Ship electric propulsion with a sensorless permanent magnet synchronous motor: A simulation study

Abstract

New general ships powered by electric propulsion always operate at low motor speeds. Popular sensorless vector control methods, including open loop and closed loop methods, are not reliable in this application. This is because the magnitude of back-electromotive force voltage is very small in the low speed region, and the performance of these methods is therefore significantly degraded. To overcome this problem, a high-frequency injection method is introduced in the control of the ship electric propulsion system. The injected periodic signal creates a high-frequency revolving field to act as a carrier. Then the desired information about the position angle of the motor can be retrieved. A simulation model of a ship electric propulsion system is established in Matlab/Simulink. The test results show that the newly proposed control system works stably with various ship operating conditions and robustly against speed variations. Its estimated position error is less than 0.3 rad. Moreover, the proposed sensorless vector control approach has been compared with the closed-loop-based model reference adaptive system. The comparison has demonstrated that the dynamic characteristics of the proposed control system are superior to the latter.