Study On Transient Stability Analysis And Control Based On Projection Energy Function Theory

Power system security and stability is the precondition of reliable power supply. Transient stability analysis is evaluation of the ability of systems to withstand specified contingencies and to survive the subsequent transient events to arrive at an acceptable steady operating condition. Researchers have been working for a fast and effective method for transient stability analysis and control and remarkable progress has been achieved. This paper tries to develop a new method for transient stability analysis and control for online application.On the basis of normalized energy function (NEF) theory, a novel concept of projection energy function (PEF) is proposed. By projection transformation, the power system dynamic in post fault duration is studied on the rotation coordinates axis. PEF overcomes the drawback of NEF that the total normalized kinetic energy only becomes minimum but not zero even though the system is stable. The variation characteristic of the minimum of projection kinetic energy (PKE) in the post-fault duration for a contingency versus fault clearing times has been studied. Based upon the above characteristic, a new way to assess critical clearing time of unstable contingency is developed.An approach for online transient stability analysis, which includes a new angle instability criterion, stability index for harmful contingency and operation mode adjustment algorithm, is proposed. Using the theory of PEF, software for online transient assessment of Tianjin power grid is developed, which provides real-time monitoring and can help the operators to find out the weakness point of the power system.The trajectory sensitivity mapping technique is utilized to evaluate the gradient of minimum PKE with respect to active power output of generators. Using the gradient, a new approach for stability-constrained generation limit assessment is proposed to develop a method for optimal power flow with transient stability constraints (OTS). Then the stability constraints represented by differential equation are converted into inequality constraints of active power outputs of generators. Thus, the OTS problem could be solved by traditional optimal power flow (OPF) method.The idea of angle norm has been introduced to develop a novel transient stability performance index. The sensitivity of the performance index relative to mechanical power input of the generators can be calculated by trajectory sensitivity method. With the sensitivity, the system stability constraints imposed by unstable contingencies are expressed by linear inequalities. Then a new generation security dispatching approach is presented for transient stability enhancement of power systems, which can optimally reallocate power generations for multiple unstable contingencies. The transient stability constraints are also introduced to congestion management. Under this framework, the generators participated in dynamic congestion management are dispatched on the principle of maintaining the possible adjustment at least cost as well as submitting thermal limit and transient stability constraints.