lec-triosU Engineering Education

t h o u g h t t h a t one oi the most i m p o r t a n t steps wh ich engineer ing educa t ion can take in t he future is to a r r a n g e m a t t e r s so t h a t each s tuden t has the oppor tun i ty t o tai lor his c u r r i c u l u m to fit his persona l character is t ics ,

Thesis Projects in Magnetic Amplifiers H . F . S T O R M MEMBER AIEE

D U R I N G A M E E T I N G of the T h e o r y S u b c o m m i t t e e of the A I E E M a g n e t i c Amplifier C o m m i t t e e , t h e discussion dwel t o n t he p r o b l e m of a c q u a i n t i n g college s tuden ts wi th m a g n e t i c amplifiers. I t was felt t h a t s tudents w h o wish to deepen their knowledge in this field find it often difficult to do so, because of a n a p p a r e n t lack of su i table thesis projects . T o r emove this difficulty a n d , the reby , s t imula te interest in s tudying this subject, t h e subcommi t t ee m e m b e r s suggested a n u m b e r of thesis projects wh ich a r e believed to h a v e :

1. H i g h - a c a d e m i c con ten t . 2. Prac t ica l impor t ance . 3. Good probab i l i ty for finding solut ion.

Such projects a r e listed in this ar t ic le . T o p rov ide init ial g u i d a n c e to t he s tudents , the p roponen t s of t h e thesis projects a re identified at t he end of t he project list by t he project n u m b e r a n d m a y be con tac ted by the s tudents . After comple t ion of the thesis project , t he s tuden t is reques ted t o send one copy of t he thesis to t he p r o p o n e n t of his project , a n d a n o t h e r copy t o the C h a i r m a n of the T h e o r y S u b c o m m i t t e e .

Lists of Thesis Projects

7. Characteristics of 2-Phase Servo Motors, Driven from Magnetic Amplifiers. A n u m b e r of magnet ic-ampl i f ier circuits have been developed for dr iv ing the con t ro l phase of 2-phase servo motors . A l t h o u g h some in­format ion has been publ i shed on the effect of var ious wave forms on the speed - to rque character is t ics of such moto r s , t he re is need for a good ana ly t ica l a n d expe r imen ta l t r e a t m e n t of this subject , cover ing t h e different types of circuits wh ich a re c o m m o n l y employed for this purpose .

2. Circuit Comparisons. S tudy exper i ­men ta l ly a n d / o r theoret ical ly t he t e c h n i q u e

A special article by the Theory Subcommittee of the AIEE Magnetic Amplifier Committee and recom­mended by the AIEE Committee on Education.

H. F. Storm is with the General Electric Company, Schenectady, Ν. Y.

r a the r t h a n be ing forced in to a p rede t e r ­m i n e d mo ld t h a t is the same for all s tuden ts . Lockstep m a y be all r ight for c r imina ls , b u t it is not the best way to t r a in engineers to take responsibi l i ty in the wor ld of t he future.

of app ly ing biased rectifiers t o increase t he effective c o n t r o l c ircui t i m p e d a n c e in t he half -wave b r idge - type m a g n e t i c amplifier, as descr ibed in N A V O R D R e p o r t N o . 4258, M a r c h 29, 1956 (Fig . 1), e.g., c o m p a r e t he mer i t s of this c i rcui t w i th those of t he R a m e y circui t .

3. Computing Amplifier. Inves t iga te t he errors i n t r o d u c e d by var ia t ions in supply vol tage , f requency, a n d w a v e shape in to c o m p u t e r circuits , ope ra t i ng on t h e pr inciples ou t l ined by Finzi a n d M a t h i a s . 1

Dynamic Properties (4 through 7).

4. Sampled-Data-System Analysis. Since t he magne t i c amplifier is basical ly a s ampl ing device, t h e t echn iques t h a t h a v e been de ­veloped for s a m p l e d - d a t a feedback systems should b e app l ied t o m a g n e t i c amplifiers. By so do ing , t he n o n c o n t i n u o u s t ransforms (Z t ransforms) of t h e m a g n e t i c amplif ier will be deve loped a n d c a n be app l ied to t he d e t e r m i n a t i o n of stabil i ty of t h e system in wh ich the amplif ier is i nco rpora t ed .

