Induction machines with two three-phase windings in convertor applications

Abstract

A w e l l known method t o r e d u c e t h e harmonic c o n t e n t i n t h e l i n e c u r r e n t when o p e r a t i n g a grid-commutated i n v e r t e r i s t o u s e a t w e l v ep u l s e c o n v e r t o r a n d a t h r e e -w i n d i n g t r a n s f o r m e r . T h i s method c o u l d b e m o d i f i e d a n d a p p l i e d i n c o n v e r t o r a p p l i c a t i o n s w i t h i n d u c t i o n m a c h i n e s . The t h r e e -w i n d i n g t r a n s f o r m e r c o u l d i n t h i s c a s e b e e l i m i n a t e d by u s i n g a two-winding i n d u c t i o n machine. With a n i n d u c t i o n m a c h i n e i n c o n v e r t o r a p p l i c a t i o n s , t h e s t a t o r w i n d i n g c o u l d be d e s i g n e d w i t h two s t a r -c o n n e c t e d s t a t o r windings d i s p l a c e d 30 e l e c t r i c a l d e g r e e s . By u s i n g a s e l f -c o m m u t a t e d i n v e r t e r , t o r q u e p u l s a t i o n s a n d r o t o r c u r r e n t h a r m o n i c s a s s o c i a t e d w i t h some s t a t o r c u r r e n t h a r m o n i c s a r e e l i m i n a t e d a l t h o u g h t h e h a r m o n i c c u r r e n t s s t i l l f l o w i n t h e w i n d i n g s . I n o r d e r t o i n v e s t i g a t e t h i s , a n 11 kW 380 V i n d u c t i o n motor h a s been re-wound w i t h two t h r e e -p h a s e s y s t e m s d i s p l a c e d 30 e l e c t r i c a l d e g r e e s . Measurements have b e e n made w i t h q u a s i s q u a r e wave s u p p l y g e n e r a t e d by two v o l t a g e s o u r c e i n v e r t e r s . The i n d u c t i o n machine was c o u p l e d v i a a t o r q u e t r a n s d u c e r t o a d c -m a c h i n e . The v o l t a g e , two p h a s e c u r r e n t s and t h e t o r q u e were m e a s u r e d w i t h a t r a n s i e n t r e c o r d e r c o n n e c t e d t o a computer. I n t h e computer t h e d a t a w e r e p r o c e s s e d w i t h a f a s t F o u r i e r t r a n s f o r m ( F F T ) p r o g r a m i n o r d e r t o d e t e r m i n e harmonics. C a l c u l a t i o n s h a v e a l s o b e e n made on a t r a n s i e n t computer model o f t h e d r i v e . The model o f t h e i n d u c t i o n machine and l o a d i s a v e r s i o n of t h e commonly known dq-machine, w i t h two t h r e e -p h a s e s t a t o r w i n d i n g s a n d a two-phase e q u i v a l e n t r o t o r winding. With a n ac-machine c o n n e c t e d t o a f r e q u e n c y c o n v e r t o r i n v a r i a b l e s p e e d o p e r a t i o n c u r r e n t harmonics and t o r q u e p u l s a t i o n s w i l l a p p e a r . Depending on t h e t y p e o f c o n v e r t o r a n d s w i t c h i n g s t r a t e g y u s e d , t h e f r e q u e n c y s p e c t r u m o f t h e h a r m o n i c s w i l l v a r y . The v i b r a t i n g t o f % u e s are o f i m p o r t a n c e ( r e f [ 5 ] ) a n d e f f o r t s are made i n c o n v e r t o r d e s i g n i n o r d e r t o r e d u c e them. However, by d e s i g n i n g t h e a c -m a c h i n e d i f f e r e n t l y , s i g n i f i c a n t r e d u c t i o n o f p ...

Additional asynchronous and pulsating torque analysis of 3-phase induction machine

“…(1) where W is energy of magnetic field in the center of air-gap and ∆ is rotor angular angle in radian.…”