THD Analysis of a Seven, Nine, and Eleven Level Cascaded H-Bridge Multilevel Inverter for Different Loads

A multilevel inverter is implemented for generating the required staircase AC voltage of output from various steps of voltages of DC sources. The multilevel inverter gives a better harmonic spectrum and a compatible quality of output. This article delves into an analytical analysis of the total harmonic distortion (THD) of different multilevel inverters which employ a multicarrier PWM technique. This technique is implemented for operating the switches at their respective angle of conduction. This paper deals with various cascaded H-Bridge multilevel inverters (CMI) with various loads that are modelled by implementing the MATLAB/Simulink platform. The output gives a better result of the proposed model in terms that it is helpful towards reducing the THD and the losses of switching

Performance Analysis of the Linear Induction Motor for the Deep-Underground High-Speed GTX

Abstract -In order to develop a deep-underground great train express (GTX) in South Korea, the specifications decision and development of a traction control system (including an inverter and a traction motor), which considers a variety of route conditions, must be advanced. In this study, we examined the running resistance properties of a high-speed traction system based on a variety of tunnel types and vehicle organization methods. Then, we studied the power requirements necessary for the traction motor to maintain balanced speed in the high-speed traction system. From this, we determined the design criteria for the development of a high-speed traction system for use in the deep-underground GTX. Finally, we designed a linear induction motor (LIM) for a propulsion system, and we used the finite element method (FEM) to analyze its performance as it travelled through deep-underground tunnels

suppression of dc link voltage unbalance in three level neutral point clamped converters

Abstract Two different control approaches for suppressing DC-link voltage unbalance in Three-Level Neutral-Point Clamped Converters (NPCs) are presented in this paper. They both guarantee DC-link voltage equalization over any NPC operating conditions, i.e. when the NPC feeds or is supplied by the main AC grid at different active and/or reactive power rates. The proposed control approaches consist of either a hysteresis or a proportional regulator, each of which synthesizes the most suitable control action based on the actual DC-link voltage unbalance. Particularly, two different PWM techniques have been developed in order to achieve DC-link voltage equalization successfully, preserving NPC voltage and current waveforms at the same time. The performances achievable by means of both the proposed control approaches have been compared to each other through an extensive simulation study in order to highlight their most important advantages and drawbacks, as well as their effectiveness over any operating conditions. Particularly, both control approaches are validated in the Matlab-Simulink environment referring to DC-link voltage equalization of an NPC that represents the point of common coupling between a DC microgrid and the main AC grid

OPTIMAL PULSE WIDTH MODULATION OF MULTILEVEL INVERTERS FOR MEDIUM VOLTAGE DRIVES

Ph.DDOCTOR OF PHILOSOPH

Comparison of Three Space Vector PWM Methods for a Three-Level Inverter with a Permanent Magnet Machine Load

Much work exists on multilevel space vector pulse width modulation (PWM) to drive induction machines, in which the rotor currents are induced by stator rotating field effects. However, there are few investigations that analyze these modulation methods applied to permanent magnet (PM) and wound-field synchronous machines, in which the rotor induces a back emf in the stator. In this thesis, three different three-level space vector PWM switching sequences are applied to a three-level neutral-point-clamped (NP) inverter driving an internal permanent magnet (IPM) machine load. The inherent qualities of each of the switching sequences when under the influence of a forcing function (the back emf) created by the permanent magnets of the machine are investigated. In particular, output voltage quality, output current quality, and dc bus neutral point balance are analyzed and compared. Two machine operating conditions are considered: rated speed, rated load and half speed, rated load. By considering these two different operating speeds, the three switching sequences may be analyzed under both two-level operation and three-level operation of the inverter. A circuit model based on the machine state space model in the abc current frame of reference is used to model the IPM machine load. First, a short introduction to two-level inverters and a theoretical development of two-level space vector PWM are presented to introduce these basic principles. Then, an overview of the three main multilevel inverter topologies including their associated advantages and disadvantages is presented. A theoretical development of three-level space vector PWM is built upon the concepts introduced in the two-level case, and the three switching sequences under investigation are explained. The system model, including the IPM machine load, the three-level NPC inverter, and the space vector PWM algorithms, is implemented using MATLAB Simulink. All simulation results are analyzed based on output voltage and current distortion and neutral point imbalance, and a comparison between the three switching sequences is presented

