Research On Transient Stability Of Power System Based On Measured Trajectory

The destruction of the security and stability in the power system has always been one of the severest failure. Once the power system lose its stability, a wide range of blackouts will cause huge losses of the national economy and serious injury to people’s lives. In some severe cases, it may cause the collapse of the power system. Therefore,how to ensure the safety and stability of the power system has became a major issue for researchers and operators concerned.The research of the power system has much more difficulty under the influence of many factors such as continuous expansion of the power system, the disturbances of failure and the dynamic behavior of nonlinear loads. To simplify the power system has become one of the major goals of researchers. And the network of the power system can be simplified into a two-node system with Thevenin equivalence at a node. In this way the stability of the power system can be analyzed easily and quickly. In this paper,traditional model of the Thevenin equivalent is introduced, and the physical meaning of every parameter is fully explained. The reason for parameters drift during the calculation process is that the coefficient matrix may be ill. According to the characteristics of the actual operating state of the power network, an improved Thevenin equivalent model is presented in this paper. Variable forgetting factor recursive least square estimation technique is applied to estimate online Thevenin equivalent parameters. The analysis results of single-machine system and IEEE9 bus system demonstrate that the method can be used for on-line tracing the Thevenin equivalent parameters effectively and rapidly and be applied in actual power systems.In recent years, the research that can tell the transient stability of the power system by forecasting disturbed trajectory which is based on phasor measurement unit(PMU)to get real-time data has attracted the interest of many researchers. However, it’s still difficult to get the effective information. In this paper a new method which is based on real-time trajectory to analyze the transient stability of the power system is proposed.Transient energy value is calculated after a system failure to quickly judge transient stability of the system.Currently, the construction of smart grid has become a trend in the development of the power system. And the one of the most urgent problems is how to on-line analyze the transient stability of a multi-machine system. In this paper, the equal area criterion to analyze the one-machine infinity-bus system is introduced. Then the difficulty in analyzing the transient stability of a multi-machine system has been illustrated by the example of a two-machine system. With the transmission line as the basic unit, a complex and interconnected system can be equivalent into a easily analyzed two-machinesystem by the improved Thevenin equivalence. In this paper, a new method in how to study the transient stability of a multi-machine system after fault is proposed. And with this method it will be easy to find out the weak line in the power system. Case studies in IEEE39 system are provided to illustrate the effectiveness of the proposed method.