Electric vehicles play an ever increasing role in our lives. Once restricted largely to the industrial sector, the number of on-road EVs continues to grow as technology improves and a new generation of vehicles like the Nissan LEAF and Renault Twizy are launched. As interest has grown, major advances in technology have been achieved to improve the performance of EVs. Nowhere is this more obvious than in electric drivetrains and specifically the technology that ensures the effective delivery of power from the battery to the motor: the motor controller, or ‘brains’ of the vehicle.
The vast majority of today’s motor controllers are AC controllers, controlling either AC induction (asynchronous) motors or PMAC motors (permanent magnet synchronous), like those used in the Nissan LEAF. While DC motors were once the technology of choice, AC motors are now the norm due to their high efficiency, improved performance and low maintenance. The widespread adoption of AC motors has been driven by advances in microprocessor-based motor controllers, which are increasingly powerful, intelligent and lightweight, like the new Sevcon Gen 4 series.
While DC motors were once the technology of choice, AC motors are now the norm due to their high efficiency, improved performance and low maintenance.
In recent years, major improvements have been achieved thanks not only to advances in power electronics – which has resulted in more powerful motor controllers with lower losses, lower costs and high reliability – but also state-of-the art microprocessor controls, delivering better torque accuracy and higher efficiency. Such characteristics are essential given the increased performance demands of today’s AC motors which, unlike DC motors, are three-phase and need more complicated electronics and far greater processing power. More feedback is typically required, making real-time tracking of the motor more complex.
Today’s motor controllers are also helping to recover energy from the motor and send it back to the battery, recharging the battery as the vehicle slows down. Known as ‘regenerative braking’, this is helping to increase the range of the vehicle.
An additional advantage is the level of miniaturisation that has been achieved through the use of lightweight materials – a major benefit in on-road EVs where space is at a premium. Silicon technology improves year-on-year, creating smaller, more efficient devices. Promising developments in solid state materials such as silicon carbide or gallium arsenide could lead to further miniaturisation.
In future, we are also likely to see greater integration between motors and controllers. Rather than having separate motors and controllers, it is likely they will be combined – perhaps with auxiliaries such as DC/DC converters too. The overall benefits of this are a system that is more compact with simpler electrical wiring and ultimately better on-road performance.
It is likely that the pace of change in motor controller and drivetrain technology will continue to increase to meet the performance demands of an emerging market.
Improvements in this area will make installation easier, as there will be fewer connections and the performance of the motor and controller will already be optimised ‘out of the box’. For high voltage systems, high level integration means less interconnect cables running around the vehicle, minimising high voltage areas on a vehicle, making a safer overall system. Another area of change could be in the development of electric drivetrains using advanced switched reluctance technology. This would reduce the reliance on rare earth metals used in current EV motors.
It is always difficult to predict exact trends in electric vehicles, particularly as higher volume production occurs. However, it is likely that the pace of change in motor controller and drivetrain technology will continue to increase to meet the performance demands of an emerging market.
The opinions expressed here are those of the author and do not necessarily reflect the positions of Automotive World Ltd.
Dave Lamb is Global Applications Engineering Manager at Sevcon. For more information about motor controllers visit www.sevcon.com
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