A new topology was recently developed to drive generators, aiming to avoid power electronic devices directly connected to the grid, and making possible the hybridization of the wind power with other sources. The system is composed by an induction machine with rotor in squirrel cage, and a rotating armature endowed with a three-phase winding that may be fed by a secondary source. The previous purpose was to convert a variable velocity imposed by the wind turbine to the armature in a constant velocity to be developed by the cage rotor, driving a shaft of synchronous generator. This article proposes the use of an induction generator instead of a synchronous one in order to explore the maximum available wind energy (MPPT). The simulation results show that the proposed topology is viable and supports both variations in wind speed and disturbances in power grid.

The power quality analysis is an essential issue in the integration of distributed energy resources to the grid. Recent standards regulate the harmonics disturbances due to the increasing penetration of intermittent energy sources interconnected with the grid employing power converters. This paper aims to analyze the power quality of an interconnected wind turbine system based on a Squirrel Cage Induction Generator (SCIG) driven by an Electromagnetic Frequency Regulator (EFR). The steady state of the EFR harmonic model is developed in the stationary frame based on the conventional induction generator modeling, which allows the study of the harmonic disturbances in the electrical and mechanical variables due to the PWM inverter of the EFR’s armature voltage. There is no electrical connection between the EFR and SCIG, and the results show that the inherent system inertia contributes to the mitigation of the harmonic content at the grid side generated by the switching. In addition to the steady-state results, the Total Rated Distortion (TRD), which considers the harmonics and interharmonics components, was computed and presented a good performance compared to the IEEE 1547 standard and real data extracted of a single Doubly Fed Induction Generator (DFIG). Finally, the harmonic performance of the proposed system was evaluated considering the impact of the equivalent Thevenin impedance of the grid at the Point of Common Coupling (PCC).

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The major objective of the investigation reported in this article is to demonstrate the feasibility of controlling a Doubly Fed Induction Generator actuating directly on the rotor voltage produced by the Rotor Side Converter, as its reference value may be determined analytically, after definition of the control objective. Two usual objectives are here considered: maximum power extraction from wind (MPPT) and stator reactive power equal to zero. This last objective defines the reference slip to be considered in the formulation of developed power that, jointly with the reactive power equation, forms the system to calculate the rotor reference voltages. The process is completed by specifying the desired dynamical response. Thus, the angular velocity of the rotor should quickly reach its reference value, which requires maximal power acceleration at the beginning, but respects the restriction that no overshoot should be allowed. This is achieved by means of a constrained optimization process solved in real time. Following recent trends, only measurements obtained from stator (voltages and currents) sensors are used. This way, angular velocity and rotor currents are estimated in real time. An algorithm for inductance estimation is also included, which prevents deviations of nominal values that could lead to false reference voltages.

Eventually, limit violations may occur during power systems operation, such as: overloads in transmission lines and power transformers, voltages at buses outside admissible range, etc. Thus, it is important to create ways to maintain the supply of electrical energy even in contingency operation situations, with fast and lowcost measures, keeping load restriction as the last control action. Corrective Switching is a technique capable of controlling the power flow in meshed networks by changing the network topology. The main advantage of this control tool is that it does not involve additional costs, since its implementation depends on maneuvers of elements already present in the network. In previous works, several techniques and methodologies were developed to reduce the computational effort needed to implement the technique, aiming its application in real-time operation. This work presents a new linear methodology to simulate overloads rerouting without changing the admittance matrix, avoiding extra computational effort for new factorization. Furthermore, the parameters calculated by linearization are able to build a relief function to identify switching variants capable to reconfigure the network in real-time through the technique of Corrective Switching. Resumo: Eventualmente, podem ocorrer violações de limites durante a operação de sistemas elétricos, tais como: sobrecargas nas linhas de transmissão e transformadores de potência, tensões nos barramentos fora da faixa admissível, etc. Dessa forma, é importante desenvolver técnicas para manter o fornecimento de energia elétrica mesmo em situações de operação em contingência, com medidas rápidas e de baixo custo, mantendo a restrição de carga como último recurso. A técnica de Chaveamentos Corretivos é capaz de controlar o fluxo de potência em redes malhadas, alterando a topologia da rede. A principal vantagem desta técnica é que não envolve custos adicionais, uma vez que a sua implementação depende de manobras em equipamentos já presentes na rede. Em trabalhos anteriores, foram desenvolvidas várias técnicas e metodologias para reduzir o esforço computacional necessário à implementação da técnica, visando a sua aplicação em tempo real. Este trabalho apresenta uma nova metodologia linear para simular o redirecionamento de sobrecargas sem alterar a matriz de admitâncias, evitando um esforço computacional adicional para a nova fatoração. Além disso, as grandezas calculadas através da linearização são capazes de construir uma função de alívio para identificar variantes de chaveamento capazes de reconfigurar a rede em tempo real através da técnica de Chaveamentos Corretivos.