The Influence Of Large Inertia Ratio Hydro-power Unit On The Stability Of Modern Electric Systerm

A new era of power system has come with large power grid,large generator units,ultra-high pressure and AC-DC hybrid.Hydraulic power unit plays an important role in the safe,stable and efficient operation of power systems,especially with the trends toward high permeability with intermittent energy sources.Some key problems on hydraulic unit in power system has been researched in this paper,such as the power system stability with large inertia ratio unit,the influence and tie-line inhibition strategy for hydraulic power unit farm to power oscillation on AC-DC hybrid transmission grid,the influence of load and hydraulic unit to the disturbance source location of low frequency oscillation,Hydraulic units control strategy for the synergy of hydro-wind resources system,etc.The details are as follows:(1)With the construction of the low head and long water diversion pipeline power station,the inertia time constant and the inertia ratio of many units has been far beyond the scope of the current standard of the control systems for hydraulic turbines.This paper analyzes and compares the applicable conditions of the domestic and overseas standards for the controlled systems,counts the parameters and operates conditions of the existing typical power plants in China.The stable domain and regulation quality are analyzed based on mathematical model of the control systems for hydraulic turbines.The results show that those power plants still have a larger stability domain and the units can operate safely and reliably.As long as the control parameters are adjusted properly,better regulation quality can be obtained.It also puts forward some suggestions for the revision of the current national standard.(2)In the AC-DC hybrid transmission grid which has a group of hydraulic power plantsas the sending terminal,the power oscillation of tie line will be caused.This paper analyzes the mathematical mechanism for the influence caused by DC restarting and DC blocking and influence of power side parameters and different control measures on power oscillation of tie line after DC restarting and DC blocking.In this paper,a dynamic side cooperative control strategy is proposed.The simulation shows that the strategy can effectively solve the problem of high power oscillation after DC reboot and DC locking.(3)In order to explore the influence of the hydropower unit and the load fluctuation on the disturbance source location,the energy function of the system under different disturbance is established.The influence of the load fluctuation on the disturbance source positioning is analyzed and the influence law of the system is given.(4)For the purpose of improving the speed motion of the hydroelectric unit to compensate the random fluctuation of the wind power,the PI-PD control strategy is applied to the control of the hydraulic turbine governing systems.The PI-PD parameter setting principle is given through the frequency characteristic analysis.On the basis of the establishment of the wind-hydro complementary model,the control efficiency of the conventional PID,fuzzy PID and PI-PD algorithm is adopted.The comparison of the results show that the PI-PD control strategy can obtain faster adjustment speed and smaller reversion amount,and the rational tuning of PI-PD control parameters can effectively suppress the active power oscillations of the wind power,providing an effective way for the wind power accommodatio.