Academic literature on the topic 'Electric motors, Induction. Harmonic functions'

The effects of magnetic saturation on the operation of induction motors driven by static converters are analyzed. A mathematical model based on magnetic harmonic functions is used to account for saturation. Distortions on the air gap flux due to non-linear magnetic characteristics lead to appearance of space harmonics in the resultant flux density distribution. This causes specific distortions in stator and rotor time quantities, which are different from those due to static converter. Operation with six pulse and sinusoidal PWM converters under saturated conditions is considered. Comparisons of experimental and simulated results are presented and found to be in very good agreement.

This paper aims to present the analysis and development of a complete electronic smart meter that is able to perform four-quadrant measurements, act as a three-phase shunt active power filter (APF), and control three-phase induction motors by stator flux estimation. A transmission control protocol together with Internet protocol (TCP/IP) communication protocol for the remote access of measurement data is embedded into the application to securely transmit reliable information. An artificial neural network trained with particle swarm optimization is used for stator flux estimation, and a fuzzy logic controller is adopted to regulate the power converter DC bus voltage. The present work gathers knowledge from multidisciplinary fields, and all applied techniques have not been proposed altogether before. All control functions are embedded into a field-programmable gate array (FPGA) device, using VHSIC Hardware Description Language (VHDL), to enhance efficiency taking advantage of parallelism and high speed. An FPGA-in-the-loop cosimulation technique was first applied to prove the control functions’ functionality, and, later, experimental evaluations are conducted to finally prove equipment operation and reliability.

Global energy systems are undergoing a transition process towards renewable energy and energy efficiency practices. Induction motors play an important role in this energy transformation process since they are widely used as industrial loads, representing more than 53% of global energy consumption. With more countries adopting minimum energy performance standards through more efficient induction motors, comparisons between these new technologies in the presence of electrical disturbances must be systematically evaluated before adopting a substitution policy in the industry. To this end, this work presents a comparative analysis of the impact of harmonic voltages on the performance and temperature rise of electric motors classes IE2, IE3 and IE4 in the same operational conditions in view of future substitutions. The results show that under ideal operating conditions the IE4 class permanent magnet motor has better performance in terms of consumption and temperature, however presenting non-linear characteristics. In the presence of voltage harmonics, this scenario changes completely according to the harmonic content. Finally, aiming to analyze the harmonics influence in the motor temperature rise a statistical analysis by means of Spearman correlation matrices is presented.

The analysis and systematization of research methods of thermal state of induction motors including traction ones is done. It is shown that for each type of motor it is necessary to develop its own mathematical model of thermal processes, and its verification should be carried out only on the basis of experimental investigations. The structure and operating principles of the complex developed physical model of the traction electric drive with induction motors is represented. The motors have a cooling system with variable-speed electric fan and subsystem of measurement and recording of monitored parameters. The method and the results of experimental study of the processes of heating and cooling of the induction motor are illustrated. Transfer functions and approximation curves of transients are proposed, their parameters are defined.

Modern multiphase electric machines take advantage of additional degrees of freedom for various purposes, including harmonic current injection to increase torque per ampere. This new approach introduces a non-sinusoidal air gap flux density distribution causing additional technical problems and so the conventional assumptions need to be revised. The paper presents a methodology for synthesis of air gap magnetic field generated by a symmetrically distributed multiphase windings including the rotor field reaction due to the machine’s load. The proposed method is suitable either for single-layer or double layer windings and can be adopted either for full-pitched or chorded winding including slots effects. The article analyses the air gap flux density harmonic content and formulates conclusions important to multiphase induction motors. It also discusses effects of time harmonic currents and illustrates the principle of changing number of pole-pairs typical for harmonic currents being injected to increase torque.

Se presenta una detallada revisión del estado del arte de las técnicas de procesamiento de señales utilizadas para el análisis de la distorsión armónica generada por variadores de frecuencia en motores de inducción con rotor jaula de ardilla, referenciando algunas de las investigaciones más relevantes relacionadas con este tema. Finalmente, son identificadas oportunidades de investigación que a la fecha no han sido tratadas por la comunidad científica en este campo del conocimiento.Signal Processing Techniques Used for Analyzing Harmonic Distortion Generated by Variable Frequency Drive in Induction Motors Abstract This article presents a detailed review of the state of the art of signal processing techniques used for the analysis of harmonic distortion generated by variable frequency induction motors with squirrel cage rotor is presented, referencing some of the most relevant research related with this issue. Finally, are identified research opportunities that to date have not been addressed by the scientific community in this field of knowledge.Keywords: electric motor-driven system, state of the art, harmonic distortion, signal processing techniques.

