This paper summarizes the great contributions of AC motor variable frequency speed regulation technology to energy saving, environmental protection, manufacturing industry (production and quality improvement), traffic traction and household appliances.

1. Frequency control

AC motor, especially cage asynchronous motor, has a series of advantages, such as small volume, light weight, simple structure, convenient maintenance, low manufacturing cost and operation cost, and reliable operation in harsh environment. However, in the past, due to the difficulty in speed regulation or the inefficiency of some speed regulation methods, the DC speed regulation is still occupied in the field of speed regulation for a long time, and the advantages of AC motor have not been brought into play in the speed control drive. Until the early 1970s, with the rapid development of power electronics, Microelectronics (integrated circuit) and microcomputer technology, the long-term desired variable frequency governor has been industrialized.

1.1 the so-called variable frequency governor -- it transforms three-phase power frequency (50 Hz) AC power supply (or any power supply) into three-phase AC power supply with adjustable voltage and frequency. Sometimes, the variable frequency governor is called VVVF. It is mainly used to adjust the speed of AC motor (asynchronous machine or synchronous machine).

1.2 an AC motor variable frequency speed regulation system is composed of three parts: variable frequency governor driver, AC motor and controller. The key equipment is frequency converter, which can realize the smooth change of motor voltage and frequency.

1.3 variable frequency speed regulation is incomparable with the former voltage regulation speed regulation, pole changing speed regulation, cascade speed regulation, slip speed regulation and hydraulic coupling speed regulation in the aspects of frequency regulation range, static precision, dynamic quality, system efficiency, perfect protection function, easy realization of automatic control and process control. It is recognized as the most ideal and promising speed regulation scheme of AC motor, and represents the development direction of electric drive in the future.

1.4 in the past 30 years, frequency control has been widely used in steel, metallurgy, petroleum, chemical industry, textile, chemical fiber, light industry, papermaking, rubber, plastic, power, water and other industries. The application of variable frequency speed regulation of low voltage motor has been very popular and mature. High voltage motor frequency control is also being concerned and gradually applied. In addition to excellent speed regulation performance, AC motor frequency conversion speed regulation has significant functions of saving electric energy and protecting environment. It is an ideal speed regulating device for enterprise technical transformation and product upgrading.

2. Frequency control and energy saving of fan and water pump

2.1 there is a large power gap between the contradiction between power supply and demand (the supply exceeds demand), which requires power saving.

According to the statistics of relevant departments, in 2002, China's installed power generation capacity was 31.9 billion kw, and the annual power generation was 134.6 billion kwh. Although the power scale ranks the second in the world, the per capita power consumption is the bottom of the world. Moreover, China's rapid economic development needs more power. If the national economic growth rate is 8%, the power generation capacity of China should be 570-600 million KW by 2010, and the annual power generation capacity will reach 28000-2900 billion kwh. In the summer of 2003, the continuous high temperature caused the shortage of power supply in some provinces and cities, and forced to take measures to limit power supply. Due to the overburden of power network, the instability of local power system is caused.

The above shows that China's power supply and demand imbalance, supply is less than demand. Therefore, it is necessary to save electricity.

2.2 energy saving benefits of frequency conversion speed regulation of fan and water pump

2.2.1 the total installed capacity of motor in China is 450 million KW, which consumes about 65% of the national power generation. Therefore, it is very important to realize the motor power saving. There are two ways to save energy in general motors: one is to improve the efficiency of the motor itself to achieve long-term and efficient operation, which is mainly used for constant speed machinery; the other is to improve the control accuracy of motor speed to make the motor run at the most energy-saving speed.

2.2.2 fans, pumps and compressors are motor driven equipment with large amount and wide range in national economic production. The total motor capacity reaches 150 million, and the power consumption accounts for about 35% of the national power generation. About 20% ~ 30% of the fan water pumps need to be adjusted.

