Transcript Motors, Controllers, and Regenerative Braking

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
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No brushes, no friction
No parts to replace
Position is always known

Startup is consistent
 How it works:
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Hall effect sensors are used to
determine the location of the stator
relative to the rotor
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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
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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
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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)
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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

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Meanwhile the capacitor discharges through a resistor into the battery
pack
The cycle repeats continually v  L
dl
20A
(100 H)(
)  2000V
dt
1s
Questions?