Research On The Countermeasures To Inhibit Sub-synchronous Resonance Of Power Systems

High-voltage and long-distance transmission series capacitor compensation is easy to cause sub-synchronous resonance of power systems. It will damage the shaft of steam turbine and cause serious economic losses. In order to solve this problem, this thesis analysis the mechanism of sub-synchronous resonance, then mainly research on TCSC and SEDC inhibit SSR. The results and conclusions are as follows:(1) TCSC will present power frequency and sub-synchronous frequency in the practical application. The complex expression of fundamental frequency impedance is derived and selection principle of TCSC conduction angle is proposed. The fundamental frequency reactance of TCSC is capacitive or inductive and its resistance will be negative or positive. The sub-synchronous reactance of TCSC will also be capacitive or inductive and the sub-synchronous resistance is always positive with conduction angle’s influence. Inductive reactance plays a major role for SSR mitigation and power frequency negative resistance provides energy to the positive resistance under sub-synchronous frequency. TCSC conduction angle’s selection should make sure that the reactance should be capacitive under power frequency, and inductive under sub-synchronous frequency, meanwhile the power frequency resistance should be negative. Then research on the IEEE first standard model through MATLAB/SIMULINK simulation, the results show that TCSC can mitigate SSR effectively based on the above basis, which provides theoretical basis for TCSC’s control strategy.(2) The design idea of supplementary excitation damping controller is to inhibit SSR by increasing the modal damping. It is implementation through the gain and phase compensation link. The article analysis SEDC’s module function and mechanism to inhibit SSR. Then the supplementary excitation damping controller is designed and its design principles is determined. Research on mechanical side parameters’ effect on SSR, the shafting mutual damping can effectively restrain SSR. The simulation of IEEE first standard model and second phase of a certain power plant show that the design can effectively restrain SSR and its retreat has no significant impact on the conventional excitation function. Field test shows that SEDC can continue to provide damping for the unit, which proves the effectiveness of SEDC.