Sensorless control and start-up strategy of permanent magnet synchronous motor

In order to realize sensorless vector control of permanent magnet synchronous motor, a novel method based on improved flux observer was adopted. A low-pass filter was used instead of a pure integrator, which reduced the errors caused by the initial value and DC offset. The magnitude and phase errors of the stator flux linkage introduced by the low-pass filters were compensated in the polar coordinate to make accurate estimation of speed and rotor position. In order to start motor successfully under the load conditions, a start-up method called I-f control was used, which can avoid the problem of overcurrent. A new switching strategy was also adopted. The given position was switched to the estimated according to weighting function. At the same time the given stator current was changed accordingly. It ensured that motors could switch from I-f control mode to vector control mode smoothly and reliably. The experimental results verify that the sensorless control system can work reliably and stably with smooth switching process and good control performance. ©, 2015, Editorial Department of Electric Machines and Control. All right reserved.