Investigation Of Direct Torque Control Technique Of Ship Electric Propulsion System

In order to master the key control techniques and solve the existing problems in ship electric propulsion system, and provide the theoretical basis and experience for the localization of above control system, the direct torque control (DTC) technique of AC motor drives with high-capacity and large-inertia for the ship electric propulsion system is studied in this article.Firstly, after studying the developing history and implementation status of ship electric propulsion system and investigating the developing process, existing problems and hotspots in DTC system, the special requirements and the improving direction for DTC technique in ship electric propulsion system are analyzed.Secondly, based on the establishment of the DTC system models, the reasons for producing output torque ripple are analyzed in detail and the assessment index of torque ripple in DTC system is proposed. Then the control strategies for reducing the torque ripple is discussed.Thirdly, after the qualitative and quantitative analysis of regulating function of zero voltage vectors to direct torque control, the effect and the quantitative relationship with other variables of zero voltage vectors is discussed, which provides the theoretical basis for the suitable use of zero voltage vectors. Based on that, the 12-sector dividing theory of space vector control and the regional interpolation of zero voltage vectors are proposed. According to above control strategies, the unexpected problems of the applied effect of zero voltage vectors are solved in the conditions of not increasing the numbers of power electronic devices in main control system. The zero voltage vectors possess special regulation function to the electromagnetic torque and can effectively reduce the torque ripple, which provides the control ideas for the ship electric propulsion motor drives with high-capacity and large-inertia.Fourthly, according to the mathematic analysis for the various space vectors of control variables, the control predictive algorithm of DTC is proposed and the predictive unit of flux linkage amplitude is designed. Then the calculation equations of flux linkage amplitude increment and electromagnetic torque are provided, which provides the theoretical basis for the predictive control technique of the DTC system.After that, according to the qualitative and quantitative analysis of angleαto the regulating function of voltage vectors and combining the internal characteristics and the operation requirement of the ship electric propulsion system and the problems existing in DTC general control strategy for high-capacity and large-inertia motor drive system, the reasons and essence of non-symmetry of torque regulation is analyzed systematically. The above study provides the theoretical foundation for rational utilization of the non-symmetry of torque regulation; increase the dynamic response speed of the control system, and assurance for the dynamic features and static regulating precision of the DTC system.Finally, based on the action effect of zero voltage vectors, the dividing theory of 12-sectors, the regional interpolation algorithm of zero voltage vectors, and the analytical conclusions of non-symmetry of torque regulation, the DTC adaptive control system for ship electric propulsion system is designed under the condition of not increase the hardware. Through the comparative analysis with the practical ship testing data, the effectiveness of above conclusions is proved...