Damping Of Sub-synchronous Oscillation By Using Excitation System Based On Full-Controlled-Devices

The geographic characteristics of reverse distribution of energy resources and economic development area, made our country's electric power industry development toward large capacity, long distance, cross-regional pattern. In order to improve the system stability and load capacity of the transmission line, using series capacitance compensation has become an economic and effective method. It can get considerable economic benefit, at the same time has the potential to cause sub-synchronous oscillation phenomenon. It can cause serious generator shafting damage accidents, and become a threat to the safe and stable operation of power system. Therefore, the research of the mechanism of sub-synchronous oscillation(SSO) and suppressing method become significantly important from both engineering and practical point of view. In this paper, the basic problems of sub-synchronous oscillation are introduced in detail. Besides, complex torque coefficient method has been used as the main analysis methodology to study suppressing sub-synchronous oscillation by using full-controlled-devices excitation system, this paper mainly includes:(1) After evaluating the pros and cons of various methods of analyzing sub-synchronous oscillation, complex torque coefficient method is used as the main research method of this paper. From the angle of mathematics, we expound in detail the principle of complex torque coefficient method. Then, establish the criterion of this method, the conditions the method can apply for and concrete steps to implement in the time domain simulation.(2) Introduce basic working principle of excitation system based on full-controlled-devices. The main circuit topology structure of excitation system has been built. For the main circuit topology structure development, we introduce control strategy of VSC converter and chopper control strategy of novel excitation system.(3) Taking IEEE First Benchmark Model as the study model,the influence of SSO caused by excitation control system is studied by using complex torque coefficient method. Based on the solution, series-configuration PSS and parallel-configuration PSS are designed based on phase compensation principle,whose effectiveness for damping SSO is validated by the electrical damping analysis and the time domain simulation.Simulation calculation shows that two PSS models can suppress SSO.(4) Modeled the principle of phase compensation of PSS, design supplementary excitation damping controller(SEDC) is designed to suppress sub-synchronous oscillation. Using complex torque coefficient analysis method, we study single channel SEDC and multimodal SEDC influence on sub-synchronous oscillation respectively. Based on PSCAD simulation analysis, the analysis results show that SEDC can effectively reduce the sub-synchronous oscillation caused by small disturbance.(5) The mechanism of suppressing sub-synchronous oscillation using the ac side of excitation system based full-controlled-devices is analyzed. Based on dq decoupling control strategy, we propose synchronous current injection control strategy and only used to suppress sub-synchronous oscillation control strategy to suppress SSO. Simulation results show that proposed control strategy can effectively suppress sub-synchronous oscillation caused by big disturbance.