A sensorless, stable V/f control method for permanent-magnet synchronous motor drives

When permanent-magnet synchronous motors (PMSMs) are used for pumps and fans applications, V/f control methods can be used to control them. The problem with open-loop V/f control of PMSMs without having damper windings in the rotor is the inherent instability after exceeding a certain applied frequency. In this paper, a new V/f control method is proposed for those motor drives for stable operation in a wide frequency range. The magnitude of the voltage is controlled in order to maintain a constant stator flux linkage in the PMSM. The applied frequency is modulated proportionally to the input power perturbations to stabilize the drive for a wide frequency range. No position sensor is required to implement this stabilizing technique. The small signal analysis and the experimental results confirm the effectiveness of this stabilizing technique. The experimental results also indicate the satisfactory performance of the drive for pumps and fans applications.