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EETE NOV 2015

Automotive Electronics More power magnetics for less polluting cars NBy Patrick Fouassier owadays, the market of hybrid and electrical vehicles (HEVs) is growing quite fast. These are alternative solutions to common thermal engine cars to reduce the global pollution, especially in terms of rejected CO2 or other NOx (nitrogen oxides) pollutants as well as toxic thin particles. Such new models require more and more power electronics inside, not only for the electrical motor supply, with speed and torque control through a power inverter, but also for battery chargers and stable in-car continuous low-voltage (LV) power supplies. For electrical and full-hybrid vehicles, onboard high-voltage (HV) batteries (200-450V) are firstly used to supply the electrical motor (power train). This source is also used in the vehicle to feed the whole set of embedded electrical or electronic equipments (lamps, air conditioning system, GPS system, radio-set, electronic computer units…) that require only 12V to 14V low voltage (10-16V in the extended range). As for the electrical car, the plug-in hybrid version enables the charging of the battery through an external power cord connected to the mains. In terms of electronic power stages within the car, we consequently Fig. 1: Expected trend in HEVs from 2013 to 2024. find an AC (alternative current) to (direct or continuous current) DC battery charger and a DC to DC converter. The first equipment is dedicated to charge the batteries from the mains 50/60Hz network. Its power range varies from 3-4kW (complete charging in 7-8 hours) to 6-7kW (approx half-a-day charging) when plugged to the usual 1-phase domestic network. The power can be increased from 11-22kW (from the AC 3-phase network) to 50kW (DC network) for ultra-fast 30-60 minutes charging but it requires special charging stations to be installed through the cities. This is still a limiting factor in the devolvement of HEVs. Of course, Governments’ incentive policies in this would still help to make the park grow. The second power module is used to supply in energy all the electronic devices present in the vehicle (air conditioning system, radio, headlights…) from the HV batteries. The corresponding power range depends on the car size and needs in energy. It can vary from 1.6kW for small electrical city cars to 3-4kW for full-hybrid medium to big sedan, estate or SUV cars. As well as for the battery charger, a reinforced isolation is mandatory between high-voltage live parts and the end low-voltage with which the user can be in direct contact through conventional 12V plugs like the cigarette lighter socket. A third possible onboard power application that requires a DC/DC electronic converter concerns the mild-hybrid system which is the coming improvement of current Start&Stop systems. Better than just launching the thermal engine at every start, it enables the car to operate like an electrical vehicle up to a 20km/h speed before the thermal engine takes the lead. The topology is based on a starter-generator electrical motor coupled to the train and also to an additional 48V Lithium-ion battery for interim energy storage. The small electrical motor can also boost the engine during a high acceleration phase. On the other hand, it can supply back energy to the battery during regenerating breaking. Additionally, a DC/DC 48V/12V converter is used to ensure the interoperability with the lowvoltage 12V electrical network. Based on such a principle, the announced CO2 emission reduction is so interesting (up to -30%) that this system should become a must for any next generation of cars. Patrick Fouassier is Inductive Components R&D Manager at Grupo Premo – www.grupopremo.com Fig. 2: New onboard electrical networks and power supplies of several kW are key in HEVs. 22 Electronic Engineering Times Europe November 2015 www.electronics-eetimes.com


EETE NOV 2015
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