Research on suppression strategy of DC Side Voltage Fluctuation of Flexible Multi-state Switching

Flexible multi-state switch (FMSS) is a new feeder interconnection device composed of multi-terminal common DC bus converters. When the power grid voltage is unbalanced, it will cause the fluctuation of DC bus voltage, which will seriously affect the stability of the whole system. The common single-sequence double-closed-loop control method cannot control the negative sequence current. To solve this problem, a positive and negative sequence dynamic model of the grid-connected converter in the forward dq + coordinate system was established, the voltage fluctuation of the DC side was analyzed, and a negative sequence outer loop controller was designed to directly control the voltage of the DC bus with the double frequency doubling, while the inner loop used the double-sequence decoupling control to sequence the current. In addition, in order to improve the robustness and anti-interference ability of the control system, RBF neural network is used to obtain the gradient information online identification, and the parameters of PI controller are adaptive adjusted online based on the gradient information, and the original control system is improved. Finally, the simulation model is built in MATLAB/Simulink, and the simulation results show that the method can effectively suppress the DC side voltage fluctuation.