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

Power Quality Enhancement in Electricity Grids with Wind Energy Using Multicell Converters and Energy Storage

In recent years, the wind power industry is experiencing a rapid growth and more wind farms with larger size wind turbines are being connected to the power system. While this contributes to the overall security of electricity supply, large-scale deployment of wind energy into the grid also presents many technical challenges. Most of these challenges are one way or another, related to the variability and intermittent nature of wind and affect the power quality of the distribution grid. Power quality relates to factors that cause variations in the voltage level and frequency as well as distortion in the voltage and current waveforms due to wind variability which produces both harmonics and inter-harmonics. The main motivation behind work is to propose a new topology of the static AC/DC/AC multicell converter to improve the power quality in grid-connected wind energy conversion systems. Serial switching cells have the ability to achieve a high power with lower-size components and improve the voltage waveforms at the input and output of the converter by increasing the number of cells. Furthermore, a battery energy storage system is included and a power management strategy is designed to ensure the continuity of power supply and consequently the autonomy of the proposed system. The simulation results are presented for a 149.2 kW wind turbine induction generator system and the results obtained demonstrate the reduced harmonics, improved transient response, and reference tracking of the voltage output of the wind energy conversion system.Peer reviewedFinal Accepted Versio

Seven Level Modified Cascaded Inverter for Induction Motor Drive Applications

In this paper, an H-bridge inverter topology with reduced switch count technique is introduced. This technique reduces the number of controlled switches used in conventional multilevel inverter. To establish a single phase system, the proposed multilevel inverter requires one H-bridge and a multi conversion cell. A multi conversion cell consists of three equal voltage sources with three controlled switches and three diodes. In conventional method, twelve controlled switches are used to obtain seven levels. Due to involvement of twelve switches the harmonics, switching losses, cost and total harmonic distortion are increased. This proposed topology also increases the level to seven with only seven controlled switches. It dramatically reduces the complexity of control circuit, cost, lower order harmonics and thus effectively reduces total harmonic distortion. Keywords: Cascaded Multilevel Inverter, H-bridge Inverter, Total Harmonic Distortion, Sinusoidal Pulse Width Modulation, Insulated Gate Bipolar Transisto

Fault diagnosis in a five-level multilevel inverter using an artificial neural network approach

Introduction. Cascaded H-bridge multilevel inverters (CHB-MLI) are becoming increasingly used in applications such as distribution systems, electrical traction systems, high voltage direct conversion systems, and many others. Despite the fact that multilevel inverters contain a large number of control switches, detecting a malfunction takes a significant amount of time. In the fault switch configurations diode included for freewheeling operation during open-fault condition. During short circuit fault conditions are carried out by the fuse, which can reveal the freewheeling current direction. The fault category can be identified independently and also failure of power switches harmed by the functioning and reliability of CHB-MLI. This paper investigates the effects and performance of open and short switching faults of multilevel inverters. Output voltage characteristics of 5 level MLI are frequently determined from distinctive switch faults with modulation index value of 0.85 is used during simulation analysis. In the simulation experiment for the modulation index value of 0.85, one second open and short circuit faults are created for the place of faulty switch. Fault is identified automatically by means of artificial neural network (ANN) technique using sinusoidal pulse width modulation based on distorted total harmonic distortion (THD) and managed by its own. The novelty of the proposed work consists of a fast Fourier transform (FFT) and ANN to identify faulty switch. Purpose. The proposed architecture is to identify faulty switch during open and short failures, which has to be reduced THD and make the system in reliable operation. Methods. The proposed topology is to be design and evaluate using MATLAB/Simulink platform. Results. Using the FFT and ANN approaches, the normal and faulty conditions of the MLI are explored, and the faulty switch is detected based on voltage changing patterns in the output. Practical value. The proposed topology has been very supportive for implementing non-conventional energy sources based multilevel inverter, which is connected to large demand in grid.Вступ. Каскадні багаторівневі інвертори H-bridge все частіше використовуються в таких пристроях, як розподільні системи, електричні тягові системи, системи прямого перетворення високої напруги та багато інших. Незважаючи на те, що багаторівневі інвертори містять велику кількість перемикачів, що управляють, виявлення несправності займає значний час. У конфігурації аварійного вимикача увімкнено діод для роботи в режимі вільного ходу в умовах обриву несправності. При короткому замиканні аварійні стани виконуються запобіжником, який може визначити напрямок струму вільного ходу. Категорія несправності може бути визначена самостійно, а також відмова силових вимикачів, що порушує функціонування та надійність каскадних багаторівневих інверторів H-bridge. У цій статті досліджуються наслідки та характеристики обривів та коротких замикань багаторівневих інверторів. Характеристики вихідної напруги 5-рівневого інвертору часто визначаються характерними несправностями перемикача, при цьому при аналізі моделювання використовується значення індексу модуляції 0,85. В імітаційному експерименті значення індексу модуляції 0,85 в місці несправного перемикача створюються односекундні обриви і коротке замикання. Несправність ідентифікується автоматично за допомогою методу штучної нейронної мережі з використанням синусоїдальної широтно-імпульсної модуляції на основі спотвореного повного гармонійного спотворення та керується самостійно. Новизна запропонованої роботи полягає у застосуванні швидкого перетворення Фур’є та штучної нейронної мережі для ідентифікації несправного перемикача. Мета. Пропонована архітектура призначена для виявлення несправного комутатора при розмиканні та короткочасних відмовах, що має знизити повне гармонійне спотворення та забезпечити надійну роботу системи. методи. Запропонована топологія має бути спроектована та оцінена з використанням платформи MATLAB/Simulink. Результати. Використовуючи підходи швидкого перетворення Фур’є та штучної нейронної мережі, досліджуються нормальні та несправні стани багаторівневих інверторів, і несправний перемикач виявляється на основі моделей зміни напруги на виході. Практична цінність. Запропонована топологія дуже сприятлива для реалізації нетрадиційних джерел енергії на основі багаторівневого інвертора, пов'язаного з великим попитом у мережі

