Future-ready Wire Harness: Page 3 of 4

April 29, 2019 //By Óscar Ciordia, KDPOF
Future-ready Wire Harness
In the cars of the future with their pronounced dependence on the safe functioning of electronic circuits, electromagnetic interference fields represent a real challenge. But there are strategies and techniques that promise to remedy the situation.

Noise Propagation in HEV/EV Powertrains

The powertrains of hybrid electrical (HEV) and electrical vehicles (EV) require multiple electronic units placed all around the car. These Electronic Control Units (ECUs) regulate and control the electrical flow of the energy between the batteries, converters, and motors/generators. The energy flow and conversion generate electrical noise which will affect other areas of the car like the infotainment or navigation systems today and the autonomous control systems tomorrow.

Connecting the ECUs optically isolates all noise within the ECU that originates it, avoiding its propagation to all the other ECUs dispersed all over the car. It is very difficult and expensive to try to achieve a similar isolation with a copper-based network. This translates into a longer engineering development cycle and a more expensive and complex ECU, which may then again turn out in lower reliability.

Fig. 2: Electromagnetic noise in a hybrid prowertrain

Fault Protection in 48-/12-volt Systems

Mixed 48-/12-volt energy systems will be the mainstream in next generation HEVs and PHEVs (Plug-in HEVs). 48 volts are reserved for "hungry" electrical modules like starters, alternators or battery modules, while 12 volts are dedicated for the more "delicate" electronic modules like Infotainment or ADAS processing units. Both domains share the same ground system, the car chassis. The ECU in the 48-volt domain is designed with electronic components sized for such voltages. These components are typically rated to withstand more than 70 volts. The 12-volt ECUs are designed with electronic components that typically support up to 60 volts. In case of an event like a loss of ground in a 48-volt ECU, and if there are non-galvanic isolated links between the 48-volt and the 12-volt domains, there will be an electrical path between both domains. This will expose the 12-volt ECUs and their components to voltages higher than the ones they were rated to support, causing failures or a reduction of their service life. Since galvanic isolation is native in optical networks, there is no need to include protections to prevent such events or design the 12-volt ECU to withstand potential events at 48 volts or higher.

Fig. 3: BMS failure modes

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