Author: Liu Liang Xi [Abstract] This paper reviews the AC motor frequency control technology, a significant contribution to energy saving, environmental protection, manufacturing (production and quality improvement) traffic traction and household appliances. 1, Frequency Control AC motor, especially the cage induction motor, with small size, light weight, simple structure, easy maintenance, low manufacturing costs and operating costs, reliable operation in harsh environments and a series of advantages. However, due to the difficulty of speed regulation or inefficiency of some speed control methods in the past, it has long been occupied by DC speed control in the field of speed control, and the advantages of AC motor can not be obtained in speed control transmission. Until the early seventies of last century, with the rapid development of power electronics, microelectronics (integrated circuit) and microcomputer technology, the long-awaited inverter has realized the industrialized production. 1.1 The so-called frequency converter - it will be three-phase power frequency (50Hz) AC power (or any power) into three-phase voltage adjustable, adjustable frequency AC power supply, and sometimes the variable-frequency drive called Transformer VVVF inverter. Mainly used for AC motor (asynchronous machine or synchronous machine) speed regulation. 1.2 An AC motor frequency control system consists of frequency converter drive AC motor and controller composed of three parts. One of the key core equipment is the frequency converter, by which to achieve a smooth change in motor voltage and frequency. 1.3 Frequency Control In FM range, static accuracy, dynamic quality, system efficiency, perfect protection, easy to achieve automatic control and process control and other aspects of the past is the pressure regulator, variable pole speed, cascade speed, Slip speed and hydraulic coupler speed and other unmatched. It is recognized as the most promising AC motor optimal speed control program, on behalf of the future direction of the development of electric drive. 1.4 Frequency conversion speed regulation in the past 30 years has been widely used in such industries as steel, metallurgy, petroleum, chemical industry, textile, chemical fiber, light industry, papermaking, rubber, plastic, power and water. Low-voltage motor frequency control applications have been very popular and mature. High-voltage motor frequency control is also being concerned about and gradually applied. AC motor speed control in addition to excellent performance, there are significant energy conservation and environmental protection and other major role, is the technological transformation of enterprises and product updates ideal speed governor. 2, frequency control and fan pump energy saving 2.1 power supply and demand contradiction (in short supply) there is a large power gap, you need to save electricity. According to statistics of related departments, in 2002, China's installed capacity of power generation was 31.9 billion kW, with an annual generating capacity of 1.3466 trillion kWh. Although the electricity scale ranks second in the world, the per capita electricity consumption is the world's last position. Moreover, China's rapid economic development needs more power. According to the 8% increase of the national economy, the electricity demand will increase by 11%. By 2010, China's power generation capacity should be 570-600 million kW and its annual power generation will reach billion kWh. Continued high temperatures in the summer of 2003 caused some provinces and cities to have tight power supply and were forced to take measures to cut off power supply. As the power grid overburdened, resulting in instability in the local power system. The above shows that China's power supply and demand imbalance for less than demand. Therefore, you need to save electricity. 2.2 fan pump frequency control energy-saving benefits 2.2.1 China's motor total installed capacity of 450 million kW, about 65% of the country generating capacity. Therefore, how to achieve motor saving is very important. General motor energy saving has two ways: First, improve the efficiency of the motor itself to achieve long-term high-efficiency operation, mainly for constant speed machinery; the other is to improve the motor speed control accuracy, the motor running at the most energy-efficient speed. 2.2.2 Fans Pumps and compressors are a large number of motor-driven equipment with a large-scale production in the national economy. The total motor capacity reaches 150 million and the electricity consumption accounts for about 35% of the national generating capacity, of which about 20% to 30% Need speed. 2.2.3 Frequency control fan pump energy saving is the best solution. According to fluid theory, centrifugal fan pump shaft power is the third power function. When the speed is reduced, its power consumption will be significantly reduced, for example, 50% speed, the shaft mechanical power is only 12.5%. Of course, the speed difference between the efficiency of the program is very large, slip slip speed regulator is not efficient, η ≈ (1-S), at 50% speed, ηvs ≈ 50%, while the frequency converter efficiency, High efficiency factor, ηvvvF ≈ 95% ~ 98%, and approximately the same. Therefore, many speed control programs in the best energy-saving speed control, should be the preferred solution. [Example] For the same fan pump, the shaft power is 100% at 100% speed and 50% at 50% speed. If the baffle is used, the valve will control 50% of the flow, still need to draw 70-80% of the power from the power grid; if the slip inefficient speed is adjusted to 50%, then the power should be taken in by 25% from the power grid; Efficient speed to 50% of the flow, only 10% of the power drawn from the grid. 2.2.4 Fan Pumps There are a variety of ways to regulate the flow, each with its own characteristics, but it can be summed up into three types: (1) traditional mechanical methods to adjust the fan's baffle, deflector and pump valve opening degree; 2) the use of electromagnetic slip clutch or hydraulic coupling fan speed adjustment fan (while the motor constant speed operation); (3) AC motor frequency control program. The following table is the comparison of three types of fan pump flow control methods and conclusions. (See Table 1) 2.2.5 Today should be in high-capacity high-pressure motor-driven fan pumps and compressors to promote the use of high-voltage frequency control energy-saving. The reason is simple, the larger the installed capacity at the same percentage of power-saving, the greater the absolute power-saving. 3. Frequency control and environmental protection: 3.1 Motor drive is a large power consumption, accounting for more than 60% of the total electricity consumption in China. Excessive electricity consumption depletes coal and oil (natural gas) fuels and at the same time, it causes pollution to the environment, destroys the ozone layer and affects or even endanger human survival due to the large emission of CO2 and NO2. As human beings continue to suffer painful lessons from the destruction of the living environment and the waste of energy resources, protecting the living environment of mankind has become the common call of the people all over the world, setting off a wave of reducing energy conservation and environmental protection and benefiting the society . 