Abstract:

Affected by the control strategy of photovoltaic inverters, the photovoltaic station has weak-feedback and current-phase-controlled characteristics. As a result, the measured impedance of the distance protection on the photovoltaic side of the transmission line cannot correctly reflect the location of the fault, and the ability to withstand fault resistance variations is significantly reduced. First, the solution equations of the line short-circuit impedance are derived according to the fault component sequence network diagram of the transmission line system. At the same time, the traditional low-voltage-ride-through (LVRT) control strategy is changed based on the superconducting magnetic energy storage (SMES) connected to the DC bus of the photovoltaic station. The unknowns in the equations are eliminated by the control and protection coordination, and then the line short-circuit impedance is solved. Finally, the distance protection scheme for outgoing line of photovoltaic station based on SMES is proposed. Compared with the existing methods for deriving the line short-circuit impedance, there is no approximate calculation in the method. As a result, the accuracy of the calculation is greatly improved. In addition, compared with other control and protection coordination schemes, while ensuring the reliable operation of the distance protection, the scheme also takes into account the reactive power support for the power grid during the fault period. Instead of being weakened, the LVRT capability is even enhanced.

Key words: photovoltaic station, transmission line, control strategy, distance protection, superconducting magnetic energy storage