Nady Rocha - Academia.edu (original) (raw)

Papers by Nady Rocha

In this paper, a novel single-phase five-level inverter is proposed. It is composed of eight swit... more In this paper, a novel single-phase five-level inverter is proposed. It is composed of eight switches and one flying-dc-source. Compared with the conventional active-neutral-point-clamped five-level inverter, the proposed structure has the same number of active devices and it does not require any sensor or balancing circuits to control the split dc-link capacitors. Thereby, the proposed converter reduces the cost and the complexity of the control system. Additionally, the proposed inverter has the capability of boosting the input voltage by a factor of two, which means it allows a reduction of 50 % in the DC-link voltage requirement and it does not require an intermediate DC-boosting stage for applications such as, photovoltaic panels and full-cells systems, characterized by a low and unregulated input voltage. Experimental results have been performed in order to validate the theoretical analysis of the proposed system.

IEEE Transactions on Industry Applications, Jul 1, 2016

An unidirectional three-phase to three-phase dc-link converter is proposed, in this paper. It is ... more An unidirectional three-phase to three-phase dc-link converter is proposed, in this paper. It is composed of three unidirectional ac-dc-ac three-leg converters with a shared-leg. The three-leg converter is composed of a non-controlled leg, two controlled legs and a dc-link. A suitable model and control strategy of the systems, including a synchronization method, are proposed. The synchronization method, associated with the PWM strategy allow the grid currents and load voltages have the same phase angle of the input converter voltages. This method ensures sinusoidal grid currents and mitigate the zero-crossing distortions normally caused by the use of diodes. Simulation and experimental results are also presented for validation purposes.

IEEE Transactions on Industry Applications, 2023

Iet Power Electronics, 2011

Iet Power Electronics, 2010

This study proposes a distributed generation system managed by a power converter with reduced num... more This study proposes a distributed generation system managed by a power converter with reduced number of components. Such converter operates with the same characteristics of the full-bridge converter. The distributed generation system is constituted by an induction generator with a prime mover (PM), a singlephase utility grid and a photovoltaic panel. A wind, hydraulic or another controlled power source is adopted to drive the induction generator, operating as a pm. The advantages of the four-leg power converter are explored in this application, such as reduced number of switches, high performance and dc-link voltage equal to that of standard converter with five legs. In addition, the control system is able to operate with a controlled mechanical power, allowing a bidirectional power flow. Simulated and experimental results are presented. This paper proposes a distributed generation system managed by ac-dc-ac power conversion with reduced number of components (see Fig. 2b), which operates with the same characteristics of the full-bridge converter 892

An AC-DC-AC unidirectional single-phase converter is presented in this paper. The configuration i... more An AC-DC-AC unidirectional single-phase converter is presented in this paper. The configuration is composed of a unidirectional rectifier and full controlled inverter and it is made out of two-level and three-level legs, a total of six controlled switches. The three-level leg presents lower voltage stress on switches, when compared with the two-level one (for a same DC-link voltage). Furthermore, it can allow reduction in harmonic distortion for a same switching frequency. Suitable modeling of the systems is presented, as well as a control strategy for synchronization between modulated voltage at grid side and grid current. This control scheme is necessary due to the grid voltage dependence of the current polarity. The SV-PWM strategy is analyzed and balancing of capacitor in DC-link is also shown. Simulated and experimental results are presented as well.

ABSTRACT This paper presents single- to three-phase dc-link converters with a reduced number of c... more ABSTRACT This paper presents single- to three-phase dc-link converters with a reduced number of controlled switches for either usual or reduced currents in switches of the rectifier. A suitable model and a control strategy, including a synchronization approach, are developed to obtain the maximum dc-link voltage utilization. Such a synchronization method, associated with the pulse-width-modulated generation signal, forces the input current to have the same phase angle as the input voltage. The main advantage of the proposed converters along with the synchronization method is the reduction of the zero-crossing distortion normally caused by the use of diodes. Simulated and experimental results are presented to confirm the validity of the theoretical expectations.

This paper discusses the fault tolerance performance of two hybrid six-phase drive systems under ... more This paper discusses the fault tolerance performance of two hybrid six-phase drive systems under single-phase opencircuit fault. The topologies are considered to be hybrid because each of the two three-phase groups of the six-phase machine is connected to a different type of converter. One group is connected to a two-level converter and the other group is connected to a dual converter in an open-end arrangement. A compensation strategy is discussed in order to keep the rated operation even after the occurrence of the fault. The six-phase machine mathematical model after the fault is presented and utilized to elaborate the compensation strategy. Simulation and experimental results show the validity of the discussed solutions. It is observed that the use of the degree of freedom represented by zerosequence components makes stator currents assume lower amplitudes after a singlephase open-circuit fault than the case in which these components are not present. This fact brings the possibility of operation with rated torque/power after the fault or lower reduction in torque/power to meet the thermal windings requirements.

