Browsing by Author "Fernandes, Marcelo Carvalho"

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    Dispatchable distributed generation using a back-to-back converter for grid-forming improvements based on feed-forward action with load current prediction.
    (2020) Fogli, Gabriel Azevedo; Souza, Igor Dias Neto de; Fernandes, Marcelo Carvalho; Almeida, Pedro Machado de; Barbosa, Pedro Gomes
    This work deals with the control law design and experimental verification of a grid-forming dispatchable distributed generation based on a back-to-back converter. The proposed system brings several improvements to the prime mover as well as to the microgrid voltage quality. The control strategy is based on an inner current and an outer voltage loop for both sides of the converter. The external loop of the back-to-back input side, which is connected to the generator, is responsible for regulating the DC voltage. On the other hand, in the output side, the voltage loop ensures a high-quality AC waveform to feed the loads. A comprehensive discussion regarding the current controller with harmonic mitigation is performed to justify the controller's choice. It is shown that a suitable current controller significantly improves the disturbance rejection. A feed-forward compensation based on the load current prediction without any additional sensor is proposed to improve the output voltage quality. Experimental results are used to validate the proposed control law and to show the improvements and benefits of the system.
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    Systematic design of a DLQR applied to grid-forming converters.
    (2020) Almeida, Pedro Machado de; Ribeiro, Adeilson da Silva Borges; Souza, Igor Dias Neto de; Fernandes, Marcelo Carvalho; Fogli, Gabriel Azevedo; Cuk, Vladimir; Barbosa, Pedro Gomes; Ribeiro, Paulo Fernando
    This article proposes a systematic state-space procedure to design an optimal discrete-time linear quadratic regulator applied to grid-forming converters. A comprehensive mathematical modeling of a voltage-sourced converter with an LC output filter is performed and a systematic way of including digital resonant compensators is addressed. The choice of weights is based on the minimization of selected transfer functions infinity norm, as well as on the stability margin and bandwidth. The effects of weighting on closed-loop transfer functions shape are analyzed and important points are discussed in order to establish a methodical way of choosing the weighting matrices. Experimental results are presented to validate the design and to demonstrate the system effectiveness with high loading and highly nonlinear balanced and unbalanced loads.