Comparison of Sensor and Sensor-less Vector Control Techniques for Induction Motor in EOT Crane Low Speed Applications

This paper presents a comparison between Sensor or Indirect Field Oriented Control (IFOC) and Sensor-less Field Oriented Control (SFOC) in low frequency region for Induction Motor (IM). These two strategies can be considered among the family of Vector Control (VC) methods and provide a solution for high-performance drives. Most of the Electrically-operated Overhead Travelling (EOT) Crane IMs are controlled with vector control techniques. IM performance will deteriorate as frequency falls below 5 Hz due to its stator resistance drop. There are some critical requirements which needs rocket segments and satellite needs to be positioned in very precise position. For this EOT crane has to run in creep speed which needs drive has to run below 5 Hz. In this paper, the analysis is carried out on IFOC and SFOC methods and implemented to IM drives. In IFOC, flux magnitude and angle is achieved by imposing a slip frequency derived from the rotor dynamic equations with monitored rotor speed using external sensor such as encoder. Whereas SFOC does not require any sensor for estimation of flux magnitude and position, with monitored stator voltages and stator currents, flux magnitude and position can be achieved. Advantages and disadvantages of two control methods are emphasized in low frequency region (0-5 Hz). The theoretical results are found to be consistent with experimental results performed on 100 HP, three phase IM. It is concluded that IFOC method is better than SFOC method in low frequency region.