1972, Stockholm, Sweden, the first declaration of the world's human environment and Japan's Kyoto agreement in 1994, all signatories should make their country's CO2 and other greenhouse gas emissions to control 1990 levels. Fully explain the importance of environmental protection and the people of the world's attention. 3.2 It is estimated that the impact of electrical products on the environmental pollution accounts for about 30%, so saving energy and reducing waste have become important factors in fulfillment of the Kyoto Protocol commitments. What are the functions and contributions of variable frequency speed regulation and frequency conversion technology? (1) Popularization of energy-saving technology of frequency conversion and speed regulation of fan pump can achieve a saving rate of 20% ~ 30%, so as to reduce the power consumption of the thermal power plant and reduce the generation of SO2, SO, CO2 and dust and reduce the atmospheric pollution; 2) The application of traction variable-frequency locomotive does not need coal and oil to reduce emission pollution; (3) The development of urban rail transit (subway and maglev train) and fuel cell vehicles reduce CO2 emissions. (4) To promote the use of electric bicycles (brushless DC motor, self-made frequency control), disable fuel-assisted vehicles and so on. 4. Frequency Control and Manufacturing: 4.1 Frequency Control to Increase Output The AC motor design allows the 5-10% overspeeding of the motor for long-term operation (20% short-term test) at approximately the same air-gap flux. For example, in some countries, the motor can run at 50/60 Hz for a long time (V / F = Cont, of course, should be guaranteed). As long as the motor bearing can withstand it, it is feasible to increase the speed by 5-10%. A chemical fiber company with a combination of frequency conversion speed control, an appropriate increase in the output frequency of the inverter, has brought considerable yield. (2) VVVF can improve product quality VVVF has the advantages of wide speed range, high speed precision, good dynamic response, etc. For the multi-unit synchronization of chemical fiber spinning machine, textile printing and dyeing machine, paper machine and injection molding machine Transmission or proportional synchronous (drafting) transmission is very suitable, both the performance of the DC drive before, there are exchange machine solid, reliable, easy to maintain features, making the product quality has greatly improved. Increase the degree of automation to reduce the labor intensity of workers. (3) VVVF and some special processing equipment Due to frequency conversion technology, VVVF is more suitable for harsh environments (explosion, corrosion, underwater nuclear radiation, etc.) Very high speed or non-descending gear without gear Very low speed, and precise position control (variable frequency servo, stepper system, manipulator and robot) system. 5, frequency control and soft start, soft start, soft stop 5.1 power network and production process need motor soft start, soft stop 5.1.1 AC motor starting current is generally 5-7 times the rated current, if the direct start of the grid will cause Impact, affect the same electrical grid on the normal operation of other electrical equipment. In addition huge starting current will cause serious electromagnetic stress and mechanical stress on the motor and mechanical equipment and shorten the service life of the equipment, so the power system hopes to be able to start soft (especially high-voltage high-capacity motor). 5.1.2 Some processing machines, such as automatic assembly line (bottles, cans and packing lines, conveyors, etc.), require a smooth starting and stopping to prevent them from colliding with each other. The water pump also needs soft start and Soft stop (preferably "pump control" dedicated soft start and soft stop). 5.2 The characteristics of the inverter as a soft starter Different from the electronic solid-state motor soft starter, because the inverter starts, the motor voltage and frequency change at the same time, the motor can maintain the same flux (electronic soft starter only pressure does not change Frequency conversion, so the motor starts to weaken the flux), so the inverter soft start with a larger starting torque. Very suitable for heavy-duty, high inertia equipment, such as blast furnace fans. This occasion can not match the performance of electronic motor soft starter or simply not capable of both soft start and adjustable speed drive, the application prospect is very optimistic. Currently due to price factors can not be widely promoted, unless the individual heavy-load start and large inertia start the occasion, the inverter is not only used as a soft starter. Maybe a few years later, to be further price reducer will be widely used. 6, Frequency Control (including inverter technology and household appliances) In ordinary households, the largest proportion of the power consumption is the air conditioner, followed by electric appliances, and finally lighting and audio-visual appliances, etc., frequency control (including frequency conversion technology) Can play a role in saving electricity and protecting the environment. 6.1 Inverter Air Conditioner - Due to the configuration of the inverter (with its conventional inverter and homemade inverter, that is, two brushless DC motor speed), non-stop compressor to continuously control the compressor cooling capacity, to achieve Effective operation, is conducive to energy saving. In addition, the frequency of air conditioner rapidity and comfort is very good, but also conducive to environmental protection. 6.2 High-frequency induction cooker and rice cooker - The use of frequency conversion technology to produce (20-30) KHZ high-frequency power supply so that the cooker itself induction heating (IH-Induction heating), the cooking efficiency of about 80% (than the previous resistance heater Of the rice cooker efficiency increased by 30%), is conducive to energy saving. 6.3 Inverter-type lighting equipment - The use of frequency conversion technology to produce (20-70) KHZ high-frequency power to the fluorescent lamp can save 15% of the electric power, at the same time can be immediately lit, there is no labor frequency fluorescent flashing, suitable for work or study , But also conducive to environmental protection. 6.4 Other household appliances such as frequency refrigerators, frequency conversion washing machines, microwave ovens, etc. have also appeared one after another. [Conclusion]: According to statistics, in 2000 China inverter market sales of about 3 billion yuan (60% for fan pump energy saving), accounting for only about 15% of demand, so the inverter market is very optimistic about the future development trend of roughly : Master control integration, miniaturization of equipment, environmental protection of green power supply (EMC compatible), specialization and systematization of equipment. In addition, the cost of low-cost conducive to the further promotion and application.
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