1. Classified by the stages of transformation: It can be divided into AC-AC frequency converters, which directly convert power frequency AC into AC with adjustable frequency and voltage, also known as direct frequency converters; AC-DC-AC frequency converter, also known as indirect frequency converter, is a widely used universal frequency converter that first converts AC into DC through a rectifier, and then converts DC into AC with adjustable frequency and voltage.

2. Classified by the nature of DC power supply: (1) Current type frequency converter. The characteristic of current type frequency converter is that a large inductor is used as the energy storage link in the middle DC link to buffer reactive power, that is, to suppress the change of current and make the voltage close to a sine wave. Due to the high internal resistance of this DC, it is called current source type frequency converter (current type). The characteristic (advantage) of current type frequency converter is that it can suppress frequent and rapid changes in load current. Often used in situations where the load current changes significantly. (2) The characteristic of a voltage type frequency converter is that the energy storage element in the middle DC link uses a large capacitor, which buffers the reactive power of the load. The DC voltage is relatively stable, and the internal resistance of the DC power supply is small, equivalent to a voltage source. Therefore, it is called a voltage type frequency converter and is often used in situations where the load voltage changes greatly. In addition, frequency converters can be classified according to output voltage regulation methods, control methods, main switch components, and input voltage levels.