A simple approach to sensorless control for permanent magnet synchronous motors

Traditionally, encoders or resolvers are used to get the position feedback in permanent magnet synchronous motor (PMSM) drives. However, due to the drawbacks associated with these sensors, significant research has been conducted in the area of sensorless control. Most of the sensorless control methods such as neural network, particle swarm optimization, sliding-mode observer, or their combinations, require sophisticated algorithms to achieve the estimation of rotor position. In this paper, a simple approach is proposed to obtain its primitive value by adopting necessary current sensors and the 120-degree difference relationship between the two phase current signals. The estimated rotor angle is given by proportionally tuning the position error for considering the factors of speed command and speed sampling period. As a result, the complexity and computing ability of the processor used in the drive will be reduced and cheaper at the product stage. Furthermore, the conventional proportional-plusintegral (PI) control is adopted for the controlled system. With the aid of Bode diagram, an extension of the frequency zone-based method can decouple the multiple tuning gains so that the PI gain constants may be adjusted individually. Finally, the experimental results of the proposed method implemented in a DSP-based motor drive system with a 2-kg disc load are presented to show the effectiveness.