Research On Intelligent Fault-tolerant Control For Ship Electrical Propulsion System

Ship electric propulsion systems integrate propulsion power with other electricity consumption,which is characterized by the reduced volumes of power units and the enhanced operation reliability together with the unified energy utilization and managements,and has become the main development direction of smart ships in the future.The use of multiple generator sets,various electrical loads and smart substation equipment has changed the topology and operation characteristics of ship electric propulsion systems,and has raised a huge challenge to the analytical fault-tolerance control.Therefore,it is of great significance to study the intelligent fault-tolerance control technology of ship electric propulsion systems by considering the fault behavior characteristics and fault-tolerance control architecture.In this paper,several key problems of intelligent fault-tolerance control for ship electric propulsion systems are studied:Firstly,the fault-tolerance control architecture and mathematical modeling of ship electric propulsion systems are carried out.The basic structure and functional characteristics of ship medium voltage direct current(MVDC)electric propulsion systems are clarified.Considering the multi-layer structure and integrated design of fault-tolerance control system,a hierarchical and intelligent fault-tolerance control architecture framework of ship MVDC electric propulsion systems is proposed,which can uniformly describe the internal relations among system state monitoring,health assessment,fault diagnosis and fault-tolerance control strategy.The mathematical models of power generation subsystem,propulsion subsystem,regional load set,and power distribution subsystem are established,which provides the theoretical framework and model basis for the research of fault-tolerance control.The six-phase permanent magnet synchronous motors(PMSMs)and propeller load characteristics in the propulsion subsystem are highlighted.Secondly,the intelligent assessment is performed on the typical failure modes and effects analysis of ship electric propulsion systems.Considering the reliability of expert evaluation,the uncertainty of fuzzy information,and the inherent correlation between failure modes and causes,an intelligent assessment method of failure mode effects based on fuzzy logic and decision-making trial and evaluation laboratory(DEMATEL)is proposed.The comprehensive weight allocation combining information entropy and qualitative analysis is used to determine the credibility weights of expert opinions.The fuzzy language term sets and fuzzy numbers are introduced to obtain the fuzzy evaluations and relative fuzzy weights.The benchmark adjustment search algorithm is designed to calculate the alpha-level sets of fuzzy risk priority numbers(RPNs).The centroid defuzzification idea and alpha-level set theory are synthesized to defuzzify the fuzzy RPNs.The defuzzified RPNs are regarded as the inputs of DEMATEL technique to investigate the causal degrees and risk prioritization of failure modes.Taking the typical failure modes of propulsion subsystem as an example,the effectiveness of proposed intelligent assessment method is verified,which provides a theoretical foundation for the subsequent design of fault-tolerance control strategy.Then,the intelligent fault-tolerance control strategy of six-phase PMSMs with winding open-phase for ship electric propulsion systems is carried out.A mathematical description of open-phase fault-tolerance system for six-phase PMSMs with parameter perturbations and load disturbances is established.Combined with the open-phase fault detection mechanism,a decision-making system of zero-order current commands is presented,which does not need to deduce the decoupling model according to the different open-phase situations and the connection modes of neutral points.A vectorial and decoupled speed/current fault-tolerance control framework is formed.In order to solve the problem of speed tracking and torque ripple caused by open-phase faults in six-phase PMSMs,based on the vector fault-tolerant structure,a robust adaptive backstepping sliding mode fault-tolerance control strategy is proposed.The adaptive estimation technique and robust control energy dissipation inequality are used to compensate the internal parameter perturbations and external load disturbances of backstepping sliding mode system respectively.The speed tracking,disturbance rejection and fault tolerance optimization of six-phase PMSM system with open-phase faults are realized.Considering the difficulties of gain parameter tuning and poor robustness in the adaptive law design,an intelligent observer with recurrent wavelet fuzzy neural network is proposed and applied to the online estimation of uncertain parameter perturbations in the robust backstepping sliding mode fault-tolerance system.The asymptotic stability of six-phase PMSM fault-tolerance control system with robust backstepping sliding mode and intelligent observer is guaranteed.The effectiveness of proposed fault-tolerance control strategy is verified by the open-phase fault simulation test results.Finally,the coordination fault-tolerance control of rudder/propeller output forces in the ship electric propulsion system is studied.The coupling relationship between ship speed and course,and the influence of propeller on course control and rudder on course control are discussed.A mathematical description of ship speed/course control system including wave interferences and parameter calculation errors(called the compound disturbances)is established.Aiming at the partial failure of dual rudders and dual propellers,a nonlinear observer is designed to compensate the uncertain compound disturbances online.Based on the failure coefficients and disturbance observer,an adaptive sliding mode fault-tolerance control strategy is proposed.The priority level of faulty actuators is modified by the effectiveness coefficient matrix.A pseudo-inverse allocation mechanism with fault penalty is designed.In view of the multiple failure modes for dual rudders and dual propellers,such as partial failure,interruption,offset and stuck fault,a mathematical description of ship speed/course control system with multiple actuator faults and compound disturbances is given.The adaptive update laws are designed to estimate the failure factors,stuck factors,upper and lower bounds of stuck faults,and upper and lower bounds of compound disturbances.Based on the estimats of fault parameters and compound disturbances,a nonlinear adaptive backstepping fault-tolerant control strategy is proposed for the integrated design of control law reconfiguration and control allocation.Speed/course tracking,compound disturbance rejection and minimum energy consumption are realized.The simulation platform of rudder/propeller coordination fault-tolerance control in the ship electric propulsion system is constructed,and the feasibility of proposed fault-tolerance control strategies is verified respectively.The research results of this paper have important theoretical significance and application prospects,which can provide the technical foundation and experience accumulation for the engineering application of intelligent fault-tolerance control of ship electric propulsion systems,and realize the reliable operations and health managements of ship electric propulsion systems.In addition,the research results can also be applied to other objects,which will help other engineering fields to learn and promote in the relevant technical levels.