Detection of Near-propeller Bubbles and Thrust Power in a Constant Torque Control Motor Propulsion System

Abstract

The AC motor drive system is widely used in electric propulsion systems. This motor drive system has a far faster response time (by up to several milliseconds) than a conventional system. It is also possible to monitor the state (current, voltage, torque, rotational speed) of the motor accurately in real time. If bubbling in the vicinity of the propeller is detected by monitoring the motor state, an additional special device such as a torque meter can be omitted from the propulsion system. Furthermore, a faster response time allows advanced propeller control, enabling the suppression of bubble formation and the resulting effects in real time. This paper demonstrates the detection of bubbles and fluctuating thrust due to bubble entrainment by monitoring signals from the motor, as it is driven in constant torque control mode. A fluctuating thrust force can be detected and well correlated with any bubble interactions using the monitoring signal.