The motor is a machine that realizes the conversion between mechanical energy and electrical energy based on the phenomenon of electromagnetic induction, including two main categories: rotating machines and transformers. Rotating motors are electromechanical energy conversion devices, mainly used as generators to convert mechanical energy into electrical energy, or as motors to convert electrical energy into mechanical energy. Some motors are also used as phase shifters to improve the power factor of the power grid. In addition, there are micro-special motors widely used in automatic control systems. Transformers are electrical energy conversion devices without relative motion between components, widely used in electrical energy transmission, voltage, current, impedance conversion, and circuit isolation.

Human production labor is inseparable from various energy sources. In modern industrialized society, various natural energy sources generally cannot directly drive production machinery; they must first be converted into electrical energy, and then the electrical energy is converted into the required energy forms (such as mechanical energy, thermal energy, sound energy, light energy, etc.) for utilization. This is because electrical energy is extremely convenient in production, transmission, distribution, usage, control, and energy conversion. Motors are energy conversion machines related to electrical energy, and they are important devices commonly used in industry, agriculture, transportation, national defense engineering, medical equipment, and daily life.

The main functions of motors are reflected in three aspects:

1. Production, transmission, and distribution of electrical energy

In power plants, generators are driven by steam turbines, gas turbines, diesel engines, or water turbines. The generator converts the energy from burning fuel, nuclear fission, or the potential energy of water into mechanical kinetic energy, which is then transmitted to the generator, where it is converted into electrical energy. The electrical energy is then stepped up in voltage by transformers and transmitted through power lines to the areas of use, where it is stepped down in voltage again by transformers for user consumption.

2. Driving various production machinery and equipment

In agriculture, industry, transportation, national defense, and living facilities, various electric motors are widely used to drive production machinery, equipment, and tools. For example, electric motors are generally used to drive machine tools, power drainage, agricultural product processing, ore mining and transportation, traction for trams and electric locomotives, pumping, blowing, lifting, steel rolling, papermaking, medical equipment, and household appliances.

3. Important components in various control systems and automation, intelligent devices

With the increasing level of automation in agriculture, industry, and national defense facilities, various control motors have emerged. They serve as execution, detection, amplification, and calculation components in control systems, automation, and intelligent devices (such as electronic computers and robots). These motors generally have smaller power but come in various types and serve different purposes, such as automatic selection and display in elevators, remote control of valves, automatic positioning of artillery and radar, launching and attitude control of aircraft, automatic control and display in machine tool processing, as well as operation control, detection, or recording display in computer peripherals, various automatic recording instruments, audio-visual recording and playback equipment, medical devices, and modern household appliances.

A brief history of motor development

As introduced in the preface, in October 1831, Faraday created the first model of an induction generator. Since then, the research and application of electricity have rapidly developed, and electricity, as a new and powerful energy source, has begun to play an increasingly significant role in human production and life.

Driven by the direct needs of production, practical generators and motors have emerged one after another, continuously improved and perfected in application. The initial generators were water magnetic generators, which used permanent magnets as field magnets. Due to the limited magnetic field strength of permanent magnets, permanent magnet generators could not provide strong power and lacked practicality. To increase the output power of generators to meet practical requirements, it was necessary to transform various components of the generator. The main components of the generator are the field magnet, armature, commutator, and brushes. In 1845, British physicist Wheatstone successfully used an external power source to excite the coil, replacing the permanent magnet with an electromagnet. He then improved the armature winding, thus creating the first electromagnetic generator. In 1866, German scientist Siemens produced the first self-excited generator using an electromagnet. The success of the Siemens generator marked a breakthrough in the construction of large-capacity generators, thus obtaining strong power. Therefore, the Siemens generator has epoch-making significance in the history of electrical development.

The discovery of the self-excitation principle is a key link in the development of permanent magnet generators to excited generators. Self-excitation refers to the process where a DC generator uses a portion of the electrical power it induces to excite the field magnet, thus forming an electromagnet. In the improvement process of the generator, the change of the magnetic field has gone from water magnetic to excitation; while current excitation has gone from separate excitation to self-excitation, and self-excitation has gone through the development process from series excitation to parallel excitation, and then to compound excitation. Therefore, DC generators can be divided into separate excitation and self-excitation types based on their excitation methods, and self-excited generators include series, parallel, and compound forms.

In 1870, Belgian engineer Gram (1826–1901) relied on the principles proposed by Wally and adopted the tooth-shaped armature structure invented by Italian Pacinotti (1841–1912) in 1865 to create a ring-shaped slotless closed armature winding, producing a ring armature self-excited DC generator. In 1873, German electrical engineer Hefner-Alteneck (1845–1904) further improved the armature of the DC generator, successfully developing a drum-shaped armature self-excited DC generator. He absorbed the advantages of Gram and Pacinotti's generator rotors, simplified the manufacturing method, thus greatly improving the efficiency of the generator and reducing production costs, bringing the generator into the practical stage. By this time, the basic structure of the DC generator had reached standardization. In 1880, American inventor Edison manufactured a large DC generator named "Giant" and exhibited it at the Paris Exposition in 1881.

At the same time, the research and development of motors were also underway. American engineer Davenport was the first to attempt to drive machinery with a motor in 1836. In 1834, Russian physicist Jacobi invented a rod-shaped iron core motor with a power of 15W.

Generators and motors are two different functions of the same machine; when used as a current output device, it is a generator, and when used as a power supply device, it is a motor. This reversible principle of motors was accidentally proven in 1873. That year, at the industrial exhibition in Vienna, a worker mistakenly connected a wire to a running Gram generator, resulting in the rotor of the generator changing direction and immediately rotating in the opposite direction, turning into a motor. Before this, motors and generators had developed independently. Since then, people realized that DC motors could operate as both generators and motors, and this unexpected discovery had a profound impact on the design and manufacture of motors.

