Electric Motor ComparisonOctober 3, 2007
I want to take what I did with battery specs, and do a quick review of the various electric motors being planned for HEV/PHEV/EV use. I’ve sampled the top spec motors from five manufacturers: UQM, AC Propulsion, Raser Technologies, PMLFlightlink, and Tesla Motors. The two really defining criteria are power density and efficiency. Increased power density reduces the weight and form factor of the motor needed for the application, and high efficiency helps reduce overall energy losses.
(click to enlarge image)
Data efficiency for several of the motors is not publicly listed. However, power density is fairly easy to calculate, provided one includes the mass of the motor controller, whose size varies along with the motor. Some caveats: for the Raser Symetron, their controller modules are only rated for 180 kW, so I played it safe, and included the mass for two controllers to roughly equal the max output of their most powerful motor.
Tesla also does not list the weight of their PEM (power electronics module), so I could not include them on the graph.
That said, the claimed power density of the Raser and PML Flightlink motors is staggeringly above that of more conventional systems. What’s more, the output has been achieved using two different approaches – brushless DC, and AC induction.
Some important considerations, however:
1) PMLFlightlink’s technology is intended for in-wheel motor use. Assuming PML’s claims are true, the fact that they are accomplished using permanent magnet technology probably means that the motors aren’t scalable beyond their current size, lest they suffer from the efficiency losses that come about through hysterisis and eddy losses. As engineers from GM, Aerovironment, and Tesla have frequently pointed out, AC induction motors are best suited for larger, more powerful motors. Then again, many cars won’t require power needs beyond 120kW.
2) The deal with Raser Technologies is essentially one of “put up or shut up”. The company is legitimate enough to have marketed their alternator technology to Wilson, but we’ve yet to see any substantial independent verification of their claims.