Navegando por Assunto "Voltage control"

Agora exibindo 1 - 4 de 4

Acesso aberto (Open Access)
Avaliação de estratégias de controle de potência reativa de aerogeradores síncronos em redes elétricas
(Universidade Federal do Pará, 2009-18-11) NASCIMENTO, André Cavalcante do; BEZERRA, Ubiratan Holanda; http://lattes.cnpq.br/6542769654042813; NUNES, Marcus Vinícius Alves; http://lattes.cnpq.br/9533143193581447
In the present work a methodology of reactive power injection in electric grids during voltage dips provoked by short-circuit, in connected wind farms, adopted at some countries with technological maturity in the production of wind energy in the world is evaluated. In the developed studies, the direct drive synchronous wind generator was used with full converter due to the high controllability of the converter connected to the electric grid and for possessing high capacity of reactive power supply, compared to other wind generators technologies. In Brazil, the grid code to connect wind farms to the electric grids, defined by the National Operator of the Electrical System, doesn't stipulate yet the need of adoption of such methodology during faults in the electric grid. It just specifies the ride through apability curve for voltage dips that the wind generators should follow to avoid the trip of the undervoltage relay. Criteria of the synchronous wind generators protection are evaluated starting from short-circuit simulations in a test grid with adoption of the Brazilian grid code, without reactive power injection, being compared with those of other countries that adopt reactive power injection curves.
Acesso aberto (Open Access)
Desenvolvimento de um sistema multiconversor para a realização de estudos experimentais em microrredes de corrente contínua
(Universidade Federal do Pará, 2015-08-10) COSTA JUNIOR, Fernando José da; BARRA JUNIOR, Walter; http://lattes.cnpq.br/0492699174212608
This paper presents the design and development of a Multiconverter System based on a Microgrid comprised of a DC bus and static power converters DC-DC and DC-AC. This system is located at the Power Systems Control Laboratory (LACSPOT) at Federal University of Pará (UFPA). The Multiconverter System consists in three power converters, two in step-down Buck topology and the third a three-phase inverter. The first converter feeds a direct current voltage controlled bus that provides voltage to a second Buck converter. On the second Buck converter is also applied a voltage control strategy in order to maintain a constant power supply. The three-phase inverter is also powered by a DC bus can be connected to the local power grid, allowing studies with grid-tied systems and distributed generation. To test the buck converter studied in this work, were developed digital controllers, based on indirect digital control design method. Both controllers were developed using the output voltages as feedback signals in order to maintain the voltage and power as constant as possible, on the primary and secondary converters, respectively. Besides inner difficult in systems with parametric uncertainties and nonlinearities shown in power converters, the power converter with voltage control also feeds the second power converter. That introduces non-linear characteristics that may cause bar voltage instability. For that reason, it is necessary to develop a control strategy with the goal of keeping the voltage near to the voltage bus reference. To sum up, several tests were performed both in computer simulation, as in the real system in order to check the effectiveness of control techniques studied and applied. The obtained results shown that the Multiconverter System was able to provide a good performance under the designed control strategy.
Acesso aberto (Open Access)
Impacto técnico e econômico da integração de uma geração distribuída de alta capacidade em um sistema de distribuição com reguladores de tensão em cascata
(Universidade Federal do Pará, 2019-11-14) COSTA, Marcelo Sousa; VIEIRA, João Paulo Abreu; http://lattes.cnpq.br/8188999223769913
This dissertation analyzes the technical and economical impact of the integration of a high capacity distributed generation (DG) in a distribution system composed of two feeders, both with two cascaded step voltage regulators (SVRs). Distribution networks with the presence of high capacity DG may subject SVR to reverse active power flow scenarios, which, depending on the control modes “Active Bidirectional Flow up to Opposite Limit” and “Reverse Flow by Cogeneration”, result in abnormal situations that lead the SVR to lose its regulating capacity. As a consequence, consumers may be subjected to severe undervoltage or overvoltage. This phenomenon, in which the SVR loses its ability to control the desired bus voltage, is known in technical literature as the reverse power tap changer runaway condition. In addition, high capacity GDs, depending on their location in the distribution system, can cause critical overvoltages. Some actions can be taken to reduce or mitigate this effect, such as distribution system reconfiguration, adjusting the SVR setpoint, and modifying DG control mode. The economic assessment was accomplished for all studied operating scenarios, highlighting technical and financial impacts on the utility and customers.
Acesso aberto (Open Access)
Otimização de controladores utilizando algoritmos genéticos para melhoria da capacidade de sobrevivência a afundamentos de tensão de aerogeradores de indução duplamente excitados
(Universidade Federal do Pará, 2009-12-01) VIEIRA, João Paulo Abreu; BEZERRA, Ubiratan Holanda; http://lattes.cnpq.br/6542769654042813; NUNES, Marcus Vinícius Alves; http://lattes.cnpq.br/9533143193581447
It is proposed in this thesis a methodology to obtain optimal controllers gains for the rotorside converter of doubly fed induction generators (DFIGs) using a genetic algorithm approach. The main objective is to enhance the operational security and robustness of the power system, by a more effective contribution of the DFIG controllers to the system controllability. To reach this goal, the crow-bar protection scheme is activated during the fault period when severe voltage sags occur in order to maintain the rotor-side converter connected to the DFIG. Immediately after the fault is cleared the crow-bar protection scheme is deactivated and simultaneously the rotor-side converter optimal controllers are turned on which permits the improvement of the converter ride-through capability and also contribute to enhance the overall power system stability margin. The effectiveness of this proposed methodology was assessed for the DFIG-based plants using a real electrical network, in three different operational conditions.