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This paper presents a three-phase multilevel power factor correction (PFC) rectifier employing multistate switching cells. A generalized converter structure is presented based on the connection of switching networks of Vienna-type rectifier topologies through multiinterphase transformers (MIPTs). The resulting rectifier presents the intrinsic benefits to the employed building blocks and the ones added by a modular construction that enables the reduction of passive components and overall losses. The operation of the PFC rectifier is described, including appropriate modulation and control strategies. Design guidelines for the magnetic components are derived for the MIPTs, boost inductors, and power semiconductor devices. Finally, a lab prototype is used to present experimental results. This prototype is rated at 7.5 kW and uses a modular structure to assemble a four legs per phase rectifier. Efficiency above 98% from 40% load and IEC61000-3-2 requirements are observed.

This paper presents a new nonisolated buck/boost-type multilevel dc-dc converter suitable for high-power and medium/high-voltage application. The main features of the proposed topology are as follows: low voltage across the semiconductors, low switching losses, and reduced volume of the output filter. The theoretical analysis is carried out for a five-level bidirectional structure of the proposed converter, operating in Buck mode. The proposed topology presents some capacitors, and their voltage must be balanced for proper operation of the converter. Thus, a capacitor voltage balancing active control using a feedforward technique is proposed and analyzed in detail. In order to validate the theoretical analysis, a prototype with 10 kW output power capability, 1.3 kV to 800 V input-to-output voltage, and 20 kHz of switching frequency was built and experimented. The results attest the advantages of the new dc-dc topology, as well as the new capacitor voltage control technique.

Alternating current (ac) active electronic loads (AELs) based on pulsewidth modulation (PWM) converters, capable of emulating nonlinear loads, require effective current control techniques and power stages. These two aspects of an AEL are interdependent mainly due to the presence of electromagnetic compatibility filters to reduce electromagnetic emissions. However, the filter components affect the dynamics of the system. In this context, this paper proposes a digitally implemented control strategy comprising the state feedback, robust observer, phase-locked loop, and linear current controller to cope with ac AEL applications. The control-oriented modeling and the control system design are presented. Experimental results obtained from a 10-kW three-phase three-level PWM converter prototype illustrate and demonstrate the feasibility of the proposed AEL control strategy.

Novel simple indirect control concepts for an active power filter (APF) application are proposed here. The concepts are exemplarily presented to control a modified APF structure. The main advantage over other control strategies is the achieved excellent simplicity-to-performance ratio. The proposed control strategies are based on the concept of virtual impedance emulation to provide high power factor in a system. To validate the operating principle, a single-phase low-power prototype has been built and experimentally tested. This prototype operates at a remarkably low switching frequency of 5 kHz and is digitally controlled by a digital signal processor.

A novel three-phase hybrid multilevel converter is proposed for medium-voltage applications. The converter employs a conventional three-phase voltage source inverter (VSI) linking series connected half-bridge modules at each phase. With the proposed connection, a large portion of energy can be processed by the VSI by employing a single multi-pulse rectifier, while smaller power shares are processed within the half-bridge modules. Thus, the requirements for galvanically insulated dc sources are reduced. Modularity is naturally achieved. A modulation scheme for a four-level version is proposed and analyzed in detail. This scheme allows unidirectional power flow in all dc sources and, consequently, enables diode bridges to be employed in the rectification input stage for unidirectional applications.

The single-phase multilevel power-factor correction rectifier employing multistate switching cells is analyzed regarding different operational aspects. The generalization of the number of switching states is performed in order to clarify issues such as the input current ripple, the output currents rms values, power semiconductor stresses, and others. A discussion on the optimal number of switching states is carried out, based on the generated models. In this context, this work is a first step aiming in the efficiency-based optimization of the concept.

Novel symmetric hybrid multilevel topologies are introduced for both single- and three-phase medium-voltage high-power systems. The topology conception is presented in detail, where a three-level switching cell with low component count, and its modulation pattern give the origin of the proposed converters. Voltage sharing and low output-voltage distortion are achieved. The theoretical frequency spectra are derived. Switching devices are separated into high- and low-frequency devices, generating hybrid converters. Five-level three-phase topologies are generated from only three insulated dc sources, while the number of semiconductors is the same as for the cascaded H bridge. Both simulation and experimental results are provided showing the validity of the analysis.

