DC Motor Control
There are a number of variations of the DC motor and each
has different characteristics and requires different means of control.
A traditional D.C Motor comprises a wound stator or field,
and a wound rotor known as the armature. Voltage is applied to the armature
by means of a commutator and a set of brushes. The armature consists of
a number of discrete windings which are terminated on the commutator which
is in effect a rotary switch.The DC motor can be configured as a series
connection, shunt connection or a compound connection.
Shunt Wound DC Motors
Shunt Wound DC Motors have separate field and armature supplies.
Typically, the field voltage is supplied from a fixed supply and the armature
is supplied from a controlled supply.
Series Wound DC Motors
Series Wound DC Motors have the field and armature connected
in series so the field current and armature current are equal. Increasing
armature speed reduces the field current, reducing the induced back emf.
This results in there being effectively no upper speed limit. Extreme
care must be taken running a series wound motor with no load as it can
accelerate to destruction.
Compound Wound DC Motors
Compound Wound DC Motors include both series and shunt field
DC Motor Controllers
Most larger Industrial DC motors are shunt wound motors
requiring a fixed field supply and an adjustable armature supply.
Brushless DC Motors
Brushless DC Motors have an electronic switching "inverter"
to create the AC voltage required to establish the rotating magnetic field.
Commonly, the "field" is provided by permanent magnets on the
rotor and the "armature" is provided by a stator winding. Hall
effect sensors are used to determine the position of the rotor and this
synchronises the AC voltage applied to the stator. The brushless DC machine
does not have brushes and so requires far less maintenance than a traditional
DC motor. The speed of the brushless DC motor is determined by the electronics
and so better speed accuracy can be achieved than in standard DC motors.
The maximum size of the brushles DC motor is limited by the size an strength
of the permanent magnets that can be used.
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