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

Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

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A review of single-phase improved power quality AC-DC converters

New regulations impose more stringent limits on current harmonics injected by power converters that are achieved with pulsewidth-modulated (PWM) rectifiers. In addition, several applications demand the capability of power regeneration to the power supply. This work presents the state of the art in the field of regenerative rectifiers with reduced input harmonics and improved power factor. Regenerative rectifiers are able to deliver energy back from the dc side to the ac power supply. Topologies for single- and three-phase power supplies are considered with their corresponding control strategies. Special attention is given to the application of voltage- and current-source PWM rectifiers in different processes with a power range from a few kilowatts up to several megawatts. This paper shows that PWM regenerative rectifiers are a highly developed and mature technology with a wide industrial acceptance.

http://www.lcda.cl/descargas/rodriguez_dixon_pont_espinoza_lezana05.pdf

PWM regenerative rectifiers: state of the art

In the first part of this paper, three-phase power factor correction (PFC) rectifier topologies with sinusoidal input currents and controlled output voltage are derived from known single-phase PFC rectifier systems and/or passive three-phase diode rectifiers. The systems are classified into hybrid and fully active pulsewidth modulation boost-type or buck-type rectifiers, and their functionality and basic control concepts are briefly described. This facilitates the understanding of the operating principle of three-phase PFC rectifiers starting from single-phase systems, and organizes and completes the knowledge base with a new hybrid three-phase buck-type PFC rectifier topology denominated as Swiss Rectifier. Finally, core topics of future research on three-phase PFC rectifier systems are discussed, such as the analysis of novel hybrid buck-type PFC rectifier topologies, the direct input current control of buck-type systems, and the multi-objective optimization of PFC rectifier systems. The second part of this paper is dedicated to a comparative evaluation of four rectifier systems offering a high potential for industrial applications based on simple and demonstrative performance metrics concerning the semiconductor stresses, the loading and volume of the main passive components, the differential mode and common mode electromagnetic interference noise level, and ultimately the achievable converter efficiency and power density. The results are substantiated with selected examples of hardware prototypes that are optimized for efficiency and/or power density.

The Essence of Three-Phase PFC Rectifier Systems—Part II

Based on the combination of a three-phase diode bridge and a DC/DC boost converter, a new three-phase three-switch three-level pulsewidth modulated (PWM) rectifier system is developed. It can be characterized by sinusoidal mains current consumption, controlled output voltage, and low-blocking voltage stress on the power transistors. The application could be, e.g., for feeding the DC link of a telecommunications power supply module. The stationary operational behavior, the control of the mains currents, and the control of the output voltage are analyzed. Finally, the stresses on the system components are determined by digital simulation and compared to the stresses in a conventional six-switch two-level PWM rectifier system.

A novel three-phase utility interface minimizing line current harmonics of high-power telecommunications rectifier modules

Based on an analysis of basic realization possibilities, the structure of the power circuit of a new single-stage three-phase boost-type pulsewidth modulated (PWM) rectifier system (VIENNA Rectifier II) is developed. This system has continuous sinusoidal time behavior of the input currents and high-frequency isolation of the output voltage, which is controlled in a highly dynamic manner. As compared to a conventional two-stage realization, this system has substantially lower complexity and allows the realization of several isolated output circuits with minimum effort. The basic function of the new PWM rectifier system is described based on the conduction states occurring within a pulse period. Furthermore, a straightforward space- vector-oriented method for the system control is proposed which guarantees a symmetric magnetization of the transformer. Also, it makes possible a sinusoidal control of the mains phase currents in phase with the associated phase voltages. By digital simulation, the theoretical considerations are verified and the stresses on the power semiconductors of the new converter system are determined. Finally, results of an experimental analysis of a 2.5-kW laboratory prototype of the system are given, and the direct startup and the short-circuit protection of the converter are discussed. Also, the advantages and disadvantages of the new converter system are compiled in the form of an overview.