The paper presents the new approach for motor driver constructions and control systems. Authors of the work proposed the device that can control both AC and DC electric motors without any additional hardware modification. In order to meet this goal the universal motor driver has been constructed and some improvements in output waveform modulation system have been introduced. In the paper the three different method of a motor control have been discussed briefly and a hardware setup has been presented. Tests have been carried out for three types of electric motors, i.e. a magnetoelectric DC motor, single-phase and three-phase induction motor. The obtained results in form of output waveforms of current and voltage have been analyzed in terms of harmonic distortion using a popular Fast Fourier Transform FFT and discussed in the paper.

Hazardous states of the mine zonal electrical network are caused by the reversed energy flows of induction motors of the energy-consuming equipment in the run-down mode after the power supply is switched off. The electromotive force (EMF) induced in the powered-off stator windings of the dual-speed motors due to the transformer effect also pose a danger of electric shock. The paper presents a methodology and the results of studying the formation of induced EMFs in the powered-off stator windings of dual-speed induction motors, including the run-down mode and the functions that impact on the electromagnetic parameters. Analysis of the impact degree of these induced EMFs on the electrical safety parameters as part of the mine zonal electrical network is presented.

This work deals with the behavior of fermions in a configuration supposed to exist in magnetar’s corona. For a static magnetic induction parallel to a time-harmonic electric field, the solution to the U(1)-gauge invariant Dirac equation is expressed in terms of Laguerre polynomials and Mathieu’s functions of complex parameter. Using the Fourier series valid before the branching point, we are computing the conserved current density components.

Electric transportation has made rapid developments and significant steps toward the full electrical powertrain systems. With the increased use of electric vehicles energy conversion systems several technologies have been developed and reached a high degree of performance. Since electric vehicles and hybrid are the more cost competitive technology available today, the evolution toward a more reliable powertrain combining different electric powertrain systems is needed. Induction machine and permanent magnet generators/motors integrated powertrains have some significant advantages over other types of systems such as no need of excitation, low volume and weight, high precision, and no use of a complex gearbox for torque/speed conversion. A electric vehicle powertrain for EV propulsion with a induction motor and a matrix converter is proposed in this paper. The induction motor is controlled using the direct torque flux algorithm. The traditional power conversion stages consist of a rectifier followed by an inverter and bulky DC link capacitor. It involves 2 stages of power conversion and, subsequently, the efficiency of the overall EV is reduced because of power quality issues mainly based on total harmonic distortion. The proposed solution incorporates a matrix converter is mainly utilized to control the induction electric motor for propulsion. The matrix converter is a simple and compact direct AC-AC converter. The proposed EV with matrix converter is modeled using PSIM.

In high power induction motor drives, the switching frequency of the inverter is quite low due to the high losses in the power devices. Real-time PWM strategies, which result in reduced harmonic distortion under low switching frequencies and have maximum possible DC bus utilisation, are developed for such drives in the present work. The space vector approach is taken up for the generation of synchronised PWM waveforms with 3-Phase Symmetry, Half Wave Symmetry and Quarter Wave Symmetry, required for high-power drives. Rules for synchronisation and the waveform symmetries are brought out. These rules are applied to the conventional and modified forms of space vector modulation, leading to the synchronised conventional space vector strategy and the Basic Bus Clamping Strategy-I, respectively. Further, four new synchronised, bus-clamping PWM strategies, namely Asymmetric Zero-Changing Strategy, Boundary Sampling Strategy-I, Basic Bus Clamping Strategy-II and Boundary Sampling Strategy-II, are proposed. These strategies exploit the flexibilities offered by the space vector approach like double-switching of a phase within a subcycle, clamping of two phases within a subcycle etc. It is shown that the PWM waveforms generated by these strategies cannot be generated by comparing suitable 3-phase modulating waves with a triangular carrier wave. A modified two-zone approach to overmodulation is proposed. This is applied to the six synchronised PWM strategies, dealt with in the present work, to extend the operation of these strategies upto the six-step mode. Linearity is ensured between the magnitude of the reference and the fundamental voltage generated in the whole range of modulation upto the six-step mode. This is verified experimentally. A suitable combination of these strategies leads to a significant reduction in the harmonic distortion of the drive at medium and high speed ranges over the conventional space vector strategy. This reduction in harmonic distortion is demonstrated, theoretically as well as experimentally, on a constant V/F drive of base frequency 50Hz for three values of maximum switching frequency of the inverter, namely 450Hz, 350Hz and 250Hz. Based on the notion of stator flux ripple, analytical closed-form expressions are derived for the harmonic distortion due to the different PWM strategies. The values of harmonic distortion, computed based on these analytical expressions, compare well with those calculated based on Fourier analysis and those measured experimentally.

