Dissertations / Theses on the topic 'Development of brushless DC (BLDC)'

Commutation is a fundamental feature of all DC machines. In conventional DC machines the commutation function is performed by the commutator and brushes. These act as both position sensors and switches. The mechanical commutator has obvious disadvantages. Overcoming those disadvantages has been a major reason behind the development of brushless DC (BLDC) machines. In brushless DC machines commutation is performed by power electronic devices forming part of an inverter bridge. However, switching of the power electronic devices has to be synchronised with rotor position. Position sensing is therefore an essential requirement. This can be done by using sensors such as Hall Effect devices or a sensorless approach may be adopted. Advantages of sensorless techniques include reduced cost and wiring. The most common sensorless method is based on detection of the zero crossing of back EMF signals. But this technique works only above a certain speed since back EMF is directly proportional to speed. As a result BLDC systems which rely solely on back EMF signals for commutation suffer from relatively poor starting performance characterised by back rotation of up to one hundred and eigthty electrical degrees and large fluctuations in electromagnetic torque resulting from non-ideal commutation instants. This may not be acceptable for some applications and many researchers have attempted to overcome those problems. The aim of this project has been to investigate the possibility of a sensorless technique which does not cost more than the back EMF method but with a performance at start-up comparable with that obtained when Hall sensors are used. Initial investigations led to a saliency based method. Detailed theoretical analysis is presented which shows that the method is insensitive to variations in operational parameters such as load current and circuit parameters such as power device voltage drops and winding resistances. There is a close parallel between it and the back EMF method and this makes it easy to swap to the latter method at high speed if necessary. A starting strategy, relying on saliency related measurements, is proposed which offers starting performance much better than the back EMF method and almost as good as Hall sensor based techniques. Experimental evidence is provided to confirm that commutation instants determined by the proposed method are practically coincident with those obtained when Hall sensors are used.

This work was carried out on behalf of Science Safari. Science Safari wants to create a product that facilitates the understanding of how much physical work is required to create electrical energy. This is done by cranking the pedals of a bicycle. The purpose of this work is to create a control unit that keeps the torque required to crank the pedals close to constant. The torque can be kept constant by creating a variable load for the generator, in this case, a pulse modulated JFET is used. The output of the current sensor and the Hall-effect sensor are used to calculate the required resistance of the JFET to keep constant torque. All this is controlled via a Raspberry Pi 3 Model B (RPi) which also shows real-time values on a display. The functionality of the sensors and JFET has largely been completed, but the assembly of all components is lacking in this work.<br>Detta arbete är utfört i uppdrag av Science Safari. Science Safari vill skapa en produkt som underlättar förståelsen av hur mycket fysiskt arbete som krävs för att skapa elektrisk energi. Detta genom att användaren vevar på en cykels pedaler för hand. Syftet med detta arbete är att skapa en styrenhet som ungefär håller ett konstantvridmomentet på en cykels pedaler. Vridmomentet kan hållas konstant genom att skapa en variabel last till generatorn, med hjälp av en pulsmodulerad JFET. För att beräkna vilken resistans JFETen ska ha för att hålla konstant vridmoment används en strömsensor och en Hall-effect sensor. Allt detta styrs via en Raspberry Pi 3 ModelB som även visar värden i realtid på en display. Funktionaliteten av sensorerna och JFET har till stor del färdigställts men sammansättning av alla komponenter saknas i detta arbete.

The aim of this work is to reduce the cost and size of a brushless dc motor (BLDC) drive as well as increase the reliability and ruggedness of that drive. Traditional BLDC drives use Voltage Source Inverters (VSI) that utilize hard switching, thereby generating switching losses and entail the use of large heatsinks. VSI needs a huge dc link capacitor that is inherently unreliable and is one of the most expensive components of a drive. Hence, a Current Source Inverter (CSI) is used to replace the hard switchings by natural turn-off, thereby eliminating the heatsinks as well as the large dc link capacitor. A controlled rectifier together with a large inductor act as the current source. The only disadvantage is the large value of the dc link inductor and the huge number of turns needed to achieve these values of the inductances lead to huge resistive losses. Therefore, it is shown that it is possible to replace the controlled rectifier and the large inductor with a suitable dc-dc converter based current source switching at high frequencies and a much smaller value of the dc link inductor. Switching at high frequencies makes it possible to reduce the value of the dc link inductor without increasing the current ripple. Hence, it is possible to have the advantages of using a CSI as well as reduce the value of the dc link inductor without a corresponding increase in the heat sink and snubber requirements.

Brushlesss dc (BLDC) motors and their drives are penetrating the market of home appliances, HVAC industry, and automotive applications in recent years because of their high efficiency, silent operation, compact form, reliability, and low maintenance. Traditionally, BLDC motors are commutated in six-step pattern with commutation controlled by position sensors. To reduce cost and complexity of the drive system, sensorless drive is preferred. The existing sensorless control scheme with the conventional back EMF sensing based on motor neutral voltage for BLDC has certain drawbacks, which limit its applications. In this thesis, a novel back EMF sensing scheme, direct back EMF detection, for sensorless BLDC drives is presented. For this scheme, the motor neutral voltage is not needed to measure the back EMFs. The true back EMF of the floating motor winding can be detected during off time of PWM because the terminal voltage of the motor is directly proportional to the phase back EMF during this interval. Also, the back EMF voltage is referenced to ground without any common mode noise. Therefore, this back EMF sensing method is immune to switching noise and common mode voltage. As a result, there are no attenuation and filtering necessary for the back EMFs sensing. This unique back EMF sensing method has superior performance to existing methods which rely on neutral voltage information, providing much wider motor speed range at low cost. Based on the fundamental concept of the direct Back EMF detection, improved circuitry for low speed /low voltage and high voltage applications are also proposed in the thesis, which will further expand the applications of the sensorless BLDC motor drives. Starting the motor is critical and sometime difficult for a BLDC sensorless system. A practical start-up tuning procedure for the sensorless system with the help of a dc tachometer is described in the thesis. This procedure has the maximum acceleration performance during the start-up and can be used for all different type applications. An advanced mixed-signal microcontroller is developed so that the EMF sensing scheme is embedded in this low cost 8-bit microcontroller. This device is truly SOC (system-on-chip) product, with high-throughput Micro core, precision-analog circuit, in-system programmable memory and motor control peripherals integrated on a single die. A microcontroller-based sensorless BLDC drive system has been developed as well, which is suitable for various applications, including hard disk drive, fans, pumps, blowers, and home appliances, etc.<br>Master of Science

This thesis focuses on BLDC motor control algorithms with model based design approach. Models and control algorithms were programmed in LabView, the NI MyRIO was used as a hardware platform. For hall-sensor feedback controlled application an already finished power inverter was used from a Honeywell rotary actuator. For sensor-less motor control an indirect sensing of BEMF signal is applied using motor phase current measurement. The time-critical parts of the algorithms are programmed for FPGA, the non-time-critical parts are programmed for LabView Real-Time module.

