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This paper discusses a variety of four-wire (4W) multilevel shunt compensators to deal with either harmonic or reactive power compensation. The converter configurations are generalized for K-stages and the main benefits of the proposed topologies lie on multilevel waveforms generation, single dc-link unit, and modular characteristic. The configurations are based on cascaded transformers along with three-phase-bridge converters. These converters are directly connected to the transformer primary side. A suitable pulse-width modulation strategy combined with an appropriate transformer turns ratio guarantees the desired multilevel output waveforms. The modularity feature provides simple maintenance and makes the proposed shunt active power filters an attractive solution in comparison with conventional configurations. The configuration model and overall control are addressed as well. Simulation and experimental results are presented for theoretical validation. [ABSTRACT FROM PUBLISHER]

This paper proposes a multilevel shunt active power filter (SAPF) to deal with either harmonic current compensation or reactive power compensation. Such a device can reduce the harmonic distortion at the grid currents provided by nonlinear loads located in stiff systems. The proposed SAPF is based on three-phase bridge converters connected to cascaded single-phase transformers. The transformer arrangement permits the compensator to use a single dc-link unit, which simplifies the control strategy and the number of sensors. The multilevel waveforms are generated by using a suitable pulse-width modulation (PWM) strategy associated with the transformer turns ratio. Modularity and simple maintenance make the proposed SAPF an attractive solution compared with some conventional configurations. The model, the PWM technique, and the control strategy are presented, as well as studies considering harmonic distortion and semiconductor losses estimation. Simulation and experimental results are presented in order to validate theoretical approaches. [ABSTRACT FROM AUTHOR]

This paper proposes and investigates a new three-phase ac–dc–ac multilevel conversion system obtained from cascaded three-leg converters. Such configuration presents advantages in terms of reduced switch blocking voltages and consequently lower dc-link voltage rating. Operating principles, a pulse-width modulation (PWM) technique based on vector approach, and a control strategy are presented. The operation with different dc-link voltage values and a balancing method are discussed, and is supported by simulation and experimental results. The PWM technique is able to generate multilevel voltage waveforms, which permits reducing the switching frequency stress leading to reduced semiconductor losses. Simulation results are used to compare the proposed configuration with a conventional solution in terms of harmonic distortion and semiconductor losses. Experimental results demonstrate the feasibility of the studied converter, and were obtained by using a downscaled prototype with insulated gate bipolar transistors with dedicated drives and a digital signal processor with appropriated plug-in boards and sensors. [ABSTRACT FROM PUBLISHER]

This paper proposes a multilevel series compensator (MSC) to deal with voltage sags/swells, harmonic compensation, or reactive power compensation. Such a device can be considered as a dynamic voltage restorer or a series active power filter (Series-APF). The MSC can improve the power quality of loads located in stiff systems. The configuration is based on three-phase bridge (TPB) converters connected by means of cascaded single-phase transformers. This arrangement permits the use of a single dc-link. A generalization for $K$ -stages in which $K$ -transformers are coupled with $K$-TPB converters is presented. The topology permits generating a high number of levels in the voltage waveforms with a low number of power switches in comparison with a classic topology. The multilevel waveforms are generated by the converters through a suitable pulsewidth modulation (PWM) strategy that takes into consideration the transformer turns ratios. Modularity and simple maintenance make the proposed MSC an attractive solution compared with some conventional configurations. Model, PWM strategy, and overall control are discussed in this paper. Simulation and experimental results are presented as well. [ABSTRACT FROM PUBLISHER]

This paper proposes a hybrid modular multilevel drive system based on a modular multilevel cascade inverter (MMCI) with double-star chopper cells (DSCC) and a two-level (2L) inverter to feed three-phase induction motors with open-end windings (OEWs). The proposed system is an alternative for high-speed motor drives based on a small-scale DSCC topology. A voltage reference technique is presented based on the analysis of the degrees of freedom of the system for generating the output voltage references, considering any voltage ratios of the dc links. The proposed system is evaluated in a symmetric scenario, in which the dc-link voltages are equal. Thus, the 2L inverter is set up to operate at the fundamental frequency, while the DSCC inverter synthesizes the output voltage references from high-quality waveform with a significant number of voltage levels. Experimental results obtained from a downscaled 10-kVA 380-V prototype driving a full loaded 3.7-kW OEW induction motor are provided to verify the viability of the proposed system. [ABSTRACT FROM PUBLISHER]