碩士
國立臺灣大學
機械工程學研究所
105
With increasing climate change, greenhouse gas emissions has become a serious issue. To reduce these emissions, governments continue providing new standards stricter than they were. For example, Euro 6 standard has been implemented in EU and EEA member states in 2014, having a lower level of nitrogen oxide emissions in diesel cars. Taiwan will also implement new emission standard, planned to follow the Euro 6 standard, in 2019. With a lower emission level, internal combustion engine vehicles (ICEV) are getting harder to meet these standards, and will be eliminated from the new car market. For instance, petrol or diesel cars will not be sold in Norway by 2025, and Germany will also calls for a ban on combustion engine by 2030. Therefore, Cars with low exhaust emissions, hybrid electric vehicles (HEV), or zero exhaust emissions, electric vehicles (EV), have become the subject of research and production made by car makers. Electric motors, the main component in electric vehicle transmission system, are also getting more and more concerned. Beyond numerous kind of electric motors, squirrel cage induction motor might be the best candidate for electric vehicle because of its inexpensive cost, robustness and controllability. However, due to its complex interactions between stator and rotor harmonics, squirrel cage induction motors often suffer from parasitic torques, vibrations, noises and additional stray losses. Therefore, designing a squirrel cage motor with low harmonic effects is quite important for electric vehicle. This thesis starts with a brief design procedure used in industrial, providing an interpretation of its physical meaning. This thesis also presents a novel analysis and design procedure for winding, allowing designers to determine winding factor of any order harmonic for arbitrary winding. On the other hand, this thesis provides derivations of slots combination preventing parasitic torques, noises and vibrations, additional stray losses. With these derivations, we realize that air gap flux density and the number of slots affect harmonic effect the most. Lastly, this thesis presents an innovative optimal design procedure for electric vehicle induction motor and apply this procedure to a2.2kw, four pole induction motor. As a result, efficiency, power factor and torque ripple are all significantly improved.

