Research On The Subsynchronous Oscillations Damping Characteristic And Complex Torque Coefficient Method

In order to improve power system stability and enhance the level of power transfer capability of existing transmission lines, series capacity compensations and HVDC transmission systems will be widely used in our country.Electromachenic torsional interaction and SSO caused by device can by analyzed by complex torque coefficient method which can achieve the tendency of electrical damping torque coefficient in the subsynchronous frequency range. For its high engineering value, it is widely used in SSO problem analyses. While how to achieve the complex torque coefficient approach by time-domain simulation method effectively has not been specified. With the simulation study of different systems like HVDC system, AC system with series compensation device, etc, amplitude, injection time and additivity of injected oscillating torques are discussed. A set of conclusion to the method is drawn for reference.The problem of SSO to some classical system like series capacitor compensation system, HVDC system and HVDC light system are analyzed as follows:(1) The structure, operation mode and control strategy of thyristor controlled series compensator (TCSC) is studied. In the system with TCSC, the electrical damping torque coefficient is changed by compensation degree and mode of TCSC.(2) The mechanism of SSO cause by HVDC is studied. In the HVDC system, the electrical damping torque coefficient is changed by DC power level, rectifier control mode and parameter settings of the HVDC controller.(3) SSO can be suppressed by HVDC light is proved by simulation results. The control parameter lightly changes the electrical damping torque coefficient.