Modeling Of Wind Power System Based On Amplitude-Phase Motion Equation Method And Its Small Signal Stability Analysis

With the continuous increasement of installed wind power generation,the dynamic stability of power system with high wind power penetration becomes more and more complex.The wind turbines are connected to the grid via a large number of power electronic equipment for regulation and control,which brings much faster dynamics into the system and results in multiple time-scale control problem of the whole system,comparing with that of traditional fossil fuel driven generators.The modeling of wind power system under electromechanical time-scale is an important step to analyze its stability characteristic.In addition,the distribution of wind energy and energy demand in China is not exactly match,hence the long-distance and large-capacity power transmission is needed.In order to reduce the electric distance of transmission and increase the transmission line voltage,the series capacitor compensation device is usually added on the transmission line.However,the sub-synchronous oscillation（SSO）it brought is seriously threatening the stable operation of the wind power system.In this thesis,the transient simulation model of Double-Fed Induction Generator（DFIG）under electromechanical time-scale is established and improved,and the sub-synchronous oscillation of DFIG grid-connected system is suppressed by the SSO control device designed in this thesis.First of all,the Amplitude-Phase Motion Equation（APME）method is used to establish the electromechanical transient simulation model of wind turbine in this thesis.In order to enhance the transient stability of the typical model,the q-axis current together with the amplitude of the terminal voltage are incorporated into the phase error of the phase lock-loop based on the typical GE model.After that,the output phase of the terminal voltage is more directly conbined by the q-axis current and the amplitude of terminal voltage.The simulation results,in the Four-Machine-Two-Area with DFIG participating,under the situations of wind speed mutation and load change,shows that the optimated APME model proposed this thesis have the ability to maintain a stable operation when experiencing a sharp disturbance on wind speed and run smoothly,whose strike ratio of voltage and current is twice or five-times lower than that of the typical APME model under some wind-changing situations.Secondly,based on the study of sub-synchronous oscillation on DFIG grid-connected system,the key parameters that dominant oscillation are found by impedance analysis method.What’s more,a SSO control device is designed to suppress the sub-synchronous oscillation of DFIG grid-connected system in the thesis.In the outer power control loop and inner current control loop of DFIG control block,the surplus energy generated by oscillation is used to generate an electromagnetic torque,which can damp the sub-synchronous oscillation,so as to suppress the oscillation of power system.The control effects of changing the electrical parameters of the wind power system,adding typical PI control method and adding this oscillation suppression device are simulated and verified in the DFIG grid-connected system.The results show that both proposed methods can effectively suppress the sub-synchronous oscillation,while the SSO control device designed in this thesis has a faster convergence time and lower amplitude distortion than that of changing the system parameters and PI control method.