2.2.3 frequency control is the best scheme for energy saving of fan and water pump. According to fluid theory, the shaft power of centrifugal fan pump is a cubic function of rotational speed. When the speed is reduced, the power consumption will be greatly reduced. For example, when the speed is 50%, the mechanical power of the shaft is only 12.5%. Of course, the efficiency of the speed control scheme varies greatly. The efficiency of the hydraulic speed control device after slip is not high, η ≈ (1-s). At 50% speed, η vs ≈ 50%, while the efficiency factor of frequency conversion governor is high, η VVVF ≈ 95% ~ 98%, and it is almost unchanged. Therefore, in many speed regulation schemes, frequency conversion speed regulation has the best energy-saving benefit and should be the first choice.

[example] for the same fan water pump, the shaft power is 100% when the speed is 100% and the shaft power is reduced to 50% when the speed flow is 50%.

If the damper is used and the valve is controlled to 50% flow, 70-80% power still needs to be absorbed from the power grid; if the slip low efficiency speed regulation is adopted to 50%, the power of ≈ 25% needs to be absorbed from the power grid; if the frequency conversion is used to speed up to 50% flow, only 10% power needs to be drawn from the grid.

2.2.4 there are various methods for regulating the flow of fan and water pump, and each has its own characteristics, but it can be divided into three types

(1) The traditional mechanical method is used to adjust the opening degree of fan baffle, deflector and water pump valve;

(2) Electromagnetic slip clutch or hydraulic coupling is used to adjust the speed of fan and water pump (while the motor runs at constant speed);

(3) AC motor frequency control scheme.

The following table shows the comparison of flow regulation methods of three types of fans and water pumps and the conclusions.

2.2.5 nowadays, it is more necessary to promote the application of high-voltage frequency conversion speed regulation and energy-saving on fans, pumps and compressors driven by large capacity high-voltage motors. The reason is very simple. The larger the installed capacity, the greater the absolute power saving.

3. Frequency control and environmental protection:

3.1 motor drive is a large consumer of electric energy, accounting for more than 60% of total electricity consumption in China. Excessive power consumption makes coal and oil (natural gas) fuel exhausted. At the same time, a large number of CO2 and NO2 emissions cause environmental pollution, destroy the ozone layer, and even endanger human survival.

Human beings have constantly learned a painful lesson from the destruction of living environment and the waste of energy resources. Therefore, the protection of human living environment has become the common voice of the people all over the world, and set off a wave of reducing energy conservation and environmental protection and benefiting the society. In 1972, the first World Declaration on the human environment in Stockholm, Sweden, and the Kyoto agreement of Japan in 1994 stipulated that all the contracting countries should control their CO2 and other harmful gas emissions which produce greenhouse effect to the level of 1990. It fully demonstrates the importance of environmental protection and the concern of people all over the world.

3.2 it is estimated that the impact of electrical products on environmental pollution accounts for about 30%. Therefore, saving electric energy and reducing waste have become important factors in fulfilling the commitment of Kyoto protocol. What role and contribution can frequency conversion speed regulation and frequency conversion technology play?

(1) The popularization of fan pump frequency conversion speed control energy saving technology can achieve 20% ~ 30% power saving rate, which can reduce the construction of thermal power plants and power generation, that is, less emissions of SO2, so, CO2 and dust, and reduce air pollution;

(2) Traction frequency conversion locomotive application, no coal and oil burning, reduce emission pollution;

(3) Develop urban rail transit (Metro and maglev train) and fuel cell vehicles to reduce CO2 emissions.

(4) It is advocated to adopt electric bicycle (brushless DC motor, self-made frequency conversion speed regulation) and stop using fuel moped.

４。 Frequency control and manufacturing production:

4.1 variable frequency speed regulation can increase output

AC motor is designed under the condition that the air gap flux is approximately constant, and the motor is allowed to run for a long time (20% short-term test) at the speed of 5-10%. For example, in some countries, the motor can operate at 50 / 60 Hz for a long time (of course, V / F = cont) should be guaranteed. As long as the motor bearing can bear it, it is feasible to increase the speed by 5-10%. A chemical fiber factory of our company has brought considerable production increase effect by properly increasing the output frequency of frequency converter combined with the transformation of frequency conversion and speed regulation.