Thesis deals with the challenges in the field of BLDC motors control with the utilization of Field Programmable Gate Arrays (FPGA). Using the modular dSPACE hardware with the FPGA board, these issues are solved: sensored and sensorless control, real-time simulation of BLDC motor and control of BLDC motor in degraded mode. FPGA design is made using the System Generator for DSP from Xilinx. The side effect of work is to show that with the expansion of high-level tools for FPGA design, the implementation of algorithms for FPGA is relatively quick and efficient and does not require years of experience and big knowledge of field programmable gate arrays. The implementation of algorithms on FPGA instead of processors brings many advantages, in the first place the high speed processing and low latency.

This dissertation proposes a novel control technique for power density maximization of the brushless DC (BLDC) generator which is a nonsinusoidal power supply system. In a generator of given rating, the weight and size of the system affect the fuel consumption directly, therefore power density is one of the most important issues in a stand-alone generator. Conventional rectification methods cannot achieve the maximum power possible because of a distorted or unsuitable current waveform. The optimal current waveform for maximizing power density and minimizing machine size and weight in a nonsinusoidal power supply system has been proposed theoretically and verified by simulation and experimental work. Also, various attributes of practical interest are analyzed and simulated to investigate the impact on real systems.

In this thesis, position and current control systems for a brushless DC (Direct Current) motor are designed and integrated into one FPGA (Field Programmable Gate Array) chip. Experimental results are obtained by driving the brushless DC motors of Control Actuation System of a guided missile. Because of their high performance, brushless DC motors are widely used in Control Actuation Systems of guided missiles. In order to control the motor torque, current controller is designed and implemented in the FPGA. Position controller is designed to fulfill the position commands. A soft processor in the FPGA is used to connect and configure the current controller, position sensor interfaces and communication modules such as UART (Universal Asynchronous Receiver Transmitter) and Spacewire. In addition<br>position controller is implemented in the soft processor in the FPGA. An FPGA based electronic board is designed and manufactured to implement control algorithms, power converter circuitry and to perform other tasks such as communication with PC (Personal Computer). In order to monitor the behavior of the controllers in real time and to achieve performance tests, a graphical user interface is provided.

O objetivo deste trabalho é desenvolver a simulação de um sistema de controle de velocidade para compressores herméticos domésticos utilizando motores brushless DC controlados por uma estratégia do tipo sensorless. O ponto central é o desenvolvimento da simulação global de controle a partir de um modelo adequado do motor BLDC com base no programa Matlab/Simulink. São abordadas algumas estratégias de controle sensorless além de alguns métodos de partida para este tipo de máquina. As estratégias de controle e partida propostas para o trabalho são analisadas detalhadamente e simuladas através do Matlab em ambiente Simulink utilizando as ferramentas do power system blockset (PSB). Os resultados destas simulações são apresentados e discutidos no final deste trabalho.<br>The aim of this work is to develop the simulation of a speed control system for household hermetic compressors using brushless DC motors controlled by a sensorless strategy. The main point of the work is the development of the control global simulation from a suitable BLDC motor model based on Matlab/Simulink program. Some sensorless control strategies and even some starting methods for this type of machine are approached. The control and starting strategies proposed for this work are analyzed in detail and simulated by Matlab in Simulink program using power system blockset (PSB) tools. The simulation results are presented and discussed at the end of this work.

This thesis is focused on problematics of control of brushless DC motor in the sensor and also in the sensorless mode. Also it interprets possibilities of BLDC motor control with one faulty sensor and derivation and simulation of mathematical model. First part mentions options of rotor position sensing as well as existing methods of sensorless BLDC motor control. Second part describes control algorithms of sensor and sensorless motor control realised on device dSPACE and also realisation of faulty sensor control algorithm. Third part deals with derivation of mathematical model, its realisation using Matlab Simulink software and identification of its parameters. Last part concludes results and compares control methods used on the real system.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>This master thesis presents a sensorless speed control drive of Brushless DC motors used in reciprocating compressors. These compressors cause periodic load torque variations on the motor, consequently mechanical vibrations and acoustic noise are presented as well. As a result, a discrete speed controller based on the internal model principle is proposed. This controller aims to track the speed reference and to reduce the periodic torque disturbances caused by the compressor. The proposed controller consists of a rotor position and speed estimator, and a discrete speed controller with variable sampling frequency that depend on the rotor speed. The discrete estimator is based on the zero crossing point detection of the back-electromotive force. This method is optimized by using a Least Squares algorithm. The speed controller consists of two control actions, repetitive and proportional-derivative actions. In order to complement the drive system operation, a new procedure to start a BLDCM with current control is proposed. This technique ensures the maximization of the electromagnetic torque during startup and to avoid demagnetization of the permanent magnet by the stator current. Finally, simulation and experimental results are presented to demonstrate the performance of the techniques adopted, as well as the main advantages, disadvantages and operational limitations of the experimental implementation. In addition, the performance of the load torque rejection is evaluated by comparing the harmonic spectrum of the torques produced by the proposed speed controller and a PI controller.<br>Esta dissertação apresenta um sistema de acionamento e controle de velocidade sensorless para motores Brushless DC utilizados em compressores alternativos. Estes compressores provocam variações periódicas de carga sobre o motor causando vibrações mecânicas e ruído acústico. Em vista disso, um controlador discreto de velocidade baseado no princípio do modelo interno é proposto. Este controlador visa o rastreamento assintótico de uma velocidade de referência e a redução dos distúrbios cíclicos de conjugado provocados pelo compressor. Para isso, o sistema proposto é constituído por um estimador discreto da posição e da velocidade do rotor, e um controlador discreto de velocidade com frequência de amostragem variável em função da velocidade de rotação. O estimador discreto baseia-se na deteção do cruzamento da força contra-eletromotriz por zero, a qual é otimizada por meio de um algoritmo de Mínimos Quadrados. O controlador de velocidade é composto por duas ações de controle, uma ação repetitiva e uma proporcionalderivativa. De forma a complementar a operação do sistema de acionamento, um novo procedimento de partida com controle de corrente é proposto para o BLDCM. Este procedimento possibilita a maximização do conjugado eletromagnético do motor durante a partida e ainda evita a desmagnetização dos ímãs pela incidência de altas correntes estatóricas. Por fim, resultados de simulação e experimentais são apresentados para demonstrar o desempenho das técnicas adotadas, assim como as principais vantagens, desvantagens e limitações operacionais da implementação experimental. Além disso, a performance da rejeição parcial do conjugado de carga é avaliada com a comparação do espectro harmônico dos conjugados produzidos pelo controlador de velocidade proposto e por um controlador proporcional-integral.

