1,721,177 research outputs found
Health Condition Monitoring and Fault-Tolerant Operation of Adjustable Speed Drives
Get PDFAdjustable speed drives (ASDs) have been extensively used in industrial applications over the past few decades because of their benefits of energy saving and control flexibilities. However, the wider penetration of ASD systems into industrial applications is hindered by the lack of health monitoring and fault-tolerant operation techniques, especially in safety-critical applications. In this dissertation, a comprehensive portfolio of health condition monitoring and fault-tolerant operation strategies is developed and implemented for multilevel neutral-point-clamped (NPC) power converters in ASDs. Simulations and experiments show that these techniques can improve power cycling lifetime of power transistors, on-line diagnosis of switch faults, and fault-tolerant capabilities.The first contribution of this dissertation is the development of a lifetime improvement Pulse Width Modulation (PWM) method which can significantly extend the power cycling lifetime of Insulated Gate Bipolar Transistors (IGBTs) in NPC inverters operating at low frequencies. This PWM method is achieved by injecting a zero-sequence signal with a frequency higher than that of the IGBT junction-to-case thermal time constants. This, in turn, lowers IGBT junction temperatures at low output frequencies. Thermal models, simulation and experimental verifications are carried out to confirm the effectiveness of this PWM method. As a second contribution of this dissertation, a novel on-line diagnostic method is developed for electronic switch faults in power converters. Targeted at three-level NPC converters, this diagnostic method can diagnose any IGBT faults by utilizing the information on the dc-bus neutral-point current and switching states. This diagnostic method only requires one additional current sensor for sensing the neutral-point current. Simulation and experimental results verified the efficacy of this diagnostic method.The third contribution consists of the development and implementation of a fault-tolerant topology for T-Type NPC power converters. In this fault-tolerant topology, one additional phase leg is added to the original T-Type NPC converter. In addition to providing a fault-tolerant solution to certain switch faults in the converter, this fault-tolerant topology can share the overload current with the original phase legs, thus increasing the overload capabilities of the power converters. A lab-scale 30-kVA ASD based on this proposed topology is implemented and the experimental results verified its benefits
Fault Tolerant Operations of Induction Motor-Drive Systems
No full textThis dissertation presents fault-tolerant/ limp-home strategies of ac motor soft starters and adjustable-speed drives (ASDs) when experiencing a power switch open-circuit or short-circuit fault. The present low-cost fault mitigation solutions can be retrofitted into the existing off-the-shelf soft starters and ASDs to enhance their reliability and fault tolerant capability, with only minimum hardware modifications. The conceived fault-tolerant soft starters are capable of operating in a two-phase mode in the event of a thyristor/SCR open-circuit or short-circuit switch-fault in any one of the phases using a novel resilient closed-loop control scheme. The performance resulting from using the conceived soft starter fault-tolerant control has demonstrated reduced starting motor torque pulsations and reduced inrush current magnitudes. Small-signal model representation of the motor-soft starter controller system is also developed here in order to design the closed-loop regulators of the control system at a desired bandwidth to render a good dynamic and fast transient response. In addition, the transient motor performance under these types of faults is investigated using analytical closed-form solutions, the results of which are in good agreement with both the detailed simulation and experimental test results of the actual hardware. As for ASDs, a low-cost fault mitigation strategy, based on a quasi-cycloconverter-based topology and control, for low-speed applications such as self-healing/limp-home needs for vehicles and propulsion systems is developed. The present approach offers the potential of mitigating both transistor open-circuit and short-circuit switch faults, as well as other drive-related faults such as faults occurring in the rectifier bridge or dc-link capacitor. Furthermore, some of the drawbacks associated with previously known fault mitigation techniques such as the need for accessibility to a motor neutral, the need for larger size dc-link capacitors, or higher dc-bus voltage, are overcome here using the present approach. Due to its unique control algorithm, torque pulsations are introduced as a result of the non-sinusoidal current waveforms. Simulation and experimental work have been performed to demonstrate the efficacy and validity of the conceived fault-tolerant solutions for induction motor fault mitigation applications
