AC motors, especially cage-type asynchronous motors, have a series of advantages such as small size, light weight, simple structure, convenient maintenance, low manufacturing cost and low operating cost, and reliable operation in harsh environments. However, in the past, due to the difficulty of speed regulation or the inefficiency of some speed control methods, it has long been occupied by DC speed regulation in the field of speed regulation. The advantages of AC motors have not been realized in the speed control transmission. Until the early 1970s, with the rapid development of power electronics, microelectronics (integrated circuits) and microcomputer technology, the long-awaited inverters achieved industrial production.
1.1 The so-called frequency converter adjusts the three-phase power frequency (50Hz) AC power (or any power supply) into an AC power with adjustable three-phase voltage and adjustable frequency. Sometimes the inverter is called a variable voltage inverter. VVVF. Mainly used for the adjustment of the speed of the AC motor (asynchronous machine or synchronous machine).
1.2 An AC motor variable frequency speed control system consists of three parts: the inverter motor driver AC motor and controller. The key core equipment is the inverter, which is used to achieve a smooth change in motor voltage and frequency.
1.3 Frequency control In the aspects of frequency modulation range, static accuracy, dynamic quality, system efficiency, perfect protection function, easy to realize automatic control and process control, etc., it is the previous voltage regulation, variable pole speed regulation, cascade speed regulation, Slip speed regulation and hydraulic coupler speed regulation are unmatched. It is recognized as the most ideal and most promising speed control solution for AC motors, representing the future development direction of electric drives.
1.4 In the past 30 years, frequency conversion speed regulation has been widely used in steel, metallurgy, petroleum, chemical, textile, chemical fiber, light industry, paper, rubber, plastics, electric power, water and other industries. The application of low-voltage motor frequency conversion speed regulation has been very popular and mature. The high-frequency motor frequency conversion speed regulation is also being paid attention to and gradually applied. In addition to excellent speed regulation performance, AC motor frequency conversion speed regulation also has significant functions of saving energy and protecting the environment. It is an ideal speed control device for technological transformation and product upgrading.
2, frequency control and fan pump energy saving
2.1 The contradiction between power supply and demand (supply in short supply) has a large power gap and needs to save electricity.
According to the statistics of relevant departments, in 2002 China's power generation installed capacity was 31.9 billion kW, and the annual power generation was 1,346.6 billion kWH. Although the power scale ranks second in the world, the per capita electricity consumption is the world's countdown position. Moreover, China's rapid economic development requires more electricity. If the national economy grows by 8% and the power is increased by 11%, by 2010 China's power generation capacity should be 5.7-600 million kW, and the annual power generation will reach 28,000~290 billion kWH. The continuous high temperature in the summer of 2003 caused some provinces and cities to have tight power supply and was forced to take measures to cut power. Due to the excessive burden of the power network, the local power system is unstable.
The above shows that China's power supply and demand is not balanced, and supply is less than demand. Therefore, it is necessary to save electricity.
2.2 Fan pump frequency conversion speed regulation energy saving benefit
2.2.1 China's total installed capacity of electric motors reaches 450 million kW, which consumes about 65% of the country's electricity generation. Therefore, how to achieve motor power saving is very important. Generally, there are two ways to save energy in the motor: one is to 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 control precision of the motor speed, so that the motor runs at the most energy-saving speed.
2.2.2 Fans, pumps and compressors are large-scale motor-driven equipments produced by the national economy. The total motor capacity is 150 million, and the electricity consumption accounts for about 35% of the national power generation, of which about 20% to 30% are fan pumps. Need speed regulation.
