Study On Power Flow Calculation And Optimal Power Flow Based On The Theory Of Electrothermal Coordination

The transmission lines always work under harsh outdoor conditions, the transmission capacity of lines is limited by the maximum operating temperature. The traditional analysis of power system uses static thermal rating or dynamic thermal rating as a transmission line ampacity calculation’s standard that don’t consider the influence of the dynamic temperature process to power flow, thus limiting transmission capacity. The theory of electrothermal coordination uses the resistance as a link, calculating the conductor’s heat balance equation and power flow equation coupled, and representing the transmission ampacity with temperature constraints directly, which can effectively use the thermal inertia in the process of conductor’s temperature rising, dig the transmission capacity deeply, and improve the economy and reliability of the grid operation, It has important theoretical significance and engineering value. Therefore, this article studied the power flow calculation and dynamic optimal power flow based on the theory of electrothermal coordination.Firstly of all, this article discussed the heat transfer process and the heat balance equation of bare overhead conductors in actual operation, analyzed the calculation model of heat gain, heat loss and simplified calculation method of its parameters. On this basis, the calculation method of transmission line ampacity is discussed, and the influence of the sunshine density, the environment temperature, the wind speed and the wind direction to transmission line ampacity is analyzed with the case. This study gained the electrothermal coupling characteristics of transmission line which can provide a theoretical basis for further research.The model of power flow calculation based on the electrothermal coordination is studied. The two cases of common power system fluctuations (load jump and temporary line outage) are analyzed. Focus on the time discrete algorithms such as Euler method, Improved Euler method and Runge-Kutta method, the effects of the power flow calculation accuracy at different time steps conditions is mainly studied according to the load jump case, The results show when time step is 0.5 min, the calculation results of all algorithms are basically the same and have high precision, but with the increase of the time step, each algorithm has error in different degrees. Among them, Runge-Kutta method’s error increases the minimum, and Euler method’s error increases the maximum. According to this model calculation, when time step is small, Euler method is available because of the small amount of calculation; when time step is larger, Improved Euler method or Runge-Kutta method should be selected depending on the accuracy requirements and computational scale. The study can provide a reference basis for the model of power flow calculation based on the electrothermal coordination to choose time discrete algorithms properly.Finally, this article studied the model principle of dynamic optimal power flow based on the electrothermal coordination, and the prime-dual interior point method which its solution required. The minimum cost of system power generation as a target, combining with instance the advantage of electrothermal coordination for power flow optimization control has been proved. On this basis, the electrothermal coordination is introduced to the optimal power flow model of minimum load-shedding, and the two fluctuation cases of load jump and temporary line outage is analyzed. The results showed that compared with the traditional model, the electrothermal coordination model can effectively reduce the amount of system load shedding, avoid unnecessary load-shedding operation and improve the ability of power supply.