frequency conversion

1. Classified according to the conversion link: it can be divided into AC-AC inverter, which is to directly convert power frequency AC into frequency and voltage adjustable AC, also known as direct inverter; AC-DC-AC inverter is first The power frequency AC is converted into DC by a rectifier, and then the DC is converted into an AC with adjustable frequency and voltage, also known as an indirect frequency converter, which is a general-purpose frequency converter widely used at present.

2、Classified according to the nature of the DC power supply: (1) Current-type inverter The characteristic of the current-type inverter is that the middle DC link uses a large inductance as the energy storage link to buffer reactive power, that is, to control the change of current and make the voltage close to a sine wave. The internal resistance is large, so it is called a current source type inverter (current type). The characteristic (advantage) of the current-mode inverter is that it can suppress frequent and sharp changes in the load current. It is often used in occasions where the load current changes greatly. (2) Voltage-type inverter The characteristic of voltage-type inverter is that the energy storage element of the intermediate DC link adopts a large capacitor, and the reactive power of the load will be buffered by it, the DC voltage is relatively stable, and the internal resistance of the DC power supply is small, which is equivalent to a voltage source. Therefore, it is called a voltage-type inverter, and it is often used in occasions where the load voltage changes greatly. In addition, the inverter can also be classified according to the output voltage adjustment method, according to the control method, according to the main switch components, and according to the input voltage level.