The performance characteristics of separately excited DC motors and the development of power electronics, allowed variable speed manufacturing equipment that controls virtually every important engine parameters, allowing their use in all types of industrial applications. Such applications range from engine speed control to position control (servo drives).
DC motors have numerous drawbacks, as they need continuous power feeds. In addition to the same power, these machines are of dimensions and higher costs than induction motors and require more maintenance due to the switch. The advantages of DC motors is that they can provide high starting torque, its speed is great margin above and below the nominal values and regulatory process is easier and cheaper than those for induction motors.
For the reasons stated above, are still using DC motors and therefore the variable speed motor for this type have been further developed especially in regard to their stage of control (computer communications, digital panel programming Auto-tuning, etc..), because its power amplifier (controlled rectifier using thyristors or transistors) remains unchanged.
SPEED VARIATION
From the above equation is the speed n depends on:
Therefore, controlling the speed of a DC motor is achieved by varying the armature voltage (Va) or by variation of the magnetic flux field (proportional to I f).
Until the advent of electronic speed DC motor, the regular forms of speed were by procedures listed below:
a. - by varying the armature terminal voltage Va:
Control voltage rheostatic armor. Electric traction.
Using a booster / reducer.
Modifying the coupling of two engines through gears.
Ward-Leonard system.
b. On the variation of flow-field
Rheostat regulation field.
INVESTMENT OF MONEY OF DC MOTORS
The reverse rotation of a DC motor is needed in many applications. To change the direction of rotation is to vary the magnetic field in one of two circuits of the motor (armature or field). In practice, the variation of the magnetic field direction is the armature winding as shown in Figure 1. In this case the switch we can change the direction of the polarity of the DC voltage received by the armor and thus change the direction of motor rotation.
Figure 1
DC MOTOR BRAKING
The braking or quick stop is one of the important moves to make in the control of a motor. This goal can be achieved by:
Braking energy recovery, also known as regenerative.
Dynamic Braking, also known as dynamic.
reverse current braking armor.