Master thesis deals with solutions of BLDC motors (brushless DC motors) control. It analyses microcontrollers and electronic components suitable for BLDC motor controllers under conditions of serial production. It mentions some common problems in practical aplication like dynamic motor braking, synchronization, recuperation and constant revolutions.

Small electric uninhabited aerial vehicles (UAV) represent a rapidly expanding market requiring optimization in both efficiency and weight; efficiency is critical during cruise or loiter where the vehicle operates at part power for up to 99% of the mission time. Of the four components (battery, motor, propeller, and electronic speed controller (ESC)) of the electric propulsion system used in small UAVs, the ESC has no accepted performance model and almost no published performance data. To collect performance data, instrumentation was developed to measure electrical power in and out of the ESC using the two wattmeter method and current sense resistors; data was collected with a differential simultaneous data acquisition system. Performance of the ESC was measured under different load, commanded throttle, bus voltage, and switching frequency, and it was found that ESC efficiency decreases with increasing torque and decreasing bus voltage and does not vary much with speed and switching frequency. The final instrumentation was limited to low-voltage systems and error propagation calculations indicate a great deal of error at low power measurements; despite these limitations, an understanding of ESC performance appropriate for conceptual design of these systems was obtained. MODELING AND TEST OF THE EFFICIENCY OF ELECTRONIC SPEED CONTROLLERS FOR BRUSHLESS DC MOTORS

Electric propulsion has been studied for a long time. Most of the electrically propelled vehicles that have been developed however have been ground vehicles. Recent research by NASA has promoted the development of electric aircraft. Most aircraft are currently powered by heavy gas turbine engines that require fueling. The development of electric motors to replace gas turbines would be a big step towards accomplishing more efficient aircraft propulsion. The primary objective of this research extends previous work by developing a high power density motor for aircraft propulsion. This design is novel because it does not require a dynamometer to provide the torque to drive the vehicle. Equally important for successful testing of the motor was the design and development of a spin pit interface that was used as a containment vessel during testing. The research led to a designed, fabricated, assembled, modeled, and tested motor. Voltages, currents and power outputs of the motor were measured and used to determine the motor’s efficiency. The gaps between the motor’s magnets were related to the current and power it produced, and modifications were made based on this relation. The vibrations of the motor were also studied and MATLAB codes were written and used to reduce these vibrations. Significant among the objectives was monitoring the temperatures of the motor’s stators due to their close association with the rotating parts. The windage and friction losses between the stators and the magnets provided a challenging hurdle in the research. These windage and friction losses were predicted, analyzed and measured, and modifications were made to reduce them. Finally, results were compiled, tabulated, and analyzed. Results obtained before and after the modifications were compared, and these comparisons were used to assess the necessity and effectiveness of the modifications. The efficiency of the motor was found to be 82.9% and the power density was evaluated as 33.1 W/lb based on a rotor weight of 497 lb. It was concluded that the litz wire used in the motor has high, frequency related impedances that could be reduced but not eliminated.

The aim of this diploma thesis is to design and implement a universal driver unit designed to control electric motors of small voltages – electronically commutated, DC and stepper. This involves creating topology and selecting appropriate components based on the required parameters. It also includes the manufacture of printed circuit board (PCB), soldering of the components and programming of the necessary functions. Thesis contains the analysis of three selected types of motors – the principle of operation, wiring and control. Testing of the control unit was performed at the end of the work.

Switched Reluctance Machines (SRMs) are receiving significant attention from industries in the last decade. They are extremely inexpensive, reliable and weigh less than other machines of comparable power outputs. Although the design principles of the machine are available as a concatenation of many different sources, the need for a unified, step-by-step design procedure from first principles of electromagnetics is an absolute requirement. This dissertation discusses a procedure that can be applied by engineers with a basic background in electromagnetics. Subsequent to the design of the machine, existing finite element software can do the analysis of the machine. However, this is a laborious process and the need for an analytical method is preferable to verify the design procedure before the final verification by finite elements. The analytical procedure as well as a procedure to calculate iron losses is also developed in this dissertation. A prototype machine has been developed as an example of the design process and an existing prototype is analyzed to verify the analysis procedure. The similarities between the SRM and the Permanent Magnet Brushless DC Machine (PMDBC) beg the consideration of the development of a converter that can be used to drive either machine. One such converter has been developed in this dissertation. The design of the drive for both the machines is seen to be very similar. As a consequence, a universal controller that can be used to operate both machines has been developed and implemented with a DSP. Simulations and experimental correlation for both drives have been presented.<br>Ph. D.

Given today’s trend with environment being very important, there has been an ongoing attempt in the rotating machine industry to create machines with highest efficiency possible. And so, permanent magnet synchronous machines represent types of machine with very high efficiency and are gradually replacing other machines in many applications. This work deals with familiarization of the properties of permanent magnet synchronous motor as well as typical design choices. The main focus of this work is the design of permanent magnet EC motor and following comparison of results obtained from analytical design and analysis in the RMxprt program. Finally, the results of design methods are compared.

The goal of the thesis was to design and create one-way speed controler for brushless DC motors, that is used in air modeling. The circuit is controlled by the Atmel AVR. As power unit for motor is used Li–pol accumulator. The controller is equipped with BEC to power the receiver and allows monitoring of current consumption and voltage on the accumulator. Measured data can be upload to a PC where they can be displayed by RegulatorPC in graphical form.

碩士<br>南臺科技大學<br>電機工程系<br>104<br>This thesis proposes the drive design of a brushless DC motor (BLDC), employing an Arduino DUE as the core processor. In recent years, power electronics and permanent magnet materials technology have been mature, and the microcontroller functions have been increasingly powerful with low cost. Based on these advantages, the BLDC motors with low production cost will have more widespread industrial applications, and be popular in people's daily lives. Though Arduino boards are application-oriented, they are for general purposes, not aimed for real-time controller design for the BLDC motors. The Arduino instruction set is derived from the Atmel instruction set. Thus the Arduino instruction set is more complex, but readable at the expense of immediacy. To enhance the efficiency of the BLDC drive design, we should apply as many Atmel instructions as possible, instead of the Arduino instructions, in the programming design. From drive theory to circuit implementation, the thesis presents how to apply Arduino DUE to finish BLDC drive design . Moreover, the PI controller is applied to carry out motor speed control. Experimental results demonstrate the accuracy of the proposed design. Arduino has been popular for being an open-source electronics platform, but to date, there are few further industrial applications. We hope this thesis can promote more industrial applications using more Arduino chips in the near future.

