modelling & torque pulsation reduction of switched reluctance motor

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MODELLING & TORQUE PULSATION REDUCTION OF SWITCHED RELUCTANCE MOTOR

G.PRASHANT

Edited By

Sarath S Nair

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www.technologyfuturae.comCONTENTS

• INTRODUCTION• CONSTRUCTIONAL FEATURES• OPERATING PRINCIPLE• SYSTEM DESCRIPTION AND MODELING• STUDY OF TORQUE PULSATION• ADVANTAGES• APPLICATIONS• CONCLUSION

www.technologyfuturae.comINTRODUCTION

•The name switched reluctance describes two features : a) switched- the m/c must be operated in continuous switching mode b) reluctance- it is the true reluctance m/c in the sense that both stator and rotor have variable reluctance magnetic circuit

• It is a double salient machine.• It illuminates permanent magnet, brushes &

commutators.• Due to inherent simplicity it has reliable and

low-cost variable-speed drive

www.technologyfuturae.comCONSTRUCTIONAL

•Stator consist of steel laminations forming the salient pole

•With no rotor winding,the rotor is basically a piece of steel (and laminations) shaped to form salient poles. Hence no Cu loss in rotor winding

• It is the only motor with salient poles in rotor & stator.

www.technologyfuturae.com6/4 switched reluctance machine with

one phase excited

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•One phase of stator is energized at a time by dc voltage pulses.• The rotor experiences a torque and moves to a position to align with stator pole so that the reluctance is minimum & inductance is

maximum. If rotor continues past the aligned position braking

torque is produced Current is switched off to remove this condition of

breaking torque

www.technologyfuturae.comMATHEMATICAL MODEL OF

SR MOTOR

The motor is single phase excited ; that is it carries one winding on the stator.

The excited winding is wound on the stator & the rotor is free to rotate.

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SYSTEM DESCRIPTION

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Contd..•System consists of four major parts-

motor, current-regulated converter , controller and sensors

•Controller computes the error and outputs the current command to the converter

•Sensors used are current and speed sensors

•System consists of current and speed loop only

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MODELING•Stationary frame model

▫Self-inductance of the motor is related to the position of rotor

▫Assuming self-inductance of each phase isn’t related to its phase current

▫The flux linkage of the rotor can be expressed as

▫

▫Where j=a,b,c

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Contd..•The dynamic equation of each phase

voltage is

•And the torque equation is given as

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Contd…•Synchronous frame model

the transformation from abc to dq axis can be expressed as

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Contd..•The synchronous d-q axis voltage

equation are

•The torque equation is

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TORQUE PULSATION •Major disadvantage of SRM is that its

torque pulsation is larger than other machines

•Self-inductance’s value changes according to the position of stator and rotor

•From the self-inductance waveform the current control commands can be obtained for producing maximum and minimum torque

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Contd..•The real self-inductance can be expressed

as

▫Where j=a,b,c.

•ϴe=Nrϴrm

•ϴrm= mechanical shaft angle

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Contd..• Neglecting the harmonic components and hence

considerring only the fundamental components

• where L’j is the values of the self-inductances in the abc stationary frame.

• its approximate value in dq synchronous frame is

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•The equivalent value obtained is

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ADVANTAGES• Performance- much greater torque output• Low cost- low manufacturing cost, low material &

maintenance cost. It does not use magnets.• Cooling- most of the heat is generated in which is relatively

easy to cool.

www.technologyfuturae.comAPPLICATIONS

• SRMs are used in some washing machine designs.• SRM drives are ideal for aircraft applications such as a jet

engine starter motor generator.• Bearingless switched reluctance motor for all electric

propulsion system

www.technologyfuturae.comSUMMARY

•The construction, operating principle & key features of switched reluctance motor are explained.

•The mathematical model & flux linkage characteristics are analysed.

•The torque pulsation problem of the switch reluctance motor was also discussed

www.technologyfuturae.comREFERENCES

[1] Miller, 7: J. E., Switched Reluctance Motors and Their Control, Clarendon Press, Oxford, 1992.

[2] R. Krishnan, Switched Reluctance Motor Drives: Modelling, Simulation, Analysis, Design, and Applications, CRC Press, 2001

[3] R. S. Wallace, D. G, Taylor, "A balanced commutator for switched reluctance motors to reduce torque ripple," IEEE Trans. Pow. Electron., vol. PE-7, 110. 4, pp. 617-626, Oct. 1992.

[4] D. S. Reay, M. M. Moud, T. C. Green, and B. W.Williams, "Switched reluctance motor control via fuzzy adaptive systems," IEEE Control Systemsvol. 15, no. 3, pp. 8-15, June 1995.

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