Abstract
Keywords - EMC, EMI, RFI, 42/14V, Electromagnetic Measurements
Abstract - The automotive industry has to face with new demands for comfort and safety. New systems like electric power steering, electric brakes, electronic traction control or active suspensions are more convenient than mechanical counterparts. But a 14 V system wouldnt be enough to supply the needed power. The introduction of the 42 V architecture will make all of these systems possible.
The migration from 14 V to 42 V has to deal with the initial lack of 42 V components. The intermediate solution consists of hybrid architectures composed by 14 and 42 V nets working together. This configuration implies the use of a DC-DC converter working like a very-high-efficiency switching supply and generating high EMI levels.
The main radiating elements of a 42/14 V DC-DC converter are the cables to supply the power to the 14 and 42 V systems. This means that EMI measurements are only significant when the converter is installed in the vehicle with the harness involved. Component measurements are not adequate in this situation because they dont include the effects of the harness and its routing. Near-field measurements inside the car are needed.
When measuring electromagnetic interference from an electronic system, the frequency spectrum to be measured is usually unknown a priori. This is the reason why broadband antennas (as biconic, log periodic or bilog) and frequency selective measuring instrumentation (as spectrum analyzers or EMI receivers) are used. These equipments allow us to study the interference at selected frequencies to predict the effect on the other electronic systems.
To measure inside the car neither large usual antennas nor small commercial broadband probes can be used. Large selective antennas are not adequate because of its size and because of the present of a conductive cable which distorts the field to be measured. Commercial small probes are connected to the measuring system with a fibre optic link which is adequate for this purpose. The problem with these probes is that they integrate the whole spectrum and gives just a number as a result, with no information about the frequency contents.
To solve these problems a new self-made probe has been used. The probe measures at the same time, and separately, electric and magnetic fields. The frequency spectrum content is sent to an EMI receiver by an optical link so there arent problems of field distortion with extra cabling inside the car. The measurements presented in this paper have been done inside a SEAT Cordoba bodywork with an installed converter working with realistic loads. The results allow us to study the distribution of the EMI inside the car and they can be used to predict the most and the less convenient places to install susceptible electronic components.