Almost two decades of research on unidirectional three-phase multilevel boost-type pulsewidth modulation (PWM) rectifiers have shown the benefits of employing this technology to comply with power quality standards while assuring high efficiency and low volume and weight. However, the unidirectional topologies directly derived from the conventional three-level bidirectional converters, such as the neutral point clamped (NPC), the flying capacitor and the cascaded H-bridge converters have not been properly analyzed. This letter introduces some of the unidirectional topologies that arise from the inspection of the widespread conventional bidirectional converters. Special emphasis is put in the analysis of the NPC-based three-phase/-level PWM rectifier operating as power factor corrector.

DC-DC step-up converters for high-output voltage applications typically demand high voltage devices, leading to high conduction and switching losses. This identified demand has motivated research on active clamping and multi-level topologies. On this context, this study presents the study of a novel DC-DC boost converter with three-level boost-type active clamping, zero-voltage switching (ZVS) soft-switching and constant frequency pulse-width modulation. As shown analytically and through experimental results, high efficiency and reduced voltage ratings for the power semiconductors are achieved, thus, making the topology suitable for converters requiring high-output DC voltage. Furthermore, a topological modification for achieving ZVS operation in all semiconductors and other types of switching cells for boost-type converters is introduced.

Este trabalho apresenta e compara estratégias de controle de corrente e de tensão de conversores trifásicos a três e a quatro fios no sistema de referências abc. Para o controle de corrente se considera o uso de um filtro de potência indutivo. Já para o controle de tensão se considera o uso de um filtro LC, além do uso do controle em cascata. Essa estratégia considera o uso de uma malha de corrente interna e uma de tensão externa. O trabalho foi desenvolvido com base numa abordagem multivariável, utilizando-se de representações no espaço de estados e de matrizes de transferência para descrever o comportamento dos sistemas trifásicos. O comportamento dos sistemas trifásicos foi comparado com o do sistema do conversor monofásico. Demonstrou-se que é possível desacoplar as malhas de controle dos conversores trifásicos no sistema de referência abc ao se utilizar uma estrutura de controle de corrente com N-1 controladores (N é o número de fios) que anula as componentes de sequência zero dos sinais de controle. A partir desse resultado, o projeto de controle multivariável foi reduzido para um projeto de controlador Single-Input Sigle-Output (SISO). A metodologia de projeto consistiu: na modelagem dos sistemas a serem controlados; no projeto dos parâmetros do controle de corrente e depois do controle de tensão; na simulação computacional; e na implementação dos controladores escolhidos em uma plataforma conversora trifásica real funcionando como uma fonte de tensão trifásica programável. As estratégias de controle estudadas foram: Dead-Beat, Proporcional (P), Proporcional-Integral (PI), Proporcional-Ressonante (PR), Proporcional com Múlitplos Ressonantes (P+MR) e Repetitivo baseado no filtro DFT (Digital Fourier Transform). Ao final do trabalho, um controlador P foi escolhido para a malha interna de corrente e um controlador P+MR para a malha externa de tensão. Foram realizados feedforwards (FF) para a tensão de carga e para a corrente de saída. This work presents and compares current and voltage control strategies for three and four-wire converters in the abc reference system. For the current control, it is considered the use of an inductive power filter. As for the voltage control, the use of a LC filter and of cascaded control loops are considered. This strategy considers the use of an internal current loop and an external voltage loop. The work was developed based on a multivariable approach, utilizing state space representations and transfer matrices to describe the behavior of the three-phase systems. The behavior of the three-phase systems was compared to that of the single-phase converter. It was demonstrated that it is possible to decouple the three-phase converters control loops in the abc reference frame by using a current control structure with N-1 controllers (N is the number of wires) that cancels the zero-sequence components of the control signals. With that result, the multivariable control project was reduced to a Single-Input Single-Output (SISO) controller project. The project methodology consisted of: the modeling of the systems to be controlled; the project of the parameters for the current control and later for the voltage control; computer simulation; and the implementation of the chosen controllers in a real three-phase converter platform functioning as a programmable three-phase voltage source. The studied control strategies were: Dead-Beat, Proportional (P), Proportional-Integral (PI), Proportional-Resonant (PR), Proportional with Multiple Resonants (P+MR) and Repetitive based on the DFT (Digital Fourier Transform) filter. At the end of this work, a P controller was chosen for the internal current loop and a P+MR controller for the external voltage loop. Feedforwards (FF) were utilized for the load voltage and for the output current.