Motors, Controllers, and Regenerative Braking
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Motors, Controllers, and Regenerative Braking THIS PRESENTATION HAS BEEN UPLOADED TO THE WIKI. Brushed DC vs. Brushless Advantages Construction is simple Implementation is simple No controller required Disadvantages Brushes cause friction Brushes wear down Startup is imperfect Position is unknown Brushed DC vs. Brushless Why Brushless is Better No brushes, no friction No parts to replace Position is always known Startup is consistent How it works: Hall effect sensors are used to determine the location of the stator relative to the rotor 3 Hall effect sensors completely determine location A computer tracks where the the motor is now and where it will be next Pulses sent to each each of three phases to move the motor to the next position Rinse and repeat Hall Effect Sensor How they work A current is applied perpendicular to the expected magnetic field When magnetic flux passes perpendicular to current, it creates a force This force displaces the electrons, creating separation of charge This voltage is related to the strength of the magnetic field What would happen if the sensor were turned so that the magnetic flux ran parallel to the current? Motor Controller Main Task Read hall effect sensors, determine location Get desired speed from user Set the next phase to occur to match that speed Extra tasks Limit acceleration Monitor temperature Regenerative Braking Regenerative Braking Basic Concept A motor and a generator are essentially the same When you apply the brakes, the motor switches into a generator The detail (the brake has just been pressed) The terminals of the motor are disconnected from power, and connected to to a inductor circuit Once current has built up in the inductor, it is shorted into a capacitor The capacitor is given time to charge The inductor circuit is reconnected Meanwhile the capacitor discharges through a resistor into the battery pack The cycle repeats continually v L dl 20A (100 H)( ) 2000V dt 1s Questions?
