Popular science, summary of industrial applications and development trends of various motors

Electric motor (English: Electric machinery, commonly known as "motor") refers to an electromagnetic device that realizes the conversion or transmission of electrical energy according to the law of electromagnetic induction, and is represented by the letter M (the old standard is D) in the circuit. Its main function is to generate driving torque as a power source for electrical appliances or various machinery.

1. The use of the motor

Control motors in the fields of industry, agriculture, and transportation mainly include servo motors, stepper motors, torque motors, switched reluctance motors, and brushless DC motors.

Among the various motors, the most widely used is the AC asynchronous motor (also known as the induction motor). It is easy to use, reliable in operation, low in price and firm in structure, but has a low power factor and is difficult to regulate. Synchronous motors are commonly used in large-capacity and low-speed power machines, because synchronous motors not only have high power factor, but also their speed has nothing to do with the size of the load, but only depends on the frequency of the power grid, and the work is relatively stable. DC motors are often used in occasions requiring wide-range speed regulation, but they have commutators, complex structures, high prices, difficult maintenance, and are not suitable for harsh environments.

After the 1970s, with the development of power electronic technology, the speed regulation technology of AC motors has gradually matured, and the price of equipment has been gradually reduced, which has begun to be applied. The maximum output mechanical power that the motor can bear under the specified working mode (continuous, short-time operation, intermittent cycle operation) without causing the motor to overheat is called its rated power. When using it, pay attention to the regulations on the nameplate. .

When the motor is running, pay attention to matching the characteristics of its load with the characteristics of the motor to avoid flying or stalling. There are many speed regulation methods for electric motors, which can adapt to the requirements of different production machinery speed changes. Generally, when the motor speed is adjusted, its output power will change with the speed. From the perspective of energy consumption, speed regulation can be roughly divided into two types: one is to keep the input power unchanged, and by changing the energy consumption of the speed regulating device, the output power is adjusted to adjust the speed of the motor; the other is to control the input power of the motor to adjust the motor. speed.

2. The development of electric motors

As far as the current development of electric motors is concerned, energy saving is the development purpose, intelligent control is the development trend, and brushless DC motors are the development hotspot.

Energy saving is the key to development

With the increasingly prominent global energy crisis, governments and enterprises around the world are striving to find ways to sustainably develop energy, and increasing income and reducing expenditure is the current common method. At present, my country is also faced with many problems in terms of energy constraints, and it is particularly urgent to balance the relationship between energy and economic development.

From the perspective of saving energy and protecting the environment, high-efficiency motors are the current international development trend. According to the running time of the motor, the CEMEP standard formulated by Europe divides the efficiency into three levels: eff1 (highest), eff2, and eff3 (lowest). In 2003- It was implemented step by step in 2006. The IEC 60034-30 standard divides the motor efficiency into four levels: IE1 (corresponding to eff2), IE2 (corresponding to eff1), IE3, and IE4 (the highest). my country promises to implement IE2 and above standards from July 1, 2011. Both the international requirements and the domestic energy shortage situation require the energy-saving development of electric motors as the primary task.

Intelligent control is the trend

With the development of communication technology, intelligent control has also become a hot topic in the field of motors. The fully automatic washing machines and automatic curtains used in our lives all transmit intelligent signals. Motor control also tends to be simplified and intelligent. PLC, FPGA , DSP and these technologies are increasingly integrated into the motor industry chain.

The functions of intelligent motor control are much more than those of traditional motor control. The intelligent motor realizes low-carbon operation, and the failure probability and downtime are also greatly reduced. It has become an inevitable trend in the development of motor control. For example, an intelligent power module can be used to form a power interface between the microcontroller or DSP and the motor, which can reduce the size of the motor and simplify the design.

The advantages of this module over previous discrete solutions are lower parasitic inductance and higher reliability, because all power devices in the module use the same batch of chips and have consistent test performance. This smart power module can interface directly with microcontroller low-voltage TTL or CMOS outputs with protection circuitry.

The module has built-in thermistors to monitor the junction temperature, logic protection circuits to prevent shoot-through between the upper and lower arms, dead time control, and drive waveform shaping circuits to minimize EMI, etc. In the module, each driver IC can be optimized to switch power devices with minimal EMI and drive losses. It is a great promotion for energy saving.

Brushless DC Motors Are Hot

After years of development and application of motors, the industry is now focusing on brushless DC motors, which has become a hot spot in the development of micro-motors. The brushless DC motor uses semiconductor switching devices to realize electronic commutation, and replaces traditional contact commutators and brushes with electronic switching devices, which has outstanding advantages such as high reliability, no commutation sparks, and low mechanical noise.

Energy-saving transformation of the motor system, the use of new technology and new materials to improve energy consumption, and improve the efficiency of the motor by reducing the loss of electromagnetic energy, thermal energy and mechanical energy. At present, the DC inverter widely publicized in the household appliance industry is a model of energy-saving design.

