An Overmodulation Algorithm With Neutral-Point Voltage Balancing For Three-Level Converters In High-Speed Aerospace Drives

In this paper, a virtual space vector (VSV)-based overmodulation algorithm is presented for three-level neutralpoint- clamped (3L-NPC) converters in high-speed aerospace motor drives. With the proposed inscribed polygonal-boundary compression technique, the output voltage capability is enhanced under a lower crossover angle and compression coefficient. As a result, it brings an opportunity for the operation of the studied aircraft electric starter/generator (ESG) systems easily extending from the linear modulation range into the overmodulation region. Furthermore, an active capacitor voltage balancing control method is investigated to recover neutral-point (NP) potential imbalance in the case of high modulation index and low power factor operating conditions. To simplify the digital implementation of the algorithm, a fast calculation approach is adopted in this work. The modulation performance of the proposed strategy is verified by both simulation and experimental results with a 45 kW, 32 krpm ESG prototype system

Common-mode voltage elimination in multilevel power inverter-based motor drive applications

The industry and academia are focusing their efforts on finding more efficient and reliable electrical machines and motor drives. However, many of the motors driven by pulse-width modulated converters face the recurring problem of common-mode voltage (CMV). In fact, this voltage leads to other problems such as bearing breakdown, deterioration of the stator winding insulation and electromagnetic interferences (EMI) that can affect the lifespan and correct operation of the motors. In this sense, multilevel converters have proven to be a useful tool for solving these problems and mitigating CMV over the past few decades. Among other reasons, because they provide additional degrees of freedom when comparing with two-level converters. However, although there are several proposals in the scientific literature on this topic, no complete information has been reviewed about the CMV issues and the different multilevel alternatives that can be used to solve it. In this context, the objective of this work is to determine how multilevel power converters provide additional degrees of freedom to make the reduction of the CMV possible by using specific modulation techniques, making it easier for engineers and scientists in this field to find solutions to this problem. This document consists of a descriptive study that collects the strengths and weaknesses of most important multilevel power converters, with special emphasis on how CMV affects each of them. In addition, the differences of modulation techniques aimed to the CMV reduction are explained in terms of output voltage, operating linear range, and generated CMV. Considering this last, it is recommended to use those modulation techniques that allow the generation of CMV levels of 0 V in order to be able to completely eliminate said voltage.This work was supported in part by the Government of the Basque Country within the Fund for Research Groups of the Basque University System under Grant IT978-16; in part by the Research Program ELKARTEK under Project ENSOL2-KK-2020/00077; in part by the Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya; in part by the Ministerio de Ciencia, Innovacion y Universidades of Spain under Project PID2019-111420RB-I00 and Project PID2020-115126RB-I00; and in part by the FEDER Funds.Peer ReviewedPostprint (author's final draft

デュアルインバータ駆動オープン巻線誘導電動機の位相制御変調を用いた低負荷領域における高調波低減に関する研究

国立大学法人長岡技術科学大

The Quantum Walk Microscope

In this thesis, I present single-site detection of neutral atoms stored in a three-dimensional optical lattice using a numerical aperture objective lens (NAdesign = 0.92). The combination of high-resolution imaging with state-dependent trapping along two-direction of the lattice opens up the path towards quantum simulations via quantum walks. Suppressing the interactions of a quantum system with the environment is essential for all quantum simulation experiments. It demands a precise control of both the external magnetic (stray) fields and the polarization properties of laser beams inside the vacuum chamber. I designed a metal shielding to reduce magnetic field fluctuations and designed, assembled and characterized a novel ultra-high vacuum glass cell. The glass cell consists of special glass material and exhibits an ultra-low birefringence Δn of a few times 10^-8 to highly suppress polarization disturbances originating from stress birefringence in vacuum windows. Furthermore, anti-reflection coatings avoid reflections on all window surfaces. The cell hosts the assembled vacuum-compatible objective, that exhibits a diffraction limited resolution of up to 453 nm and allows to optically resolve the spacing of the optical lattice. Fluorescence images of single trapped atoms are used to characterize the imaging system. The filling, orientation and geometry of the optical lattice is precisely reconstructed using positions of atoms that can be determined from fluorescence images. Furthermore, I present a scheme to realize state-dependent transport and discuss its robustness against experimental imperfections in a technical implementation. This transport scheme enable the realization of discrete-time quantum walks with neutral atoms in two dimensions. These quantum walks pave the way towards the simulation of artificial magnetic fields and topologically protected edge states

