Gregory Arthur de Almeida Carlos

Dynamic Voltage Restorer Based on Three-Phase Inverters Cascaded Through an Open-End Winding Transformer

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.

Investigation on Dynamic Voltage Restorers With Two DC Links and Series Converters for Three-Phase Four-Wire Systems

This paper proposes three dynamic voltage restorer (DVR) topologies. Such configurations are able to compensate voltage sags/swells in three-phase four-wire (3P4W) systems under balanced and unbalanced conditions. The proposed systems in this work use two independent dc-links. The complete control system, including the PWM technique, is developed and comparisons between the proposed configurations and a conventional one are performed. Simulation and experimental results are provided to validate the theoretical approach.

Shunt Active Power Filter With Open-End Winding Transformer and Series-Connected Converters

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

Shunt compensator based on three-phase interconnected converters

This paper investigates a three-phase shunt power filter based on three standard three-phase interconnected converters. Compared with the usual three-phase shunt filter, the proposed converter permits to reduce the dc-link voltages and reduce either harmonic distortion or switching frequency. Control strategies suitable to control the filter and circulating currents as well as the three dc-link voltages are presented. A PWM strategy is designed to command the converter according to the reference voltage generated by the controllers. Simulation and experimental results are presented.

Hybrid multilevel inverter system for Open-End Winding (OEW) induction motor drive based on Double-Star Chopper-Cells (DSCC) converter

This paper proposes a hybrid multilevel topology for Open-End stator Winding (OEW) induction motor drive based on Modular Multilevel Cascade Inverter (MMCI) with Double-Star Chopper-Cells (DSCC) and 2-Level Voltage Source Inverter (2L-VSI). An efficient Voltage Reference Technique is proposed to generate the pole voltages of both inverters. As a result, the DSCC inverter is commanded in high-switching frequency, while the 2L-VSI operates at the fundamental frequency. A voltage-balancing control of the floating DC capacitors of the DSCC is presented to ensure the energy balance. At last, to investigate the proposed system and control strategy, experimental results are presented.

Flexible Series/Parallel AC–DC–AC Motor Drive System

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 seriesand 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 machines 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.

Hybrid Modular Multilevel DSCC Inverter for Open-End Winding Induction Motor Drives

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.

Series compensator based on cascaded transformers coupled with three-phase bridge converters

This paper proposes a multilevel series compensator (MSC) to deal with: (i) voltage sags/swells, (ii) harmonic compensation or (iii) reactive power compensation. Such a device can be considered as a dynamic voltage restorer (DVR) 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 to use a single dc-link. A generalization for K-stages in which K-transformers are coupled with K-TPB converters, is presented. The topology permits to generate a high number of levels in the voltage waveforms with a low number of power switches. The multilevel waveforms are generated by the converters through a suitable PWM strategy that takes into consideration the transformer turns ratios. Modularity and simple maintenance makes proposed MSC an attractive solution compared to some conventional configurations. Model, PWM strategy and overall control are discussed in this paper. Simulation and experimental results are presented.

Shunt active power filter based on cascaded transformers coupled with three-phase bridge converters

This paper proposes a multilevel shunt active power filter (SAPF) to deal with either harmonic currents compensation or reactive power compensation. Such a device can reduce the harmonic distortion at the grid currents provided by non-linear loads located in stiff systems. The proposed SAPF is based on three-phase bridge (TPB) converters connected to cascaded single-phase transformers. The transformers arrangement permits the compensator to use a single dc-link unit which simplifies the control strategy and number of sensors. The multilevel waveforms are generated by using a suitable PWM strategy associated with the transformers turns ratio. Modularity and simple maintenance make the proposed SAPF an attractive solution compared to some conventional configurations. The model, PWM technique and 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.

Shunt Compensator Based on Interconnected Three-Phase Converter

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.