Control Strategy Based on Second-Order Linear Active Disturbance Rejection for Flexible DC Grids

Aiming at the problem of large fluctuations of instantaneous power and DC side voltage and current caused by asymmetric faults on the AC side of flexible DC grid, and then affecting the stable operation of the system, a station-level control strategy for flexible DC grids based on Linear Active Disturbance Rejection Control (LADRC) is proposed. Based on the second-order LADRC theory, the positive and negative sequence current inner loop controllers are designed, respectively. Finally, a four-terminal flexible DC grid model is built based on PSCAD/EMTDC platform for example analysis. The results show that the proposed control strategy can not only reduce the fluctuation of instantaneous power and DC side voltage and current, but also decrease the adverse effect of negative sequence current on system operation.