A Space Vector Modulation Scheme for Reduction of Dead-Time Effects on Common Mode Voltage of an Open End Winding Induction Machine

In recent times, the demand for high voltage and high current rating motor drives for electric vehicles applications has increased. These conditions place a great deal of stress on the semiconductor switches, which are usually based on silicon. Multilevel converters provide an alternative that reduces the stress on the switch and also improves the quality of the voltage output. On the other hand, 2-level power converters have proven to be reliable over a number of years. Therefore, they have been used as building blocks to achieve higher voltage and/or currents, by creating a multilevel effect to improve the quality of the voltage waveforms supplied to the motor. In this project, a power configuration with dual 2-level inverters supplying an Open End Winding Machine (OEWM) was studied. This thesis investigates the Space Vector Modulation (SVM) switching strategy for an open end winding machine, fed by dual 2-level inverters. One DC voltage source is employed to feed the both inverters. In addition, the problem of Common Mode Voltage (CMV) in this configuration was discussed in depth and the cause of this problem was explored. The existing SVM strategy to eliminate the CMV due to switching states was discussed in depth and it was modified in order to eliminate the effect of dead-time on the common mode voltages. The existing modulation strategy was adjusted to re-align the switching states according to the phase current direction in order to obtain a proper sequence. The proposed scheme is also applicable for n-level inverters. The performance of the system under the proposed strategy in terms of current and voltage quality was investigated and duly presented. The studies were conducted in MATLAB/Simulink software in the time-domain. Loss calculation using PLECS toolbox is also provided in this thesis

Three-level neutral point-clamped (NPC) traction inverter drive for electric vehicles

The motivation of this project was to develop a three level neutral point clamped (NPC) traction inverter for a permanent magnet synchronous machine drive. The three-level inverter helps to reduce the total inverter losses at higher switching frequencies, compared to a two-level inverter for electric vehicle applications. The three-level inverter has also more power switches compared to the two-level inverter. This helps to reduce the voltage stress across the switches and the machine winding. In addition, it also allows an increase in the DC-link voltage, which in turn helps to reduce the DC-link current, phase conductor size and the associated losses. Moreover, at higher DC-bus voltages the power switches will have lower thermal stress when compared to the 2-level. However, the NPC inverter topologies have an inherent problem of DC-link voltage balancing. In the initial part of this thesis, a novel space vector based DC-link voltage balancing strategy is proposed. This strategy can keep the two DC-link capacitor voltages balanced during transient changes in both speed and torque. The performance of the three-level inverter system is then compared with a two-level inverter based drive to validate its performance improvement. The results showed a significant reduction in total voltage and current harmonic distortions, reduced total inverter losses (by 2/3rd) and was even was able to keep the neutral point fluctuation low at all operating load power factor conditions. The second motivation of this thesis was to reduce the computational time in the real-time implementation of the control logic. For this purpose, a modified carrier and hybrid-carrier based PWM strategy was proposed, which also kept the DC-link capacitor voltages balanced. The modified carrier based strategy was able to reduce the switching losses compared to the conventional strategies, while the hybrid-carrier based strategy kept the advantages of both carrier and the space vector techniques. Finally, a performance comparison study was carried out to compare the total harmonic distortion, switching loss distribution, and total inverter loss of all the four proposed strategies

