Power Flow Algorithm Analysis For AC/DC Hybrid System

In recent years, distributed generation which used solar and wind to generate electricity have received more and more attention because of their advantages of cleanliness and renewable. But the large scale application of distributed generation makes power output diversity, AC/DC hybrid power system can meet distributed generation grid-connection of the AC and DC form Simultaneously. And it is more advantageous to the application of distributed generation. But compared with the flow calculation method for AC system which is already very mature, the flow calculation method for AC/DC hybrid system has not been developed the same level.Therefore, this paper is aimed at researching AC/DC hybrid system power flow calculation.Firstly, this paper introduces a mathematical model and the common method of calculation which were used in the flow calculation for AC/DC transmission systems.The first is the unified iterative method and the other is named the alternate iteration method. Then a new power flow calculation method is proposed for AC/DC micro-grid. This method is based on alternating iteration theory, and it is adopted to AC/DC microgrid to solve the AC equation and the DC equation respectively by using the forward-backward sweep method. When solving the DC system equations,the AC system is equivalent to a balanced node, and the node voltage is maintained constant through adjusting the size of the injection power. When calculating the flow distribution for AC system, the DC system is equivalent to a load that the active power and reactive power are known. The universal program which is suitable for AC/DC microgrid power flow calculation is compiled in Matlab software, and the simulation calculation is conducted by using the test system of IEEE33 node as the example to verify the feasibility of the algorithm. The simulation results show that the method can accurately calculate the flow distribution of AC/DC microgrid. And the computational efficiency is improved when the calculation precision is same. Thesimulation for AC/DC microgrid which is connected to distributed generation with different type, different type permeability and different type layout is carried. This paper provides a comprehensive analysis about the distributed generation effect for AC/DC microgrid, included power distribution, power loss, node voltage and the number of iterations, and gets the influence law of different distributed generation to the microgrid, and lays a theoretical foundation for the further research on AC/DC microgrid.