Research On Dynamic Power Flow Algorithm For High Power Deficit

It is an important measure to improve Chinese energy structure that develop the renewable clean energy.Chinses land area is large and the resources are scattered.Wind power resources and hydropower resources are mostly distributed in economically underdeveloped areas,away from the load center.In order to use the renewable energy,it is necessary to develop UHVDC Transmission technology.Nevertheless,with the UHVDC transmission line put into operation,the following single-and-double DC blocking event for both sides of power systems caused a great power deficit.If not handled correctly or quickly,the system is likely to be low-frequency load shedding or crashing.Affected by the accident,the system appeared high power deficit.The dynamic change process of the system power flow is quite different from the steady state.For the rapid and correct handling of high power deficits,it should be clearly aware of the system power flow changes.There is a significant deficiency in steady state analysis;but the existing dynamic analysis methods are difficult to give a high accuracy results of the line transmission power dynamic process.Under this background,this paper clarifies the system generator and load changes.And combing the existing power flow calculation methods,the advantages and disadvantages of various methods in analyzing the transmission power of the line are discussed.A dynamic power flow algorithm for high power deficit is proposed based on the analysis,and the objectives and structure of the algorithm is proposed.And in solving the dynamic power flow at each moment,it proposes two solutions: iterative simulation method and extended equation analysis method.Iterative simulation method makes the transmission loss as the iteration criterion and constantly corrects the active power injection of the node.And each moment power flow from the moment of disturbance to the end of frequency regulation will be calculated.Nevertheless,this method needs to constantly modify the node injection power and repeatedly calculate the system power flow.It takes a lot time to calculate and makes the algorithm structure complex.And there are some errors in the simulation results affected by iterative accuracy.On this basis,the relationship between the known quantity and the unknown quantity is analyzed.And it presents the extended equation analysis method.The loss-unbalanced power equation is added to the common power flow equation.It use only one calculation step to get one moment power flow.The algorithm structure is simplified,and the results are more accurate.Finally,the simulation of the proposed algorithm is carried out by IEEE-39 node system.The results show that the two methods can simulate the trend of the system power flow at any time from the moment of disturbance to the end of primary frequency regulation.But there are some errors in the simulation results affected by iterative accuracy.And the extended equation analysis method has a more satisfactory calculation speed,which can quickly analyze the fluctuation of the line transmission power after disturbance.The results show that the change of the power flow is fast and obviously.And it is very likely to threaten the safe operation of the line.And it provides a strong foundation for the safe and stable operation of the power system.