Distance protection of transmission lines emanating from photovoltaic power plants based on superconducting magnetic energy storage

Due to influences of a control strategy reliant on photovoltaic(PV) inverters, weak feedback of PV power plants and controlled characteristics of current phases make the measured impedance of PV-side distance protection of outgoing transmission lines unable to reflect the location of faults. In this paper, the solution equations of the line short-circuit impedance are accurately derived according to the fault component sequence network diagram of the transmission line. Based on the superconducting magnetic energy storage (SMES) connected to the DC bus of the photovoltaic station, the traditional low-voltage-ride-through(LVRT) control strategy is changed. The unknowns in the equations are eliminated by the control and protection coordination, and then the short-circuit impedance is solved. Compared with the existing methods, there is no approximate calculation in this method, and the accuracy of the calculation is greatly improved. In addition, while reasonably solving the unreliable action of distance protection, it also takes into account the reactive power support of the photovoltaic station for the power grid during the fault period. Instead of being weakened, the LVRT capability is even enhanced.