With the development of power generation and supply technologies, the design and manufacturing of motors have also become increasingly refined. In 1878, the iron core slotting method was introduced, which embedded the winding into slots to enhance the stability of the winding and reduce eddy current losses within the wires. The structures of the slotted iron core and drum-shaped winding that emerged at that time are still in use today. In 1880, Edison proposed the laminated core method, and Maxim proposed the principle of radial ventilation ducts in the core to solve the heat dissipation problem of the core. In 1882, the double-layer armature winding was proposed, in 1883 the laminated magnetic pole was invented, in 1884 the compensating winding and commutation pole were invented, and in 1885 carbon powder was invented for making brushes. The magnetic circuit calculation method was established in 1836, and the theory of direct current armature winding was established in 1891. By the 1890s, direct current motors had all the main structural characteristics of modern direct current motors.

Although direct current motors have been widely used and have generated considerable economic benefits in applications, their inherent disadvantages have restricted their further development. This is because direct current cannot solve the problems of long-distance transmission and voltage conversion, leading to the rapid development of alternating current motors. During this period, two-phase and three-phase motors were successively introduced. In 1885, Italian physicist Galileo Ferraris (1841-1897) proposed the principle of the rotating magnetic field and developed a two-phase asynchronous motor model. In 1886, Nikola Tesla, who moved to the United States, independently developed a two-phase asynchronous motor. Russian electrical engineer Dolivo-Dobrovolsky produced a three-phase single-cage asynchronous motor in 1888. The development of alternating current motors, especially the successful development of three-phase alternating current motors, created conditions for long-distance transmission and elevated electrical engineering technology to a new level.

Around 1880, British engineer Ferranti improved the alternating current generator and proposed the concept of high-voltage alternating current transmission. In 1882, British engineer Gordon manufactured a large two-phase alternating current generator. In 1882, Frenchman Gaulard (1850-1888) and British John Gibbs obtained a patent for "methods of distributing electricity for lighting and power" and successfully developed the first transformer with practical value, which is the most critical device in the alternating current transmission and distribution system.

The basic structure of a transformer consists of an iron core and windings, as well as components such as an oil tank and insulating sleeve. Its working principle is based on the mutual induction phenomenon discovered by Faraday in 1831, which is the phenomenon where a change in current in one circuit induces an electromotive force in a nearby circuit. By winding a primary winding and a secondary winding on the same iron core, when alternating current flows through the primary winding...

...the continuous change in current causes the magnetic field it generates to also change continuously. In the primary winding, an electromotive force is induced. The transformer relies on this working principle to increase the voltage output from the generator while reducing the voltage at the user's end. With the transformer, the basic conditions for high-voltage alternating current transmission are established. In 1884, British engineer Edward Hopkinson (1859-1922) invented a transformer with a closed magnetic circuit. Later, Westinghouse (1846-1914) improved the structure of Gibbs' transformer, making it a transformer with modern performance. In 1891, Blok manufactured a high-voltage oil-immersed transformer in Switzerland, and later developed a giant high-voltage transformer. Continuous improvements in transformers have made significant progress in long-distance high-voltage alternating current transmission.

After more than 100 years of development, the theory of motors has become quite mature. However, with the advancement of electrical engineering, computer science, and control technology, the development of motors has entered a new stage. Among them, the development of alternating current speed-regulating motors is particularly noteworthy.

As early as more than half a century ago, the principles of traditional methods for changing voltage, cascade, and variable frequency for alternating current speed regulation had already been thoroughly researched. However, due to the need for circuit components and rotating conversion units to implement these methods, and because their control performance could not match that of direct current speed regulation, they were not widely promoted for a long time. After the 1970s, with the advent of power electronic conversion devices, issues such as the need to reduce equipment, minimize size, lower costs, improve efficiency, and eliminate noise in speed regulation devices were gradually resolved, leading to a leap in alternating current speed regulation. After the invention of vector control, the static and dynamic performance of alternating current speed regulation systems was further improved. However, implementing vector control requires complex electronic circuits, making their design, manufacturing, and debugging quite troublesome. After adopting microcomputer control, vector control algorithms can be implemented through software, standardizing hardware circuits, thereby reducing costs, improving reliability, and potentially enabling more complex control technologies. Thus, the rapid advancement of power electronics and microcomputer control technology is the driving force behind the continuous updating of alternating current speed regulation systems.

In addition, the development of high-performance permanent magnet materials and superconducting materials has also injected new vitality into the development of motors.

Permanent magnet motors, due to their simple structure, good reliability, high efficiency, and energy savings, are superior to ordinary motors when considering cost, performance, investment, maintenance, and reliability. However, in the past, the magnetic energy product of permanent magnet materials was relatively small, which limited their widespread application. In recent years, with the rapid development of rare earth permanent magnet materials and power electronics technology, permanent magnet motors have made significant progress. Motors and generators using neodymium-iron-boron permanent magnet materials have been widely applied, from large ship propulsion to small artificial heart pumps.

Superconducting motors have already been used in power generation and the propulsion of high-speed magnetic levitation trains and ships.

With the advancement of science and technology, the improvement of raw material performance, and the enhancement of manufacturing processes, motors are now available in thousands of varieties and specifications, with power levels ranging widely (from fractions of a watt to over 1000 MW), an extremely broad range of speeds (from several days per revolution to hundreds of thousands of revolutions per minute), and very flexible environmental adaptability (such as on flat ground, plateaus, in the air, underwater, in oil, in cold, temperate, humid, and dry tropical regions, indoors, outdoors, on vehicles, on ships, and in various different media), meeting the needs of various sectors of the national economy and human life.