طراحي يك مبدل براي موتور سوئيچ رلكتانس به منظور كاهش ريپل گشتاور و بهبود ضريب توان در روش كنترل مستقيم گشتاور

چكيده انگليسي :

88 A Specially designed Converter for Minimizing SRM Torque Ripple and Improving its Power Factor Loghman Samani l samani@ec iut ac ir Date of Submission Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Sayed Morteza Saghaiannezhad saghaian@cc iut ac ir Abstract Switched reluctance motors have received great attention for domestic and industrial applications overthe past two decades The disadvantage however is their inherent torque ripple due to their protruding motorstator and rotor poles To overcome this drawback useful control methods have been recently proposed which may be classified into the two general categories of direct and indirect methods The indirect methodinvolves using TSF in which torque ripple is minimized by applying the current profile These profiles are however calculated offline for constant performance points at a high memory cost in the microcontrollersystem Direct methods in contrast take advantage of a DITC for the direct control of motor instantaneoustorque Conventional converters use diode bridge rectifiers and large filter capacitors for SRM The motorpower factor is thus reduced when rectifiers draw the pulse current from an AC source They are thus associated with problems of low power factor and big pulse current Like in other electric machines back emfvoltage increases with speed At a high speed performance the back emf voltage is considerable whencompared to that of the dc link which in turn causes the torque and current to decrease Due to the reducedtorque the total torque cannot be adjusted at all times within the hysteresis band cycle which leads toincreased torque ripple and reduced control accuracy This is because the average torque in this case starts toreduce and to deviate from the reference Four level converters are therefore used both to enhance thecurrent slope at the initial moment and to reduce the current along the conduction of the single phase due tothe increased back emf In fast excitation DC link voltage VDC and boost voltage VB are supplied to phasewinding A number of problems arise when the speed increases One such problem is the reduced excitationtime which makes it difficult for the desired phase current to build up Another is the larger torque ripple athigher motor speeds However the boost voltage of the 4 level topology breaks through voltage limitation quickly building up the excitation current and rising voltage when current and torque decrease Thedisadvantages of this converter include the low power factor and in most of convertors controlling of boostcapacity is important problem To control of it the phase voltage should be increased when voltage increase isnot necessity until boost capacity be discharged In proposed converters when the current falls due toincreasing back emf voltage VDC VB voltage excites the phase to prevent torque reduction Additionally current pulsing is prevented by drawing current from the source at times when the voltage source is capableof providing the required current a process which leads to reduced current amplitude and improved powerfactor Keywords Direct Instantaneous Torque Control DITC Hysteresis control power factor Switched Reluctance Motor

ساماني، لقمان

طراحي يك مبدل براي موتور سوئيچ رلكتانس به منظور كاهش ريپل گشتاور و بهبود ضريب توان در روش كنترل مستقيم گشتاور

كنترل گشتاور بر اساس DITC