A unidirectional AC-DC-AC three-level three-leg converter is proposed in this paper. This convert... more A unidirectional AC-DC-AC three-level three-leg converter is proposed in this paper. This converter is composed of a unidirectional Neutral Point Clamped leg (NPC) and two bidirectional NPC legs. A bidirectional NPC leg is shared between rectifier and inverter sides. Compared with the two-level leg, the three-level leg presents voltage stress reduction on switches for the same DC-link voltage level and also allows a reduction in harmonic distortion for the same switching frequency. Suitable modeling, PWM and control strategies of the system are presented. Also, it is shown a method for balancing DC-link capacitor voltages. As the converter is unidirectional, the grid current and the generated voltage at load side must be synchronized with generated voltage at grid side. That eliminates the zero-crossover distortion in the grid current caused by the use of diodes without the hysteresis control. Simulation and experimental results are also presented.

IEEE Transactions on Industry Applications, Sep 1, 2017

An unidirectional single-phase three-wire rectifier is proposed in this paper. Such topology is c... more An unidirectional single-phase three-wire rectifier is proposed in this paper. Such topology is composed of a noncontrolled leg, two controlled legs and a capacitor bank. A suitable model, Pulse Width Modulation (PWM) and control strategies of the system are proposed as well. The control strategy includes the synchronization method, in which imposes the grid currents with the same phase angle of the voltages generated by the rectifier. This method ensures sinusoidal grid currents and mitigates the zero-crossover distortions normally caused by the use of diodes. A comprehensive comparison with two conventional configurations is also presented in this paper. Simulation and experimental results are also presented for validation purposes.

IEEE Transactions on Industry Applications, 2023

Revista Principia, Aug 25, 2008

O objetivo deste artigo é apresentar uma nova abordagem de filtro paralelo para uma topologia de ... more O objetivo deste artigo é apresentar uma nova abordagem de filtro paralelo para uma topologia de conversor monofásico trifásico de baixo custo. Tal topologia foi proposta a princípio para acionamento de motores trifásicos. O conversor é controlado para corrigir o fator de potência da carga e reduzir os harmônicos, melhorando assim a qualidade de energia no sistema monofásico. Entre os benefícios pode-se destacar aumento indireto da capacidade do sistema, liberando a capacidade dos condutores e transformadores; menores níveis de harmônicos de tensão no PCC (ponto de conexão comum), diminuindo os harmônicos de tensão para os consumidores. Apresentação, análise, simulação e resultados experimentais são mostrados no presente artigo. Palavras chaves: Filtro Shunt (paralelo), Conversores Monofásicos-trifásicos, Conversores com estágio CC.

In this paper a Wind Energy Conversion System based on Doubly-Fed Induction Generator (DFIG) with... more In this paper a Wind Energy Conversion System based on Doubly-Fed Induction Generator (DFIG) with a three-phase series active filter without additional transformer is proposed. The series active filter acts to eliminate the distortions of the grid voltages in the stator windings of the DFIG. The proposed system operates with single dc-link. The control system regulates the circulating current between the Grid Side Converter and the series active filter. Simulation and experimental results are presented to evaluate the proposed system with series active filter.

ABSTRACT This paper presents a shunt active power filter (SAPF) based on the concept of open-end ... more ABSTRACT This paper presents a shunt active power filter (SAPF) based on the concept of open-end winding (OEW) transformers for three-phase three wire systems (3P3W). The proposed configuration is constituted of two converters, with three legs in each one, 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 multilevel 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.

In this paper, the basic structure and generalization of a cascaded transformer multilevel invert... more In this paper, the basic structure and generalization of a cascaded transformer multilevel inverter (CTMI) is proposed. Such a topology is based on cascaded symmetrical transformers associated to three-level (3L) neutral-point clamped (NPC) and two-level (2L) legs, of which one 2L leg is shared between the transformers. Also, it is presented a generalized modulation technique based on duty-cycle functions that is readily implementable on a digital signal processor (DSP). Compared to two conventional CTMIs, the proposed configuration can generate almost the double of levels using equal number of transformers or the same number of levels using half of the transformers, in such a way that a higher levels-per-switch ratio can be offered. In addition, the proposed system offer a natural balancing property that can self-regulate the dc-link capacitor voltages. Simulations and experimental tests are presented in order to demonstrate the performance and feasibility of the proposed configuration.

