Fast sensorless startup method for ultra-high-speed PMSMs with air bearings

Traditional sensorless drives do not have a strict requirement for their acceleration time. Therefore, I-F startup is widely used in these drives. I-F startup cannot successfully operate with very fast acceleration slew rates. Thus, a slow slew rate is generally used for the startup process. However, in the case of the ultra-high-speed (UHS) motors with air bearings, one of the critical requirements is to reach the floating speed of the air bearing as fast as possible, which is generally within the range of 0.5 to 0.8 s. Therefore, to reduce the acceleration time of UHS motors, a new sensorless startup sequence is proposed. It includes a new self-correcting method based on the mechanical equation used for the initial acceleration. The proposed startup sequence also includes one new intermediate stage, which consists of a flux-derivative-based position estimator. The flux derivative estimator is able to provide reliable position information at a lower speed, which makes it possible for the motor to continue its acceleration at the maximum rate around the end of the first revolution. To verify its feasibility, a set of simulations is conducted. Finally, an experimental setup is built, and the acceleration characteristics of both methods are demonstrated on an actual high-speed machine.