Research On Emergency Power Control And Splitting Algorithm For Tie-line Fault

The Transmission section of power system refers to the cutset of tie-lines between two regional grids.The rapid development of UHV project expends the power scale and enhances the grid structure complexity of China with AC/DC hybrid transmittion line.Long distance transmission line greatly improves the power exchange efficiency and resource allocation ability among regions,but also brings with potential risk to the synchronous operation of power grid.As the power capacity of transmittion line becomes larger,the greater disturbance may follow if the transmittion line is open after a serious fault,and thus results in a hunge imbalance power to the connected two power grids.In this paper,a brif introduction of the general research background and privious achievements of emergency control technology on power system is outlined in chapter 1.Then,a study of emergency control technology based on power dispatching and direct current(DC)transmission line is demonstrated in chapter 2 and 3 seperately,followed by an optimized algorithm on power system splitting strategy in chapter 4.The contribution of this thesis can be summarized as follows.This paper first introduces some typical causes for tie-line faults,and analyses the possible bad influences to the power system if a tie-line is open all of a sudden.A mathematical model for emergency power dispatching after tie-line fault is established according to power balance criteria.This includes two situations: a)if the spinning power researve is sufficient,the target is to minimize the economic loss of power dispatching.b)if the spinning power researve is insufficient,the target is to minimum load/generator loss,which is related to the power limitation of transmission section to the neibour grids.An assistant decision system is put forward and two cases on power dispatching after DC line fault are demonstrated to prove this method.By deriving the equation of rotor angle and accelerating power criteria in a two generator and one DC line system,we conclude that the emergency power support from DC lines can improve the transient stability of power system by changing the accelerating/decelerating area.Next,a discussion on the overload capatity and modulation method of DC line is introduced,followed by a further discussion on the optimized technical parameters for DC emergency power control.Finally,a coordinated control scheme for emergency control on multi-DC line is proposed.Two case studies are given in this part to prove this method.Finally,a graph theory based optimized power system splitting method is put forward.This method does not take the traditional train of solution to search every branch of the whole system,but focuses on the topology connecting generator groups in different coherence.This brilliant idea reduces the dimension of the calculation matrix.Next,a three-stage ‘step by step' solution is put forward to achieve the best power system splitting strategy with minimum load losses.The proposed algorithm is verified by the New British 10 machine 39 nodes system as well as the Sichuan&Chongqing 500kV/220 kV power grid.