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...

Examples

Embodiment Construction

[0027] The specific algorithm of the active frequency offset islanding detection method of the present invention is as follows:

[0028] Detect the current grid frequency f i , and judge f i > f N +Δf N1 or f i N -Δf N2 , where f N is the rated frequency of the grid, f N2 is the frequency negative offset allowed by the grid, f N1 is the positive offset allowed by the grid;

[0029] If it is, it is considered that an island or grid frequency exceeds the limit, and the grid-connected inverter will immediately protect and shut down;

[0030] If not, judge the current reactive power sign of the inverter or judge the current power factor;

[0031] If the reactive power is positive, apply a frequency disturbance in the positive direction to the output voltage of the inverter, namely f i+1 = f i +Δf, where f i+1 is the frequency that the inverter needs to output voltage next time, Δf is the frequency offset, Δf>0;

[0032] If the reactive power is negative, a frequency d...

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...

Examples

Embodiment Construction

[0027] The specific algorithm of the active frequency offset islanding detection method of the present invention is as follows:

[0028] Detect the current grid frequency f i , and judge f i > f N +Δf N1 or f i N -Δf N2 , where f N is the rated frequency of the grid, f N2 is the frequency negative offset allowed by the grid, f N1 is the positive offset allowed by the grid;

[0029] If it is, it is considered that an island or grid frequency exceeds the limit, and the grid-connected inverter will immediately protect and shut down;

[0030] If not, judge the current reactive power sign of the inverter or judge the current power factor;

[0031] If the reactive power is positive, apply a frequency disturbance in the positive direction to the output voltage of the inverter, namely f i+1 = f i +Δf, where f i+1 is the frequency that the inverter needs to output voltage next time, Δf is the frequency offset, Δf>0;

[0032] If the reactive power is negative, a frequency d...