Types
EMI falls into distinct categories – emissions and immunity – both conducted and radiated. Emissions need to be considered concerning their effect on internal systems, other vehicles and the immediate environment in general; and conducted EMI can come from outside via charging stations, as well as from internal systems. Radiated EMI can originate from a car’s own communication systems, as well as externally from other vehicles or from high-power sources such as broadcast transmitters.
Conducted interference, in the form of extraneous communication signals or noise, can be split further into ‘common mode’ (CM) and ‘differential mode’ (DM). DM interference is between connections and their intended current return path. CM interference appears on electrical connections with respect to the local ground or chassis and can be difficult to identify and control (Figure 2).
In addition, increasing use of plastic and carbon-fibre panels means that the classic metal chassis cannot be guaranteed as a screening ‘cage’ or even as a low impedance overall ground.
Mitigation
Designing-in good EMC performance is an obvious point and simulation tools can help in this process. But as well as demanding a high level of emissions and susceptibility performance from components and modules, it is also important to consider interconnections, grounding and shielding and, naturally, compromises will be required in terms of cost and weight.