I. Introduction to the Working Principle of Frequency Converters
Inverters adjust the voltage and frequency of the output power supply by switching on and off internal power switches (such as IGBTs), providing the required power voltage according to the actual needs of the motor, thereby achieving energy saving and speed regulation.
In addition, frequency converters have many protection functions, such as overcurrent, overvoltage, and overload protection. With the continuous improvement of industrial automation, frequency converters have been widely used.
The main working principle of a frequency converter is: AC → DC → AC. This process is mainly accomplished by a rectifier (AC/DC) circuit, an inverter (DC/AC) circuit, and a control circuit (main control board, drive protection circuit, fault detection circuit, etc.).
The three circuits are designed on two layers and two circuit boards. The rectifier and inverter circuits, referred to as the high-voltage circuits of the frequency converter, are located on the lower layer. The control circuit, referred to as the low-voltage circuits of the frequency converter, is located on the upper layer. The specific functions of each circuit are described below.
(1) Rectifier circuit: Its main function is to rectify the AC power from the power grid to obtain DC power.
(2) Inverter circuit: The inverter bridge is composed of inverter transistors (IGBTs, etc.). Its main function is to "invert" the rectified DC power into AC power with adjustable frequency. This is the specific execution link for the frequency converter to achieve frequency conversion, and therefore it is the core high-voltage part of the frequency converter.
(3) Control circuit: Its main function is to periodically control the inverter tubes to achieve adjustable output voltage frequency. This is the control link of the frequency converter, and therefore the core low-voltage part of the frequency converter.
II. Applications of Frequency Converters
(I) Application of frequency converters in the power industry
Today, my country is the world's second-largest power generation country after the United States. In the power industry, frequency converters play a crucial role, permeating the entire power generation process. Frequency converters can be used in wind power generation, hydropower generation, coal-fired power generation, waste disposal, and exhaust gas transportation. Furthermore, among these systems, only the coal conveying system does not primarily rely on fans and pumps for its main functions. Frequency converters can effectively control fans and pumps, altering air and water supply volumes to adapt to system changes, achieving energy savings and safety, and ensuring continuous and stable system operation.
(II) Application of frequency converters in the oil and gas drilling and production industry.
China is a major consumer of oil and gas, importing large quantities while continuously increasing its exploration and development of domestic oil and gas resources. Since the turn of the millennium, the oil and gas drilling and production industry has experienced rapid growth, with exploration costs increasing significantly every year. In recent years, China has continuously discovered oil and gas fields with promising reserves, such as the 200 million-ton Tahe oil field in Xinjiang, the 1 billion-ton Nanpu oil field in Hebei, and the 500 billion-cubic-meter gas field in Longgang, Sichuan. It is foreseeable that investment in resource exploration will continue to increase in the future. Frequency converters can be applied to load-bearing motors in the oil and gas drilling and production industry, such as gas compressors, water injection pumps, oil pumping units, oil transfer pumps, and submersible pumps, significantly improving energy efficiency and reducing emissions.
(III) Application of frequency converters in the building materials industry.
Real estate is a vital industry in my country, and building houses requires materials, thus creating a large market for building materials domestically. The building materials industry is mainly divided into three categories, with frequency converters primarily used in motors for crushers, blowers, exhaust fans, rotary kilns, conveyors, and other equipment. With technological advancements and progressive thinking, we are increasingly emphasizing green environmental protection, energy conservation, and emission reduction, leading to a year-on-year increase in demand for high-power frequency converters in the building materials industry. Data shows that installing frequency converters can save approximately 30% of electricity; across the entire industry, this represents a significant energy saving. In some developed Western countries, the usage rate of frequency converters has reached 70%, and China is gradually improving its practices to approach this level.
(iv) Application of frequency converters in the coal industry.
my country's power generation still relies heavily on coal, making it the world's largest coal producer. Coal is a non-renewable resource in the short term and is highly polluting. Currently, China's coal industry is labor-intensive, consuming a large amount of human resources and resulting in significant waste, thus requiring a shift towards a skills-intensive model. Improving automation levels necessitates the development of advanced technologies, with frequency converters being one such example. Used in mine hoists, they offer remarkable energy savings. They not only enhance the automation level and transmission capacity of motors but also reduce electricity consumption.
