Study On Dominant Characteristic And Its Applications In Power Grid Under A Given Operation Mode

The introduction of market competition mechanisms, as well as the complexity of power grid, make the intuitiveness of power systems' operation, dispatch and control more and more worse. Therefore, it is of great importance to explore a simple and intuitive approach to analyze the regularity of power flow in a complex grid, and to monitor the security of power grid with the regularity.The changes of power generation and load in power systems follow some certain rules. Under a given operation mode, this thesis reveals the simple regularity in complex power grid, namely the dominant characteristic. And then the thesis gives discussion and study on the dominant characteristic in depth.Taking the active power transmission as the subject investigated, this thesis proposes the basic concepts of operation mode, transmission path, dominant path and its monotone, and reveals the theoretical foundation of existence of dominant characteristic under a given operation mode staring from the linear systems, and then studies the power systems' dominant characteristic qualitatively combining the concept of sensitivity. The simple examples show that the dominant characteristic continues to maintain when the reactive power is sufficient.Based on the discussion of transmission elements model and the concepts of operating circle and limiting circle, the limiting value of active power flow in transmission elements is amended. Under a given operation mode, the thesis studies the dominant characteristic of power systems from the simple to the more complex in three situations as following. Firstly, on the basis of DC power flow model, taking the sine nonlinearity into consideration, the monotone relationship between active power flow in transmission elements and injective active power, and the existence of dominant characteristic are proven mathematically. And then, an algorithm is proposed to find the dominant interval in which the dominant characteristic maintains. Secondly, taking resistance, namely power losses, into consideration, the monotone relationship between active power flow in transmission elements and injective active power, and the existence of dominant characteristic continue to maintain. Comparing to the no-loss situation, the dominant interval shifts according to the value of r/x when the loss is considered. Thirdly, the impact of voltage level and reactive power on the dominant characteristic is discussed qualitatively. A comparison test with 5-bus system is following, in which the certification about the above three situations is done.Based on the above mentioned researches, the application of dominant characteristic in power systems is discussed. A method of dominant path identification is proposed based on a certain time-level load forecasting data. The applications of dominant path and its dominant characteristic in the area of network transmission capability assessment, security early warning and network structure evaluation are discussed. This thesis points out that the fundamental reason for the complexity of power grid is the existence of KVL.The study on the Shandong 500kV power grid shows that, dominant characteristic research is able to evaluate the transmission ability and monitor the system security correctly in real power systems. And the function of the method mentioned in this thesis is the same as the traditional transmission section surveillance. And what's more, the dominant characteristic method is more intuitive and direct, which is of great significance to simplify the ISO's work, and to carry out the real-time and advanced security control, as well as the decision-making.