July 15, at
Speed control is a different concept from speed regulation where there is natural change in speed due change in load on the shaft. Speed control is either done manually by the operator or by means of some automatic control device. One of the important features of DC motor is that its speed can be controlled with relative ease.
So speed can be varied by changing Terminal voltage of the armature V. External resistance in armature circuit Ra. The first two cases involve change that affects armature circuit and the third one involves change in magnetic field.
Therefore speed control of DC motor is classified as Armature control methods Field control methods. This is the most common method employed.
Here the controlling resistance is connected directly in series with the supply of the motor as shown in the fig. The power loss in the control resistance of DC series motor can be neglected because this control method is utilized for a large portion of time for reducing the speed under light load condition.
This method of speed control is most economical for constant torque. This method of speed control is employed for DC series motor driving cranes, hoists, trains etc.
The combination of a rheostat shunting the armature and a rheostat in series with the armature is involved in this method of speed control. The voltage applied to the armature is varies by varying series rheostat R1.
The exciting current can be varied by varying the armature shunting resistance R2. This method of speed control is not economical due to considerable power losses in speed controlling resistances. Here speed control is obtained over wide range but below normal speed. Armature terminal voltage control: The speed control of DC series motor can be accomplished by supplying the power to the motor from a separate variable voltage supply.
This method involves high cost so it rarely used. Here the field flux can be reduced by shunting a portion of motor current around the series field. Lesser the diverter resistance less is the field current, less flux therefore more speed.
This method gives speed above normal and the method is used in electric drives in which speed should rise sharply as soon as load is decreased.
Tapped Field Control This is another method of increasing the speed by reducing the flux and it is done by lowering number of turns of field winding through which current flows.
In this method a number of tapping from field winding are brought outside. This method is employed in electric traction. An increase in controlling resistances reduces the field current with a reduction in flux and an increase in speed.
This method of speed control is independent of load on the motor. Power wasted in controlling resistance is very less as field current is a small value. This method of speed control is also used in DC compound motor.
Limitations of this Method of Speed Control Creeping speeds cannot be obtained. Top speeds only obtained at reduced torque. The speed is maximum at minimum value of flux, which is governed by the demagnetizing effect of armature reaction on the field.
Field Voltage Control This method requires a variable voltage supply for the field circuit which is separated from the main power supply to which the armature is connected. Such a variable supply can be obtained by an electronic rectifier.
Armature Resistance Control In this method armature circuit is provided with a variable resistance. Field is directly connected across the supply so flux is not changed due to variation of series resistance. This is applied for DC shunt motor.At least in DC you knew your gate number long before the scheduled departure so you had some chance of positioning yourself for the coming rush.
Journal of Engineering and Applied Sciences is an online peer-reviewed research journal aiming at promoting and publishing original high quality research in all disciplines of Engineering Sciences and Technology.
Speed Control of DC Shunt Motor Speed of DC shunt motor is controlled by the factors stated below.
Field Control of DC Shunt Motor By this method speed control is obtained by any one of the following means – Field Rheostat Control of DC Shunt Motor In this method, speed variation is accomplished by means of a variable resistance inserted in series with the shunt field/5(14).
This paper discusses the speed and torque control of a shunt DC motor through MATLAB Simulink simulations.
The DC shunt motor is Vdc with rated speed of revolutions per minute. Backtrack magazine:illustrated journal about railway and locomotive history.
PMSM motors – Field-oriented control (FOC) Permanent Magnet Synchronous Motors (PMSM) at a glance: Require alternating stator current; Stator is a 3-phase winding.