Dynamic Analysis And Control Of Wind Power System Based On Fractional Order Theory

In the growing trend of wind power system installed capacity and scale,a large number of power electronic devices,generators and other dynamic components have been introduced,which will affect the stability of the whole system.Non-linear factors such as internal machinery,electricity,and magnetism in the wind power system are easily to stimulate oscillation behavior,which will lead to bifurcation and chaos.Fractional order modeling and control have higher degrees of freedom and better control performance,and most systems in nature can be described in fractional order form.Therefore,with the introduction of fractional calculus theory,the thesis systematically studied the analysis and control of nonlinear oscillation characteristics such as machine,electricity and magnetism in wind power systems.The specific research work is as follows:(1)The integer order dynamical model of wind power system was established,which mainly includes:wind turbine shaft system model,permanent magnet synchronous wind generator model,grid interconnected power system model and ferroresonance model of power system,and the basic knowledge of the definition,properties,solving algorithm and stability theorem of fractional calculus were also introduced,which would lay the foundation for the stability theory derivation,analysis and control of the fractional 'order equation in subsequent chapters.(2)For the problem of the dynamic characteristic analysis and control of wind turbine shafting model,the dynamic characteristics of autonomous shafting model were analyzed without considering the time-varying stiffness and external excitation.Considering the time varying stiffness,the combined external excitations of mechanical input torque of wind turbine and electromagnetic torque of the generator,the bifurcation equation of non-autonomous system was obtained by using multi-scale method,and the influence law of combined excitation on system dynamic behavior was revealed.In addition,on the basis of the transmission shaft torque equation,the fractional order damping force and nonlinear stiffness were introduced,and the fractional order model of the wind turbine shaft system was established.The response characteristics of the system under combined excitations were analyzed by the separation method of fast and slow variables,and the effect of fractional damping on system dynamics was discussed.In order to suppress the torsional vibration of the shaft system quickly and effectively,considering the uncertainties of system combination external disturbances,an adaptive fixed-time terminal sliding mode control method was proposed.Compared with the finite-time method,the proposed method had less overshoot,almost no chattering,faster convergence and independent of the initial value.Simulation results demonstrated the effectiveness and superiority of the proposed method.(3)For the problem of dynamic characteristic analysis and chaos control of permanent magnet synchronous wind generator,the stability discriminant at the equilibrium point was deduced for the system with or without external excitation,and the minimum order was also calculated.The influence law of internal parameters and external excitation on the dynamic characteristics of the system were analyzed.The phenomena of chaos and bifurcation and their motion paths were proved under different orders.In order to reduce or even eliminate the nonlinear chaotic oscillation of the system,considering the uncertainty of system parameters and external disturbances,the adaptive update law was designed,and a fixed time fractional sliding mode adaptive control method was proposed.Compared with the existing methods,the proposed control method had higher performance advantages.(4)Aiming at the problem of bifurcation and chaos oscillation in the power system due to the active power of the wind farm and the reactive power consumed by the load,based on the double-parameter integer order dynamic model,the complex dynamic behavior of the system with different double-parameter was shown.Furthermore,the integer order model was extended to fractional order,and the minimum order of chaotic oscillation was analyzed.The bifurcation and chaos characteristics of the system with different double-parameter and orders were studied.In order to suppress the chaotic oscillation of the system,considering the uncertainty of system parameters and taking the system equilibrium point as the control objective,a fractional finite time sliding mode control method was proposed.Compared with the traditional sliding mode method,the proposed method with better parameter identification effect and stronger robustness can be stable to the equilibrium point in finite time.(5)Aiming at the problem of the ferroresonance chaos mechanism analysis and suppression in wind farm power system,based on the ferroresonance model of wind farm power system,the basic conditions for entering a chaotic state were analyzed.Considering the resonance phenomenon of external excitation,the approximate solution of the main parameter resonance was calculated by using the multi-scale method,and the steady state solution and stability condition were determined.The effect of external excitation on the dynamic characteristics of ferroresonance was discussed.The model was further extended to fractional order,the complex dynamic behavior of the system with different orders and nonlinear exponentials of magnetic flux linkage were studied.In order to suppress the chaotic oscillation of the system,a fractional-order finite time terminal sliding mode controller was proposed on the basis of the frequency distribution model of time-frequency domain conversion.The chaotic phenomenon in resonant overvoltage was suppressed in finite time.Compared with the traditional sliding mode method,the effectiveness and superiority of the proposed controller were proved.