Power Flow Calculation Of Distribution System With Converter

Distributed generation system plays an important role in the development of modern power system. The development of micro-grids is the top priority for future development of power system. Distributed generation has many advantages. However, its grid connection is bound to have effect on large power grid. Power flow calculation is an important means to quantify and analyze the impact.Among all types of distributed generations, some generate direct current which can realize interconnection through power electronic converters. This paper studies power flow calculation with converters.First, on the basis of the characteristics of converters and interconnection commonly used in distributed generation system and the power flow of distribution network, this paper proposes a delta-connected model of three-phase converter suitable for power flow calculation with distributed generation system. This model which can be applied to three-phase unbalanced distribution system has the capacity of capturing unbalanced current in the system. This paper describes calculation of various parameters of converter models, and also studies its applicability in two-phase operating conditions and possible causes of errors.According to the characteristics of distribution network, the paper chooses the implicit Z bus Gauss method for power flow calculation. Implicit Z bus Gauss method has a good ability to handle unbalance power flow, but also has some ability to deal with weak-link system. It can be used in the power flow calculation of distribution network with complex environment. The paper describes the process of applying the implicit Z bus Gauss method, and finishes the program flow chart. Also, this paper improves the traditional implicit Z bus Gauss method on the converter, adopts delta-connected model for the inverter, adds state variable on behalf of the model of inverter to the nodal analysis equation and makes it capable of dealing with AC and DC current simultaneously. This paper studies the improvements of the nodal admittance matrix and the processing method of implicit Z bus Gauss method and forms the program flow chart.Finally, the paper uses several groups of practical examples to test implicit Z bus Gauss method based on delta-connected model of converter and verifies its superiority and feasibility.