Design and Control of Power Converters 2019

In this book, 20 papers focused on different fields of power electronics are gathered. Approximately half of the papers are focused on different control issues and techniques, ranging from the computer-aided design of digital compensators to more specific approaches such as fuzzy or sliding control techniques. The rest of the papers are focused on the design of novel topologies. The fields in which these controls and topologies are applied are varied: MMCs, photovoltaic systems, supercapacitors and traction systems, LEDs, wireless power transfer, etc

The investigation of electromagnetic radial force and associated vibration in permanent magnet synchronous machines

The rising public awareness of climate change and urban air pollution has been one of the key drivers for transport electrification. Such trend drastically accelerates the quest for high-power-and-torque-density electric drive systems. The rare-earth permanent magnet synchronous machine, with its excellent steady-state and dynamic characteristics, has been the ideal candidate for these applications. Specifically, the fractional-slot and concentrated-winding configuration is widely adopted due to its distinctive merits such as short end winding, low torque pulsation, and high efficiency. The vibration and the associated acoustic noise become one of the main parasitic issues of high-performance permanent magnet synchronous drives. These undesirable features mainly arise from mechanical connection failure, imperfect assembly, torque pulsation, and electromagnetic radial and axial force density waves. The high-power-and-torque-density requirement will only be ultimately fulfilled by the reduction of both electromagnetic active material and passive support structure. This results in inflated electromagnetic force density inside the electric machine. Besides, the sti.ness of the machine parts can be compromised and the resultant natural frequencies are significantly brought down. Therefore, the vibration and acoustic noise that are associated with the electromagnetic radial and axial force density waves become a burden for large deployment of these drives. This study is mainly dedicated to the investigation of the electromagnetic radial forced density and its associated vibration and acoustic noise in radial-flux permanent magnet synchronous machines. These machines are usually powered by voltage source inverter with pulse width modulation techniques and various control strategies. Consequently, the vibration problem not only lies on the permanent magnet synchronous machine but also highly relates to its drive and controller. Generally, the electromagnetic radial force density and its relevant vibration can be divided into low-frequency and high-frequency components based on their origins. The low-frequency electromagnetic radial force density waves stem from the magnetic field components by the permanent magnets and armature reaction of fundamental and phase-belt current harmonic components, while the high-frequency ones are introduced by the interactions between the main low-frequency and sideband highfrequency magnetic field components. Both permanent magnets and armature reaction current are the main sources of magnetic field in electric machines. Various drive-level modeling techniques are first reviewed, explored, and developed to evaluate the current harmonic components of the permanent magnet synchronous machine drive. Meanwhile, a simple yet e.ective analytical model is derived to promptly estimate the sideband current harmonic components in the drive with both sinusoidal and space-vector pulse width modulation techniques. An improved analytical method is also proposed to predict the magnetic field from permanent magnets in interior permanent magnet synchronous machines. Moreover, a universal permeance model is analytically developed to obtain the corresponding armature-reaction magnetic field components. With the permanent magnet and armature-reaction magnetic field components, the main electromagnetic radial force density components can be identified and estimated based on Maxwell stress tensor theory. The stator tooth structure has large impacts on both electromagnetic radial force density components and mechanical vibration behaviors. The stator tooth modulation e.ect has been comprehensively demonstrated and explained by both finite element analysis and experimental results. Analytical models of such e.ect are developed for prompt evaluation and insightful revelation. Based on the proposed models, multi-physics approaches are proposed to accurately predict low-frequency and high-frequency electromagnetic radial vibration. Such method is quite versatile and applicable for both integral-slot and fractional-slot concentrated-winding permanent magnet synchronous machines. Comprehensive experimental results are provided to underpin the validity of the proposed models and methods. This study commences on the derivations of the drive parameters such as torque angle, modulation index, and current harmonic components from circuit perspective and further progresses to evaluate and decouple the air-gap magnetic field components from field perspective. It carries on to dwell on the analytical estimations of the main critical electromagnetic radial force density components and stator tooth modulation e.ect. Based on the stator mechanical structure, the corresponding electromagnetic radial vibration and acoustic noise can be accurately predicted. Various analytical models have been developed throughout this study to provide a systematic tool for quick and e.ective investigation of electromagnetic radial force density, the associated vibration and acoustic noise in permanent magnet synchronous machine drive. They have all been rigorously validated by finite element analysis and experimental results. Besides, this study reveals not only a universal approach for electromagnetic radial vibration analysis but also insightful correlations from both machine and drive perspectives

