SPEED CONTROL OF DC MOTOR USING COMBINED
ARMATURE AND FIELD CONTROL
Mustafa Aboelhassan
Doctoral Degree Programme (2), FEEC BUT
E-mail:
[email protected]
Supervised by: Jiří Skalický
E-mail: skalicky@feec
...
SPEED CONTROL OF DC MOTOR USING COMBINED
ARMATURE AND FIELD CONTROL
Mustafa Aboelhassan
Doctoral Degree Programme (2), FEEC BUT
E-mail:
[email protected]
Supervised by: Jiří Skalický
E-mail:
[email protected]
ABSTRACT
The aim of this investigation is to describe the principle of DC motor speed control using
nonlinear combined control (armature voltage and field current). For the armature control
mode, the field current is held constant and an adjustable voltage is applied to the armature. In
the field control mode, the armature voltage is held constant and an adjustable voltage is
applied to the field. The mathematical model of a separately excited DC motor (SEDM) with
independent armature/filed control can be obtained by considering the electrical system,
electromagnetic interaction and mechanical system. Simulation models of DC motor speed
control methods and feedback control system for DC motor drives have been developed using
MATLAB/Simulink.
1. INTRODUCTION
DC motors consist of rotor-mounted windings (armature) and stationary windings (field
poles). In all DC motors, except permanent magnet brushless motors, current must be
conducted to the armature windings by passing current through carbon brushes that slide over
a set of copper surfaces called a commutator, which is mounted on the rotor.
The commutator bars are soldered to armature coils. The brush/commutator combination
makes a sliding switch that energizes particular portions of the armature, based on the
position of the rotor. This process creates north and south magnetic poles on the rotor that are
attracted to or repelled by north and south poles on the stator, which are formed by passing
direct current through the field windings. It's this magnetic attraction and repulsion that causes
the rotor to rotate.
The greatest advantage of DC motors may be speed control. Since speed is directly
proportional to armature voltage and inversely proportional to the magnetic flux produced by
the poles, adjusting the armature voltage and/or the field current will change the rotor speed.
Today, adjustable frequency drives can provide precise speed control for AC motors, but they
do so at the expense of power quality, as the solid-state switching devices in the drives
produce a rich harmonic spectrum. The DC motor has no adverse effects on power quality.
