Research On Low Frequency Oscillation Energy Analysis And Control Of Doubly-Fed Induction Generator Grid-Connected Power System

Promoting the green and low-carbon transformation of energy is a major strategy for China,and new energy power generation led by wind power has been vigorously developed.While new energy equipment brings many benefits to the power system,it also brings some difficulties to the stability analysis and control of the power system.One of the important reasons for this problem is that the internal characteristics of new energy equipment are not clear.The existing energy analysis of new energy is mostly based on external characteristics.And there is an urgent need for a more detailed analysis of the characteristics of new energy equipment.Therefore,this thesis analyzes the internal energy structure of the doubly-fed induction generator(DFIG)with complex operating characteristics and wide application,explores the key factors affecting the energy of DFIG,reveals the influence of DFIG energy on system energy,and improves the energy structure of high-proportion wind power grid-connected power system.Based on this,combined with the control algorithm,the oscillation suppression energy regulation strategy is designed,which provides a theoretical basis for the study of the planning,operation,and control of a highproportion doubly-fed induction generator,and has important practical application significance.The specific research contents of this thesis are as follows:Firstly,according to the detailed model and control strategy of the doubly-fed induction generator,the internal structure of the doubly-fed induction generator is analyzed in layers,and the energy structure of the doubly-fed induction generator is modeled in detail.The detailed energy function which can reflect the dynamic characteristics of the doubly-fed induction generator and consider the internal control link of the doubly-fed induction generator is constructed.The energy function lays a theoretical foundation for the subsequent analysis and regulation of energy characteristics of the doubly-fed induction generator.Secondly,using the detailed energy function model,the energy of the doubly-fed induction generator is analyzed hierarchically,and its detailed composition is analyzed.Combining theory with simulation,a single-machine and four-machine system with wind power is built in simulink.The influence of doubly-fed induction generator parameters and state variables on energy is analyzed.According to the sensitivity of state variables,the key factors affecting energy are explored,and the damping evaluation index based on detailed energy function is constructed.Through simulation verification,it is found that the energy of the DFIG is mainly concentrated on the rotor side,and the relevant control variables on the rotor side are more sensitive to energy.In addition,according to the internal energy distribution of the doubly-fed induction generator,the order of the energy can be initially reduced.At the same time,it can also be used as a basis for the design of the oscillation suppression energy control strategy.Finally,according to the detailed energy function of the DFIG,the power system energy function with the doubly-fed induction generator is established.The relationship between the internal variables of the doubly-fed induction generator and the system energy is analyzed.With the asymptotic stability of the total potential energy of the system as the constraint,combined with sliding mode control,the extended state observer(ESO)is used to estimate the variables that are difficult to determine,and the oscillation suppression energy control strategy is designed.The scheme can suppress the oscillation quickly and ensure good robustness by adjusting the energy of the doubly-fed induction generator.The effectiveness and feasibility of the proposed controller are tested in the 4-machine 2-area system with wind power.