Study On Influence Of VSC-HVDC On The Small Signal Stability In Interconnected Power Grid

Due to the reverse distribution of load centers and resource centers in China,the national large-area power systems networking structure has gradually formed to solve the problems of primary energy consumption and the power-shortage of demand-side.This kind of situation alleviates the pressure of energy transfer and the grid load gathering area.But the interconnection of national power grids brings new issues into power system stability and control,especially low-frequency oscillation.With the maturing of power electronic devices and the decrease of cost of full-control power electronic devices and the development of pulse width modulation(PWM)technology,the high voltage DC(VSC-HVDC)which based on voltage source converter has been widely studied and applied.A higher level of active power and reactive power controllability has been achieved.Compared with ordinary high voltage DC and AC power,for it has flexible and fast control performance,it can realize the active power and reactive power decoupling control,so that it can enhance the system damping by supplementary damping controller and suppressing the effect of the system low frequency oscillation.This paper making an introduction of the principle of low frequency oscillation and the forms of it firstly,and explains that the causing of interconnected power grid low-frequency damping are analyzed mainly from the perspective of damping torque in the low-frequency phenomena,then explains the interconnection of common space truss structure has a weaken effect on the damping and explained the effects of primary structure such as the strength of the tie line on damping of the system.Secondly,the paper analyzes the mathematical model,topology structure and control principle of the VSC-HVDC.Explaining why it can realize active reactive power decoupling control and how the supplementary damping controller improve the system damping,confirming the VSC-HVDC structure can improve the system damping,suppress low frequency oscillation.Finally,through the simulation of the southwest and central area power grid,as well as the planning of Chongqing-Hubei back-to-back VSC-HVDC transmission project,this paper verified that after the project was put into operation,it can improve the system damping phenomenon.Additionally,this paper considers the influence of Ya-an strengthen tie lines,the result of simulation illustrates the strengthen of connection structure has restrained the low-frequency oscillation phenomenon between connected power systems.