Research On PMSM Braking Process In Ship Electric Propulsion System

In recent decades,with the development of power electronic and the maturation of large-power AC motor variable frequency speed control technology,the ship electric propulsion technology make a show of advantage in civil and military ship little by little and becomes the development trend of future ship power plant.In the process of the braking,in terms of the motor of electric propulsion ship supplied by the AC-DC-AC frequency converter,the motor is in a state of renewable braking.The mechanical dynamic energy deposited by the motor rotor and the propeller can be transformed into electricity energy,which is returned to the DC capacitance of the frequency converter.At the same time,leads to pumping voltage.If the energy could not be timely released,it will bring the exceeding-voltage protecting action,or result in the large power parts over-voltage broken of the main loop circuit.So,the ship brakeing is related to safe operation of the frequency converter device and have influence on the ship's safety and the personal safety of the seafarers.At present,the study of electric propulsion ship's braking technology is a new subject in China.Therefore,laboratory modeling and simulation is important for the theory research and production development of ship electric propulsion technology.First of all,the structure and characterstic of electric propulsion system is introduced and analyzed the advantage and disadvantage compared with general propulsion.Then,the Azipod thruster's moment of inertia,the free navigation characteristic,reversal characteristic and the resistance characteristic were studied and the hull-motor-propeller energy relationship was elaborated.And,the origin of the yantai-dalian train ferry course and the ship's basic condition were introduced briefly. Secondly,the PMSM's mathematical model and its electric dragging movement function were established based on the coordinate conversion.Then,the work principle of AC-DC-AC voltage source inverter and the DTC control strategy of PMSM were studied.The research was emphasized on the principle of the large electric propulsion ship braking leading to pumping voltage and returning energy,in addition a kind of pumping voltage detection unit was designed.From the point of view of energy conversion,a relative accurate calculating expression of the power resistor was deduced.Thirdly,the PMSM,frequency converter DTC,azipod thruster and the ship's braking process were simulated in this paper.The simulation results were validated and analyzed.Some exploring research on ship electric propulsion system taking the PMSM as the main propulsion motor has been developed in this paper.Some significant conclusions have been drawn by academic analysis and simulation.