5. Transfer Function of Magnetic Amplifiers. M a n y m a g n e t i c amplifiers exhib i t a doub le -va lued response, d e p e n d i n g u p o n t h e d i rec­t ion of t h e con t ro l s ignal . I n system analyses for se rvomechanisms , Nyquis t a n d Bode d i a g r a m s a r e often used, bu t these

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Fig. 1 . Project 2, Circuit Comparisons.

m e t h o d s c a n n o t be direct ly appl ied where a doub le -va lued response is present . T h e object ive of this thesis project is to s tudy t h e response ( t ime cons tan t , d e a d - t i m e lag, e tc . ) of self-saturat ing magne t i c amplifiers, hav ing doub le -va lued response, in o rde r t o a r r ive at a transfer function sui table for app l ica t ion in Nyquis t or Bode d iag rams .

6. Effect of Supply Frequency on Figure of Merit. S o m e p re l iminary s ta tements h a v e been m a d e in t h e l i t e ra tu re r ega rd ing t h e effect of supply frequency on figure of mer i t . N o w t h a t be t t e r informat ion is avai lable o n magne t i c -core character is t ics a n d the in­fluence on amplifier per formance , a good ana ly t ica l t r e a t m e n t of this subject m a y b e possible. Such a t r e a t m e n t should t a k e accura te ly in to accoun t the var ia t ion of core character is t ics wi th frequency.

7. Bistable Circuit. I n bis ta te m a g n e t i c -amplifier circui ts , t he switching t i m e from o f f t o o n a n d from o n t o o f f a p p e a r s t o be a funct ion of several var iables , inc lud ing the m a g n i t u d e of signal a n d t h e a m o u n t of r egenera t ion . An objective of this thesis project w o u l d be to s tudy the factors in­fluencing t h e switching t ime a n d t o d e ­t e r m i n e some a p p r o p r i a t e cr i ter ia w h i c h w o u l d re l a t e t he ra t io of power gain (switch­ing r a t i o ) a n d the switching t ime .

8. High-Frequency Operation. If a m a g ­net ic amplif ier is ope ra t ed from a h i g h carr ier f requency, its b a n d w i d t h m a y b e m a d e wide e n o u g h t o accept low-frequency a-c signals w i thou t d e m o d u l a t i o n . T h e circui t m a y be designed t o p r o v i d e b o t h vol tage a n d p o w e r gain at t he low frequency. A n object of this thesis project w o u l d b e t o d e t e r m i n e o p t i m u m coupl ing circuits t o t h e load . Cons ide ra t ion should also b e given to over-a l l c ircui t efficiency ( ra t io of h igh-frequency p o w e r suppl ied t o low-frequency p o w e r o u t p u t ) .

9. Interstage Coupling. If t w o m a g n e t i c amplifiers of the self-saturated t y p e a r e g r o u p e d toge the r t o form a 2-stage m a g n e t i c amplifier , t he a m p e r e - t u r n ga in of t he 2-stage m a g n e t i c amplif ier usual ly is less t h a n the p r o d u c t of t he gains of t h e t w o ind iv idua l amplif iers . T h e object of this thesis projec t is t o s tudy the m e c h a n i s m of ga in r educ t ion a n d to ar r ive a t recom­m e n d a t i o n s for r e d u c i n g or e l imina t ing t h e a fo rement ioned ga in r educ t ion .

Low-Level Amplifiers ( 70 and 77). 70. Input-Stage Design. W o r k is needed

on t h e design of con t ro l circuits a n d i n p u t stages of m a g n e t i c amplifiers ope ra t ing at ext remely low p o w e r levels. Th is work , t o be effective, m a y r equ i r e t h e redesign or o r ig ina t ion of t r ansduce r s t h a t wil l gene ra te t h e r e q u i r e d signals a n d transfer t h e m in o p t i m u m m a n n e r t o t h e i n p u t s tage. W o r k is also n e e d e d in t h e op t imiza t ion of mul t i ­s tage amplif iers for best closed-loop d y n a m i c pe r fo rmance .

77. Control Hysteresis. M a k e invest igat ion of con t ro l -c i rcu i t hysteresis in second-

942 Electrical Engineering Education ELECTRICAL ENGINEERING

El oc-tri o al Engineering Education

' harmonic- type m a g n e t i c amplif ier . I n case sufficient m a t e r i a l has been pub l i shed a l ready on this top ic , a l i t e ra tu re s tudy a lone m a y be useful.

