Under Voltage Load Shedding Based On The Node Maximum Self-starting Motor Power For Distribution Network

According to the ability of the power system to withstand large disturbances,China had established three lines of defense for the power system.The under voltage load shedding(UVLS)is an important part of the third line of defense,which is an important measure to prevent voltage collapse or even large-scale power outage after large interference.The load shedding and speed of load shedding are two important factors that affect the success of under voltage load shedding.It has not yet formed a unified configuration method and calculation standard for the under voltage load shedding.Generally,the load shedding is calculated base on the experience of the engineers.And the speed of load shedding is fixed in the current scheme,which is not conducive to voltage recovery if the voltage drops rapidly.Therefore,it is great theoretical and engineering significance to improve the voltage stability of the power system by perfecting the under voltage load shedding strategies and measures.Induction motors are the main cause of voltage collapse in the distribution network.Under the condition of the induction motor as the load shedding power,a under voltage load shedding for the distribution network,which is based on the maximum self-starting motor power is proposed in this thesis.The main work is as follows:(1)The simulation model of the distribution network is established by MATLAB software.The effects of static load model,induction motor load ratio,load power and line reactance on the voltage stability of the distribution network are analyzed through simulation.The greater the ratio of the induction motor,the more easily the voltage is unstable.(2)The dynamic simulation shows that the essence of the dynamic process after under voltage load shedding is the self-starting process of retaining induction motors in the distribution network.,and the most important successful sign of under voltage load shedding is the induction motors self-starting successfully.The analysis shows that the self-starting of the induction motor is related to the node voltage and the initial speed.On this basis,the maximum self-starting motor power and its influencing factors are analyzed in detail.It is concluded that the maximum self-starting motor power is related to the system voltage,initial speed,grid and induction motor parameters.If the system voltage,grid and induction motor parameters are fixed,the maximum self-starting motor power is only related to the initial speed.When the induction motor is used as load shedding,there is a complementary relationship between the minimum load shedding and the maximum self-starting motor power.(3)The calculation of the load shedding is based on the maximum self-starting power with different initial speeds,so as to solve the problem that the load shedding is difficult to calculate accurately.In each round,the voltage change rate is used as an acceleration criterion to selectively accelerate the load shedding.Finally,the simulation example proves that the proposed method can not only improve reliability of load shedding success,but also effectively control the load shedding to ensure the reliable operation of important loads.