Switched reluctance motors (SRMs) are promising candidates for electric vehicles due to lower manufacturing costs, higher efficiency, and robustness operation in a harsh envi-ronment. For accurate control of the SRM, the real-time rotor position is needed for phase computation. To obtain position information, position-sensorless control techniques have been developed to take the role of position sensors in commercial SRM drives for cost reduction or sensor-fault tolerance capability. Nowadays, the position-sensorless control of SRMs still suffers from a technical problem: the dependence on magnetic characteris-tics. Existing position estimation algorithms often require time-consuming offline meas-urement of magnetic parameters, limiting the broad applications due to the low generality. It is therefore of great significance to develop universal position-sensorless control tech-niques with less magnetic parameter dependence. Zero- and low-speed position-sensorless control of the SRM needs high-frequency in-jection into the idle phase to measure the stator inductance. Rotor position is often esti-mated from the prestored inductance lookup table but is replaced by a new regional phase-locked loop (RPLL) with a self-commissioning process in this thesis. The modeling of the unsaturated stator inductance can be established automatically via the pulse voltage injection at the initial stage without offline testing. The RPLL embedded with a three-phase heterodyne design can estimate the full-cycle rotor position from the idle-phase in-ductance based on the unsaturated inductance model. The proposed low-speed position estimator can also realize robust sensorless control in four-quadrant operation and magnet-ic saturation conditions without complicated magnetic characteristics. Besides, local sta-bility of the position estimator is proved, and an optimized parameter design scheme is given. Although pulse voltage injection offers accurate position estimation in low-speed op-eration, the induced pulse current results in additional copper loss and torque ripples. This problem is overcome in the thesis by regulating the magnitude of induced current at a minimal level. The induced current regulator is designed as a terminal sliding-mode con-troller that adjusts the injection voltage online over the whole idle-phase period. Proper control parameter selection based on the convergence analysis and stability proof ensures robust control performance against parameter uncertainties. The proposed pulse injection scheme combined with the RPLL can guarantee accurate position estimation while reduc-ing copper losses and torque ripples significantly. Due to the shortened idle-phase duration when the rotor speed increases, pulse injec-tion methods are infeasible for high-speed position estimation. To solve the problem, this thesis proposes a nonlinear observer based on feature position estimation in conduction phases for high-speed sensorless control. A self-commissioning method is adopted to cap-ture a two-dimensional flux linkage curve at a feature position, which avoids offline measurement of the complete three-dimensional characteristics. However, the estimated feature position has low resolution, and its estimation accuracy is degraded by nonideal flux linkage errors. To improve the sensorless control performance, a nonlinear state ob-server using online Fourier series is then designed to eliminate disturbances in position es-timation. Parameter design based on a small-signal analysis is also given to guarantee ac-curate position and speed estimation. High-speed position-sensorless control is further simplified using a new quadrature flux estimator without using any flux linkage characteristics. The method requires neither offline measurement nor online self-commissioning. This advantage is realized by adopt-ing a speed-adaptive bandpass filter to extract the fundamental flux linkage. A three-phase phase-locked loop is then used to estimate the rotor position from the orthogonal flux linkage signals without a priori knowledge of the SRM magnetic characteristics. The magnetic-parameter-free position estimation can facilitate the application of sensorless control in a general-purpose SRM converter. A wide-speed range position estimation scheme is realized by combining both the low-speed and high-speed position estimation approaches. Consequently, a universal posi-tion-sensorless control scheme is proposed in the thesis, covering the full-speed range and not requiring offline measurement effort. The proposed position estimation schemes are verified on a 5.5 kW 12/8 SRM test bench. / Thesis / Doctor of Philosophy (PhD)

