Research On Online Assessment Method Of Voltage Stability

In order to meet the increasing demand of load and realize the optimal allocation of resources between regions,China's power grid is developing towards large scale and long distance transmission.With the increasing of the proportion of the external power,the problem of voltage stability in the receiving power grid is becoming more and more prominent.Therefore,it is of great practical significance and application value to study the on-line evaluation method of voltage stability.First,the voltage stability of simple impedance circuit is studied with small disturbance method,the impedance criterion of voltage stability deduced,the leading role of load recovery characteristic in the process of voltage instability revealed,the influence of dynamic behavior of elements in power system for voltage stability analyzed,the key technical problems of online voltage stability assessment pointed out.Then,the study of the power system Thevenin equivalent method is carried out.Aiming at the error of two points parameter identification method,an improved method is proposed.However,the real or imaginary part of the improved identification parameter is negative,and the computation speed is limited.To solve this problem,this paper proposes an on-line Thevenin equivalent parameters computing method based on GPU accelerated branch-adding,instead of the inversion of system admittance matrix.The accuracy and speed of the method proposed are verified by simulation and real case respectively.Finally,the study of the impedance criterion of the voltage stability criterion is carried out.Actually,the traditional impedance modulus criterion regards the transmission power limit as the boundary of voltage stability,which does not consider the load characteristic.To solve this problem,a dynamic model considering load recovery characteristics is established.Based on this,an improved impedance modulus criterion is deduced theoretically.The case analyses show that the improved impedance modulus criterion can more accurately indicate the distance between the current point of the system and the boundary of voltage stability.