Energy Storage Systems for Traction and Renewable Energy Applications
Get PDFEnergy storage systems are the set of technologies used to store various forms of energy, and by necessity, can be discharged. Energy storage technologies have a wide range of characteristics and specifications. Like any other technology, each type of energy storage has its pros and cons. Depending on the application, it is crucial to perform a tradeoff study between the various energy storage options to choose the optimal solution based on the key performance objectives and various aspects of those technologies. The purpose of this thesis is to present a thorough literature review of the various energy storage options highlighting the key tradeoffs involved. This thesis focuses on evaluating energy storage options for traction and renewable energy applicationsHybrid Electric Vehicles (HEVs) is one key application space driving breakthroughs in energy storage technologies. The focus though has been typically on using one type of energy storage systems. This thesis investigates the impact of combining several types of batteries with ultracapacitor. A case study of integrating two energy storage systems in a series-parallel hybrid electric vehicle is simulated by using MATLAB-SIMULINK software.The other key application space is renewable energy especially wind and solar. Due to the intermittent nature of renewable energy sources, energy storage is a must to achieve the required power quality. Therefore, this thesis aims to investigate different cases of combining different types of energy storage with wind and solar. Hybrid Optimization Model for Electric Renewables (HOMER) software is utilized to study the economic and sizing aspects in each case
Bidirectional AC-DC Converter for Vehicle-to-Grid (V2G) Applications
Get PDFElectric vehicles are growing at a rapid pace in the internal combustion engine dominated transportation sector, and bring environmental and economic benefits to society. Electric vehicles produce nearly zero carbon emission, provided that they are charged through renewable energy sources. Electric vehicles reduce our dependency on foreign oil and also offer additional benefits like Vehicle-to-grid (V2G). V2G is a technology that allows electric energy stored in the electric vehicle batteries to be returned to the grid during peak demand. V2G can also provide voltage regulation, voltage shaving, reactive power compensation and distributed generation. This necessitates that an electric vehicle battery charger be bi-directional, capable of sinking or sourcing real and reactive power. The state of the art battery charging converter is unidirectional and has multiple stages of power conversion. In this thesis, a single phase, single stage, isolated, bi-directional Silicon Carbide (SiC) AC-DC converter based on Dual Active Bridge (DAB) topology is proposed and analyzed. Direct-quadrature axis (DQ) current control of the DABbased topology is implemented with phase shift modulation. Simulation results are presented with various operating conditions showing the converter’s ability to sink or source real and reactive power in the AC grid. Hardware and firmware implementation of a single phase bi-directional AC-DC converter operating at 100 kHz utilizing Silicon Carbide (SiC) MOSFETs are discussed in detail. Experimental results are shown confirming simulation results. A single phase bi-directional AC-DC converter uses large electrolytic capacitors to filter ripple currents in the DC bus. Electrolytic capacitors are bulky and are prone to failure. These electrolytic capacitors can be eliminated by rejecting the ripple current in the DC bus. The ripple current is rejected by injecting a current of same magnitude and opposite phase to the ripple current. A rigorous analysis is performed on the ripple rejection technique used in single phase bi-directional AC-DC converters. Simulation results are presented to verify the analysis. A three phase bi-directional AC-DC converter improves the charging time of the electric vehicles by charging the batteries at a higher power level. A three phase, single stage, isolated, bi-directional AC-DC converter is analyzed. DQ current control of the three phase AC-DC converter is implemented in simulation to verify the analysis
Three Stator/rotor Winding ABC Representation Equivalence for Modeling and Simulation of Squirrel-Cage Induction Motors
