Study And Design Of Marine Electric Propulsion Automatic Control System

The podded electric propulsion system is taken as the object of study in this thesis, and in-depth analysis and research on the electric propulsion system are carried out. On the basis, using programmable logic controller, a control system of podded electric propulsion system is made. The main job of the thesis has two parts:firstly the design and programming of podded electric propulsion control system, secondly the mathematical modeling and simulation of direct torque control (DTC) on asynchronous motor.The system designed in the thesis uses PLC as the center of control unit. Slewing motors and propulsion motors are of the asynchronous induction type. There are two sets of control system to realize system redundancy. When the master system break down, the reserved system will replace it automatically, so the reliability of the system is improved greatly. PLC controls the motors by inverters, and the position of pod and the speeds of the propulsion motors are fed back to it through absolute value encoders and speed sensors. The master PLC station, reserved PLC station and distributed I/O modules are connected by PROFIBUS.The converters are controlled by the analog and digital output points in the distributed I/O modules. The absolute value encoders communicate with the PLC via Synchronous Serial Interface (SSI). The main system is programmed in LAD language by step7. The main function of the system includes:the detection and control of propulsion motors’speeds; the detection and regulation of slewing motors’ position.In the end of the thesis, mathematical model of asynchronous motor is made and DTC is simulated in MATLAB. Firstly the mathematical model of asynchronous motor is analyzed and built in the two-phase coordinate by coordinate transformation. The theory of converter is also discussed. The DTC adjusts the speed of motor by controlling both the magnitude and direction of its stator flux. The detection of flux uses the u-i model. At last, DTC is simulated in MATLAB and the results of simulation is analyzed particularly.