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Introd_to_AC_motors

# Introd_to_AC_motors - 1 Introduction to AC machines 1 The...

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Introduction to AC machines 1. The very first experience with electric (linear) motors a) Reluctance (linear) synchronous motor (piece of iron dragged by the magnetic field of permanent magnet) –the traveling magnetic field of the “stator” is produced by the permanent magnet moving with the speed v. The name reluctance means that the rotor reluctance changes along its length, and due to that the magnetic field energy W f varies with the space co-ordinate x . According to equation ( 29 , f m W x f x Φ = - (1) the magnetic force f m is produced. N R o t o r ” ( F e ) S t a t o r ” ( p e r m a n e n t m a g n e t ) Φ ( m a g n e t i c f l u x ) S v ( s p e e d ) x y f m Fig.1 Dragging the permanent magnet (stator) with a speed v under the table-top the piece of iron (rotor) is moving with the same speed being attracted by the magnetic field of the stator The magnetic force acting on the “rotor” is ' 2 2 0 0 2 2 2 2 f g g m g g W B B f A g A x g μ μ = = = �� (2) The force driving the “rotor” in x direction is m y x f f f = - (3) b) Permanent magnet (linear) synchronous motor 1 1 f m f x f y

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N R o t o r ” ( p e r m a n e n t m a g n e t ) S t a t o r ” ( p e r m a n e n t m a g n e t ) S v x N S Fig.2 Traveling magnetic field produced by moving permanent magnet of the “stator” pulls (drives) the permanent magnet “rotor” c) Permanent magnet (linear) synchronous motor r o t o r ” N S s t a t o r ” N S v c o i l s u p p l i e d w i t h d c c u r r e n t Fig.3 “Stator” magnetic field is produced by the coil supplied from dc source 2. Electromotive force and electromagnetic force Fig.4 illustrates the generation of electromotive force (EMF) e , and mechanical force F . Symbols: B – magnetic flux density, Φ – magnetic flux, i – current, v - speed (a) (b) N S N Φ l v e ( Β 29 + N S N Φ l F i ( Β 29 Fig.4 Generation of: (a)
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Introd_to_AC_motors - 1 Introduction to AC machines 1 The...

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