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

Modified SVPWM Algorithm for 3-Level Inverter Fed DTC Induction Motor Drive

In this paper, a modified space vector pulse width modulation (MSVPWM) algorithm is developed for 3-level inverter fed direct torque controlled induction motor drive (DTC-IMD). MSVPWM algorithm  simplifies conventional space vector pulse width modulation (CSVPWM) algorithm for multilevel inverter(MLI), whose complexity lies in sector/subsector/sub-subsector identification; which will commensurate with number of levels. In the proposed algorithm sectors are identified as in two level inverter and subsectors/sub-subsectors are identified by shifting the original reference vector to sector 1 (S1). This is valid due to the fact that a three level space vector plane is a composition of six two level space planes, and are symmetrical with reference to six pivot states. Switching state/sequence selection is also very important while dealing with SVPWM strategy for MLI. In the proposed algorithm out of 27 available switching states apt switching state is selected based on sector and subsector number, such that voltage ripple is considerably less. To validate the proposed algorithm, it is tested on a three level neutral point clamped (NPC) inverter fed DTC-IMD. The performance of the MSVPWM algorithm is analyzed by comparing no load stator current ripple of the three level DTC-IMD with two level DTC-IMD. Significant reduction in steady state torque and flux ripple is observed. Hence, reduced acoustic noise is a distinctive facet of the proposed method. Keywords: CSVPWM, DTC, MSVPWM, MLI, NPC, VS

Conventional Space-Vector Modulation Techniques versus the Single-Phase Modulator for Multilevel Converters

Space-vector modulation is a well-suited technique to be applied to multilevel converters and is an important research focus in the last 25 years. Recently, a single-phase multilevel modulator has been introduced showing its conceptual simplicity and its very low computational cost. In this paper, some of the most conventional multilevel space-vector modulation techniques have been chosen to compare their results with those obtained with single-phase multilevel modulators. The obtained results demonstrate that the single-phase multilevel modulators applied to each phase are equivalent with the chosen wellknown multilevel space-vector modulation techniques. In this way, single-phase multilevel modulators can be applied to a converter with any number of levels and phases avoiding the use of conceptually and mathematically complex space-vector modulation strategies. Analytical calculations and experimental results are shown validating the proposed concepts