Sensorless flying start method for starting of induction motors

Electrical variable speed drives (VSDs) are the most widely used power-electronics-based equipment in the industry that controls the performance (speed and torque) of AC induction motors (IMs). One of the main tasks of the VSDs is soft starting the IM. VSDs are usually programmed to start the IM from standstill (zero speed). In many industrial applications, due to high inertia of load or external forces such as wind, the IM may spin while the drive is in standby or off state. In such cases, high electrical and mechanical shock will be applied to the IM (and VSD) if the start command is sent. However, in cases that the IM rotation speed and direction is estimated, the VSD can control the IM from the estimated speed without any stress. The starting method without any sensor (or encoder) is called sensorless flying start (SFS). In this paper, a new SFS method for VSDs is introduced and verified in MATLAB/SIMULINK environment.