Sensitivity Analysis And Example Calculation For Coherent Generator Identification Of Large-scale Power System

Now China's power system is rapidly developing towards the direction of high-capacity, long-distance and extra-high voltage. Five inter-provincial power systems have been founded. What's more, connections between these inter-provincial power systems are also being established. A national wide power system is under research and investigation. However the increasingly expanding scale of power system makes it more difficult to carry out transient stability analysis and power calculation. The calculation time, accuracy and complexity are faced with great challenges, thus the power system is simplified by dynamic equivalent to reduce the scale of power system.Generally speaking, when analyzing power system we are just interested in a certain part of the system which is called research system. The rest parts are external system. Although we don't care these parts, their influence to the research system must be taken into consideration. Dynamic equivalent is to simplify the external system under the precondition that the research system stays unchanged. Meanwhile, we must guarantee that the simplified system will not cause any distortion to research system. The equivalent is very important for physical simulation and real-time online security of large-scale power system.In this paper, the dynamic equivalent can be divided into two major parts:ε-coherent identification of generators and the equivalent simplification of power system. Theε-coherent identification is based on the state-space. It proposes a necessary and sufficient condition for identifying coherent generators according to controllability Grammian of the system. Grammian can be approximately expressed by the steady-state solution of linear differential equations, which involves the calculation of Lyapunov equation, Hessenberg transformation and QR decomposition. The equivalent simplification of network has two steps: simplifying the buses of coherent generators and combining the load buses of external system. The dynamic equivalent method discussed in this paper has strict mathematical foundation. It avoids complicated calculation, thus time is saved to a large extent. This method is extremely efficient when multi-faults are analyzed at the same time.This paper uses the classic IEEE39 system and the 585-bus Shandong power system as two examples to verify the dynamic equivalent method. The scale of IEEE39 power system is small, so it promotes us to obtain the key results of calculation and have a deeper understanding about the equivalent algorithm. The scale of Shandong 585-bus power system is largely reduced after dynamic equivalence. It can be easily known through this example that desired results have been achieved without any distortion occurring to the simplified system.