Research On The Scene And Control Strategy Of Oscillation Center Intrusion Into The Cluster

In recent years,the power transmission base in my country has been developing towards increasing the single unit capacity at the sending end,strong interconnection of power grids,and greater power grid density at the receiving end.Therefore,the equivalent impedance of the transmission line and the receiving end system decreases while the equivalent impedance of the sending end system increases.Under this development trend,when the system oscillates due to out-of-step,the oscillation center tends to migrate to the sending end system cluster.According to its definition,when the oscillation center invades the inside of the cluster,the low-voltage protection of the auxiliary equipment of the power plant and the out-of-step protection of the generator set will malfunction,and then a large number or even all of the units in the cluster will be removed,which will cause the "avalanche" cut-off.Therefore,the scenario where the oscillation center invades the sending-end cluster needs to be analyzed urgently.In view of its harm,an oscillation center extrapolation strategy is proposed,and the migration characteristics of the oscillation center and its extrapolation strategy are studied under the scenario of DC transmission lines connected to the AC system.The main research results obtained for the above research content are as follows:(1)Under the background of the development trend of existing power transmission bases,the possibility of the existence of an oscillation center intruding into the aircraft cluster is analyzed,and its existence scene is analyzed in combination with theory and practice.From the perspective of system impedance,the coefficient expression of the oscillation center position is derived.On this basis,the intrusion of the oscillation center into the aircraft cluster is obtained,and the impact of the oscillation center intruding into the aircraft cluster is analyzed from two aspects of power plant auxiliary equipment low-voltage protection and generator out-of-step protection.(2)Based on the consideration of system impedance,the strategy of launching the cluster outside the oscillation center is analyzed.On this basis,an extrapolation strategy of oscillation center based on three-terminal adjustment of transmission and transmission is proposed.Increase the equivalent reactance of the transmission corridor by adjusting the trigger angle of TCSC or cutting off part of the heavy load line.increase the generating capacity or put in standby units at the sending end to reduce the number of receiving end units to reduce the equivalent reactance of the sending end system.Or by cutting off the receiving end unit and corresponding load,and then increasing the equivalent reactance of the receiving end system.When the system oscillates,firstly,based on the oscillation center,the equivalent reactance adjustment value of the system is comprehensively predicted for the internal conditions of the fleet,and the reactance adjustment restriction constraints are further formulated,and finally the specific transmission end,transmission corridor and receiving end adjustment plan are determined.(3)In the scenario where the DC transmission line is connected to the AC system,the situation in which the oscillation center invades the interior of the cluster is analyzed.In order to ensure the stable operation of the system,an extrapolation strategy of oscillation center based on adjusting the DC transmission line is proposed.Based on adjusting the DC voltage or the trigger delay angle of the rectifier and the arc extinguishing lead angle of the inverter to change the equivalent reactance value of the DC transmission system,the equivalent reactance after the adjustment of the DC system is predicted,and the impedance adjustment limit constrain t is formulated.Under the premise of satisfying the adjustment constraints,determine the specific DC system adjustment plan.The PSCAD was used to build a power delivery base model to verify the accuracy of the reason for the oscillation center's intrus ion into the cluster and its impact.Furthermore,under the scenario of the oscillation center invading the inside of the cluster,the oscillation center extrapolation strategy proposed in this paper based on the three-terminal adjustment of the transmissi on and transmission is simulated,and the feasibility of the proposed strategy is verified through the impedance trajectory and the power angle change curve.Finally,a scenario where the DC transmission line is connected to the oscillation center of the A C system and invades the inside of the cluster is established to verify the feasibility of the oscillation center extrapolation strategy based on adjusting the DC transmission line.Simulation results show that the effect of this extrapolation strategy is relatively small,and it needs to be combined with a three-terminal adjustment scheme in some serious scenarios.