01 Jun 2011 09:06:57
Electric vehicles become electronic
Electric vehicles become electronic
By Dr Peter Harrop, chairman, IDTechEx
About 80% of the value of a military jet aircraft lies in the circuitry, up from almost nothing a century ago. Civil airliners are about 50% electric and electronic, whereas the family car is around 30% so far, all these percentages steadily rising. The point is that an aircraft has far more than the radar, communications and other instruments accessed by the pilot: it is a sea of sensors, fuel controls and servo systems in the engines, wings and elsewhere. Even the family car adds much more than the satnav, phone, proximity sensors and other electronics directly assisting the driver, the MEMS accelerometer controlling the air bags being just one of an increasingly huge number of out-of-sight safety and other measures controlled by circuitry.
Electric vehicles fill with circuitry
The advent of hybrid and pure electric vehicles accelerates this trend to more and more circuitry. It is well known that the traction battery pack can be up to 50% of the cost of an electric vehicle whether land, water or airborne. Less known is the fact that this battery pack can have as little as 50% of its value lying in the cells. Lithium Balance is therefore taking a new approach to these battery management Systems BMS. Electric and electronic circuitry monitors cell temperature, protects the cells from overload, stores and provides power surges with ultracapacitors, converts energy harvesting and charger station inputs into the appropriate DC currents and voltages and manages shut down on impact, fire, cell runaway or other excursion.
Electronics takes over motors
It is not just the traction battery that is becoming an electronic device. Traction motors have become mainly AC induction rather than DC, though DC motors are still favoured for high speed as with electric aircraft and high power as with buses and many in-wheel motors are DC. Adoption of AC motors started with golf cars and forklifts and now it is true of most of the leading electric cars from GM. BMW, Fiat, Ford and others, with Toyota also switching over for new models. In this way, the Tesla Roadster is said to achieve a battery-to-wheels efficiency of 88%—three times better than a conventional car. Other reasons include inherent safety, avoiding the need for permanent magnets and therefore scarce neodymium and improving reliability and durability. They also provide regenerative braking and the equivalent by air and sea, without extra parts. An induction motor can be cooled passively and often dispense with the radiator, cooling fan, water pump and associated plumbing. Siemens and AC Propulsion are among the leading AC traction motor suppliers.
AC motors are more easily programmable and that is important as in-wheel motors become more popular, reverse is simple to provide and installation is relatively easy. However, although the AC induction motor has simpler construction and lower cost than the most common equivalent series DC motor and is very reliable, and available in a great variety of the sizes and working voltages, higher power models usually have higher voltage and lower current than DC motors. This can lead to improved efficiency of power distribution but there are challenges in such circuitry.
DC traction motors are still used for high performance such as best acceleration from zero and for disk shape in wheels etc. For example, the SWIGZ.COM Pro Racing team has recently set a top speed record for an electric motorcycle of 190.6 mph in the Mojave Mile Shootout powered by a DC motor from UQM Technologies. The nose wheel motor that will make airliners into electric vehicles is being developed by DLR German Aerospace Center and it is DC for performance. Nonetheless, AC motors are rapidly acquiring these capabilities too. The Tesla Roadster's 0 to 60 mph (0-97 km/h) acceleration time is 3.9 seconds. Indeed, Evans Electric in Australia is preparing to launch an in-wheel AC motor system that will deliver a total of 280kW and a 0-100km/h time of less than three seconds.
The complexity and cost of the inverters for AC motors have largely been overcome. In effect, commutators in DC motors are being with replaced by circuitry in DC electric motors – another part of the move from plumbing to circuitry in electric vehicles. In parallel with these changes, the control electronics of the vehicle is becoming more sophisticated and capable – more electrics and electronic circuitry.
Energy harvesting circuits multiply
The temperature of the motor and exhaust of a hybrid vehicle will soon be harvested into electricity by thermoelectric circuits and there is interest in both cooling and heat harvesting circuits on batteries and electric motors. Meanwhile, their temperature is monitored. The interest of Fiat in autonomous lighting clusters in cars is part of the move to wireless circuitry with local harvesting and printed electrics and electronics to save power, weight and space.
Simplifying the bird's nest of electronics and electrics
So how do we improve the ever larger bundle of wiring and circuits that constitute the electric vehicle of the future? Rogers Corporation replaces the bent metal of copper power conductors with its Directly Bonded Copper DBC on ceramic. Lower power and signals are increasingly handled by fully or partially printed electronics. Eventually much of the printed circuitry, laminar lighting, photovoltaics, wide area sensors and so on may form smart skin on the vehicle or at least the battery pack. This has the advantage of self cooling not just cost, weight and space.
T-Ink has already made overhead and dashboard control clusters using conformal printed and laminar lighting, actuators etc on top of each other – plywood electronics if you will. This will soon appear in a leading electric car saving up to 40% of space, weight and cost over conventional mechanical/electric devices, while improving weatherproofing and reliability. The inks literally stretch to shape as the subsequent plastic structural part is moulded. T-Ink is raising $20 million in order to go mainstream on this capability, even replacing the kilograms of expensive copper wiring throughout electric vehicles with printed conductors on tape.
Flexible Electronics Concepts is producing innovative concepts and samples of printed electronics and electrics and Daimler AG researches smart fabrics. The next generation traction battery cells from Oxis Energy will be printed or use printing-like processes as do the flexible, conformal CIGS photovoltaics on Kopf Solarschiff solar boats.
Most of the organisations mentioned in this article are presenting at Electric Vehicles: Land, Sea & Air Europe 2011 taking place in Stuttgart, Germany on 28–29 June. The full event will include a two-day conference, an exhibition, seminars and optional visits to regional centres of excellence for electric vehicles on the day before and after. There will also be an investment seminar and an awards ceremony.
For information on either event or to apply for a press pass, please contact Cara Harrington.