Modulation and control strategies for multilevel five-phase open-end winding drives

Industrial and automotive trends clearly demonstrate an increased interest in medium- and high-power variable speed drives. Despite constant progress in the technology, the semiconductor characteristics are still the bottleneck in drive designs, due to their limitations to block high voltage (several kilovolts) and conduct high current (several hundreds of amperes per-phase). For this reason and numerous other advantages, solutions based on multilevel inverters and multiphase machines are considered in recent years. The open-end winding drives are an alternative approach for drives construction. This thesis investigates carrier based pulse width modulation schemes for five-phase open-end winding drives. Two drive topologies, with isolated dc-links of two inverters, are considered. The first one consists of two two-level inverters and a five-phase machine. The second topology utilises one three- and one two-level five-phase inverter. It is shown that the same drive structure can produce a different number of phase voltage levels, when different dc-link voltages of two inverters are in use. Hence, dc-link voltage ratio is considered as an additional degree of freedom. An open-end winding structure that comprises of two two-level inverters offers harmonic performance equivalent to three- and four-level single-sided supply. The second drive structure under analysis is able to produce four, five and six voltage levels, depending on utilised dc-link voltage ratio. Modulation schemes are classified in two categories. So-called coupled modulation schemes are developed under the assumption that open-end winding drives are equivalent to certain single-sided multilevel solutions. This enables the application of slightly modified modulation methods for multilevel inverters, to the open-end winding configurations. As a consequence, number of utilised voltage levels can be higher than the sum of two inverters’ number of levels. However, this boost in number of levels relies on simultaneous switching in two inverters’ legs connected to the same drive phase,which causes so-called dead-time spikes. The second group, referred to in this thesis as decoupled modulation schemes, rely on the separate modulation of two inverters, using voltage references obtained by splitting the overall phase voltage reference, proportionally to inverters’ dc-link voltages. Hence, this kind of modulation offers somewhat worse harmonic performance, when compared to coupled modulation schemes. Special attention is paid to the stability of dc-link voltage levels, which is one of the most important figures of merits of quality for multilevel drives. Using a novel analysis approach, it is demonstrated that utilisation of optimal harmonic performance offered by coupled modulation methods leads to unstable dc-link voltages, but only in the cases where dc-link voltage ratio is used for increment of available number of voltage levels. Decoupled modulation methods offer stable dc-link voltages, regardless of drive configuration. One of the drawbacks of the analysed open-end winding drives is the need for two isolated dc sources, which form dc-link voltages of two inverters. For that reason, a possibility to use only one dc-source in open-end winding drives with isolated inverters is considered. Analysis shows that both drive topologies can be operated using so-called bulk and conditioning inverter control, where bulk inverter is supplied from an active dc source, but operates in staircase mode, while conditioning inverter performs high-frequency pulse width modulation, in order to suppress low-order harmonic content. This kind of operation is investigated in details for two specific configurations in which two inverters never operate at the same time in PWM mode, when coupled modulation methods are used. Comparison of the results shows that topology which comprises from one three- and one two-level inverter is more suitable for this kind of control. Together with previously analysed configurations and modulation strategies, dynamic performance of this novel drive is tested under the closed-loop speed control. Experimental results show that open-end winding drives are suitable for a wide range of applications