Inductive components are key elements in electric cars

23rd March 2009

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Batteries, energy converters and electric motors are the components which will power up the cars to a new technology level. To power up all the auxiliary electronics inside the cars, a 1.5kW to 3kW DC-DC converter is used. This converter must isolate the 14 VDC voltage output from the high voltage 400V batteries to protect users from electric discharges. The key element to perform this task is the high power transformer. This transformer must withstand a 3000 V isolation level during one minute in a 20 square centimetre converter size. Also the current passing through this inductor is very high, from 90 to 200 A, with minimum power losses, no more than 30W. With these restrictions, old inductive wire wound manufacturing technologies are obsolete, and here is where PREMO offers the new HPT series.

The HPT series has been developed with this target in mind, the auxiliary dc-dc converter that power up all the electronics in the car. In a profile size of only 33mm and with encapsulation technology that assures the highest isolation level (up to 5kV), the HPT transformer is able to perform with very high efficiency, typical 99%. Against the efficiency of the classic wire wound technology, this means in the life of a medium-level car a 20% less of petrol wasted per year and same level of CO2 emissions savings to the atmosphere.

In the micro-hybrid implementations or start/stop systems, a smaller dc-dc converter, uses the energy from the current batteries (14V) to charge a capacitor and power up an electric motor integrated in the transmission belt. The system stops the gas engine automatically in the traffic lights or short-stops of the car, reducing the gas consumption and CO2 emissions. The power level is up to 750W (12V / 65Amp) using different kinds of topologies (boost, buck, cuk, push-pull, etc).

This converter has a very high restriction in EMC efficiency. Due to high switching frequency operation (greater than 200kHz), no switching noise can came out from the converter to the rest of the car, to protect the rest of the electronics in the vehicle from disturbances and interferences that may affect safety. Therefore, it is mandatory to include high current differential inductors at the converter output in order to filter the switching frequency harmonics. The inductance value needed is from 1 to 4uH with saturation levels up to 70 Amps.

Again, size and weight limitations are high, inductors with current levels of around 70A must fit in profiles of 25mm. This means 11 A by square centimetre. New ideas and developments are needed to perform this filtering task. PREMO develops these kind of filtering chokes totally custom made to fit in small dimensions (25mm x 25mm x 25mm), 35 grams of weight and lowest DC resistance (0.5 mOhm) with the best EMC performance due totally close magnetic field construction, avoiding to generate any noise outside the converter.