Virtual Synchronous Generator Control Of Doubly-fed Induction Generator Based On Inertia Regulation

Wind energy,as a clean energy,has attracted increasing attention and become the fastest growing renewable energy in recent years.Doubly-fed induction generator(DFIG)has become the mainstream wind turbines in the market due to its advantages of small converter capacity,low overall cost,low power loss and high system efficiency.However,the rotor side is connected to the power grid through the back-to-back converter,so that there is no direct coupling relationship between the wind turbine speed and the power grid frequency.The rotating kinetic energy of the wind turbine is "hidden",and its contribution to the inertia of the power system is almost zero.As a result,the wind turbine lacks sufficient inhibition on the power oscillation of the system.Therefore,the DFIG system needs to simulate the inertial support capability of the synchronous machine by adding control strategy.At the same time,it is necessary to establish a unified quantitative analysis method to quantitatively describe the inertia compensation effect of additional control strategies,so as to compare and analyze the suppression capacity of different control strategies of virtual synchronous generator(VSG)in terms of system frequency oscillation.Based on the definition of matrix norm,this paper quantitatively describes the frequency oscillation suppression capability of DFIG system by using the H2/H? norm of system transfer function matrix,and verifies the effectiveness of this method by using MATLAB/Simulink simulation software.Based on the results of norm analysis,a inertia control strategy of VSG based on sliding mode control theory is proposed,and the inertia compensation effect of the additional control method is verified in the IEEE30 system.The main research contents and achievements are as follows:(1)According to the working principle of DFIG system,the complete mathematical modeling of each part is carried out.The influence of grid connection of DFIG on the system frequency stability is analyzed theoretically,and it is proved that the inertia support capacity of DFIG system is small,and it is not enough to suppress the frequency oscillation when the system is disturbed.(2)A method of frequency response analysis based on the norm of the system transfer function matrix is proposed,and discusses the quantitative relationship between the H2/H?norm of system transfer function matrix and the suppression ability of frequency oscillation of DFIG system.The frequency response models of the DFIG system under the controls of different VSG are established with frequency disturbance as system input,and the control effect of the three control strategies(virtual inertia control,DC capacitor control and curve optimization control)on frequency oscillation suppression are analyzed by using the H2/H?norm.It is verified by system simulation that the H2/H? norm can quantitatively describe the suppression ability of the system to frequency disturbance from the perspective of energy.Based on the time domain analysis of the system response curve,the correspondence between the H2/H? norm and the system frequency overshoot and the response time is obtained.(3)According to the theoretical analysis results of the system norm,an additional inertia compensation control strategy based on sliding mode control is proposed.The frequency support ability is improved by adding control on the dc capacitance side,and inertia compensation is achieved by combining the idea of sliding mode control.The frequency response of the control strategy is analyzed by using wo-area and four-machine system,and the effectiveness of the control strategy is demonstrated by norm analysis.The effectiveness of the additional inertial control strategy was verified in IEEE30 system by MATLAB/Simulink simulation.Based on the H2/H? norm of the system transfer function matrix,the frequency oscillation suppression capability of the DFIG system is quantitatively analyzed.It is used as an evaluation index to measure the inertia of the system,and provides parameter selection for the control strategy from the perspective of inertia compensation,so as to achieve the goal of inertia regulation.