Research On Oscillation Energy Characteristics And Suppression Methods Of Wind Power Connected Grid With Virtual Inertia Control

With large-scale and high-permeability wind power connected to power grid through long-distance delivery,the inertia distribution and frequency characteristics of the power system have changed significantly.The introduction of virtual inertia enables the wind turbines to provide inertia support for the power system within a certain range,but its dynamic characteristics will be coupled with the power system,which will inevitably bring new impact to the power angle stability.Therefore,ensuring the power angle stability while improving the overall safe operation level of the power grid has become an important practical requirement.The paper studies the oscillation energy characteristics and suppression measures of wind power connected system with virtual inertia.The main contents and results include:The detailed model based on instantaneous values can fully describe the dynamic characteristics of the wind turbine,however,it is not conducive to computational analysis because the order is too high.Aiming at the above problems,the paper takes the DFIG as example and analyzes the time scale and coupling characteristics of each control link.Based on the electromechanical transient time-scale dynamic model,the energy model of the DFIG is constructed and the damping energy part is extracted from it.If the damping energy is negative,it indicates that the DFIG emits energy during the system oscillation process and plays a negative damping effect.Its size is affected by the current operating state of the system and parameters of the phase-locked loop and virtual inertia.The simulation results verify the above conclusions.Through the methods based on the point-by-point,only the oscillation mode and damping characteristics can be obtained.It is difficult to make an overall evaluation of the operating state of the wind power connected system.Aiming at the above problems,the paper analyzes the energy structure of wind power connected system including synchronous generator,network and load,and establishes the energy stability region of wind power connected system in power node injection space.The boundary of the energy stability region is obtianed by point-by-point calculation and fitting method.By analyzing the relative relationship between the system operating point and the stability domain boundary,information such as stability margin can be obtained.The simulation results show that the energy stability region can effectively reflect the overall stability level of the wind power grid-connected system,and its boundary is related to the control parameters of the DFIG.The control strategy based on additional damping has not considered how to ensure the stability of the system power angle under the condition of providing frequency support,as well as lacked of fully consider the use of the key internal control parameters of the DFIG to stabilize the oscillation.Aiming at the above problems,the paper quantifies the distance from the current operating point to the stable boundary of the system,and constructs a stable index based on energy distance.Taking the optimal index of stability as aim,the control parameters of the DFIG as decision variable,the guarantees the system with virtual inertia and frequency support and static stability as constraint,an online adjustment strategy of the control parameters of the wind power connected system is proposed.The simulation results show that the optimization of the parameters of the key control of DFIG can effectively suppress the oscillation of the wind power connected system.