Research On Frequency Stability Of AC/DC Hybrid Power System

HVDC has obvious advantages in long-distance and high-capacity transmission.Cross-and-DC interconnected power grids in trans-region and across-river basins have brought many new technical problems at the same time to enhance transmission capacity and provide more flexible operation mode.In AC/DC hybrid Power system,DC system does not need to consider the frequency problem,but in the transmission of power,the power unbalance of AC side system and the blocking fault of DC system will affect the frequency stability of AC/DC hybrid system.The frequency of the power system is an important index of the quality and safety of the operation,so the frequency deviation is the precondition of maintaining the safe and stable operation of the power system within a reasonable range.Therefore,in AC-DC hybrid transmission system,it is more beneficial for the system to study the coordination between AC system and DC system to solve the problem of frequency stability.Firstly,based on the mechanism modeling method,the AC/DC hybrid Power system simulation model for FM analysis is established in Matlab/simulink.The model mainly includes generator,prime mover,load model,automatic generation control model(AGC)model,etc.Based on the simulation model,the primary frequency modulation,two FM analysis and the direct current frequency modulated control strategy of AC/DC hybrid system are studied.Based on the actual load data,the validity of the model is validated.Second,based on a regional AC/DC hybrid system,the influence of the key parameters of Secondary FM on the frequency modulation effect of AC/DC hybrid system is studied,including the unit unequal rate,the frequency modulation dead zone,the two frequency modulation sampling period and the two frequency FM integrator gain,and the setting requirements of Secondary FM key parameters of AC/DC hybrid system are proposed.Thirdly,based on the principle of DC auxiliary frequency modulation,the mathematic model of DC Auxiliary frequency modulator is established,and the additional DC auxiliary frequency modulation limiter is designed by using the method of overlapping decomposition and linear two-second optimal control theory.Based on the analysis of the influence of DC auxiliary frequency modulator on the frequency stability of power grid,the influence of DC auxiliary frequency modulator parameters on frequency stability is analyzed,and the optimization method of DC Auxiliary frequency modulator parameters is proposed.Finally,the BP Neural network controller is applied to the two FM system of automatic Generation Control(AGC),the neural network is trained by the actual historical data,and the AGC based on neural network controller is simulated by MATLAB.The results show that intelligent control is used to optimize the stability of frequency fluctuation.In the future,the Intelligent control system scheduling scheme is proposed,and the intelligent controller is further considered to be applied to the whole power network dispatching.