Research On Inertia Control Strategy Of Wind Power System Based On Virtual Synchronous Generator

As a representative of clean and renewable energy,wind power has been developing rapidly in recent years.However,wind turbines are generally gridconnected via power electronics,with no coupling between generator speed and grid frequency,lacking active support capability for grid frequency.As the proportion of wind power in the power system continues to climb,resulting in a continuous decline in the total inertia level of the system,it will pose a serious threat to the frequency stability of the system.In this thesis,we study the virtual inertia control strategy of direct-drive permanent magnet synchronous wind turbines to improve the grid frequency stability containing wind power.The grid-connected topology and operating principle of the direct-drive permanent magnet synchronous wind turbine are described,the mathematical model of its main module is established,and the grid-connected control strategy of the wind turbine is also designed: the machine side converter adopts rotor magnetic chain directional vector control,and the grid side converter adopts the grid voltage directional vector control.In addition,the impact of wind power grid connection on the system frequency characteristics is analyzed from the theoretical level,and the role of inertia on the system frequency is clarified.Virtual Synchronous Generator(VSG)is compared with the mathematical model and working principle of the synchronous generator,according to which the activefrequency and reactive-voltage control links of VSG are designed,and the effects of virtual inertia and damping on the transient characteristics of the system are also analyzed.The impact of virtual inertia and damping on the transient characteristics of the system is also analyzed.The inertia control strategy of the VSG-based direct-drive permanent magnet synchronous wind turbine is studied for the problem that the wind turbine cannot actively respond to the system frequency change.The grid-side converter is controlled by VSG,and the machine side converter is controlled by a constant DC bus voltage.Based on this,a wind turbine inertia adaptive control strategy is proposed to adjust the virtual inertia parameters in real time according to the frequency change for the problem of difficult selection of virtual inertia parameters.Simulation results show that the proposed control strategy not only improves the inertia support capability of the wind turbine at frequency,but also improves the dynamic response performance at frequency.In order to further improve the support capability of direct-drive permanent magnet synchronous wind turbine for system frequency,a virtual inertia integrated control strategy based on energy storage assisted wind power is proposed.The joint wind-storage system is constructed and the positive virtual inertia control is used to simulate the inertial response function of the synchronous generator;the negative virtual inertia control considering the battery charge state and system frequency deviation is studied to accelerate the frequency recovery process;meanwhile,in order to fully utilize the capacity of energy storage devices,the virtual droop control is proposed to participate in grid primary frequency regulation by taking into account the battery state of charge.From the perspective of complementary advantages,the combination of positive and negative virtual inertia and virtual droop control constitutes an integrated virtual inertia control method for the combined wind-storage system.Simulation results show that the proposed control strategy can effectively improve the inertia support and primary frequency regulation capability of the windstorage system,while avoiding the occurrence of overcharging and overdischarging of the storage battery and other out-of-limit behaviors.