Rotor position estimation of switched reluctance machines (SRMs) is the main focus of this work. Rotor position sensors are a crucial component of optimal motor controls. Fail-safe operation and system cost reduction have been extensively researched and implemented in industry and academia. Position sensorless control on switched reluctance machines introduces a new challenge due to high nonlinearity under different operating conditions. A comprehensive review of SRM analytical modeling is presented, detailing each technique's main advantages and drawbacks. A least square-based analytical model (LSA) is proposed, which provides a simpler implementation and improved performance when compared to the methods commonly used in the literature. A literature review of rotor position sensor technology, position sensor fail modes, and position sensorless control is presented, providing a good roadmap of potential development and current limitations of the current technology. A wide speed range sensorless control is usually required when considering fail-safe techniques, fail detection methods, and low-cost applications. A unified nonlinear optimization-based sensorless control is proposed in this thesis, where a single method is used for startup, low and high speeds, with reduced memory allocation where a look-up table is not required, optimal transient response due to the elimination of a phase-locked-loop (PLL), and robustness against parameter variation. The method is validated at a wide speed range and torque conditions, thus showing the performance against conventional methods. / Thesis / Doctor of Philosophy (PhD)

This thesis focuses on utilizing the persistent voltage vector injections by finite control set model predictive control (FCSMPC) to enable simultaneous estimations of both position and parameters in order to realize robust sensorless interior permanent magnet synchronous machine (IPMSM) drives valid at the entire operating region including no-load standstill without any additional signal injection and switchover. The system (here, IPMSM) needs to meet certain observability conditions to identify the parameters and position. Moreover, each combination of the parameters and/or position involves different observability requirements which cannot be accomplished at every operating point. In particular, meeting the observability for parameters and position at no-load standstill is more challenging. This is overcome by generating persistent excitation in the system with high-frequency signal injection. The FCSMPC scheme inherently features the persistent excitation with voltage vector injection and hence no additional signal injection is required. Moreover, the persistent excitation always exists for FCSMPC except at the standstill where the control applies the null vectors when the reference currents are zero. However, introducing a small negative d axis current at the standstill would be sufficient to overcome this situation.The parameter estimations are investigated at first in this thesis. The observability is analyzed for the combinations of two, three and four parameters and experimentally validated by online identification based on recursive least square (RLS) based adaptive observer. The worst case operating points concerning observability are identified and experimentally proved that the online identification of all the parameter combinations could be accomplished with persistent excitation by FCMPC. Moreover, the effect of estimation error in one parameter on the other known as parameter coupling is reduced with the proposed decoupling technique. The persistent voltage vector injections by FCSMPC help to meet the observability conditions for estimating the position, especially at low speeds. However, the arbitrary nature of the switching ripples and absence of PWM modulator void the possibility of applying the standard demodulation based techniques for FCSMPC. Consequently, a nonlinear optimization based observer is proposed to estimate both the position and speed, and experimentally validated from standstill to maximum speed. Furthermore, a compensator is also proposed that prevents converging to saddle and symmetrical ( ambiguity) solutions. The robustness analysis of the proposed nonlinear optimization based observer shows that estimating the position without co-estimating the speed is more robust and the main influencing parameters on the accuracy of the position estimation are d and q inductances. Subsequently, the proposed nonlinear optimization based observer is extended to simultaneously estimate the position, d and q inductances. The experimental results show the substantial improvements in response time, and reduction in both steady and transient state position errors. In summary, this thesis presents the significance of persistent voltage vector injections in estimating both parameter and position, and also shows that nonlinear optimization based technique is an ideal candidate for robust sensorless FCSMPC. / Thesis / Doctor of Philosophy (PhD)