No full textThe multiple coupled circuit approach is traditionally used in designing control systems for squirrel-cage induction motors. In this approach, the rotor is represented by coupled rotor loops (circuits), each of which contributes a state variable to the whole model. Consequently, this increases the difficulty of directly using such detailed models in adjustable speed drive (ASD) control systems analysis and design due to the resulting large number of rotor related state space variables. The conventional d-q transformation and resulting equivalent circuit representation, though providing relatively simplified models to simulate the behavior of squirrel-cage induction motors, can only include the fundamental components of winding mmfs and flux density waveforms. That means higher order space harmonic effects on the winding inductances, due to a machine\u27s physical configurations, are necessarily neglected. In this thesis work, this author presents a systematic approach to the determination of an ABC-based equivalent 3-stator-phase/3-rotor-phase (3-3) wound-rotor type induction motor representation to a 3-phase, P-pole, Nb-bar squirrel-cage induction motor, whose various inductances include the space harmonic components due to the geometric characteristics of the machine. These space harmonic inductance terms can be obtained from the winding function-winding distribution method. It is shown in this thesis that this virtual equivalent 3-3 wound-rotor type induction motor representation has exactly the identical motor performance characteristics as the original P-pole, Nb-bar squirrel-cage induction motor model. Meanwhile, this simplified 3-3 equivalent model has greatly reduced the number of the state space variables and has led to much shorter simulation times compared with the original squirrel-cage induction motor model. Hence, this modeling approach and formulations can be useful during the motor-drive systems design stage, and for overall control strategy assessment and practical applications. In a practical case study, a l.2hp, 2-pole, 34-bar, squirrel-cage induction motor was simulated using this equivalent model, and compared with the previous simulation results based on the TSCFE-SS modeling and experimental test results for the same case study squirrel-cage induction motor. These comparisons are very favorable and hence verify this thesis model equivalence
Soft Started Induction Motor Modeling and Heating Issues for Different Starting Profiles Using a Flux Linkage ABC-Frame of Reference
No full textStarting of induction machines cause torque transients, high inrush currents, and thus heating of the machine. A popular method for starting an induction machine is applying electronically controlled soft starting voltages using series connected silicon controlled rectifiers (SCRs). A flux linkage ABC-frame of reference model of a soft started three-phase induction motor was implemented. A state-space model of the soft starter thyristor switching sequence for the motor and load was developed and implemented in a time-domain simulation to examine heating issues for different starting profiles. Simulation results of line starts and soft starts are compared with measured data through which validation of the model is established. In this thesis, different induction machine soft start profiles are shown and comparisons of starting times, torque profiles, and heating are made. Discussion of these results and conclusions as to the nearest to optimum types of profiles are delineated based on severity of torque oscillations, peak torque, starting times, and winding heating criteria
Control of PWM AC Motor-Drive Systems under Faulty Conditions
No full textAC induction motor-drive systems are considered to be the backbone for numerous industrial processes as well as many other critical applications such as aerospace, medical equipment, thermal and nuclear power generation plants. This is in addition to various marine and land transportation systems. The wide-spread use of such motor-drive systems is mainly due to their reliability, high efficiency, controllability, and high power density. However, the utilization of such systems in numerous critical applications mandate extremely high levels of reliability and survivability. These applications were the main incentive to trigger numerous investigations in the areas of early fault diagnostics and reconfigurable fault-tolerant designs of such systems, such that a fault can be detected in an incipient stage in order to safely shutdown the system and avoid catastrophic failures, as well as minimize such systems\u27 repair costs and downtimes. The other alternative was to isolate the fault and provide a reconfigurable arrangement that enables continued operation of such a motor-drive system with a tolerable/acceptable, though partially impaired performance. The main contribution of this dissertation is the conception and development of a new control strategy that allows Delta-connected induction motors to operate under a faulty two-phase open-Delta mode of operation with a resulting performance characterized by nearly balanced line currents and acceptable levels of torque pulsations in either the open-loop mode of operation, or the vector-controlled mode of operation. The main aim and accomplishment of this control strategy is to maintain a quality of performance of a two-phase open-Delta mode of operation of a faulty motor as close as possible to the quality of performance of such a motor under normal healthy three-phase Delta-connection. That is, one anticipates that such a procedure would be triggered after the process of isolating the faulty phase is accomplished successfully..
