Load Torque Observer Based Sliding Mode Control Of Ship Propulsion PMSM

With the increasing development of power electronics and variable frequency speed regulation techniques for AC motors,the AC electric propulsion system of a ship has achieved rapid development and has become a crucial issue. Note that the working condition of the ship propulsion motor suffers from severe diversity and complexity, in addition to significant torque disturbances, which would destroy the stability and safety of an electric propulsion ship. To compensate and eliminate the influence of load torque disturbances on an electric propulsion control system, we propose an approach by employing a load torque observer, and thereby enhancing the robustness and disturbance rejection for the load torque of a ship propulsion motor control system.First, a comprehensive survey on the ship electric propulsion, AC motor variable frequency speed control technology and the load disturbance rejection of PMSM has been presented in this thesis. Moreover, the vector control of ship propulsion PMSM and the fundamental principle of sliding mode control have also been covered.In addition, the sliding mode controller based on load torque observers has been designed to replace the traditional PI speed regulator such that the load torque disturbance rejection ability of the closed-loop control system can be improved. Moreover, simulation studies and comparative analysis on the cases of no load, suddenly increasing load and decreasing load are comprehensively carried out to demonstrate the effectiveness and superiority of the proposed method.Furthermore, a double sliding mode control scheme using sliding mode speed controller and sliding mode observer of load torque for a PMSM vector control system is proposed in this thesis. To be specific, the estimate from sliding mode observer of load torque is directly fed to the sliding mode speed controller such that the amplitude of discontinuous item pertinent to the sliding mode controller is dramatically reduced. As a sequence, the sliding-mode chattering can be significantly supressed and the dynamic robustness and load torque disturbance rejection can be enhanced.Finally, the proposed sliding mode speed control strategy based on load torque observer is applied to ship propulsion PMSM control system. Simulation results and comparative analysis on the cases of constant speed and constant load torque, load torque disturbance and ship propeller load conditions demonstrate the feasibility and effectiveness of the proposed control strategy.