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In order to reduce costs while maintaining superior performance, this paper presents a new control methodology of a three-phase grid connected photovoltaic system without using the intermediary DC/DC converter. Based on the synchronized nonlinear model of the whole photovoltaic system, two controllers have been proposed for the three-phase inverter in order to ensure the operation of the PV system at the maximum power point with unity power factor and minimum grid disturbance. Grid synchronization has been ensured by a three-phase 2nd order PLL (Phase-Locked Loop). The stability of each controller is demonstrated by means of Lyapunov analysis and evaluated under changing atmospheric conditions using the Matlab/Simulink environment, the simulation results clearly demonstrate the performance provided by each controller. [ABSTRACT FROM AUTHOR]

The most significant drawback of the Doubly Fed Induction Generator (DFIG) is its susceptibility to grid fault due to its stator windings being directly connected to the grid. The stator and rotor of the DFIG are electromagnetically coupled, therefore, the resulting stator current surge during low voltage dip provokes inrush current at the delicate back-to-back converters and an overcharge of the DC-link capacitor. In this paper, a robust nonlinear controller, under the context of Lyapunov stability theory, is first employed to control the Rotor and Grid Side Power Converters under normal grid conditions. Under grid fault, the nonlinear controller is then coupled with Active crowbar and DC chopper protection schemes to ameliorate the performance of the DFIG system to ride through fault. Simulation of a 1.5MW wound rotor induction generator under MATLAB/SIMULINK is carried out using the PI-controller (PIC) and Adaptive Backstepping Controller (ABC). Analysis and comparisons are made for different operating scenarios: speed variation, grid fault, grid fault with protection schemes activated. [ABSTRACT FROM AUTHOR]

This paper presents the analysis, the model and the advanced control strategy of a photovoltaic system connected to a three phase grid and a nonlinear load. The model is based on electrical equations of the system and the controller is realized by using instantaneous reactive power theory, dq transformation and it applies the sliding mode technique in order to extract the maximum power produced by the Photovoltaic array, to control the power flow between Photovoltaic generator PVG and the grid, and to compensate the reactive power and harmonic components caused by nonlinear load. Simulation results demonstrate the performance of this controller. So, the Maximum Power Point Tracking MPPT is realized with high precision and Unity Power Factor is achieved under complex conditions: climatic changes, system's perturbation and different kind of load. Moreover, the robustness of this controller represents a better advantage compared to other strategies developed for the studied topology of the photovoltaic system. [ABSTRACT FROM AUTHOR]

We address in this paper the control of a three phase single stage grid connected PV system based on Nonlinear Continuous-time Generalized Predictive Control (NCGPC). Without using the intermediate DC/DC converter, the three-phase inverter must operate the photovoltaic system at its maximum power with a unit power factor. The NCGPC controller is based on a synchronized nonlinear model of the PV system. Grid synchronization is provided by a three-phase PLL (Phase-Locked Loop). The closed-loop stability is ensured by the convergence of the outputtracking errors to zero. The performance of the proposed control strategy is evaluated using rapid changes in atmospheric conditions, acting on the PV system, in MATLAB/SIMULINK environment. Obtained results demonstrate the high performance of the proposed control scheme. [ABSTRACT FROM AUTHOR]

The development of photovoltaic systems has increased due to the high demand for clean and green energy. Used worldwide for distributed power generation, the photovoltaic power must not only be maximized, but also adapted to the global standards on harmonic emissions limits. Therefore, tracking the Maximum Power Point and filtering harmonics became necessary. A three-phase grid-connected Photovoltaic system consisting of a photovoltaic (PV) array, a boost converter and a three-phase PWM inverter coupled through a low-pass filter to the electrical grid is studied in this paper. Two new control designs are developed to maximize power in the side of PV panels and to impose a unity power factor in the side of the grid, the first for the three-phase grid-connected systems with an L-filter and the second for the same systems with an LCL-filter. Both controls are analyzed and compared in details and their stability is demonstrated using Lyapunov analysis. The theoretical analysis and simulation results clearly illustrate that the proposed controllers have achieved the objectives. In order to demonstrate the good performance of the LCL-filter in minimizing the harmonics produced by the inverter, a comparison between the frequency responses of the injected currents using the LCL-filter and the L-filter is carried out. [ABSTRACT FROM AUTHOR]