Research On The Power Quality And Stability Of Wind-hydro Complementary Power System

Uncontrollable wind speed and random fluctuations lead to poor power quality of wind power generation systems.With the continuous increase of grid-connected capacity,the penetration rate of wind power in the power grid is increasing,which poses serious challenges to the safe and stable operation of the power grid.Hydropower,as the most mature clean energy in the current power system,has flexible adjustment capability and stable power supply quality.Complementary wind and hydro power generation is an effective way to solve the current development problems of wind power.However,at present,the actual operation and control of hydropower is still mainly to undertake the power generation tasks of the traditional power system.The research of the wind-hydro complementary power system is mostly focused on optimal dispatch and coordinated control.The power quality of the wind-hydro complementary power system is a key indicator reflecting the complementary characteristics of the system,and the stability of the hydro power system is a guarantee for the safe and reliable operation of the complementary system.Therefore,it is very necessary to study the power quality of the wind-hydro complementary power system and the stability of the hydro generate unit.The paper is arranged as follows:(1)Grid-connection stability analysis of hydro power unit with stochastic water head disturbance.To explore the transient stability of the hydropower unit during the connection into the new energy power system,a nonlinear model of the hydro-turbine regulation system during the startup and grid-connection process was established.In the modeling process,the transfer coefficient at small fluctuation conditions is described as the dynamic transfer coefficient that gradually decays to a fixed value with time.At the same time,considering the effect of random disturbance on the water head,stochastic factors are introduced to the head.Through numerical simulation and calculation processing,the speed rule of the hydro-generator unit during the startup process is analyzed.And the influence of the water head on the grid-connection stability of the hydro power unit under different stochastic intensities disturbance.Finally,the effect of different system parameters on the grid-connection stability of hydro power unit with different stochastic disturbance is studied.(2)Modeling and model verification of wind-hydro complementary power system.On seconds-scale time scale,using modular modeling methods,the detailed wind power and hydro power system models are established.The wind power system and the hydro power system are coupled with the IEEE 9-bus model to establish a wind-hydro complementary power system model.Through numerical simulation,the simulation results are compared with the conclusions of the existing literature to verify the correctness of the complementary model.(3)Research on the power quality of wind-hydro complementary power system.First,based on the established wind-hydro complementary power system model,the effects of different ratios and different wind speeds on the power quality of wind power,hydropower and complementary powersystems were analyzed.Second,formulate power quality assessment indicators for power system power quality standards,and quantitatively assess the effect of wind-water ratio on the active power,frequency and voltage of complementary power generation systems.Finally,considering the frequent occurrence of voltage drops in the transient power quality problem of power systems,the influence rule of the power system voltage drop amplitude and drop duration on the power quality stability of the complementary power system is studied.(4)Study on the stability of the shafting system of the hydro power unit of the wind-hydro complementary power system.First,from the perspective of the stability of the hydro power system,the axial coefficient model of the hydro power unit is established,and it is coupled with the wind-hydro complementary power system model.Secondly,considering the influence of the randomness and fluctuation of wind speed on the shaft system,six typical wind speeds are selected to explore the vibration characteristics of the shaft generator rotor and the turbine runner.Finally,further explore the influence of wind-hydro ratio on the shaft system,and analyze the dynamic evolution of the generator rotor,turbine runner and the entire shaft system.