Switched reluctance motor has features like robust structure, low cost, and wide speed extension range over conventional induction and synchronous motors. These features make it a promising choice for many applications from electric vehicle to aerospace industry. However, due to its silent structure, the characteristics of switched reluctance motor are highly nonlinear. The nonlinearity makes it difficult to control and results in degraded performance such as high torque ripple and acoustic noise compared with conventional induction machine or synchronous machine. New power converters and control methods have to be developed to improve its performance. In order to reduce the current ripple and torque ripple, a novel three-level converter for switched reluctance motor is proposed. The operation modes and modulation method are presented in detail. Simulation and experimental results show that compared to conventional two-level converter, the proposed three-level converter is able to reduce current ripple, torque ripple and acoustic noise significantly without increasing cost. A fast and accurate current controller is essential for the torque control of switched reluctance motor. An adaptive current controller for the three-level converter is developed to avoid the performance degradation caused by manufacture inconsistency. This controller has the ability to adjust its parameters according to the specific motor it drives. Fast dynamic and high accuracy could be achieved through parameter adaption. In order to reduce the cost, and compete with the well-developed sensorless brushless DC and induction motor drive system, a new position sensorless control method for switched reluctance motor is proposed. This method is effective under both low speed operation and high speed operation. It can start with heavy load. It does not have to align the machine before start up as what is needed for many sensorless brushless DC drive systems. The proposed converter and control methods are all verified by simulation and experimental results. / Thesis / Doctor of Philosophy (PhD)

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The focus of this thesis is position sensorless control of a transverse-laminated reluctance synchronous machine. Rotor position information is required for high-performance closedloop control of the reluctance synchronous machine and is conventionally supplied by unreliable hardware position resolvers. In addition a FPGA-based rapid prototyping system is completed as part of the research term for control of the machine drive system. For the first time the unified active- ux (AF) method is investigated and implemented for position sensorless control of the transverse-laminated reluctance synchronous machine in this study. The method is based on the torque equation of the machine and is basically the same for any AC machine. The estimation scheme is implemented for closed-loop position sensorless control from low- to rated speed in the entire rated load range with simulation and measured results confirming its capabilities. A number of characteristics of the machine (including generator operation) have implications for implementation of the active- ux (AF) method and are therefore investigated. Another position estimation method investigated is the arbitrary injection (AI) scheme which is derived to be completely machine parameter independent. The method simply requires a current progression at each calculation step allowing use of a smaller injection voltage. This method is implemented again on the reluctance synchronous machine and is shown to be capable of position sensorless current and speed control of the drive from standstill to rated speed with simulation and measured results. However, when the machine is operating above low speeds it is shown that this technique is only capable of position sensorless control at low loads. To deliver position sensorless control in the entire rated speed and load range a new hybrid controller scheme is designed and implemented. The hybrid scheme is speed and load dependent with hysteresis regions for stability at specific working points. The active- ux (AF) method is implemented in the low to rated speed range at medium to rated loads while the arbitrary injection (AI) method is implemented elsewhere. Measured results show that the scheme is capable of position sensorless control in the entire rated speed