Feed-forward Space Vector Modulation for Single-Phase Multilevel Cascade Converters with any DC voltage ratio

Modulation techniques for multilevel converters can create distorted output voltages and currents if the DC link voltages are unbalanced. This situation can be avoided if the instantaneous DC voltage error is not taken into account in the modulation process. This paper proposes a feed-forward space vector modulation method for a single-phase multilevel cascade converter. Using this modulation technique, the modulated output voltage of the power converter always generates the reference determined by the controller even in worst case voltage unbalance conditions. In addition the possibility of optimizing the DC voltage ratio between the H-bridges of the power converter is introduced. Experimental results from a 5kVA prototype are presented in order to validate the proposed modulation technique

A modified modulation scheme for three-level diode-clamped matrix converter under unbalanced input conditions

The three-level diode-clamped matrix converter topology has outstanding performance under ideal operating conditions. However, input disturbance can influence the waveforms at the output side of the converter due to the direct coupling between the input and output. This paper proposes a modified modulation scheme for three-level diode-clamped matrix converter during operation with unbalanced input voltages and when different transformer turns ratios are used for an isolation transformer at the input. With this modulation technique, sinusoidal and balanced output voltages are guaranteed and the input current harmonics are minimized. Experimental results are presented to demonstrate the feasibility and effectiveness of the proposed modulation scheme

Multilevel Multiphase Feedforward Space-Vector Modulation Technique

Multiphase converters have been applied to an increasing number of industrial applications in recent years. On the other hand, multilevel converters have become a mature technology mainly in medium- and high-power applications. One of the problems of multilevel converters is the dc voltage unbalance of the dc bus. Depending on the loading conditions and the number of levels of the converter, oscillations appear in the dc voltages of the dc link. This paper presents a feedforward modulation technique for multilevel multiphase converters that reduces the distortion under balanced or unbalanced dc conditions. The proposed modulation method can be applied to any multilevel-converter topology with any number of levels and phases. Experimental results are shown in order to validate the proposed feedforward modulation technique.Ministerio de Ciencia e Innovación DPI2009-07004Ministerio de Eduación y Ciencia TEC2007-6187

Speed control of induction machine based on direct torque control method

Dissertação para obtenção do Grau de Mestre em Engenharia Electrotécnica e de ComputadoresMulti-level converters have been receiving attention in the recent years and have been proposed as the best choice in a wide variety of medium voltage applications. They enable a commutation at substantially reduced voltages and an improved harmonic spectrum without a series connection of devices, which is the main advantage of a multi-level structure. The use of multi-level inverters contributes to the performances amelioration of the induction machine control. In fact, the use of three level inverter (or multilevel inverter) associated with DTC control can contribute to more reducing harmonics and the ripple torque and to have a high level of output voltage. A variation of DTC-SVM with a three level neutral point clamped inverter is proposed and discussed in the literature. The goal of this project is to study, evaluate and compare the DTC and the proposed DTC-SVM technique when applied to induction machines through simulations. The simulations were carried out using MATLAB/ SIMULINK simulation package. Evaluation was made based on the drive performance, which includes dynamic torque and flux responses, feasibility and the complexity of the systems

Active Harmonic Elimination in Multilevel Converters

The modulation technique for multilevel converters is a key issue for multilevel converter control. The traditional pulse width modulation (PWM), space vector PWM, and space vector control methods do not completely eliminate specified harmonics. In addition, space vector PWM and space vector control method cannot be applied to multilevel converters with unequal DC voltages. The carrier phase shifting method for traditional PWM method also requires equal DC voltages. The number of harmonics that can be eliminated by the selective harmonic elimination method is restricted by the number of unknowns in the harmonic equations and available solutions. For these reasons, this thesis develops a new modulation control method which is referred to as the active harmonic elimination method to conquer some disadvantages for the existing methods. The active harmonic elimination method contributes to the existing methods because it not only generates the desired fundamental frequency voltage, but also completely eliminates any number of harmonics without the restriction of the number of unknowns in the harmonic equations and available solutions for the harmonic equations. Also the active harmonic elimination method can be applied to both equal DC voltage cases and unequal DC voltage cases. Another contribution of the active harmonic elimination method is that it simplifies the optimal system performance searching by making a tradeoff between switching frequency and harmonic distortion. Experiments on an 11-level multilevel converter validate the active harmonic elimination method for multilevel converters

