Replying to
Alistair, who said...
"Okay you two, this is how it works, and you better be paying attention, I heard this is going to be on the midterm. These UW Mailing Services Bullitt bikes are running Grin Technologies Phaserunner motor controllers which is a big deal, because they use Field Oriented Control (FOC) commutation, NOT the trapezoidal method of commutation that you find on cheaper e-bikes that run budget motor controllers. These Phaserunner controllers are doing a lot of number crunching, calculating what voltages should be applied to each of the motor's three phases, based on throttle position, vehicle speed, and feedback from the Hall effect motor position sensors. The motor controller generates the necessary Pulse Width Modulation signals (digital square waves with varying duty cycles) in order to realize the required phase voltages, and the Pulse Width Modulation signals control the gates of the H-Bridge Mosfets. These Mosfets switch on and off at high frequency in order to create the effect of the average voltage on each phase that corresponds to the desired sinusoidal waveform. This is how the controller synthesizes the necessary three phase alternating current wave forms, from the single phase (battery supplied) direct current. Now, don't forget that Field Oriented Control is also known as "Vector Control" which relates to the fact that FOC transforms the three phase currents in the stator into a rotating reference frame (via Clark and Park transforms) that aligns with the axis of the rotor's magnetic field. In this way the controller can keep the Direct Axis Current at zero, and put all the current into the Quadrature Axis "vector", effectively ensuring that the magnetic field of the stator is always at 90 degrees to the rotor's magnetic field. This allows the motor to produce maximum torque at all times and also allows very precise torque control, better efficiency, and smooth operation, even at low speeds. Ok, so you guys understand how this all works now? Great! Now lets fly over to the Henry Art Gallery. It's about the time that the woman who feeds us that delicious cat food will be there. Word.