Toroidion super car: a challenge for power electronics
Toroidion electric car’s release in Monaco 2015 attracted huge international attention. Its promised power of 1 megawatt, or over 1 300 hp, ferocious acceleration and operational range of 500 km left the experts' jaws open. The father of the car idea, Pasi Pennanen, has made a long career in design tasks with cars like the Formulas, Jaguar, Aston Martin and Honda. Pennanen needed experienced experts for every component to design the technology of the car.
Let’s define some basic concepts before having a closer look at Toroidion.
”Electronics is all about signals, power electronics is all about energy. Power electronics is built on switches”, summarizes Heikki Mentula. He has got over 20 years of experience in designing power electronics.
Power electronics is based on using semiconductor components as a switch, usually controlled by microelectronics. In this project, the switching frequency of the power converter is well above the human hearing range.
Power electronics appear in most of today’s electrical appliances like power supplies of communications devices, household equipment, HVAC, elevators and energy conversion. Typical design objects for Etteplan’s power electronics include industrial electric motors, but power electronics are also needed for smaller devices. The power of a big industrial motor may reach up to dozens of megawatts; the electrical power of an economical, battery-powered industrial sensor may well be a couple of milliwatts.
Enthusiasm fires in both designers’ eyes, when the conversation returns to Toroidion. What kind of an engineer would not be interested in a megawatt-powered racing car.
Strict targets for the design
An electric motor divided into so-called sub-motors increases the amount of required power electronics. The external rotor structure of a permanent magnet based electric motor is instead rather the headache of mechanical designers.
”The biggest challenge for Toroidion’s power electronics is to combine enormous maximum power with good durability of the batteries. Additionally, both the electronics and the structures need to be as light as possible. Excellent power conversion efficiency of the electronics is also required, both to minimize the amount of wasted energy and to ensure that the cooling infrastructure does not weigh too much or take too much footprint”, lists Mentula.
”We really had to beat our brains out. All the solutions did not show up just like that”, admit both Mentula and Vuorsalo. The team is satisfied with the project for successfully achieving excellent power density.
International collaboration was used to develop a test bench for the project, to for example collect and analyse substantial amount of data needed for development of electronics and embedded software.
Control software is an essential part or power electronics. ”Besides the control electronics, we developed also all the control algorithms and embedded software needed. The motor control is based on Field Oriented Vector control developed by our team", says Mentula.
The efficiency of Toroidion’s powertrain electronics is approximately 97 percent. With the peak power of one megawatt this still means 30 kilowatts of power to be dissipated. However, the temperatures remain under control and the structures compact, since peak power is cranked from the motors only momentarily. A constant 30 kilowatts would keep a whole family house warm in freezing weather.
Compromises need to be made
Sharp accelerations and braking are characteristic for racing cars. Braking energy should be regenerated as much as possible to increase the range. Batteries, especially the energy-efficient ones, however, are far more reluctant to receive than release power.
A swift energy receiver called super capacitor was briefly considered as a solution. It would, however, have doubled the amount of electronics needed. The capacitor, electronics and related cooling elements together would have significantly increased the weight of the car, had the battery size not been negotiable.
It was therefore concluded, that the best way to achieve the targets did not include the super capacitor.
The concept was proved functional. However, a lot remains to be developed before we can talk about an actual product. There is also always room for improvement and optimization. The next big design step is waiting for investment decisions.
Simo Vuorsalo, Senior HW Engineer, Power Electronics, Etteplan