions
Graphic shows the unwanted electromagnetic noise transfer from a source to a receiving (disrupted) system or circuit function.
The rise of the connected and networked vehicle
Modern vehicles are full of interconnected electronic systems. Sleek infotainment displays and advanced driver assistance systems (ADAS) make our road journeys safer. There are many potential EMI sources and susceptible systems within vehicles. This is particularly true for electric vehicles (EVs), where high power conversion and drivetrain functions may generate significant electrical interference that can impact other electronic control units (ECUs).
Electric vehicles have an alarming fast dynamic response rate, with some capable of accelerating from 0 to 60 mph in under 5 seconds. During acceleration, the electrical load generated through the drivetrain and associated circuitry can reach up to 1,000 amps and generate instantaneous dV/dt transients into tens of thousands of volts. Compare that with the low voltage signals from, for example, a steering wheel turning sensor used for ADAS lane guidance. The integrity of the lane guidance function would be severely compromised if any drivetrain transients interfered with the ADAS ECU.
The architecture in modern vehicles is increasingly moving to a zonal approach, using high-speed networks to connect zones and associated ECUs.
Zonal architectures in a modern vehicle
Modern vehicles utilize a zonal networking architecture to connect electronic control units.
(Source: Avnet)
Also, wireless connectivity for passenger infotainment, vehicle-to-infrastructure (V2X), and vehicle-to-vehicle (V2V) communication extend the potential for EMI. So many interconnected systems with electrically sensitive processors and long networking cabling put a higher potential on EMI artifacts being generated that could disrupt and compromise the vehicle’s operation.
Achieving electromagnetic compatibility
There are two critical aspects to EMC in an electric vehicle. The first involves ensuring that circuits capable of generating any form of EMI do not conduct or radiate interference. The second is protecting systems that are susceptible to EMI.
The wildcard is the many different scenarios a vehicle, driver and passenger might encounter, even on a short journey. There is a chance that EMI from an infotainment display becomes sufficiently high to impact other systems when, for example, a passenger operates the touch controls, thereby becoming an antenna and radiating unwanted signals.
Immunity to EMI has become a serious aspect of vehicle testing, with conformance to standards such as EU ECE R10, CISPR 25, or ISO 11451/2 essential in most countries around the world. These standards cover EMC susceptibility from sources within the vehicle and external sources. Likewise, external emissions from the vehicle are also regulated.
For the automotive electronics engineer, several established methods of achieving EMC conformance exist.
- Analyze and investigate EMI hotspots: Spectrum analyzers and specialist EMI receivers equipped with H-field and E-field probes can identify sources of noise coming from PCB traces and active devices such as switching transistors, microcontrollers and wireless modules. Circuit modeling and simulation techniques are also valuable resources, with specialist software available to model emissions and susceptibility.
- Implement EMI countermeasures: Once noise artifacts have been narrowed down to a particular component or function, EMI reduction measures include ground planes, metal shielding, passive filters, ferrite cores and shielded interconnects. Metallic gaskets and screens are necessary for some RF-sensitive and high-power applications. Likewise, circuits susceptible to EMI should also be protected. A differential signaling method is popular for many automotive networking applications due to its inherent immunity to EMI; however, maintaining signal integrity is crucial.
Spectrum analyzer with a near-field probe measuring EMI
A spectrum analyzer with a near-field probe measures EMI from a microcontroller board. (Source: Robert Huntley)
- PCB design and mechanical enclosures: Careful PCB design is a crucial aspect of EMC, with specialist planning PCB layout and resources engineers can follow. Where possible, using metal enclosures, shielded interconnect and decoupled power supply rails greatly aids in achieving compliance with the required standard.
Achieving EV electromagnetic compatibility
There are no shortcuts to achieving compliance with internationally recognized EMC standards. The route to success depends on starting with careful engineering design decisions and a thorough understanding of fundamental techniques. This article introduced the basic concepts of EMI, ESD and EMC, together with some initial checklist items.