Study On Subsynchronous Oscillation Induced By Series Compensation Of Doubly Fed Wind Farm

Wind energy has been becoming one of the most potential renewable energies in the world for the advantages of cleanness,low using cost and reproducibility.Wind resources is very rich in our country and wind power generation technology is developing rapidly.Many large-scale wind farms have been built and put into operation,but most of wind farms are located in remote areas,where is far away from load center.Series compensation capacitor technology can improve the capacity of long-distance transmission and improve the system stability,thus it is widely used in large scale wind power transmission system.But the actual operation results show that the series compensation technology may bring the threat of sub-synchronous oscillation to the system.In this paper,the most widely used doubly-fed wind power generator is chosen as the research object.Sub-synchronous oscillation mechanism for the doubly-fed wind farms grid-connected through series compensation is deeply analyzed.A mixed sub synchronous oscillation suppression measure is put forward on the basis of the mechanism analysis.The modeling of doubly fed wind turbine is studied first and each part of the double fed wind turbine generator's mathematical model which is suitable for the analysis of sub-synchronous oscillation is established,including air dynamic model,the drive train model,the transmission system model,the pitch angle control system model,the rotor side converter and its control model,the stator side converter and its control model.And the detail process of space vector pulse width modulation of voltage type converter is prezented.Secondly,the mechanism of sub-synchronous oscillation of a certain wind farm is analyzed in detail on the basis of the complete model of doubly-fed induction generator.The change in the electromagnetic torque caused by the change in the rotational speed is divided into the change in the rotor torque and the change in the stator torque by the stator-rotor analysis method.The mechanism of the sub-synchronous oscillation is obtained by analyzing the vector diagram of the change of electromagnetic torque and the transfer function of the rotational speed.Furthermore,a synchronous oscillation suppression method based on the rotor-side converter is proposed according to the subsynchronous oscillation generation mechanism.The system produces an additional torque that is inversely proportional to the change in speed by introducing additional damping control in the rotor speed control loop and the reactive power control loop respectively.The additional torque produced has a positive damping to the sub-synchronous oscillation,and the sub-synchronous oscillation suppression effect is achieved.