Analysis On The Influence Of DC Modulation Controller On Low Frequency Oscillation Of System

With the rapid development of Chinese power system,grid interconnection reflects the development trend of the power grid.Grid interconnection brings higher economic benefits,comprehensive social benefits and grid security and reliability to the whole society.At the same time,the interconnection of the power grid also makes the stability of the power grid more complicated,and the transient stability shows new features.The dynamic stability and voltage stability problems tend to be serious.In particular,the small interference stability problem represented by low-frequency oscillation poses a new challenge to grid stability.At the same time,the use of power system stabilizers to suppress low-frequency oscillations between regions requires a large number of installations,which will greatly increase the cost of power grid construction.Based on this,this paper will conduct a series of research on the influence of DC modulation controller on the low frequency oscillation of the system.Firstly,this paper introduces the current research situation of power system interconnection,the research status of low-frequency oscillation at home and abroad and the research status of DC modulation technology,and expounds several commonly used research methods for analyzing low-frequency oscillation problems.Then,starting from the classification of power system stability,the small interference is stabilized,and then the low-frequency oscillation problem of the power system is brought out.The basic concepts,generation mechanism and common suppression measures of low frequency oscillation are expounded in detail.The basic types and control structures of DC modulation controller are introduced.The basic principle of low frequency oscillation of DC modulation suppression system is analyzed by using single machine infinite power system.The theoretical support of DC modulation on the suppression of low-frequency oscillation of the system,the similarity and difference between DC power modulation and DC frequency modulation is studied.Then,the voltage-current relationship of the DC transmission system,the DC power controller,the phase-locked loop and the small-signal model of the DC power modulation controller are derived,and the amplitude-phase kinematics models of the rectifier side and the inverter side are further derived.Moreover,the correctness of the amplitude-phase kinematics model of the converter is verified by the method of time domain simulation.Finally,based on the model of four-machine two-zone AC-DC hybrid system with additional DC modulation controller,the influence of DC modulation on the low-frequency oscillation of the system is studied.Among them,the effects of low-frequency oscillation of the system and the effect of modulator parameters on the suppression of low-frequency oscillation are analyzed from the two scenarios of DC power modulation and DC frequency modulation.The similarities and differences between the two modulation schemes are further summarized and analyzed.