IEEE Transactions on Power Electronics, Mar 1, 2020

This paper presents a new single-phase AC-DC-AC three-level three-leg converter composed of three... more This paper presents a new single-phase AC-DC-AC three-level three-leg converter composed of three coupledinductors and six active switches. The system model, operation principles and a control strategy are presented and discussed. Additionally, a space-vector PWM technique is developed to double the effective frequency of the grid and load voltages and to reduce the switching losses. The proposed converter is compared to other similar converters in terms of switch count, harmonic distortion and power losses. The results show that the proposed topology has improved power quality and uses fewer switches and gate drive circuits. These characteristics can potentially reduce the costs and the complexity of the system. In addition, the proposed converter eliminates the requirement for dead-time to prevent short-circuit of the DC-link. In order to validate the theoretical analysis, simulated and experimental results are presented and discussed.

A single-phase to three-phase ac-dc-ac converter is proposed and analyzed in this paper for appli... more A single-phase to three-phase ac-dc-ac converter is proposed and analyzed in this paper for application in electric rail systems and in rural distribution grid. This system is composed of two cascaded transformers multilevel converter and two conventional two-level three-phase inverter feeding an openend winding induction motor. Model and a control strategy of the system are developed. Compared to the conventional single-phase to three-phase converter, the proposed topology has lower voltage and power ratings in power switches. In addition, the control system ensures balanced dc-link voltages and sinusoidal grid current with high power factor. Simulated and experimental results are also presented to demonstrate the feasibility of the proposed circuit.

This paper investigates a single-phase multilevel dc-ac converter composed of four series/paralle... more This paper investigates a single-phase multilevel dc-ac converter composed of four series/parallel-connected H-bridges with floating capacitors. System model, pulse-width modulation (PWM) strategies, and a control strategy have been presented. An important variable is the control of the dc-links voltages in the floating capacitor. Thus, an individual balancing of dc-links voltages using auxiliary variables and redundant voltage vectors are shown in this work for different dc-link voltage ratios. Simulations and experimental results with several power levels show how the operating characteristics.

IEEE Transactions on Industry Applications, Mar 1, 2021

This article presents a new single-phase ac–dc–ac five-leg multilevel converter, which is compose... more This article presents a new single-phase ac–dc–ac five-leg multilevel converter, which is composed of a three-leg converter cascaded with an H-bridge converter by means of a transformer. As a result, its output voltages have five, seven, and nine levels when a transformer turns ratio equal to <inline-formula><tex-math notation="LaTeX">$\eta =1$</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">$\eta = 2$</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">$\eta =3$</tex-math></inline-formula>, respectively, is used. The system model, operation principles, and a control strategy are presented and discussed. Additionally, two space-vector pulsewidth modulation techniques are developed to optimize the proposed converter. The proposed converter was compared with the conventional three-leg converter in terms of power semiconductor losses, harmonic distortion, and dc-link voltage requirement. The reduction in the dc-link voltage is of 50%, 66.7%, and 75%, for <inline-formula><tex-math notation="LaTeX">$\eta = 1$</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">$\eta = 2$</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">$\eta =3$</tex-math></inline-formula>, respectively. This characteristic reduces the voltage rating of the power devices, leading to the use of cheaper devices with better characteristics. Furthermore, when compared to other multilevel solutions presented in the literature, the proposed topology has a simple control structure and fewer power devices. As a multilevel topology, the proposed converter present competitive efficiency and can be applied with good performance in applications such as universal power filters and uninterruptible power supplies. To validate the theoretical analysis, simulated and experimental results are presented and discussed.

This paper presents a single-phase hybrid six-leg AC-DC-AC multilevel converter. The configuratio... more This paper presents a single-phase hybrid six-leg AC-DC-AC multilevel converter. The configuration is composed of a three-leg neutral point clamped (NPC) converter connected in series with a three-leg two-level converter. The proposed converter provides a sinusoidal input current with unitary input power factor and it feeds the load with a stable AC voltage. The system model, operation principles and a control strategy are presented and discussed. Additionally, a space-vector PWM technique is developed to control the dc-link capacitors, produce optimal voltage waveforms and to reduce the switching losses. The space-vector strategy guarantees nine-level output voltage waveforms at both input and output converter sides. Experimental and simulation results are presented to validate the theoretical studies.

