Damping Control Method Of VSC-HVDC System For Low Frequency Oscillation And Design Of Control Parameters

In recent years,with the interconnection of Large Power Grid,the increasing unit capacity and the implement of new power electronic devices,the scale of the grid is increasing while the operating mode of grid is becoming more complex.Power system stability problems have become increasingly prominent,particularly the low frequency oscillation problem.Low frequency oscillation occurred in both domestic and abroad,mainly due to the lack of damping in interconnected systems in long-distant,heavy-load transmission lines.It is more likely to occur in the conditions of modern fast,high top value excitation system.Voltage-sourced converter based high voltage direct current transmission(VSC-HVDC)uses full-controlled devices and PWM modulation technology,it has the ability of four-quadrant operation,enabling fast independent control of active and reactive power,and without reactive power compensation.The target of this paper is to apply VSC-HVDC power system to suppress low frequency oscillation,and related researches has been conducted on:The mechanism of low frequency oscillation and analysis methods and suppression measures were discussed;the VSC-HVDC control structure and working principle were studied;parameters of the control system have been theoretically analyzed and designed;the system model of VSC-HVDC connected to the single machine infinite bus system have been designed.Contrast to conventional control strategy,based on the use of VSC-HVDC quick power regulation characteristics,the VSC-HVDC were used in the design of active modulation of additional control strategy,and the influence of additional control on the system damping and the influence of different control parameters on the system damping,this paper firstly introduces an additional damping control in the voltage source converter based high voltage direct current(VSC-HVDC).The small signal model of the system is then established.Based on the root locus,the mechanism of the influence of the additional damping control on the stability of the system is explained.The calculation method of the control parameter for system maximum damping is further obtained.Finally,PSCAD software is used to simulation test and the simulation results verify the correctness of theoretical analysis and calculation.The conclusion are as follows:a)The fast active power regulation characteristic of VSC-HVDC can be used to suppress the low frequency oscillation of AC system:b)The damping control parameter Kw is not as large as possible.With the help of MALAB's root locus analysis and the golden formula,for the three order system,the maximum damping control parameter Kw can be obtained.