Research On Transient Stability Of AC Power System Including HVDC

It is necessary to search long-distance transmission technologies to transfer energy resources in west China to meet the load demand in east China.High voltage direct current(HVDC)which has been developed rapidly has significant technical and economic advantages in long-distance and large capacity transmission.A kind of system called AC power system including HVDC is emerged with the development of HVDC.The vulnerability of HVDC and its interaction with AC power system lead to new transient behavior differ from traditional power system.To ensure the stable operation of AC power system including HVDC,it is necessary to reveal the disturbed behavior characteristics of HVDC and its interaction with AC power system,and to construct a new transient stability analysis method and propose suitable post-fault emergency control strategy.In this paper,the topological characteristics of AC power system including HVDC are analyzed,the interaction mechanism of the DC commutation failure disturbance on the power fluctuation of the parallelled AC transmission line is revealed by establishing the equivalent mathematical model of the AC power system.The key factors determining the peak value of the first swing of the power fluctuation of the AC transmission line are investegated.The characteristics of the behavior of HVDC under disturbance and its interaction with AC power system are clarified.The interaction between the AC power system and the DC system under the disturbance near the DC receiving bus is analyzed.It is revealed that the transient behavior of AC power system including HVDC is different from that of traditional AC power system.A new transient stability analysis method is proposed.Based on the method,how the related factors such as operating conditions of AC/DC system,critical fault clearing time,inertia,influencing on the stability of AC power system including HVDC are quantitatively analyzed.The single/double pole blocking caused by continuous commutation failure of HVDC system severely disturbed the AC power system.Based on the new transient stability analysis method,the critical blocking time is derived,and the power impact on AC power system due to blocking is described.The post-fault emergency control strategy with minimum energy loss,i.e.minimum generator tripping and load shedding of AC power system,is proposed.The influences of operating condition,fault switching sequence on emergency control strategy are analyzed.The effectiveness of the emergency control strategy is verified by numerical simulation.The simulation model of an AC power system including HVDC is built on the platform of advanced digital power system simulator(ADPSS),the transient behavior of the AC power system near the DC receiving bus is simulated.The characteristics of disturbance interaction between HVDC and AC power system are verified.The simulation results verify the effectiveness of transient stability analysis method and emergency control strategy.