Multilevel inverters are very popular for medium and high-voltage induction motor (IM) drive applications. They have superior performance compared to 2-level inverters such as reduced harmonic content in output voltage and current, lower common mode voltage and dv/dt, and lesser voltage stress on power switches. To get nearly sinusoidal current waveforms, the switching frequency of the conventional inverters have to be in¬creased. This will lead to higher switching losses and electromagnetic interference. The problem in using lower switching frequency is the introduction of low order harmonics in phase currents and undesirable torque ripple in the motor. The 5th and 7th harmonics are dominant for hexagonal voltage space-vector based low frequency switching. Dodecagonal voltage space-vector based multilevel inverters have been proposed as an improvement over the conventional hexagonal space vector based inverters. They achieve complete elimination of 5th and 7th order harmonics throughout the modulation range. The linear modulation range is also extended by about 6.6%, since the dodecagon is closer to circle than a hexagon. The previous works on dodecagonal voltage space vector based VSI fed drives used voltage controlled PWM (VC-PWM). Although these controllers are more popular, they have inferior dynamic performance when compared to current controlled PWM (CC¬PWM). VSIs using current controlled PWM have excellent dynamic response, inherent short-circuit protection and are simple to implement. The conventional CC-PWM tech¬niques have large switching frequency variation and large current ripple in steady-state. xix As a result, there has been significant research interest to achieve current controlled VSI fed IM drives with constant switching frequency. Two current error space vector (CESV) based hysteresis controllers for dodecagonal voltage space-vector based VSI fed induction motor drives are proposed in this work. The proposed controllers achieve nearly constant switching frequency at steady state operation, similar to VC-SVPWM based VSI fed IM drives. They also have fast dynamic response while at the same time achieving complete elimination of fifth and seventh order harmonics for the entire modulation range, due to dodecagonal voltage vector switching. The first work proposes a nearly constant switching frequency current error space vector (CESV) based hysteresis controller for an IM drive with single dodecagonal voltage space vectors. Parabolic boundaries computed offline are used in the proposed controller. An open-end winding induction motor is fed from two inverters with asymmetrical DC link voltages, to generate the dodecagonal voltage space vectors. The drive scheme is first studied at different frequencies with a space vector based PWM (SVPWM) control, to obtain the current error space vector boundaries. The CESV boundary at each frequency can be approximated with four parabolas. These parabolic boundaries are used in the proposed controller to limit the CESV trajectory. Due to symmetries in the parabolas only two set of parabola parameters, at different frequencies, need to be stored. A generalized next vector selection logic, valid for all sectors and rotation direction, is used in the proposed controller. For this an axis transformation is done in all sectors, to bring the CESV trajectory to the first sector. The sector information is obtained from the estimated fundamental stator phase voltage. The proposed controller is extensively studied using vector control at different frequencies and transient conditions. This controller maintains nearly constant switching frequency at steady state operation, similar to VC-SVPWM inverters, while at the same time achieving better dynamic performance and complete elimination of 5th and 7th order harmonics throughout the modulation range. In the second work the nearly constant switching frequency current hysteresis con¬troller is extended to multilevel dodecagonal voltage space-vector based IM drives, with online computation of CESV boundaries. The multilevel dodecagonal space-vector dia¬gram has different types of triangles, and the previously proposed methods for multilevel hexagonal VSI based current hysteresis controllers cannot be used directly. The CESV trajectory of the VC-SVPWM, obtained for present triangular region, is used as the reference trajectory of the proposed controller. The CESV reference boundaries are com¬puted online, using switching dwell time and voltage error vector of each applied vector. These quantities are calculated from estimated sampled reference phase voltages, which are found out from the stator current error ripple and the parameters of the induction motor. Whenever the actual current error space vector crosses the reference CESV tra¬jectory, an appropriate vector that will force it along the reference trajectory is switched. Extensive study of the proposed controller using vector control is done at different fre¬quencies and transient conditions. This controller has all the advantages of multilevel switching like low dv/dt, lesser electromagnetic interference, lower switch voltage stress and lesser harmonic distortion, in addition to all the dynamic performance advantages of the previous controller. The third work proposes an elegant 5th and 7th order harmonic suppression tech¬nique for open end winding split-phase induction motors, using capacitor fed inverters. Split-phase induction motors have been proposed to reduce the torque and flux ripples of conventional three-phase IM. But these motors have high 5th and 7th order harmonics in the stator windings due to lack of back-emf for these frequencies. A space-vector harmonic analysis of the split-phase IM is conducted and possible 5th and 7th order harmonic sup¬pression techniques studied. A simple harmonic suppression scheme is proposed, which requires the use of only capacitor fed inverters. A PWM scheme that can maintain the capacitor voltage as well as suppress the 5th and 7th order harmonics is also proposed. To test the performance of the proposed scheme, an open-loop v/f control is used on an open-end winding split-phase induction motor under no-load condition. Synchronized PWM with two samples per sector was used, for frequencies above 10 Hz. The har¬monic spectra of the phase voltages and currents were computed and compared with the traditional SVPWM scheme, to highlight the harmonic suppression. The concepts were initially simulated in Matlab/Simulink. Experimental verifica¬tion was done using laboratory prototypes at low power. While these concepts maybe easily extended to higher power levels by using suitably rated devices, the control tech¬niques presented shall still remain applicable. TMS320F2812 DSP platform was used to execute the control code for the proposed drive schemes. For the first work the output pins of the DSP was directly used to drive the inverter switches through a dead-band circuit. For the other two works, DSP outputs the sector information and the PWM signals. The PWM terminals and I/O lines of the DSP is used to output the timings and the triangle number respectively. An FPGA (XC3S200) was used to translate the sector information and the PWM signals to IGBT gate signal logic. A constant dead-time of 1.5 µs was also implemented inside the FPGA. Opto-isolated gate drivers with desaturation protection (M57962L) were used to drive the IGBTs. The phase currents and DC bus voltages were measured using hall-effect sensors. An incremental shaft position encoder was also connected to the motor to measure the angular velocity. The switches were realized using 1200 V, 75 A IGBT half bridge modules.

