Research On Interaction Mechanism And Sub-synchronous Oscillation Characteristics Between D-PMSG Wind Farm And LCC-HVDC

In recent years,with the increase of wind power installed capacity and the rapid construction of line-commutated-converter based high voltage direct current(LCC-HVDC),more and more wind power bases are located near the sending end of LCC-HVDC.At this time,due to the weakening of the support capacity of conventional power supply,the sub-synchronous interaction between wind farm and LCC-HVDC is intensified,and the risk of inducing sub-synchronous oscillation(SSO)increases.At present,the research on sub-synchronous interaction between direct-drive permanent magnet synchronous generator(D-PMSG)-based wind farm and LCC-HVDC is still in its infancy,and the existing research methods are difficult to reveal the sub-synchronous interaction between them,so it is urgent to carry out relevant research.To solve the above problems,the sub-synchronous interaction mechanism and SSO characteristics of D-PMSG-based wind farm and LCC-HVDC are studied as follows:Aiming at the D-PMSG-based wind farm through LCC-HVDC transmission system,based on the dynamic process modeling idea of retaining the dominant oscillation components,the traditional damping torque analysis is extended to power electronic equipment through mathematical derivation.Aiming at the oscillation mode dominated by DC capacitor,phase-locked loop(PLL)and DC inductor in the system,the linearized models reflecting the dynamic process of various components are established respectively,and the open-loop transfer function block diagram of various equipment and the closed-loop interconnection transfer function block diagram of the system are constructed.The correctness of the linearized model is verified by step response.Based on the closed-loop transfer function diagram of the D-PMSG-based wind farm sent out by LCC-HVDC,the path of disturbance transfer between the D-PMSG-based wind farm and LCC-HVDC is explored.The interaction mechanism between them is revealed from the perspective of the mutual drive of voltage and current disturbance at the point of common coupling.Based on the superposition principle of linear system,the damping reconstruction method of oscillation mode is proposed.The influence of the sub-synchronous interaction between D-PMSG-based wind farm and LCC-HVDC on the damping characteristics of DC capacitance oscillation mode,PLL oscillation mode and DC inductive oscillation mode is analyzed,and the time domain simulation is carried out.The results show that the disturbance transfer path between D-PMSG-based wind farm and LCC-HVDC presents an "8" type coupling relationship,which leads to a sub-synchronous interaction between them,the sub-synchronous interaction between D-PMSG-based wind farm and LCC-HVDC can provide negative damping for the above three modes.For the three oscillation modes of D-PMSG-based wind farm through LCC-HVDC system,the damping characteristics of the controller parameters are analyzed by the damping characteristic curve,and the time domain simulation is carried out.The results show that for the three oscillat ion modes in this paper,the damping of oscillation mode increases when the proportional coefficient of PI controller related to oscillation leading element increases or its integral coefficient decreases.When the proportional coefficient of the PI contro ller of another subsystem participating in the sub-synchronous interaction increases,the damping of the oscillation mode can also be increased.When the power level of LCC-HVDC increases,the damping of DC inductance oscillation mode decreases.