VIENNA rectifier II-a novel single-stage high-frequency isolated three-phase PWM rectifier system

In this paper the stationary operational behavior of a three-phase/switch/level PWM rectifier is analyzed for asymmetrical loading of the output partial voltages. For the considerations a sinusoidal mains current shape, resistive behavior of the mains current fundamental and constant pulse frequency are assumed. Based on analytical calculations it is shown that the average value of the neutral point current (which has to be formed for asymmetrical load) has an approximately linear dependency on the distribution of the overall relative on-time of the switching states of the system being redundant concerning the voltage formation between begin and end of a pulse half interval. The maximum admissible load of the neutral point (capacitive output voltage center point) is calculated. This load is given as a function of the amplitude of the mains current and the voltage transfer ratio of the system. The calculations are checked by results of a digital simulation of the system behavior. Furthermore, the increase of the rms value of the ripple of the mains current of the rectifier is analyzed as it results in forming of an average value of the neutral point current. As a basis for comparison, the ripple rms value is used which results in harmonic-(sub)optimal control and negligible average value of the neutral point current. Finally, the current stress on the power semiconductors and on the output capacitors of the system are compiled in the form of diagrams which can be applied directly for dimensioning the system.

Current handling capability of the neutral point of a three-phase/switch/level boost-type PWM (VIENNA) rectifier

Based on an analysis of basic realization possibilities, the structure of the power circuit of a new single-stage three-phase boost-type PWM rectifier system (VIENNA Rectifier II) is developed. This system has continuous sinusoidal time behavior of the input currents and high-frequency isolation of the output voltage which is controlled in a highly dynamic manner. As compared to a conventional two-stage realization, this system has substantially lower complexity and allows to realize several isolated output circuits with minimum effort. The basic function of the new PWM rectifier system is described based on the conducting states occurring within a pulse period. Furthermore, a straightforward space vector oriented method for the system control is proposed which guarantees a symmetric magnetization of the transformer. Also, it makes possible a sinusoidal control of the mains phase currents in phase with the associated phase voltages. By digital simulation the theoretical considerations, the stresses on the power semiconductors of the new converter system are determined. Finally, problems of a practical realization of the system are discussed, as well as the direct start-up and the short circuit protection of the converter. Also, the advantages and disadvantages of the new converter system are compiled in the form of an overview.

This paper treats the control of the the capacitive output voltage center point of a unidirectional three-phase three-level PWM rectifier system. It is shown that, for hysteresis control of the input phase currents and resistive fundamental mains behavior, the center point potential can be controlled by an offset of the phase current reference values. Based on the results of a digital simulation, the transfer function is determined which describes the dynamic behavior of the system part to be controlled. Furthermore, the dimensioning of the center point voltage control is discussed. There, the considerations are related to an application of the PWM rectifier system for supplying the DC link of an uninterruptible power supply (8 kW rated power). Finally, the control behavior for stationary operation and for a step change of the load of the output voltage center point is examined for verifying the controller dimensioning. >

Space vector based analysis of the variation and control of the neutral point potential of hysteresis current controlled three-phase/switch/level PWM rectifier systems

Integrated control circuits being available for the input current control of single-phase power factor correctors are frequently applied also for realizing a simple current control for each phase of a three-phase PWM rectifier system. There, the input currents are controlled independently although the three phases are mutually coupled, i.e., the sum of the phase currents is forced to zero for missing connections between the mains star point and the output voltage center point. However, ignoring of the coupling of the three phases results in increased amplitudes of harmonics with switching frequency and/or in a significantly higher ripple of the rectifier input current. This is shown in this paper by a detailed analysis of different current control concepts for a three-phase three-switch three-level boost-type PWM rectifier (VIENNA Rectifier I) with unity power factor. The theoretical considerations are verified by digital simulations and an experimental analysis of a laboratory prototype and are valid in general for three-phase boost-type voltage DC link PWM rectifier systems.

U. Drofenik

Papers

VIENNA rectifier II-a novel single-stage high-frequency isolated three-phase PWM rectifier system

Current handling capability of the neutral point of a three-phase/switch/level boost-type PWM (VIENNA) rectifier

VIENNA rectifier II-a novel single-stage high-frequency isolated three-phase PWM rectifier system

Space vector based analysis of the variation and control of the neutral point potential of hysteresis current controlled three-phase/switch/level PWM rectifier systems

Comparison of not synchronized sawtooth carrier and synchronized triangular carrier phase current control for the VIENNA rectifier I