When starting the motor the magnetic field rotates too fast for the permanent magnets to lock themselves with the rotating magnetic field. So in order to start the motor it would need a variable speed drive. With a slower rotating magnetic field, the magnets can easily lock themselves with the stators rotating magnetic field.
To know how the variable speed drive should operate, the motor uses a resolver that tells the position of the rotor angle. Now the variable speed drive can calculate and steer the rotating magnetic field according to the rotors position.
There is also a possibility to start a permanent magnet synchronous motor direct on line but then in additions to the magnets, it would also need to integrate a squirrel cage in the rotor. These types of motors are usually referred to as hybrid permanent magnet motors.
Now the motor will just work like a 3-phase asynchronous motor until it picks up enough speed for the permanent magnets to lock themselves with the magnetic field and the motor will start to spin at the same speed as the rotating magnetic field.
There are many different types of permanent magnet motors with different rotor designs. As seen from the chart here the magnets position could either be on the rotor core surface or inside the rotor core. Each design has its pros and cons and one type could not really be compared to the other.
Figure 18. Different kinds of magnet positions in a rotor One can also choose from several kinds of magnets to be used in the rotor when developing the motor. They can either be made from rare-earth magnet materials like Neodymium iron boron or Samarium cobalt or be of ferromagnetic type for example Alnico, an alloy of Aluminum, nickel and cobalt.