Subsynchronous Oscillation Analysis Of Power System With Shunt Reactors And Permanent Magent Synchronous Generators

It is one of the important strategies in China that transmitting massive wind power and thermal power from west to east.Although it has optimized allocation of resources to a great extent,the safe and stable operation of the power system has to be faced with some new problems.While the subsynchronous oscillation of power system,which is an important segment in stability has always been the focus of many scholars.Therefore,based on the sub-synchronous oscillation accident which occurred in Xinjiang-Hami DDPMSG wind farm in 2015,this paper studies the influence of shunt reactors on sub-synchronous oscillation in power system and explores the factors that affect the subsynchronous oscillation characteristics of the DDPMSG wind farm.Meanwhile,a DDPMSG wind farm equivalent strategy for subsynchronous oscillation analysis is proposed.In the first place,the basic theories and relevant concepts of the small disturbance stability analysis of power system are introduced,so are the analysis steps of that.Secondly,due to the shunt reactors exist on the actual long distance series compensation circuit,the linear state space model of power system with shunt reactors is established and the stability of the system before and after importing shunt reactors is analyzed.Then the participation factor of each state variable to the subsynchronous oscillation is calculated and the influence of different parameters to the oscillation frequency and damping ratio is discussed.The results show that considering the shunt reactors access partly makes the system become unstable.When the impedance value decreases,the damping of the system gradually increases.Therefore,when designing long-distance transmission lines,it is necessary to reasonably consider line series compensated and the value of shunt reactors to avoid the occurrence of subsynchronous oscillation accidents in the power system.Finally,the accuracy of the single-machine equivalence of large-scale wind turbine cluster is studied in the subsynchronous oscillation analysis of DDPMSG wind farm grid-connected system.While the linearized state-space model of single-machine and two-machine systems is derived,and the influence of operating conditions,controller parameters and the interconnection tie on the oscillation characteristics of equivalent systems are explored before and after.The results show that the DDPMSG output,the proportional integral gain of the outer voltage loop and the proportional gain of the inner current loop at the side of the inverter can affect the accuracy of the system equivalence to different degrees.Based on the above analysis,a dynamic multi-machine equivalence strategy for DDPMSG wind farm is proposed in order to reduce the complexity of wind farm simulation model and represent the subsynchronous oscillation mode.Clustering is realized in two steps.The first step is to group the DDPMSG of the same type(pararmeter).After that,the DDPMSG in each group is clustered according to the principle of close output power.Finally,the DDPMSGs in each group are equivalent to obtain the equivalent model of the wind farm.Though establishing the small disturbance model and verifying in the time-domain simulation,the results show that the method can effectively reflect the subsynchronous oscillation mode,especially the weakly damped mode of the wind farm and is suitable for the analysis of the sub-synchronous oscillation of the DDPMSG wind farm.