A simple starting method for self-controlled synchronous motors in electric propulsion systems for ships

A new method for starting a self-controlled synchronous motor used for propelling a ship is proposed. First, a simple detecting method without any sensor for the initial rotor position is revealed. The initial rotor position can be detected easily by observing the electromotive forces induced in the armature windings due to the change in the field current when the rotor is at a standstill. According to this method, initial rotor position can be detected every 30deg of the rotor position. The starting method, in which the initial rotor position detecting method is incorporated, for the self-controlled synchronous motor is then given. The proposed starting method is based on the DC link current chopping with controlling the DC source voltage during starting period. It is shown that the motor can be started up without reverse rotation, supporting the usefulness of the proposed method. Finally, the speed control systems for the self-controlled synchronous motor after starting period are discussed. It is shown that the basic speed control system with a speed feedback loop is apt to become unstable. It is also clarified that the system with two feedback loops, a speed feedback loop and a current feedback loop, is very effective for the system stabilization after starting.