Integrated AC/DC Systems Power Flow Solution Using Improved Broyden Approach

High Voltage Direct Current (HVDC) technology has advantage in the situation of high-power and long-distance electricity transmission and interlinking of power systems because of its fast power adjustment and reliable operation. HVDC technology will take key role in the implementation of the projects for transmitting power from west to east in the Western China Development Strategy, as well as the project of nationwide interconnection of power grids. At present, the methods of AC system power flow solution have been perfected, but the methods to solve AC/DC systems power flow did not reach the same level because of its complexity. Therefore, this paper makes in depth and meticulous research to power flow solution of AC/DC systems.First of all, this paper outlines the development of HVDC technology, the research of the AC/DC power systems in worldwide and the urgent problems. Then, it introduces a model of the AC-DC converter and the AC/DC systems power flow solution using normal method. The approaches are categorizing into two kinds. The first is the sequential method and the other is named the unified approach. Then, it makes a detailed analysis to the Broyden method and Improved Broyden method which have been used to solve the nonlinear equation effectively in the field of mathematics. They avoid the shortcomings of Newton method that calculates the derivative of the state function in the current iteration point which determines the new direction during each iteration. Consequently, its computational efficiency is more effective. And then, a unified iterative method for AC/DC power flow solution based on the improved Broyden method is proposed and the corresponding power flow program is developed.Finally, a series of tests to the power flow solution using improved Broyden approach are carried out. The results show that the new method has the characteristics of quasi-Newton method and high efficiency. The program based on the improved Broyden method is simple to implement and has strong applicability to different structures and power system operating modes.The new method is an effective approach for solving AC/DC power flow fast and reliably. It has a very important theoretic and practical meaning for the research to the steady operation and the regulation for the AC/DC systems.