Research On Adaptive Sliding Mode Control Of Doubly-Fed Wind Generator DC Grid-Connected Syste

The double-fed asynchronous generator(DFIG)is currently one of the mainstream models in the field of variable speed and constant frequency systems.With the increasing demand for long-distance power transmission,wind power systems that can be directly connected to the grid have become a hot research topic in the field of wind power,where double converter DFIG system can effectively and low-cost to achieve DC grid connection of wind farms.However,due to the aerodynamic and internal structure effects,the non-linear and strongly coupled nature of the system makes the operation of traditional control schemes unsatisfactory.Therefore,this thesis investigates the problem of maximum power point tracking control for double converter DFIG system,with the following innovative work:(1)An adaptive sliding mode control strategy based on feedback linearisation is proposed for the maximum power point tracking problem of the double converter DFIG system.Firstly,the non-linear and strongly coupled characteristics of the system will lead to increased difficulty in the design of the system controller,so this thesis adopts the input-output feedback linearization algorithm to decouple the system,and designs the sliding mode controller based on the feedback linearization to realize the maximum power point tracking control of the double converter DFIG system,and designs adaptive variable parameters for the discontinuous terms in the sliding mode controller to weaken the negative impact of high frequency jitter on the system operation.Then system stability is demonstrated with using the Lyapunov function.Finally,the effectiveness of the control strategy proposed in this section is verified by simulation.(2)A sliding mode control strategy based on a finite-time disturbance observer is proposed to address the problem that the double converter DFIG system is affected by external environmental changes,unmodelled dynamics and parameter perturbation.Firstly this section collates the mathematical model of the double converter DFIG system to obtain a system model containing unknown perturbations,and designs a finite-time perturbation observer to estimate the unknown perturbations to the system,Based on this,a control strategy combining finite-time perturbation observer and sliding mode control(FLC-DOSMC)is proposed for the DFIG system after feedback linearisation to achieve maximum power point tracking control of the system.Then a rigorous finite-time stability proof is performed with using Lyapunov stability theory.Finally,the effectiveness of the control strategy proposed in this section is verified by simulation.(3)The convergence time of the system state under finite-time control depends on the initial value of the system,and if the initial state of the wind power system is far from the desired state,the convergence time will become larger.In order to improve the response speed of the system,this section applies fixed-time control theory into the control system design and proposes a fixed-time sliding mode control strategy(FLC-FTSMC)for achieving maximum power point tracking control of a double converter DFIG system.Then a rigorous fixed-time stability proof is performed using Lyapunov stability theory.Finally,the effectiveness of the control strategy proposed in this section is verified by simulation.