博士<br>國立清華大學<br>電機工程學系<br>89<br>Since the brushless DC motor (BDCM) drive with position sensorless control possesses higher capability in many industry applications, the major purpose of this dissertation is to establish a DSP-based sensorless BDCM drive, and to develop some key technologies for improving its driving control performance. For facilitating the implementation of the developed sophisticated control rules and the performance test, an experimental motor drive is first constructed. The motor is powered by a voltage source inverter with properly designed isolating drive circuits. The TMS320C240 DSP augmented with a specific ASIC is utilized to build up the digital control computer. This configuration makes the fully digital control for motor drives become possible. Although many BDCM sensorless control methods have been proposed till now, their performances are rather sensitive to the variations of system parameters and operating condition. To improve this, an intelligent sensorless control strategy is developed in this dissertation. The rotor position for making commutation is first roughly estimated by a proposed switching signal generation scheme using motor terminal voltages. Then the commutation instant is finely adjusted to yield better torque generating capability. This is achieved by a simple but stable self-tuning algorithm for seeking the minimization of motor line drawn current. In addition to the proper commutation, the winding current waveform also significantly affects the torque generating performance of a BDCM. As generally recognized, better motor driving control performance can be obtained for any type of BDCMs if the current-mode PWM control is applied. Accordingly, a robust current-mode control scheme is developed to let the BDCM drive possess fast and robust winding current tracking response. Since no commutation signals are available from the sensed motor terminal voltages at standstill, a suitable means is indispensable for starting a sensorless BDCM drive. A simple method is developed to start the BDCM stably and smoothly like a synchronous motor until a steady-state speed is reached. As to the speed monitoring and control, a speed estimation approach is proposed. And based on the estimated speed, the dynamic model is estimated and a speed controller considering the effect of system dead-time is developed. Finally, a switch-mode rectifier is employed as the input stage of the inverter for drawing power with good power quality from utility grid. The robust voltage ripple cancellation and current control approaches are developed such that good tracking control performance in input current waveform is obtained even if the output filtering capacitor with reasonably small value is used. The effectiveness of all the developed control approaches and the driving performance of the established sensorless BDCM drive are demonstrated experimentally.

Η παρούσα διπλωματική εργασία πραγματεύεται την μελέτη, το σχεδιασμό και την κατασκευή κυκλώματος οδήγησης κινητήρα τύπου DC Brushless. Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Η οδήγηση του κινητήρα τύπου DC Brushless γίνεται ηλεκτρονικά με τη χρήση τριφασικού αντιστροφέα ισχύος. Σκοπός λοιπόν της παρούσας εργασίας είναι η κατασκευή του παραπάνω κυκλώματος. Ο κινητήρας τύπου DC Brushless είναι Σύγχρονος Κινητήρας Μόνιμου Μαγνήτη, επομένως το πρώτο που πραγματεύεται η διπλωματική εργασία είναι ο ορισμός κάποιων θεμελιωδών ιδιοτήτων του μαγνητικού πεδίου, και η μελέτη των χαρακτηριστικών των μαγνητικών υλικών που χρησιμοποιούνται σε αυτού του τύπου τις μηχανές. Στη συνέχεια μελετώνται οι Σύγχρονοι Κινητήρες Μόνιμου Μαγνήτη τραπεζοειδούς και ημιτονοειδούς παλμού ως προς τα κατασκευαστικά τους χαρακτηριστικά και την αρχή λειτουργίας τους. Παρατίθενται επίσης τα πλεονεκτήματα και μειονεκτήματά τους σε σχέση με άλλους τύπους μηχανών και αναφέρονται κάποια πεδία στα οποία οι κινητήρες αυτοί βρίσκουν εφαρμογές. Ακόμα καταγράφονται λεπτομερώς οι μαθηματικές εξισώσεις λειτουργίας τους καθώς και η χαρακτηριστική ροπής ταχύτητας. Στο επόμενο βήμα γίνεται μια θεωρητική ανάλυση του κυκλώματος του μετατροπέα που κατασκευάστηκε καθώς και όλων των υπόλοιπων κυκλωμάτων και στοιχείων που είναι αναγκαία για την λειτουργία του. Επιπροσθέτως, αναλύεται η μέθοδος παλμοδότησης των διακοπτικών στοιχείων του μετατροπέα, που είναι η Διαμόρφωση Εύρους Παλμών (PWM) και κατόπιν περιγράφεται αναλυτικά η κατασκευή και η υλοποίηση των παραπάνω κυκλωμάτων. Η παρούσα διπλωματική εργασία προχωράει με την περιγραφή των ιδιοτήτων του μικροελεγκτή που χρησιμοποιήθηκε και την ανάλυση της παλμοδότησης του αντιστροφέα. Τέλος, ολοκληρώνεται με την παράθεση και το σχολιασμό των παλμογραφημάτων που προέκυψαν μετά την ολοκλήρωση της κατασκευής .<br>This diploma thesis deals with the study, design and construction of a converter topology for a DC Brushless motor drives. The project was conducted at the Laboratory of Electromechanical Energy Conversion of the Department of Electrical and Computer Engineering of School of Engineerings, of University of Patras. Three-Phase DC Brushless motors are known to be controlled electronically using three-phase voltage inverter. Therefore, the aim of this paper is to construct this circuit. DC Brushless motors are Synchronous Permanent Magnet Motors so that the first thing we deal with in this diploma thesis is the definition of some fundamental properties of the magnetic field and the study of the characteristics of magnetic materials used in this type of motors. Then we examine the synchronous permanent magnet motors with trapezoidal and sinusoidal supply on the construction characteristics and the principle of operation. We also list some of their the advantages and disadvantages compared with other types of motors and mention some areas where these motors are finding application. We also record in detail the mathematical equations of operation and the torque-speed characteristics. The next step is a theoretical analysis of the circuit of the converter that was constructed and of all the other circuits and components necessary for its operation. Furthermore, we describe the method of pulse generation which is Pulse Width Modulation (PWM) and then we describe in detail the construction and implementation of these circuits. This essay goes on to analyze the properties of the microcontroller used and finally, it concludes with oscillograph figures and measurements, occurred from the experiments transacted after the finalization of the construction.

碩士<br>國立中興大學<br>電機工程學系<br>91<br>In general, a brushless DC motor (BLDCM) operates under the conditions that the magnetic position of the rotor should be detected via the Hall effect sensors. However, using hall position sensors to detect the rotor position, the control system of the BLDCM becomes very unreliable, in harsh environments. Therefore, in order to improve the BLDCM’s capabilities, the purpose of thesis focuses on developing BLDCM drivers utilizing the ST72141 microcontroller without the dedicated hall position sensors. Through using the appropriate pulse width modulation (PWM) signal and measuring the terminal voltage, the zero crossing of the back electromagnetic force (BEMF) is detected directly and is not susceptive to noise. Moreover, in order to enhance the performance of the sensorless BLDCM drive, detecting the zero crossing of the demagnetization current is utilized herein. On the other hand, the gain scheduling control is employed to upgrade the transient speed response. In this thesis, the principle of BLDCM’s operation is described and some experimental results are provided to verify this proposed method.

