Here are some common classificationways.

(1) Classification according topowerexchangeways

a. AC-DC-AC frequencyinverter

It first converts power frequency AC into DC through a rectifier, and then inverts DC into AC with adjustable frequency and voltage. It is also called an indirectfrequencyinverter and is a universalfrequencyinverter that is currently widely used.

b.AC-AC frequency inverter

That is, it directly converts power frequency AC into AC with adjustable frequency and voltage, also known as direct frequencyinverter. It is mainly used in high-power (above 500kW) low-speed AC transmission systems, and has been used in rolling mills, blowers, crushers, ball mills, winches and other equipment. This frequencyinverter can be used for both asynchronous motors and synchronous motors for speed control.

(2) Classification according to the nature of power supply

a. Voltage-typefrequencyinverter

The characteristic of the voltage-typefrequencyinverter is that the energy storage element in the intermediate DC link uses a large capacitor, and the reactive power of the load will be buffered by it. The DC voltage is relatively stable, and the inner cathode of the DC power supply is small, equivalent to a voltage source.It is often used in situations where the load voltage changes greatly. This type of transformer is widely used.

b. Current-typefrequencyinverter

The characteristic of current-type inverters is that a large inductor is used in the intermediate DC link as an energy storage link to buffer reactive power, that is, to suppress changes in current. Make the voltage close to a sine wave. Since the DC internal resistance is large, it is called a current source type inverter (current type). The characteristic, also theadvantage,of the current-typefrequencyinverter is that it can suppress frequent and sharp changes in the load current. It is often used in situations where the load current changes greatly.

(3) According to control method

a.V/f control frequencyinverter;

b. Vector control frequencyinverter;

c. Direct torque controlfrequencyinverter;

d. SF control frequencyinverter (slip frequency control). Slip frequency control is to control the torque and current by controlling the slip frequency. It is a high-precision closed-loop control, but has poor versatility and is generally used for vehicle control.

(4) Classification according to voltage level

a. High voltage frequencyinverter: 3KV, 6KV, 10KV;

b. Medium voltage frequency inverter: 660V, 1140V;

c. Low voltage frequency inverter: 220V, 380V.

Frequency inverter relies on the switching of the internal IGBT to adjust the voltage and frequency of the output power supply, and provides the required power supply voltage according to the actual needs of the motor, thereby achieving the purpose of energy saving and speed regulation. In addition, thefrequencyinverter also has many protection functions,such as overcurrent, overvoltage, overload protection, etc. With the continuous improvement of industrial automation, frequencyinverters have also been widely used.