Active Frequency Offset Island Detection Method Based on Synchronous Rotating Coordinate System

Abstract

The invention provides an island detection method of AFD (active frequency drift) based on a synchronous rotation coordinate system, relating to an island detection method of AFD. The method can be used to meet access requirements of a distributed power supply in a middle or low pressure power distribution network. An island detection algorithm of the AFD based on the synchronous rotation coordinate system is compared with a passive island detection algorithm, and when the load power is matched with the power output of an inverter, detection dead zones do not exist; and the island detection algorithm of the AFD based on the synchronous rotation coordinate system is compared with a traditional AFD algorithm, a distortion position does not generate at a current zero-crossing position, and active currents do not fluctuate, thus DC (direct current) busbar voltages do not fluctuate consequently. The method is applied to the island detection.

Description

technical field [0001] The invention relates to an active frequency offset island detection method. Background technique [0002] Since the photovoltaic grid-connected power generation system is directly connected to the grid, it is necessary to consider the protection measures of the system in the event of a grid failure. When the grid is disconnected, the photovoltaic power generation system continues to supply power to the local load as an isolated power source, which forms an "island effect". . The islanding effect may cause huge damage to electrical loads and grid maintenance personnel. Therefore, the corresponding international standards clearly state that photovoltaic grid-connected inverters must have anti-islanding functions that meet their standards, that is, after the islanding phenomenon occurs, within the specified Within a short period of time, the photovoltaic system can detect the occurrence of the island phenomenon and stop power generation in time to elimi...

AI Technical Summary

Problems solved by technology

Its advantage is that there is no detection blind zone when the grid-connected inverter matches the local load power. However, nonlinear factors in the actual system may cause the total harmonic distortion rate of the access point voltage to be higher than the current standard under normal grid conditions. It may be misjudged when the power grid is normal because the detection threshold is too small

The second is over-undervoltage, over-underfrequency detection method. This method judges whether an island is formed by detecting whether the voltage amplitude and frequency of the access point are abnormal. This method is more practical, but when the grid-connected inverter matches the local load power detection blind zone

While the traditional frequency offset method introduces nonlinear changes in the phase angle (frequency), it also introduces nonlinear distortions into the actual active and reactive currents, and the fluctuations in active currents will cause fluctuations in the DC bus voltage.

Images