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

Direct torque control for dual three-phase induction motor drives

A direct torque control (DTC) strategy for dual three-phase induction motor drives is discussed in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The DTC strategy is based on a predictive algorithm and is implemented in a synchronous reference frame aligned with the machine stator flux vector. The advantages of the discussed control strategy are constant inverter switching frequency, good transient and steady-state performance, and low distortion of machine currents with respect to direct self-control (DSC) and other DTC schemes with variable switching frequency. Experimental results are presented for a 10-kW DTC dual three-phase induction motor drive prototype

Self-Commissioning of Inverter Nonlinear Effects in AC Drives

The paper presents a novel technique for an accurate identification of the inverter nonlinear effects, such as the dead-time and on-state voltage drops. The proposed technique is very simple and it is based only on a current control scheme. If the inverter load is an AC motor, the inverter effects can be identified at drive startup using as measured quantities the motor currents and the inverter DC link voltage. The identified inverter error is stored in a Look-Up Table (LUT) that can be subsequently used by the vector control algorithm. The proposed method has been tested on a 1 kVA inverter prototype and the obtained results demonstrate the feasibility of the proposed solutio

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

Self-Commissioning Algorithm for Inverter Non-Linearity Compensation in Sensorless Induction Motor Drives

In many sensorless field-oriented control schemes for induction motor (IM) drives, flux is estimated by means of measured motor currents and control reference voltages. In most cases, flux estimation is based on the integral of back-electromotive-force (EMF) voltages. Inverter nonlinear errors (dead-time and on-state voltage drops) introduce a distortion in the estimated voltage that reduces the accuracy of the flux estimation, particularly at low speed. In the literature, most of the compensation techniques of such errors require the offline identification of the inverter model and offline postprocessing. This paper presents a simple and accurate method for the identification of inverter parameters at the drive startup. The method is integrated into the control code of the IM drive, and it is based on the information contained in the feedback signal of the flux observer. The procedure applies, more in general, to all those sensorless ac drives where the flux is estimated using the back-EMF integration, not only for IM drives but also for permanent-magnet synchronous motor drives (surface-mounted permanent magnet and interior permanent magnet). A self-commissioning algorithm is presented and tested for the sensorless control of an IM drive, implemented on a fixed-point DSP. The feasibility and effectiveness of the method are demonstrated by experimental result

Engineering design project : series 1

This book is a compilation of engineering design projects which illustrates a detail explanation on the design process including all tools and methods involved in each design stage. The presented projects have been selected to prepare engineering students with the adequate knowledge and skills required in organizing product based project, formulating problems, generating and evaluating alternatives, preparing technical documentation and considering the sustainable and economic constraints for the product development and realization stage using the integration of various disciplines in mechanical and manufacturing engineering. This book is generally suitable as a reference to project-oriented problem-based learning (POPBL) activities at engineering institutions

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

Fuzzy Controller for Matrix Converter System to Improve its Quality of Output

In this paper, Fuzzy Logic controller is developed for ac/ac Matrix Converter. Furthermore, Total Harmonic Distortion is reduced significantly. Space Vector Algorithm is a method to improve power quality of the converter output. But its quality is limited to 86.7%.We are introduced a Cross coupled DQ axis controller to improve power quality. The Matrix Converter is an attractive topology for High voltage transformation ratio. A Matlab / Simulink simulation analysis of the Matrix Converter system is provided. The design and implementation of fuzzy controlled Matrix Converter is described. This AC-AC system is proposed as an effective replacement for the conventional AC-DC-AC system which employs a two-step power conversion.Comment: 11 page

Design and Development of Low Torque Ripple Variable-Speed Drive System With Six-Phase Switched Reluctance Motors

Switched reluctance motor (SRM) drives conventionally use current control techniques at low speed and voltage control techniques at high speed. However, these conventional methods usually fail to restrain the torque ripple, which is normally associated with this type of machine. Compared with conventional three-phase SRMs, higher phase SRMs have the advantage of lower torque ripple: To further reduce their torque ripple, this paper presents a control method for torque ripple reduction in six-phase SRM drives. A constant instantaneous torque is obtained by regulating the rotational speed of the stator flux linkage. This torque control method is subsequently developed for a conventional converter and a proposed novel converter with fewer switching devices. Moreover, modeling and simulation of this six-phase SRM drive system has been conducted in detail and validated experimentally using a 4.0-kW six-phase SRM drive system. Test results demonstrate that the proposed torque control method has outstanding performance of restraining the torque ripple with both converters for the six-phase SRM, showing superior performance to the conventional control techniques