This paper presents a proposal to control active and reactive power of small wind turbines employing permanent magnet synchronous generator (PMSG) in distributed generation systems. A three-phase AC-DC-AC electric power converter is employed to process the energy generated by the PMSG. Direct power control is applied to generate the PWM signals at the DC-DC converter, which allows controlling the active power through an adaptive PI controller by means of a gain scheduling adaptation mechanism. A voltage source inverter (VSI) is utilized to connect the machine to the electrical grid following stability and low harmonic distortion requirements. In addition, VSI has the role of controlling the reactive power exchanged with the grid. Simulation results have shown that the proposed system is reliable, leading to good results for a small-scale wind turbine. Moreover, direct power control is a strong and low-cost alternative for maximum power point tracking application. The reactive power control, in turns, adds a suitable extra degree of freedom to the system, which can be used to reduce the impact of voltage fluctuations and short-circuit on the grid.

The central inverter topology presents some advantages such as simplicity, low cost and high conversion efficiency, being the first option for interfacing photovoltaic mini-generation, whose shading and panel orientation studies are evaluated in the project planning phase. When it uses only one power converter, its control structures must ensure synchronization with the grid, tracking the maximum power generation point, appropriate power quality indices, and control of the active and reactive power injected into the grid. This work develops and contributes to mathematical models, the principles of formation of control structures, the decoupling process of the control loops, the treatment of nonlinearities, and the tuning of the controllers of a single-stage photovoltaic system that is integrated into the electrical grid through a three-phase voltage source inverter. Using the parameters and configurations of an actual inverter installed at the power plant CRESP (Reference Center for Solar Energy of Petrolina), mathematical modeling, implementation, and computational simulations were conducted in the time domain using MatLab^® software (R2021b). The results of the currents injected into the grid, voltages, active powers, and power factor at the connection point with the grid are presented, analyzed, and compared with real measurement data during one day of operation.

This paper presents a comprehensive computational model to represent a variable speed wind energy conversion system (WECS) connected to typical AC systems. The arrangement proposed consists of a modern tendency to use multiple synchronous generators. Besides representing the power components, the paper also takes into account the control strategy so as to provide the adjustment of the aerodynamic power and the voltage at the point of common coupling (PCC). The control targets are focused having in mind the maximization of the primary energy conversion and simultaneously the PCC busbar support so as to attend national standards. As the model is derived from time domain component representations, both transient, dynamic and steady state operation conditions can be fully investigated. These are highlighted in simulation cases followed by discussions

In order to develop a tool that facilitates the understanding of photovoltaic modules simulation, this work presents a methodology for representing these modules using only linear elements. Taking as a starting point the four-parameter representation of a photovoltaic module, a discrete equivalent is obtained based on the Newton-Raphson method for solving nonlinear equations. The characteristic curves, I-V and P-V, obtained with this methodology for a commercial module and its behavior when coupled to an RLC circuit are then presented.

This work evaluated the performance of small-scale photovoltaic systems installed in Petrolina city, Brazil, operating under different meteorological conditions, through real production measurements, electrical quantities, inverter efficiency, also merit indices such as final yield and capacity factor. The measurement data showed the versatility of the inverters under different loading conditions, as well as correct operation in face of phenomena such as anti-islanding and clipping. It was verified that changes in meteorological conditions don’t affect the efficiency, remaining almost always higher than 95%, except for loading levels lower than 5%. The merit indices enabled the comparison between different photovoltaic systems, confirming the high energy potential in the Brazil northeast, regardless of the orientation used for the photovoltaic modules. The comparison between the actual production and the generation projections, revealed that the new irradiation indices, provided by Reference Center for Solar and Wind Energy Sérgio de S. Brito (CRESESB), present better agreement with the real data, allowing more reliable projection for photovoltaic generation.