Direct current drives are easy to apply and technologically straight forward. They work by rectifying AC voltage from the power line to DC voltage, then feeding adjustable voltage to a DC motor. With permanent magnet.
DC motors, only the armature voltage is controlled. The more voltage supplied, the faster the armature turns. With wound-field motors, voltage must be supplied to both the armature and the field. In industry, the following three types of DC drives are most common:
DC SCR Drives:
These are named for the silicon controlled rectifiers (also called thyristors) used to convert AC to controlled voltage DC.
Inexpensive and easy to use, these drives come in a variety of enclosures, and in unidirectional or reversing styles.
Inexpensive and easy to use, these drives come in a variety of enclosures, and in unidirectional or reversing styles.
Regenerative SCR Drives:
Also called four quadrant drives, these allow the DC motor to provide both motoring and braking torque. Power coming back from the motor during braking is regenerated back to the power line and not lost.
Pulse Width Modulated DC Drives:
Abbreviated PWM and also called, generically, transistorized DC drives, these provide smoother speed control with higher efficiency and less motor heating. Unlike SCR drives, PWMtypes have three elements. The first converts AC to DC, the second filters and regulates the fixed DC voltage, and the third controls average voltage by creating a stream of variable width DC pulses. The filtering section and higher level of control modulation account for the PWM drive’s improved performance compared with a common SCR drive.