Hanna Plesko, a doctoral student at the Power Electronic Systems Laboratory of ETH Zurich has worked out a better and less costly to produce power electronic converters for hybrid cars.
Plesko says, “It’s rumored that hybrid vehicles can improve your image, but in some cases the automobile companies have difficulties to cover their costs.” With Hollywood stars like Leonardo DiCaprio and Cameron Diaz driving up to the red carpet in their hybrid cars, hybrids have become increasingly interesting to the conventional car market. Hybrid cars in a combination of a combustion engine and an electric motor have increasingly become the focus of research projects in many universities.
Now, you see them more and more frequently the roads, but hybrid cars are not mass-produced at the levels of conventional drives as their production costs are still relatively high. Plesko’s research has developed a new concept described on the platform of her doctoral thesis that integrates power electronic functions and the electric motor, which could reduce the costs of producing hybrid cars.
Plesko asks the question, how hybrid vehicles can be constructed more cost-effectively. A substantial proportion of the costs are swallowed up by the electric motor and the power electronic energy management system, in which inverters and DC/DC converters play the fundamental role. Plesko’s approach is based on a new concept where these components, i.e. the power electronics and the electric motor perform several functions simultaneously. The multiple uses of the electronic parts and the motor also saves in the component volume needed.
In the research group “Future Automotive Power Electronics” headed by senior scientist Jürgen Biela, Plesko has developed a system for her doctoral thesis that integrates the inverter, the DC/DC converter and the electric motor functionally. In hybrid vehicle designs batteries power the electric motor, but also the radio, ventilation and the lights. The electrical drive system, for which a high DC voltage of 200 – 600V should to be converted into a three-phase AC voltage for best efficiency, while a low DC voltage of 12V is sufficient to power a car radio. Inverters, which convert the direct current into an alternating current, and DC/DC converters, which transfer the power between two of the batteries for the two voltage levels, are therefore important power electronic components in hybrid or electric vehicles. For current hybrid vehicles, these converters are located outside the electric motor.
Plesko has developed a system that integrates the inverter, the DC/DC converter and the electric motor functionally. By condensing the functions of the drive and the DC/DC converter in combination, certain electronic components and the motor lamination stack can be shared. Large quantities of such functionally integrated systems will be cheaper to produce, as fewer raw materials are needed. Beyond that, Plesko’s design is less complex, making it much easier to produce.
Plesko’s prototype uses a very small motor with an output power of 3 kW. 50 kW would have been more real world, but the test set-up was not designed for such high power levels. She is convinced that her design will also work for real engine power. Two patents have been applied for in anticipation of a license program with initial talks with one of the big car companies, but whether a collaboration will materialize remains unclear as yet.
Plesko’s supervisor Johann Kolar, a professor of power electronics points out the implementation of new concepts in the field of hybrid vehicles is often difficult for entrenched car manufacturers. The difficulty lies in bringing their traditionally dominant engineering expertise adding new areas like power electronics, storage technologies and electromechanical energy conversion for a forward-looking overall concept with excellent performance. Kolar says Japanese automobile manufacturers have assumed a pioneering role in this respect: mechanical and electrical engineers work hand in glove, resulting in a very wide range of expertise with great technological depth. This extends to the production of the automobile companies’ own power semiconductors.
Kolar expresses belief that Plesko’s new concept is a useful advancement, a position this writer shares. Whether it will make it onto the hybrid market, however, remains to be seen. But Plesko’s innovation could have interesting applications for industrial automation, robotics and the field of “more electric aircraft”, where new concepts are being developed e.g. for electric actuation of fight control surfaces and air conditioning as well as for onboard electrical energy management.
Plesko illustrates that innovation by combining roles, using component structures for multiple uses and refining the electronics to simplify and modularize the control set can have significant cost reduction potential. Hybrids are sure to be in the market for quite some time, even if battery or ultracapacitors have a major impact. But the point of the thesis is clear, significant savings from research and innovation both in building electric drive sets and the costs of operations are just beginning with much more to come.
Plesko’s doctoral thesis is due to be finished in December. “And I don’t even own a car!” she laughs.