A Research On UFLS Strategy Of Power System Considering Demand-side Flexible Load Resources

With the improvement of interconnection of large power grids in our country,the problem of maintaining the safe and stable operation of power grids in large disturbance and other fault scenarios is becoming more serious.Frequency stability is an important indicator of power system operation,which reflects the supply and demand of real-time active power in power system.Under frequency load shedding(UFLS),as the third line of defense for safe and stable operation of power grid,can effectively prevent frequency collapse and avoid large-scale blackouts of power grid,which plays a vital role.With the advancement of smart grid engineering,advanced communication technology and demand response technology provide technical support for fast regulation of flexible loads on demand side.Flexible loads have been widely used in power grid regulation for the advantages of flexible use,easy control and fast response.Thus,UFLS with the participation of flexible loads can provide auxiliary frequency regulation services for power system,which has become a new research focus of UFLS.This paper has mainly studied the methods and strategies of UFLS with the participation of thermostatically controlled loads(TCLs),electric vehicles(EVs)and other flexible loads.Firstly,typical flexible load operation characteristics,state models and cluster control methods have been studied.From the point of view of logical subject and communication connection,a distributed control architecture of flexible load participating in UFLS has been designed.Then,the active power-frequency response relations of power grid have been analyzed,and the traditional UFLS algorithm has been studied.Based on above,we have improved the UFLS algorithm by considering flexible interruptible regulation characteristics of flexible loads.Further,the scheme of the improved UFLS is designed from three aspects:improving mechanism,load shedding task allocation and coordinated regulation.The rationality of the proposed scheme has been verified based on DIGSILENT platform.Finally,the influence of communication delay and packet loss on frequency drop depth and recovery degree has been analyzed,and the strategy of UFLS with flexible load participation considering communication state and control equilibrium has been proposed.MATLAB/SIMULINK has been used to simulate and verify the superiority of the proposed strategy.