Islanding Detection Method of Photovoltaic Grid-connected Inverter Based on Negative Sequence Current Injection

Abstract

The invention provides a photovoltaic grid connected inverter island detection method based on negative sequence current injection, belonging to the technical field of power system relay protection and automatic control. According to the method, an inverter is started to inject negative sequence current when a voltage harmonic distortion rate is larger than a fixed value, common connection point voltage unbalanced degree and voltage harmonic distortion rate are detected, when both the common connection point voltage unbalanced degree and the voltage harmonic distortion rate are larger than the respective fixed value and the duration time exceeds a set time, the generation of island is determined, and the rapid detection of the island is realized. According to the method, the setting difficulty of a criterion is reduced, the improvement of the detection speed is facilitated, the interference on a power grid is reduced as much as possible in the condition that the normal operation is ensured, the influence of a power grid asymmetrical fault is avoided, and there is no detection blind area. The simulation verification is carried out in the condition that the island detection is most not facilitated, and an island operation state still can be rapidly and accurately detected according to the method. A good method is provided for the operation withdrawal of a distributed power supply in the island or the turning of power grid connected operation into island operation control mode power system safe operation and the detection.

Description

technical field [0001] The invention relates to a photovoltaic grid-connected inverter island detection method based on negative-sequence current injection, and belongs to the technical field of relay protection and automatic control of power systems. Background technique [0002] With the aggravation of global environmental pollution and the gradual depletion of conventional energy sources, the development and utilization of new energy sources has gradually become a current research hotspot. As one of the important forms of power generation, photovoltaic power generation (Photovoltaic, PV) still has three main problems: maximum power tracking control, grid-connected technology and islanding detection. The island effect means that when the power grid is interrupted due to electrical failure, misoperation or natural factors, the distributed generation (Distributed Generation, DG) system fails to detect the power outage and breaks away from the grid, and still provides power t...

AI Technical Summary

Problems solved by technology

While operating in an isolated island, on the one hand, the nonlinear loads in the island, such as distribution transformers, will be highly distorted in voltage under the excitation of current harmonics, usually the third harmonic; large loads, making V PCC produce large harmonics

Therefore, in theory, a THD-based islanding detection method can be constructed by selecting an appropriate threshold, but there are difficulties in practical application: it is difficult to select a threshold that can not only ensure grid-connected operation or system failure, but also ensure islanding operation. threshold

And when the load in the island has a strong low-pass characteristic, the input harmonic current required by the nonlinear load matches the inverter output current, and the inverter has high-quality and low-distortion output, this method may also fail.

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