| In the interconnected regional power grid with high wind power penetration.The variable speed wind turbines with controllable virtual inertia will provide inertial support and improve the frequency stability of the system.Meanwhile,the virtual inertial time constant will also become a controllable parameter for maintaining the system dynamic stability.If the power system integrated with large wind farm is only concerned with the frequency characteristics,it can not ensure the safety introduction of the wind turbine.Analyzing the influence of virtual inertia on the system transient stability will be the key to assessing whether the wind power inertial support is reliable to the system.This paper mainly studies the influence of wind power with controllable inertia on the power angle transient stability of the interconnected power grid.The main research results are as follows.Firstly,the mathematical models of doubly fed induction wind turbine are established.The working principle and the virtual inertial control scheme of DFIG are deeply studied.The system models of DFIG with the virtual inertia control are built by using DIgSILENT/PowerFactory software,which lays the foundation for the following work.Secondly,the linear state equation of the two machine interconnected power system is derived.The influence mechanism of the wind turbine virtual inertia on the stability of the power angle initial swing is studied.On this basis,the control strategies adapted for the two side regional networks are proposed respectively.By coordinating the inertia in both sub-regions,the transient stability level of the system can be improved.Thirdly,based on the transient energy function method,the mathematical models of multi-machine system with high wind power penetration are derived.The influence of the virtual inertia on the power angle transient stability of the interconnected system is analyzed.By the small interference stabilization method,the influence mechanism of the virtual inertia time constant on the oscillation characteristics of the system is derived.Combining the power angle stability and damping characteristics of the system,a new integrated virtual inertia control strategy for double fed variable speed wind turbines is proposed.Fourthly,a simulation model of interconnected power grids with high wind penetration is established.The dynamic simulation of interconnected system with controllable inertia is carried out to verify the effectiveness of the proposed control strategy.The simulation results show that the proposed control strategy can provide inertial support for the regional power grids.Considering the power angle,damping and frequency characteristics of the system,the proposed control strategy can coordinate and solve the contradiction between multiple control objectives.So as to achieve the integrated virtual inertial control target of variable speed wind turbines,which makes the virtual inertial control have more reliable and comprehensive support ability. |