碩士<br>國立臺北科技大學<br>冷凍空調工程系所<br>94<br>Mechanical vibrations occur in the normal DC brushless fan working. The large magnitude vibrations may indicate the defects of the fan rolling parts. In this study, an on-line diagnosis system was developed to monitor the fan vibration and judge the failure conditions. Due to the complex mechanical interferences, spectrum analysis results can’t give enough information for the experimental judge of the fan failures. The artificial neural networks analysis was employed for the on-line diagnosis system to realize the automatic fan defects. The networks weighting was performed by the back propagation algorithm. After well system trainingprocesses, the on-line system can judge the DC brushless fan failures according to the vibrations spectra and the 80% hit rate can be achieved.

碩士<br>國立臺灣科技大學<br>電機工程系<br>93<br>This thesis is concerned with the design and implementation of a direct-drive system for brushless dc motors. On the grid side, a current-controlled single-phase power converter is designed to improve current harmonics and power factor, while on motor side, Hall-effect sensors are used to detect the position of rotor to estimate speed. In addition, the speed and current of motor are fed back to control speed and torque, respectively. In order to control the brushless dc motor in high speed, the phase-advancement control of six-step square waves is proposed to extend field-weakening region to 2.5 times of rated speed. Theoretical analysis of the proposed system is given first. The implementation of hardware and software follows subsequently. A digital signal processor (DSP, TMS320F2407A) is used for the core control of the system to reduce cost and hardware components. Under input source of 110 V, 60 Hz and the dc-link voltage command of 200 V, the output of the system realized is 400 W. The associated power factor is 0.98 and the harmonic distortion of input current is 8.9 % on the grid side. Besides, the output torque under the low-speed range of -100 to 100 rpm is 20 N-m, whereas the maximum speed can reach as high as 500 rpm by high-speed control with the output torque of 4 N-m. The features of low-speed, high-torque and high-speed, constant-power operations are developed to facilitate gearless direct-drive applications.

碩士<br>中原大學<br>機械工程研究所<br>98<br>Abstract The applications of motors are very common in the machinery and electrical machinery related industry. Furthermore, the localization precision of the servomotor is more superior to the other motors; therefore the servomotor is used in the related industry more than the others. If there are some errors of the phase change position of brushless DC motor and the optical encoder gauges the position, when the motor is driven for any application, the motor main body would feel hot and operate not smoothly or even affects the automatic station operation, no matter the errors are assembly mistake as the motor leaves the plant or reassembly mistake as makes the maintenance service. Therefore, this research in view of the servomotor encoder position gauging and the adjustment designs a set of semi-automatic gauging system for the brushless DC servomotor. We will pick up the three-phase counter electromotive force profile voltage signals to make sure the rotor position and then to adjust the encoder and to focus the disk position of the encoder precisely. The research contains the gauging organization and the examination circuit design, the LabVIEW software composition and the optical encoder and the phase change signal relative relational discussion. We use the semi-automatic measurement system to measure the waveform of the voltage signals of counter electromotive force to decide the phase change signal to compare with the signal of encoder to detect the position error and to complete the adjustment work. The test results show that the proposed system could measure the two signals and adjust the disk position precisely to maintain the efficiency of the servomotor. Keywords: brushless DC servomotor , encoder , LabVIEW

碩士<br>國立臺灣科技大學<br>電機工程系<br>90<br>This thesis presents the analysis and implementation of a wide-speed control system for brushless dc motors. A digital signal processor (DSP TMS320F240) is used to complete the whole digital control system to reduce hardware complexity and increase the speed response. A Hall-effect sensor is also used to detect rotor position and estimate rotor speed. In addition, speed and current feedback are invoked to realize the proposed high performance system. Specifically, a current feedback technique which is conducted by peak phase current control algorithm is implemented to control output current. This will not only reduce control complexity in three-phase system, but also promote linearity of the proposed control system. Finally, a current regulator is also introduced to adjust current command automatically through the error between command current and armature current of motor to reduce output current ripple. A 200W brushless dc motor is built and experiments are given to justify the analysis.

碩士<br>明志科技大學<br>電機工程系碩士班<br>103<br>This thesis presents the development of rotor position sensorless control for brushless DC motor drives. The back-EMF detection is firstly used to estimate rotor position, and the linear interpolation method is proposed to implement closed-loop field-oriented control to drive brushless DC motor without rotor position sensor. In this thesis, the mathematical models of brushless DC motor and inverter are analyzed. Then, the voltage space vector modulation is used to increase the voltage utilization from the inverter. A high-performance and low-cost digital signal processor (DSP, TMS320F28069) is used to control the system for reducing the circuit complexity. Experimental results indicate that the motor operates under 1500 RPM by the proposed rotor position estimator technique.

碩士<br>國立臺灣海洋大學<br>電機工程學系<br>103<br>In recent years, owing to the rising awareness of environment protection, people ask for higher living standard. However, carbon emission by automobile hasn’t been reduced but got much higher these years, which leads to the rise of temperature and the loss of summer ice in Atlantic. The climate change and the degradation of the environment now again arouse the issues of conservation of energy and reduction of carbon emission. If electric vehicles substitute for ones powered by fossil fuel, it will not only lower the consumption of fossil and the emission of carbon dioxide but improve our living standard. In this paper, the system architecture is divided into two parts, one is the drive circuit design and the other is a control unit, driver circuit includes a three-phase inverter and a gate drive circuit, gate drive circuit uses a bootstrap circuit design, control unit uses Microchip the company's digital signal microprocessor dsPic30F4011 as the control kernel, according to Hall sensors detect the rotor position signals to estimate the rotor speed and angle, confirm the position of the motor rotor, exciter stator and rotor affect each other to produce a rotating magnetic field of the motor rotation, to achieve space-vector control. The purpose of this paper is to develop a brushless DC motor drive can be applied to electric vehicles, using space vector pulse width modulation techniques (SVPWM), make the brushless DC motor can be smooth and stable output torque to achieve good driving performance.

碩士<br>國立臺灣科技大學<br>電機工程系<br>98<br>This thesis is concerned with the development of the control system for brushless dc (BLDC) motor in high speed applications. A control policy which combines pulse-amplitude modulation with pulse-width modulation is proposed to control the input voltage according to the speed command for BLDC motor drives. A dc-dc power converter is designed to change the voltage from 140~200 to 24~48 volt. The BLDC motor drives use three hall-effect sensors to detect rotor position and calculate motor speed for six-step square-wave and closed-loop control of speed. In this thesis, the digital signal processor, dsPIC30F4011, is adopted as the control core. C-language is used for dc-dc power converter control, BLDC motor drives control and realization of control policy which combines pulse-amplitude modulation with pulse-width modulation. A prototype of 80W is built and accuracy of speed command is below 1.5% for high speed control drives from 1 k to 20 k rpm speed. The experimental results verify the proposed performance.