Some experts say that if only the newly added motors and their driving systems are replaced with high-efficiency and energy-saving motors, more than 100 billion kilowatt-hours of electricity can be saved every year, which will exceed the annual total power generation of the Three Gorges Power Station, and can also reduce Nearly 100 million tons of carbon dioxide emissions. "Individual saving is a small step, collective saving is a big step", and the overall energy-saving effect of promoting high-efficiency energy-saving motors is still very optimistic.

Although the state is actively promoting, there are still five major problems in energy saving of motor systems: basic work such as technical standards needs to be strengthened; efficient general-purpose and special equipment needs to be developed; reasonable matching of motor systems and operating efficiency need to be improved; third-party energy-saving service team construction needs to be Strengthen; incentive policies and institutional mechanisms also need to be improved.

3. Detailed explanation of various motors

Servo motor

Servo motors are widely used in various control systems, which can convert the input voltage signal into the mechanical output on the motor shaft, and drag the controlled element to achieve the control purpose.

Servo motors are divided into DC and AC; the earliest servo motors are general DC motors, and when the control accuracy is not high, general DC motors are used as servo motors. In terms of structure, the current DC servo motor is a low-power DC motor, and its excitation mostly adopts armature control and magnetic field control, but usually adopts armature control.

Classification of rotating electrical machines, DC servo motors can well meet the requirements of the control system in terms of mechanical characteristics, but due to the existence of the commutator, there are many deficiencies: sparks are easily generated between the commutator and the brush, which interferes with the work of the driver. , can not be used in the occasion of flammable gas; there is friction between the brush and the commutator, which will produce a large dead zone; the structure is complex and the maintenance is more difficult.

AC servo motor is essentially a two-phase asynchronous motor, and there are three main control methods: amplitude control, phase control and amplitude-phase control.

In general, servo motors require that the speed of the motor be controlled by the applied voltage signal; the speed can change continuously with the change of the applied voltage signal; the motor must respond quickly, be small in size, and have low control power.

Stepper motor

The so-called stepping motor is an actuator that converts electrical pulses into angular displacement. More generally speaking: when the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in the set direction.

We can control the angular displacement of the motor by controlling the number of pulses, so as to achieve the purpose of precise positioning; at the same time, we can also control the speed and acceleration of the motor rotation by controlling the pulse frequency, so as to achieve the purpose of speed regulation.

At present, the more commonly used stepping motors include reactive stepping motors (VR), permanent magnet stepping motors (PM), hybrid stepping motors (HB) and single-phase stepping motors.

The difference between a stepping motor and an ordinary motor is mainly in the form of its pulse drive. It is this feature that allows a stepping motor to be combined with modern digital control technology. However, the stepper motor is not as good as the traditional closed-loop control DC servo motor in terms of control accuracy, speed variation range, and low-speed performance; therefore, it is mainly used in occasions where the accuracy requirements are not particularly high.

Because the stepping motor has the characteristics of simple structure, high reliability and low cost, the stepping motor is widely used in various fields of production practice; especially in the field of CNC machine tool manufacturing, since the stepping motor does not require A/D conversion, it can It directly converts the digital pulse signal into angular displacement, so it has always been regarded as the most ideal CNC machine tool actuator.

In addition to applications in CNC machine tools, stepper motors can also be used in other machinery, such as motors in automatic feeders, as motors in general-purpose floppy disk drives, and in printers and plotters.

In addition, the stepping motor also has many defects; due to the no-load starting frequency of the stepping motor, the stepping motor can run normally at low speed, but if it is higher than a certain speed, it cannot start, and it will be accompanied by a sharp whistling sound; different The precision of the subdivision driver of the manufacturer may vary greatly. The larger the number of subdivisions, the more difficult it is to control the precision; and the stepper motor will have larger vibration and noise when it rotates at low speed.

Torque motor

The so-called torque motor is a flat multi-pole permanent magnet DC motor. The armature has more slots, commutation segments and series conductors to reduce torque ripple and speed ripple. There are two types of torque motors: DC torque motors and AC torque motors.

Among them, the self-inductance reactance of the DC torque motor is very small, so the responsiveness is very good; its output torque is proportional to the input current and has nothing to do with the speed and position of the rotor; it can be directly connected to the load in a state of close to the locked rotor. No gear reduction is required, so a high torque-to-inertia ratio can be generated on the loaded shaft and system errors due to the use of reduction gears can be eliminated.

AC torque motors can be divided into two types: synchronous and asynchronous. At present, squirrel-cage asynchronous torque motors are commonly used, which have the characteristics of low speed and large torque. Generally, AC torque motors are often used in the textile industry, and their working principle and structure are the same as those of single-phase asynchronous motors, but due to the large resistance of squirrel-cage rotors, their mechanical properties are softer.

Switched Reluctance Motor

Switched reluctance motor is a new type of speed regulating motor with extremely simple and sturdy structure, low cost and excellent speed regulation performance.

Brushless DC Motor

Brushless DC motor (BLDCM) is developed on the basis of brushed DC motor, but its driving current is an uncompromising AC; BLDCM can be divided into brushless speed motor and brushless torque motor . Generally, there are two types of drive currents for brushless motors, one is a trapezoidal wave (usually a "square wave"), and the other is a sine wave.

