Performance enhancement of a 720-step stepper motor for solar array drive of Indian remote sensing satellites to achieve low power micro-stepping

This paper presents the design and analysis done on the 720 step hybrid stepper motor used to drive solar array drive mechanism of Indian remote sensing satellites (IRS). The original design reported in PEDS 1995, develops a peak holding torque of 1.1 NM, saturating at 42 Volts. The authors then, introduced a phenomenon called "torque saturation" different from material saturation to explain the phenomenon of saturation. Recent investigation on the same motor using electro-magnetic FE CAD tools together with circuit simulation tools showed that the torque saturation in the motor is purely due to material saturation. The magnetic circuit was then optimized to remove all saturation effects. FE analysis showed that the motor could develop a peak holding torque of 5 NM for the same excitation. Hardware verification model with de-saturation of stator alone developed 2.6 NM. In addition a method is evolved to reduce the spatial harmonic content in the holding torque. Using the de-saturated stepper motor, a power optimal micro-stepping mode of operation is being realized for use in future IRS missions.