Abstract : To achieve good economic benefits from the rational and economical use of frequency converters, this paper analyzes the technical performance and control methods of commonly used high- and low-voltage frequency converters, and discusses their design and selection in cement plants. Keywords : AC-DC-AC frequency converter; three-level; unit series multi-level Introduction Variable frequency speed control technology, due to its significant energy-saving effect, excellent soft-start characteristics, and continuous stepless speed regulation performance, was initially used in the cement industry for speed regulation of small-power metering scales, ordinary fans, and pumps. In recent years, it has been applied to speed regulation of some high-power equipment such as high-temperature fans, vertical mill fans, and rotary kilns. It has gradually replaced slip control, hydraulic coupling, and DC rectifier equipment for speed regulation, and valves for flow regulation in fans, pumps, etc. There are many types of frequency converters. In engineering design, frequency converters should be selected and used rationally and economically according to load characteristics and operating conditions to fully utilize their excellent performance and functions. Therefore, this paper provides a preliminary discussion of the technical performance, control methods, applicable operating conditions, and engineering application design of commonly used frequency converters in cement plants. 1. Topology and Performance of Frequency Converters Frequency converters can be classified into two categories based on their conversion stage: AC-AC converters and AC-DC-AC converters. AC-AC converters directly convert the mains frequency AC into AC with adjustable frequency and voltage. Because this type of converter uses thyristor natural commutation, its maximum output frequency is only 1/3 to 1/2 of the mains frequency. It has many harmonics, a low power factor, and is generally only used in low-voltage, low-speed equipment due to the current limitations of power device voltage. [b][align=center]For more details, please click: Commonly Used High and Low Voltage Variable Frequency Speed ​​Control Technology and its Engineering Design in Cement Plants[/align][/b]