Sometimes the former is called a DC brushless motor, and the latter is called an AC servo motor, which is exactly a type of AC servo motor. In order to reduce the moment of inertia, the brushless DC motor usually adopts a "slender" structure. The brushless DC motor is much smaller in weight and volume than the brushed DC motor, and the corresponding moment of inertia can be reduced by about 40%-50%. Due to the processing of permanent magnet materials, the general capacity of brushless DC motors is below 100kW.

This kind of motor has good linearity of mechanical characteristics and adjustment characteristics, wide speed regulation range, long life, easy maintenance, low noise, and there is no series of problems caused by brushes, so this kind of motor has a great role in the control system. application potential.

Inverter motor

The construction principle of variable frequency motor

The speed regulation and control of the motor is one of the basic technologies for various industrial and agricultural machinery and electrical equipment for office and people's livelihood. With the amazing development of power electronic technology and microelectronics technology, the AC speed regulation method of "special variable frequency induction motor + frequency converter" is leading a replacement of traditional speed regulation in the field of speed regulation with its excellent performance and economy. The change of the replacement of the speed regulation method.

The good news it brings to all walks of life is: greatly improving the degree of mechanical automation and production efficiency, saving energy, improving product qualification rate and product quality, correspondingly increasing the capacity of the power supply system, miniaturizing equipment, and increasing comfort. The fast speed replaces the traditional mechanical speed regulation and DC speed regulation scheme.

Due to the particularity of the variable frequency power supply, and the system's requirements for high-speed or low-speed operation and dynamic response of the rotational speed, strict requirements are put forward for the motor as the main body of power, which brings new issues to the motor in terms of electromagnetism, structure and insulation. .

Application of variable frequency motor

Variable frequency speed regulation has now become the mainstream speed regulation scheme, which can be widely used in continuously variable transmission in all walks of life. Especially with the increasing application of frequency converters in the field of industrial control, the use of frequency conversion motors is also becoming more and more extensive. It can be said that due to the advantages of frequency conversion motors compared with ordinary motors in frequency conversion control It is not difficult to see the figure of the inverter motor.

Linear Motor

It is used in various motion control systems, especially the servo system, because the AC synchronous motor (referred to as synchronous motor) has its own reliability and maintenance, power factor, motor size and moment of inertia, control accuracy, field weakening ratio, etc. For large-capacity motors, countries around the world have basically tended to use synchronous motors. For example, high-power air compressors, water pumps in industrial applications, high-power hoists in the coal and non-ferrous metal industries, and large-capacity rolling mills in steel mills are all driven by synchronous motors.

In recent years, the application of linear motors in the feed servo system of machine tools has been paid attention to in the world machine tool industry, and the "linear motor fever" has been set off in the industrially developed regions of Western Europe. In the machine tool feed system, the biggest difference between the direct drive of the linear motor and the original rotary motor drive is that the mechanical transmission link from the motor to the worktable (carriage) is cancelled, and the length of the machine tool feed transmission chain is shortened to zero Therefore, this transmission method is also called "zero transmission".

The "zero-drive" transmission mode brings performance indicators and advantages that the original rotary motor drive mode cannot achieve. High-speed response Because some mechanical transmission parts (such as lead screws, etc.) with large response time constants are directly cancelled in the system, the dynamic response performance of the entire closed-loop control system is greatly improved, and the response is extremely sensitive and fast.

The precision linear drive system cancels the transmission gap and error caused by the mechanical mechanism such as the lead screw, and reduces the tracking error caused by the delay of the transmission system during the interpolation movement. Through the linear position detection feedback control, the positioning accuracy of the machine tool can be greatly improved. High dynamic stiffness Due to the "direct drive", the motion lag phenomenon caused by the elastic deformation, friction and wear and backlash of the intermediate transmission link during starting, shifting and reversing is avoided, and the transmission stiffness is also improved.

Secondly, the speed is fast and the acceleration and deceleration process is short. Since the linear motor was first used in the maglev train (the speed can reach 500Km/h), it is used in the feed drive of the machine tool to meet the maximum feed speed of its ultra-high-speed cutting (requires up to 500 km/h). 60 to 100 M/min or higher) of course there is no problem.

Also due to the high-speed responsiveness of the above-mentioned "zero transmission", the acceleration and deceleration process is greatly shortened. In order to achieve instant high speed when starting, and instant accurate stop when running at high speed. Higher acceleration can be obtained, generally up to 2~10g (g=9.8m/s2), while the maximum acceleration of ball screw drive is generally only 0.1~0.5g. The stroke length is not limited. By connecting linear motors in series on the guide rail, the stroke length can be extended indefinitely.

Quiet movement and low noise Since the mechanical friction of the drive screw and other components is cancelled, and the guide rail can be used as a rolling guide rail or a magnetic pad suspension guide rail (no mechanical contact), the noise during movement will be greatly reduced. High efficiency Since there is no intermediate transmission link, the energy loss during mechanical friction is eliminated, and the transmission efficiency is greatly improved.

(Source Motor Technology and Applications)