碩士<br>國立臺灣科技大學<br>電機工程系<br>92<br>This thesis is concerned with the analysis, simulation, modeling, and implementation of a new control strategy for dual-winding permanent-magnet brushless dc motor drive systems. The characteristics of the motor such as magnetic field distribution and steady-state property are analyzed by Flux2D using finite-element method. In addition, the magnetic saturation and back electromotive force distortion caused by armature reaction are also considered. Then the mathematical models of dual-winding permanent-magnet brushless dc motor and dual-inverter are built. Torque and current analyses for dual-channel pulse-width modulation with interleaved and non-interleaved control strategies are given. The result shows that the interleaved control will yield less torque fluctuation and current ripple. Besides, both analysis and experiment indicate that dual-winding permanent-magnet brushless dc motor with dual-inverter using dual-channel pulse-width modulation will share the output power and enhance system reliability as expected. A single-chip microcomputer (H8/3672) is used to serve as the core controller. It generates the dual-channel pulse-width modulation signals to implement a 1 kW dual-winding permanent-magnet brushless dc motor with low-cost dual-inverter prototype drive system. Simulation and experimental results are given to justify the proposed control strategy.

碩士<br>元智大學<br>電機工程學系<br>92<br>ABSTRACT The objective of this paper is to analyze and design a brushless DC motor driver for blowers embedded in advanced patient care beds. The blower embedded in the electric medical bed system is responsible for recharging and releasing air for healing. In this paper, we employed a two-phase on six-step square wave control strategy to control the brushless DC motor. Also, Matlab/Simulink computer software was adopted to simulate the dynamic performance of the driver. The simulation data can analyze the capabilities of the control strategy for the motor driver. To accomplish the motor driver for commercial use, we setup an experimental system where a digital signal processor, TMS320F241, was used as a controller to implement the control strategy. Experimental results showed that the design brushless DC motor driver has met the specifications of the blower embedded in the medical system.

碩士<br>國立臺灣科技大學<br>電機工程系<br>91<br>This thesis presents a three-phase step-down dc power converter for brushless dc motor drives. The converter developed can provide a regulated stable dc-link voltage, high power factor and low current distortion. The current prediction control is applied to track demanded currents for better performance. On the other hand, proper coordination of power source phase and converter operation mode is conducted to reduce switching loss for higher efficiency. Besides, speed control of brushless dc motor is achieved by using the magnetic pole position fed back through Hall effect sensors and the proposed six-step-flux energizing algorithm. Moreover, the dc-link voltage of the converter can be adjusted spontaneously in accordance with the speed command to increase the overall efficiency. A 16-bit digital signal processor (DSP TMS320F2407) is used as the control kernel of the ac-to-dc power converter. All the control algorithms are implemented by software for cost reduction and reliability enhancement. With the power source of 60Hz, 220V line-to-line, experimental results show that the dc-link voltage is stable and adjustable from 30 to 210V. In addition, under the output power of 336.6W, the efficiency of whole system is 78.30%.

碩士<br>國立臺灣科技大學<br>電機工程系<br>105<br>This thesis aims to design and implement a speed control system for brushless dc (BLDC) motors with single-phase power factor correction (PFC). The system contains two major parts: the boost type PFC with two-phase interleaving control and sensor-less control for three phase BLDC motors used, respectively, on the grid and load sides. The former can yield high power factor as well as low total harmonic distortion (THD) on the input, and ripple voltage reduction of the dc-link, thereby reducing the inductance volume and increasing the power density. While the latter is driven by sensor-less control via detecting zero-induced electro-motive-force to obtain the actual motor speed. A microcontroller is used to control the two functional blocks mentioned above and conduct dynamic voltage boosting regulation on the interleaving PFC in accordance with the error speed between commanding and actual motor speeds. The proposed control method can reduce switching loss of three-phase inverter, improve the operation efficiency of motor, keep high input power factor and low current THD. The single-phase input voltage is 110V, 60Hz and the dc-link voltage range of power factor correction is from 190V to 380V. The speed range of BLDC motor under control is from 1160rpm to 2160rpm. Experimental results show that for the BLDC under 2160rpm and 2 N-m, dynamic voltage boosting regulation and speed control give the current THD of 5.38%, the input power factor of 0.996 and the overall efficiency of 87.1%. The feasibility of the proposed system is verified experimentally.