In this paper, a novel single-phase five-level inverter is proposed. It is composed of eight swit... more In this paper, a novel single-phase five-level inverter is proposed. It is composed of eight switches and one flying-dc-source. Compared with the conventional active-neutral-point-clamped five-level inverter, the proposed structure has the same number of active devices and it does not require any sensor or balancing circuits to control the split dc-link capacitors. Thereby, the proposed converter reduces the cost and the complexity of the control system. Additionally, the proposed inverter has the capability of boosting the input voltage by a factor of two, which means it allows a reduction of 50 % in the DC-link voltage requirement and it does not require an intermediate DC-boosting stage for applications such as, photovoltaic panels and full-cells systems, characterized by a low and unregulated input voltage. Experimental results have been performed in order to validate the theoretical analysis of the proposed system.

IEEE Transactions on Industry Applications, Jul 1, 2016

An unidirectional three-phase to three-phase dc-link converter is proposed, in this paper. It is ... more An unidirectional three-phase to three-phase dc-link converter is proposed, in this paper. It is composed of three unidirectional ac-dc-ac three-leg converters with a shared-leg. The three-leg converter is composed of a non-controlled leg, two controlled legs and a dc-link. A suitable model and control strategy of the systems, including a synchronization method, are proposed. The synchronization method, associated with the PWM strategy allow the grid currents and load voltages have the same phase angle of the input converter voltages. This method ensures sinusoidal grid currents and mitigate the zero-crossing distortions normally caused by the use of diodes. Simulation and experimental results are also presented for validation purposes.

IEEE Transactions on Industry Applications, 2023

Iet Power Electronics, 2011

Iet Power Electronics, 2010

This study proposes a distributed generation system managed by a power converter with reduced num... more This study proposes a distributed generation system managed by a power converter with reduced number of components. Such converter operates with the same characteristics of the full-bridge converter. The distributed generation system is constituted by an induction generator with a prime mover (PM), a singlephase utility grid and a photovoltaic panel. A wind, hydraulic or another controlled power source is adopted to drive the induction generator, operating as a pm. The advantages of the four-leg power converter are explored in this application, such as reduced number of switches, high performance and dc-link voltage equal to that of standard converter with five legs. In addition, the control system is able to operate with a controlled mechanical power, allowing a bidirectional power flow. Simulated and experimental results are presented. This paper proposes a distributed generation system managed by ac-dc-ac power conversion with reduced number of components (see Fig. 2b), which operates with the same characteristics of the full-bridge converter 892

An AC-DC-AC unidirectional single-phase converter is presented in this paper. The configuration i... more An AC-DC-AC unidirectional single-phase converter is presented in this paper. The configuration is composed of a unidirectional rectifier and full controlled inverter and it is made out of two-level and three-level legs, a total of six controlled switches. The three-level leg presents lower voltage stress on switches, when compared with the two-level one (for a same DC-link voltage). Furthermore, it can allow reduction in harmonic distortion for a same switching frequency. Suitable modeling of the systems is presented, as well as a control strategy for synchronization between modulated voltage at grid side and grid current. This control scheme is necessary due to the grid voltage dependence of the current polarity. The SV-PWM strategy is analyzed and balancing of capacitor in DC-link is also shown. Simulated and experimental results are presented as well.

ABSTRACT This paper presents single- to three-phase dc-link converters with a reduced number of c... more ABSTRACT This paper presents single- to three-phase dc-link converters with a reduced number of controlled switches for either usual or reduced currents in switches of the rectifier. A suitable model and a control strategy, including a synchronization approach, are developed to obtain the maximum dc-link voltage utilization. Such a synchronization method, associated with the pulse-width-modulated generation signal, forces the input current to have the same phase angle as the input voltage. The main advantage of the proposed converters along with the synchronization method is the reduction of the zero-crossing distortion normally caused by the use of diodes. Simulated and experimental results are presented to confirm the validity of the theoretical expectations.

This paper discusses the fault tolerance performance of two hybrid six-phase drive systems under ... more This paper discusses the fault tolerance performance of two hybrid six-phase drive systems under single-phase opencircuit fault. The topologies are considered to be hybrid because each of the two three-phase groups of the six-phase machine is connected to a different type of converter. One group is connected to a two-level converter and the other group is connected to a dual converter in an open-end arrangement. A compensation strategy is discussed in order to keep the rated operation even after the occurrence of the fault. The six-phase machine mathematical model after the fault is presented and utilized to elaborate the compensation strategy. Simulation and experimental results show the validity of the discussed solutions. It is observed that the use of the degree of freedom represented by zerosequence components makes stator currents assume lower amplitudes after a singlephase open-circuit fault than the case in which these components are not present. This fact brings the possibility of operation with rated torque/power after the fault or lower reduction in torque/power to meet the thermal windings requirements.

