The winner of this year’s automotive category, and the winner of the C2I 2019 Grand Prix trophy, is a UK developed magnet-free electric motor that holds huge promise for the growing electric vehicle sector.
Collaborate To Innovate 2019
Category: Automotive
Winner: Magnet Free Traction Motors for Commercial Vehicles: HDSRM
Partners: Advanced Electric Machines Limited with Tevva Motors, Newcastle University, Motor Design Limited
Sponsor:Comsol
A new, magnet-free electric motor design promises to combine the performance of existing traction motors with greater sustainability.
The culmination of six years of research, the High Density Switched Reluctance Motor (HDSRM) has recently gone into production and will be powering commercial vehicles on the road within months.
The project is led by Advanced Electric Machines (AEM), a spin-out company from Newcastle University, in collaboration with commercial vehicle maker Tevva Motors, the university itself, and software specialist Motor Design.
Among the motor’s main attributes is the elimination both of rare earth permanent magnets and copper, both of which make end of life disposal more difficult.
The motor is expected to be used in a wide range of applications, but initial development has focused on the commercial vehicle market. Commercial vehicles have to cope with higher utilisation than passenger cars. They often operate at the peak of their performance range for hours at a time, covering a large number of motorway miles. A robust technology which can operate at peak efficiency for long durations is therefore needed.
The commercial vehicle sector is also heavily focused on total cost of ownership. AEM believes that successful electric vehicle technologies will be those that provide cost savings as well as environmental benefits. This means taking into account efficiency in operation, the cost of servicing and disposal costs.
Up to now, electric vehicles have used permanent magnet motors. Advanced Electric Machines chief executive Dr James Widmer said: “It struck us that the automotive industry was heading down the road of building future electric vehicles using materials with associated problems in the short, medium and long term.” These include rare earth elements used in permanent magnets, as well as copper for the motor windings.
Advanced Electric Machines chief executive Dr James Widmer
The idea for the HDSRM arose from a PhD thesis in the late 2000s and “appeared to have real potential, especially for commercial vehicles”, said Dr Widmer.
Switched reluctance motors have existed almost as long as the internal combustion engine, but have suffered from weaknesses in performance which have limited their use in electric vehicles.
Unlike common DC motor types, in a switched reluctance motor power is delivered to windings in the stator rather than the rotor. This simplifies mechanical design because power does not have to be delivered to a moving part.
The rotor is made of a “soft” magnetic material such as laminated steel, with projecting magnetic poles. The stator also has a number of poles. When power is applied to the stator windings, the rotor moves to align the rotor pole with the nearest stator pole. To keep the rotor moving, an electronic control system switches on the windings of successive stator poles ahead of the rotor, so it continues to rotate.
However, switched reluctance motors gained a reputation for being noisy. They also suffered from torque ripple – fluctuations in torque as the rotor rotates – which made them unsuitable for traction applications. They required different power electronics from permanent magnet machines to drive them, which, without economies of scale, were expensive.
AEM’s breakthrough, the subject of a patent, has been to make it possible to drive the SR motor using the same power electronics as a permanent magnet motor. And although it appears to the power electronics as a standard three-phase motor, it is in fact a six-phase design, which solves the torque ripple and noise problems.
The switched reluctance motor is more sustainable in three ways, says Dr Widmer.
First, environmentally, the mining and refinement of rare earth elements pose significant problems if not properly managed, and also produce large quantities of carbon dioxide. Second, China controls more than 90% of the world’s supply of rare earth minerals. Third, rare earth elements are expensive – typically $100/kg (a motor for a vehicle such as the Nissan Leaf needs around 2kg), and prices are volatile, particularly given the current US-China trade war. “So our motor provides like-for-like performance, environmental advantages and cost savings,” says Widmer.
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