72. Polyphase Amplifiers. M o r e work ( a n d publ i shed p a p e r s ) is needed on the analysis of po lyphase magne t i c amplifiers. Th i s work should explore the var ious types of po lyphase circui ts , t h e m e t h o d s of connec t ­ing cont ro l windings , ope ra t ion wi th var ious types of loads, a n d stabi l i ty . Usab le expres­sions for ga in a n d t ime cons tan t should be der ived as functions of t he core m a t e r i a l , geometry , windings , a n d in te rconnec t ion .

Prediction of Control Characteristics ( 13 through 16).

13. Relation between Control Characteristics and B-H Loop of Cores. W o r k should be con­t inued on t h e p red ic t ion of t h e con t ro l characterist ics of m a g n e t i c amplifiers from the measured curves of φ versus t ime wi th H as a p a r a m e t e r . M e t h o d s for d e t e r m i n i n g such curves from the physics or t h e m e t a l ­lurgy of t he m a t e r i a l shou ld b e deve loped .

74. Doubler Circuit. A m a g n e t i c a m p l i ­fier circuit wh ich exhibits m a n y in teres t ing characterist ics inc lud ing h igh p o w e r ga in , well-filtered o u t p u t , a n d h igh o u t p u t vol tage is shown in Fig. 2. N o a t t e m p t has yet been m a d e t o ana lyze this c i rcui t in o r d e r to predic t its m o d e of ope ra t ion a n d de ­t e rmine design equa t ions for its pe r fo rmance . T h u s , t he object of this thesis project w o u l d be t o ana lyze t h e circui t behav io r a n d establish design equa t ions .

75. Amplifier with Counter-Emf Load. I t is felt t h a t a theory is needed for t he self-sa tu ra ted magne t i c amplif ier work ing in to a coun te r -emf load , such as a s torage ba t te ry or t h e a r m a t u r e of a d-c m o t o r . Such a theory should b e a i m e d t o p r o d u c e design informat ion a n d , therefore , its findings a n d conclusions should b e p resen ted in a m a n n e r which can be easily g rasped a n d uti l ized.

76. Effects of Winding Capacitances. H o w a re t h e t h r ee basic magne t ic -ampl i f ie r circuits, name ly " d o u b l e r , " b r idge , a n d cen te r - t ap , influenced, favorably or un­favorably, by c a p a c i t a n c e in t h e wind ings of the coils? T o w h a t ex ten t d o these effects d e p e n d on t h e proper t i es of t h e core m a ­terial? At wh ich frequencies d o capac i ­t a n c e effects b e c o m e apprec iab le? O n e way t o d e t e r m i n e w i n d i n g capac i t ances

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79. Stabilizing of Closed-Loop Systems. T h e a r e a of stabi l iz ing m e t h o d s for feedback systems inco rpo ra t i ng m a g n e t i c amplifiers needs cons iderab le work . Both t h e specific t echn iques a n d the ana ly t ica l me thods for p red ic t ing t h e pe r fo rmance of t he stabil ized system need a t t en t ion .

Project Number Proponents and Addresses.

Fig. 2. Project 14, Doubler Circuit.

w o u l d be to m e a s u r e c a p a c i t a n c e of coils w o u n d on n o n - m a g n e t i c core forms.

77. Push-Pull Circuits. T o study t h e var ious conven t iona l s ingle-stage push-pu l l a-c a n d / o r d-c o u t p u t m a g n e t i c amplif iers wi th a view to d e t e r m i n i n g the o p t i m u m m e t h o d s of mix ing the t w o s ingle-ended o u t p u t s a n d the effect of bias a n d con t ro l circuit conf igura t ion on j u m p s or discon­t inui t ies in the transfer curve , w h e n a low-frequency s inusoidal s ignal is app l ied .

