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A consortium led by Prodrive is developing a technology for electric and electric hybrid vehicles that will reduce the weight and space taken by the electrical power system.

The three-year project to develop a flexible DC-DC converter is supported by investment from the government-backed Technology Strategy Board.

Prodrive is joined by Manchester University, Raytheon Systems, Scisys, International Transformers and the Tata Motors European Technical Centre.

The first year of the project will be devoted to fundamental research, followed by two years of application and development, leading to a driveable demonstration car by the end of the third year; market introduction is said to be five to seven years away.

Current practice is to integrate DC-DC converters into the power management system to step down or step up the battery voltage to meet the needs of different devices such as traction motors, cabin electrical systems, fuel-cell stacks or supercapacitors.

In complex architectures, this requires several converters.

A single, flexible converter will save cost, weight and package space, enabling vehicle manufacturers to move more easily to the next generation of sophisticated plug-in and range-extended hybrids.

Pete James, Prodrive’s technical specialist, said: ‘Existing hybrids, such as the Toyota Prius, need one DC-DC converter for the traction motor and another for the vehicle’s 12V system.

‘In future, there will be further voltage steps for supercapacitors or fuel cells; it isn’t viable to keep adding extra converters for every additional voltage.

‘Having worked hard to reduce the cost, weight and size of battery packs and motors on hybrid vehicles, manufacturers are clearly unwilling to see those gains swallowed up by growth in the power management hardware,’ he added.

The flexible converter, being developed to solve this problem, will have to be capable of handling multiple voltages simultaneously on both the input and output sides, while achieving conversion efficiencies equal to the best single-range converters currently available.

Prodrive specialises in the development and integration of electric and flywheel hybrid systems and future powertrains.

According to James, the company takes a whole-vehicle approach by concentrating on the the control systems, architecture, strategy and techniques for efficiency enhancement.

A DC-DC converter is an electronic circuit that converts a source of direct current (DC) from one voltage level to another.

This is said to be important in hybrid and electric vehicles because the battery cell voltage varies with state of charge, which would cause vehicle performance to vary with battery state of charge without a DC-DC converter to maintain the voltage level.

Generator charging voltage varies with speed and would, without a converter, present a variable charging voltage to the battery that would affect battery life and limit the practical speed range in which regenerative charging was possible.

Switched DC-DC converters convert one DC voltage level to another by storing the input energy temporarily in inductors and capacitors and then releasing that energy to the output at a different voltage.

Physically small inductors and capacitors can be used by operating at high switching frequencies; high efficiencies are possible when using high-power, high-frequency devices such as insulated gate bipolar transistors (IGBTs).

A switched DC-DC converter regulates the output voltage, presenting a constant voltage to the output device (such as a traction motor drive).

While most DC-DC converters work in one direction only, hybrid and electric vehicles require bidirectional control to recover energy from regenerative braking.

Bidirectional DC-DC conversion provides a constant supply voltage to the traction system, stepping up the battery voltage during motoring operation and providing a controlled charging current to the battery during regenerative braking.

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