Permanent magnet motors use permanent magnets to generate the magnetic field of the motor, without the need for excitation coils or excitation current, with high efficiency and simple structure, they are good energy-saving motors. 

With the introduction of high-performance permanent magnet materials and the rapid development of control technology, the application of permanent magnet motors has become more widespread.

1, The nature of the magnetic field is different:

Permanent magnet motor and ordinary motor rotor structure is different, permanent magnet motor rotor installed with permanent magnet poles; ordinary motor rotor installed on the excitation coil, the need for electric current into the magnetic field.

2, Power density: 

Compared with ordinary motors, permanent magnet motors have high power density, mainly refers to the small size of permanent magnet motors and power generation or output power.

3, More energy efficient: 

Compared with traditional motors, any point of speed are saving power, especially in the lower speed when this advantage is especially obvious, compared with ordinary motors energy saving up to 20% -40%. Most modern submarines use large-diameter, low-speed 7-bladed large side-slope propeller or pump-jet propeller, low speed, high propulsive efficiency. 

Moreover, the submarine underwater more low noise speed maneuvering, so that this advantage of permanent magnet motor is better embodied and play. 

4, Small size, light weight:

Permanent magnet motor structure is simple, due to the use of high-performance permanent magnetic material to provide magnetic field, so that the permanent magnet motor air gap magnetic field is greatly enhanced compared with the ordinary motors, and the volume and weight of the permanent magnet motor most of the ordinary motors is greatly reduced, the motor size and shape are also flexible. 

5, Lower failure rate, widely used: 

Due to the use of high-performance rare-earth permanent magnet materials to provide the magnetic field, so the failure rate is lower, the use of more common. 

6, Large starting torque:

Due to the normal operation of the permanent magnet motor rotor winding does not work, and thus in the design of the rotor winding can be made to fully meet the requirements of the high starting torque, for example, from 1.8 times up to 2.5 times, or even greater.