Suppression Strategy for Fault Current of Flexible Multi-state Switch in Distribution Network Fault State

The fault current may be injected into the short-circuit point by the Flexible Multi-State Switch (FMSS) during the AC faults of the distribution network. In order to suppress this, this paper firstly uses the instantaneous symmetrical component decomposition method based on the decoupled dual synchronous reference frame to analyze the distribution network during an asymmetric fault, and the negative sequence and zero sequence currents appearing on the FMSS fault side port are suppressed. Secondly, the system vector diagrams of the FMSS are derived under different operating conditions when the three-phase short-circuit ground fault occurs in the distribution network. The symmetrical component method is used to establish a composite sequence network with the FMSS distribution network faults, the fault current of distribution network in symmetrical fault and asymmetric fault is analyzed, and a reactive power droop control strategy with voltage dead zone is proposed to effectively suppress the fault current injected into the short-circuit point of the FMSS under the fault state. At the same time, the controller modifies the reactive power outer loop control command value according to the change of bus voltage amplitude of distribution network, uses FMSS to provide reactive power support to the distribution network, and improve the quality of the feeder voltage. The MATLAB/SIMULINK is used to build a three-terminal FMSS model for simulation analysis, which verifies the effectiveness and correctness of the proposed method. © 2021, Power System Technology Press. All right reserved.