Islanding detection method and system
The present invention provides an islanding detection method and an islanding detection system. The method includes: acquiring a voltage signal at a grid-connected node of a power generation system, and extracting phase information of the voltage signal; constructing a slip-mode frequency shift islanding detection curve in the form of a quadratic function according to the phase information; and generating a disturbance signal according to the slip-mode frequency shift islanding detection curve, and sending the disturbance signal to an inverter of the power generation system. The method and system can avoid a non-detection zone, and can perform an inverter islanding detection in a fast and accurate manner under simple control.
1. An islanding detection method, comprising:
acquiring a voltage signal at a grid-connected node of a power generation system, and extracting phase information of the voltage signal;
constructing a slip-mode frequency shift (SMS) islanding detection curve in the form of a quadratic function based on the phase information; and
generating a disturbance signal based on the SMS islanding detection curve, and sending the disturbance signal to an inverter of the power generation system.
2. The method of claim 1 , wherein the SMS islanding detection curve constructed in the form of the quadratic function is as follows:
θ=Δ f ( a|Δf|+b ), − M≦θ≦M
wherein θ is the phase of the disturbance signal, Δf=f−f g , f g is a rated frequency of a power grid, f is the frequency of a currently acquired voltage signal, M is the preset maximum amplitude of the disturbance signal, a and b are preset parameters.
3. The method of claim 2 , wherein a generated disturbance signal is as follows:
(ω t )=ω t+θ
wherein ωt is the extracted phase information, (ωt)′ is the generated disturbance signal, θ is the phase of the disturbance signal.
4. The method of claim 3 , further comprising:
obtaining a voltage peak and a frequency based on the acquired voltage signal and the extracted phase information;
if the voltage peak of the voltage signal at the grid-connected node exceeds a preset voltage range or if the frequency of the voltage signal at the grid-connected node exceeds a preset frequency range, cutting off a connection between the inverter of the power generation system and a local load.
5. The method of claim 2 , wherein f g =50 Hz.
6. The method of claim 5 , further comprising:
obtaining a voltage peak and a frequency based on the acquired voltage signal and the extracted phase information;
if the voltage peak of the voltage signal at the grid-connected node exceeds a preset voltage range or if the frequency of the voltage signal at the grid-connected node exceeds a preset frequency range, cutting off a connection between the inverter of the power generation system and a local load.
7. The method of claim 2 , further comprising:
obtaining a voltage peak and a frequency based on the acquired voltage signal and the extracted phase information;
if the voltage peak of the voltage signal at the grid-connected node exceeds a preset voltage range or if the frequency of the voltage signal at the grid-connected node exceeds a preset frequency range, cutting off a connection between the inverter of the power generation system and a local load.
8. The method of claim 1 , further comprising:
obtaining a voltage peak and a frequency based on the acquired voltage signal and the extracted phase information;
if the voltage peak of the voltage signal at the grid-connected node exceeds a preset voltage range or if the frequency of the voltage signal at the grid-connected node exceeds a preset frequency range, cutting off a connection between the inverter of the power generation system and a local load.
9. The method of claim 8 , wherein the preset voltage range is between 0.8V and 1.2V, and the preset frequency range is between 49.5 Hz and 50.5 Hz.
10. An islanding detection system, comprising:
an acquisition module, adapted to acquire a voltage signal at a grid-connected node of a power generation system and to extract phase information of the voltage signal;
an islanding detection module, adapted to construct a slip-mode frequency shift (SMS) islanding detection curve in the form of a quadratic function based on the phase information; and
a drive module, adapted to generate a disturbance signal based on the SMS islanding detection curve, and to send the disturbance signal to an inverter of the power generation system.
11. The system of claim 10 , wherein the SMS islanding detection curve constructed by the islanding detection module in the form of the quadratic function is as follows:
θ=Δ f ( a|Δf|+b ), − M≦θ≦M
wherein θ is the phase of the disturbance signal, Δf=f−f g , f g is a rated frequency of a power grid, f is the frequency of a currently acquired voltage signal, M is the preset maximum amplitude of the disturbance signal, a and b are preset parameters.
12. The system of claim 11 , wherein a disturbance signal generated by the drive module based on the SMS islanding detection curve is as follows:
(ω t )=ω t+θ
wherein ωt is extracted phase information, (ωt)′ is the generated disturbance signal, θ is the phase of the disturbance signal.
13. The system of claim 12 , wherein the islanding detection module is further adapted to make a decision based on a voltage peak and a frequency that are obtained according to the acquired voltage signal and the extracted phase information, and if the voltage peak of the voltage signal at the grid-connected node exceeds a preset voltage range or if the frequency of the voltage signal at the grid-connected node exceeds a preset frequency range, the islanding detection module is further adapted to cut off a connection between the inverter of the power generation system and a local load.
14. The islanding detection system of claim 12 , wherein the acquisition module includes a sensor, a conditioning circuit and a phase-locked loop that are serially connected.
15. The system of claim 11 , wherein the islanding detection module is further adapted to make a decision based on a voltage peak and a frequency that are obtained according to the acquired voltage signal and the extracted phase information, and if the voltage peak of the voltage signal at the grid-connected node exceeds a preset voltage range or if the frequency of the voltage signal at the grid-connected node exceeds a preset frequency range, the islanding detection module is further adapted to cut off a connection between the inverter of the power generation system and a local load.
16. The islanding detection system of claim 11 , wherein the acquisition module includes a sensor, a conditioning circuit and a phase-locked loop that are serially connected.
17. The system of claim 10 , wherein the islanding detection module is further adapted to make a decision based on a voltage peak and a frequency that are obtained according to the acquired voltage signal and the extracted phase information, and if the voltage peak of the voltage signal at the grid-connected node exceeds a preset voltage range or if the frequency of the voltage signal at the grid-connected node exceeds a preset frequency range, the islanding detection module is further adapted to cut off a connection between the inverter of the power generation system and a local load.
18. The islanding detection system of claim 17 , wherein the acquisition module includes a sensor, a conditioning circuit and a phase-locked loop that are serially connected.
19. The islanding detection system of claim 10 , wherein the acquisition module includes a sensor, a conditioning circuit and a phase-locked loop that are serially connected.