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

Fault Diagnostic System for Cascaded H-bridge Multilevel Inverter Drives Based on Artificial Intelligent Approaches Incorporating a Reconfiguration Technique

A fault diagnostic and reconfiguration system in a multilevel inverter drive (MLID) using artificial intelligent based techniques is developed in this dissertation. Output phase voltages of a MLID can be used as valuable information to diagnose faults and their locations. It is difficult to diagnose a MLID system using a mathematical model because MLID systems consist of many switching devices and their system complexity has a nonlinear factor. Therefore, a neural network (NN) classification is applied to the fault diagnosis of a MLID system. Multilayer perceptron (MLP) networks are used to identify the type and location of occurring faults. The principal component analysis (PCA) is utilized in the feature extraction process to reduce the NN input size. A lower dimensional input space will also usually reduce the time necessary to train a NN, and the reduced noise may improve the mapping performance. The genetic algorithm is also applied to select the valuable principal components. The comparison among MLP neural network (NN), principal component neural network (PC-NN), and genetic algorithm based selective principal component neural network (PC-GA-NN) are performed. Proposed neural networks are evaluated with simulation test set and experimental test set. The PC-NN has improved overall classification performance from NN by about 5% points, whereas PC-GA-NN has better overall classification performance from NN by about 7.5% points. Therefore, the application of a genetic algorithm improves the classification from PC-NN by about 2.5% point. The overall classification performance of the proposed networks is more than 90%. A reconfiguration technique is also developed. The effects of using the developed reconfiguration technique at high modulation index are addressed. The developed fault diagnostic system is validated with experimental results. The developed fault diagnostic system requires about 6 cycles at 60 Hz to clear an open circuit and about 9 cycles at 60 Hz to clear a short circuit fault. The experimental results show that the developed system performs satisfactorily to detect the fault type, fault location, and reconfiguration

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

Investigations of New Fault-Tolerant Methods for Multilevel Inverters

The demands of power electronics with high power capability have increased in the last decades. These needs have driven the expansion of existing power electronics topologies and developing new power electronics generations. Multilevel inverters (MLI) are one of the most promising power electronics circuits that have been implemented and commercialized in high-voltage direct current (HVDC), motor drives, and battery energy storage systems (BESS). The expanding uses of the MLI have lead to creation of new topologies for different applications. However, one of the disadvantages of using MLIs is their complexity. MLIs consist of a large number of switching devices, which can result in a reduction of system reliability. There are significant challenges to the design of a reliable system that has the MLI’s capability with integrated fault-tolerance. In other words, design a system that can handle the fault, totally or partially, while maintaining high power capabilities and efficiency. This aim of this dissertation is to investigate the fault-tolerance of MLIs from two different points of view: 1- Develop new solutions for existing MLI topologies. In other words, add some features to existing MLIs to improve their reliability when a fault occurs. 2- Design new MLIs that have a fault-tolerant capability. A new open-circuit fault detection is proposed in this dissertation. The new fault detection method is based on monitoring the output voltage of each cell and leg voltage polarity along with each switch state. By monitoring each cell output voltage and leg voltage, the faulty cell can be detected and isolated. A novel circuit to maintain system operation under the condition of one (or more) components suffering from a faulted condition is also proposed in this dissertation. This results in a topology that continues to operate at full capability. Additionally, a new topology is proposed that offers reducing the number of batteries by 50%. Also, it has the ability to operate under non-unity power factor, which enables it to be suitable for battery energy storage systems, and static compensator (STATCOM) applications. Another novel hybrid cascaded H-bridge (CHB), known as the X-CHB, for a fault-tolerant operation is proposed in this dissertation. It ensures seamless operation of the system under an open/short circuit switching fault or dc supply fault

Study of the performance of fault-tolerant multi-level inverter included in shunt active power filter

Nowadays, the large number of shunt active power filters (SAPF) is installed in many grid networks to eliminate the source currents harmonics and enhance power quality. These filters are installed in different places according to the filtration requirements. The connection between SAPF and grid network has a negative effect during the open-circuit fault of the insulated gate bipolar transistor (IGBT) switch of the SAPF. This paper proposes the application of the new diagnostic method based on the trigonometric circle and mean value variations techniques to the early detection and precise location of the open-circuit fault of the IGBT switches, and the inclusion of the modified reconfigurable inverter topology to allow the perfect continuity of the filter currents, and improve the diagnostic of the open-circuit fault. A single-sided amplitude spectrum technique (SSAS) is applied on the source currents to get the THDi% value. The obtained simulation results prove, the great success of the proposed diagnostic method, the ability of the modified reconfigurable inverter to be adapted to the grid network, the short response time between the diagnosis and the reconfiguration process is about 7 ms which is very sufficient to guarantee the rapid continuity of the shunt active power filter

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

The Age of Multilevel Converters Arrives

This work is devoted to review and analyze the most relevant characteristics of multilevel converters, to motivate possible solutions, and to show that we are in a decisive instant in which energy companies have to bet on these converters as a good solution compared with classic two-level converters. This article presents a brief overview of the actual applications of multilevel converters and provides an introduction of the modeling techniques and the most common modulation strategies. It also addresses the operational and technological issues