The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics

The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future

Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

Comparison of Hybrid Propulsion Drive Schemes

This paper provides a brief overview of a hybrid drives which have become popular in recent years. These drives combine two or more multilevel power inverters to obtain exceptional power quality which is necessary for Naval propulsion applications. Furthermore, for ship propulsion, where it may be difficult to obtain several isolated dc voltage sources, the inverter control can be set so that only one real dc power source is needed (or one per phase in the case of a series H-bridge type). Three types of hybrid drives considered and their advantages and limitations are described. Commonalities of the control of each hybrid drive type is discussed and three control schemes are applied to the various topologies in a set of simulation examples

A multilevel converter with a floating bridge for open-ended winding motor drive application

In this thesis, a dual inverter topology is considered as an alternative to a multilevel converter for the control of high speed machines. Instead of feeding to one end of the stator with a single power converter, this topology feeds from both sides of the stator winding using two converters, thus achieving multilevel output voltage waveforms across the load. A large amount of published work in the area of open end winding power converter topologies are focused on symmetrical voltage sources. This published research recognises the advantages of the converter system in terms of increased reliability, improved power sharing capability and elimination of common mode voltages when compared to traditional single sided three phase converter solutions. However isolated DC supplies come with the price of additional components thus increase size, weight and losses of the converter system. The aim of this project is, therefore, to investigate on reducing size, weight and losses of the open end winding motor drive by eliminating the need for isolated supply as well to achieve multilevel output voltage waveform. A traditional open-end winding induction motor drive has been analysed in terms of weight and losses and it has been clearly identified that the isolation transformer not only increases the size and weight of a drive system but also includes additional losses. A modified dual inverter system has then been proposed where one of the bridge inverters is floating, thus eliminated the need for isolated supplies. An asymmetric DC voltage sources ratio of 2:1 is utilised to achieve multilevel output voltage waveform across the load. The switching sequences are also analysed to identify the charging and discharging sequences to achieve control over floating capacitor voltage. This thesis describes the theoretical derivation of the modified converter model and algorithms as well as experimental results from an 11kW laboratory prototype

Hybrid Cascaded H-Bridge Multilevel-Inverter Induction-Motor-Drive Direct Torque Control for Automotive Applications

International audienceThis paper presents a hybrid cascaded H-bridge multilevel motor drive direct torque control (DTC) scheme for electric vehicles (EVs) or hybrid EVs. The control method is based on DTC operating principles. The stator voltage vector reference is computed from the stator flux and torque errors imposed by the flux and torque controllers. This voltage reference is then generated using a hybrid cascaded H-bridge multilevel inverter, where each phase of the inverter can be implemented using a dc source, which would be available from fuel cells, batteries, or ultracapacitors. This inverter provides nearly sinusoidal voltages with very low distortion, even without filtering, using fewer switching devices. In addition, the multilevel inverter can generate a high and fixed switching frequency output voltage with fewer switching losses, since only the small power cells of the inverter operate at a high switching rate. Therefore, a high performance and also efficient torque and flux controllers are obtained, enabling a DTC solution for multilevel-inverter-powered motor drives

A multilevel converter with a floating bridge for open-ended winding motor drive application

In this thesis, a dual inverter topology is considered as an alternative to a multilevel converter for the control of high speed machines. Instead of feeding to one end of the stator with a single power converter, this topology feeds from both sides of the stator winding using two converters, thus achieving multilevel output voltage waveforms across the load. A large amount of published work in the area of open end winding power converter topologies are focused on symmetrical voltage sources. This published research recognises the advantages of the converter system in terms of increased reliability, improved power sharing capability and elimination of common mode voltages when compared to traditional single sided three phase converter solutions. However isolated DC supplies come with the price of additional components thus increase size, weight and losses of the converter system. The aim of this project is, therefore, to investigate on reducing size, weight and losses of the open end winding motor drive by eliminating the need for isolated supply as well to achieve multilevel output voltage waveform. A traditional open-end winding induction motor drive has been analysed in terms of weight and losses and it has been clearly identified that the isolation transformer not only increases the size and weight of a drive system but also includes additional losses. A modified dual inverter system has then been proposed where one of the bridge inverters is floating, thus eliminated the need for isolated supplies. An asymmetric DC voltage sources ratio of 2:1 is utilised to achieve multilevel output voltage waveform across the load. The switching sequences are also analysed to identify the charging and discharging sequences to achieve control over floating capacitor voltage. This thesis describes the theoretical derivation of the modified converter model and algorithms as well as experimental results from an 11kW laboratory prototype

Special Power Electronics Converters and Machine Drives with Wide Band-Gap Devices

