A motor controller is the component responsible for modulating the speed of the electric motor in electric vehicles and series-hybrid vehicles. It is essentially put in-line with the power supply to the motor, and is able to control the amount of current and voltage fed to the motor from nothing to wide-open throttle.
The reason this component is so expensive (Just a touch under $2000 with the required interface) is that it uses massive transistors to control the power. With a technique called PWM, or Pulse-Width Modulation, the controller turns the power supply on and off thousands of times a second to simulate a lower power level for the motor. The control is continuously variable, and can recieve a signal from a potentiometer (variable resistor) tied to the 'gas' pedal.
The reason for using PWM instead of a really big variable resistor, like an oversized light dimmer, is that resistors are somewhat wasteful. Instead of holding back voltage or current like a water valve, resistors redirect extra energy and turn it into heat. Because it's important to retain as much efficiency as possible, resistors or resistor-type controllers are not really an option.
With the Zilla controller I will be able to set current limits, both on the motor side of the controller and on the battery pack side. This opens up some interesting possibilities for range and efficiency control. I could potentially set the battery pack current very low, and keep from pulling too much energy from the batteries; in effect, reducing the ability of the motor. While not very exciting from a performance standpoint, this might be useful to keep drivers not focused on efficiency from killing the economy of the vehicle.
There are less expensive PWM
controller options out there, but I reached the conclusion that the Zilla
would be a good choice for a 'large' vehicle like mine. It is able to
provide a peak current throughput of 1000 amps. Assuming that I will have
a pack voltage of 144 volts:
For even more information on controllers, try visiting Cafe Electric, makers of the Zilla controller.