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Motors feed

 

Type Advantages Disadvantages Typical Application Typical Drive
AC Induction
(Shaded Pole)		 Least expensive
Long life
high power		 Rotation slips from frequency
Low starting torque		 Fans Uni/Poly-phase AC
AC Induction
(split-phase capacitor)		 High power
high starting torque		 Rotation slips from frequency Appliances Uni/Poly-phase AC
AC Synchronous Rotation in-sync with freq
long-life (alternator)		 More expensive Industrial motors
Clocks
Audio turntables
tape drives		 Uni/Poly-phase AC
Stepper DC Precision positioning
High holding torque
Requires a controller		 Positioning in printers and floppy drives Multiphase DC
Brushless DC electric motor Long lifespan
low maintenance
High efficiency		 High initial cost
Requires a controller		 Hard drives
CD/DVD players
electric vehicles		 Multiphase DC
Brushed DC electric motor Low initial cost
Simple speed control (Dynamo)		 High maintenance (brushes)
Low lifespan		 Treadmill exercisers
automotive starters		 Direct PWM

Synchronous electric motor
A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the alternating current and resulting magnetic field which drives it. Another way of saying this is that it has zero slip under usual operating conditions. Contrast this with an induction motor, which must slip in order to produce torque. Synchronous motor is like an induction motor except the rotor is excited by a DC field. Slip rings and brushes are used to conduct current to rotor. The rotor poles connect to each other and move at the same speed hence the name synchronous motor.

Induction motor
An induction motor (IM) is a type of asynchronous AC motor where power is supplied to the rotating device by means of electromagnetic induction. Another commonly used name is squirrel cage motor because the rotor bars with short circuit rings resemble a squirrel cage (hamster wheel). An electric motor converts electrical power to mechanical power in its rotor (rotating part). There are several ways to supply power to the rotor. In a DC motor this power is supplied to the armature directly from a DC source, while in an induction motor this power is induced in the rotating device. An induction motor is sometimes called a rotating transformer because the stator (stationary part) is essentially the primary side of the transformer and the rotor (rotating part) is the secondary side. Induction motors are widely used, especially polyphase induction motors, which are frequently used in industrial drives.

Brushed DC motors
The classic DC motor design generates an oscillating current in a wound rotor, or armature, with a split ring commutator, and either a wound or permanent magnet stator. A rotor consists of one or more coils of wire wound around a core on a shaft; an electrical power source is connected to the rotor coil through the commutator and its brushes, causing current to flow in it, producing electromagnetism. The commutator causes the current in the coils to be switched as the rotor turns, keeping the magnetic poles of the rotor from ever fully aligning with the magnetic poles of the stator field, so that the rotor never stops (like a compass needle does) but rather keeps rotating indefinitely (as long as power is applied and is sufficient for the motor to overcome the shaft torque load and internal losses due to friction, etc.)

Brushless DC motors

Some of the problems of the brushed DC motor are eliminated in the brushless design. In this motor, the mechanical "rotating switch" or commutator/brushgear assembly is replaced by an external electronic switch synchronised to the rotor's position. Brushless motors are typically 85-90% efficient or more (higher efficiency for a brushless electric motor of up to 96.5% were reported by researchers at the Tokai University in Japan in 2009, whereas DC motors with brushgear are typically 75-80% efficient.

Modern DC brushless motors range in power from a fraction of a watt to many kilowatts. Larger brushless motors up to about 100 kW rating are used in electric vehicles. They also find significant use in high-performance electric model aircraft.

Universal motors and series wound DC motors
A wound field DC motor with the field and windings connected in series is called either a "series-wound motor" or a "universal motor," because of its ability to operate on AC or DC power. The ability of to operate on AC or DC power is because the current in both the field winding and the armature (and hence the resultant magnetic fields) will alternate (reverse polarity) at the same time, and hence the mechanical force generated is always in the same direction. Usually, the use of the term "universal motor" indicates a motor that has been specifically designed.

AC motors

In 1882, Nikola Tesla invented the rotating magnetic field, and pioneered the use of a rotary field of force to operate machines. He exploited the principle to design a unique two-phase induction motor in 1883. In 1885, Galileo Ferraris independently researched the concept. In 1888, Ferraris published his research in a paper to the Royal Academy of Sciences in Turin.

 

Tesla had suggested that the commutators from a machine could be removed and the device could operate on a rotary field of force. Professor Poeschel, his teacher, stated that would be akin to building a perpetual motion machine Tesla would later attain U.S. Patent 0,416,194, Electric Motor (December 1889), which resembles the motor seen in many of Tesla's photos. This classic alternating current electro-magnetic motor was an induction motor.

 

Michail Osipovich Dolivo-Dobrovolsky later invented a three-phase "cage-rotor" in 1890. This type of motor is now used for the vast majority of commercial applications.

Components

A typical AC motor consists of two parts:

  • An outside stationary stator having coils supplied with AC current to produce a rotating magnetic field, and;
  • An inside rotor attached to the output shaft that is given a torque by the rotating field.

Efficiency

To calculate a motor's efficiency, the mechanical output power is divided by the electrical input power:

where ? is energy conversion efficiency, Pe is electrical input power, and Pm is mechanical output power.

In simplest case Pe = VI, and Pm = T?, where V is input voltage, I is input current, T is output torque, and ? is output angular frequency.
 
Source: wikipedia