Minimization of power loss in newfangled cascaded H-bridge multilevel inverter using in-phase disposition PWM and wavelet transform based fault diagnosis

AbstractNowadays multilevel inverters (MLIs) have been preferred over conventional two-level inverters due to reduced harmonic distortions, lower electromagnetic interference, and higher DC link voltages. However, the increased number of components, complex PWM control, voltage-balancing problem, and component failure in the circuit are some of the disadvantages. The topology suggested in this paper provides a DC voltage in the shape of a staircase that approximates the rectified shape of a commanded sinusoidal wave to the bridge inverter, which in turn alternates the polarity to produce an AC voltage with low total harmonic distortion and power loss. This topology requires fewer components and hence it leads to the reduction of overall cost and complexity particularly for higher output voltage levels. The component fault diagnostic algorithm is developed using wavelets transform tool. Finally an experimental prototype is developed and validated with the simulation results

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

Evaluation of a dual-T-type converter supplying an open-end winding induction machine

The multilevel inverter is a promising technology compared to two-level inverters in the applications of ac-drives and smart-grid applications. In this paper, a dual-T-type three-level inverters is used to drive an open-end winding induction machine. The Space-Vector Pulse-Width Modulation is selected as a good-performing control strategy to control the dual-inverter. Furthermore, an optimized method is used to select the proper switching state for the new configuration to decrease the converter losses. A comparison between the proposed configuration and the conventional diode clamped converter is made. The proposed drive system is designed and modelled by using Matlab/Simulink. It is shown that the converter can give the same hexagon, wave forms and harmonic spectrum of the five level converter. An optimized switching state selection is used to reduce the converter losses. The advantages and drawbacks of the dual-T-type configuration are discussed. In addition, the harmonic analysis and the loss calculations of the dual-T-type converter are provided and compared to the T-type three-level converter and the conventional five-level diode-clamped-converter

Integration of energy storage components with cascaded H-bridge multilevel converters

In recent years, multilevel converters have gained considerable attention in medium-voltage motor drive and grid applications. This popularity is owed to their reduced voltage stress on the semiconductor devices used in their structure. In addition, multilevel converters generate near sinusoidal outputs with low harmonic distortions. Other advantages of such converters include inherent modularity and low dv/dt stresses. In general, multilevel power electronic converters are classified into three main topologies: diode-clamped, flying-capacitor, and cascaded H-bridge. A cascaded H-bridge multilevel converter is created when several H-bridge cells are placed in series. Each H-bridge cell must be fed by a stiff voltage source. In earlier implementations, every one of these voltage sources had to contribute to the overall power supplied to the load. Later, it was demonstrated that under certain operating conditions, one can replace all but one of these sources with energy storage devices, e.g., capacitors. In other words, the entire power can be supplied by only one source. The replacing capacitors must only maintain a constant dc voltage supplying zero net power. Although this approach benefits from cost reductions, balancing the voltages across the replacing capacitors turns out to be a challenge. In this thesis, the operating conditions under which the capacitor voltage regulation is feasible are first analytically investigated. The results show that the amplitude of the output voltage as well as the power factor of the load current determines the regulation range when the staircase modulation method is employed. In order to extend the regulation range for the replacing capacitors, a new control scheme - phase shift modulation - is proposed. This method is more robust when compared to existing methods. In this method, the main H-bridge cell of the multilevel converter operates at the fundamental frequency and the auxiliary cells run at the PWM frequency. Finally, the sigma-delta modulation method has been utilized to extend the capacitor voltage regulation range. This method benefits from simplicity in implementation in comparison to PWM techniques. The analytical and simulation results prove the effectiveness of the proposed approaches. They are also consistent with the results of the experiment --Abstract, page iv

A comparative study of Total Harmonic Distortion in Multi level inverter topologies

This paper presents a detailed harmonic analysis in terms of Total Harmonic Distortion (THD) for different power circuit topologies of multi level inverter fed induction motor drives. The most common multilevel inverter topologies are the neutral-point-clamped inverter (NPC), flying capacitor inverter (FC), and cascaded H-bridge inverter (CHB). This work is to analyze the performance of all the power circuit topologies of multilevel inverter with various multi carrier PWM control techniques. Simulation and results shows that the superiority of these inverters over two-level pulse width modulation based inverter fed drives. Keywords: Medium-voltage drives, Multi Carrier PWM, Multi level inverter, Induction motor drives