Sensorless control of nonsalient permanent magnet synchronous motor drives using rotor position tracking PI controller

This paper presents a new velocity estimation strategy of a nonsalient permanent magnet synchronous motor drive without high frequency signal injection or special PWM pattern. This approach is based on the d-axis current regulator output voltage of the drive system which has the information of rotor position error. The rotor velocity can be estimated through a rotor position tracking PI controller that controls the position error to zero. For zero and low speed operation, the PI gain of rotor position tracking controller has a variable structure according to the estimated rotor velocity. Then, in zero speed, the rotor position and velocity has a sluggish dynamics because the varying gains are very low in this region. In order to boost the bandwidth of PI controller in zero speed, loop recovery technique is applied to the control system. Analyzing this control system by the frequency domain specification such as phase margin and bandwidth assignment, the PI tuning formulas are also derived.