Power Flow Calculation Of DC Grid With Multiport DC Power Flow Controller

In the DC grid,it is of great significance to install the DC power flow controller to improve the degree of freedom in calculation and control of DC power flow and to ensure the safe and stable operation of the DC grid.With the development of the DC grid,the scale of the DC grid is getting larger and larger and the structure is becoming more and more complex.When a complex DC grid contains multiple ring networks,It is necessary to install multiple DC power flow controllers and coordinate control at the same time on multiple branches.Its high cost and low reliability.In this paper,a multi-port DC power flow controller(MDCPFC)for DC power flow calculation method is proposed for a complex DC power grid.First,this paper analyzes the DC grid and MDCPFC.The evolution and characteristics of DC grid are summarized.The working principles,advantages and disadvantages of three simple two-port DC power flow controllers are analyzed,The topology of MDCPFC with modular multilevel converters is analyzed.The topology of an MDCPFC with modular multi-level converter is analyzed,and its working principle is analyzed from the perspective of the circuit.Then,this paper deduces the method applicable to the calculation of the DC grid power flow.This article analyzes the mathematical model of the DC grid.By comparing the differences in the electrical quantities in the AC and DC grids,based on the AC grid power flow calculation methods,two kinds of power flow calculation methods suitable for DC grids are deduced: the cow pull method and the PQ decomposition method,and take the three-terminal DC power grid as an example to verify the effectiveness of the proposed method.Finally,this paper presents a DC power flow calculation method with multi-port DC power flow controller.The sensitivity analysis method was used to study the influence of MDCPFC on the distribution of power flow in DC power grid.The MDCPFC power flow calculation model was established.In order to solve the problem of increasing the number of nodes when using the conventional power flow calculation method,making the calculation efficiency lower and the algorithm convergence difficult,the change of the DC network after the installation of MDCPFC in this paper is expressed by the injection power correction amount of the node installed at the end of the branch,making the calculation simple.Improve the efficiency of the operation.This paper will install the MDCPFC after the DC network.The changes that occur are expressed by the correction amount of the injection power of the nodes at the end of the installation branch,which makes the calculation simple and improves the calculation efficiency.On this basis,taking Zhoushan five ends of the flexible HVDC project as an example,By comparing the results of thepower flow calculation with the multi-port power flow controller and the calculation results of the PSAT software and the calculation results of the two DC power flow controllers,the control effect of the multi-port DC power flow controller and the effectiveness of the method.