Luciano M. Barros

A Carrier-Based PWM Technique for Capacitor Voltage Balancing of Single-Phase Three-Level Neutral-Point-Clamped Converters

In this paper is presented a PWM technique for single-phase neutral-point-clamped converters for capacitors voltage balancing. The technique is based on the injection of a common mode voltage signal into the sinusoidal modulating signals of the conventional carrier-based pulse width modulation. Although several strategies have been reported for such a problem by using the voltage signal injection, the proposed method is very simple with easy implementation. It is presented a set of equations to demonstrate how the injected voltage signal introduces a dc component on the neutral-point current, which can be controlled in order to allow the capacitors voltages balancing. Selected results have been used demonstrate the effectiveness of the proposed strategy.

Three-Phase-to-Three-Phase AC/AC DC-Link Five-Leg Converters Based on Three- and Two-Level Legs

The five-leg back-to-back converter shares a leg between the grid and load sides. In the conventional five-leg converter, all legs are of same type, i.e., either two- or three-level legs. This paper presents topologies of five-leg converters based on the combination of two- and three-level legs. The proposed configurations permit one to obtain intermediary characteristics between the five-leg converter with all three-level legs and that with all two-level legs. The choice of the number of two- and three-level legs and how combine them are shown in order to obtain some characteristics of the grid- and load-side converter voltages. The modeling of the system and the pulsewidth-modulation strategy based on carrier-based and space-vector approaches is presented. Analysis of the total harmonic distortion and power switches losses are also addressed to characterize the configurations. Experimental and simulated results show the system feasibility.

Pulse width modulation for reduction of power losses in three-phase neutral point clamped inverters

This paper investigates the digital implementation of a modulation strategy that can completely remove the low-frequency voltage oscillation, which appears in the neutral point, for all the operating points and for any kind of loads. The implementation is based on a hybrid modulation technique that produces low switching losses and is simple to implement. Losses, average switching frequency, and performance in terms of voltage balance and low frequency neutral point oscillation, THD, and WTHD are investigated. Simulation and experimental results confirm the feasibility of the approach.

Comparative analysis of cascaded inverters based on 5-level and 3-level H-bridges

This paper investigates two converters composed of a five-level H-bridge cell cascaded with a three-level one. Two types of 5-level H-bridges are used, the first one is composed of a NPC leg and a 2-level leg (in the first topology), and the second one is composed of NPC legs only (in the second configuration). In both topologies the 5-level cell is cascaded with a 3-level H-bridge. Both converters were analyzed for the DC-link voltage ratios 1:1, 1:4 and 1:6 between the two power cells. These cases have been chosen due to the synthesis of equally spaced converter voltage levels. A generic PWM strategy for both configurations that covers any DC-link voltage ratio is presented. In all cases, both converters were compared in therms of harmonic distortion and semiconductor power losses, as well as in terms of redundant switch states. Experimental results are presented in order to show the feasibility of the topologies and the validity of the discussed PWM strategies.

Three-phase/four-wire dc/ac converters based on three- and two-level legs

In this paper, four three-phase/four-wire dc/ac converter topologies assembled with three-level and two-level legs are proposed. Several relevant characteristics of the converters are addressed, such as voltage capability, harmonic distortion, and power losses. Experimental and simulated results are presented.

Three-phase drive systems based on OEW configurations with reduced controlled switch count

This paper proposes ten alternative drive topologies with reduced number of controlled switches. The topologies are composed by three-level (3L) and two-level (2L) legs combinations. All of them aim to feed a three-phase machine based on the concept of open-end-winding (OEW). Conventional OEW configurations are considered for comparison purposes. The proposed topologies are named accordingly to the number of levels associated in each leg. For example, a topology with one 3L leg and five 2L legs is named 322-222. The other configurations are named in a similar manner. The OEW based systems using proposed configurations aim to give intermediate alternative solution in terms of cost-benefit rather than using conventional configurations. Some simulation and experimental results are presented in order to validate the theoretical approaches.

DVR with five-level converter based on three-and two-level legs connections

This paper proposes three topologies of multilevel dynamic voltage restorer (DVR) with application in three-phase systems (balanced and unbalanced) to compensate sags/swells. The topologies use three independent dc-links (one per phase) and each converter is mounted with one three-level NPC leg (3L) and one two-level leg (2L), furnishing a five-level (5L) voltage at its output. This proposed topologies aims to give an intermediate solution between the 2L converter and the 3L converter (e.g., 5L NPC converter). The control system, including the PWM technique, is presented and comparisons between the proposed topologies and conventional topologies are discussed. Simulation and experimental results are presented in order to validate the theoretical approaches.

A carrier based PWM technique for capacitor voltage balancing of single-phase three-level neutral-point-clamped converters

In this paper, a pulsewidth-modulation (PWM) technique with neutral point capacitor voltage balancing in single-phase neutral-point-clamped converters is presented. The technique is based on the injection of a common-mode voltage signal into the sinusoidal modulating signals of the conventional carrier-based PWM. Although several strategies have been reported for such a problem by using the voltage signal injection, the proposed method is very simple with easy implementation. A set of equations is presented to demonstrate how the injected voltage signal introduces a dc component on the neutral-point current, which can be controlled in order to allow the capacitor voltages balancing.

Three-phase to three-phase AC/AC De-link converters based on three-level and two-level legs

This paper presents five topologies of back-to-back power converters based on a combination of two-level and three-level legs. Moreover, the proposed configurations share a leg between the grid side and load side converters. Analysis of THD and power switches losses are also addressed. Experimental and simulated results show the systems feasibility.