Impedance measurement islanding detection method for DC power system with multiple photovoltaic power sources connected to the grid

Abstract

The invention belongs to the technical field of power system analysis, in particular to an island detection method for impedance measurement of a DC power system with multi-photovoltaic power supply and a grid, which comprises the following steps of: using an intermittent blocking DC / DC converter sub module to inject high-frequency harmonic disturbances with specific frequencies into the DC systemat a fixed time interval. PCC point voltage and current signals are collected in the time period of harmonic injection, the information of injection frequency is extracted by Fourier algorithm, and the harmonic reactance is calculated and measured. The island is judged according to the change of reactance amplitude. The high-frequency reactance is selected as the characteristic quantity to amplify the characteristic difference before and after island while reducing the effect of DC load variation on the protective action threshold. The effect of low duty cycle intermittent injection on powerquality is reduced. The method is suitable for DC power systems connected with single-machine or multi-machine photovoltaic power supply, adding injection equipment is not needed, the method has little influence on power quality, and can quickly and accurately detect the phenomenon of island operation.

Description

technical field [0001] The invention belongs to the technical field of power system analysis, and in particular relates to a harmonic impedance measurement type islanding detection method suitable for a DC power system in which multiple photovoltaic power sources are connected to the grid. Background technique [0002] In recent years, distributed photovoltaic power generation has developed rapidly. In 2017, the capacity of new distributed photovoltaic power generation units was about 19.4GW, a year-on-year increase of 462%. With the increasing number of DC loads such as household appliances, uninterruptible power supplies, rechargeable vehicles, and DC motors, directly distributing the energy output by photovoltaic power supplies to DC loads can avoid power loss in the AC-DC conversion link and improve the efficiency of power utilization. Therefore, the DC power system has become a new hotspot of research at home and abroad. In the PV DC grid, unplanned island operation wi...

AI Technical Summary

Problems solved by technology

However, in the DC power grid with multiple machines connected to the grid, due to the limitation of electrical parameters, the synchronization of disturbances injected by different DC / DC converters is difficult to guarantee. Scattered low-intensity disturbances will slow down the detection speed and even cause detection failures.

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