and load range with some limitations on dynamics. Because of the limitations on dynamics of the hybrid scheme an assisted fundamental model position estimation scheme was investigated. Simulation results show that this controller requires further investigation. / AFRIKAANSE OPSOMMING: Die fokus in hierdie tesis is die posisie-sensorlose beheer van 'n transvers-gelamineerde reluktansie sinchroonmasjien. Rotor posisie inligting word benodig vir geslote-lus beheer van die reluktansie sinchroonmasjien met ho e-werkverrigting, en word normaalweg deur onbetroubare hardeware sensors verskaf. As deel van die navorsings-termyn is 'n FPGAgebaseerde beheerstelsel vir die masjien stelsel voltooi. Die \aktiewe-vloed" posisie-afskattings metode is ondersoek en vir die eerste keer ge mplementeer vir posisie-sensorlose beheer van die transvers-gelamineerde reluktansie sinchroonmasjien. Die metode is dieselfde in konsep vir alle WS masjiene en word basseer op die vergelyking vir wringkrag van die masjien. Vollas geslote-lus posisie-sensorlose beheer van die masjien in die lae tot ho e spoedbereik is suksesvol ge mplementeer met simulasie en gemete resultate. Verkskeie inherente eienskappe van die masjien het implikasies vir gebruik van die \aktiewe-vloed" metode (insluitend generator werking) en is dus ondersoek. Die \arbitr^ere injeksie" metode wat afgelei is om onafhanklik van masjien parameters te wees is ook odersoek. Hierdie metode verlang slegs 'n stroom-afgeleide by elke tydstip en benodig dus 'n kleiner injeksie-spanning. Hierdie metode is weer ge mplementeer op die reluktansie sinchroon masjien met suksesvolle posisie-sensorlose beheer in die hele spoed bereik getoon in simulasie en praktiese resultate. Dit word egter getoon dat hierdie metode slegs onder lae-las toestande posisie sensorlose beheer bo lae-spoed kan bewerkstellig. Ten einde posisie-sensorlose beheer in die hele spoed en wringkrag bereik te verkry is 'n nuwe hibriede beheerskema ontwerp en ge mplementeer. Die skema is spoed en las afhanklik met histerese vir stabiliteit by 'n spesi eke werkpunt. Die \aktiewe-vloed" metode word gebruik bo lae spoed teen 'n minimum las terwyl die \arbitr^ere injeksie" andersins ge mplementeer word. Gemete resultate toon dat die skema posisie-sensorlose beheer van die masjien in die hele spoed en las bereik toelaat met sommige beperkings op dinamika. Met inagneming van die beperkings op die hibriede metode is 'n ondersteunde fundamentele model afskattingskema ondersoek. Simulasie resulate toon dat hierdie beheerder verdere ondersoek benodig.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The position sensorless controllability of the reluctance synchronous machine (RSM) is investigated in this thesis with the focus on industry applications where variable and dynamic torque is required from startup up to rated speed. Two low speed as well as one medium to high speed position sensorless control (PSC) method for RSMs are investigated. These methods are extended to operate in the entire rated speed region with a hybrid PSC structure that makes use of phase locked-loop synchronisation and a hysteresis changeover method. It is shown in this thesis that PSC of the lateral rib rotor RSM is not possible from zero up to ± 0.2 p.u current. It is shown through finite element (FE) simulations that PSC of the ideal rotor RSM however, is possible at zero reference current. A novel construction method is used to build two ideal rotor RSMs. Measured flux linkage curve results of the ideal rotor RSMs correlate well with simulation results and it is shown that the electrical angle of the machine can be tracked successfully at zero reference current. The FE simulation package is used to compare the saliency of the RSM on a per-unit scale to three types of field intensified permanent magnet (FI-PM) synchronous machines and a field weakening interior permanent magnet synchronous machine. It is shown that the saliency of the RSM is larger than that of the investigated PM machines from zero up to rated load. It is thus concluded that the RSM is well suited to saliency-based PSC (SB-PSC) methods, which are used to control synchronous machines at startup and low speeds. The hybrid PSC methods developed in this thesis, are tested and evaluated on three proposed industry applications. The first is a reluctance synchronous wind generator with an inverter output LC filter. The LC filter allows long cables to be used and reduces the voltage stress on the stator windings of the machine. The combination of the LC filter and hybrid PSC method allows the power electronics and controller to be stationed in the base of the turbine tower. A new stator quantity estimation method is