A unidirectional AC-DC-AC three-level three-leg converter is proposed in this paper. This convert... more A unidirectional AC-DC-AC three-level three-leg converter is proposed in this paper. This converter is composed of a unidirectional Neutral Point Clamped leg (NPC) and two bidirectional NPC legs. A bidirectional NPC leg is shared between rectifier and inverter sides. Compared with the two-level leg, the three-level leg presents voltage stress reduction on switches for the same DC-link voltage level and also allows a reduction in harmonic distortion for the same switching frequency. Suitable modeling, PWM and control strategies of the system are presented. Also, it is shown a method for balancing DC-link capacitor voltages. As the converter is unidirectional, the grid current and the generated voltage at load side must be synchronized with generated voltage at grid side. That eliminates the zero-crossover distortion in the grid current caused by the use of diodes without the hysteresis control. Simulation and experimental results are also presented.

IEEE Transactions on Industry Applications, Sep 1, 2017

An unidirectional single-phase three-wire rectifier is proposed in this paper. Such topology is c... more An unidirectional single-phase three-wire rectifier is proposed in this paper. Such topology is composed of a noncontrolled leg, two controlled legs and a capacitor bank. A suitable model, Pulse Width Modulation (PWM) and control strategies of the system are proposed as well. The control strategy includes the synchronization method, in which imposes the grid currents with the same phase angle of the voltages generated by the rectifier. This method ensures sinusoidal grid currents and mitigates the zero-crossover distortions normally caused by the use of diodes. A comprehensive comparison with two conventional configurations is also presented in this paper. Simulation and experimental results are also presented for validation purposes.

IEEE Transactions on Industry Applications, 2023

Revista Principia, Aug 25, 2008

O objetivo deste artigo é apresentar uma nova abordagem de filtro paralelo para uma topologia de ... more O objetivo deste artigo é apresentar uma nova abordagem de filtro paralelo para uma topologia de conversor monofásico trifásico de baixo custo. Tal topologia foi proposta a princípio para acionamento de motores trifásicos. O conversor é controlado para corrigir o fator de potência da carga e reduzir os harmônicos, melhorando assim a qualidade de energia no sistema monofásico. Entre os benefícios pode-se destacar aumento indireto da capacidade do sistema, liberando a capacidade dos condutores e transformadores; menores níveis de harmônicos de tensão no PCC (ponto de conexão comum), diminuindo os harmônicos de tensão para os consumidores. Apresentação, análise, simulação e resultados experimentais são mostrados no presente artigo. Palavras chaves: Filtro Shunt (paralelo), Conversores Monofásicos-trifásicos, Conversores com estágio CC.

In this paper a Wind Energy Conversion System based on Doubly-Fed Induction Generator (DFIG) with... more In this paper a Wind Energy Conversion System based on Doubly-Fed Induction Generator (DFIG) with a three-phase series active filter without additional transformer is proposed. The series active filter acts to eliminate the distortions of the grid voltages in the stator windings of the DFIG. The proposed system operates with single dc-link. The control system regulates the circulating current between the Grid Side Converter and the series active filter. Simulation and experimental results are presented to evaluate the proposed system with series active filter.

ABSTRACT This paper presents a shunt active power filter (SAPF) based on the concept of open-end ... more ABSTRACT This paper presents a shunt active power filter (SAPF) based on the concept of open-end winding (OEW) transformers for three-phase three wire systems (3P3W). The proposed configuration is constituted of two converters, with three legs in each one, 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 multilevel 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.

In this paper, the basic structure and generalization of a cascaded transformer multilevel invert... more In this paper, the basic structure and generalization of a cascaded transformer multilevel inverter (CTMI) is proposed. Such a topology is based on cascaded symmetrical transformers associated to three-level (3L) neutral-point clamped (NPC) and two-level (2L) legs, of which one 2L leg is shared between the transformers. Also, it is presented a generalized modulation technique based on duty-cycle functions that is readily implementable on a digital signal processor (DSP). Compared to two conventional CTMIs, the proposed configuration can generate almost the double of levels using equal number of transformers or the same number of levels using half of the transformers, in such a way that a higher levels-per-switch ratio can be offered. In addition, the proposed system offer a natural balancing property that can self-regulate the dc-link capacitor voltages. Simulations and experimental tests are presented in order to demonstrate the performance and feasibility of the proposed configuration.