(2) Frequency control can improve product quality

Variable frequency speed regulation has the advantages of wide speed range, high speed regulation accuracy and good dynamic response. It is very suitable for multi unit synchronous transmission or proportional synchronous (Draft) transmission for chemical fiber spinning machines, textile printing and dyeing combined machines, paper machines and injection molding machines. It not only has the transmission performance of DC machine before, but also has the characteristics of firm, reliable and simple maintenance of AC machine, which makes the quality of products larger To improve. Improve the degree of automation, reduce the labor intensity of workers.

(3) Frequency control and some special processing equipment

Due to the progress of frequency conversion technology, variable frequency speed regulation is more suitable for very high speed without speed up gear or very low speed without speed down gear in harsh environment (explosion, corrosion, underwater nuclear radiation, etc.), as well as precise position control (frequency conversion servo system, stepping system, manipulator and robot) system.

5. Frequency control and soft start, soft start and soft stop

5.1 the power grid and production process require soft start and soft stop of motor

5.1.1 the starting current of AC motor is generally 5-7 times of rated current. If it is started directly, it will cause impact on the power grid and affect the normal operation of other electrical equipment in the same grid. In addition, the huge starting current will also cause serious electromagnetic stress and mechanical stress on the motor and mechanical equipment, shorten the service life of the equipment, so the power system hopes to be able to soft start (especially high voltage and large capacity motor).

5.1.2 some processing machinery, such as automatic flow production line (bottle, can packaging line, conveyor, etc.), shall start and stop smoothly to avoid mutual collision and skew; in order to prevent water hammer and surge, water pump also hopes to start and stop (it is better to use soft start and soft stop for "pump control characteristics").

5.2 characteristics of frequency converter as soft starter

Different from the soft starter of electronic solid-state motor, because the voltage and frequency of the motor change at the same time when the frequency converter is started, the magnetic flux of the motor can be maintained unchanged (the electronic soft starter only changes the voltage and does not change the frequency, so the motor starts under the weakening magnetic flux), so the soft starting of the frequency converter has greater starting torque. It is very suitable for heavy load and large inertia equipment, such as blast furnace fan. In this situation, the performance of electronic motor soft starter is incomparable or not competent at all. The frequency converter can be used both in soft starting and speed regulation, and its application prospect is very good. At present, due to the price factor, the inverter can not be widely used, except for individual heavy load starting and large inertia starting occasions, frequency converter is not only used as soft starter. Maybe after a few years, the inverter will be widely used after further price reduction.

6. Frequency control (including inverter technology and household appliances)

In ordinary families, the air conditioner is the largest power consumption, followed by electric heating appliances, and finally lighting and audio-visual electrical appliances. Frequency conversion speed regulation (including frequency conversion technology) can also play a role in energy saving and environmental protection.

6.1 frequency conversion air conditioner: with frequency converter (there are two kinds of conventional frequency converter and self-made frequency converter, i.e. DC brushless motor speed regulation), the non-stop compressor can continuously control the refrigeration capacity of the compressor, realize effective operation, and is conducive to energy saving. In addition, frequency conversion air conditioner is very fast and comfortable, which is also conducive to environmental protection.

6.2 high frequency electromagnetic cooker and rice cooker: frequency conversion technology is used to generate (20-30) kHz high-frequency power supply to make the cooking heat efficiency of the rice cooker itself reach about 80% (30% higher than that of the previous resistance heater), which is conducive to energy saving.

6.3 frequency conversion lighting equipment: frequency conversion technology is used to generate (20-70) kHz high-frequency power supply to fluorescent lamps, which can save 15% of electric power, and can be turned on immediately. There is no flicker of power frequency fluorescent lamps. It is suitable for work or study, and also conducive to environmental protection.

6.4 other household appliances, such as variable frequency refrigerator, variable frequency washing machine and frequency conversion microwave oven, have also appeared one after another.