Feature: Automotive
Achieving similar isolation in a copper-
based network is diffi cult and expensive, requiring long development cycles and more complex and, possibly, less reliable ECUs.
Fibre optics provide inherent galvanic isolation
Low weight and robustness Plastic optical fi bre (POF) cables are the most reliable solution: plastic optical fi bre withstands harsh environments, vibrations, misalignment, dirtiness, humidity, wide temperature ranges, and more. It also withstands fast dynamic bending, tight static bending and immersion in liquid. Additionally, optical Ethernet generates very low noise yet can operate in noisy environments, such as RF electronics. With optical and copper in parallel, the optical network provides ASIL-D safety architecture (Automotive Safety Integrity Level, with D being the most stringent level) ASIL-D = ASIL-B + ASIL-B. Fibre optics technology also has a
signifi cant advantage regarding weight. With weighing only 10g/m and 2 x 2.3mm diameter, POF reduces the harness weight by over 30%, compared to shielded twisted pair of copper wires (STP), where JTP copper is 13g/m and STP copper sums up to 25g/m at a diameter of 5mm.
Electromagnetic compatibility With their inherent electromagnetic compatibility, optical data networks are the best technology for new powertrains – whether fully electric or hybrid. POF is inherently immune to electromagnetic fi elds due to its inherent isolation. In many cases, optical networking has solved issues caused either by EMI/EMS or lack of galvanic isolation on copper-based networks in the powertrain of hybrid (HEVs) and electric vehicles (EVs).
www.electronicsworld.co.uk September 2021 31 T e powertrains of these vehicles
require multiple electronic control units (ECU) placed all around the car, which (among other tasks) regulate and control the fl ow of energy between batteries, converters and motors/generators. However, energy fl ow and conversion generate electrical noise, which aff ects other areas of the car, like the infotainment or navigation systems, or worse in autonomous cars. By optically connecting the ECUs, it is possible to confi ne noise to the ECU it originates in, avoiding its propagation elsewhere.
Isolation in battery management systems Propulsion batteries in H/EVs are grouped into clusters controlled by the battery management system (BMS). Although the volume of data moving back and forth between the clusters and the control module is not very high (typically below 100Mb/s), communication between them is crucial and must be very reliable. BMS links are critical to avoiding battery damage, and must be suitable to emergency situations like crashes or fi res. Optical links between the BMS control module and battery clusters prove highly reliabile, since copper-based communications create parasitic loops, which in the case of emergency events may translate into dangerous conditions for driver and occupants. For monitoring battery cells, wireless
communication is ideal, in coexistence with optical Ethernet links to connect the HV and LV ECUs.
Traditional BMS architecture
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