MU LT I L E V E L inverters are becoming the preferred choice for medium voltage high power applications. Multilevel inverters have a number of inherent advantages over conventional two level inverters. The output voltage has multiple steps or levels, resulting in reduced dV/dt, which leads to lower electromagnetic interference, making it easier to meet electromagnetic compatibility (EMC) regulations. Multilevel inverters have a much lower effective switching frequency, which leads to a reduction in switching losses. The output voltage of multilevel inverters has a much lower harmonic content. In applications such as power conversion or grid-connection, filters need to be much smaller, or can be eliminated. In motor drive applications, the low harmonic content results in smoother, ripple-free shaft torque. The neutral-point clamped (NPC), cascaded H-bridge (CHB) and flying capacitor (FC) topologies were among the earliest multilevel topologies. NPC topologies require additional clamping diodes to clamp the output to the DC bus midpoint. CHB topologies use a number of isolated DC suplies to generate multilevel output. FC topologies work with a single DC link but use additional floating capacitors. Since then, a number derivatives and improvements to these topologies have been proposed. Topologies with low switch counts are desirable because of the corresponding reduction in system size and cost. A low total component count is also desirable since it results in better reliability. Induction motors in high power applications are often operated in the open-end configuration. Here, the start terminals of the motor phase windings are connected to one three phase inverter, while the end terminals are connected to a second three-phase inverter. The two inverters are typically powered by isolated supplies to prevent the flow of common mode currents through the motor. The open end configuration has a number of advantages It can be used with nearly all high power motors with no need for electrical or mechanical modification, since all six winding terminal are available externally. The two inverters driving the open-end motor are effectively cascaded. As a result, two inverters of lower voltage and power rating can replace a single inverter with higher voltage and power rating. In addition, if one of the inverter fails, it can be bypassed and the system can be operated at reduced power. In many applications such as heating, ventilation and air conditioning (HVAC), the load power is proportional to the cube of the shaft speed, so a 50% reduction in power translates to only 20% reduction in speed, thereby improving overall system reliability. The cascading of inverters also enables multilevel operation, which is exploited for the topologies proposed in this thesis. In the open-end configuration it is important to ensure that both the DC supplies deliver power to the load. Otherwise, power can circulate through the motor windings. In addition, if the two inverters are powered by rectifier supplies, the DC bus of one inverter can charge uncontrollably, resulting in distortion of phase voltages and currents. If DC bus overcharging continues unchecked the DC bus voltage can even exceed the system rating, resulting in permanent damage. This thesis proposes two novel topologies for open-end induction motor drives with low switch counts. Both topologies are powered by two unequal, isolated DC sources having DC voltages in a 3:1 ratio. Multiple levels in the output voltage are obtained using a number of floating capacitors in each phase. Modulation and control schemes are also proposed for both topologies to ensure that DC bus overcharging never occurs, while all the capacitor voltages are kept balanced at their nominal values. The first of these two topologies is a nine level inverter for open end induction motor drives. It consists of two three-level flying capacitor inverters connected to the induction motor in the open end configuration. The two inverters are powered by DC sources of voltage 6VDC/8 and 2VDC/8, which generates an effective phase voltage having nine levels in steps of VDC/8. This topology has only eight switches and two floating capacitors per phase. The space vector structure for this topology is hexagonal, and has 217 space vector locations. A space-vector based formulation is used to determine the pole voltage of the inverter such that DC bus over charging is prevented. In addition, selection of