78. Stability of Amplifiers. T h e r e is need for an ana ly t i ca l a n d e x p e r i m e n t a l c o m ­par i son of t h e s tabi l i ty of var ious m a g n e t i c -amplif ier circuits wi th respect t o changes in core a n d rectifier character is t ics . T h e resul t of a projec t such as this should be a q u a n t i ­ta t ive c o m p a r i s o n of t h e drift a n d ga in s tabi l i ty of var ious types of m a g n e t i c -amplif ier c ircui ts , inc lud ing var ious types of feedback, assuming c o m p a r a b l e changes in core a n d rectifier character is t ics in al l

1, 6, 18 R . A. R a m e y , Wes t inghouse E l e c ­t r ic C o r p o r a t i o n , Eng ineer ing Cen te r , Eas t P i t t sburgh , Pa .

2, 16 J . J . Suozzi , Bell T e l e p h o n e Labora to r i e s Inc . , Whippany , R o a d , W h i p p a n y , N . J .

3, 11 T . G. B lancha rd , R . J . Dist ler , Bell T e l e p h o n e Labora tor ies I n c . , W h i p p a n y R o a d , W h i p ­p a n y , N . J .

4, 10, 12, A. Kusko , Massachuse t t s Ins t i tu te 1 3 , 1 9 of T e c h n o l o g y , R o o m 10-150,

C a m b r i d g e , Mass . 5 , 9 , 1 5 H . F . S t o r m , G e n e r a l Electr ic

C o m p a n y , 1 River R o a d , Bui ld­ing 37, Schenec tady , Ν . Y.

7 , 8 , 1 4 D . F e l d m a n , Bell T e l e p h o n e Labo ra to r i e s I n c , W h i p p a n y R o a d . , W h i p p a n y , N . J .

17 T . G. Wi lson , Magne t i c s Inc . , But ler , Pa .

REFERENCE

1. An Application of Magnetic Amplifier Circuits ta Perform Multiplication and Other Analytical Opera­tions, L. A. Finzi, R. A. Mathias. AIEE Transactions\ vol. 72, pt. I, 1953, pp 455 6 1 .

Magnetic Amplifiers Serve To Teach Power Modulators H . C. B O U R N E MEMBER AIEE

R . M . S A U N D E R S MEMBER AIEE

M A G N E T I C A M P L I F I E R S a r e a n ex­a m p l e of a who le g r o u p of devices h a v i n g c o m m o n charac te r i s t ics a n d b e i n g a m e n a b l e t o a c o m m o n m e t h o d of analysis . T h e c o m ­m o n charac ter i s t ics of this class of e q u i p m e n t a re t h a t they con t ro l a n d m o d u l a t e t h e flow of p o w e r a n d energy a n d a r e m e c h a n i c a l l y s tat ic . T h i s a r t ic le descr ibes a m e t h o d of ana lyz ing such s tat ic p o w e r m o d u l a t o r s b y app ly ing t h e t e chn iques t o m a g n e t i c a m p l i ­fiers in p a r t i c u l a r .

T h e s e m e t h o d s , r e ly ing as they d o u p o n t h e knowledge of c i rcui t analysis at the c o m ­m a n d of a n a d v a n c e d s t u d e n t , m a k e it pos ­sible for a n u n d e r g r a d u a t e s tuden t t o ga in cons ide rab le insight i n t o non l i nea r m a g n e t i c c i rcui t analysis , as wel l as p rov ide h i m wi th tools for exploi t ing m o r e compl i ca t ed s i tua­t ions in t he future .

F ig . 1 shows a block in to wh ich a signal b e a r i n g inte l l igence is in jec ted; it is desired t h a t t h e s ignal m o d u l a t e the flow of power f rom t h e source in to t h e load in acco rdance w i t h t h a t s ignal . Ac tua l ly , t he genera l power m o d u l a t o r of Fig. 1 m a y involve m e c h a n i c a l m o t i o n if any of the t e rmina l s involve m e c h a n i c a l d i sp lacement or velocity, such as in d-c a n d a-c m o t o r s . Fig. 1 may also represen t a s ta t ionary power m o d u l a t o r >

w h e r e al l i npu t s a n d o u t p u t s a re t he s a m e

Full text of conference paper presented before a session of the AIEE Committee on Magnetic Amplifiers, AIEE Summer and Pacific Meeting, San Francisco, Calif., June 25-29, 1956.

H. C. Bourne and R. M. Saunders are with the Univer­sity of California, Berkeley, Calif.

O C T O B E R 1956 Electrical Engineering Education 943