| 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-distan t,heavy-load trans mission 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-H VDC)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 pow er compensation.Based on this characteristic,if it is possible to design a strategy of indirect control of increasing system damping to suppress low frequency oscillation occurs when VSC-HVD C transfer power to the system,this work will be of great research value to enhance the system stability.The target of this paper is to apply VSC-HVDC pow er 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 mode l 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-H VDC quick power regulation characteristics,the VSC-HVDC were used in the design of active and reactive modulation of additional control strategy and theoretically explain ed the mechanism of two additional control increase system damping.The model of the system was established based on the simulation software PSCA D/ EMTDC.When the three-phase short-circuit fault occurs suddenly in the system,the conventional control,active and reactive modulation of additional control are compared by the simulation.The conclusion are as follows: a)two additional damping control strategycan increase the system damping effectively,suppress low frequency oscillation rapidly and improve the operational stability of the power system;b)compared to the reactive modulation of additional control,the impact of active modulation of additional control on the voltage of public access points is relatively small,which is more suitable for VSC-HVDC to suppress low frequency oscillation. |
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