Choke coils made from compacted surface-insulated soft magnetic composite (SMC) iron powders have been produced by Sumitomo Electric Industries Ltd (SEI) in Itami, Japan, for a number of years for use in fuel injectors in clean diesel engines. Now the company reports that it has optimised the composition of the SMC material so that it can be applied as dust cores in choke coils for the electric motors in hybrid and electric vehicles. The new SMC dust cores are designed to increase the capacity of in-vehicle power devices, whilst at the same time reducing the size and weight of the power device.
A report in SEI World states that compared with conventional dust cores, the newly developed cores can achieve volume reduction of up to 50% and can reduce the need for coil copper wire by approx. 30%.
The company states that there is a trend towards higher-power motors (operating at higher voltage and current) for use in environmentally friendly automobiles such as HEVs and EVs. This is to provide driving performance comparable to that of conventional gasoline-powered cars, as well as fuel economy improvements, and to increase consumer acceptance of HEV and EV vehicles.
In order to increase motor power, various converters are required; for example a step-up converter (power transformer) that boosts battery voltage and, in a plug-in hybrid vehicle, a voltage converter to supply power to the battery from the electric utility grid.
The SMC choke coil incorporated in these converters is used for electrical-magnetic energy conversion and current noise removal (for rectification). SEI dust cores have successfully increased flux density by compacting the SMC iron powder to high density. A choke coil incorporating this dust core increases the operating frequency range of high-current power devices from the conventional 10 kHz to 300 kHz, substantially improving conversion capacity. Moreover, in comparison to conventional ferrite materials, the newly developed dust core also increases operating flux density.