Basics of DC Drives by Siemens

DC motors and DC drives have been used in industrial applications for years. Coupled with a DC drive, DC motors provide very precise control .DC motors can be used with conveyors, elevators, extruders, marine applications, material handling, paper, plastics, rubber, steel, and textile applications to name a few

English: An armature from a small DC fan motor.

English: An armature from a small DC fan motor. (Photo credit: Wikipedia)

Permanent Magnet Motors

The permanent magnet motor uses a magnet to supply field flux Permanent magnet DC motors have excellent starting torque capability with good speed regulation A disadvantage of permanent magnet DC motors is they are limited to the amount of load they can drive These motors can be found on low horsepower applications Another disadvantage is that torque is usually limited to 150% of rated torque to prevent demagnetization of the permanent magnets

Series Motors

In a series DC motor the field is connected in series with the armature  The field is wound with a few turns of large wire because it must carry the full armature current  A characteristic of series motors is the motor develops a large amount of starting torque  However, speed varies widely between no load and full load  Series motors cannot be used where a constant speed is required under varying loads  Additionally, the speed of a series motor with no load increases to the point where the motor can become damaged  Some load must always be connected to a series-connected motor  Series-connected motors generally are not suitable for use on most variable speed drive applications

Shunt Motors

In a shunt motor the field is connected in parallel (shunt) with the armature windings  The shunt-connected motor offers good speed regulation  The field winding can be separately excited or connected to the same source as the armature  An advantage to a separately excited shunt field is the ability of a variable speed drive to provide independent control of the armature and field  The shunt-connected motor offers simplified control for reversing  This is especially beneficial in regenerative drives

Compound Motors

Compound motors have a field connected in series with the armature and a separately excited shunt field   The series field provides better starting torque and the shunt field provides better speed regulation  However, the series field can cause control problems in variable speed drive applications and is generally not used in four quadrant

 

Here is the link to Siemens pdf about DC drive and its basics.

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