The Research Of Frequency Stability Analysis And Control Strategy Of Isolated Power Grid Based On GPSS

In recent years,VSC-HVDC technology has developed rapidly,many transmission lines between regional power grids are changed from AC lines into flexible DC back-to-back transmission lines.Therefore,the sending-end and receiving-end of the interconnected system have changed from the original AC-DC synchronous mixed connection to DC asynchronous connection.The advantage of VSC-HVDC technology is that it reduces the interaction between regional grids on both sides of the flexible DC transmission system,The disadvantage is that the flexible DC transmission limits the mutual support ability of AC power grid on both sides.In addition,after the interconnected power network turns to the asynchronous networking mode,the power network structure changes fundamentally and the operation characteristics also change greatly.It is necessary to re-analyze the stability of the asynchronous interconnected power grid and propose corresponding solutions to the existing stability problems.In view of the above problems,this paper analyzes the stability of the sending-end power grid of the flexible DC asynchronous networking system,and formulates the stability control strategy.The specific contents are as followsFirstly,The stability analysis of the sending-end power network with N-2 fault is carried out.It is found that when N-2 fault occurs,the local power grid at the sending-end loses contact with the AC main network and turns into an island operation.There is a serious frequency stability problem due to the influence of power gaps,and a VSC-HVDC emergency power support strategy is formulated for this problem.Simulation results show that this strategy can stabilize the frequency basiclySecondly,in order to solve the problem that the effect of frequency stability is not ideal in some operation modes on the basis of the emergency DC power support measures,the governer power system stabilizer(GPSS)is designed to compensate the damping of the generator governer side and reduce the weak mechanical damping brought to the system by the phase angle lag of the governor.Meanwhile,the power system stabilizer(PSS)of the generator is installed on the excitation side and the PSS parameters are optimized.The system damping is enhanced under the joint action of GPSS and PSS,and the simulation results show that the proposed GPSS and PSS additional stability control strategies can further improve the frequency stability of the isolated island.Finally,the coordination control strategy of GPSS and PSS is proposed.The necessity of coordinated control of GPSS and PSS in multi-machine system is analyzed at first,then the coordinated control scheme of GPSS and PSS in the isolated power grid is formulated,and the parameter of GPSS is optimized.The frequency stabilization effect of each scheme on the isolated island system is compared by simulation,It is verified that the coordination strategy proposed in this paper can improve the frequency stability of the sending-end power grid.In this paper,the stability analysis of the sending-end power network after asynchronous interconnection is carried out.Aiming at the frequency stability problem of the sending power grid when the N-2 fault occurs,an emergency power support strategy is developed,GPSS is designed to compensate for the damping of the generator governor side of the isolated power grid,and the coordinated control strategy of GPSS and PSS for the isolated island is proposed.So that the power grid at the sending-end can be restored to a stable state as soon as possible in case of serious faults,and the stable operation level of the system can be improved.