Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate DC sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.

Multilevel inverters: a survey of topologies, controls, and applications

Multilevel voltage source converters are emerging as a new breed of power converter options for high-power applications. The multilevel voltage source converters typically synthesize the staircase voltage wave from several levels of DC capacitor voltages. One of the major limitations of the multilevel converters is the voltage unbalance between different levels. The techniques to balance the voltage between different levels normally involve voltage clamping or capacitor charge control. There are several ways of implementing voltage balance in multilevel converters. Without considering the traditional magnetic coupled converters, this paper presents three recently developed multilevel voltage source converters: (1) diode-clamp, (2) flying-capacitors, and (3) cascaded-inverters with separate DC sources. The operating principle, features, constraints, and potential applications of these converters are discussed.

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Multilevel converters-a new breed of power converters

The aim of this paper is to present a review of current control techniques for three-phase voltage-source pulsewidth modulated converters. Various techniques, different in concept, have been described in two main groups: linear and nonlinear. The first includes proportional integral (stationary and synchronous) and state feedback controllers, and predictive techniques with constant switching frequency. The second comprises bang-bang (hysteresis, delta modulation) controllers and predictive controllers with on-line optimization. New trends in current control-neural networks and fuzzy-logic-based controllers-are discussed, as well. Selected oscillograms accompany the presentation in order to illustrate properties of the described controller groups.

Current control techniques for three-phase voltage-source PWM converters: a survey

The matrix converter is an array of controlled semiconductor switches that connects directly the three-phase source to the three-phase load. This converter has several attractive features that have been investigated in the last two decades. In the last few years, an increase in research work has been observed, bringing this topology closer to the industrial application. This paper presents the state-of-the-art view in the development of this converter, starting with a brief historical review. An important part of the paper is dedicated to a discussion of the most important modulation and control strategies developed recently. Special attention is given to present modern methods developed to solve the commutation problem. Some new arrays of power bidirectional switches integrated in a single module are also presented. Finally, this paper includes some practical issues related to the practical application of this technology, like overvoltage protection, use of filters and ride-through capability.

Matrix converters: a technology review

This paper presents a review of advanced control techniques for microgrids. This paper covers decentralized, distributed, and hierarchical control of grid-connected and islanded microgrids. At first, decentralized control techniques for microgrids are reviewed. Then, the recent developments in the stability analysis of decentralized controlled microgrids are discussed. Finally, hierarchical control for microgrids that mimic the behavior of the mains grid is reviewed.

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Advanced Control Architectures for Intelligent Microgrids—Part I: Decentralized and Hierarchical Control

The way in which a practical control method using derived torque feedback signal has made it possible to obtain the same high bandwidth torque control with standard cage induction motors as can be achieved with dc motors is demonstrated. In contrast with previous torque control systems, this method does not require the angular position of a motor field vector to be determined for control purposes. The versatility of this torque controller is illustrated with measured torque responses obtained from a transitorized servo drive, a cycloconvertor, and a current source inverter.

High Performance Torque-Controlled Induction Motor Drives

The invention resides in providing bilateral switches between the respective phase lines of an AC input source and a common phase line of an AC output to form a phase line group of said bilateral switches on each AC output line; in fact, controlling the bilateral switches of each group so as to generate with AC input lines a DC link voltage with respect to the associated AC output line, and secondly in controlling the bilateral switches in such group to modulate such DC link voltage in relation to a desired AC voltage for such associated AC output line, each of said groups being operated with a corresponding phase shift to provide a corresponding phase shift between the respective output phase lines.

Hidden DC-link AC/AC converter using bilateral power switches

A regenerative two-quadrant power converter which is suitable for interfacing between the AC mains and the DC link of a voltage source inverter is described. The circuit provides highly reliable commutation in the regeneration mode using only a single fully controlled static switch and a minimum configuration of thyristors and diodes. The circuit has been applied successfully in commercial PWM (pulsewidth-modulated) inverter products with power ratings up to 160 hp. >

A regenerative two-quadrant converter for DC-link voltage source inverters

A three-phase flat-top waveform generator which may be utilized in a pulse-width modulator. Transfer function means receive a three-phase input signal and produce therefrom a zero sequence signal. Under steady-state and balanced conditions, the zero sequence signal will generally have a fundamental frequency three times the frequency of the input signal. Summing means add the zero sequence signal to each phase of the input signal to produce the desired flat-top signal.

Colin D. Schauder

Papers

High Performance Torque-Controlled Induction Motor Drives

Hidden DC-link AC/AC converter using bilateral power switches

A regenerative two-quadrant converter for DC-link voltage source inverters

Flat-top waveform generator and pulse-width modulator using same

Unified power flow controller for FACTS