Research On Permanent Magnet Direct Drive Wind Power System Based On Virtual Synchronization Control Strategy

As the proportion of wind power generation in the power system continues to grow rapidly,the dynamic characteristics of the wind power system have a profound impact on the frequency and voltage dynamic behavior of the power system.In typical phase-locked synchronous vector control,wind power does not have the inertial response capability of traditional synchronous generators,which makes the inertial support capacity of high-scale wind power grid-connected systems insufficient,grid frequency instability and other problems highlighted;in addition,the random change of wind speed It will cause the voltage drop and fluctuation of the Point of Common Coupling(PCC)of the wind power grid,which will adversely affect the stability of the power system.The use of Static Synchronous Compensator(STATCOM)can suppress the grid connection of the wind power system Voltage disturbance,but it is hindered by the PCC voltage amplitude and frequency fluctuations,it cannot track the grid frequency correctly,thereby worsening the overall compensation performance.At present,the Virtual Synchronous Generator(VSG)technology is an effective solution because it can simulate the operating characteristics of synchronous generators,which can not only avoid the stability problems caused by traditional phase-locked loops,but also improve The frequency and voltage regulation capability of the system.In view of this,this thesis takes the permanent magnet direct-drive wind power system as the research object,and studies the wind power system based on the virtual synchronous control strategy.Mainly complete the following:(1)A mathematical model of a typical permanent magnet direct-drive wind power system is established,and the influence of grid connection of wind turbines through "back-to-back" converter on system stability is analyzed.Compared with the working principle of the synchronous generator,the VSG control algorithm and its operating characteristics are introduced,and the principle of selecting the droop coefficient and the inertia response characteristics of the VSG control are clarified.(2)The virtual synchronous control strategy of permanent magnet direct drive wind power system under load-reduction operation mode isproposed.This strategy introduces the VSG control algorithm in the turbine-side converter control of the permanent magnet direct-drive wind power system,and uses the scheme of the fan's own overspeed control and pitch control to make the wind turbine fully reduce the load at full wind speed to retain active power.The spare capacity provides additional power support for the system,and realizes a new type of virtual synchronous control of wind power without additional energy storage,which can effectively improve the system's inertia and frequency support capabilities.(3)The STATCOM virtual synchronous control strategy in the permanent magnet direct-drive wind power grid-connected system is proposed,which further expands the application of VSG technology.This strategy introduces the VSG control algorithm in the static synchronous compensator control to suppress the PCC voltage disturbance of the grid-connected permanent magnet direct-drive wind power system.A STATCOM controller based on VSG is designed.Compared with the traditional dq coordinate controller,the controller verifies that the VSG-based STATCOM controller can exhibit better voltage regulation capability at the grid connection point of the wind power system.