Active DC voltage balancing PWM technique for high-power cascaded multilevel converters

In this paper a dedicated PWM technique specifically designed for single-phase (or four wire three-phase) multilevel Cascaded H-Bridge Converters is presented. The aim of the proposed technique is to minimize the DC-Link voltage unbalance, independently from the amplitude of the DC-Link voltage reference, and compensate the switching device voltage drops and on-state resistances. Such compensation can be used to achieve an increase in the waveform quality of the converter. This is particularly useful in high-power, low supply voltage applications where a low switching frequency is used. The DC-Link voltage balancing capability of the method removes the requirement for additional control loops to actively balance the DC-Link voltage on each H-Bridge, simplifying the control structure. The proposed modulation technique has been validated through the use of simulation and extensive experimental testing to confirm its effectiveness

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

A hybrid multilevel converter for medium and high voltage applications

This paper investigates the suitability of the hybrid multilevel converter for medium and high voltage application. The converter operation, modulation, and capacitor voltage balancing method are described in detail. The ability of the hybrid multilevel converter to operate with different modulation indices and load power factors is investigated. It has been established that the hybrid multilevel converter is capable of operating independent of load power factor. Operation with variable modulation index increases voltage stresses on the converter switches and does not alter the fundamental voltage magnitude as in all known voltage source converter topologies. The viability of the hybrid multilevel converter for medium and high voltage applications is confirmed by simulations

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

Transformer-Less Cascaded Voltage Source Converter Based STATCOM

In this work, a transformer-less voltage source converter (VSC) based STATCOM is proposed with a combination of cascaded conventional three-phase voltage source inverters. This modular structure provides multilevel operation with reduced switch count and independent DC-link capacitors. The actual contribution of this paper is the transformer-less configuration of a conventional cascaded voltage source converter which provides reduced cost and volume as compared to other transformer-less converter configurations. The system provides reactive power compensation with better power quality when connected to the nonlinear power electronics load also. A simple control system is provided for balancing the Dc link capacitor voltage and reactive power compensation. The validation of the proposed model is analyzed with simulation using MATLAB/SIMULINK software and the results are obtained with different linear and nonlinear load configurations

A comparative study of capacitor voltage balancing techniques for flying capacitor multi-level power electronic converters

With the advent of multilevel converters for high power applications in industry, a need to develop simpler topologies and control techniques has arisen. The flying capacitor multilevel inverter (FCMLI) is one such topology which is gaining popularity in recent years with many advantages such as extra ride-through capabilities because of the capacitor storage, redundancy in switching states, low common mode voltage ratio, improved power quality, etc. In this thesis, different basic multilevel converter topologies and their advantages and applications are discussed. The thesis mainly focuses on single-phase five-level FCMLI topology. Different control techniques for capacitor voltage regulation like staircase modulation, and PWM techniques including phase disposition PWM (PDPWM), and natural balancing technique are implemented. The disadvantages of these methods are discussed. To overcome these, a new method called the split natural balancing technique which is based on the Unipolar PWM method is proposed in this thesis. In addition, a feedback control technique called amplitude modulation adjustment (AMA) method is devised to regulate the voltage across capacitors around the desired value irrespective of their initial values. Harmonic analysis of the output voltage for all the implemented methods is performed and compared --Abstract, page iii

A comprehensive review on modular multilevel converters, submodule topologies, and modulation techniques

The concept of the modular multilevel converter (MLC) has been raising interest in research in order to improve their performance and applicability. The potential of an MLC is enormous, with a great focus on medium- and high-voltage applications, such as solar photovoltaic and wind farms, electrified railway systems, or power distribution systems. This concept makes it possible to overcome the limitation of the semiconductors blocking voltages, presenting advantageous characteristics. However, the complexity of implementation and control presents added challenges. Thus, this paper aims to contribute with a critical and comparative analysis of the state-of-the-art aspects of this concept in order to maximize its potential. In this paper, different power electronics converter topologies that can be integrated into the MLC concept are presented, highlighting the advantages and disadvantages of each topology. Nevertheless, different modulation techniques used in an MLC are also presented and analyzed. Computational simulations of all the modulation techniques under analysis were developed, based on four cascaded full-bridge topologies. Considering the simulation results, a comparative analysis was possible to make regarding the symmetry of the synthesized waveforms, the harmonic content, and the power distribution in each submodule constituting the MLC.This work has been supported by FCT—Fundação para a Ciência e Tecnologia, within the R&D Units Project Scope UIDB/00319/2020. Mr. Luis A. M. Barros is supported by the doctoral scholarship PD/BD/143006/2018, granted by the Portuguese FCT foundation

Cascaded Converters For Integration And Management Of Grid Level Energy Storage Systems

ABSTRACT CASCADED CONVERTERS FOR INTEGRATION AND MANAGEMENT OF GRID-LEVEL ENERGY STORAGE SYSTEMS by ZUHAIR ALAAS December 2017 Advisor: Dr. Caisheng Wang Major: ELECTRICAL ENGINEERING Degree: Doctor of Philosophy This research work proposes two cascaded multilevel inverter structures for BESS. The gating and switching control of switching devices in both inverter typologies are done by using a phase-shifted PWM scheme. The first proposed isolated multilevel inverter is made up of three-phase six-switch inverter blocks with a reduced number of power components compared with traditional isolated CHB. The suggested isolated converter has only one battery string for three-phase system that can be used for high voltage and high power applications such as grid connected BESS and alternative energy systems. The isolated inverter enables dq frame based simple control and eliminates the issues of single-phase pulsating power, which can cause detrimental impacts on certain dc sources. Simulation studies have been carried out to compare the proposed isolated multi-level inverter with an H-bridge cascaded transformer inverter. The simulation results verified the performance of the isolated inverter. The second proposed topology is a Hierarchal Cascaded Multilevel Converter (HCMC) with phase to phase SOC balancing capability which also for high voltage and high power battery energy storage systems. The HCMC has a hybrid structure of half-bridge converters and H-bridge inverters and the voltage can be hierarchically cascaded to reach the desired value at the half-bridge and the H-bridge levels. The uniform SOC battery management is achieved by controlling the half-bridge converters that are connected to individual battery modules/cells. Simulation studies and experimental results have been carried on a large scale battery system under different operating conditions to verify the effectiveness of the proposed inverters. Moreover, this dissertation presents a new three-phase SOC equalizing circuit, called six-switch energy-level balancing circuit (SSBC), which can be used to realize uniform SOC operation for full utilization of the battery capacity in proposed HCMC or any CMI inverter while keeping balanced three-phase operation. A sinusoidal PWM modulation technique is used to control power transferring between phases. Simulation results have been carried out to verify the performance of the proposed SSBC circuit of uniform three-phase SOC balancing