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The growing interest in clean and sustainable electric energy pushes toward increasing the interconnection of wind energy conversion systems (WECSs) to utility grids. The designs of the majority of WECSs employ power electronic converters (PECs), which generally have nonlinear and switched characteristics. The characteristics, operation, and control of PECs in WECSs can result in nonconventional voltage–current behaviors during faults. This paper investigates the voltage–current behaviors during faults that occur in grid-connected WECSs. Two types of WECSs are considered in this paper, which are the doubly fed induction generators and permanent magnet generator based WECSs. The voltage–current behaviors are investigated in experimentations for different faults occurring in different parts of the test grid-connected WECSs. [ABSTRACT FROM PUBLISHER]

This paper presents the implementation and performance evaluation of a new digital protection for microgrid systems, The proposed digital protection is based on utilizing the wavelet packet transform (WPT) for extracting the first-level high-frequency subband contents present in the $d$– $q$-axis current components. The utilized WPT is realized by a half-band digital high-pass filter, whose coefficients are determined by the Daubechies $db4$ wavelet basis functions. The $d$– $q$ WPT-based digital protection is implemented for offline and experimental performance evaluation. Offline tests are conducted using data collected from a simulation model of a microgrid located in Fermeuse, NL, Canada. The experimental tests are conducted on a laboratory microgrid system that is constructed as a scaled version of the Fermeuse microgrid. Several transient disturbances occurring in different parts of the test microgrid systems are investigated both offline and in experimentation. Performance results demonstrate significant abilities of the $d$– $q$ WPT-based digital protection for fast, accurate, and reliable detection, classification, and response to different transient disturbances. In all tested faults, the developed digital protection is able to generate a trip signal in less than a quarter cycle based on the 60-Hz system operating frequency. [ABSTRACT FROM PUBLISHER]

Photovoltaic (PV) systems have become a popular type of distributed generation units (DGUs) for small and medium levels of renewable energy generation. When grid connected, these DGUs are designed and operated to deliver electric power to their host grid through power electronic converters. The nonlinear and switched natures, along with the control actions, of these PECs can influence the voltage–current behaviors during faults in grid-connected PV systems. This paper experimentally investigates the voltage–current behaviors during faults occurring in grid-connected PV systems. Results of these investigation show that voltages and currents at the point-of-common-coupling (PCC) experience changes in their magnitudes and harmonic distortions due to faults occurring on both sides of PCC. These results can be incorporated in the improvement of the accuracy and reliability of protective devices used for grid-connected PV systems. [ABSTRACT FROM PUBLISHER]