PWM Techniques for Control of Dual-Inverter Supplied Six-Phase Drives

Among the different multiphase ac drive solutions, one of the most widely reported in the literature is the six-phase machine. The machines can be realised into two different configurations, symmetrical and asymmetrical. For the symmetrical configuration, the stator winding consists of two sets of three-phase windings that are spatially shifted by 60 degrees where spatial displacement between any two consecutive phases is the same and equal to 60 degrees. For the asymmetrical configuration, the two sets of three-phase windings are spatially shifted by 30 degrees. As a result, the spatial shift between consecutive phases becomes non-equidistant.In this thesis, modulation techniques for both symmetrical and asymmetrical six-phase machines are investigated. The machines are configured in open-end winding configuration where both ends of the stator winding are connected to separate isolated inverters in a topology known as dual-inverter supply. Compared to conventional single-sided supply topology where one end of the winding is connected to an inverter while the other side is star-connected, some additional benefits are offered by the dual-inverter supply topology. First, fault tolerance of the drive is improved, since the supply is realised with two independent inverters. In case one of the inverters is faulted, the other can continue to provide power to the machine. Second, the same phase voltages can be achieved with half the dc-link voltages on the two inverter inputs compared to the single-sided supply, which can be useful in applications such as electric and hybrid electric vehicles and medium sized ships, where the dc voltage levels are limited. Further, due to the nature of the topology, additional diodes and capacitors like in the Neutral Point Clamped (NPC) and Flying Capacitor (FC) VSIs are not required. The latter results in a further advantage - capacitor voltage balancing techniques are not required.Two pulse width modulation (PWM) techniques for control of the dual-inverter supplied six-phase drives are proposed in this thesis. The first is a reference sharing algorithm where the inverters are modulated using reference voltage that is shared equally and unequally between the two modulators. For both symmetrical and asymmetrical six-phase drives, a better performance, in term of total harmonic distortion (THD) of phase voltage is obtained when the reference is shared unequally between the two modulators. The second technique is carrier-based modulation where the modulation of the two inverters is determined by the disposition of the carrier signals. Three variations of carrier signals disposition are investigated namely; the phase disposition (PD-PWM), alternate phase opposition disposition (APOD-PWM) and phase-shifted PWM (PS-PWM). For the symmetrical six-phase drive, the best phase voltage and current THDs are obtained using APOD-PWM while for asymmetrical six-phase drive, the APOD-PWM produces the worst current THD despite having the best voltage THD among the three methods.All the developed modulation techniques are analysed using simulations and experiments undertaken using a laboratory prototypes. The waveforms and spectra of phase voltage and load current obtained from the simulation and experimental works are presented in this thesis together with the THD of both the voltage and current over entire linear modulation range

Continuous and discontinuous modulation techniques for multiphase drives: analysis and contributions

