Research On AC/DC Power Flow Algorithm Considering DC Control Modes Transformation

Compared to traditional AC transmission, HVDC(High Voltage Direct Current Transmission)has complete superiority in the aspects of asynchronous networking, distance power transmission and fast power control etc. With the development of economy and the construction of power network, HVDC is used more and more far-ranging in electric power system. Power flow calculation is the most basic calculation in power system analysis; it is the basis of transient stability, voltage stability and other analysis calculation etc. Due to DC system has many kinds of controlling modes, which requires us to consider the control function of DC system in Power flow calculation of AC/DC power system, so it becomes very important to research and analyze power flow calculation of AC/DC power systemBy analyzing HVDC system model, on the basis of the simultaneous algorithm of power flow calculation of AC/DC power system, a mathematical model of power flow calculation was constructed for two-terminal HVDC transmission system. Combined with the characteristics of mathematical model, in power flow calculation, consider tap adjustment and discrete adjust of converter transformer. And in allusion to the reactive power control problems of DC converter station, through the analysis of cutting control rule of the reactive power compensation device in converter station, to formulate an adjustment strategy of reactive power compensation in AC/DC power flow calculation, and finally to consider combining it with converter transformer tap adjustment into the process of AC/DC power flow calculation. With the power flow program compiled by Matlab software and adjustment strategy of examples testify is effective.The operation characteristic of HVDC in typical control modes is regarded as the research object. The changing rule of DC system parameter and the transforming condition of operation modes have been analyzed when operating condition is changed. And a kind of AC/DC power flow calculation method based on the transition of state is put forward. The method is based on the operational characteristics of DC system and decomposes the changes DC system into a number of operational states. In power flow calculation to reflect the control function of converter transformer tap and the conversion of the operation modes of DC system in the form of state transition. According to the convergence results of the power flow, through judging the conversional logic to realize the conversion among different states, and to complete the power flow solution though the independent power flow subprograms called by main program and standing for different states. The power flow program according to the method has clear structure and distinct levels. The results of emulational calculation also show that the method to calculate has high reliability and good convergency. The results of power flow calculation correspond to control laws of DC system...