IEEE Transactions on Power Electronics, Mar 1, 2020

This paper presents a new single-phase AC-DC-AC three-level three-leg converter composed of three... more This paper presents a new single-phase AC-DC-AC three-level three-leg converter composed of three coupledinductors and six active switches. The system model, operation principles and a control strategy are presented and discussed. Additionally, a space-vector PWM technique is developed to double the effective frequency of the grid and load voltages and to reduce the switching losses. The proposed converter is compared to other similar converters in terms of switch count, harmonic distortion and power losses. The results show that the proposed topology has improved power quality and uses fewer switches and gate drive circuits. These characteristics can potentially reduce the costs and the complexity of the system. In addition, the proposed converter eliminates the requirement for dead-time to prevent short-circuit of the DC-link. In order to validate the theoretical analysis, simulated and experimental results are presented and discussed.

A single-phase to three-phase ac-dc-ac converter is proposed and analyzed in this paper for appli... more A single-phase to three-phase ac-dc-ac converter is proposed and analyzed in this paper for application in electric rail systems and in rural distribution grid. This system is composed of two cascaded transformers multilevel converter and two conventional two-level three-phase inverter feeding an openend winding induction motor. Model and a control strategy of the system are developed. Compared to the conventional single-phase to three-phase converter, the proposed topology has lower voltage and power ratings in power switches. In addition, the control system ensures balanced dc-link voltages and sinusoidal grid current with high power factor. Simulated and experimental results are also presented to demonstrate the feasibility of the proposed circuit.

This paper investigates a single-phase multilevel dc-ac converter composed of four series/paralle... more This paper investigates a single-phase multilevel dc-ac converter composed of four series/parallel-connected H-bridges with floating capacitors. System model, pulse-width modulation (PWM) strategies, and a control strategy have been presented. An important variable is the control of the dc-links voltages in the floating capacitor. Thus, an individual balancing of dc-links voltages using auxiliary variables and redundant voltage vectors are shown in this work for different dc-link voltage ratios. Simulations and experimental results with several power levels show how the operating characteristics.

IEEE Transactions on Industry Applications, Mar 1, 2021

This article presents a new single-phase ac–dc–ac five-leg multilevel converter, which is compose... more This article presents a new single-phase ac–dc–ac five-leg multilevel converter, which is composed of a three-leg converter cascaded with an H-bridge converter by means of a transformer. As a result, its output voltages have five, seven, and nine levels when a transformer turns ratio equal to <inline-formula><tex-math notation="LaTeX">$\eta =1$</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">$\eta = 2$</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">$\eta =3$</tex-math></inline-formula>, respectively, is used. The system model, operation principles, and a control strategy are presented and discussed. Additionally, two space-vector pulsewidth modulation techniques are developed to optimize the proposed converter. The proposed converter was compared with the conventional three-leg converter in terms of power semiconductor losses, harmonic distortion, and dc-link voltage requirement. The reduction in the dc-link voltage is of 50%, 66.7%, and 75%, for <inline-formula><tex-math notation="LaTeX">$\eta = 1$</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">$\eta = 2$</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">$\eta =3$</tex-math></inline-formula>, respectively. This characteristic reduces the voltage rating of the power devices, leading to the use of cheaper devices with better characteristics. Furthermore, when compared to other multilevel solutions presented in the literature, the proposed topology has a simple control structure and fewer power devices. As a multilevel topology, the proposed converter present competitive efficiency and can be applied with good performance in applications such as universal power filters and uninterruptible power supplies. To validate the theoretical analysis, simulated and experimental results are presented and discussed.

This paper presents a single-phase hybrid six-leg AC-DC-AC multilevel converter. The configuratio... more This paper presents a single-phase hybrid six-leg AC-DC-AC multilevel converter. The configuration is composed of a three-leg neutral point clamped (NPC) converter connected in series with a three-leg two-level converter. The proposed converter provides a sinusoidal input current with unitary input power factor and it feeds the load with a stable AC voltage. The system model, operation principles and a control strategy are presented and discussed. Additionally, a space-vector PWM technique is developed to control the dc-link capacitors, produce optimal voltage waveforms and to reduce the switching losses. The space-vector strategy guarantees nine-level output voltage waveforms at both input and output converter sides. Experimental and simulation results are presented to validate the theoretical studies.