A Smooth and Fast I/f Control Method for PMSM Startup by Current Compensation Method

Sensorless control of permanent magnet synchronous motors (PMSM) has been well applied in many industrial applications due to its cost reduction and mechanical simplicity. The back-EMF based sensorless control has poor performance in low-speed range. Therefore in some applications where low-speed accurate control is not required, I/f control method is used for startup and switching to back-EMF-based sensorless control. During the startup, a large load torque disturbance causes large speed fluctuation and lead to oscillation even out of synchronism. This paper analyzes the causes and influencing factors of speed fluctuation, and based on that a control method by current compensation during startup is proposed The proposed method can be effectively applied to reduce the speed ripples without extending the startup time.