Power electronic converters play a key role in power generation, storage, and consumption. The major portion of power losses in the converters is dissipated in the semiconductor switching devices. In recent years, new power semiconductors based on wide band-gap (WBG) devices have been increasingly developed and employed in terms of promising merits including the lower on-state resistance, lower turn-on/off energy, higher capable switching frequency, higher temperature tolerance than conventional Si devices. However, WBG devices also brought new challenges including lower fault tolerance, higher system cost, gate driver challenges, and high dv/dt and resulting increased bearing current in electric machines. This work first proposed a hybrid Si IGBTs + SiC MOSFETs five-level transistor clamped H-bridge (TCHB) inverter which required significantly fewer number of semiconductor switches and fewer isolated DC sources than the conventional cascaded H-bridge inverter. As a result, system cost was largely reduced considering the high price of WBG devices in the present market. The semiconductor switches operated at carrier frequency were configured as Silicon Carbide (SiC) devices to improve the inverter efficiency, while the switches operated at fundamental output frequency (i.e., grid frequency) were constituted by Silicon (Si) IGBT devices. Different modulation strategies and control methods were developed and compared. In other words, this proposed SiC+Si hybrid TCHB inverter provided a solution to ride through a load short-circuit fault. Another special power electronic, multiport converter, was designed for EV charging station integrated with PV power generation and battery energy storage system. The control scheme for different charging modes was carefully developed to improve stabilization including power gap balancing, peak shaving, and valley filling, and voltage sag compensation. As a result, the influence on the power grid was reduced due to the matching between daily charging demand and adequate daytime PV generation. For special machine drives, such as slotless and coreless machines with low inductance, low core losses, typical drive implementations using conventional silicon-based devices are performance limited and also produce large current and torque ripples. In this research, WBG devices were employed to increase inverter switching frequency, reduce current ripple, reduce filter size, and as a result reduce drive system cost. Two inverter drive configurations were proposed and implemented with WBG devices in order to mitigate such issues for 2-phase very low inductance machines. Two inverter topologies, i.e., a dual H-bridge inverter with maximum redundancy and survivability and a 3-leg inverter for reduced cost, were considered. Simulation and experimental results validated the drive configurations in this dissertation. An integrated AC/AC converter was developed for 2-phase motor drives. Additionally, the proposed integrated AC/AC converter was systematically compared with commonly used topologies including AC/DC/AC converter and matrix converters, in terms of the output voltage/current capability, total harmonics distortion (THD), and system cost. Furthermore, closed-loop speed controllers were developed for the three topologies, and the maximum operating range and output phase currents were investigated. The proposed integrated AC/AC converter with a single-phase input and a 2-phase output reduced the switch count to six and resulting in minimized system cost and size for low power applications. In contrast, AC/DC/AC pulse width modulation (PWM) converters contained twelve active power semiconductor switches and a common DC link. Furthermore, a modulation scheme and filters for the proposed converter were developed and modeled in detail. For the significantly increased bearing current caused by the transition from Si devices to WBG devices, advanced modeling and analysis approach was proposed by using coupled field-circuit electromagnetic finite element analysis (FEA) to model bearing voltage and current in electric machines, which took into account the influence of distributed winding conductors and frequency-dependent winding RL parameters. Possible bearing current issues in axial-flux machines, and possibilities of computation time reduction, were also discussed. Two experimental validation approaches were proposed: the time-domain analysis approach to accurately capture the time transient, the stationary testing approach to measure bearing capacitance without complex control development or loading condition limitations. In addition, two types of motors were employed for experimental validation: an inside-out N-type PMSM was used for rotating testing and stationary testing, and an N-type BLDC was used for stationary testing. Possible solutions for the increased CMV and bearing currents caused by the implementation of WGB devices were discussed and developed in simulation validation, including multi-carrier SPWM modulation and H-8 converter topology

OPTIMAL PULSE WIDTH MODULATION OF MULTILEVEL INVERTERS FOR MEDIUM VOLTAGE DRIVES

Ph.DDOCTOR OF PHILOSOPH

Power Converter of Electric Machines, Renewable Energy Systems, and Transportation

Power converters and electric machines represent essential components in all fields of electrical engineering. In fact, we are heading towards a future where energy will be more and more electrical: electrical vehicles, electrical motors, renewables, storage systems are now widespread. The ongoing energy transition poses new challenges for interfacing and integrating different power systems. The constraints of space, weight, reliability, performance, and autonomy for the electric system have increased the attention of scientific research in order to find more and more appropriate technological solutions. In this context, power converters and electric machines assume a key role in enabling higher performance of electrical power conversion. Consequently, the design and control of power converters and electric machines shall be developed accordingly to the requirements of the specific application, thus leading to more specialized solutions, with the aim of enhancing the reliability, fault tolerance, and flexibility of the next generation power systems