The brushless DC motor overcomes the shortcomings (brushes and commutators) of the DC motor. Its characteristics are as follows:
In the permanent magnet excitation type DC motor, the excitation with permanent magnets (on the stator side) and the armature coil (on the rotor side) are exchanged. The excitation with permanent magnets is configured on the rotor side and the armature coil is on the stator side.
The electrical commutation using brushes based on the change in the position of the commutator has been replaced by using Hall elements to detect the rotor position signal. The signal is first fed back to the frequency converter and then the electrical power is controlled.
This is the brushless DC motor.
Since the drive voltage emitted by the frequency converter becomes alternating current, therefore, the permanent magnet synchronous motor, which is driven by alternating current, can also be regarded as an alternating current motor. However, in this book, it is regarded as a brushless DC motor in an independent field.
Since the rotation principle is similar to that of a DC motor, the relationship between torque and speed is almost the same as that of a DC motor.
While having the excellent control performance of DC motors, compared with DC motors, due to the absence of brushes, it also has various characteristics such as advantages in electromagnetic interference and service life, high efficiency, energy saving, and strong design freedom, making it easy to conduct equipment assembly design. Therefore, it is not only applied to information such as HDD (Hard Disk Drive) and CD-ROM drives where such advantages can be exerted, but also widely used in household appliances such as refrigerators and washing machines.
During the emergence and development of brushless DC motors, distributed windings were used for the stator coils in the initial stage, but recently, concentrated windings have been basically used. Regarding distributed windings and concentrated windings, please refer to "Distributed Windings and Concentrated Windings" in the column.
