Analysis And Control For Power System Frequency With Large Scale Wind Power Integration

There are harsh challenges emerging for power system active power balance and frequency regulation with large scale wind power integration.From the perspective of steady-state operation,it grows to be more difficult to realize secure and reliable active power schedule due to the inherent stochastic fluctuation of wind power,which increases the risk of encountering unsafe frequency deviation under wind power uncertainty.On the other hand,variable speed wind turbines cannot naturally response to the system frequency change since they are connected into the grid via power electronics converters.Therefore,the system inertial response is severely eroded and it make frequency instability more possible after significant activwe power imbalance.In order to improve frequency security and stability for the power system with a large proportion of wind power generation,this dissertation study focus on system frequency analysis and control,including the system frequency response estimation method,and constructive measures to improve system frequency response performance,where wind power prediction is selected to enhance the steady-state frequency performance,and inertial control is selected to improve the dynamic frequency performance.The research contents of this dissertation are summarized as follows.In terms of short-term wind power prediction,chapter two proposes a correlation analysis-based input selection method and ANFIS-based hybrid prediction methodology.The results in practical wind farm demonstrates the contribution of the proposed methods to the improvement of prediction accuracy.Then the steady-state system frequency series caused by wind power prediction errors are yielded by employing the existing steady-state system frequency calculation method.It has been proved that the high-accuracy wind power prediction plaies an important role in maintaining the secure steady-state system frequency.A hybrid equivalent model(HEM)is proposed in chapter three for system post-disturbance frequency response prediction,which combines measurement and model information.It is comprised of an equivalent rotor model,equivalent governor model,and equivalent load model.The equivalent governor model is estimated form discrete data through continuous-time system identification method.The equivalent load model approximately takes into account the voltage effect of active loads based on the system identification technology.Practical power system simulation data is used to validate the advance of HEM.On the basis of HEM,the frequency response analysis model is established for power system with large scale wind power integration.By utilizing this model,chapter three also studies the system frequency response with the grow of wind power penetration rate,and the impact of primary frequency control of wind power plant on system frequency response.Considering wind power plant inertial control,the system frequency response model is established via state space modelling.It is then used to analytically study the influence of inertial control gains on steady-state system frequency.Then simulations are implemented to analyze the influence of inertial control gains on dynamic system frequency,from which the optimal selection direction of inertial control gains and their influence on system stability are concluded.On the basis of system frequency response state space model,nonlinear bifurcation theory is introduced to study the influence of inertial control gains on system stability.According to the bifurcation theory-based stability analysis,two stable wind power plant inertial control strategies are presented,and simulation results show their decent frequency control performances and stability.