Abstract : This paper discusses the structural forms and performance characteristics of commonly used frequency converter main circuits, and introduces relevant usage points in conjunction with practical applications. Keywords : Frequency converter; two-level 6-pulse; three-level circuit; multiplexing technology; performance characteristics, usage points 1 Introduction With the continuous emergence of new power electronic devices and the continuous development of new frequency conversion technologies, various types of frequency converters have flooded the market. The first step in selecting and using the required frequency converter is to have a clear understanding of the structural forms and performance characteristics of the key part of the frequency converter—the main circuit. This paper discusses the above issues in three types of frequency converters: low-voltage, medium-voltage, and high-voltage, and introduces their usage points in conjunction with practical applications, hoping to improve this aspect of work. 2 Low-voltage frequency converters Low-voltage frequency converters refer to frequency converters with voltage ≤500V. All domestic and foreign brands of low-voltage frequency converters use a voltage source type AC-DC-AC structure in their main circuit, which is almost always a two-level 6-pulse circuit, using IGBTs as inverter switches, as shown in Figure 1. It features stable operation, wide speed range, good output waveform, low input current harmonic content, high power factor, high efficiency, and simple circuitry, making it widely used. When using it, it should be noted that: when the motor power is ≤200kW, a low-voltage power supply of 380～500V can directly enter the rectification stage of the main circuit; when the motor power is >200kW, to reduce losses on the transmission line, Chinese design specifications stipulate that high-voltage power supply should be used, and a step-down transformer should be installed between the high-voltage power supply and the low-voltage frequency converter. [b][align=center]For details, please click: Performance Characteristics and Usage Points of Common Frequency Converter Main Circuits[/align][/b]