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How to Reach 200 MPH on Hydrogen Fuel Cells
the_manatee writes "Ford's 999 hydrogen-powered speedster is making waves for its upcoming speed record attempt in the Bonneville Salt Flats, but details on what's actually going on under the hood have been scarce. As it turns out, there are NASCAR-style brakes, steering, and suspension components, along with 16 Ballard Mk902 fuel cells that produce 350 kW of electricity. All that juice spins up a 770-hp motor and the rest is (hopefully) history. One final ingredient: 400 lbs of ice for cooling, which will melt in seconds once the car gets up to speed."
Installing a motor in every wheel is intuitively a nice idea. Unfortunately, electric motors have a great deal of inertia. At high speeds, the effects of this rotational inertia dramatically affect the stability of the vehicle when it hits a bump.
At lower speeds, vehicle performance is maximized when the motors torque/speed curve is matched to the maximum speed of the vehicle while simultaneously matching motor diameter to wheel diameter. Unfortunately, the wheel diameter, tire diameter, motor diameter, and peak motor RPM rarely agree. Thus mechanical gearing often helps.
For this application, they will be using an induction AC motor. This is not a synchronous AC motor. Induction motors eliminate the permanent magnets of Brushless DC motors and the rotating electromagnets of synchronous motors. Replacing the rotating magnets with a "squirrel cage" results in a small net weight savings, and a considerable inertia reduction.
In all likelihood the locomotives that you are talking about are also using induction motors. At locomotive power levels, induction motors allow for some nice tricks that blur the line between a conventional induction motor and a conventional synchronous motor. Specifically, if you have a separate power source / load for the inductive rotor, the resulting motor design looks like a synchronous motor, but is really a specialized induction motor. GE even has patents on this technology.
The power research group at my local university even did a research contract with a major multinational on how to exploit induction motor properties for use in new electric car designs. For weight sensitive applications (like a car) over 1 kW, almost all the motors are induction. Even for high-accuracy applications with servo capability, like CNC machines, all the large spindle motors are induction motors. With modern control electronics, an induction motor is all you need.