Classification of General-Purpose Motors

Permanent Magnet Brushless Motors

Brushless motors originated in the late 1960s and developed rapidly alongside permanent magnet material technology, microelectronics and power electronics technology, and motor technology. A brushless motor is a typical electromechanical integrated product, mainly composed of the motor body, position sensor, and electronic switching circuitry. A brushless motor with a rotor made of permanent magnet material is also called a permanent magnet brushless motor, and the vast majority of brushless motors use permanent magnet rotors.

Permanent magnet brushless motors can be divided into two types: brushless DC motors (BLDCM) driven by square wave (injected with square wave current into the stator windings of the motor body) and permanent magnet synchronous motors (PMSM) driven by sine wave. Compared to traditional brushed DC motors, BLDCMs replace the mechanical commutation of traditional DC motors with electronic commutation and reverse the stator and rotor (the rotor uses permanent magnets), thus eliminating the need for a mechanical commutator and brushes. PMSMs, on the other hand, replace the excitation windings in the rotor of a wound-rotor synchronous motor with permanent magnets, while keeping the stator unchanged, thus eliminating the need for excitation coils, slip rings, and brushes. Because the stator current of a BLDCM is driven by a square wave, it is much easier for the inverter to obtain a square wave under the same conditions compared to the sinusoidal drive of a PMSM. Furthermore, its control is simpler than that of a PMSM (although its performance at low speeds is worse than that of a PMSM-mainly due to the influence of pulsating torque). Therefore, BLDCMs have gained wider attention.

Permanent magnet brushless motors have garnered increasing attention due to their superior performance and irreplaceable technological advantages. Especially since the late 1970s, rapid advancements in supporting technologies such as rare earth hydromagnetic materials, power electronics, and computer control, along with continuous improvements in micro-motor manufacturing processes, have led to continuous improvements in the technology and performance of permanent magnet brushless motors. Initially used in small and medium-sized servo drives in aerospace, robotics, and home appliances, they are now widely applied in electric vehicles, electric multiple units, and electric ships. In the future, with the continuous development of permanent magnet brushless DC motor technology and related supporting technologies, as well as the ongoing progress of human society, permanent magnet brushless motors will find even wider applications.

Linear Motors

Significant progress has been made in motor design theory, promoting the application of linear motors and bringing them back into the spotlight.

In recent years, linear motors have been practically applied in industrial machinery, rail transportation, elevators, aircraft carrier aircraft launchers, electromagnetic guns, missile launchers, and electromagnetic propulsion submarines. The so-called "space elevator" being researched by the United States and other countries involves using linear motors to launch space shuttles or spacecraft into space.

In computer disk drives, there is a type of motor that drives the read/write head called a voice coil motor, which can also be considered a type of linear motor.

Linear motors are not limited to electric motors; there are also linear generators. Figure 2-7 shows a wave-driven linear generator.

Stepper Motors
Stepper motors convert electrical pulse signals into angular displacement to control rotor rotation, serving as actuators in automatic control devices. Each input pulse signal causes the stepper motor to move one step forward, hence it is also called a pulse motor. With the development of microelectronics and computer technology, the demand for stepper motors is increasing daily, and they are used in all sectors of the national economy.

The drive power supply for a stepper motor consists of a frequency converter pulse signal source, a pulse distributor, and a pulse amplifier, which provides pulse current to the motor windings. The operating performance of a stepper motor depends on the good coordination between the motor and the drive power supply.

Stepper motors are classified into two basic types based on their motor type: electromechanical and magnetoelectric. Electromechanical stepper motors consist of an iron core, coils, and gear mechanisms. When the solenoid coil is energized, it generates magnetic force, which actuates the iron core, causing it to move. The gear mechanism rotates the output shaft by an angle, and an anti-rotation gear keeps the output shaft in the new working position. When the coil is energized again, the shaft rotates by another angle, and so on, performing stepping motion. Electromagnetic stepper motors mainly come in three forms: permanent magnet, reactive, and permanent magnet induction.

Superconducting Motors Superconducting motors are not much different from ordinary motors in terms of electromechanical energy conversion principles, except that their windings use superconducting materials, which can greatly reduce size and save energy. Because superconductivity requires refrigeration equipment, the structure is particularly complex, and therefore they are generally only used in large generators or motors (such as those used for propelling massive ships). Figure 2-9 shows a superconducting DC motor for ships.

Ultrasonic Piezoelectric Motors Ultrasonic piezoelectric motors are a new type of drive device developed in the mid-1980s. They have no magnetic field or windings, and their principle is completely different from traditional electromagnetic motors. It utilizes the inverse piezoelectric effect of piezoelectric materials to convert electrical energy into ultrasonic vibration of an elastic body, and then converts friction transmission into rotational or linear motion of the moving body. This type of motor has advantages such as low operating speed, high output, compact structure, small size, and low noise. Moreover, it is unaffected by environmental magnetic fields and can be applied in fields such as biological life sciences, optical instruments, and high-precision machinery.