Contributions to Modulation and Control Algorithms for Multilevel Converters

Las actuales tendencias de la red eléctrica han lanzado a la industria a la búsqueda de sistemas de generación, distribución y consumo de energía eléctrica más eficientes. Generación distribuida, reducción de componentes pasivos, líneas DC de alta tensión son, entre otras, las posibles líneas de investigación que están actualmente siendo consideradas como el futuro de la red eléctrica. Sin embargo, nada de esto sería posible si no fuera por los avances alcanzados en el campo de la electrónica de potencia. El trabajo aquí presentado comienza con una breve introducción a la electrónica de potencia, concretamente a los convertidores de potencia conectados a red, sus estrategias de control más comunes y enfoques ante redes desbalanceadas. A continuación, las contribuciones del autor sobre el control y modulación de una topología particular de convertidores, conocidos como convertidores multinivel, se presentan como el principal contenido de este trabajo. Este tipo de convertidores mejoran la eficiencia y ciertas prestaciones, en comparación con convertidores más tradicionales, a costa de una mayor complejidad en el control al incrementar la cantidad de los componentes hardware. A pesar de que existen numerosas topologías de convertidores multinivel y algunas de ellas son brevemente expuestas en este trabajo, la mayoría de las aportaciones están enfocadas para convertidores del tipo diode-clamped converter. Adicionalmente, se incluye una aportación para convertidores del tipo multinivel modular, y otra para convertidores en cascada. Se espera que el contenido de la introducción de este trabajo, junto a las contribuciones particulares para convertidores multinivel sirva de inspiración para futuros investigadores del campo

Flying-capacitor multilevel converter voltage balance dynamics for pure resistive load

Multilevel converters need voltage balancing to be able to generate an output voltage with high quality. Flying capacitor converter topology has a natural voltage balancing property. Voltage balance dynamics analytical research methods reported to date are essentially based on a frequency domain analysis using double fourier transform. These complicated methods are not truly analytical, which makes an understanding of parameter influence on time constants difficult. In this paper, a straightforward time domain approach based on stitching of switch intervals piece-wise analytical solutions to a DC modulated H-bridge flying capacitor converter is discussed. This method allows to obtain time-averaged discrete and continuous voltage balance dynamics models. Using small-parameter approximation for pure resistive loads, simple and accurate expressions for voltage balance time constants are deduced, revealing their dependence on load parameters, carrier frequency and duty ratio

High-performance motor drives

This article reviews the present state and trends in the development of key parts of controlled induction motor drive systems: converter topologies, modulation methods, as well as control and estimation techniques. Two- and multilevel voltage-source converters, current-source converters, and direct converters are described. The main part of all the produced electric energy is used to feed electric motors, and the conversion of electrical power into mechanical power involves motors ranges from less than 1 W up to several dozen megawatts

Space-vector-modulated three-level inverters with a single Z-source network

The Z-source inverter is a relatively recent converter topology that exhibits both voltage-buck and voltage-boost capability. The Z-source concept can be applied to all dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc power conversion whether two-level or multilevel. However, multilevel converters offer many benefits for higher power applications. Previous publications have shown the control of a Z-source neutral point clamped inverter using the carrier based modulation technique. This paper presents the control of a Z-source neutral point clamped inverter using the space vector modulation technique. This gives a number of benefits, both in terms of implementation and harmonic performance. The adopted approach enables the operation of the Z-source arrangement to be optimised and implemented digitally without introducing any extra commutations. The proposed techniques are demonstrated both in simulation and through experimental results from a prototype converter

PERFORMANCE ANALYSIS OF FIVE LEVEL Z SOURCE NEUTRAL POINT CLAMPED MULTILEVEL INVERTER USING SPWM AND SVPWM

The scope of this paper is to reduce the harmonic content and to boost the output voltage by introducing an emerging technique termed as Z-Source multilevel inverter. The Z-Source inverter had overcome many drawbacks in traditional inverters (Voltage source & Current source Inverters).The main advantage of Z- Source inverter is the presence of a shoot through the period (Short circuit) which plays an important role in boosting the voltage. When the number of levels in the output voltage of multilevel inverter is increased then accordingly the harmonic content is also reduced. Normally for a multilevel inverter the output voltage is restricted to the summation of all the input voltage values.To enhance this feature Z-Source is introduced with a multilevel inverter to obtain boosted voltage along with low harmonic distortion.The proposed methodology analysis the Z-Source Neutral point clamped inverter using the Space vector modulation technique with MATLAB/Simulink model and the related parameters is analyzed