Research On Active Power Control Of Wind Power And VSC-HVDC Transmission System

The emergence of VSC-HVDC transmission system solves the problem of long-distance transmission of wind power,not only reduces the loss in the process of power transmission,but also has a high degree of controllability.With the increase of the proportion of wind power in the power system,the high proportion of wind power needs the active power control of the auxiliary system,and the wind power needs the regulation ability of the traditional generator.In this paper,the active power control strategy of DFIG through the network of VSC-HVDC transmission system is studied to improve the inertial response level of DFIG to the grid and the ability of primary frequency modulation of auxiliary grid,to improve the transient control and the ability of active power recovery after fault,and to enhance the stability of the system.Firstly,based on the analysis of the power characteristics of the wind turbine,this paper establishes the mathematical model of the doubly fed induction generator,analyzes the vector control strategy of the rotor side and grid side converter,establishes the mathematical model of the main circuit of the VSC-HVDC transmission system,analyzes the vector control strategy of the converter stations at both ends of the VSC-HVDC system,and focuses on the ability of the vector control to decouple the active and reactive power,and carry out simulation verification.Then,the synchronization power control strategy is studied,and the synchronization power control technology is improved and applied to the doubly fed induction generator.The mathematical model of the wind farm connected to the grid through the VSC-HVDC transmission is analyzed,and the influence of the inertia coefficient on the system is analyzed.At the same time,the additional frequency control strategy of the converter station of the VSC-HVDC system is proposed to make the wind farm have the inertia support to the grid.And the ability of primary frequency modulation to realize the fast response of the small disturbance of the power system.Finally,the voltage-frequency hybrid control strategy of the auxiliary system transient control and active power recovery when the wind power is connected to the grid through VSC-HVDC is studied.Based on the application of synchronous power control to DFIG,the system response characteristics when the AC fault occurs at the receiving end are analyzed.The AC voltage d-axis component and the DC voltage of the VSC-HVDC system are selected as the control variables of the state machine,and the VSC-HVDC under the transient condition is adopted.The additional control of the VSC can realize the direct power reduction operation of the wind turbine after symmetrical fault and the active power recovery of the system after fault removal.Because the hybrid voltage frequency control strategy is adopted,the response characteristics of the wind turbine are improved.The research of this paper can make doubly fed induction generator have the ability of auxiliary power system primary frequency modulation and transient control.On the basis of ensuring the safe operation of wind power and VSC-HVDC transmission system,the advantages of synchronous power control strategy are fully exerted,and the frequency stability of the system is improved.