Abstract : AC variable frequency speed control is widely used in various fields of production and life due to its reliability, energy saving, and good speed regulation performance. However, the principle and circuit characteristics of the frequency converter itself also bring about various problems caused by harmonics. This paper takes the AC-DC-AC type frequency converter as an example to analyze the causes of harmonics generated in the main circuit of the AC variable frequency speed control device, analyzes the characteristics of harmonics in its rectifier circuit and inverter circuit, and points out the impact of harmonics on the power grid, other electrical equipment, and the drive system itself. Finally, it points out several important measures to suppress harmonic interference. This paper has certain practical guiding significance for the design and application of frequency converters. Keywords: frequency converter; main circuit; harmonics 1 Introduction AC variable frequency speed control technology is a new technology built on the foundation of automatic control, electronics, power electronics, and communication. This transmission system has the advantages of energy saving, good speed regulation performance, simple maintenance, and reliable operation. It has been widely used in various industrial control fields, such as energy, transportation, metallurgy, construction, and machinery manufacturing. It can not only ensure the regulation accuracy, but also reduce the labor intensity of workers and improve economic efficiency. Due to their energy-saving characteristics, frequency converters have begun to enter people's daily lives, such as in variable frequency air conditioners. However, the widespread use of frequency converters has also brought some problems. On the AC input side, they transmit the generated harmonics into the power grid, which can cause power pollution in severe cases and affect the normal operation of other equipment in the grid. On the output side, the voltage waveform of the output voltage contains voltage spikes (high-frequency harmonics) and large voltage gradients, causing problems for motors. In addition, the frequency converter control system is composed of electronic components, computer chips, etc., and the high-order harmonics contained in the voltage and current on the input and output sides of the frequency converter's main circuit can cause serious interference. Therefore, it is necessary to prevent the high-order harmonics generated by the frequency converter during operation from interfering with other equipment, and also to prevent harmonics generated by other electrical equipment and the frequency converter from affecting itself, which is the so-called electromagnetic compatibility (EMC). Internationally and domestically, a series of EMC standards have been issued to regulate the level of EMC to be achieved. The overall trend is that the world is paying more and more attention to the EMC performance and standards of products. [b][align=center]For detailed information, please click: Analysis of Harmonics in AC Variable Frequency Drives and Their Suppression Measures[/align][/b]