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This paper presents a topology for wideband piezoelectric wind energy harvesting and a design optimization method for capturing maximum available energy considering the wind speed distribution model. The proposed device is useful for powering of wireless sensor nodes in smart monitoring applications. The device includes a piezoelectric beam that vibrates due to the interactions between miniaturized permanent magnets (PMs) embedded in a small turbine and a magnet at the tip of the beam. The design method determines the resonance frequency of the beam with respect to the wind speed distribution model. Compared to the conventional wideband topologies that include multiple beams for resonating at different frequencies, the suggested topology uses a single beam and achieves the wideband feature via the arrangement of PMs within the turbine. This feature enhances the power density of the piezoelectric wind energy harvester. The wideband feature of the device is experimentally verified using a device prototype in which the beam resonance occurs at the fan rotational speeds of 155.0, 193.5, 257.9, and 387.0 rad/s. The maximum power density, maximum efficiency, and cut-in wind speed of the device are 0.59 mW/\textcm^3, 24%, and 2.1 m/s, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a robust controller design method for wind turbine generators using the concepts of fractional calculus. It also compares features of fractional order control systems with those of classic integer order controllers. The proposed method uses isodamping feature, which desensitizes the phase-frequency variations about a gain crossover frequency. This increases the robustness of a fractional order control system against uncertainties. In conventional integer order control systems, realization of isodamping feature requires a controller with very high-order transfer function whereas a fractional order system can readily realize this feature in a compact form. The proposed method is applied to a study system consisting of a permanent magnet wind turbine generator. The test system investigates the tracking performance of the control system considering the backlash and aging phenomenon within the dynamic model of the wind turbine generator. The study results based on a time-domain simulation show the superior capabilities of fractional order controller compared with classic controllers in the presence of model uncertainties. It has been shown that the concept of fractional calculus can be used as a promising robust control approach for the future high performance feedback control systems with application to wind energy systems. [ABSTRACT FROM PUBLISHER]

This paper presents an analytical design method for the dc collector systems of offshore wind farms and proposes an improved topology to overcome the limitations of the conventional series–parallel (SP) topology. During a severe failure in the SP topology, bypassing the faulty units imposes overvoltage on fault-free units and leads to the disconnection of the series branch from the collector system. By providing auxiliary connection paths, the suggested topology reduces the overvoltage of the units and hence maintains fault-free units operational following a severe failure. Hence, the efficiency of a wind farm increases considerably upon any failure occurrence. To show the merits of the suggested topology, the captured power during a failure has been calculated and fairly compared with that of the conventional SP topology, considering the excess cost of the suggested topology due to additional connection paths. To investigate the performances of both topologies and their feasibility, a collector system including 12 wind turbine generators has been simulated in time domain software environment. Then, various failure scenarios have been investigated to evaluate the transient behavior of the dc collector system following slight and severe failures. The study results reveal the feasibility of the proposed topology as a promising structure for future dc collector systems. [ABSTRACT FROM PUBLISHER]

This paper introduces a small-signal dynamic model of a fixed-frequency (induction machine based) wind farm connected to an electrical power system. The model represents the system small-signal dynamics in the frequency range of a fraction of Hz to 50/60 Hz. The model includes the dynamics of the wind energy capturing mechanism, the rotating shaft system, the generator electrical system of each wind energy unit, the wind farm collector system, and the utility grid. Based on the proposed model, two performance indices are introduced to i) investigate sensitivity of the system modes, e.g., torsional modes, to the system parameters, and ii) evaluate the system capability to reject electrical and mechanical disturbances, e.g., a wind gust. The application of the model to the analysis of a system with two wind units is presented and the study results are validated based on comparison with the time-domain simulation results obtained in the PSCAD/EMTDC environment. [ABSTRACT FROM AUTHOR]