Abstract: Regarding the problem of instability in the start-up process of permanent magnet synchronous motor

（PMSM）air-conditioner compressor caused by different operating conditions，and combined with the characteristics of shaft error speed closed-loop control，a set of three-stage start-up application program pertinent to rotor position recognition→I/f open-loop startup→error angle feedback closed-loop switching was proposed. Through three individual phase and two directional injections，the initial position of the rotor was accurately detected to determine the best initial phase angle. The current closed-loop I/f starting strategy with torque-angle self-balancing characteristics was adopted to ensure the successful start-up of the compressor. Through the error angle feedback，the stator current was adjusted to reduce the shaft deviation，and the smooth switching to the double closed-loop control of current and speed could be realized. Based on the simulations and experiments，the good start-up characteristic of PMSM airconditioner compressor under different load conditions were verified，which has been applied in small central airconditioner systems successfully.

      Key words: permanent magnet synchronous motor（PMSM）；air-conditioner compressor；position sensorless

vector control；I/f start-up control；shaft error