types of vfd drives

Types Of VFD Drives

There are 3 general types of VFD drives:

Each of these types of VFD drives can be divided into different variations. Every type of VFD drive system runs an electric motor and a speed control unit. VFD drive technology in today’s manufacturing processes mainly consist of solid state electronic components in a single control system. Older VFD drive systems use mechanical moving parts that in short periods of time, result in equipment failure due to worn parts from constant motion.

Eddy Current Systems – Types Of VFD Drives

types of vfd drivesThese types of VFD drives use an eddy current electric motor system. An eddy current type of VFD drive consists of a fixed speed motor and an eddy current clutch. The clutch contains a fixed speed rotor and a variable speed rotor separated by a small air gap. A direct current in a field coil produces a magnetic field that determines thetorquetransmitted from the input to the output rotor. The controller provides closed loop speed regulation by varying the clutch current, allowing the clutch to transmit enough torque to operate at the desired speed. Speed feedback is provided by an integral AC tachometer.

Eddy current VFD drives are less efficient than all other types of variable frequency drives.Nearly all eddy current motor drive systems are obsolete today. Eddy Current motor drives were designed and manufactured decades ago and there are very few manufacturing facilities across the globe that still use them in production. When an Eddy Current motor drive system fails, it’s usually too expensive to repair and impossible to replace. When an Eddy Current motor drive reaches the end of its life cycle and can no longer be repaired, manufacturers retrofit the Eddy Current Drive Systems with an AC Induction Motor and an AC VFD Drive system.

DC Systems – Types Of VFD Drives

types of vfd drivesThese types of VFD drives use DC (direct current) electric motors. DC (direct current) motors have a rotating armature winding (winding in which a voltage is induced) but non-rotating armature magnetic field, and a static field winding (winding that produces the main magnetic flux) or permanent magnet. Different connections of the field and armature winding provide different inherent speed/torque regulation characteristics. The speed of a DC motor can be controlled by changing the voltage applied to the armature or by changing the field current. The introduction of variable resistance in the armature circuit or field circuit allowed speed control. Modern DC motors are often controlled bypower electronicssystems called DC VFD drives.

There are different types of DC VFD drives, but the most common are known as DC Motor Speed Control Systems.The speed of a DC motor is directly proportional to armature voltage and inversely proportional to motor flux; either armature voltage or field current can be used to control the motor speed. DC Motors have become expensive and today most DC motor speed control systems are retrofitted with an AC induction motor and AC VFD drive. AC VFD drives are less expensive than DC Drive systems, are more available, and are more energy efficient than DC VFD Drive systems.

AC Systems – Types Of VFD Drives

types of vfd drivesThese types of VFD drives use AC (alternating current) electric motors. AC VFD drives are also known as Variable Frequency Drives, VSDs (variable speed drives), AFDs (adjustable speed drives), inverters, and micro drives. AC variable frequency drives are used in many applications such as AC Servo Systems, Air Compressors, Conveyor Systems, Lathes, Mills, Food Processing production lines, Waste Water treatment systems, Submersible Pumps, HVAC fans and blowers, and many more applications.Approximately one third of the world’s electrical energy is supplied by electric motors in fixed-speed centrifugal pump, fan, and air compressor applications. This proves thatsignificant energy efficiency improvement opportunities are available if older DC motor speed control systems and eddy current drive systems are retrofitted with AC variable frequency drive systems.Most industrial manufacturers replace their eddy current and DC variable frequency drive systems with AC variable frequency drive systems.

Technology has reduced the physical size and cost of AC variable frequency drives, and has improved performance through advances in semiconductor switching devices, simulation, control techniques, and control hardware and software.Manufacturers capitalize on AC VFD drive technology to save money on power consumption, increase quality control, decrease production downtime, and improve overall efficiency on production lines.

 

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