Falta palabras clavesThe study of multiphase machines applications is an emergent field of research mainly because of the high reliability they offer for high power applications. Nowadays, they are predominantly supplied from two-level voltage source inverters (VSIs). For the purpose of the inverter control, both carrier-based and space vector pulse width modulation (PWM) techniques have been developed, for various phase numbers, which are capable of generating required sinusoidal output voltages. Both methods are usually a general extension of modulation methods used in the three-phase case. The relationship between continuous carrier-based and space vector PWM has been reported in the scientific literature for the multiphase case, stating analogies and differences. Discontinuous PWM techniques for multiphase inverters have also received some attention as well, but at a lesser extent than the continuous PWM techniques, always in relation to multiphase systems. In this work for filling aforementioned gap, discontinuous modulation methods are first analysed in multiphase drives. The natural consequence of the existence of different PWM strategies is the inherently different behaviour with regard to the performance indicators that can be used to assess the quality of output waveforms. Among these performance indicators, one of the most interesting used in three phase induction machines for the evaluation of switching characteristics and the current ripple are the ux harmonic distortion factor (HDF). However, HDF has been only very recently introduced in the multiphase case, and for asymmetrical six-phase induction machines that can be considered like two three phase machines in the same case. Consequently, there is quite few work in the scientific literature and the multiphase induction machine case in the evaluation of switching characteristics and the current ripple using HDF. Therefore, the extension of HDF for the evaluation of switching characteristics and the current ripple in the multiphase case is studied and analysed like a second main goal of this Thesis. Notice that SVM has been also extended to the multiphase case. However, most scientific literature relates the general case, where linear operation regions are only considered. A third goal of the work is the extension of the operation region of the SVM-multiphase scheme. In this field, non linear operation in the overmodulation region is also considered, guaranteeing a smooth and linear transition characteristic between linear and overmodulation regions, minimizing the unwanted voltage amplitude of low order voltage harmonic components. Then, a simple algorithm is proposed with the ability to minimize xy voltage and current components in any multiphase induction machine with any odd number of phases. Finally, the reduction of Common Mode Voltage (CMV) is an interesting topic in the modulation techniques field because it is known to be the cause of electromagnetic interference (EMI), breakdown of windings insulation, fault activation of current detector circuits and leakage currents problems that can damage the motor bearings. The commonmode voltage issue is also studied in this Thesis, and a SVM method is proposed to minimize its content in the electromechanical system. Major contributions of this dissertation have been published in seven journal and three conferences papers, although related work have been also published in another four journal papers. The main contributions covered in this work are the following: Paper 1: D. Dujic, M. Jones, E. Levi, J. Prieto, F. Barrero, “Switching Ripple Characteristics of Space Vector PWM Schemes for Five-Phase Two-Level Voltage Source Inverters-Part 1: Flux Harmonic Distortion Factors," IEEE Transactions on Industrial Electronics, vol.58, no.7, pp.2789-2798, July 2011. Paper 2: M. Jones, D. Dujic, E. Levi, J. Prieto, F. Barrero, “Switching Ripple Characteristics of Space Vector PWM Schemes for Five-Phase Two-Level Voltage Source Inverters-Part 2: Current Ripple," IEEE Transactions on Industrial Electronics, vol.58, no.7, pp. 2799-2808, July 2011. Paper 3: J. Prieto, M. Jones, F. Barrero, E. Levi, S. Toral, “Comparative Analysis of Discontinuous and Continuous PWM Techniques in VSI-Fed Five-Phase Induction Motor," IEEE Transactions on Industrial Electronics, vol.58, no.12, pp.5324-5335, Dec. 2011. Paper 4: J. Prieto, F. Barrero, E. Levi, S. Toral, M. Jones, M. J. Durán, \Analytical Evaluation of Switching Characteristics in Five-Phase Drives with Discontinuous Space Vector Pulse Width Modulation Techniques", EPE Journal, vol.23, no.2, pp.24-33, Jun. 2013. Paper 5: J. Prieto, E. Levi, F. Barrero, S. Toral, “Output current ripple analysis for asymmetrical six-phase drives using double zero-sequence injection PWM," Proceedings of 37th Annual Conference on IEEE Industrial Electronics Society (IECON 2011), pp.3692-3697, Nov. 2011. Paper 6: M.J. Dur_an, J. Prieto, F. Barrero, J.A. Riveros, H.Guzmán, “Space- Vector PWM With Reduced Common-Mode Voltage for Five-Phase Induction Motor Drives," IEEE Transactions on Industrial Electronics, vol.60, no.10, pp.4159- 4168, Oct. 2013. Paper 7: M.J. Duran, J. Prieto, F. Barrero, “Space Vector PWM With Reduced Common-Mode Voltage for Five-Phase Induction Motor Drives Operating in Overmodulation Zone," IEEE Transactions on Power Electronics, vol.28, no.8, pp.4030-4040, Aug. 2013. Paper 8: J. Prieto, F. Barrero, M. J. Durán, S. Toral, M.A. Perales, \SVM Procedure for n-phase VSI With Low Harmonic Distortion in the Overmodulation Region," IEEE Transactions on Industrial Electronics, vol.61, no.1, pp.92-97, Jan. 2014. Notice that all the proposals were validated using simulation and experimental results, and different five-phase and asymmetrical six-phase induction machines available at the labs of the Liverpool John Moores University and the University of Seville, being the candidate one of the main contributors to the obtained publications.Premio Extraordinario de Doctorado U