Σκοπός της εργασίας αυτής είναι η μελέτη, εξομοίωση και κατασκευή ενός ηλεκτρονικού τριφασικού αντιστροφέα ισχύος, ο οποίος μετατρέπει μια σταθερή συνεχή τάση σε τριφασική εναλλασσόμενη , μέσω της οποίας ελέγχεται ένας τριφασικός σύγχρονος κινητήρας μόνιμου μαγνήτη (Brushless DC, BLDC). Η συνεχής αυτή τάση προέρχεται από έναν ηλεκτρονικό μετατροπέα ισχύος ανύψωσης συνεχούς τάσης σε συνεχή, ο οποίος ανυψώνει και σταθεροποιηθεί στα 50 V την τάση, η οποία παράγεται από μία πηγή κυψελών καυσίμου (Fuel Cells). Αρχικά έγινε ενδελεχής μελέτη διαφόρων τριφασικών αντιστροφέων με σκοπό την εμβάθυνση στη δομή και λειτουργία τους, ώστε να διευκολυνθούμε στο σχεδιασμό και κατασκευή του αντιστροφέα για τη συγκριμένη εφαρμογή και τελικά επιλέχτηκε να σχεδιαστεί, να εξομοιωθεί και να κατασκευαστεί ένας ηλεκτρονικός μετατροπέας ισχύος έξι παλμών τετραγωνικής κυματομορφής εξόδου, όπου το πλάτος και η συχνότητα της εναλλασσόμενης τάσης εξόδου ελέγχεται μέσω της τεχνικής διαμόρφωσης του εύρους των παλμών (PWM) των ημιαγωγικών διακοπτικών στοιχείων ισχύος του αντιστροφέα. Τα ημιαγωγικά διακοπτικά στοιχεία ισχύος του αντιστροφέα επιλέχθηκαν να είναι MOSFET, αφού ύστερα από υπολογισμούς και συγκρίσεις των διαφόρων ημιαγωγικών στοιχείων μεταξύ τους αυτά κρίθηκαν ως τα πιο κατάλληλα. Έπειτα έγινε εξομοίωση του συστήματος μετατροπέα-κινητήρα μέσω του προγράμματος Matlab/Simulink προκειμένου να βρεθεί η καταλληλότερη μέθοδος παλμοδότησης των έξι ημιαγωγικών στοιχείων ισχύος και να εξετασθούν διάφορα μεγέθη απαραίτητα για την σχεδίαση του αντιστροφέα. Ακολούθησε η σχεδίαση του τυπωμένου κυκλώματος του μετατροπέα καθώς και του κυκλώματος ελέγχου σε κοινή πλακέτα μέσω του προγράμματος Kicad, το οποίο έπειτα συναρμολογήθηκε και προγραμματίστηκε στο Εργαστήριο. Για τη σωστή λειτουργία του κινητήρα απαιτείται η συγχρονισμένη και διαδοχική τροφοδότηση των τριών τυλιγμάτων του στάτη του κινητήρα, έτσι ώστε να μην υπάρξει αποσυγχρονισμός. Για το σκοπό αυτό χρησιμοποιούνται τρεις αισθητήρες Hall, οι οποίοι είναι ενσωματωμένοι στη μηχανή και τοποθετημένοι σε γωνία 120ο ηλεκτρικών μοιρών μεταξύ τους (οι 120ο ηλεκτρικές μοίρες αντιστοιχούν σε 30ο χωρικές μοίρες για έναν οχταπολικό κινητήρα). Τα σήματα που παράγουν οι αισθητήρες Hall χρησιμοποιούνται για να ορίσουν τη θέση του δρομέα και οδηγούνται στη βαθμίδα, η οποία καλείται «ελεγκτής καταστάσεων μετάβασης» (commutation logic block) και ελέγχει την παλμοδότηση των έξι ημιαγωγικών διακοπτικών στοιχείων ισχύος του αντιστροφέα. Ο κινητήρας λόγω της χρήσης της παραπάνω λογικής στην τροφοδότησή του αδυνατεί να αποσυγχρονιστεί, διότι ο ελεγκτής καταστάσεων μετάβασης δεν επιτρέπει λανθασμένη τροφοδοσία τυλίγματος. Έτσι, η ηλεκτρική συχνότητα ισούται πάντα με τη συχνότητα περιστροφής του άξονα επί 4, δεδομένου ότι η μηχανή έχει τέσσερα ζεύγη πόλων. Ο έλεγχος του ρεύματος γίνεται μέσω του λόγου κατάτμησης (duty cycle) των διακοπτών. Σε λειτουργία κλειστού βρόχου το αποτέλεσμα της σύγκρισης του ρεύματος αναφοράς και του ρεύματος ανάδρασης οδηγείται σε έναν ελεγκτή PI και στη συνέχεια με τεχνική PWM ελέγχεται η κατάσταση των ημιαγωγικών διακοπτικών στοιχείων. Τέλος στο προαναφερθέν σύστημα προστέθηκε μία γεννήτρια συνεχούς ρεύματος μόνιμου μαγνήτη ως φορτίο και πραγματοποιήθηκαν πειραματικές δοκιμές για διάφορες καταστάσεις λειτουργίας της διάταξης. Μετρήσεις έγιναν για τις φασικές και πολικές τάσεις του κινητήρα καθώς και για τα ρεύματα αυτού για 1500min-1 και για 3000 min-1 (ονομαστικός αριθμός στροφών) με αφόρτιστη τη γεννήτρια συνεχούς ρεύματος.<br>This thesis deals with the study, design and construction of a converter topology for a DC Brushless motor drives. Three-Phase DC Brushless motors are known to be controlled electronically using a three-phase voltage inverter. Therefore, the aim of this paper is to construct this circuit. This circuit converts a 50 V DC voltage which comes from fuel cells source and has already been stabilized with a power electronic boost converter to a three-phase voltage which drives the motor. Firstly a deep study was done between many different kinds of three-phase voltage inverter in order to find the most appropriate for this job. Finally it was chosen to be studied, designed and constructed a six pulse power converter producing a square waveform output. The amplitude and the frequency of the AC square output voltage is controlled by the method of pulse generation which is Pulse Width Modulation (PWM). The power electronic components were chosen to be MOSFET because after some calculations and comparison between the different types of power electronic switches these (MOSFET) where consider to be the most appropriate. Afterwards the system ’’power converter-motor’’ was simulated trough the Matlab/Simulink program in order to find the best pulse generation method for the six power components and observe some current and voltage figures essential for the further design of the inverter. For the right function of the motor is required the synchronous and succession feed of its stator windings so as not to be unsynchronized. For this purpose three hall sensors are used. These sensors are an integral part of the motor and have 120 electrical degrees distance between each other. Those three hall signals are used to define rotor’s position and are driven to commutation logic block which controls the six pulses of the six MOSFETS. Due to the fact of the upper logic for giving pulses, the motor can’t be unsynchronized because the commutation logic block doesn’t allow a wrong winding to be fed. So electrical frequency is every time four times bigger than the mechanical (rotor) frequency (this BLDC motor has eight poles). Current control is possible via duty cycle control. In close loop operation, the result of the comparison between reference current and feedback current is driven to a PI controller which controls the output via duty cycle control. Finally a DC permanent magnet generation has been added to the upper system and several experimental tests took place in lab. Measurements were done at 1500 and 3000rpm (nominal rotation number) for BLDC motor’s voltages and motor’s currents while there was no load to the generator at that time.

碩士<br>大葉大學<br>機電自動化研究所碩士班<br>96<br>In recent years, as the environmental protection and global warming has risen, it is important to reduce the pollution of environment. According to The World Energy Council (WEC) estimation, the petroleum of world will be use up in 40-50 year. A solution way is necessary to develop not the sole internal combustion engine (ICE) of compound vehicle. Thus, hybrid electric vehicles (HEVs) are recognized as one of the most promising technologies in significantly reducing the petroleum fuel consumption, and toxic and emissions of greenhouse gases. Based on the importance of HEV, a high output torque HEV system and 20 kW brushless direct current (BLDC) motor is studied in this thesis. For the high power system requirement, a 20 kW high power motor driver with high torque output will be established. On the other hand, the HEV system needs a high performance controller. This controller can provide the stable and robust property. The overall electric controller of the HEV system can achieve the effect of the energy conservation. It should be pointed out that although the low power BLDC motor driver research and design are already complete, compared the high efficiency type over ten thousand Watts BLDC motor driver research were still few. As everyone knows, the high power motor driver is more complicated for the low power driver of motor system. In this thesis, it is achieved several important tasks in the high power driver system design and implementation. In this thesis, the experimental platform of the novel HEV system is already established. By way of the experimental platform test, we had completed the driver of the high performance. Finally, the novel HEV system achieve the energy saving and carbon reduction.

