Synchronous Reluctance Motor

By JAIKRISHNA . V

Edited By Sarath S Nair ww w w w. tech te chn n olo ol o g y f utur ut uraa e . co com m www.technologyfutur www .technologyfuturae.com ae.com

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Introduction

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Principle of Operation

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Mathematical Model of Synchronous Reluctance Motor

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Advantages Advan tages and Disadvantages Disadvantages

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Comparison with other motors

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Summary

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References www.technologyfutur www .technologyfuturae.com ae.com

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Synchronous reluctance motor is a true ac motor

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Synchronous reluctance motors were developed to provide an efficient efficie nt constant constant speed machine. mach ine.

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There are no brushes, slip sli p rings etc.

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Its principle is almost similar simil ar to salient pole synchronous motor.

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In principle, principl e, the Synchronous Reluctance Motor Motor is similar to the traditional salient sali ent pole synchronous motor but does not have an excitation winding in its rotor. The rotor is constructed with salient sali ent poles The SynRM includes includes a squirrel cage on the rotor to provide provide the starting torque for line-start. The squirrel cage was also needed as a damper winding in in order to maintain synchronism under sudden load torques When 3 phase supply is given given to to the stator, stator, a rotating flux f lux is produced. Initially emf is induced in damper winding and the motor starts like an induction machine. As it approaches synchronous speed spe ed the reluctance reluctan ce torque torque takes over and the motor locks into synchronous speed. www.technologyfutur www .technologyfuturae.com ae.com

1)

d-q equation of synchronous syn chronous reluctance motor


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In synchronous syn chronous reluctance motor mo tor,, the the excitation winding does not not exist. The basis for the d – q equations equations for a synchronous reluctance machine can be obtained from parks equation v d = rs ids + dλ ds ds/dt – wr λ qs qs v q = rs iqs + dλ qs qs/dt + wr λ ds ds (1)

Where λ ds ds = Lls ids + Lmd ids = Lds ids λ qs qs = Lls iqs + Lmq iqs = Lqs iqs www.technologyfutur www .technologyfuturae.com ae.com

(2)

where Lls - stator leakage inductance Lmd – direct axis magnetizing inductance Lmq – quadrature axis magnetizing inductance

Te = (3/2)*(P/2)*( (3/2)*( P/2)*(λ ds ds iqs - λ qs qs ids)


(3)


The variable in equation (1) will become constant in steady state .ie., d/dt terms can be eliminated qs + rs V ds ds Ids = we Lqs V qs rs² + we² Lds Lqs (5) Iqs = -we Lds V ds ds + rs V qs qs rs² + we² Lds Lqs Neglecting stator resistance we get get Ids = V qs , Iqs = - V ds (6) qs ds we Lds we Lqs 


Single phasor phas or equation from a steady state version of equation (1) can be obtained by multiplying multiplyin g first firs t line of(1) ie. v ds by – j and and adding adding to the second line ie. v qs v qs (7) qs – jv ds ds = rs(Iqs – jIds) + we(λ ds ds + jλ qs qs) or using (2) and (7) v qs (8) qs - jv ds ds = rs(Iqs – jIds) + we(Lds Ids + jLqs Iqs) It can be changed to V qs (9) qs – jV ds ds = rs(Iqs – jIds) + jwe Lds(-jIds) + jwe Lqs Iqs In phasor notation (10) www.technologyfutur www .technologyfuturae.com ae.com

(11) Except frequencies frequencie s near zero, in all frequencies neglecting stator resistance (12)

Substituting V ds and V qs obtained from phasor diagram we get www.technologyfutur www .technologyfuturae.com ae.com

(13) The torque varies as square of volt per Hertz and as the sine of twice t wice of the angle ∂. When the volt/Hertz is fixed, the maximum torque is clearly reached when ∂=45˚. Therefore Maximum torque (14)


substituted into the torque If λ ds and λ qs is directly substituted equation Te can also be written in terms term s of stator d-q current as: (15) Substitute Substitute the value of Ids and Iqs (16)


Electromagnetic Electromagneti c torque torque can be expressed in terms term s of stator current amplitude and mmf m mf angle ε as

(17)


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Freedom from permanent magnets magn ets A wide speed range range at constant constant power power Synchronous operation leading to high efficiency Ability to maintain full torque torque at zero speed


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In small motors mo tors the torque/ampere torque/ampere and the torque/ volume volume are lower lower than in PM motors motors

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The air gap is small when compared to induction motors


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Induction motor Rotor losses lower lower than those of the induction i nduction machine

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High power factor and higher continous torque rating

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The full load efficiency at rated speed and the speed range at const constant ant power, power, also also exceed exceed the values values obtainable with induction motors. www.technologyfutur www .technologyfuturae.com ae.com

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Switched reluctance motors

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does not suffer from high torque ripple.

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Power Po wer density lower than Switched reluctance reluc tance motor


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Principle of operation of synchronous syn chronous reluctance motor are discussed.

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The mathematical model of Synchronous reluctance motor was also discussed.

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Comparisons with different motors has been done


[1] Srge S rge Edward Lyshevski, Alexander Alex ander Nazarov, Nazarov, Ahmed El- Antably Anta bly,, Charles Yokomoto, A.S.C. Sinha, Maher Rizkalla and Mohamed El – Sharkawy , “Design and Optimization, Steady S teady -State -State and Dynamic Analysis of Synchronous Reluctance Motors Controlled by Volta Voltagege-Fed Converters With Nonlinear Controllers”, Controllers”, IEEE Trans. Industry Applications, Sept.1999. [2] Peyman Niazi, “Permanent Magnet Assisted Synchronous Reluctance Motor Design And Performance Improvement”, Texas A&M University University [3] R. E. Betz, R. Lagerquist, M. Jovanovic, T. J. E. Miller and R. H. Middleton, “Control of synchronous reluctance machines,” IEEE Trans. Industry Industr y Applications, vol. vol. 29, no. n o. 6, pp. pp. 11 10-1 122, 1993. www.technologyfutur www .technologyfuturae.com ae.com

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Synchronous Reluctance Motor

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