Multilevel single phase isolated inverter with reduced number of switches

This paper proposes a cascaded single phase multilevel inverter using an off-the-shelf three-phase inverter and transformer. The concept is based on a cascaded connection of two inverter legs using a typical three phase inverter in such a way that the third leg is shared between the other two phases. The cascaded connection is achieved through an integrated series transformer with a typical three-phase transformer core. Utilization of a special transformer design has been previously proposed in the Custom Power Active Transformer. However, cascaded connection of inverter legs has not been previously investigated with such a concept. In this way, a three-leg inverter and a three-phase transformer are converted into an isolated multilevel single-phase inverter based on an unique configuration and modulation technique.Postprint (author's final draft

Nueva metodología para el cálculo de transformadores en convertidores de potencia multinivel

(Eng) This paper presents a new methodology for the correct design of transformers used in power multilevel inverters common source type. The proposed methodology represents a solution to the problems of distortion in the waveform, voltage drop and loss of efficiency caused by the miscalculation of the transformer using conventional methodology. To validate the methodology two prototypes under different perspectives were built, conventional and proposed, in order to verify the results, which support the solution to the problems described and shown an improvement in performance of the power converter.(Spa) En este trabajo se presenta una nueva metodología para el correcto diseño de transformadores utilizados en inversores de potencia multinivel tipo fuente común. La metodología propuesta representa una solución a los problemas de distorsión en la forma de onda, decaimiento de pulsos en la tensión y pérdida de rendimiento causada por el cálculo del transformador utilizando la metodología convencional. Para validar la metodología se construyen dos prototipos bajo diferentes perspectivas, convencional y propuesta, con el fin de verificar de forma experimental la solución a los problemas descritos y mostrar la mejoría en el rendimiento del convertidor de potencia

Common-Ground-Type Single-Source High Step-Up Cascaded Multilevel Inverter for Transformerless PV Applications

The cascaded multilevel inverter (CMI) is one type of common inverter in industrial applications. This type of inverter can be synthesized either as a symmetric configuration with several identical H-bridge (HB) cells or as an asymmetric configuration with non-identical HB cells. In photovoltaic (PV) applications with the CMI, the PV modules can be used to replace the isolated dc sources; however, this brings inter-module leakage currents. To tackle the issue, the single-source CMI is preferred. Furthermore, in a grid-tied PV system, the main constraint is the capacitive leakage current. This problem can be addressed by providing a common ground, which is shared by PV modules and the ac grid. This paper thus proposes a topology that fulfills the mentioned requirements and thus, CMI is a promising inverter with wide-ranging industrial uses, such as PV applications. The proposed CMI topology also features high boosting capability, fault current limiting, and a transformerless configuration. To demonstrate the capabilities of this CMI, simulations and experimental results are provided

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

Three-phase isolated multi-modular converter in renewable energy distribution systems

Multilevel converters are widely used in medium and high voltage applications. Their high performance, power quality, efficiency and smaller filters make them interesting for renewable energy distribution systems. In utility- scale photovoltaic plants, these topologies could provide multiple benefits since they are able to connect string of photovoltaic panels to independent modules. However, high floating voltages caused by high number of modules limit multilevel converters in medium and high voltage applications, since all of them are not suitable to provide isolation to each module. To offer a solution, this paper presents a novel multi-modular converter that provides multiple isolated modules connected in series through low frequency transformers to operate at medium voltage levels. This topology is able to achieve the power balancing between the connected modules and independently adjust the dc voltage of each module by means of controlling a circulating current which flows through the arms. Furthermore, the topology implemented in photovoltaic renewable energy systems and the control strategy required to regulate the circulating and the output current are presented. The main principle behind this concept and the performance of the converter are evaluated and validated through simulation and experimental results.Peer ReviewedPostprint (author's final draft

MATLAB/SIMLINK Model for Three Phase Hybrid Multilevel Inverter Based on Half Bridge Modules

Nowadays the multilevel inverters are widely used in power electronic applications. The multilevel inverters are recommended for medium and high voltage applications. Multilevel inverters have become more popular due to reduced switching losses, low costs, low harmonic distortion and high voltage capability when compared to traditional PWM inverters. This paper deals with hybrid multilevel converter which is synthesize of neutral point clamped and cascaded multilevel inverter. The hybrid multilevel converter is proposed for medium voltage large power ratings. The proposed converter consisting of voltage source inverter connected with half bridge modules at each phase. With the proposed connection large portion of energy can be preceded by the VSI by connecting single multi pulse rectifier. The smaller power shares processed within the half bridge modules. The modulation scheme for hybrid multilevel inverter is naturally achieved by using logic circuit. The modulation scheme for four-level version is analyzed in detail for higher modulation (HM), three level version is analyzed for lower modulation (LM). This modulation scheme allows unidirectional power flow in all DC sources. For unidirectional application, the diode bridges are employed at rectification input side. The modulation schemes of sinusoidal pulse width modulation (SPWM), space vector PWM (SVPWM) are analyzed by using MATLAB/SIMLINK. The comparison of THD’s for SPWM and SVPWM modulation techniques done by using MATLAB/SIMLINK. Keywords:Hybrid Converters, Multilevel Converters, PWM Modulation, Three Phase Inverters

Solid state transformer technologies and applications: a bibliographical survey

This paper presents a bibliographical survey of the work carried out to date on the solid state transformer (SST). The paper provides a list of references that cover most work related to this device and a short discussion about several aspects. The sections of the paper are respectively dedicated to summarize configurations and control strategies for each SST stage, the work carried out for optimizing the design of high-frequency transformers that could adequately work in the isolation stage of a SST, the efficiency of this device, the various modelling approaches and simulation tools used to analyze the performance of a SST (working a component of a microgrid, a distribution system or just in a standalone scenario), and the potential applications that this device is offering as a component of a power grid, a smart house, or a traction system.Peer ReviewedPostprint (published version

Coconut dehusker machine

Generally, coconut is dehusked manually using either a machete or a spike. These methods required skill labor and tiring to use. Attempts made so far in development of dehusking tools have been only partially successful and not effective in replacing manual methods. The reasons quoted for the failure of these tools include unsatisfactory and incomplete dehusking, breakage of the coconut shell while dehusking, spoilage of useful coir, greater effort needed than manual methods, etc