In the past two decades the core aircraft technology is going through a drastic change. The traditional technologies that is almost half a century old, is going through a complete revamp. In the new “More Electric Aircraft” technology many mechanical, pneumatic and hydraulic systems are being replaced by electrical and power electronic systems. Airbus-A380, Boeing B-787 are the pioneers in the family of these new breed of aircrafts. As the aircraft technology is moving towards “More Electric”, more and more electric motors and motor controllers are being used in new aircrafts. Number of electric motor drive systems has increased by about ten times in more electric aircrafts compared to traditional aircrafts. Weight of any electric component that goes into aircraft needs to be low to reduce the overall weight of aircraft so as to improve the fuel efficiency of the aircraft. Hence there is an increased need to reduce weight of motors and motor controllers in commercial aircraft. High speed ironless axial flux permanent magnet brushless dc motors are becoming popular in the new more-electric aircrafts because of their ability to meet the demand of light weight, high power density, high efficiency and high reliability. However, these motors come with very low inductance, which poses a big challenge to the motor controllers in controlling the ripple current in motor windings. Multilevel inverters can solve this problem. Three-level inverters are proposed in this thesis for driving axial flux BLDC motors in aircraft. Majority of the motors in new more electric aircrafts are in the power range of 2kW to 20kW, while a few motor applications being in the range of 100kW to 150kW. Motor controllers in these applications run from 270Vdc or 540Vdc bus which is the standard in new more electric aircraft architecture. Multilevel Inverter is popular in the industry for high power and high voltage applications, where high-voltage power switching devices like IGBT, GTO are popularly used. However multilevel inverters have not been tried in the low power range which is appropriate for aircraft applications. A detail analysis of practical feasibility of constructing three-level inverter in lower power and voltage level is presented in this thesis. Analysis is presented that verify the advantages of driving low voltage and low power (300Vdc to 600Vdc and less than 100kW) motors with multilevel inverters. Practical considerations for design of MOSFET based three-level inverter are investigated and topological modifications are suggested. The effect of clamping diodes in the diode clamped multilevel inverters play an important role in determining its efficiency. SiC diodes are proposed to be used as clamping diodes. Further, it is realised that power loss introduced by reverse recovery of MOSFET body diode prohibits use of MOSFET in hard switched inverter legs. Hence, a technique of avoiding the reverse recovery losses of MOSFET body diode in three-level NPC inverter is conceived. The use of proposed multilevel inverter topology enables operation at high switching frequency without sacrificing efficiency. High switching frequency of operation reduces the output filter requirement, which in turn helps reducing size of the inverter. In this research work elaborate trade-off analysis is done to quantify the suitability of multilevel inverters in the low power applications. For successful operation of three-level NPC inverter in aircraft electrical system, it is important for the DC bus structure in aircraft electric primary distribution system to be compatible to drive NPC inverters. Hence a detail study of AC to DC power conversion system as applied to commercial aircraft electrical system is done. Multi-pulse rectifiers using autotransformers are used in aircrafts. Investigation is done to improve these rectifiers for future aircrafts, such that they can support new technologies of future generation motor controllers. A new 24-pulse isolated transformer rectifier topology is proposed. From two 15º displaced 6-phase systems feeding two 12-pulse rectifiers that are series connected, a 24-pulse rectifier topology is obtained. Though, windings of each 12-pulse rectifiers are isolated from primary, the 6-phase generation is done without any isolation of the transformer windings. The new 24-pulse transformer topology has lower VA rating compared to standard 12-pulse rectifiers. Though the new 24-pulse transformer-rectifier solution is robust and simple, it adds to the weight of the overall system, as compared to the present architecture as the proposed topology uses isolated transformer. Non-isolated autotransformer cannot provide split voltage at the dc-link that creates a stable mid-point voltage as required by the three-level NPC inverter. Hence, a new front-end AC-DC power conversion system with switched capacitor is conceived that can support motor controllers driven by three-level inverters. Laboratory experimental results are presented to validate the new proposed topology. In this proposed topology, the inverter dc-link voltage is double the input dc-link voltage. An intense research work is performed to understand the operation of Trapezoidal Back EMF BLDC motor driven by three-Level NPC inverter. Operation of BLDC motor from three-Level inverter is primarily advantageous for low inductance motors, like ironless axial flux motors. For low inductance BLDC motor, very high switching frequency is required to limit the magnitude of ripple current in motor winding. Three-level inverters help limiting the magnitude of motor ripple current without increasing the switching frequency to very high value. Further, it is analysed that dc link mid-point current in three-level NPC inverter for driving trapezoidal BLDC motor has a zero average current with fundamental frequency same as switching frequency. Because of this, trapezoidal BLDC motors can easily be operated from three-level NPC inverter without any special attention given to mid-point voltage unbalance. One non-ideal condition arrives in practical implementation of the inverter that leads to non-zero average mid point current. Unequal gate drive dead time delays from one leg to other leg of inverter introduce dc-link mid-point voltage unbalance. For the motoring mode operation of trapezoidal BLDC motor drive, simple gate drive logic is researched that eliminates need of the gate drive dead-time, and hence solves the mid-point voltage unbalance issue. Simple closed loop control scheme for mid-point voltage balancing also is also proposed. This control scheme may be used in applications where very precise control of speed and torque ripple is warranted. All the investigations reported in this thesis are simulated extensively on MATHCAD and MATLAB platform using SIMULINK toolbox. A laboratory experimental set-up of three-Level inverter driving axial flux BLDC motor is built. The three-level inverter, operating from 300Vdc bus is built using 500V MOSFETs and 600V SiC diodes. All the control schemes are implemented digitally on digital signal processor TMS320F2812 DSP platform and GAL22V10B platforms. Experimental results are collected to validate the theoretical propositions made in the present research work. At the end, in chapter 5, some future works are proposed. A new external voltage balance circuit is proposed where the inverter dc-link voltage is same as the input dc-link voltage. This topology is based on the resonant converter principle and uses a lighter resonant inductor than prior arts available in literature. Detail simulation and experimentation of this topology may be carried out to validate the industrial benefits of this circuit. It is also thought that current source inverters may work as an alternative to voltage source inverters for driving BLDC motors. Current source inverters eliminate use of bulky DC-link capacitors. Long term reliability of current source inverters is higher than voltage source inverters due to the absence of possibility of shoot-through. Further, in voltage source inverters, the voltage at the motor terminal is limited by the source voltage (dc-link voltage). This issue is eliminated in current source inverters. An interface circuit is conceived to reduce the size of dc-link inductors in current source inverters, pending detail analysis and experimental verification. The interface circuit bases its fundamentals on the principles of operation of multilevel inverters for BLDC motors that is presented in this thesis.