switching states is used to balance the voltages of all floating capacitors. This scheme allows the floating capacitors to be charged up during system startup, thereby eliminating the need for separate pre-charging circuitry. A level-shifted carrier PWM based modulation scheme has been developed, which can be used with both scalar and vector control schemes. The gating signal for switches turning on must be delayed by a small amount (to allow the complementary switch to turn of), failing which current shoot through can occur. This delay is called dead time, during which gate signals to both complementary devices are turned of. Under certain conditions in the flying capacitor topology, the pole voltage can contain large undesirable transients during the dead time which result in phase current distortion, and electromagnetic noise. A novel scheme to eliminate this problem is proposed using a digital state machine approach. The switching state for each subsequent switching interval is determined based on the present switching state such that the pole voltage does not contain a transient, without affecting the phase voltage of the inverter, and irrespective of the current magnitude or direction. The state machine was implemented using an FPGA, and required an additional computation time of just 20ns, which is much smaller than the inverter dead time duration of typically 2.5µs. The second novel topology proposed in this thesis is a seventeen level inverter for an open end induction motor drive. Here, one three-level inverter and one seven-level inverter are connected to the two ends of the induction machine. The three-level inverter is a flying capacitor inverter. The seven-level inverter is a hybrid topology – it consists of an H-bridge cascaded to each phase of a three level flying capacitor inverter. This scheme is also powered by two isolated DC sources in 3:1 ratio with magnitudes 12VDC/16 and 4VDC/16. The effective phase voltage has seventeen levels in steps of VDC/16. This topology has a total of twelve switches and three floating capacitors per phase. The space vector structure for this topology is hexagonal, and has 817 space-vector locations. Space vector analysis was used to determine the pole voltages, and the switching states such that DC bus overcharging is prevented while also balancing the voltages of the floating capacitors. A non-iterative algorithm was developed for determining the switching states, suitable for implementation in digital logic using an FPGA. The scheme is able to charge the all capacitors at startup as well, eliminating the need for separate pre-charging circuits. Hardware prototypes were built for both the topologies described above for experimental verification, and used to drive a three phase 50Hz, 1.5kW, four pole induction motor in V/f control mode. The inverters topologies were built using 1200V, 75A IGBT half-bridge modules (Semikron SKM75GB12T4) with hybrid opto-isolated gate drivers (Mitsubishi M57962). Three phase rectifiers were used to create the asymmetric DC supplies Hall effect sensors were used to sense the DC link and floating capacitor voltages and phase currents (LEM LV20P voltage sensors and LA55 current sensors). Signal conditioning circuitry was built using discrete components. The PWM signals and V/f controller were implemented using a digital signal processor (Texas Instruments TMS320F28335). Synchronous PWM with was used to eliminate sub-harmonics from the phase voltage, and to ensure three-phase and half-wave symmetry. The internal ADC of the DSP was used for sampling all voltages and currents. The remaining digital logic for switch state selection was implemented on a FPGA (Xilinx Spartan3 XC3S200). Dead time functionality was also implemented within the FPGA, eliminating the need for separate dead time hardware. Both topologies were first tested for steady state operation over the full modulation range, and the pole voltages, phase voltages and phase currents were recorded. System startup, and the ability of the controllers to balance all the capacitors at startup was tested next. The capacitor voltages were also observed during sudden loading, by quickly accelerating the motor. Finally, the phenomenon of DC bus overcharging was also demonstrated. These results demonstrate the suitability of the proposed topology for a number of applications, including industrial drives, alternate energy systems, power conversion and electric traction.

