Linear Induction Generator
These magnetically couple into the rotor and generate electrical energy by slowing the rotor slightly. The power from this is used to drive the track electronics. They are only used on the track, the turnaround sections can be powered directly.
The simplest design is simply a wheel with permanent magnetic poles on it, that puts a field through the rotor as it passes. The wheel will be pulled by eddy currents, and the shaft can drive a generator/rectifier.
More complex designs involve a dynamo-type structure.