Adaptive target positioning control for permanent magnet synchronous motors with low-resolution shaft encoders

For a high-performance adjustable-speed permanent magnet synchronous motor (PMSM) drive, an accurate speed feedback is required. However, in some applications, only low-resolution incremental encoder is used because of the constraint of costs. In this paper, a closed-loop speed observer with inertia estimation is presented to improve the speed estimation accuracy, and a model-reference adaptive controller (MRAC) is designed as the speed controller. Besides, there are applications that require these adjustable-speed drives to stop at a target position, such as automatic sewing machines, automatic transferring systems, etc. Conventionally, these applications are solved by using inverter drives with programmable logic controllers (PLC) and electromagnetic brakes. However, these kinds of solutions are expensive, slow response, inaccurate, and may induce significant errors due to large load variations. This paper proposes a motion trajectory-scheduling controller (MTSC) for target positioning control. The proposed adaptive control scheme was realized by using a single-chip DSP controller with fixed-point arithmetic. Simulation and experimental results are given to illustrate the performance of the designed PMSM servo drive with one 100 pulses-per-revolution (PPR) encoder.