For medium and high-voltage drive applications, multilevel inverters are very popular. It is due to their superior performance compared to 2-level inverters such as reduced harmonic content in the output voltage and current, lower common mode voltage and dv=dt, and lesser voltage stress on power switches. The popular circuit topologies for multilevel inverters are neutral point clamped, cascaded H-bridge and flying capacitor based circuits. There exist different combinations of these basic topologies to realize multilevel inverters with modularity, better fault tolerance, and reliability. Due to these advantages, multilevel converters are getting good acceptance from the industry, and researchers all over the world are continuously trying to improve the performance of these converters. To meet such demands, three multilevel inverter topologies are proposed in this thesis. These topologies can be used for high-power induction motor drives, and the concepts presented are also applicable for synchronous motor drives, grid-connected inverters, etc. To get nearly sinusoidal phase current waveforms, the switching frequency of the conventional inverter has to be increased. It will lead to higher switching losses and electromagnetic interference. The problem with lower switching frequency is the intro- duction of low order harmonics in phase currents and undesirable torque ripple in the motor. The 5th and 7th harmonics are dominant for hexagonal voltage space-vector based low frequency switching, and it is possible to eliminate these harmonics by dodecagonal switching. Further improvement in the waveform quality is possible by octadecagonal voltage space-vectors. In this case, the complete elimination of 11th and 13th harmonic is possible for the entire modulation range. The concepts of dodecagonal and octadecagonal voltage space-vectors are used in the proposed inverter topologies. The first topology proposed in this thesis consists of cascaded connection of two H-bridge cells. The two cells are fed from unequal DC voltage sources having a ratio of 1 : 0:366, and this inverter can produce six concentric dodecagonal voltage space- vectors. This ratio of voltages can be obtained easily from a combination of star-delta transformers, since 1 : 0:366 = ( p 3 + 1) : 1. The cascaded connection of two H-bridge cells can generate nine asymmetric pole voltage levels, and the combined three-phase inverter can produce 729 voltage space-vectors (9 9 9). From this large number of combinations, only certain voltage space-vectors are selected, which forms dodecagonal pattern. In the case of conventional multilevel inverters, the voltage space-vector diagram consists of equilateral triangles of equal size, but for the proposed inverter, the triangular regions are isosceles and are having different sizes. By properly placing the voltage space-vectors in a sampling period, it is possible to achieve lower switching frequency for the individual cells, with substantial improvement in the harmonic spectrum of the output voltage. During the experimental veri cation, the motor is operated at di erent speeds using open loop v=f control method. The samples taken are always synchronised with the start of the sector to get synchronised PWM. The number of samples per sector is decreased with increase in the fundamental frequency to limit the switching frequency. Even though many topologies are available in literature, the most preferred topology for drives application such as traction drives is the 3-level NPC structure. This implies that the industry is still looking for viable alternatives to construct multilevel inverter topologies based on available power circuits. The second work focuses on the development of a multilevel inverter for variable speed medium-voltage drive application with dodecagonal voltage space-vectors, using lesser number of switches and power sources compared to earlier implementations. It can generate three concentric 12-sided polygonal voltage space-vectors and it is based on commonly available 2-level and 3-level inverters. A simple PWM timing computation method based on the hexagonal space-vector PWM is developed. The sampled values of the three-phase reference voltages are initially converted to the timings of a two-level inverter. These timings are mapped to the dodecagonal timings using a change of basis transformation. The voltage space- vector diagram of the proposed drive consists of sixty isosceles triangular regions, and the dodecagonal timings calculated are converted to the timings of the inner triangles. A searching algorithm is used to identify the triangular region in which the reference vector is located. A front-end recti er that may be easily implemented using standard star-delta transformers is also developed, to provide near-unity power factor. To test the performance of the inverter drive, an open-loop v=f control is used on a three-phase induction motor under no-load condition. The harmonic spectra of the phase voltages were computed in order to analyse the harmonic distortion of the waveforms. The carrier frequency was kept around 1.2 KHz for the entire range of operation. If the switching frequency is decreased, the conventional hexagonal space-vector based switching introduce signifi cant 5th, 7th, 11th and 13th harmonics in the phase currents. Out of these dominant harmonics, the 5th and 7th harmonics can be completely suppressed using dodecagonal voltage space-vector based switching as observed in the first and second work. It is also possible to remove the 11th and the 13th harmonics by using voltage space-vectors with 18 sides. The last topology is based on multilevel octadecagonal (18-sided polygon) voltage space-vectors, and it has better harmonic performance than the previously mentioned topologies. Here, a multilevel inverter system capable of producing three octadecagonal voltage space-vectors is proposed for the fi rst time, along with a simple timing calculation method. The conventional three-level inverters are only required to construct the proposed drive. Four asymmetric power supply voltages with 0:3054Vdc, 0:3473Vdc, 0:2266Vdc and 0:1207Vdc are required for the operation of the drive, and it is the main drawback of the circuit. Generally front-end isolation transformer is essential for high-power drives and these asymmetric voltages can be easily obtained from the multiple windings of the isolation transformer. The total harmonic distortion of the phase current is improved due to the 18-sided voltage space-vector switching. The ratio of the radius of the largest polygon and its inscribing circle is cos10 = 0:985. This ratio in the case of hexagonal voltage space-vector modulation is cos30 = 0:866, which means that the range of the linear modulation for the proposed scheme is signifi cantly higher. The drive is designed for open-end winding induction motors and it has better fault tolerance. It any of the inverter fails, it can be easily bypassed and the drive will be still functional with reduced speed. Open loop v=f control and rotor flux oriented vector control schemes were used during the experimental verifi cation. TMS320F2812 DSP platform was used to execute the control code for the proposed drive schemes. For the entire range of operation, the carrier was synchronized with the fundamental. For the synchronization, the sampling period is varied dynamically so that the number of samples in a triangular region is fi xed, keeping the switching frequency around 1.2 KHz. The average execution time for the v=f code was found to be 20 S, where as for vector control it took nearly 100 S. The PWM terminals and I/O lines of the DSP is used to output the timings and the triangle number respectively. To convert the triangle number and the timings to IGBT gate drive logic, an FPGA (XC3S200) was used. A constant dead-time of 1.5 S is also implemented inside the FPGA. Opto-isolated gate drivers with desaturation protection (M57962L) were used to drive the IGBTs. Hall-effect sensors were used to measure the phase currents and DC bus voltages. An incremental shaft position encoder with 2500 pulse per revolution is also connected to the motor shaft, to measure the angular velocity. 1200 V, 75 A IGBT half-bridge module is used to realize the switches. The concepts were initially simulated and experimentally verifi ed using laboratory prototypes at low power. While these concepts maybe easily extended to higher power levels by using suitably rated devices, the control techniques presented shall still remain applicable.

