Fractional-order Sliding-mode Control Approach For Stand-Alone Power Generation System Based On A Brushless Doubly-Fed Induction Generator

Sliding-mode control has been widely used in theoretical and practical fields owing to its simplicity of implementation and high robustness against uncertainties which satisfy the so-called matching condition.However,the sliding-mode control is failed to deal with the mismatched uncertainties existing in the uncontrolled channel cannot satisfy the matching condition.Thus,the control problem of the systems with mismatched uncertainties has been a hot topic in the research of sliding mode control theory.The integral sliding-mode control method and the disturbance observer-based sliding-mode control method is limited by the strict uncertainty condition of constraint,and can only compensate constant or slow time-varying mismatched uncertainties.The proposed full-order terminal sliding-mode control method breaks through the limitation of uncertainties.However,the derivative of the virtual control law exists in the actual control law introduces the switching term into the actual control signal.In the ship shaft power generation,the stand-alone generation system of brushless doubly-fed induction generator(BDFIG)is a typical nonlinear,multivariable,strongly coupled system with unmatched uncertainties.The BDFIG is a new type of AC excitation induction motor which eliminates the brushes and slip rings.Thus,it has the wide operation speed range,long service life and easy maintenance.The brushless doubly-fed induction generator can be used for the grid-connected power generation or stand-alone power generation,and has a broad application in the fields of wind power generation and ship shaft power generation.However,the working environment of the stand-alone generation control system of BDFIG on a ship is complex,which leads the control system should achieve more satisfactory dynamic performance and strong robustness to uncertainties such as load mutation interference and machine parameter perturbation.Therefore,there are profound theoretical significance and important practical values to further improve the sliding-mode control theory,solve the compensation problem of the mismatched uncertainties and chattering problem,propose control system of the BDFIG with higher control performance.In this thesis,a fractional-order sliding-mode approach is proposed to solve the singular the chattering problem and achieve high performance control performance of the nonlinear system with mismatched uncertainties.Furthermore,basing on the proposed control approach,a novel fractional-order sliding-mode controller design method is proposed to enhance the robustness to machine parameter perturbation and the output power quality of the BDFIG stand-alone generation system.Finally,the correctness and effectiveness of the proposed method has been demonstrated by the simulation and experimental results.The specific contents are as follows.(1)This thesis proposed a virtual control technique based fractional-order sliding-mode control approach to solve the control problem of the nonlinear system with mismatched uncertainties.The singular problem in the actual control signal can be solved by the reasonable sliding manifold design.The designed fractional-order integral-type control law can eliminate the chattering in the actual control signal.In order to solve the chattering problem completely,this thesis proposed a super-twisting algorithm based fractional-order sliding-mode control method,the designed fractionalorder integral-type control law can eliminate the chattering completely.The proposed fractional-order sliding-mode control method exhibited the fast convergence,non-singularity,high precision and strong robustness.(2)In order to analysis the matched and mismatched uncertainties causing by the machine parameter perturbation,this thesis proposed the outer-loop voltage amplitude control subsystem with the mismatched uncertainties and the inner-loop CW current control subsystem basing on the BDFIG model under the control winding synchronous rotation in dq coordinate system.This thesis combined the proposed virtual control technique based fractional-order sliding-mode control and the subsystem with uncertainties to propose a novel controller design method to compensate the uncertainties causing by the parameter perturbation in the BDFIG control system.The proposed control approach can avoid the singularity problem and eliminate the chattering in the actual control law.Thus,the ripple of the output voltage can be weakened,the quality of output voltage can be improved.(3)In order to analysis the matched and mismatched uncertainties in BDFIG under unbalanced load,this thesis proposed the external outer-loop voltage amplitude control subsystem with the mismatched uncertainties and the inner-loop CW current control subsystem with matched uncertainties in negative sequence basing on the BDFIG r model under the control winding synchronous rotation in doubly rotating coordinate system.This thesis proposed a fractional-order sliding-mode controller design method to complete the complex uncertainties,improve the operation performance of the stand-alone generation system under the unbalanced load,reduce the output voltage ripple,improves the output power quality and balances the three-phase output voltage.