Research on Voltage Level and Simulation Model of Medium-low Voltage of DC Distribution Network

With the large expansion of urban load,traditional Ac distribution networks are under great pressure, and DC distribution networks provides new ideas for solving these problems.In the field of DC power grids,medium-low voltage DC distribution network has just started and current research is still in the initial stage. This paper discusses the voltage sequence of the DC distribution network, screening the internal and external factors that affect the voltage level firstly, dividing factors hierarchically, formulating a set of DC voltage sequence reference values according to the principle of level multiple secondly, using the fuzzy comprehensive evaluation method to evaluate the reference value reasonably.adding the geometric mean to verify and adding the current voltage range of the DC project to use more finally.All in all,proposed a suitable for DC low voltage distribution network voltage level sequence determination method,and get a set of DC medium and low voltage distribution network recommended value. Combined the AC distribution network topology and the recommended DC distribution network topology,build DC distribution network models on the RT-LAB platform.In this paper,a dc-radiation topology with two voltage levels of 10kV and 400V is established first, taking into account the influence of distributed energy, and centralized on the 10kV bus access. Wind power and access to distributed photovoltaics at 400V busbars. Subsequently, a Shenzhen DC distribution network demonstration project was set up and a +/- 10kV double-end DC distribution network was built.The steady-state operation of the DC distribution network model was established by using power flow calculation and analysis to verify the correctness and rationality of the model. At the same time, after analysis, it was found that the shunt capacitor was grounded with a high resistance to ensure that the zero-sequence current could be rapidly attenuated and the DC-to-electrode voltage would not drop significantly after the fault.