![]() Minimizing loop area simply means keeping the forward and return pathways for any circuit as close together as possible, and this applies to everything from CAN bus and Ethernet cables to battery wiring to the bus plates in an inverter. Not adhering to the first bullet point is the one that seems to cause the most problems, though it is sometimes unavoidable when equipment grounding requirements are factored in (forming the dreaded “ground loop” – a case in which the safety regulations often conflict with the EMC ones, unfortunately). Any hole, slot or seam in a conductive surface can become an antenna, too.Don’t switch any faster than you need to for reasons of data rate (digital logic) or efficiency (power conversion).Minimize the surface area and/or shield any conductors that experience high dV/dt or are high impedance.Minimize the loop area of any conductors (wires, traces, bus bars, etc) which handle high dI/dt or are low-impedance.While this is certainly true, it’s not particularly actionable advice all on its own, as almost anything conductive can be turned into an antenna, and even some things you wouldn’t think could cause any problems can become the biggest headaches of all, such as a seam in a metal enclosure! A more useful, albeit still general, set of guidelines would be: Mencken here), and in the case of EMC issues, that would arguably be: don’t make accidental antennas. Closer in (aka the “near field”), one or the other will dominate depending on circuit conditions: E-fields arise from fast changing voltages (high dV/dt) while H-fields result from fast changing currents (high dI/dt).Īs with many complex problems, there is an overwhelming desire to look for a simple explanation or solution (echoing H.L. The distance at which this combining occurs is not formally defined, but is usually considered to be 1-3 λ (wavelengths). One key concept about EMC that is sometimes overlooked is that an electromagnetic field, or EMF, is comprised of both an electric (E) and a magnetic (H) field, which only come together as an EMF some distance away from the source (and, for a bit of trivia, with a fixed V/I relationship of 377 Ω). That’s not true, of course – it just seems that way most of the time. So far it appears that complying with the safety standards is relatively straightforward (these standards are developed by committee, after all), but for many engineers, achieving EMC compliance still seems to involve more dark art and mystic incantation than science. A similarly cavalier environment also pertained to OEM EVs in their early years, but it was only a matter of time before the safety and EMC regulations that applied to mains-powered equipment were adapted for EVs. Products like high-energy multi-spark ignition systems and custom engine management ROMs are freely available, and one is unlikely to be penalized for installing them unless the vehicle has to go through an annual exhaust emissions test. As vehicle electronics got more sophisticated, the automotive OEMs developed their own set of electrical noise and safety standards, but the focus was on such things as surges from alternator “load dump,” rather than getting struck by lightning, or making sure the infotainment system didn’t crash when the engine was revved, rather than not obliterating the reception of TV and radio for miles around (as the traction inverter in an EV could easily do if given half a chance).įurthermore, compliance with the nascent automotive safety and noise (or EMC, for electromagnetic compatibility) standards was initially a mostly voluntarily affair: no OEM would use any non-complying product, of course, but it could probably still be sold in the aftermarket. This was mainly because 12 V isn’t considered a shock hazard and cars are effectively rolling Faraday cages, so they’re well shielded against both emitting and receiving electromagnetic interference, or EMI. Posted Januby Jeffrey Jenkins & filed under Features, Fleets and Infrastructure Features, Tech Features.Įngineers who design power electronics supplied by the mains have had to contend with meeting various electrical noise and safety standards for decades now, but their counterparts in the automotive industry were mostly free to do as they pleased. ![]() EMC for EVs: Understanding electromagnetic compatibility ![]()
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