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In this paper, a new passive islanding detection method for grid-connected inverter-based distributed-generation (DG) systems is proposed. A statistical signal-processing algorithm known as estimation of signal parameters via rotational invariance techniques is used to extract new features from measurements of the voltage and frequency at the point of common coupling as islanding indicators. The new features are defined based on a damped-sinusoid model for power system voltage and frequency waveforms, and include modal initial amplitudes, oscillation frequencies, damping factors, and initial phases. A set of training cases generated on the IEEE 34-bus system was used to train a naïve-Bayes classifier that discriminates islanding and nonislanding events. Cross-validation was used to evaluate the performance of the proposed islanding detection method. The results show that by using the new features extracted from ESPRIT, the classifier is capable of discriminating islanding and nonislanding events with an accuracy close to 100%. [ABSTRACT FROM AUTHOR]

Islanding detection is an essential protection requirement for distribution generation (DG). Antiislanding techniques for inverter-based DG are typically designed and tested on constant RLC loads and, hence, do not take into account frequency-dependent loads. In this paper, a new antiislanding technique, based on simultaneous P-f and Q-V droops, is designed and tested under different islanding conditions considering different load types. The behavior of frequency-dependent static loads during islanding operation is discussed. The developed antiislanding technique is designed to fully address the critical islanding cases with frequency-dependent static loads and RLC-based loads. The performance of the proposed method is tested to accommodate load switching disturbances and grid voltage distortions. Theoretical investigation coupled with intensive simulation results using the Matlab/Simulink software is presented to validate the performance of the proposed antiislanding technique. Unlike previously proposed methods, the results show that the proposed islanding detection method is robust to frequency-dependent loads and system disturbances. [ABSTRACT FROM AUTHOR]

Sandia frequency shift (SFS) falls under the active islanding detection methods that rely on frequency drift to detect an islanding condition for inverter-based distributed generation. Active islanding detection methods are commonly tested on constant RLC loads where the load's active power is directly proportional to the square of voltage and is independent on the system frequency. Since the SFS method relies primarily on frequency to detect islanding, the load's active power frequency dependence could have an impact on its performance and the nondetection zone (NDZ). In this paper, the impact of the load's active power frequency dependence on the performance of the SFS method, during an islanding condition, is analyzed. A NDZ model that takes into account the load's frequency dependence parameter is derived mathematically and validated through digital simulation. The results show that the load's frequency dependence has a significant impact on the NDZ of the SFS method and thus is an important factor to consider when designing and testing this method. [ABSTRACT FROM AUTHOR]

Although active islanding detection techniques have smaller nondetection zones than passive techniques, active methods could degrade the system power quality and are not as simple and easy to implement as passive methods. The islanding detection strategy, proposed in this paper, combines the advantages of both active and passive islanding detection methods. The distributed-generation (DG) interface was designed so that the DG maintains stable operation while being grid connected and loses its stability once islanded. Thus, the over/undervoltage and over/underfrequency protection method would be sufficient to detect islanding. The main advantage of the proposed technique is that it relies on a simple approach for islanding detection and has negligible nondetection zone. The system was simulated on PSCAD/EMTDC and simulation results are presented to highlight the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

In previous literature, constant RLC loads were assumed to impose, on the islanding detection method, the hardest detectable case. For this reason, distributed-generation (DG) islanding studies are usually analyzed and performed by using constant RLC loads. In this paper, different types of loads are taken into account by modeling the load's voltage and frequency dependence. The performance of the over/undervoltage and over/underfrequency protection (OVP/UVP and OFP/UFP) method is examined for the different load models and the results are compared with the constant RLC load case. The analysis is conducted on a constant power-controlled DG designed to operate at unity power factor. A generalized formula, for calculating the non-detection zone of the OVP/UVP and OFP/UFP method, is derived in terms of the load's voltage and frequency dependence parameters. The analysis is further extended on a constant current-controlled DG interface. [ABSTRACT FROM AUTHOR]

An active islanding detection technique for an inverter-based distributed generator (DG) is presented. Two control strategies are studied: one in which the DG only supplies active power and one in which the DG supplies both active and reactive power to improve the power factor. The nondetection zone (NDZ) of the over/under voltage and frequency protection (OVP/UVP and OFP/UFP) method for each control strategy is determined. For the presented interface control, it is observed that the NDZ of the OVP/UVP and OFP/UFP is larger when the DG interface is designed to improve the power factor. In order to decrease the NDZ, an islanding detection method is designed that is based on creating a mismatch between the load and DG reactive power, thus forcing the frequency to deviate outside the OFP/UFP limits. It is shown that the proposed islanding detection technique is robust and has a negligible NDZ. [ABSTRACT FROM AUTHOR]

Abstract-The Sandia frequency-shift (SFS) method is one of the active islanding detection methods that possesses small nondetection zones (NDZs). The effectiveness of the SFS depends to a great extent on its design parameters (cf[subo] and k). In this letter, a formula is derived to aid protection engineers to determine the optimal parameter setting for the SFS islanding detection method. It is concluded that the parameter (k) has a significant effect on the NDZ and a modified version of the SFS is proposed that relies only on this parameter. [ABSTRACT FROM AUTHOR]