This chapter deals with the diagnosis of induction motors (IM) with the so-called motor current signature analysis (MCSA). The MCSA is one of the most efficient techniques for the detection and the localization of electrical and mechanical failures, in which faults become apparent by harmonic components around the supply frequency. This chapter presents a summary of the most frequent faults and its consequences on the stator current spectrum of an IM. A three-phase IM model was used for simulation taking into account in one hand the normal healthy operation and in the other hand the broken rotor bars, the shorted turns in the stator windings, the voltage unbalance between phases of supply, and the abnormal behavior of load. The MCSA is used by many authors in literature for faults detection of IM. The major contribution of this work is to prove the efficiency of this diagnosis methodology to detect different faults simultaneously, in normal and abnormal functional conditions. The results illustrate good agreement between both simulated and experimental results.

Abstract Permanent magnet motors (PMMs) have been used in electrical submersible pump (ESP) applications worldwide, but the oil and gas industry still has questions about the value of the technology in terms of power savings; return on investment (ROI); and evaluation of power consumption, operational considerations, and reliability. Is this technology the future for ESPs? This paper will provide a real analysis based on more than 200 PMM installations in the Quifa and Rubiales Fields in Colombia, South America. The fields of study are located in a remote location in Colombia where 90% of the total oil production is achieved with ESPs, so power consumption and its efficiency became a focus to optimize the lifting cost of each barrel produced. As a standard in both fields of study, PMMs are installed in all initial completions. Part of the methodology explained in this paper covers electrical power evaluation, including a power factor study, total harmonic distortion (THD) measurements, and criteria for comparing real power savings vs. expected savings as per initial designs. The systematic approach can be used by any other company that wants to evaluate this technology in their fields. Deploying PMM technology in both fields of study has demonstrated, through formal and systematic analysis, the real efficiency that can be achieved by using this technology. Among the measurements confirmed in the field are power factors very close to 1, reactive power savings as high as 40% and active power saving as high as 10.5% (as compared with conventional induction motors). Additionally, the field case studies demonstrate that not all applications will see a direct energy in active power savings (kW) although total required surface apparent power (kVA) in all cases were reduced. An evaluation of total cost of ownership confirmed that in the field of study and similar operational conditions, PMM technology brings the best value for ESP applications. The authors evaluate several of the 239 cases of ESP applications with PMMs, disclosing best practices for performance evaluation and lessons learned while deploying this technology, including safety and economics evaluation to understand the conditions that maximize return on investment (ROI) and total cost of ownership (TCO).