This paper presents an improved Maximum Power Point Tracking algorithm for Wind Energy Conversion Systems. The proposed method significantly reduces the turbine mechanical stress with regard to conventional techniques, so that both the maintenance needs and the Medium Time Between Failures are expected to be improved. To achieve these objectives, a sensorless speed control loop receives its reference signal from a modified Perturb&Observe algorithm, in which the typical steps on the reference speed have been substituted by a fixed and well-defined slope ramp signal. As a result, it is achieved a soft dynamic response of both the torque and the speed of the wind turbine, so that the whole system suffers from a lower mechanical stress than with conventional P&O techniques. The proposed method has been applied to a wind turbine based on a Permanent Magnet Synchronous Generator operating at variable speed, which is connected to the distribution grid by means of a back to back converter.

Abstract-This paper presents a new active anti-islanding detection method for distributed power generation systems. This method is based on introducing a disturbance at the inverter output and observing the behaviour of the voltage at the point of common coupling (PCC), which depends on the impedance connected to the PCC in an islanding situation. The islanding detection is based on the Goertzel algorithm.

ElsevierCarranza Castillo, O.; Figueres Amorós, E.; Garcerá Sanfeliú, G.; González Medina, R. (2013). Analysis of the control structure of wind energy generation systems based on a permanent magnet synchronous generator. Applied Energy. 103:522-538. doi:10.1016Energy. 103:522-538. doi:10. /j.apenergy.2012 Analysis of the control structure of a wind generation system based on permanent magnet synchronous generator AbstractThis paper presents the analysis of the two control structures used in wind generation systems with permanent magnet synchronous generators, variable speed and fixed pitch, to determine which structure is most appropriate for implementation. These control structures are speed control and torque control. The analysis considers all the elements of wind power generation system, with greater emphasis on the model of the turbine where mechanical torque is considered as a system variable and not as in other studies where it is considered as internal disturbance in the system. The analysis is developed so that the control structure is independent of AC/DC converter that is used in the system. From the analysis is obtained that the speed control can be stable using classical control techniques because it is a nonminimum phase system and the torque control is unstable because it has poles and zeros in the right half plane, very low frequency and very close to each other, so it is very difficult to control using classical control theory. In the evaluation of the speed control structure, the AC/DC converter is Three-phase rectifier Boost in Discontinuous Conduction Mode with an input filter and a Peak Current Control and to avoid the need of mechanical sensors, a Linear Kalman Filter has been chosen to estimate the generator speed.

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This paper presents a comparative study of several speed estimators to implement a sensorless speed control loop in Wind Energy Generation Systems driven by power factor correction threephase boost rectifiers. This rectifier topology reduces the low frequency harmonics contents of the generator currents and, consequently, the generator power factor approaches unity whereas undesired vibrations of the mechanical system decrease. For implementation of the speed estimators, the compared techniques start from the measurement of electrical variables like currents and voltages, which contain low frequency harmonics of the fundamental frequency of the wind generator, as well as switching frequency components due to the boost rectifier. In this noisy environment it has been analyzed the performance of the following estimation techniques: Synchronous Reference Frame Phase Locked Loop, speed reconstruction by measuring the dc current and voltage of the rectifier and speed estimation by means of both an Extended Kalman Filter and a Linear Kalman Filter.

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This paper encompasses a comparative study of techniques for position and speed estimation applied to permanent magnet synchronous generators (PMSG), connected to the distribution grid by means of a back to back converter. In the context of low and medium power wind energy conversion systems, the robustness of the sensorless techniques are studied taking into account the tolerance of the PMSG parameters.

This paper presents a Peak Current Mode Control scheme of a Boost Rectifier with Low Distortion of the Input Current for Wind Power Systems based on Permanent Magnet Synchronous Generators with variable speed operation. The Three-Phase Boost Rectifier is operated in Discontinuous Conduction Mode (DCM), and power factor correction techniques are applied. It is shown that the DCM operation significantly reduces the Total Harmonic Distortion of the currents in the Permanent Magnet Synchronous Generator, increasing the Power Factor of the system, so that the vibrations and mechanical stress of the generator are minimized. The characteristics of the DCM Boost rectifier are studied considering: 1) The series resistance of the inductors; 2) The modeling and adjustment of peak current mode control yielding a stable loop; 3) The design of an input filter that reduces the switching noise in the currents of the generator.