Mid-long Term Voltage Stable Trajectory Characteristics And Control Strategies Of Urban Power Grids Based On Full Dynamic Simulation

With the rapid development of large-scale UHV AC / DC interconnected power grids and the continuous introduction and application of new equipment and technologies in various power systems,the dynamic behavior of the system becomes more complex,which makes the transient process The long-term dynamic stability problem has become increasingly prominent and gradually by the power system researchers attach great importance.The dynamic characteristics of slow dynamic components such as generator over-excitation limiter and on-load tap-changer are the key factors influencing the long-term dynamic stability of large-capacity and high-proportioned urban power grid.It is very important to construct the stability criterion and safety and stability control measures to prevent the voltage collapse of the urban power network in the long-term dynamic process.This paper based on the Beijing Electric Power Company’s science and technology project "Full dynamic simulation of Beijing power grid dynamic stability and countermeasure research",in large city power grid ring partition running as the research object,analyzed the influence and the main electrical parameters on migration characteristics of the operation point of the system in the system of dynamic PV curve in the long process of slow dynamic element action.The course of the study of the phenomenon of power load characteristics load change with the load side voltage and frequency change system and analyzed the influence of static and dynamic load model of load characteristics on long-term voltage stability are studied,reveals the excitation and OLTC action causes the system long-term mechanism of voltage instability.Based on the definition of the long-term dynamic stability control criterion and calculation method of the margin,the control strategy was proposed to improve the level of long-term stability in the corresponding means.Finally,the validity of the stability criterion and control strategy is verified by the dynamic simulation analysis of Beijing power grid.The main conclusions of this paper are as follows:1)The effects of different load models on the simulation are studied.The receiver system has different trajectories due to different load models during the action of slow moving elements.The integrated dynamic load model system with impedance and motor load is used to analyze the running principle of the running point of the slow moving element to meet the proportion of the same impedance-motor load.The simulation results show that the proportion of the motor load is larger The higher the slope of the run point migration trajectory curve.2)the whole process of dynamic simulation of slow motion components after the system is stable or not the same state after the migration of the system after the migration point of the PV curve on the location of the direct correlation.The pre-migration system operating point A corresponding to the PV curve limit power point B after the state transition occurs as the critical point of medium-and long-term dynamic stability,which can ensure the stable operation of the system after the operation point migration process caused by the slow moving element operation After migration PV curve.3)Fast response load shedding measures have a good optimization effect on the long-term stability of the system due to over-excitation and on-load regulation.The timely response of theload-cutting measures is the key to ensuring that the strategy is effective.The timely response of the load to ensure that the system operating point in the slow component before the action back to the stability of the critical point within,and thus prevent the migration point to the action after the PV curve instability caused by the collapse of the voltage.In the simulation process,it is proved that the constant impedance model and the motor model show obvious negative regulation characteristics in the dynamic regulation of the load.Therefore,when the system is overloaded,the dynamic reactive power support is insufficient and the operating point is close to the stable critical point,the on-load voltage regulation can effectively prevent the terminal voltage from collapsing.