基于超导磁储能的光伏场站送出线路距离保护

Distance Protection for Outgoing Line of Photovoltaic Station Based on Superconducting Magnetic Energy Storage

受光伏逆变器控制策略影响,光伏场站呈弱馈性和电流相位受控特性,导致送出线路光伏侧距离保护的测量阻抗无法正确反映故障所在位置,抗过渡电阻能力大大下降。根据送出线路系统的故障分量序网图推导出线路短路阻抗的求解方程组,同时基于光伏场站直流母线接入的超导磁储能(superconducting magnetic energy storage,SMES)改变传统的低电压穿越控制策略,通过控保协同消除方程组中的未知量,进而对线路短路阻抗进行求解,提出了基于超导磁储能的光伏场站送出线路距离保护方案。与现有推导线路短路阻抗的方法相比,该方法不存在近似计算,计算准确度得到很大提升;且相比于其他控保协同方案,该方案在保证距离保护可靠动作的同时也兼顾了故障期间光伏场站对于电网的无功支撑,其低电压穿越能力不仅没有被削弱,反而得到一定的提升。

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.