23/11/12

Multi-voltage DC-DC technology wins funding

A flexible multiport converter may replace multiple separate DC-DC converters on future hybrid and electric vehicles, saving cost, weight and space and increasing the driving range by up to 20 per cent.

The success of a research project to develop a multi-voltage DC-DC converter has led to funding from the U.K. government’s Technology Strategy Board (TSB) to develop the technology for manufacture. The converter, which provides a variety of voltages across the vehicle, uses silicon carbide to increase efficiency while significantly reducing the mass and packaging volume required compared to alternative solutions. Silicon carbide technology also has the potential for high temperature operation and reduced system cost.

‘The system is around a third the size of a silicon-based device,’ says Prodrive’s project leader Pete Tibbles. ‘The size comes down from that of a flight bag to more like a shoe box, with a corresponding reduction in weight.’

The new multiport DC-DC converter steps voltages up or down to meet the different demands of systems such as traction motors, cabin electrical systems, fuel cell stacks, air-conditioning pumps, lights and electric power steering. As hybrid and electric vehicles become more complex, conventional technology would require an additional converter for each voltage step, increasing cost, mass and package requirements. The multiport device accommodates all the required voltages from a single, exceptionally compact and light-weight unit, allowing each system to be optimised for maximum efficiency.

Conventional DC-DC converters, which use silicon-based power devices, are limited to a switching speed of around 25kHz. The new converter breaks through this restriction by using components based on silicon carbide, allowing switching speeds up to 150kHz. Faster switching allows the use of smaller inductors and capacitors and the high efficiency of the unit reduces the need for heavy and complex cooling systems.

Silicon carbide devices also have the ability to operate at higher voltages. Tibbles says this could lead to much higher efficiency from the traction motors and significant weight reduction. ‘Losses are related to I2R so higher voltages with lower currents mean improved efficiency. This ratio also applies to the growing range of other systems that are operated electrically, such as electric power steering and air-conditioning. Making optimised voltages available could increase the range of an electric vehicle by up to 20 per cent.’

The TSB-backed development group is led by Prodrive, which is also responsible for the vehicle integration, converter control system and low level embedded software. The converter is based around a highly efficient topology developed by the University of Manchester working in conjunction with Raytheon U.K., which has developed the silicon carbide devices, and with IST Power Products, which has developed the magnetic components. The consortium’s software specialist SCISYS has developed the high level vehicle interface software. The workscope includes the development of safety-critical software and establishing a potential supply chain to serve low volume programmes. Applications are expected to include cars, heavy-duty trucks, aerospace and defence. Prodrive welcomes approaches from tier one suppliers interested in taking the system into production.

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