基于控制模式平滑切换的离网直流变压器无扰并网策略

抑制离网直流变压器(DCT)并网所产生的冲击电流和电压振荡,可推动柔性直流电网的建设.给出DCT拓扑结构及控制模式,从DCT启动和控制模式切换2个方面来分析并网扰动形成的机理,其主要成因是电容充电和控制器输出信号跳变.针对控制器输出信号跳变的问题,分别提出了DCT控制模式平滑切换策略和光储系统控制模式平滑切换策略,通过控制模式的切换实现DCT控制与系统控制相协调,保证主从控制下的中/低压侧电压控制权归一者所有,并结合软启动方法,给出离网DCT无扰并网策略全过程.基于MATLAB/Simulink建立苏州两端型中/低压直流配电网模型,在不同并网工况仿真中,该策略均能有效抑制并网点的电压振荡和冲击电流,保证系统的稳定运行.

Undisturbed grid-connected strategy of offline DC transformer based on smooth switching of control modes

Suppressing the inrush current and voltage fluctuation caused by offline DCT(DC Transformer) grid-connection can promote the construction of flexible DC grids. The topology of the DCT and its control modes are given. The forming mechanism of the grid-connected disturbance is analyzed from two aspect of DCT start and control mode switching, and the main reasons are the capacitor charging and the output signal jumping in controller. For the problem of output signal jumping in controller, the smooth switching strategy of DCT control modes and the smooth switching strategy of PV(PhotoVoltaic) and battery system control modes are respectively proposed. DCT control is coordinated with system control through the switching of the control modes, ensuring that the control rights of bus voltage in medium-and low-side under the master-slave control are owned by one. Combined with the soft-start method, the whole process of undisturbed grid-connected strategy of offline DCT is given. Finally, Suzhou medium-and low-voltage DC distribution network model is established based on MATLAB/Simulink. In the simulation of different grid-connected conditions, the proposed strategy can effectively suppress the voltage fluctuation and inrush current at the grid-connected point and ensure the stable operation of system.