This paper investigates a dynamic voltage restorer (DVR) composed of two conventional three-phase inverters series cascaded through an open-end winding (OEW) transformer, denominated here DVR-OEW. The DVR-OEW operating with either equal or different dc-link voltages is examined. The proposed topology aims to regulate the voltage at the load side in the case of voltage sags/swells, distortion, or unbalance at the grid voltage. A suitable control strategy is developed, including space-vector analysis, level-shifted PWM and its equivalent optimized single-carrier PWM, as well as the operating principles and characteristics of the DVR. Comparisons among the DVR-OEW and conventional configurations, including a neutral-point clamped converter-based DVR, are furnished. The main advantages of the DVR-OEW compared to the conventional topologies lie on: 1) reduced harmonic distortion, 2) reduced converter losses, and 3) reduced voltage rating of the power switches. Simulated and experimental results are presented to validate the theoretical studies. [ABSTRACT FROM AUTHOR]

This paper presents a shunt power compensator based on the interconnection of three-phase two-level converters, and its comparison with two-level- and multilevel-based topologies. The shunt power compensator based on interconnected three-phase converter (ITC) is compared with compensators based on the two-level converter, three-level neutral-point clamped converter, and five-level modular multilevel converter. The comparisons were done in terms of components ratings, harmonic distortion, and semiconductor losses. Control strategies suitable to control the compensator and circulating currents, as well as the three-dc-link voltages are presented. The PWM strategy to generate the control reference voltages of the converter command is designed. Simulation and experimental results are presented. [ABSTRACT FROM AUTHOR]

This paper presents a shunt active power filter based on the concept of open-end winding (OEW) transformer for three-phase three-wire systems. The proposed configuration is constituted of two converters, with three legs in each one, series-connected throughout a three-phase OEW transformer. Model, pulsewidth modulation (PWM) strategy, and control scheme are presented as well. The main advantage of the proposed system lies on the multilevel waveform generation, which allows reduction of either harmonic distortions or switching losses. This proposed topology is suitable for medium-voltage distribution systems. Simulation and experimental results validate the theoretical study. [ABSTRACT FROM PUBLISHER]

This paper presents a three-phase ac–dc–ac drive system to cope with applications in which high performance and reliability are required with reduced dc-link and switch blocking voltages. The subsystem at the grid-side can be implemented into two alternatives, i.e., topologies G1 and G2. While G1 presents a sole three-phase transformer connected in series between the three-phase grid and converter $Ag$, whose secondary is connected to the converter $Bg$, G2 has a three-phase transformer with two taps at the secondary. The transformers in G1 and G2 process part and total system power, respectively. The subsystem at the machine-side is composed of the machine and two converters that allow series- and parallel-modes for the three-phase machine. The interesting characteristic of the system is to adapt its machine-side configuration as a function of the speed. The proposed configurations guarantee low harmonic distortion for both high speed (high voltage) and low speed (low voltage) operations with a higher modulation index. In addition, the system allows the machine's operation with high current at low speed, which is interesting for applications with constant mechanical load. A comprehensive model of the proposed systems and modulation strategies are presented. Simulated and experimental results validate the theoretical expectations. [ABSTRACT FROM AUTHOR]

This paper proposes two sets of topologies for single-phase to three-phase four-wire ac–dc–ac power conversion. All proposed configurations are characterized by reduction in the number of switches. The first set includes five configurations using ten power switches, while the second one includes six configurations using eight power switches. Such configurations are conceived for supplying three-phase four-wire loads and to guarantee bidirectional power flow between grid and load. Besides collecting different configurations, this paper proposes a synchronization technique, which can be applied for configurations with shared leg. The overall control strategy for providing dc link voltage control, grid current control, and PWM generation are presented. Simulated and experimental results are presented as well. [ABSTRACT FROM AUTHOR]