Browsing by Author "Fogli, Gabriel Azevedo"

Now showing 1 - 7 of 7
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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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    Estratégias de energização e desenergização de um compensador estático síncrono para distribuição.
    (2018) Duarte, Samuel Neves; Fogli, Gabriel Azevedo; Almeida, Pedro Machado de; Barbosa, Pedro Gomes
    Este trabalho propõe dois controladores para energizar e desenergizar compensadores estáticos síncronos destinados a serem conectados nas redes de distribuição. O primeiro circuito é baseado em um retificador semi–controlado enquanto o segundo controlador é baseado em um circuito gradador. Os dois controladores propostos são facilmente adaptados a estrutura do compensador estático sem a necessidade de realizar alterações topológicas no conversor. Um modelo matemático é usado para derivar as relações matemáticas usadas para controlar as correntes de energização e de desenergização. Aproximações lineares por partes foram usadas para reduzir o esforço computacional dos algoritmos de controle desenvolvidos. Resultados de simulação e experimentais são apresentados para validar a metodologia proposta.
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    Low-frequency underwater wireless power transfer : maximum efficiency tracking strategy.
    (2020) Lopes, Israel Filipe; Valle, Rodolfo Lacerda; Fogli, Gabriel Azevedo; Ferreira, André Augusto; Barbosa, Pedro Gomes
    This paper proposes a strategy to improve the efficiency of a low-frequency Wireless Power Transfer (WPT) system used to charge the battery of an Autonomous Underwater Vehicle (AUV) through an Inductive Power Transfer (IPT). The IPT system uses a Split-Core Transformer (SCT) to transfer power from the docking base to the AUV, without electric contact. Under gap variation, the efficiency is changed because the variation of SCT parameters. Therefore, the input frequency is changed in order to improve the efficiency of the system trough the Maximum Efficiency Point Tracking algorithm (MEPT) without communication between primary and secondary sides. Experimental results are presented to validate the theoretical analysis and to demonstrate the behaviour of the transformer under different values of gap and excitation frequency.
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    Modelling and control of an interface power converter for the operation of small diesel gen-sets in grid-connected and stand-alone modes.
    (2017) Fogli, Gabriel Azevedo; Almeida, Pedro Machado de; Barbosa, Pedro Gomes
    This paper presents the modelling and control design steps of a two-stage static conversion structure used as interface to integrate a diesel generator setinto a secondary distribution network. In order to guarantee that the inverter works within the PWM linear range, a boost converter is used to increase the DC voltage level. The proposed structure allows two operation modes, connected to the AC mains or isolated. In the isolated mode the interface converter may be controlled as grid-forming or grid-conditioning (active power filter). The inverter current controllers are designed in the synchronous reference frame together with multiple integrators in order to effectively track non-sinusoidal currents. The stability analysis is performed through the Nyquist plot. Experimental results obtained with a 5.5 kW diesel generator set are presented to validate the proposed system operation and control strategies.
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    Simple and effective digital control of a variable-speed low inductance BLDC motor drive.
    (2020) Valle, Rodolfo Lacerda; Almeida, Pedro Machado de; Fogli, Gabriel Azevedo; Ferreira, André Augusto; Barbosa, Pedro Gomes
    This paper presents a simple digital control applied to a low inductance 5 kW/48 V three-phase brushless DC motor. Controlling the VSI as a full-bridge converter allowed the use of unipolar switching strategy, increasing the output equivalent frequency up to 100 kHz. The aforementioned strategy has made it possible to control the three-phase currents using a single deadbeat controller without a back-EMF feed-forward compensation. Stability analysis is performed to show that the proposed current control presents good transient response under reasonable parametric variations, as well as zero steady-state error. Precise regulation with no overshoot was obtained using an IP controller to regulate the motor speed. Experimental results are presented to validate the theoretical analysis and to compare with a conventional PI compensator and a predictive controller.
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    A simple dead-time compensation strategy for grid-connected voltagesourced converters semiconductor switches.
    (2019) Fogli, Gabriel Azevedo; Valle, Rodolfo Lacerda; Almeida, Pedro Machado de; Barbosa, Pedro Gomes
    This paper presents a simple strategy to compensate the distorted currents synthesized by a grid-connected voltage source converter due to dead-time, turn-on and turn-off time delays of the semiconductor switches. The algorithm consider only the polarity of the fundamental component of the currents flowing through the converter terminals and the values of the time delays and voltage drops supplied by the manufacturers to the semiconductors devices. The presented compensation belongs to the group classified as average value compensation technique methodology since it does not change the pulse pattern of the converter's semiconductor switches. A simplified mathematical description of the effects caused by these unwanted time delays is presented and used to derive a correction factor to be added, in real time, to the converter output controller in order to compensate for its terminal voltages. The asymptotic stability and robustness of the proposed methodology is investigated redrawing the converter current controllers, designed in dq-reference frame, as proportional-resonant ones, in the abc coordinates, and adding the effect of the compensating signal in the feedback loop using the concept of describing function. In addition, the minimum value of the DC bus voltage necessary is also evaluated to ensure the operation of the converter in the linear modulation region when the compensation algorithm is active. Experimental results are presented to validate the theoretical analysis and to demonstrate the effectiveness of the proposed strategy for three different operation conditions of a grid-connected converter: (i) active power injection; (ii) active power consumption and (iii) reactive power support.
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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.