Research On Control Methods For Power Converters Based On Sliding Mode Variable Structure Algorithms

With the fast development of power electronics technology,power converters are becoming more and more popular in power systems,transportation,aerospace,household appliances and other fields,and they are the key equipment to achieve efficient power conversion.In order to meet the increased performance requirements of power converters in different fields,the research on related technologies of power converters has become one of the hotspots in academia and industry.The control strategy is the core of power converter technologies,which directly determines the dynamic performance and steadystate performance of converter systems.It should be noted that unknown loads and parametric uncertainties usually exist in converter systems,and power converters constantly switch between different circuits due to the turn-on and turn-off of power switching devices,which leads to nonlinear property.When linear control strategies are applied as the controllers of power converters,the system performance may be affected by the complex environment,the variations of system conditions,and unknown loads and parametric uncertainties,which may lead to some problems such as slow dynamic response speed,poor disturbance rejection ability and robustness,and poor steady-state performance.As a special nonlinear control strategy,sliding mode variable structure control strategy has the advantages of fast dynamic response and insensitivity to external disturbances and uncertainties.It has strong applicability to converters with variable structure property,and has achieved remarkable research and application results in industrial and academic fields.Therefore,it is of great theoretical significance and practical value to carry out the research on control strategies for power converters based on sliding mode variable structure control algorithms.In this dissertation,two typical power converters,including DC/DC Buck power converters and three-phase three-level NPC rectifiers,are selected as the research objects.And based on the research of terminal sliding mode control,adaptive sliding mode control,fuzzy sliding mode control,super-twisting algorithm and other sliding mode variable structure control strategies,a series of improved schemes are proposed to improve the performance of power converter systems.The specific research content and contributions of this dissertation are presented as follows:1.Based on the single-loop control structure,an observer-based adaptive non-singular fast terminal sliding mode control strategy is proposed for a DC/DC Buck power converter with unknown loads and parametric uncertainties.Firstly,in order to reduce the adverse influence of mismatched disturbance on the control accuracy,a nonlinear disturbance observer is used to estimate matched disturbances and mismatched disturbances.Secondly,an adaptive non-singular fast terminal sliding mode control strategy is designed based on the non-singular terminal sliding mode control strategy,which improves the chattering suppression ability and dynamic performance of the output voltage.Finally,the effectiveness and superiority of the proposed control strategy are proved through experiments.2.For three-phase three-level NPC rectifiers with unknown loads,an observer-based improved dual layer nested adaptive sliding mode control strategy is proposed based on the direct power control structure with three control loops.Firstly,in the power tracking loop,an adaptive super-twisting algorithm is utilized to converge tracking errors of active power and reactive power to bounded regions in finite time.Secondly,in the DC-link voltage regulation loop,a disturbance observerbased improved dual layer nested adaptive sliding mode control strategy is designed to solve the two problems of the dual layer nested adaptive sliding mode control strategy,and the DC-link voltage regulation error converges to a bounded region.Then,in the DC-link voltage balancing loop,the PI control strategy is used to balance the voltages of two DC-link capacitors.Finally,the performance of the proposed strategy is tested through experiments.3.Considering that fuzzy sliding mode control strategies are rarely studied in the field of NPC converter control,a fuzzy logic system-based sliding mode control strategy consisting of three control loops is proposed for a three-phase three-level NPC rectifier,which improves the performance of sliding mode control strategies through fuzzy logic systems.Firstly,in the power tracking loop,a fuzzy supertwisting algorithm is proposed to converge power tracking errors to bounded regions in finite time.Secondly,a fuzzy observer-based fuzzy sliding mode control strategy is designed in the DC-link voltage regulation loop,which achieves the bounded convergence of the DC-link voltage regulation error.Then,the PI control strategy is selected as the controller of the DC-link voltage balancing loop,which realizes the voltage balance of two DC-link capacitors.Finally,the effectiveness and superiority of the proposed control strategy are verified through experiments.4.A fuzzy sliding mode control strategy with fast dynamic response is proposed for a three-phase three-level NPC rectifier,which avoids the problem of limited dynamic response speed of the DC-link voltage.Firstly,in the power tracking loop,an improved super-twisting algorithm is designed to achieve fast convergence of power tracking errors.Secondly,in the DC-link voltage regulation loop,based on a super-twisting extended state observer,a continuous fuzzy sliding mode control strategy is proposed to converge the DC-link voltage regulation error to a bounded region quickly.Then,the PI control strategy is adopted in the DC-link voltage balancing loop to control the voltage difference between two DC-link capacitors.Finally,the control performance of the proposed control strategy is presented through experiment results.