An Auxiliary Directional Relay of Distribution Network with Photovoltaic Source Based on Harmonic Energy

The integration of distributed photovoltaic power sources into the distribution network leads to the transformation of the original single-source network into a multi-source network, and the existing overcurrent protection is prone to misoperation under the action of reverse photovoltaic currents. An auxiliary fault directional relay based on harmonic energy is proposed in this paper. Firstly, the fault current output of PV and system power sources are derived separately, and the difference of harmonic output between the two sources during the fault is pointed out. Then, after avoiding part of the attenuated DC time, the sub-mode is extracted using the variational modal decomposition(VMD) method to characterize the current harmonic signal in the required frequency band. Secondly, the signal energy ratio within the protection time window is calculated to reduce the interference of noise and other factors, and the fault direction discrimination results are output. Finally, the correctness of the proposed directional element is verified by simulation. The directional relay does not require communication, does not require voltage quantities, and can identify the source direction of the fault current quickly and reliably.