Research On Multi-motor Synchronous Control Based On Fractional Order Sliding Mode Control

Multi-motor synchronous control has always been one of the research hotspots in the field of motion control. It is widely applied in manufacturing processes such as textiles, paper making, printing, metallurgy, steel rolling, machine processing and so on. As the multi-motor synchronous control system is a higher-order, time-varying, multi-variable, strong coupling, and complex nonlinear system, the control performance is more and more difficult to meet continuous improving system requirements in practical work. In order to further improve static and dynamic performance of the multi-motor synchronization control system, the research of multi-motor synchronous control strategy and method possesses important theory sense and practical value.In view of the problem that multi-motor synchronous control strategy doesn’t consider sufficient error information, the thesis designs a relative coupling strategy based on the maximum, minimal, average tracking error. A fractional-order mathematical model of the permanent magnet synchronous motor (PMSM) that is more precise than the integer-order one is built. And a fractional second-order nonsingular terminal sliding mode control (F2NTSMC) algorithm is proposed. For the further improvement of multi-motor synchronous control system performance and capacity of resisting disturbance, a composite control strategy combining active disturbance rejection control (ADRC) and fractional-order sliding mode control is put forward. Simultaneously, a fractional sliding mode control (FSMC) scheme based on disturbance observer (DO) or extended state observer (ESO) is designed. The main content of this thesis falls into the following:Through deep analysis of multi-motor non-cross-coupling control strategy, cross-coupling control strategy and its various improved generation, a relative coupling strategy based on the maximum, minimal, average tracking error is proposed. The simulations reveal that the control strategy can improve dynamic and static performance of the system and robustness.The fractional mathematical model of PMSM is built by using the theory of fractional calculus. Then the theory of fractional calculus is introduced into sliding mode variable structure control, thus proposing a F2NTSMC method. The stability of the control law is proved according to the fractional Lyapunov stability theory. Through the simulation experiment of multi-motor position synchronous control based on fractional order sliding mode, the results reveal that the method can achieve effective control of multi-motor position synchronization.Considering that sliding mode control is easy to produce the chattering phenomenon near the equilibrium point and ADRC has the characteristics of simple structure, independence on the object model, strong robustness and so on, a piecewise control strategy between ADRC and F2NTSMC is applied. When the system state is far away from the equilibrium point, SMC is adopted; and when the system state is near the equilibrium point, ADRC is applied. Simultaneously, a composite control strategy that substitutes SMC for the nonlinear state errors feedback unit is proposed. The simulation and analysis verify the correctness and effectiveness of two control strategies.The DO or ESO is used to estimate and compensate the lumped system disturbances, and the F2NTSMC is employed to solve the problem of multi-PMSMs position synchronization. According to the super twisting algorithm, a nonlinear disturbance observer (NDO) is designed. The stability of the observer and the fractional-order control law based on the observer is proved. In accordance with the shortcoming that the extended state observer is difficult to suppress measurement noise, a kind of new ESO with a differentiator is designed. Simulation results show that the NDO or ESO based FSMC has good dynamic and static performance and strong robustness.