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

When permanent-magnet synchronous motors (PMSMs) are used for pump and fan 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 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 proportional 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 pump and fan applications.