No abstract

The power calculation is an indispensable element in droop-controlled inverters because the bandwidth of the measured power has a direct impact on the controller performance. This paper proposes a fast and accurate power calculation algorithm based on the combined Second Order Generalized Integrator (SOGI) filters in stationary coordinates for a three-phase system, which takes into consideration the use of nonlinear loads. The power calculation scheme is formed by the two-stage SOGI filters that are employed for obtaining the active and reactive powers required to perform a droop-based inverter operation, respectively. From the two-stage structure, the first SOGI is used as a band-pass filter (BPF) for filtering harmonics and obtaining the fundamental current of the nonlinear load; The second SOGI is used as a low-pass filter (LPF) for extracting the DC-component, which corresponds with the average power. A small-signal model of a two droop-controlled inverters system is built to obtain the dynamical response and stability margin of the system. And compared it with the dynamical behaviour of a standard droop-control method. Next, the proposed power calculation system is designed in order to achieve the same ripple amplitude voltage as that obtained with the standard droop-control method by adjusting the bandwidth gains. Through simulation and hardware in the loop (HIL) validation, the proposed approach presents a faster and more accurate performance when sharing nonlinear loads, and also drives the inverters’ output voltage with lower distortion.

This paper proposes a double conversion UPS system with power factor correction, high frequency transformer isolation and 110V/220V input voltage characteristics. It's suitable for rack type structure because it has small size and reduced weight. For both input voltages, the proposed converter has almost the same efficiency processing the same output power. Other relevant features of this structure are: soft commutation of the controlled switches of the chopper and of the boost stage, simple control strategy that can be implemented with well-known integrated circuits and the use of few batteries in series due to step-up stage. Qualitative analysis and experimental results obtained from 2kVA laboratory prototype are presented.

Resumo-Este trabalho tem por objetivo analisar o modelo do gerador de indução duplamente alimentado no referencial dq síncrono através de estudo teórico. Através da análise dos circuitos que relacionam o rotor e o estator desta máquina nos eixos direto e em quadratura, um modelo matemático em malha fechada será deduzido e analisado em detalhes. Um desenvolvimento matemático baseado em controladores proporcional e proporcionalintegral será proposto. Por fim, resultados experimentais a partir de um protótipo de 8 kW montado em laboratório, onde o comportamento dos controladores diante de variações em degrau na referência de corrente do rotor tanto no eixo direto quanto no eixo em quadratura serão apresentados e discutidos, a fim de validar a teoria proposta.

Resumo -O modelo matemático clássico do gerador de indução duplamente alimentado não considera as perdas no núcleo magnético e suplementares. Porém, ele é válido quando o gerador entrega sua potência nominal, o que não ocorre no processo de sincronização, onde o gerador está a vazio. Em geral, os modelos que consideram essas perdas tornam o equacionamento mais complexo. Neste sentido, este artigo propõe que se considerem estas perdas como agrupadas na resistência do rotor, o que mantém as equações da máquina inalteradas. Ainda, apresenta-se um mé-todo simplificado para a estimação dos parâmetros do circuito do rotor, os quais são utilizados para sintonizar os controladores de corrente durante o processo de sincronização à rede elétrica. Os resultados de simulação e experimentais confirmam a eficácia da abordagem proposta.Palavras-Chave -Estimação de Parâmetros, Gerador de Indução Duplamente Alimentado, Sincronização. PARAMETER ESTIMATION AND CONTROL OF A DOUBLY-FED INDUCTION GENERATOR DURING THE SYNCHRONIZATION WITH THE GRIDAbstract -The conventional mathematical model of the doubly-fed induction generator does not take into account the magnetic core and the stray load losses. However, this model is valid when the generator delivers its rated power, which does not occur during the synchronization process, as it is a no-load situation. In general, the models that consider these losses make the equations more complex. Thus, this paper proposes to consider these losses as grouped in the rotor resistance, which keeps unchanged the machine equations. In addition, a simplified method is presented for estimation of rotor circuit parameters, which are used to tune the current controllers during the process of synchronization with the grid. The simulation and experimental results confirm the effectiveness of the proposed approach.