Research On Subsynchronous Resonance In Multi-machine Systems Based On State-space Method

As the rapid development of China power industry, modern power system has entered the era of large unit, high voltage and long distance transmission. Modern transmission projects widely use the series compensation devices to improve power system stability and the transmission capacity, but the subsynchronous resonance cased by series compensated transmission system can not be ignored. This paper focused on the state-space modeling in multi-machine system researches on subsynchronous resonance and develops a software for multi-machine system SSR state-space analysis. The main contents include the following three points:1. For the subsynchronous resonance caused by series compensated transmission system, the state equation of network in multi-machine system is established based on the formula of linear network theory. Combing the state equation of synchronous machine, the system state equation is established with the method of interface transform. The eigenvalue could judge whether SSR occur or not and its correlation factor could find the influence factor. The results of calculation example show that this method is feasible and has practical value for SSR.2. Research on self-excitation and torsional oscillation problem related with SSR based on state-space method. The system state equation used for self-excitation is established and the eigenvalue could judge whether self-excitation occur or not and its correlation factor could find the influence factor. For the torsional oscillation, the generator shaft torsional oscillation mode, damping and mode shape can be obtained by solving the state equation. Torsional oscillation characteristics of the identical generators and non-identical generators under different operational conditions are studied. The basic rules of the generator shaft torsional oscillation are summarized by comparing the results of the equivalent machine model.3. Develop a universal software for multi-machine system SSR state-space analysis based on the object-oriented programming technique and the MATLAB GUI platform. The software uses the object-oriented programming and modular modeling idea, has the functions such as power flow calculation, shaft natural torsional frequency calculation, SSR eigenvalue calculation, torsional mode calculation. Examples show that the software has not only accurate modeling but also the good human-computer interaction interface.