Influence Mechanism Of Power Grid Sub-synchronous Oscillation On DFIG And The Study Of Oscillation Suppression Strategy

In the context of China’s active pursuit of energy transformation and full effort to achieve the goal of "dual carbon",the permeability of new energy power generation such as wind power increases,and the converter devices using power electronic power devices are also more widely used in the grid-connected control of new energy power generation.However,the popularity of new energy generation,power electronic devices and series compensation capacitors further increases the complexity of the power grid,and the risk of sub-synchronous oscillation of the power grid will increase.Therefore,it has become an important research topic to maintain the stable operation of wind power system under the sub-synchronous oscillation of the power grid.During the grid connected operation of the doubly-fed wind turbine,the power grid sub-synchronous oscillation signal willseriously affect the control performance of the rotor side converter and the grid side converter,leading to the instability of the doubly-fed wind turbine system.In order to solve the problem of interference of doubly-fed wind turbine control under sub-synchronous oscillation of power grid,this paper proposes the suppression strategy of sub-synchronous oscillation of doubly-fed wind power system.Firstly,the steady state mathematical model of the doubly-fed induction generator is established in this paper,which provides a theoretical basis for the design of the backstepping control strategy of the rotor side converter.Then the mathematical model of the grid side converter is established and the control strategy of the grid side converter is designed according to the backstepping control principle and the mathematical model.Then the mathematical model of the rotor side converter is established and the backstepping control is applied to the control of the rotor side converter,and the backstepping control strategy of the rotor side converter is designed.Finally,the simulation proves that the backstepping control strategy of the dual PWM converter designed in this paper can reliably achieve the control objectives of each converter and has well control performance,which provides a basic model for the study of sub-synchronous oscillation of the doubly fed wind power system in this paper.Then the influence mechanism of the power grid sub-synchronous oscillation on the doubly-fed wind power system is analyzed.Firstly,the generation mechanism of the power grid sub-synchronous oscillation is explained,and the relationship between the doubly-fed wind power system and the power grid sub-synchronous oscillation is defined.Secondly,the mathematical model of the grid side converter and the rotor side converter under the sub-synchronous oscillation of the power grid is established,and the influence of the sub-synchronous oscillation of the power grid on the converter control is clarified by mathematical analysis.Finally,the control results of the power grid sub-synchronous oscillation change on the dual PWM converter control and the corresponding oscillation suppression strategy are analyzed by simulation,and it is clear that the sub-synchronous oscillation frequency change is the key factor affecting the oscillation suppression strategy.Thirdly,in order to suppress the sub-synchronous components of different frequencies in the doubly-fed wind power system,a frequency adaptive quasi-resonant controller is designed by improving the quasi-resonant controller.By adding adaptive quasi-resonant controllers to the control strategy of the rotor side converter and the grid side converter,the control objectives of the rotor side converter and the grid side converter are stabilized respectively.The simulation results show that the adaptive quasi-resonant controller can suppress the sub-synchronous components of different frequencies in the system,and its control effect is better than that of the quasi-resonant controller.Finally,the corresponding control strategy of the rotor side converter and the grid side converter proposed in this paper is verified by experiments,and the control effect of the doubly-fed induction generator during the stable operation of the power grid and the generation of the power grid sub-synchronous oscillation is respectively observed by building an experimental platform of the doubly-fed wind power system under the simulation of the power grid sub-synchronous oscillation.Experimental results verify the effectiveness of the proposed backstepping control strategy and adaptive quasi-resonant control.