Resumo -Este trabalho avalia a controlabilidade do conversor Dual-Active Bridge (DAB), sob perturbações de carga, considerando que este conversor compõe um sistema com conversores em cascata. Mais especificamente, este artigo analisa o sistema de controle de um módulo de potência composto por um conversor CC-CC DAB conectado em série com um conversor CC-CA em ponte completa monofásico. A análise envolve o estudo da estabilidade através do critério das impedâncias para conversores em cascata e da controlabilidade do conversor DAB através da sua capacidade de transferência de potência sob a ocorrência de um afundamento de tensão do barramento CC, produzido por uma variação de carga na saída do módulo de potência (saída do conversor CC-CA). Um modelo equivalente em malha fechada do conversor DAB é apresentado, que representa o comportamento do afundamento de tensão CC para perturbações de carga com potência constante. Algumas restrições do projeto de controle são definidas para obter um sistema estável e controlável, e obter uma região de operação segura. Resultados experimentais são incluídos para validar a análise teórica proposta. Palavras-Chave -Controlabilidade, Conversor Dual-Active Bridge, Conversores em Cascata, Estabilidade.Abstract -This paper evaluates the controllability of the Dual-Active Bridge (DAB) converter under load disturbances, considering that it composes a system with cascaded power converters. More specifically, this paper analyzes the control system of a power module composed of a dc-dc Dual-Active Bridge converter connected in series with a single-phase full-bridge dc-ac converter. The analysis involves the study of the stability through the impedance criterion of the cascaded converters and the controllability of the DAB converter through its power transfer capability under the occurrence of a dc bus voltage sag, produced by a sudden load change at the Artigo submetido em 09/05/2018. Primeira revisão em 08/08/2018. Aceito para publicação em 21/11/2018 por recomendação do Editor Marcello Mezaroba. http://dx.output of the power module (dc-ac converter output). An equivalent closed-loop DAB model is presented to represent the dc voltage sag behavior for constant power load disturbances. Some restrictions of the control design are defined to achieve a stable and controllable system and to obtain a safe operating region. Experimental results are included for validating the proposed theoretical analysis.
The Single Input quasi-Z-Source Cascade Multilevel Inverter (SIqZS-CMI) has the ability to make use of a single DC input source and to share active power among all cascaded qZS modules. This unique feature, do not present in any other quasi-Z-Source (qZS) multilevel inverter in the literature, is accomplished by replacing one of its Z-impedance inductances by a coupled inductor. With this topology, it is possible to make use of a single low voltage PV string, favoring the use of small size residential rooftop systems. In addition, it simplifies the system grounding and the compliance with many Installation, Maintenance, and Safety Codes and Standards. The proposed control strategy enables high quality current injection into the grid, keeping the DC bus voltage regulation, ensuring precise power balancing with symmetric multilevel waveforms. Experimental results from a 5-level SIqZS-CMI prototype demonstrate the system's performance and its advantages.active power sharing, cascaded loop controller, cascaded multilevel inverter (CMI), DC-AC converter, grid-tied, photovoltaic (PV) power system, quasi-Z-source inverter (qZSI) | INTRODUCTIONRecently, Z-source and quasi-Z-source (qZS) multilevel inverters have been presented in literature. 1,2 These converters combine the advantages of cascaded multilevel inverters (CMIs) with the voltage gain provided by impedance-source List of Symbols and Abbreviations: C f , filter capacitor; C in(a,b) , input capacitor of module a and b; C 1(a,b) , capacitor 1 of module; C 2(a,b) , capacitor 2 of module; D 0(a,b) , duty-cycle of the ST; D 1(a,b) , module diode a and b; D 2(b) , module diode b; f grid , grid frequency; f s , switching frequency; i grid , grid current; i in , input current; i P , secondary winding current; I PN(a,b) , current drained from module a and a; L 1(a,b) , inductor 1 of module a and b; L 2(a,b) , inductor 2 of module a and b; L cf , converter-side inductor; L g , grid inductor; L gf , grid-side inductor; m (s), modulation index; N, turns-ratio; V a , module output voltage a; V b , module output voltage b; V grid , grid voltage; V PN(a,b) , module bus peak voltage a and b.;
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