derived to omit the need of current and voltage sensors on the machine side of the LC filter. Good maximum power point tracking laboratory results are shown with the high frequency injection-assisted hybrid PSC method. The second application investigated is a position sensorless controlled variable gear electric vehicle (EV) RSM drive. Simulation and measured results show good torque capabilities of the position sensorless controlled EV RSM. It is shown through simulation results that the fundamental current harmonic is dominant in the demodulation scheme of the high frequency injection position sensorless control (HFIPSC) method due to the high current rating of the proposed RSM. The HFI-PSC method is extended to reduce the effect of the fundamental current harmonic in the demodulation scheme without adding any additional filters. The final investigated application is a novel mine scraper winch, which uses two position sensorless controlled RSMs to retrieve ore from the blast site underground. The new design improves on the safety, efficiency and durability of the current scraper winch design. Measured results show that the position sensorless controlled winch RSM is able to deliver rated startup torque with both investigated SB-PSC methods. Finally an automation method is implemented and tested to limited the applied force on the scraper and automatically free itself when stuck. / AFRIKAANSE OPSOMMING: Die posisie sensorlose beheer eienskappe van die reluktansie sinchroonmasjien (RSM) word in hierdie tesis ondersoek met die fokus op industriële toepassings waar varierende dinamiese draaimoment vereis word vanaf stilstand tot by ken spoed. Twee lae spoed- en een ho¨e spoed posisie sensorlose beheer (PSB) metodes vir RSMe is ondersoek. Hierdie metodes is uitgebrei om twee hibriede PSB metodes to skep wat die RSM van stilstand tot by kenspoed posisie sensorloos kan beheer. Die ontwikkelde hibriede metodes maak gebruik van ’n histerese oorskakelings skema en fase geslote lus sinchronisasie Daar word in hierdie tesis bevestig dat die laterale rib RSM nie beheer kan word met die geondersoekte PSB metodes by nul stroom nie. Eindige element simulasie resultate wys egter daarop dat die ideale rotor RSM wel beheer kan word met die geondersoekte metodes by nul stroom. ’n Nuwe konstruksie metode is voorgestel om twee ideale rotor RSMe to bou. Gemete vloed omsluiting kurwes resultate korreleer baie goed met dié van die eindige element simulasies. Gemete resultate wys ook daarop dat PSB van die nuwe masjiene moontlik is by nul stroom. ’n Eindige element pakket is gebruik om die speek-koëffissiënt van die RSM te vergelyk met drie tipes veld-versterkte permanent magneet masjiene, asook een veld verswakte permanent magneet versinkte masjien. Die simulasie resultate wys dat die RSM se speek-koëffissiënt hoër is as die van die geondersoekte permanent magneet masjiene. Die RSM is dus geskik vir speek-koëffissiënt georienteerde PSB metodes, wat hoofsaaklik by stilstand en lae spoed gebruik word. Die ontwikkelde hibried PSB metodes is getoets en geëvalueer met drie voorgestelde industriële toepassings. Die eerste is ’n reluktansie sinchroon wind generator met ’n omsetter uittree laagdeurlaat filter. Die laagdeurlaat filter laat toe dat langer kabels vanaf die omsetter na die generator gebruik kan word. Die kombinasie van die laagdeurlaat filter en die PSB metodes laat toe dat die drywingselektronika en die beheerders in die toring basis geplaas kan word. Dit kan die gewig van die nasel verminder. Goeie maksimum drywingspunt volging laboratorium resultate word getoon met die hoë frekwensie ondersteunde hibried PSB metode. Die tweede geondersoekte toepassing is ’n posisie sensorlose beheerde, varierende ratkas elektriese voertuig RSM. Goeie simulasie en gemete draaimoment resultate van die RSM word getoon. Simulasie resultate toon dat die fundamentele q-as stroom harmoniek dominant is in die demodulasie skema van die hoë frekwensie PSB metode, as gevolg van die hoë ken stroom van die motor. Die hoë frekwensie PSB metode is uitgebrei om die fundamentele stroom harmoniek te onderdruk in die demodulasie skema sonder om enige filters by te voeg. Die finale toepassing is ’n nuwe myn windas wat van twee posisie sensorlose beheerde RSMe gebruik maak om klippe ondergronds te verplaas vanaf die ontploffings area. Die voorgestelde ontwerp verbeter die huidige ontwerp ten opsigte van die veiligheid, energie effektiwiteit en robuustheid. Gemete resultate wys dat ken draaimoment moontlik is met altwee speek-koëffissiënt metodes. ’n Automasie metode, wat die maksimum draaimoment op die windas beperk en automaties homself bevry indien hy vasval, is voorgestel en geëvalueer.