Induction Motors

AC motors play a major role in modern industrial applications. Squirrel-cage induction motors (SCIMs) are probably the most frequently used when compared to other AC motors because of their low cost, ruggedness, and low maintenance. The material presented in this book is organized into four sections, covering the applications and structural properties of induction motors (IMs), fault detection and diagnostics, control strategies, and the more recently developed topology based on the multiphase (more than three phases) induction motors. This material should be of specific interest to engineers and researchers who are engaged in the modeling, design, and implementation of control algorithms applied to induction motors and, more generally, to readers broadly interested in nonlinear control, health condition monitoring, and fault diagnosis

Power Electronic Transformer with Open-End Winding Electric Drive for Wind Energy Conversion Systems

University of Minnesota Ph.D. dissertation. May 2016. Major: Electrical Engineering. Advisor: Ned Mohan. 1 computer file (PDF); xii, 187 pages.Power Electronic Transformers (PETs) provide a reduction in size over line frequency transformers by operating at much higher frequencies than line frequency or grid frequency. Due to their smaller size, they could be useful in renewable energy systems where an interface with the grid is needed. As the name suggests, a power electronic interface is needed to convert line frequency voltages to high frequency voltages before they can be fed to the transformer. A PET topology that has simple control and less number of high voltage devices would be considered desirable due to lower total device cost and easy control implementation. A push-pull based PET topology has been proposed in the past which contains only two high voltage controlled switching devices and the control of those two devices is very simple. This topology could be configured for single stage ac to dc power conversion, to which an open-end winding dc to ac converter could be connected. Alternatively, it could be configured for direct ac to ac power conversion using dual matrix converters. In the first part of this thesis, the aforementioned push-pull based power electronic topology has been studied for power conversion from ac to dc and vice versa. Both single phase ac to dc and three phase ac to dc variants of the topology have been analyzed for power transfer, rms currents and soft switching. They provide attractive features which include single stage ac to dc bidirectional power conversion, unity power factor operation in open loop and control of dc side voltage using simple PI controllers. The other part of this thesis deals with open-end winding drives for suppression of common mode voltages at machine terminals. Switching frequency Common Mode Voltages (CMV) are generated by conventional Pulse Width Modulated (PWM) drives at machine terminals, which cause shaft voltage build up leading to bearing currents. These bearing currents are harmful for the machine and also cause Electromagnetic Interference (EMI). Open-end winding drives consist of one electric drive connected on each end of a three phase electric motor with the stator neutral opened up to give three more terminals. Open-end winding drives can be controlled to suppress switching frequency CMV at machine terminals. In this thesis, open-end winding two level Voltage Source Inverter (VSI) drive and open-end winding two level Matrix Converter (MC) drives have been investigated. Carrier based PWM techniques have been proposed for each of these drives for suppressing CMV. In addition, an improved four step commutation method has been proposed for the open-end winding matrix converter drive to suppress CMV spikes during the commutation process. Finally, a circuit consisting of the reduced switch PET connected with an open-end winding MC drive has been studied for single stage ac to ac power conversion with open loop power factor control