Sensorless control of a stand-alone Doubly fed induction machine for ship shaft generator systems

This paper presents a position sensorless control strategy of stand-alone doubly fed induction machine (DFIM) used for ship shaft generation systems. Direct voltage control method is used to generate constant frequency and voltage with variable load and main engine speed. The strategy does not need any signal from speed, so the position encoder or estimators are unnecessary. The space vector pulse width modulation (SVPWM) technique is used to reduce the rotor current harmonics and the modification of the reference stator vector angle is applied to achieving the reference stator voltage quickly and successfully. Simulation results are given to illustrate the efficacy of the proposed method.

I. Introduction

Using shaft generators can save energy and protect the environment, so more and more ships are being equipped with such systems. The use of shaft generators provides many advantages, such as lowering of fuel and maintenance costs, reducing cabin noise level and smaller capacity of diesel generators [1]–[3]. Shaft generators onboard ships are driven by the main engine. The shaft generators must maintain the constant amplitude and frequency of the stator voltage, although the speed of the main engine changes as the vessel travels at different sea areas or the propeller are strongly affected by water flow. The conventional shaft synchronous generator systems use an inverter between the generator and the load, so the inverter need to manage the entire of the total output power, and the synchronous condenser is required to providing the reactive power [4].