Modeling and Validation of a Fault Mitigation Method in Induction Motor-Drive Systems Using Magnetic Equivalent Circuits
Get PDFIn this thesis, a fault mitigation method for delta-connected induction motor-drive systems under a two-phase open-delta faulty operating condition is analyzed and verified. More specifically, this fault mitigation technique can provide a set of almost balanced motor line currents, and significantly reduce torque ripples, even when the machine runs under the aforementioned two-phase open-delta faulty operating condition. This condition is analyzed using a Magnetic Equivalent Circuit (MEC) model. This model is developed for a delta-connected induction motor which is coupled to its drive system, including the fault mitigation controller. That is, the MEC model is linked to its associated PWM inverter to include the electronic switching effects. This global motor-inverter model was simulated in a Matlab-Simulink environment, under both healthy and faulty operating conditions, while the inverter is operated in both the open-loop scalar control and closed-loop vector control modes. The results obtained from the global model are compared in this thesis to the results obtained from the corresponding Time-Stepping Finite Element (TSFE) simulation and experimental motor-drive test data. A comparative analysis of the motor performance obtained from these results, under the two-phase open-delta faulty operating case, is presented in this work. The simulation and experimental data show that the delta-connected MEC model can provide reasonably accurate results. Thus, the validity and applicability of the fault mitigation technique is thereby verified
Design Synthesis and Optimization of Permanent Magnet Synchronous Machines Based on Computationally-Efficient Finite Element Analysis
Get PDFIn this dissertation, a model-based multi-objective optimal design of permanent magnet ac machines, supplied by sine-wave current regulated drives, is developed and implemented. The design procedure uses an efficient electromagnetic finite element-based solver to accurately model nonlinear material properties and complex geometric shapes associated with magnetic circuit design. Application of an electromagnetic finite element-based solver allows for accurate computation in intricate performance parameters and characteristics. The first contribution of this dissertation is the development of a rapid computational method that allows accurate and efficient exploration of large multi-dimensional design spaces in search of optimum design(s). The computationally efficient finite element-based approach developed in this work provides a framework of tools that allow rapid analysis of synchronous electric machines operating under steady-state conditions. In the developed modeling approach, major steady-state performance parameters such as, winding flux linkages and voltages, average, cogging and ripple torques, stator core flux densities, core losses, efficiencies and saturated machine winding inductances, are calculated with minimum computational effort. In addition, the method includes means for rapid estimation of distributed stator forces and three-dimensional effects of stator and/or rotor skew on the performance of the machine. The second contribution of this dissertation is the development of the design synthesis and optimization method based on a differential evolution algorithm. The approach relies on the developed finite element-based modeling method for electromagnetic analysis and is able to tackle large-scale multi-objective design problems using modest computational resources. Overall, computational time savings of up to two orders of magnitude are achievable, when compared to current and prevalent state-of-the-art methods. These computational savings allow one to expand the optimization problem to achieve more complex and comprehensive design objectives. The method is used in the design process of several interior permanent magnet industrial motors. The presented case studies demonstrate that the developed finite element-based approach practically eliminates the need for using less accurate analytical and lumped parameter equivalent circuit models for electric machine design optimization. The design process and experimental validation of the case-study machines are detailed in the dissertation
A Condition Monitoring Vector (CMV) Technique for Poly-Phase Electric Machine Fault Diagnostics
No full textIn this thesis, a condition monitoring vector (CMV) technique for poly-phase induction motor stator inter-tum short-circuit faults is presented. To be more specific, the CMV includes the swing angle, the negative sequence component of motor terminal currents and voltages, as well as the input power of the induction motor. The effectiveness of the CMV is illustrated for the inter-tum short circuit diagnostics using the Time Step Finite Element (TSFE) method, as well as experimental test results of a 5-hp, 6-pole, 460-Volts, 60-Hz induction motor. Furthermore, the momentum (speed) of swing angle variation is introduced for demonstrating the deterioration process of the stator winding when the motor starts to diverge from the healthy situation to a severe faulty condition. Moreover, the Time-Averaging method is applied to improve the robustness of the condition monitoring vector concept
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