Abstract: When an asymmetric fault occurs in the power grid,the performance of the power conversion system（PCS）will not meet the requirements,which will affect the reliable operation of the grid-connected system. Aiming at the above problems,a PCS multi-variable cooperative protection strategy is proposed. Based on the flexible control strategy,the proposed strategy considers reactive power support as the primary objective and PCS operational performance as the constraint condition. The unary function of reactive power with respect to the flexible control parameter k and the active power safe operating area are constructed. Furthermore,the range of k values that meet the requirements can be obtained,and then an appropriate k value and a power reference value corresponding to this k value are selected for control according to the requirements of the system. The simulation verifies the effectiveness of the proposed control strategy.Besides,the strategy can provide corresponding reactive power support to the power grid according to the degree of voltage drop,completely utilizing the PCS capacity on the basis of ensuring system security,and PCS can be flexibly controlled within the value range of k obtained.