Research On Quantitative Modeling And Small-Signal Stability Of Interactions Among Equipment In Wind Farm Connected To High Voltage Direct Current Systems

Large-scale of wind power in the north region of China have been integrated and transmitted by line-commutated converter high voltage direct current(LCC-HVDC)system.The sub-synchronous oscillations caused by permanent magnet synchronous generator based(PMSG-based)wind turbines and LCC-HVDC system threaten the stability of the system and constrain the increase of renewable energy generations.The dynamic interactions among the equipment is one of the key factors leading to the instability.The traditional stability analysis methods in power systems cannot quantify the interactions among the equipment,let alone explain how the interactions among the equipment affect the stability of such systems.To address the above issues,this thesis gives a quantitative model of the interactions among the PMSG-based wind turbines and LCC converters by using the self/en-stabilizing coefficients.On this basis,the influence of the interactions among the equipment on the small-signal stability of the system is analyzed.The main results are shown as follows:(1)For the interactions among multiple wind turbines and the rectifier of a LCC-HVDC system,an analytical quantification method is presented to quantify the interactions among the current source converters and voltage source converters(VSCs)analytically.Based on the small-signal model of PMSG-based wind turbines and LCC-HVDC,this method quantifies the interactions among the equipment from the perspective of energy exchange among the energy storage elements.We calculate the self-stabilizing and en-stabilizing coefficients with the help of power flow in AC networks.Then,according to the quantity of the equipment participating the interactions,the overall en-stabilizing coefficient is divided into different terms to reflect different paths of the interactions.Moreover,by establishing the relationship between the self-/en-stabilizing coefficients and the stability of the system,we evaluate the influence of the interactions on the system stability through different paths of the interactions among different equipment.(2)For the interactions among multiple wind turbines,the rectifier and the inverter of a LCC-HVDC system,an analytical quantification method is presented to quantify the interactions among the equipment through the coupling of AC and DC networks.On the basis of the small-signal model of PMSG-based wind turbines and LCC-HVDC,we convert the dynamics of the inverter into the dynamics of the rectifier through the coupling of DC network first.Next,we calculate the self-/en-stabilizing coefficients according to the definitions.Then,the en-stabilizing coefficient is divided into different terms according to different effects of AC and DC networks.Finally,we analyze the influence of the interactions among different equipment on the system stability through different paths by simulation and experiments.The results can provide a new idea for the setting and tuning of control parameters in multi-equipment power systems.