Method for actively detecting frequency drift islands

Abstract

The invention relates to a method for actively detecting frequency drift islands. The method is implemented for controlling a grid-connected inverter in a distributed power generation system. The method includes steps of detecting current grid frequency f, judging whether conditions are met or not, shutting down the grid-connected inverter immediately in a protective manner if the conditions are met, and judging a current reactive power sign or a current power factor of the inverter if the conditions are not met; exerting frequency disturbance in a positive direction for output voltage of the inverter if the current reactive power sign of the inverter is positive; exerting frequency disturbance in a negative direction for the output voltage of the inverter if the current reactive power sign of the inverter is negative; exerting frequency disturbance in an optional direction for the output voltage of the inverter if the current reactive power of the inverter is zero; and enabling the grid-connected inverter to generate new output voltage according to computed f<i+1>. The method has the advantages that matching among frequency drift and load characteristics can be guaranteed, output current waveform distortion can be prevented, and the power quality is guaranteed.

Description

technical field [0001] The invention relates to an operation control technology of a grid-connected inverter in a distributed power generation system, in particular to an active frequency offset islanding detection method. Background technique [0002] In the distributed power generation system, the "island effect" means that after the public power grid is out of power, due to the existence of distributed power generation (connected to the grid and transmitting electric energy), some lines in the power outage area of ​​the power grid are still charged and the loads in the outage area are still charged. Continue to supply power, forming an isolated island powered independently by distributed power sources. [0003] In the island state, the power company loses control of the line voltage and frequency in the island area, which will bring a series of potential safety hazards and accident disputes: [0004] 1) Personal safety. [0005] After the power grid is out of power, ele...

AI Technical Summary

Problems solved by technology

[0005] After the power grid is out of power, electrical maintenance personnel enter the power outage area to work. If the distributed power generation system continues to supply power at this time, the workers may accidentally touch the live body, causing personal injury or death

[0006] 2) Equipment damage

[0009] (3) When the power company loses control of voltage and frequency during island operation, it may be difficult to determine the relevant responsibilities due to the abnormal output voltage and frequency of the photovoltaic power generation system

[0012] First, the disturbance judgment conditions of these methods have nothing to do with the load conditions. When the load is a non-resistive load, the disturbance direction may be opposite to the load frequency characteristic after the islanding occurs, offsetting the effect of the actual islanding detection;

[0013] The second is that some methods are effective when a single grid-connected inverter is running, but when multiple inverters are running in parallel, the offset direction of the disturbance of multiple inverters may be opposite, which will offset the effect of the actual island detection ;

[0014] The third is that some methods are basically based on the premise that the system operates at a unit power factor, and disturb the related variables of the inverter.

The problems of this method are: 1. The system is required to operate at a unit power factor, and misjudgment will occur in the case of reactive power compensation; 2. Due to the change of the output current frequency, the current waveform is also distorted, which affects the power quality.