Zhihong Ye

Evaluation of anti-islanding schemes based on nondetection zone concept

This paper proposes a nondetection zone (NDZ) as a performance index to evaluate different anti-islanding schemes. The NDZ for three basic passive anti-islanding schemes: under/over voltage, under/over frequency, and phase jump are derived analytically and validated by simulation. Based on the NDZ, not only can the dominant factors that influence anti-islanding protection be identified, it may also support definition of optimal combined schemes that lead to a reduced NDZ. The methodology presented in the paper can be extended to the evaluation of other anti-islanding schemes.

Investigation of anti-islanding protection of power converter based distributed generators using frequency domain analysis

The anti-islanding algorithm proposed by the Sandia national laboratories is analyzed in this study because this scheme, also known as the Sandia scheme, is considered to be effective in detecting islanding of distributed generation systems. Previously, other than heuristic approaches, there has not been any quantitative analysis for tuning the control gains of the algorithm based on the power rating and bandwidth of the distributed generation (DG) power converter. The paper interprets the components of the algorithm that affect the voltage magnitude and frequency into block diagrams that can be linearized and studied using continuous time approximations. This paper uses a frequency domain approach to analyze the range for the gains required by anti-islanding algorithm to effectively determine the disconnection of the mains grid within an acceptable time duration. The analysis provides guidelines for using Sandias national laboratory schemes under different application conditions. The results are validated using detailed time domain DG and power system simulations.

Investigation of antiislanding protection of power converter based distributed generators using frequency domain analysis

Islanding of a grid connected distributed generation (DG) unit occurs when a section of the utility system containing such generators is disconnected from the main utility, but the independent DGs continue to energize the utility lines in the isolated section (termed as an island). Unintended islanding is a concern, primarily because it poses a hazard to utility and customer equipment, maintenance personnel and the general public. The algorithm proposed by the Sandia National Laboratories is analyzed in this study because it is considered to be effective in detecting the formation of such islands. Previously, there has not been any quantitative analysis for tuning the control gains of the algorithm based on the rating and bandwidth of the DG power converter. The paper interprets the components of the algorithm that affect the voltage magnitude and frequency into block diagrams that can be linearized and studied using continuous time approximations. The model represents DG operation while connected or disconnected from the main utility. This paper uses frequency domain approach to analyze the range for the gains required by antiislanding algorithm to effectively determine the disconnection of the mains grid within an acceptable time duration. The effect of variation of DGs operating power level is studied and demonstrated how the gains of the algorithm can be set to be effective for a wide power range. The results are validated using detailed time domain DG and power system simulations.

Positive-Feedback-Based Active Anti-Islanding Schemes for Inverter-Based Distributed Generators: Basic Principle, Design Guideline and Performance Analysis

The positive-feedback-based anti-islanding schemes invented by the authors are highly effective in preventing islanding without causing any degradation in power quality. This paper presents the basic principles of these schemes and their design guidelines. Moreover, their performance is investigated for inverter-based distributed generators (DGs). The parametric study reveals the factors significantly influencing the performance of these schemes. The simulation results demonstrate the effectiveness of these schemes.