Brush-DC Equivalent control based delta modulation for a PWM inverter-fed nine-phase induction machine drive

Gunda, Lovemore (2015-12)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: A considerable amount of research has been done on the control of induction machines since the introduction of the power electronic inverter. The use of power electronic inverters has also opened the way for the design of multiphase induction machines. The current rating of the power electronic components used in multiphase inverters is lower than those used in three-phase inverters. On the machine side, the multiphase machines have higher power and torque density than their three-phase counterparts. The control of these multiphase induction machines poses a challenge for the designer of the drive system. Scalar control, direct torque control and vector control methods work well in three-phase machines. However, the analysis of vector based techniques becomes complex as the number of phases increases and new methods are being proposed to reduce the complexity of implementing machine control. The Brush-DC Equivalent (BDCE) control method was proposed to simplify the design of controllers. This method does not include complex coordinate transformations like are used in vectorbased techniques. The BDCE control method is derived from the control of separately excited brushDC machines utilising compensating windings. The induction machine controlled using the BDCE method is designed such that the phases of the machine act alternately in rime as torque-producing or field-producing phases. This is achieved by supplying the induction machine windings with specially designed trapezoidal stator current waveforms. The BDCE control method enables decoupled control of flux and torque without complex coordinate transformations. The method can be implemented for high phase-number multiphase induction machines without added complexity. In this thesis, the BDCE control method implementing a delta modulated current controller which generates pulse width modulated signals for the power electronic inverter is presented. The delta modulation technique is proposed because it gives good inverter performance characteristics and reduces torque and current ripples. It also reduces total current harmonic distortions through the use of a fixed switching frequency. The BDCE controlled drive is simulated using Matlab/Simulink. The simulation results suggest that delta modulation gives lower current and torque ripples with attenuated low order voltage harmonics. Practical evaluation of the drive is done using the delta modulated current controller to validate the simulation results. An alternative delta modulation scheme in which the reference current signal is integrated before being fed to the forward comparator is proposed, designed and tested. The alternative delta modulation scheme produces the required trapezoidal stator currents and allows decoupled control of the field and torque currents. The results of the practical evaluation compare well with the simulation results and show that a delta modulated current controller can be used in the drive. Better results are expected if stator voltages are fed back to the modulator to estimate the reference signal.

AFRIKAANSE OPSOMMING: ʼn Groot hoeveelheid navorsing is al gedoen oor die beheer van induksiemasjiene (IM) sedert die ontwikkeling van die drywingselektronika omskakelaar. Die gebruik van die drywingselektronika omskakelaars het die weg gebaan vir die ontwerp van veelfasige IM. Tans is die stroomkenwaarde van die drywingselektronika komponente wat in 'n veelfasige omsetter gebruik word laer as die van drie-fase omsetters. Aan die masjienkant, is beide die drywing en wringkrag digtheid van 'n van die veelfasige masjien hoër as die van hul drie-fase eweknieë. Die beheer van dié veelfasige IM hou 'n uitdaging in vir ontwerpers van die aandryfstelsel. Alhoewel skalaar-, direkte wringkrag- en vektor-beheer metodes goed werk vir drie-fase elektriese masjiene, raak vektor-gebaseerde metodes meer kompleks soos die aantal fases van 'n masjien toeneem. Nuwe metodes word voorgestel om die kompleksiteit van masjien beheer te vereenvoudig. Die Borsel-GS Ekwivalent (BGSE) beheer metode word voorgestel om die ontwerp van die beheerders te vereenvoudig. Die metode sluit nie komplekse koördinaat transformasies in soos met vektor-gebaseerde tegnieke nie. Die BGSE beheer metode is afgelei van die beheer van 'n afsonderlik gemagnetiseerde borsel-GS masjien met kompensasie windings. Die IM wat beheer word deur gebruik te maak van die BGSE metode word so ontwerp dat die fases van die masjien afwisselend oor tyd as wringkrag- of veld-produserende fasesoptree. Dit word gedoen deur die lM te voer met spesiaal ontwerpte trapesoïdale stator-stroom golfvorms. Die BGSE metode maak dit moontlik vir onafhanklike beheer van beide vloed en wringkrag sonder enige komplekse koördinaat transformasies. Die metode kan geïmplementeer word op hoë fase veelfasige IM sonder enige addisionele kompleksiteit. In die tesis word die BGSE metode implementering van 'n delta modulasie stoom beheerder wat pulswydte gemodulasie seine genereer vir 'n drywing elektronika krag-omskakelaar aangebied. Die delta modulasie tegniek word voorgestel, omrede dit goeie omsetter werksverrigting karakteristieke verskaf en die wringkrag en stroom rimpel verlaag. Daarby verminder dit ook die totale harmoniese distorsies van die stroom deur gebruik te maak van 'n vaste skakelfrekwensie . Die BGSE beheer aandrywer word met. Matlab/Simulink gesimuleer. Die simulasie resultate toon dat delta modulasie 'n laer stroom en wringkrag rimpel tot gevolg het as ook verlaagte lae orde spanning harmonieke. Die praktiese evaluering van die aandrywer word gedoen met die delta gemoduleerde beheerder om die simulasie resultate te verifieer. 'n Alternatiewe delta modulasie skema word voorgestel, ontwerp en getoets, waar die verwysing stroomsein eers geïntegreerd word voor dit aan die vorentoe vergelyker gestuur word. Die alternatiewe skema het die vereiste trapesoïdale stator strome geproduseer en het toegelaat vir die onafhanklike beheer van beide vloed en wringkrag strome. Die resultate van die praktiese evaluering vergelyk goed met die van die simulasie resultate en toon dat 'n delta gemoduleerde stroom beheerder gebruik kan word in die aandrywer. Beter resultate word verwag indien die stator spannings teruggevoer word na die modulator om 'n beter verwysings sein af te skat.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/97826
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